FIELD OF INVENTION

The present invention relates to an improved process for the synthesis of strobilurin fungicides.

BACKGROUND OF THE INVENTION

Kresoxim-methyl which is methyl (a£T)-a-(methoxyimino)-2-[(2-methylphenoxy) methyl]phenylacetate belongs to the strobilurin class of fungicides. Kresoxim-methyl was first disclosed in US4829085. It has the following structural formula:

US5221762 teaches process for preparation of Kresoxim-methyl. In this process for the preparation of Kresoxim-methyl, 2-o-tolyloxymethylbenzoic acid methyl ester i.e. compound of formula (1) is formed as a by-product which cannot be recovered. This leads to an increase in the effluent treatment load, feasibility and high overall cost.

Dimoxystrobin which is (£)-2-[2-(2,5-dimethylphenoxymethyl)phenyl]-2-methoxyimino-N-methylacetamide also belongs to strobilurin class of fungicides. Dimoxystrobin was first disclosed in US5395854. It has the following structural formula:

US5395854 and US5516804 described a process for preparation of Dimoxystrobin in which [2-(2,5-dimethylphenoxymethyl)phenyl]methoxyimino-acetyl chloride is coupled with dry methylamine. The process is disadvantageous on the large-scale as it involves handling of moisture sensitive acid chloride as well as dry methylamine which is a colourless gas. This drawback is eliminated in the present invention by using stable ester compound of formula V i.e. (£)-2-[2-(2,5-dimethylphenoxymethyl)phenyl]methoxyimino-acetic acid methyl ester in place of [2-(2,5-dimethylphenoxymethyl)phenyl]methoxyimino-acetyl chloride and solution of methylamine in methanol in place of dry methylamine gas.

Orysastrobin which is (2£)-2-(methoxyimino)-2-{2-[(3£,5£,6£)-5-(methoxyimino)-4, 6-dimethyl-2,8-dioxa-3,7-diazanona-3,6-dien-1 -yl] phenyl}-N-methylacetamide also belongs to strobilurin class of fungicides. Orysastrobin was first disclosed in US5948932. It has the following structural formula:

US5948932 further discloses a process for preparation of Orysastrobin. However, in this process first step of coupling of (2-bromomethylphenyl)methoxyimino-acetic acid methyl ester with pentane-2,3,4-trione-3,4-bis(0-methyloxime)-2-oxime gives only 32% yield of resulting ester compound which in turn is reacted with aqueous methylamine in tetrahydrofuran for 12 hour. Because of poor yield of ester intermediate, use of relatively expensive tetrahydrofuran and longer reaction time the process is not suitable for production of Orysastrobin on larger-scale.

The compound shown below designated as Intermediate (I) is disclosed in US5334577. An improved process for the preparation of Intermediate (I) is disclosed in WO2013/144924. Intermediate (I) is a key intermediate for the synthesis of strobilurin fungicides of the present invention viz Kresoxim-methyl, Dimoxystrobin and Orysastrobin.

The prior art processes for the synthesis of strobilurin fungicides viz Kresoxim-methyl, Dimoxystrobin and Orysastrobin suffer from drawbacks like low yield and low purity.

To ameliorate such disadvantages there is a need to develop an improved process for the preparation of strobilurin fungicides viz Kresoxim-methyl, Dimoxystrobin and Orysastrobin in good yield and high purity. There is a need to develop a commercially viable process which has the capacity to produce products in good yield and high purity.

The present inventors have developed an improved process for the synthesis of the compound of formula (I) which ameliorates the drawbacks of the prior art.

The present inventors have found that preparing compound of formula (I) by employing the process of the present invention yields product having high purity and good yield.

The present inventors have found that preparing compound of formula (I) by employing the process of the present invention yields products having purity more than 98%.

OBJECTS OF THE INVENTION

It is an object of the present invention to provide an improved process for the synthesis of strobilurin fungicides viz Kresoxim-methyl, Dimoxystrobin and Orysastrobin.

It is another object of the present invention to provide an improved process for the synthesis of substantially pure strobilurin fungicides viz Kresoxim-methyl, Dimoxystrobin and Orysastrobin from Intermediate (I) in good yield.

It is yet another object of the present invention to provide an improved process for the synthesis of strobilurin fungicides viz Kresoxim-methyl, Dimoxystrobin and Orysastrobin in good yield and high purity.

It is a further object of the present invention to provide an improved process for the synthesis of strobilurin fungicides which yields products i.e. Kresoxim-methyl, Dimoxystrobin and Orysastrobin having purity more than 98%.

