Process For Preparing Pure 1 H Pyrazolo[3,4 D] Pyrimidine Derivative

FIELD OF THE INVENTION The present invention relates to an efficient and industrially advantageous process for the preparation of pure 1H-pyrazolo[3,4-d] pyrimidine derivative. In particular the present invention provides a process for the preparation of pure 4-amino-3-(4-phenoxyphenyl)-1H-pyrazolo[3,4-d] pyrimidine, a key intermediate of 5 ibrutinib, wherein none of the intermediates have been isolated to prepare 3-amino-4-cyano- 5-(4-phenoxy phenyl)pyrazole, an important precursor. BACKGROUND OF THE INVENTION Ibrutinib (IMBRUVICA), chemically known as l-[(3R)-3-[4-amino-3-(4- 10 phenoxyphenyl)-lH-pyrazolo[3,4-d]pyrimidin-1-yl]piperidin-1-yl] prop-2-en-1-one is an orally administered drug that targets Bruton's tyrosine kinase (BTK). Ibrutinib may be used for treating both B cell-related hematological cancers/ B cell chronic lymphocytic leukemia, and autoimmune diseases such as rheumatoid arthritis, Sjogrens syndrome, lupus and asthma and is represented by following chemical 15 formula: Ibrutinib and its pharmaceutically acceptable salts were first disclosed in US patent US7,514,444. This patent discloses a process for the preparation of Ibrutinib by involving use of 4-amino-3-(4-phenoxyphenyl)-1H-pyrazolo[3,4-d]pyrimidine, as intermediate as shown below: 20 3 4-Amino-3-(4-phenoxyphenyl)-1H-pyrazolo[3,4-d]pyrimidine, a key intermediate of ibrutinib, and its preparation from 3-amino-4-cyano-5-(4-phenoxyphenyl) pyrazole was first disclosed in a PCT patent publication WO2001/019829 A2 as shown in below sche5 me. Various other publications like US patents US7,514,444; US7,718,662; US8,883,803 and PCT publications WO2012/158843A2; WO2013/010136A2 follow the same process for the preparation of 4-amino-3-(4-phenoxyphenyl)-1H10 pyrazolo[3,4-d]pyrimidine as described above. The process comprises the conversion of 4-phenoxybenzoic acid to the corresponding acid chloride, which is then taken up in mixture of toluene and tetrahydrofuranand further reacted with malononitrile in the presence of diisopropylethylethylamine in toluene. The reaction mixture is stirred overnightand 15 after completion of reaction, followed by work up 1,1-dicyano-2-hydroxy-2-(4-phenoxyphenyl)ethene is isolated as a residue and which is further purified. The resulting 1,1-dicyano-2-hydroxy-2-(4-phenoxyphenyl)ethene is reacted with trimethylsilyldiazomethane in a mixture of acetonitrile and methanol in the presence of diisopropylethylamine as a base. The resulting reaction mixture is 4 stirred for 2 days to give 1,1-dicyano-2-methoxy-2-(4-phenoxyphenyl)ethene (Omethylated product) as an oil, which is purified by flash chromatography. The O-methylated product is treated with hydrazine hydrate to give 3-amino-4-cyano-5-(4-phenoxyphenyl)pyrazole, which is further reacted with formamide at a temperature of 180°C to give 4-amino-3-(4-phenoxyphenyl)-1H-pyrazolo[5 3,4-d]pyrimidine as pale brown-grey solid. Since, the above process involves the isolation of intermediates and takes long time during reaction completion. Therefore, it is lengthy, not efficient. Further publication is silent about the purity of 4-amino-3-(4-phenoxyphenyl)-1H10 pyrazolo[3,4-d]pyrimidine. Acetonitrile solvent has been used in methylation reaction, which is carcinogenic. The cyclization reaction has been carried out at 180°C and it is observed that the cyclization reaction at high temperature of 180°C, results in grey brown solid colour of 4-amino-3-(4-phenoxyphenyl)-1H-pyrazolo[3,4-d]pyrimidine, may be 15 due to presence of inorganic impurities. The said process also requires the use of expensive (trimethylsilyl)diazomethane to obtain O-methylated product, which is sensitive to air and water, and hence, the methylation reaction has to be carried out in the absence of water, under anaerobic conditions; silica and flash chromatography are also used for purifying O20 methylated product. Since the above process involves complicated operation processes, which leads to high production cost and therefore is not an attractive option at industrially scale. PCT publication WO2014/173289A1 discloses a process for preparation of 3-amino-4-cyano-5-(4-phenoxyphenyl)pyrazole as shown below and its conversion 25 into 4-amino-3-(4-phenoxy phenyl)-1H-pyrazolo[3,4-d]pyrimidine has not been disclosed. 5 The process involves conversion of 4-phenoxybenzoic acid to the corresponding acid chloride, followed by reaction with malononitrile in the presence of diisopropylethylethylamine in tetrahydrofuran. The reaction mixture has been stirred for 16 hours and thereafter 1,1-dicyano-2-hydroxy-2-(4-phenoxypheny5 l) ethene is isolated from reaction mixture.A solution of 1,1-dicyano-2-hydroxy-2-(4-phenoxyphenyl)ethene in trimethoxymethane has been heated for 16 hours to give 1,1-dicyano-2-methoxy-2-(4-phenoxyphenyl)ethene (O-methylated product), which is then reacted with hydrazine hydrate to give 3-amino-4-cyano-5-(4-phenoxy 10 phenyl)pyrazole. The above process is inefficient, since it involves isolation of intermediates and takes long time to complete the reactions and purity of 3-amino-4-cyano-5-(4-phenoxyphenyl)pyrazole has not been disclosed. A similar approach has been described in PCT publication WO2014/082598A1 for 15 preparation of 3-amino-4-cyano-5-(4-phenoxyphenyl)pyrazole and is presented as below: The process involves conversion of4-phenoxybenzoic acid to the corresponding acyl chloride by using sulfurous dichloride, followed by reaction with 20 malononitrile in the presence of sodium hydride to obtain 1,1-dicyano-2-hydroxy- 2-(4-phenoxy phenyl)ethene, which is recrystallized from 1,4-dioxane. The 6 hydroxy moiety is then methylated using dimethyl sulphate to give 1,1-dicyano-2-methoxy-2-(4-phenoxy phenyl)ethene (O-methylated product) which is recrystallized from a mixture of hexane and