Patent ID: 7759492

Claim:
An enantioselective process for preparing a compound of formula I: comprising the steps of: (a) reacting a compound of formula II with a compound of formula III: in the presence of a catalyst selected from: to form a compound of formula IV: (b) treating said compound of formula IV with R 3 O − M + to form a compound of formula V: (c) dehydrating said compound of formula V to form the compound of formula I; wherein R 1 is H or C 1-4 alkyl; R 2 is H, C 1-4 alkyl, phenyl, or Cl; R 3 is C 1-4 alkyl or benzyl; Z is O or S; M is an alkali metal; X is SbF 6 − , BF 4 − , PF 6 − or CF 3 SO 3 − ; each Y 1 is t-butyl; i-propyl, phenyl or 1-naphthyl; each Y 2 is t-butyl, phenyl, 4-cyanophenyl, 2-chlorophenyl, 2,6-dichlorophenyl or 2,6-difluorophenyl; and Tf represents trifluoromethylsulfonyl.