SUMMARY OF THE INVENTION
According to an aspect of the present invention there is provided an improved process for the preparation of compound of formula (I), vherein, R is A and X= O, comprising the steps of:

i. Charging compound of formula II and solvent into a dry flask at a temperature range of 25-30 °C to obtain a reaction mass;

ii. Charging anhydrous potassium carbonate (K2CO3) into the reaction mass of step (i) under stirring at 25-30 °C; iii. Charging intermediate (I) Intermediate (I) into the reaction mass of step (ii) at 25-30 °C; iv. Stirring the reaction mass of step (iii) at 25-30 °C for 7.0-10.0 hours; v. Quenching the reaction mass of step (iv) in water at 25-30 °C under stirring and continue stirring for 1 hour;

vi. Filtering and drying the reaction mass of step (v) to yield compound of formula (I);
vii. Purifying compound of the formula (I) of step (vi) by recrystallization in solvent. According to another aspect of the present invention there is provided an improved process for the preparation of compound of formula (I)

i. Charging compound of formula III and solvent into a dry flask at a temperature range of 25-30 °C to obtain a reaction mass;

ii. Charging anhydrous potassium carbonate (K2CO3) into the reaction mass of step (i) under stirring at 25-30 °C;

iii. Charging intermediate (I) Intermediate (I) into the reaction mass of step (ii) at 25-30 °C; iv. Stirring the reaction mass of step (iii) at 25-30 °C for 7.0-10.0 hours; v. Quenching the reaction mass of step (iv) in water at 25-30 °C under stirring and continue stirring for 1 hour; vi. Filtering and drying the reaction mass of step (v) to yield compound of formula;

vii. Purifying compound of step (vi) by recrystallization in solvent;

viii. Charging compound of step (vii) and solvent into a dry flask at a temperature range 25-30 °C to obtain reaction mass; ix. Adding methanolic methylamine into the reaction mass of step (viii) under stirring and continue stirring the reaction mass at 25-30 °C for 5.0-7.0 hours; x. Distilling the organic volatiles from the reaction mass of step (ix); xi. Charging ethyl acetate to the reaction mass of step (x); xii. Charging water to the reaction mass of step (xi); xiii. Stirring the reaction mass of step (xii) and then separating the aqueous and organic layer; xiv. Extracting the aqueous layer with ethyl acetate; xv. Combining the organic layers and drying over anhydrous sodium sulphate; xvi. Distilling the solvent in rotovac at 40-45 °C to obtain crude mass of compound of formula (I); xvii. Purifying compound of the formula (I) of (xvi) by recrystallization in solvent.

Compound of formula (I) According to another aspect of the present invention there is provided an improved process for the preparation of compound of formula (I),
i. Charging compound of formula IV and solvent into a dry flask at a temperature range of 25-30 °C to obtain a reaction mass;
ii. Charging anhydrous potassium carbonate (K2CO3) into the reaction mass of step (i) under stirring at 25-30 °C;

iii. Charging intermediate (I) Intermediate (1) into the reaction mass of step (ii) at 25-30 °C; iv. Stirring the reaction mass of step (iii) at 25-30 °C for 7.0-10.0 hours; v. Quenching the reaction mass of step (iv) in water at 25-30 °C under stirring and continue stirring for 1 hour; vi. Filtering and drying the reaction mass of step (v) to yield compound of formula;

vii. Purifying compound of step (vi) by recrystallization in solvent;

viii. Charging compound of step (vii) and solvent into a dry flask at a temperature range 25-30 °C to obtain a reaction mass;
ix. Adding methanolic methylamine into the reaction mass of step (viii) under stirring and continue stirring the reaction mass at 25-30 °C for 5.0 - 7.0 hours;

x. Distilling the organic volatiles from the reaction mass of step (ix);

xi. Charging ethyl acetate to the reaction mass of step (x);

xii. Charging water to the reaction mass of step (xi);

xiii. Stirring the reaction mass of step (xii) and then separating the aqueous and organic layer;

xiv. Extracting the aqueous layer with ethyl acetate;

xv. Combining the organic layers and drying over anhydrous sodium sulphate;

xvi. Distilling the solvent in rotovac at 40-45 °C crude mass of compound of formula (I).
xvii. Purifying compound of the formula (I) of step (xvi) by recrystallization in solvent.
DETAILED DESCRIPTION OF THE INVENTION

The present invention provides a robust, efficient and economical synthesis of compound of formula (I) in good yield and high purity.