ethylactetate. The solution of resulting O-methylated product in ethanol was treated with hydrazine hydrate at reflux temperature to give 3-amino-4-cyano-5-(4-phenoxy phenyl)pyrazole, followed b5 y its recrystallization in hexane and further, its conversion into 4-amino-3-(4-phenoxyphenyl)-1H-pyrazolo[3,4-d]pyrimidine was not disclosed. The above process also involves isolation of intermediates; their purification which leads to longer time in reaction completion, and it does not disclose the purity of 10 3-amino-4-cyano-5-(4-phenoxyphenyl)pyrazole. Further the above process involves use of sodium hydride, which is a hazardous reagent and can ignite in air during scale up. Several alternative methods have been reported in literature, wherein process for the preparation of 4-amino-3-(4-phenoxyphenyl)-1H-pyrazolo[3,4-d]pyrimidine 15 has been disclosed and are discussed herein. A Chinese patent application CN103121999A discloses a process of preparation of 4-amino-3-(4-phenoxyphenyl)-1H-pyrazolo[3,4-d]pyrimidine, as below: The process involves reaction of 3-bromo-1H-pyrazolo[3,4-d]pyrimidin-4-amine 20 with (4-phenoxyphenyl)boronic acid in the presence of alkali agents and aprotic solvents to give 4-amino-3-(4-phenoxyphenyl)-1H-pyrazolo[3,4-d]pyrimidine. The said Chinese application is also silent about the purity of target compound and even starts with the advance intermediates, which are expensive and make the process unattractive from industrial point of view. 25 A similar approach has been described in US patent US8,940,893; PCT publication WO2013/113097A1 and WO2015/018333A1 for preparing 4-amino-3-(4-phenoxyphenyl)-1H-pyrazolo[3,4-d]pyrimidine . 7 In US patent US8,940,893 and PCT publication WO2013/113097A1, 4-amino-3- (4-phenoxyphenyl)-1H-pyrazolo[3,4-d]pyrimidine is purified by using Combiflash chromatography on silica gel. In PCT publication WO2015/018333A1, 4-amino-3-(4-phenoxyphenyl)-1H-pyrazolo[3,4-d]pyrimidine is purified by recrystallization in ethyl acetate5 . The purity of 4-amino-3-(4-phenoxyphenyl)-1H-pyrazolo[3,4-d]pyrimidine has not been reported in above publications too. Further two of the above processes involve tedious step of chromatographic purification, which is not industrial viable. Another Chinese patent application CN103965201A discloses a process for the 10 preparation of 4-amino-3-(4-phenoxyphenyl)-1H-pyrazolo[3,4-d]pyrimidine, wherein 3-bromo-1H-pyrazolo[3,4-d]pyrimidin-4-amine was reacted with trimethyl tin (4-phenoxy phenyl) to give 4-amino-3-(4-phenoxyphenyl)-1H-pyrazolo[3,4-d]pyrimidine and followed by its recrystalliztion in isopropanol, as shown below: 15 The said Chinese application is also silent about the purity of 4-amino-3-(4-phenoxyphenyl)-1H-pyrazolo[3,4-d]pyrimidine and is not cost-effective because it starts with advance intermediates, which are expensive. Therefore, said route of synthesis is not industrially applicable. Purity of an API as well as intermediates is of great importance in the field of 20 pharmaceutical chemistry. It is well documented in the art that direct product of a chemical reaction is rarely a single compound with sufficient purity to comply with pharmaceutical standards. The impurities that can be present in pharmaceutical compounds are starting materials, by-products of the reaction, products of side reactions, or degradation products. 25 According to ICH guidelines, process impurities should be maintained below set limits by specifying the quality of raw materials, their stoichiometric ratios, 8 controlling process parameters, such as temperature, pressure, time and including purification steps, such as crystallization, distillation and liquid-liquid extraction etc., in the manufacturing process. Typically, these limits should less than about 0.15 % by weight of each identified impurity. Limits for unidentified and/or uncharacterized impurities are obviously lower, typically less than 0.10 % b5 y weight. The limits for genotoxicimpurties could be much lower depending upon the daily dose of the drug and duration of the treatment. Therefore, in the manufacture of a drug substance, the purity of the starting materials is also important, as impurties may carry forward to the active pharmaceutical ingredient such as 10 ibrutinib. In view of the above, most of the prior art processes involve isolation of intermediates, additional purification steps and silent about the purity or the assay of 4-amino-3-(4-phenoxy phenyl)-1H-pyrazolo[3,4-d]pyrimidine. Thus, there is an urgent need for the development of a synthetic process which 15 produces pure 4-amino-3-(4-phenoxyphenyl)-1H-pyrazolo[3,4-d]pyrimidineor its acid addition salts. The present invention fulfills the need in the art and provides an improved, industrially advantageous process for the synthesis of pure 4-amino-3-(4-phenoxyphenyl)-1H-pyrazolo[3,4-d] pyrimidine, a key intermediate in the 20 preparation of ibrutinib, through preparation of 3-amino-4-cyano-5-(4-phenoxyphenyl)pyrazole from 4-phenoxy benzoic acid using same organic solvent and none of the intermediates have been isolated. OBJECT OF THE INVENTION The main object of the present invention is to provide an improved and industrially 25 advantageous process for the preparation of pure 4-amino-3-(4-phenoxyphenyl)- 1H-pyrazolo[3,4-d]pyrimidine, a key intermediate in the preparation of ibrutinib or pharmaceutically acceptable salt thereof. by minimizing the use of mixture of solvents during the preparation of 3-amino-4-cyano-5-(4-phenoxyphenyl)pyrazole. 