Patent ID: 7842840

Claim:
A process for the preparation of a compound of formula (I) wherein R′ is hydrogen and R″ is selected from hydrogen C 1-6 -alkyl, C 1-6 -alkoxy, aryl-C 1-6 -alkoxy, C 1-6 -alkyl-C 1-6 -alkoxy, halogen, perhalo-C 1-6 -alkyl, phenyl optionally substituted with one or two groups chosen from atoms of halogen and C 1-6 -alkyl, which comprises reacting a compound of formula (II), in cis form or as a cis/trans mixture, wherein R′ and R″ are as defined above, and R′″ is an atom of hydrogen or a Pr protecting group hydrolysable in an acid environment, with concentrated sulfuric acid, at a temperature below +20° C.