FIELD OF THE INVENTION
The present invention relates to a novel process for the production of acetylnorbomene, which is an intermediate in the synthesis of biperiden. In particular, the present invention relates to a process for producing acetylnorbomene containing higher proportion of the exo form than the endo form, which is essential for the synthesis of biperiden. The process can be applied in large scale production of acetylnorbomene and consists of preparation of 5-cyanonorbomene and its reaction with appropriate Grignard reagents.
BACKGROUND OF THE INVNETION
Exo form of 5 -Acetylnorbomene is a key intermediate for the synthesis of biperiden (I),

which is an antiparkinsonian agent of the anticholinergic type. In conventional method 5 -Acetylnorbomene is synthesized through Diels-Alder reaction between cyclopentadiene and methyl vinyl ketone (Scheme 1).

The product obtained in the conventional method contains very high endo isomer. Further, the product has to be subjected to additional step of equilibration in the presence of a base to generate desired exo/endo ratio. In addition, methyl vinyl ketone, which is used as the starting material in the prior art process, has the disadvantage of being less stable and polymerizes on standing. Further, methyl vinyl ketone is expensive and difficult to handle because of its high toxic nature.

The conventional method is not fully satisfactory for the industrial working since the reaction between cyclopentadiene and methyl vinyl ketone is highly exothermic and limits the scope for the scaling up.
Therefore, the need for a method which produces acetylnorbomene with a higher proportion of the exo form than the endo form and which overcomes the disadvantages stated above, has been in demand.
OBJECTS OF THE INVENTION
Accordingly, one of the objects of the present invention is to provide a practical method for the production of 5-acetynorbomene in a large scale, economically and efficiently.
Another object of the present invention is to provide a method for producing 5-acetylnorbomene in predominantly exo form.
SUMMARY OF THE INVENTION
In one aspect, the present invention provides a method for producing 5-Acetylnorbomene comprising the steps of a) reacting cyclopentadiene with acrylonitrile to form 5-Cyanonorbomene and b) reacting of 5-Cyanonorbomene with methyl magnesium chloride.
DETAILED DESCRIPTION OF THE INVENTION
The present invention provides a method for producing 5- Acetylnorbomene an intermediate in the synthesis of biperiden.
One embodiment of this invention is directed to a method of producing 5-Acetylnorbomene (III). The said method comprises of reaction of cyclopentadiene with acrylonitrile to provide 5-Cyanonorbomene (II) which on treatment with

methyl magnesium chloride results 5- Acetylnorbomene (III) jind the details are shown in Scheme 2.

Scheme - 2
Hereinafter the invention is explained more specifically referring to the working examples, it being understood that the examples incur no restricting effect on the invention.
Example 1:
Preparation of 5-Cyanonorbornene:
To a solution of acrylonitrile (249.4 g, 4.7 mol) in methanol (260 mL) at 40° C was added cyclopentadiene monomer (311.0 g, 4.7 mol) slowly over a period of 45 min. The temperature of the reaction was maintained between 40 and 50°C for one hour. The solvent was removed under vacuum to obtain a residue (487.3 g), which on distillation under high vacuum produced 5-cyanonorbomene (453.3 g, 80.8% yield).
Example 2:
Preparation of 5-Acetylnorborneiie:
1,4-dioxan was added slowly over a period of one hour, at room temperature to a solution of methyl magnesium chloride (263.6 mL, 3.0 M solution in THF, 0.53 mol). 5-Cyanonorbomene (30 g, 0.25 mol) was then added slowly at room temperature over a period of one hour and then the reaction mixture was refluxed for 90 min. After completion of the reaction the reaction mixture was cooled and poured into ice-cold water (200 mL). On usual work-up followed by distillation

under vacuum produced Acetylnorbomene (25.5 g, 75% yield). The ratio of exo to endo isomers is 1.8 [Gas Chromatograph analysis (area %): exo/endo = 41.80/23.16=1.8].

We Claim
1. A method for producing 5-Acetylnorbomene comprising the steps of a) reacting cyclopentadiene with acrylonitrile to obtain 5-Cyanonorbomene and b) reacting the 5-Cyanonorbomene with methyl magnesium chloride to obtain 5-Acetylnorbornene.
2. The method as claimed in claim 1, wherein cyclopentadiene and acrylonitrile are used in a molar ratio of 0.5:1 to 2:1, preferably 1:1.
3. The method as claimed in claim 1, wherein the reaction of cyclopentadiene and acrylonitrile is carried out at a temperature of-10° to 80° C, preferably 40 to 50° C.
4. The method as claimed in claim 1, wherein 5-Cyanonorbomene and methyl magnesium chloride are used in the molar ratio of 0.2:1 to 1:1.
5. The method as claimed in claim 1, wherein the reaction of 5-Cyanonorbomene and methyl magnesium chloride is carried out at a temperature of-10° to 50° C.
6. The method as claimed in claim 1, wherein the methyl magnesium chloride is used as a solution in a organic solvent.
7. The method as claimed in claim 6, wherein the organic solvent is selected from ether, tetrahydrofuran, 1,4-dioxan or toluene.
8. The method as claimed in claim 1, wherein the ratio of exo/endo forms of 5-Acetylnorbomene is from 1 to 10, particularly 1.5 to 4.0.