In an embodiment of the present invention there is provided an improved process for the preparation of compound of formula (I),

i. Charging compound of formula II and solvent into a dry flask at a temperature range of 25-30 °C to obtain a reaction mass;
ii.
ii. Charging anhydrous potassium carbonate (K2CO3) into the reaction mass of step (i) under stirring at 25-30 °C;

iii. Charging intermediate (I) Intermediate (I) into the reaction mass of step (ii) at 25-30 °C; iv. Stirring the reaction mass of step (iii) at 25-30 °C for 7.0-10.0 hours; v. Quenching the reaction mass of step

(iv) in water at 25-30 °C under stirring and continue stirring for 1 hour; vi. Filtering and drying the reaction mass of step

(v) to yield compound of formula (I); vii. Purifying compound of the formula (I) of step

(vi) by recrystallization in solvent. In another embodiment of the present invention there is provided an improved process for the preparation of compound of formula (I)

i. Charging compound of formula III and solvent into a dry flask at a temperature range of 25-30 °C to obtain a reaction mass; in

ii. Charging anhydrous potassium carbonate (K2CO3) into the reaction mass of step (i) under stirring at 25-30 °C;
iii. Charging intermediate (I) Intermediate (I) into the reaction mass of step (ii) at 25-30 °C;

iv. Stirring the reaction mass of step (iii) at 25-30 °C for 7.0-10.0 hours;

v. Quenching the reaction mass of step (iv) in water at 25-30 °C under stirring and continue stirring for 1 hour;

vi. Filtering and drying the reaction mass of step (v) to yield compound of formula;

vii. Purifying compound of step (vi) by recrystallization in solvent;

viii. Charging compound of step (vii) and solvent into a dry flask at a temperature range 25-30 °C to obtain reaction mass;

ix. Adding methanolic methylamine into the reaction mass of step (viii) under stirring and continue stirring the reaction mass at 25-30 °C for 5.0 - 7.0 hours;

x. Distilling the organic volatiles from the reaction mass of step (ix);

xi. Charging ethyl acetate to the reaction mass of step (x);

xii. Charging water to the reaction mass of step (xi);

xiii. Stirring the reaction mass of step (xii) and then separating the aqueous and organic layer;
xiv. Extracting the aqueous layer with ethyl acetate;
xv. Combining the organic layers and drying over anhydrous sodium sulphate;

xvi. Distilling the solvent in rotovac at 40-45 °C to obtain crude mass of compound of formula (I);

xvii. Purifying compound of the formula (I) of (xvi) by recrystallization in solvent. In another embodiment of the present invention there is provided an improved process for the preparation of compound of formula (I),

i. Charging compound of formula IV and solvent into a dry flask at a temperature range of 25-30 °C to obtain a reaction mass;

ii. Charging anhydrous potassium carbonate (K2CO3) into the reaction mass of step (i) under stirring at 25-30 °C;

iii. Charging intermediate (I) Intermediate (I) into the reaction mass of step (ii) at 25-30 °C;

iv. Stirring the reaction mass of step (iii) at 25-30 °C for 7.0-10.0 hours;

v. Quenching the reaction mass of step (iv) in water at 25-30 °C under stirring and continue stirring for 1 hour;

vi. Filtering and drying the reaction mass of step (v) to yield compound of formula; T .1.

vii. Purifying compound of step (vi) by recrystallization in solvent;

viii. Charging compound of step (vii) and solvent into a dry flask at a temperature range 25-30 °C to obtain a reaction mass;
ix. Adding methanolic methylamine into the reaction mass of step (viii) under stirring and continue stirring the reaction mass at 25-30 °C for 5.0 - 7.0 hours;

x. Distilling the organic volatiles from the reaction mass of step (ix);

xi. Charging ethyl acetate to the reaction mass of step (x);

xii. Charging water to the reaction mass of step (xi);

xiii. Stirring the reaction mass of step (xii) and then separating the aqueous and organic layer;

xiv. Extracting the aqueous layer with ethyl acetate;

xv. Combining the organic layers and drying over anhydrous sodium sulphate;

xvi. Distilling the solvent in rotovac at 40-45 °C to obtain crude mass of compound of formula (I);

xvii. Purifying compound of the formula (I) of step (xvi) by recrystallization in solvent. The solvent used in step (i) is selected from acetone, methyl isobutyl ketone, dimethyl acetamide, dimethyl formamide, dimethyl sulfoxide, N- methylpyrrolidine, acetonitrile, tetrahydrofuran, dioxane, dimethoxyethane, ethyl acetate, isopropyl acetate, isobutyl acetate etc.