9 Yet another object of the present invention is to provide process for the preparation of 3-amino-4-cyano-5-(4-phenoxyphenyl)pyrazole wherein none of the intermediates have been isolated. Yet another object of the present invention is to provide a process for the purification of 3-amino-4-cyano-5-(4-phenoxyphenyl)pyraz5 ole. Yet another object of the present invention is to provide process for the conversion of 3-amino-4-cyano-5-(4-phenoxyphenyl)pyrazole into pure 4-amino-3-(4-phenoxyphenyl)-1H-pyrazolo[3,4-d] pyrimidine. SUMMARY OF THE INVENTION 10 Accordingly, the present invention provides a convenient, industrially advantageous, efficient process for preparation of pure 4-amino-3-(4-phenoxyphenyl)-1H-pyrazolo[3,4-d]pyrimidine compound of formula I, a key intermediate in the preparation of ibrutinib or pharmaceutically acceptable salt thereof, Formula I 15 comprises the steps of: a) reacting 4-phenoxybenzoic acid with a suitable reagent at a suitable temperature to give 4-phenoxybenzoyl chloride of formula II; Formula II b) reacting in-situ the resulting compound of formula II with malononitrile in the presence of a base, in a suitable organic solvent at a suitable temperature for 20 sufficient time to give 2-hydroxy-ethene compound of formula III; Formula III c) reacting in-situ the resulting compound of formula III with a suitable methylating agent in the presence of a base at a suitable temperature to give 2-methoxy-ethene compound of formula IV; 10 Formula IV d) reacting in-situ the resulting compound of formula IV with hydrazine hydrate at a suitable temperature to give 3-amino-4-cyano-pyrazole compound of formula V; Formula V e) optionally, purifying 3-amino-4-cyano-5-(4-phenoxyphenyl)pyrazole compound of formula V; f) reacting resulting compound of formula V with formamide at a suita5 ble temperature to give pure 4-amino-3-(4-phenoxyphenyl)-1H-pyrazolo[3,4-d]pyrimidine compound of formula I. Another object of present invention provides a process for preparation of pure 4-amino-3-(4-phenoxyphenyl)-1H-pyrazolo[3,4-d]pyrimidine compound of formula I Formula I 10 comprises the steps of: a) reacting 3-amino-4-cyano-5-(4-phenoxyphenyl)pyrazole compound of formula V, Formula V with formamide at a suitable temperature not higher than140°C; b) isolating pure 4-amino-3-(4-phenoxyphenyl)-1H-pyrazolo[3,4-d]pyrimidine 15 compound of formula I. Another object of present invention is to provide a processes for the preparation of 3-amino-4-cyano-5-(4-phenoxyphenyl)pyrazole compound of formula V Formula V 11 starting from 4-phenoxybenzoic acid using a single and same organic solvent during all reaction steps. Another object of present invention is to provide a processes for the preparation of 3-amino-4-cyano-5-(4-phenoxyphenyl)pyrazole compound of formula V Formula V comprises the 5 steps of: a) reacting 4-phenoxybenzoic acid with a suitable reagent at a suitable temperature to give 4-phenoxybenzoyl chloride compound of formula II; Formula II b)reacting in-situ the resulting compound of formula II with malononitrile in the presence of a base, in a suitable organic solvent, at a suitable temperature for 10 sufficient time to give 1,1-dicyano-2-hydroxy-2-(4-phenoxyphenyl)ethene compound of formula III; Formula III c)reacting in-situ the resulting compound of formula III with a suitable methylating agent in the presence of base at a suitable temperature to give 1,1-dicyano-2-methoxy-2-(4-phenoxyphenyl)ethene compound of formula IV; Formula IV 15 d) reacting in-situ the resulting compound of formula IV with hydrazine hydrate at a suitable temperature to give 3-amino-4-cyano-5-(4-phenoxyphenyl)pyrazole of formula V; Formula V e) optionally, purifying the resulting compound of formula V to give pure 3-amino-4-cyano-5-(4-phenoxyphenyl) pyrazole of formula V. 12 Another object of present invention is to provide a process for the purification of 3-amino-4-cyano-5-(4-phenoxyphenyl)pyrazole of formula V comprises the steps of: a) suspending 3-amino-4-cyano-5-(4-phenoxyphenyl)pyrazole of formula V in a suitable 5 ble solvent; b) heating the reaction mixture at reflux temperature to obtain a solution; c) optionally, adding a suitable second solvent to the solution; d) cooling the reaction mixture; e) isolating pure 3-amino-4-cyano-5-(4-phenoxyphenyl)pyrazole of formula V. 10 Use of pure 3-amino-4-cyano-5-(4-phenoxyphenyl) pyrazole compound of formula V, prepared by using process of present invention in the preparation of 4-amino-3-(4-phenoxyphenyl)-1H-pyrazolo[3,4-d]pyrimidine compound of formula I, a key intermediate of ibrutinib. Use of 4-amino-3-(4-phenoxyphenyl)-1H-pyrazolo[3,4-d]pyrimidine compound of 15 formula I, prepared by using pure 3-amino-4-cyano-5-(4-phenoxyphenyl) pyrazole compound of formula V, prepared by using process of present invention, in the preparation of ibrutinib. DETAILED DESCRIPTION OF THE INVENTION The present invention provides an improved and industrially advantageous process 20 for preparation of preparation of pure 4-amino-3-(4-phenoxyphenyl)-1Hpyrazolo[ 3,4-d] pyrimidine compound of formula I, a key intermediate in the preparation of ibrutinib or pharmaceutically acceptable salt thereof. Pure 4-amino-3-(4-phenoxyphenyl)-1H-pyrazolo[3,4-d] pyrimidine compound of formula I refers to have purity greater than 95% by HPLC, preferably greater than 25 99% by HPLC and assay more than 97%, preferably greater than 98%. As used herein, the term 'assay' represents a quantitative measurement of the major component in the desired chemical substance/drug substance. It refers tocontent or potency to provide an exact result which allows an accurate statement on the content or potency of the analyte in a sample. 