Patent ID: 7531687

Claim:
A process for the preparation of a compound of formula VII useful for the preparation of oseltamivir wherein: R 1 and R 1′ are independently hydrogen or C 1-6 alkyl, R 2 is an C 1-6 alkyl and R 5 and R 6 are independently C 1-6 alkyl and OMs is mesylate which process comprises the steps of: step 1—contacting an alkyl (3R,4S,5R) 3,4,5-trihydroxy-1-cyclohexene-1-carboxylate (III) wherein R 2 is as defined above with methanesulfonyl chloride in the presence of an aprotic organic solvent and an organic base to afford the tris-mesylate of formula IV; step 2—contacting IV with an azide in an organic solvent, optionally in the presence of water and a phase transfer catalyst, to displace the C-3 mesyloxy-group and form V wherein R 2 is as defined above; step 3—contacting V with a trialkylphosphite in an organic solvent to reduce the azide and form the aziridine of formula VI wherein R 2 is as defined above and R 5 and R 6 are independently C 1-6 alkyl; step 4—contacting VI with a first alcohol solvent and a Lewis acid to open the aziridine and form VII wherein R 1 , R 1′ , R 2 , R 5 and R 6 are as defined above.