The solvent used in step

(viii) is selected from the group consisting of dichloromethane, chloroform, 1,2-dichlororethane, methanol.
The solvent used in the purification step of the final product i.e. Kresoxim-methyl, Dimoxystrobin and Orysastrobin is selected from the group consisting of methanol, ethanol, isopropanol, w-propanol, n-butanol, acetonitrile, ethyl acetate, diethyl ether, diisopropyl ether, methyl isobutyl ether etc.

In another embodiment of the present invention Kresoxim-methyl, (i.e. compound of the formula (I) wherein R is 2-methylphenoxy (A) and X is O) is obtained with purity more than 98%.

In another embodiment of the present invention Dimoxystrobin (compound of the formula (I) wherein R is 2,5-dimethylphenoxy (B) and X is NH) is obtained with purity more than 99%.

In another embodiment of the present invention Orysastrobin (compound of the formula (I) wherein R is 2,3-bis-methoxyimino-l-methylbutylideneaminooxy (C) and X is NH) is obtained with purity more than 99%.

The following examples are meant to illustrate the present invention. The examples are presented to exemplify the invention and are not to be considered as limiting the scope of the invention.

EXAMPLES

Example 1: Preparation of compound of formula (I): wherein X is O and R is 2-methylphenoxy (A) i.e. Kresoxim-methyl.

0-Cresol (Compound of formula II) (1.89 g, 0.017 moles) is dissolved in DMF (25.0 ml) 25-30 °C. To the clear solution is added potassium carbonate (12.0 g, 0.085 moles) at 25-30 °C. The reaction mixture is stirred at 25-30 °C for 15 min. To the reaction mixture is added Intermediate (I) (5.0 g, 0.017 moles) at 25-30 °C and stirred for 7-10 h. The reaction mixture is then poured on water and stirred for 1.0 h at 25-30 °C. The reaction mass is then filtered to separate solid. The crude compound is recrystallized in methanol to obtain Kresoxim-methyl having purity >98%. Yield: 4.4 g (80.7%).

Example 2: Preparation of compound of formula (I); R is 2,5-dimethylphenoxy (B) and X is NH i.e. Dimoxvstrobin.

Stage-1: Preparation of compound of formula (V)

2,5-Dimethylphenol (Compound of formula III) (2.1 g, 0.017 moles) is dissolved in DMF (25.0 ml) 25-30 °C. To the clear solution is added potassium carbonate (12.0 g, 0.085 moles) at 25-30 °C. The reaction mixture is stirred at 25-30 °C for 15 min. To the reaction mixture is added Intermediate (I) (5.0 g, 0.017 moles) at 25-30 °C and stirred for 7-10 hours. The reaction mixture is then poured on water and stirred for 1.0 hour at 25-30 °C. The reaction mass is then filtered to separate solid. The crude compound is recrystallized in methanol to obtain compound of formula (V) having purity >95%. Yield: 5.3 g (92.6%).

Stage-2: Preparation of compound of formula (I); R is 2,5-dimethylphenoxy (B) and X is NH i.e. Dimoxystrobin.

Compound of formula (V) (5.0 g, 0.017) is dissolved in DCM (50 ml) at 25-30 °C. To the clear solution was added methanolic methylamine (15.0 ml) at 25-30 °C. The reaction mixture is stirred at 25-30 °C for 5-7 hours and then concentrated to obtain yellow coloured residue. The residue was dissolved in ethyl acetate and then washed with water. The aqueous layer was separated and then extracted again in ethyl acetate. The ethyl acetate layers were combined, dried over anhydrous sodium sulphate and concentrated under vacuum at 40-45 °C to obtain crude compound which was purified by recrystallization in methanol to afford Dimoxystrobin having purity >99%. Yield: 4.7 g (94.3%).

Example 3; Preparation of compound of formula (I); wherein R is 2, 3-bis-methoxyimino-l-methylbutylideneaminooxv (C) and X is NH i.e. Orysastrobin.

Stage-1: Preparation of compound of formula (VD.

Compound of formula IV (0.065 g, 0.0035 moles) is dissolved in DMF (5.0 ml) 25-30 °C. To the clear solution is added potassium carbonate (2.4 g, 0.017 moles) at 25-30 °C. The reaction mixture is stirred at 25-30 °C for 15 min. To the reaction mixture is added Intermediate (I) (1.0 g, 0.0035 moles) at 25-30 °C and stirred for 7-10 h. The reaction mixture is then poured on water and stirred for 1.0 h at 25-30 °C. The reaction mass is then filtered to separate solid. The crude compound is recrystallized in methanol to obtain compound of formula (VI) having purity >95%. Yield: 1.1 g (80.3%).