13 Pure 3-amino-4-cyano-5-(4-phenoxyphenyl)pyrazole compound of formula V refers to have purity greater than 93% by HPLC, preferably greater than 97% by HPLC. Generally the process involves the conversion of 4-phenoxybenzoic acid to the corresponding acid chloride by reacting with a suitable reagent such as thiony5 l chloride, oxalyl chloride or sulfuryl chloride. The reaction can be carried out at a temperature of 20°C to 70 °C and it take about 1 to 5 hours for completion of reaction. Specifically the reaction is carried out using thionyl chloride. After completion of reaction, thionyl chloride may be distilled off and a suitable organic 10 solvent can be added. The suitable organic solvent can be selected from non-polar aprotic solvents such as toluene, xylene, hexane, tetrahydrofuran, 1,4-dioxane, and the like, preferably toluene and preferably toluene. In a specific embodiment, toluene is added to the resulting acid chloride and followed by distillation of solvent to give 4-phenoxybenzoyl chloride compound of formula II, which is used 15 as such in the next step. The resulting 4-phenoxybenzoyl chloride compound of formula II is then reacted in-situ with malononitrile in a suitable solvent, in the presence of a base at a suitable temperature for sufficient period of time to give 1,1-dicyano-2-hydroxy-2- (4-phenoxyphenyl)ethene compound of formula III. 20 Generally, the reaction can be performed at a temperature of 20°C to 55°C for few minutes to 5 hours. The suitable organic solvent can be selected from non-polar aprotic solvents such as toluene, xylene, hexane, tetrahydrofuran, 1,4-dioxane, and the like, and is the same organic solvent which is used during first step to remove traces of chlorinating reagent used during acid chloride formation. The base can 25 be selected from diisopropylethylamine,triethylamine, 1,8- Diazabicyclo[5.4.0]undec-7-ene (DBU) and tertiary amines;sodium bicarbonate, sodium carbonate, sodium hydride and the like, After completion of the reaction, the reaction mass can be cooled to a temperature of 15 °C to 40°C and treated with a suitable acid such as sulfuric acid. The reaction 30 mixture can be then stirred at a temperature of 15°C to 40°C for few minutes to 14 about 2 hours, preferably for 30 minutes. Thereafter, the layers can be separated and organic layer can be washed with 10 % sodium chloride solution. The resulting organic layer can be sed directly in next reaction. The resulting compound of formula III then can be reacted in-situ with a suitable methylating agent in the presence of a base at a suitable temperature to give 5 ive Omethylated product, 1,1-dicyano-2-methoxy-2-(4-phenoxyphenyl)ethene compound of formula IV. The suitable methylating agent can be selected from dimethyl sulphate, methyl iodide, dimethyl carbonate, tetramethylammonium chloride, methyl triflate 10 preferable dimethyl sulphate is used. Generally, the base can be selected from inorganic base such as sodium hydroxide, sodium carbonate, sodium bicarbonate, calcium hydroxide, and calcium carbonate. The reaction may take place at a temperature of 20°C to 90 °C for 20 minutes to 5 hours. After completion of the reaction, the resulting reaction mass may be cooled 15 to 15°C to 60°C and water is added to the reaction mass. The reaction mass can be stirred to form layers and the layers are separated. The aqueous layer is extracted with a suitable solvent. The suitable organic solvent can be selected from non-polar aprotic solvents such as toluene, xylene, hexane, tetrahydrofuran, 1,4-dioxane, and the like, and is the same organic solvent which is used during earlier steps. Both 20 the organic layers can be combined, washed with sodium chloride solution and the resulting organic layer can be used directly in next reaction. The resulting 1,1-dicyano-2-methoxy-2-(4-phenoxyphenyl)ethene compound of formula IV in-situ is reacted with hydrazine hydrate at a suitable temperature for sufficient time to complete the reaction. Generally, hydrazine hydrate can be added 25 slowly, since the reaction may be exothermic during addition of hydrazine hydrate and temperature may rise up to 50°C. Thereafter the reaction mixture can stirred at ambient temperature over a period of 20 minutes to 5 hours. After completion of the reaction, the resulting solid can be collected by any means known the art such as filtration, centrifugation, distillation, and the like and 30 preferably filtration. 15 The resulting 3-amino-4-cyano-5-(4-phenoxyphenyl)pyrazole compound of formula V can optionally be purified by combining any suitable means such as processing by extraction, treatment with activated carbon, acid-base treatment, slurry wash and recrystalliztion and solvent/ antisolvent like addition of second solvent to facilitate the crystallization. The said purification methods can optionall5 y be combined and repeated to achieve the desired purity. Particularly, the purification process involves the preparation of a solution of 3-amino-4-cyano-5-(4-phenoxyphenyl)pyrazole compound of formula V in a suitable solvent. Solution can be prepared by heating up to reflux temperature in a suitable 10 solvent. Thereafter, to the resulting solution optionally, a suitable second solvent can be added as antisolvent to facilitate the complete crystallization. Thereafter, the reaction mixture can be cooled and resulting solid can be collected to obtain pure 3-amino-4-cyano-5-(4-phenoxyphenyl)pyrazole compound of formula V. Alternatively the reaction solution can be cooled to a temperature of less than 15°C 15 to facilitate crystallization. In an alternate way, 3-amino-4-cyano-5-(4-phenoxy phenyl)pyrazole compound of formula V, can be slurry washed using a suitable solvent. The suitable solvent used for the purification of 3-amino-4-cyano-5-(4-phenoxy phenyl)pyrazole compound of formula V can be selected from alcoholic solvent such as methanol, ethanol, n-propanol, isopropanol, butanol, n-butanol; a 20 chlorinated solvent such as chloroform, dichloromethane and the like. The suitable second solvent used to facilitate the crystallization can be selected from but not limited to water, ethers such asdipropyl ether, diisopropyl ether, diethyl ether, isopropyl ether methyl tert-butyl ether, 1,2-dimethoxy ether,1,2-diethoxy ether and the like. The purification using addition of second solvent to solution of 3-amino- 25 4-cyano-5-(4-phenoxy