Patent ID: 7563912

Claim:
A process for the manufacture of an S isomer of a compound of formula (8) wherein R 1 is methyl or ethyl; and R 2 is C 2 -C 4 alkyl, C 2 -C 4 alkenyl or C 2 -C 4 alkynyl, optionally substituted by one or more halogen; said process comprising the following steps: (a) reacting a compound of formula (9) with an alcohol of formula R 1 OH, wherein R 1 is as defined for the compound of formula (8), and thionyl chloride, to obtain a compound of formula (10), (b) reacting the compound of formula (10) with a R 2 -substituted-ethyl-4-bromobutyrate, wherein R 2 is as defined for the compound of formula (8), to obtain a compound of formula (11), (c) cyclisation of the compound of formula (11) with a catalyst, and (d) isolating the S isomer of the compound of formula (8).