Stage-2: Preparation of compound of formula (I); wherein R is 2,3-bis-methoxvimino-1-methvlbutvlideneaminooxv (O and X is NH i.e. Orysastrobin.

Compound of formula (VI) (1.0 g, 0.0025) is dissolved in DCM (10 ml) at 25-30 °C. To the clear solution was added methanolic methylamine (3.0 ml) at 25-30 °C. The reaction mixture is stirred at 25-30 °C for 5-7 h and then concentrated to obtain yellow coloured residue. The residue was dissolved in ethyl acetate and then washed with water. The aqueous layer was separated and then extracted again in ethyl acetate. The ethyl acetate layers were combined, dried over anhydrous sodium sulphate and concentrated under vacuum at 40-45 °C to obtain crude compound which was purified by recrystallization in methanol to afford Orysastrobin having purity >99%. Yield: 0.85 g (85.2%).

Synthesis for preparation of compound of formula (I) wherein R is 2-methylphenoxy (A) and X is O i.e. Kresoxim-methyl can be represented as shown in scheme (D as follows:

Synthesis for preparation of compound of formula (I) wherein R is 2,5-dimethvlphenoxy (B) and X is NH i.e. Dimoxystrobin can be represented as shown in scheme (I) as follows:

Stage: 1

Synthesis for preparation of compound of formula (V) can be represented as shown in scheme (D as follows:

Stage 2:

Conversion of compound of formula (V) to compound of formula (T) wherein R is 2.5-dimethvlphenoxv (B) and X is NH i.e. Dimoxystrobin can be represented as shown in scheme (D as follows:
Synthesis for preparation of compound of formula (I) wherein compound of the formula I wherein R is 2,3-bis-methoxyimino-l-methylbutvlideneaminooxy (C) and X is NH i.e. Orysastrobin can be represented as shown in scheme (I) as follows;

Stage-1:

Synthesis for preparation of compound of formula (YD can be represented as shown in scheme (I) as follows:

Stage-2;

Conversion of compound of formula (VI) to compound of formula (D wherein R is 2.3-bis-methoxvimino-l-methvlbutylideneaminooxv (O and X is NH i.e. Orysastrobin can be represented as shown in scheme (I) as follows:

Batchwise data of regarding yield and purity of compound of the formula (I) wherein R is 2-methylphenoxy (A) and X is O. i.e. Kresoxim-methyl.

Batchwise data of regarding yield and purity of compound of the formula (V).

Batch wise data of regarding yield and purity of compound of the formula (1) wherein R is 2.5-dimethylphenoxy (B) and X is NH. i.e. Dimoxystrobin.

Data regarding yield and purity of compound of the formula (VD Data regarding yield and purity of compound of the formula (I) wherein R is 2.3-bis-methoxvimino-1-methvlbutvlideneaminooxy (C) and X is NH i.e. Orysastrobin.

Comparative data: Table: 1

WE CLAIM

1. An improved process for the preparation of compound of formula (I) wherein, R is A and X= O, comprising the steps of:

i. Charging compound of formula II and solvent into a dry flask at a temperature range of 25-30 °C to obtain a reaction mass;

ii. Charging anhydrous potassium carbonate (K2CO3) into the reaction mass of step (i) under stirring at 25-30 °C;

iii. Charging intermediate (I) Intermediate (I) into the reaction mass of step (ii) at 25-30 °C;

iv. Stirring the reaction mass of step (iii) at 25-30 °C for 7.0-10.0 hours;

v. Quenching the reaction mass of step (iv) in water at 25-30 °C under stirring and continue stirring for 1 hour;

vi. Filtering and drying the reaction mass of step (v) to yield compound of formula (I);

vii. Purifying compound of the formula (I) of step (vi) by recrystallization in solvent.