phenyl)pyrazole compound of formula V is advantageous since it removes inorganic impurities along with some unknown colored impurities and resulting compound has increased purity of 3-amino-4-cyano-5-(4-phenoxyphenyl) pyrazole compound of formula V. 16 The resulting 3-amino-4-cyano-5-(4-phenoxyphenyl)pyrazole compound of formula V prepared by using process of present invention is pure and have purity of grater than 93% by HPLC, preferably more than more than 97% by HPLC. The preparation of 3-Amino-4-cyano-5-(4-phenoxyphenyl)pyrazole compound of formula V from 4-phenoxybenzoic acid in four steps, without isolating an5 y intermediate and using a same single organic solvent during all reactions forms an inventive part of the invention. The resulting 3-Amino-4-cyano-5-(4-phenoxyphenyl)pyrazole compound of formula V can be then converted to pure 4-amino-3-(4-phenoxyphenyl)-1H10 pyrazolo[3,4-d] pyrimidine compound of formula I using any method reported in literature. Preferably 3-amino-4-cyano-5-(4-phenoxyphenyl)pyrazole compound of formula V can be reacted with a suitable reagent such as formamide at a suitable temperature to give pure 4-amino-3-(4-phenoxyphenyl)-1H-pyrazolo[3,4-d] pyrimidine compound of formula I. 15 Generally the reaction may take place at a temperature of not higher than 140°C for few hours till the completion of reaction. Preferably the reaction can be carried out at a temperature between 120°C to 140°C for 20 hours to 30 hours. After completion of the reaction, the resulting reaction mass may be cooled to 25°C to 60°C and treated with a suitable solvent such as water and resulting reaction 20 mixture is stirred for 10 to 30 minutes. The resulting solid can be collected by suitable means known the art. Generally the resulting compound can be washed with water or suitable organic solvent. The suitable organic solvent can be selected from hydrocarbon solvent selected from toluene, hexane, cyclohexane, heptane; alcohol solvent such as methanol, ethanol, propanol, isopropanol; ketone solvent 25 such acetone, tetrahydrofuran, methyl isobutyl ketone, methyl ethyl ketone and a like, preferably organic solvent selected from methanol, isopropanol, acetone and toluene. The pure 4-amino-3-(4-phenoxyphenyl)-1H-pyrazolo[3,4-d]pyrimidine compound of formula I have purity of greater than 95% by weight as determined using HPLC, preferably greater than 99% by HPLC and assay more than 97%, 30 preferably greater than 98%. 17 According to one another aspect, the present invention provides a process for the conversion of 3-amino-4-cyano-5-(4-phenoxyphenyl)pyrazole compound of formula V into pure 4-amino-3-(4-phenoxyphenyl)-1H-pyrazolo[3,4-d] pyrimidine compound of formula I. The process parameters for said conversion may be same as mentioned above5 . According to one another aspect, the present invention provides a process for the preparation of 3-amino-4-cyano-5-(4-phenoxyphenyl)pyrazole compound of formula V by using same organic solvent; wherein none of the intermediates have been isolated. 10 The process parameters for said conversion may be same as mentioned above. According to one aspect, the present invention provides a process for the purification of 3-amino-4-cyano-5-(4-phenoxyphenyl)pyrazole compound of formula V. The purification process involves suspension of 3-amino-4-cyano-5-(4- 15 phenoxyphenyl)pyrazole compound of formula V in a suitable solvent. Then, the resulting reaction mixture is then heated at reflux temperature to obtain a solution; optionally, suitable second solvent is added to the resulting solution to facilitate the crystallization, the reaction mixture is cooled and the product is filtered to obtain pure 3-amino-4-cyano-5-(4-phenoxyphenyl)pyrazole compound of formula V. 20 The suitable solvent used for the purification of 3-amino-4-cyano-5-(4-phenoxyphenyl)pyrazole compound of formula V is selected from alcoholic solvents such as methanol, ethanol, isopropanol, n-propanol, butanol, n-butanol; a chlorinated solvent such as chloroform, dichloromethane and the like. The suitable second solvent are those solvent which facilitate crystallization; preferably selected 25 from water, ethers such as diethyl ether, dipropyl ether, diisopropyl ether, isopropyl ether methyl tert-butyl ether, 1,2-dimethoxy ether,1,2-diethoxy ether and the like. The above purification is advantageous because with recrystallization in alcoholic solvent or with alcoholic solvent followed by addition of second solvent results in enhanced purity such as removal of inorganic impurities/unknown colored 30 impurities and traces of heavy metal if present. The resulting 3-amino-4-cyano-5- 18 (4-phenoxyphenyl)pyrazole compound of formula V, qualify heavy metal test i.e. less than 20ppm and residue on ignition test i.e. not more than 0.05%. According to one another aspect, the present invention provides conversion of 3-amino-4-cyano-5-(4-phenoxyphenyl)pyrazole compound of formula V, prepared by using process of present invention into 4-amino-3-(4-phenoxyphenyl)-5 1Hpyrazolo[ 3,4-d] pyrimidine compound of formula I. According to one another aspect, 4-amino-3-(4-phenoxyphenyl)-1H-pyrazolo[3,4-d] pyrimidine compound of formula I, prepared by using process of present invention can be converted to ibrutinib. 10 Generally the process involves introduction of piperidinyl moiety at IH [on NHof pyrazole moiety] of 4-amino-3-(4-phenoxyphenyl)-1H-pyrazolo[3,4-d] pyrimidine compound of formula I under known reaction conditions such as Mitsunobu reaction conditions to prepare tert-butyloxycarbonyl protected (1S)-1- [(3R)-3-piperidyl]-3-(p-phenoxyphenyl)-1,2,5,7-tetraza-1H-inden-4-ylamine of 15 formula VI. Formula VI The resulting compound of formula VI can be purified by any means such as crystallization, by using chromatographic techniques such as column chromatography or flash chromatography to remove triphenylphosphine oxide. Thereafter, tert-butyloxycarbonyl protected (1S)-1-[(3R)-3-piperidyl]-3-(p20 phenoxyphenyl)-1,2,5,7-tetraza-1H-inden-4-ylamine of formula VI is deprotected using a suitable reagent to prepare (1S)-1-[(3R)-3-piperidyl]-3-(p-phenoxyphenyl)- 1,2,5,7-tetraza-1H-inden-4-ylamine of formula VII. 19 Formula VII Boc-deprotectioncan be accomplished with strong acids such as trifluoroacetic acid neat or in a suitable solvent or with HCl in a suitable solvent. The suitable solvent can be selected from dichloromethane, chloroform, diethyl ether, 1,4-dioxane, toluene, alcohols , preferably trifluoroacetic acid is used in dichloromethane. The indenylamine compound of formula VII is then acylated using acryloy5 l chloride in the presence of a base in a suitable solvent to obtain ibrutinib. The base can be selected from triethylamine, tri-n-butylamine, diisopropylethylamine,Nmethylmorpholine, DBU and the like. The suitable solvent can be selected from dichloromethane, chloroform, dichloroethane, ether such as tetrahydrofuran, 2- 10 methyl tetrahydrofuran, 2-dimethoxy ether, 2- diethoxy ether, isopropyl ether and methyl tert butyl ether; toluene, xylene, acetonitrile and the like. The acylation reaction can be accomplished at a temperature of 0oC- 50oC and it takes 30 minutes to sevral hours to complete the reaction and preferably reaction is carried out at ambient temperature. The resulting ibrutinib can be purified by any means such as 15 crystallization, by using chromatographic techniques such as column chromatography or flash chromatography. The completion of reaction, at any stage can be monitored by any one of the chromatographic techniques such as thin layer chromatography (TLC), high pressure liquid chromatography (HPLC), ultra-high pressure liquid 20 chromatography (UPLC), IR, NMR and the like. Major advantages realized in the present invention is that the process of present invention is less time consuming, since isolation of intermediates have been avoided, cost effective and industrial friendly. The process described in present invention will be demonstrated in more details 25 with reference to the following examples, which are provided by way of illustration 20 only and should not be construed as limit to the scope of the reaction in any manner. Examples: Example 1: Preparation of 3-amino-4-cyano-5-(4-phenoxyphenyl)pyrazole 4-Phenoxybenzoic acid (200g) was slowly added to thionyl chloride (400ml) at 5 a temperature of 25-30oC and resulting reaction mixture was heated under stirring to a temperature of 60-65oC for 5 hours. Thionyl chloride was distilled off under vacuum at temperature below 60oC. Toluene (2x400ml) was added to the resulting oily residue and thereafter distilled out completely under vacuum below 60ºC to 10 remove traces of thionyl chloride to obtain 4-phenoxybenzoyl chloride as a viscous oil. The resulting viscous oil of 4-phenoxybenzoyl chloride was dissolved in toluene (2000ml). Malononitile (80g) and diisopropylethylamine (320ml) were sucessively added to the reuslting solution at a temperature of 25-30oC slowly, maintaining reaction temperature 50-55°C. The reaction mass was further stirred 15 for 30 minutes. After completion of the reaction, the reaction mass was cooled to 25-30°C and a solution of sulfuric acid (1.25 M) was added. The reaction mixture was then stirred at a temperature of 25-30°C for 30 minutes, and the layers were separated. The organic layer was washed with a solution of sodium chloride (10%) and the resulting organic layer was used directly in next reaction. 20 Dimethyl sulfate (200ml) and sodium bicarbonate (200g) were added to the resulting organic layer at a temperature of 25-30°C. Thereafter, temperature of reaction mass was raised to 80-90°C and reaction mass was stirred for 1-2 hours. After completion of reaction, the reaction mass was cooled to a temperature of 25- 30°C, demineralized water (2000ml) was added and stirred for 10-15 minutes. The 25 layers were separated and the aqueous layer was extracted with toluene (1000ml). All the organic layers were combined and washed with sodium chloride solution (10%). Activated carbon (20g) was added and reaction mixture was stirred for 30 minutes. The solution was filtered through hyflo bed and to the resulting organic layer hydrazine hydrate (120ml) was added at a temperature of 25-30°C. During the 30 addition exothermicity was observed, and temperature of the reaction mass was 21 rose up to 40-50°C. Thereafter, the reaction mass was stirred at a temperature of 25-30°C for 1-2 hours. The resulting precipitated solid was filtered, slurry washed with dichloromethane (400ml) and finally, dried to obtain title compound of formula V (140g) purity 93.28% measured by HPLC. Example 2: Preparation of 3-amino-4-cyano-5-(4-phenoxyphenyl)pyraz5 ole 4-Phenoxybenzoic acid (100g) was slowly added to thionyl chloride (200ml) at a temperature of 25-30oC and resulting reaction mixture was heated under stirring to a temperature of 50-55oC for 5 hours. Thionyl chloride was distilled off under vacuum at temperature below 50oC. Toluene (250ml) was added to the resulting 10 oily residue and thereafter distilled out completely under vacuum below 50ºC to remove traces of thionyl chloride to obtain 4-phenoxybenzoyl chloride as a viscous oil. The resulting viscous oil of 4-phenoxybenzoyl chloride was dissolved in toluene (500ml). Malononitile (35.58ml) and diisopropylethylamine (160ml) were sucessively added to the reuslting solution at a temperature of 25-30oC 15 slowly, maintaining reaction temperature around 50-55°C. The reaction mass was further stirred for 10 minutes. After completion of the reaction, the reaction mass was cooled to 25-30°C and a solution of sulfuric acid (70 ml in 1000 ml water) was added. The reaction mixture was then stirred at a temperature of 25-30°C for 30 minutes, and the layers were separated. The organic layer was washed with a 20 solution of sodium chloride (10%) and the resulting organic layer was used directly in next reaction. Dimethyl sulfate (95.11ml) and sodium bicarbonate (96.16g) were added to the resulting organic layer at a temperature of 25-30°C. Thereafter, temperature of reaction mass was raised to 80-90°C and reaction mass was stirred for 1-2 hours. 