2. An improved process for the preparation of compound of formula (I),

i. Charging compound of formula III and solvent into a dry flask at a temperature range of 25-30 °C to obtain a reaction mass;

ii. Charging anhydrous potassium carbonate (K2CO3) into the reaction mass of step (i) under stirring at 25-30 °C;
iii. Charging intermediate (I) Intermediate (I) into the reaction mass of step (ii) at 25-30 °C;

iv. Stirring the reaction mass of step (iii) at 25-30 °C for 7.0-10.0 hours;

v. Quenching the reaction mass of step (iv) in water at 25-30 °C under stirring and continue stirring for 1 hour;

vi. Filtering and drying the reaction mass of step (v) to yield compound of formula;

vii. Purifying compound of step (vi) by recrystallization in solvent;

viii. Charging compound of step (vii) and solvent into a dry flask at a temperature range 25-30 °C to obtain reaction mass;

ix. Adding methanolic methylamine into the reaction mass of step (viii) under stirring and continue stirring the reaction mass at 25-30 °C for 5.0 - 7.0 hours;

x. Distilling the organic volatiles from the reaction mass of step (ix);

xi. Charging ethyl acetate to the reaction mass of step (x); xii. Charging water to the reaction mass of step (xi);

xiii. Stirring the reaction mass of step (xii) and then separating the aqueous and organic layer; xiv. Extracting the aqueous layer with ethyl acetate; xv. Combining the organic layers and drying over anhydrous sodium sulphate;

xvi. Distilling the solvent in rotovac at 40-45 °C to obtain crude mass of compound of formula (I); xvii. Purifying compound of the formula (I) of (xvi) by recrystallization in solvent.

3. An improved process for the preparation of compound of formula (I),

i. Charging compound of formula IV and solvent into a dry flask at a temperature range of 25-30 °C to obtain a reaction mass;

ii. Charging anhydrous potassium carbonate (K2CO3) into the reaction mass of step (i) under stirring at 25-30 °C;
iii. Charging intermediate (I) Intermediate (I) into the reaction mass of step (ii) at 25-30 °C;

iv. Stirring the reaction mass of step (iii) at 25-30 °C for 7.0-10.0 hours;

v. Quenching the reaction mass of step (iv) in water at 25-30 °C under stirring and continue stirring for 1 hour;

vi. Filtering and drying the reaction mass of step (v) to yield compound of formula; VI

vii. Purifying compound of step (vi) by recrystallization in solvent;

viii. Charging compound of step (vii) and solvent into a dry flask at a temperature range 25-30 °C to obtain a reaction mass;

ix. Adding methanolic methylamine into the reaction mass of step (viii) under stirring and continue stirring the reaction mass at 25-30 °C for 5.0 - 7.0 hours;

x. Distilling organic volatiles from the reaction mass of step (ix);
xi. Charging ethyl acetate to the reaction mass of step (x);

xii. Charging water to the reaction mass of step (xi);

xiii. Stirring the reaction mass of step (xii) and then separating the aqueous and organic layer;

xiv. Extracting the aqueous layer with ethyl acetate;

xv. Combining the organic layers and drying over anhydrous sodium sulphate;

xvi. Distilling out the solvent in rotovac at 40-45 °C to obtain crude mass of compound of formula (I);

xvii. Purifying compound of the formula (I) of step (xvi) by recrystallization in solvent.

4. The process for the preparation of compound of formula (I) as claimed in any one of the preceding claims, wherein the solvent used in step (i) is selected from the group consisting of acetone, methyl isobutyl ketone, dimethyl acetamide, dimethyl formamide, dimethyl sulfoxide, N-methylpyrrolidine, acetonitrile, tetrahydrofuran, dioxane, dimethoxyethane, ethyl acetate, isopropyl acetate, isobutyl acetate.

5. The process for the preparation of compound of formula (I) as claimed in claim 1 or claim 2 or claim 3, wherein the solvent used in step (vii) is selected from the group consisting of methanol, ethanol, isopropanol, n-propanol, w-butanol, acetonitrile, ethyl acetate, diethyl ether, diisopropyl ether, methyl isobutyl ether.

6. The process for the preparation of compound of formula (I) as claimed in claim 2 or claim 3 wherein the solvent used in step (viii) is selected from the group consisting of dichloromethane, chloroform, 1,2-dichlororethane, methanol.
7. The process for the preparation of compound of formula (I) as claimed in claim 2 or claim 3 wherein the solvent used in step (xvii) is selected from the group consisting of methanol, ethanol, isopropanol, w-propanol, n-butanol, acetonitrile, ethyl acetate, diethyl ether, diisopropyl ether, methyl isobutyl ether.

8. A compound of formula (I) as claimed in claim 1 with purity >98%.

9. A compound of formula (I) as claimed in claim 1 with purity >99%.

10. A compound of formula (I) as claimed in claim 1 with purity >99%.