25 After completion of reaction, the reaction mass was cooled to a temperature of 55- 60°C, demineralized water (1000ml) was added. The reaction mass was cooled to a temperature of 25-30°C and stirred for 10-15 minutes. The layers were separated and the aqueous layer was extracted with toluene (500ml). All the organic layers were combined and washed with sodium chloride solution (10%). To the resulting 30 organic layer hydrazine hydrate (50ml) was added at a temperature of 25-30°C. 22 During the addition exothermicity was observed, and temperature of the reaction mass was rose up to 40-45°C. Thereafter, the reaction mass was stirred at a temperature of 25-30°C for 1-2 hours. The resulting precipitated solid was filtered, suck dried to obtain 3-amino-4-cyano-5-(4-phenoxyphenyl)pyrazole compound of formula V (123g) purity 86.96% measured by HPLC5 . Example 3: Purification of 3-amino-4-cyano-5-(4-phenoxyphenyl)pyrazole 3-Amino-4-cyano-5-(4-phenoxyphenyl)pyrazole (36g) was suspended in isopropanol (350ml) and temperature of the reaction mixture was raised and allowed to reflux to dissolve the solid completely to provide a clear solution. Then, 10 solvent was distilled off under vacuum to obtain a residue and isopropanol (50ml) was added and after stirring for hours the solid was filtered and dried to afford 3-amino-4-cyano-5-(4-phenoxyphenyl)pyrazole compound of formula V (26g) and having purity of 97.54 % by HPLC . Example 4: Purification of 3-amino-4-cyano-5-(4-phenoxyphenyl)pyrazole 15 3-Amino-4-cyano-5-(4-phenoxyphenyl)pyrazole (36g) was suspended in isopropanol (350ml) and temperature of the reaction mixture was raised upto reflux to dissolve the solid completely upto clear solution. Water (1050ml) was added to the solution and the reaction mixture was gradually cooled to crystallize the product. The resulting solid was filtered, washed with two volumes of isopropanol, 20 dried in vacuum oven at a temperature of 40-45 °C to afford 3-amino-4-cyano-5-(4-phenoxyphenyl)pyrazole compound of formula V (20g) and having a HPLC purity of 97.23% . Example 5: Preparation of pure 4-amino-3-(4-phenoxyphenyl)-1Hpyrazolo[ 3,4-d] pyrimidine compound of formula I 25 3-Amino-4-cyano-5-(4-phenoxyphenyl)pyrazole (20g) was suspended in formamide (100 ml) and heated at a temperature of 130°C, after completion of reaction, the reaction mixture was cooled to a temperature of 30-35°C and demineralized water (500ml) was added and the reaction mixture was stirred at a temperature of 25-30°C for 45 minutes. The resulting solid was filtered and acetone 30 (200ml) was added stirred the reaction mixture for 30-45 minutes. The resulting 23 solid was filtered, washed, dried to afford pure 4-amino-3-(4-phenoxyphenyl)-1Hpyrazolo[ 3,4-d]pyrimidine compound of formula I (12g) having purity 99.6% measured by HPLC. Example 6: Preparation of pure 4-amino-3-(4-phenoxyphenyl)-1Hpyrazolo[ 3,4-d] pyrimidine compound of formula 5 la I 3-Amino-4-cyano-5-(4-phenoxyphenyl)pyrazole (100g) was suspended in formamide (500ml) and heated at a temperature of 135-140°C, after completion of reaction, the reaction mixture was cooled to a temperature of 30-35°C and demineralized water (1000ml) was added and the reaction mixture was stirred at a 10 temperature of 20-25°C for 1 hour. The resulting solid was filtered, washed with water (500ml) then successively slurry washed with toluene (2 x 500ml) and dried to afford pure 4-amino-3-(4-phenoxyphenyl)-1H-pyrazolo[3,4-d] pyrimidine compound of formula I (70g) having purity 99.8% measured by HPLC; assay > 98%; residue on ignition 0.05%; heavy metals < 20ppm. 15 Example 7: Preparation of (1S)-1-[(3R)-3-piperidyl]-3-(p-phenoxyphenyl)- 1,2,5,7-tetraza-1H-inden-4-ylamine Diisopropyldiazodicarboxylate (DAID, 1.2 ml,) was added to a solution of 1-tertbutyloxycarbonyl- 3-(S)-hydroxypiperidine (1.0g,) and triphenylphosphine (2.59g) in tetrahydrofuran (50.0ml). To the resulting yellow solution, 3-(p20 phenoxyphenyl)-1,2,5,7-tetraza-1H-inden-4-ylamine (1.0g) was added and warmed till dissolution, and stirred overnight at room temperature. The reaction mixture was filtered and the solvent was distilled under vacuum to get an oily residue, which was further purified by flash chromatography (30-50 % ethyl acetate/ hexane) on silicagel to give 0.3 g (0.3 w/w) of tert-butyloxycarbonyl-(1S)-1- 25 [(3R)-3-piperidyl]-3-(p-phenoxyphenyl)-1,2,5,7-tetraza-1H-inden-4-ylamine as a light brown solid. The resulting solid was dissolved in dichloromethane (5 ml) and trifluoroacetic acid (0.6 ml) was added to it. After completion of reaction, water was added to reaction mass, followed by addition of methyl tert-butyl ether (20.0 ml). The layers were separated and the aqueous layer was basified with potassium 30 carbonate and extracted with dichloromethane (15.0 ml x 2). The organic layer 24 dried over sodium sulfate, filtered and evaporated to yield 0.2 g (0.6 w/w) of title compound as light yellow oil. Example 8: Preparation of l-(3-(4-amino-3-(4-phenoxyphenyl)-lH-pyrazolo [3,4-d]pyrimidin-l-yl)piperidin-l-yI)prop-2-en-l-one (Ibrutinib) To a solution of acryloyl chloride (0.06g) in tetrahydrofuran (15.0 ml), a mix5 ture of triethylamine (0.1g) and (1S)-1-[(3R)-3-piperidyl]-3-(p-phenoxyphenyl)-1,2,5,7-tetraza-1H-inden-4-ylamine (0.2g) in tetrahydrofuran (7.8 ml) was added. The reaction mixture was stirred at 25-30°C for 18 hous and filtered. The solvent was removed under vacuum to obtain crude ibrutinib, which was further purified by 10 column chromatography on silica gel to obtain pure ibrutinib as crystalline solid.

WE CLAIM: 1. A process for preparation of pure 4-amino-3-(4-phenoxyphenyl)-1Hpyrazolo[ 3,4-d]pyrimidine of formula I; Formula I comprises the steps of: a) reacting 4-phenoxybenzoic acid with a suitable reagent at a suita5 ble temperature to yield 4-phenoxybenzoyl chloride of formula II; Formula II b) reacting in-situ the resulting compound of formula II with malononitrile in the presence of a base, in a suitable organic solvent at a suitable temperature for sufficient time to yield 2-hydroxy-ethene compound of formula III; Formula III 10 c) reacting in-situ the resulting compound of formula III with a suitable methylating agent in the presence of a base at a suitable temperature to yield 2-methoxy-ethene compound of formula IV; Formula IV d) reacting in-situ the resulting ethene compound of formula IV with hydrazine hydrate at a suitable temperature to yield 3-amino-4-cyano-5-(4-phenoxy 15 phenyl)pyrazole of formula V; Formula V e) optionally, purifying amino pyrazole compound of formula V; f) reacting the resulting compound of formula V, with formamide at a suitable temperature to yield pure 4-amino-3-(4-phenoxyphenyl)-1H-pyrazolo[3,4-d]pyrimidine compound of formula I. 26 2. The process as claimed in claim 1, wherein in step a) the suitable reagent is selected from thionyl chloride, oxalyl chloride or sulfuryl chloride; the suitable temperature is 20°C to 70°C. 3.The process as claimed in claim 1, wherein in step b) the base is selected from diisopropylethylamine,triethylamine, 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU)5 , tertiary amines;sodium bicarbonate, sodium carbonate, sodium hydride; the suitable organic solvent is selected from non-polar aprotic solvents such as toluene, xylene, hexane, tetrahydrofuran, 1,4-dioxane, and the like. 4.The process as claimed in claim 1, wherein in step c) the suitable methylating 10 agent is selected from dimethyl sulphate, methyl iodide, dimethyl carbonate, tetramethylammonium chloride, methyl triflate; the base is selected from inorganic base such as sodium hydroxide, sodium carbonate, sodium bicarbonate, calcium hydroxide, and calcium carbonate; the suitable organic solvent is selected from non-polar aprotic solvents such as toluene, xylene, 15 hexane, tetrahydrofuran, 1,4-dioxane and the like. 5. A process for the preparation of 3-amino-4-cyano-5-(4-phenoxyphenyl)pyrazole compound of formula V Formula V comprises the steps of: a) reacting 4-phenoxybenzoic acid with a suitable reagent at a suitable 20 temperature to yield 4-phenoxybenzoyl chloride compound of formula II; Formula II b) reacting in-situ the resulting compound of formula II with malononitrile in the presence of a base, in a suitable organic solvent, at a suitable temperature to yield 2-hydroxy-ethene compound of formula III; Formula III 27 c) reacting in-situ the resulting compound of formula III with a suitable methylating agent in the presence of base to yield 2-methoxy-ethene compound of formula IV; Formula IV d) reacting in-situ the resulting compound of formula IV with hydrazine hydrate to give 3-amino-4-cyano-5-(4-phenoxyphenyl)pyrazole of formula 5 V; Formula V e) optionally, purifying the resulting compound of formula V to yield pure 3-amino-4-cyano-5-(4-phenoxyphenyl) pyrazole of formula V. 6. The process as claimed in claim 5, wherein intermediates of formulae II, III and IV are not isolated. 10 7. A process for preparation of ibrutinib of following formula, comprises the steps of: a) reacting 4-phenoxybenzoic acid with a suitable reagent at a suitable temperature to yield 4-phenoxybenzoyl chloride of formula II; Formula II b) reacting in-situ the resulting compound of formula II with malononitrile in the 15 presence of a base, in a suitable organic solvent at a suitable temperature for sufficient time to yield 2-hydroxy-ethene compound of formula III; Formula III 28 c) reacting in-situ the resulting compound of formula III with a suitable methylating agent in the presence of a base to yield 2-methoxy-ethene compound of formula IV; Formula IV d) reacting in-situ the resulting compound of formula IV with hydrazine hydrate at a suitable temperature to yield 3-amino-4-cyano-pyrazole compound 5 und of formula V; Formula V e) optionally, purifying 3-amino-4-cyano-5-(4-phenoxyphenyl)pyrazole of formula V; f) reacting the resulting compound of formula V, with formamide at a suitable 10 temperature to yield pure 4-amino-3-(4-phenoxyphenyl)-1H-pyrazolo[3,4-d]pyrimidine of formula I, and Formula I g) converting pyrimidine compound of formula I to ibrutinib. 8. The process as claimed in claim 7, wherein in step g) the conversion of pyrimidine compound of formula I to ibrutinib comprises the step of; 15 a) reacting pyrimidine compound of formula I with 1-boc-3-(S)-hydroxypiperidine under Mitsunobu reaction conditions to prepare compound of formula VI; Formula VI 29 b) deprotecting compound of formula VI using a suitable reagent to prepare amino compound of formula VII; Formula VII c)acylated the resulting amino compound of formula VII using acryloyl chloride in the presence of a base in a suitable solvent to prepare ibrutinib. 9. The process as claimed in claim 8, wherein in step b) the suitable reagent 5 nt is selected from strong acid such as trifluoroacetic acid or hydrochloric acid. 10. The process as claimed in claim 8, wherein in step c) the suitable base is selected from triethylamine, tri-n-butylamine, diisopropylethylamine, Nmethylmorpholine, DBU and the like; the suitable solvent is selected from 10 dichloromethane, chloroform, dichloroethane, ether such as tetrahydrofuran, 2-methyl tetrahydrofuran, 2-dimethoxy ether, 2- diethoxy ether, isopropyl ether and methyl tert butyl ether; toluene, xylene, acetonitrile and the like.