Method for producing benzylidene derivatives

A selective method for producing a given stereoisomeric benzylidene derivatives of the formula III: wherein R and R each independently is lower alkyl, lower alkoxy or halogen; Y is SO2, SO or CO; -A- is optionally substituted lower alkylene; -B- is -CH2- or -O-; or -A- and -B- taken together may form optionally substituted phenylene or optionally substituted lower alkenylene; and R is hydrogen, optionally substituted lower alkyl, cycloalkyl, lower alkoxy, hydroxy, optionally substituted aryl, optionally substituted arylalkyl; optionally substituted arylalkyloxy, heterocyclic ring or N-protecting groups, which comprises reacting a compound of the formula I: wherein R and R are as defined above and X is lower alkoxy or halogen with a compound of the formula II: wherein Y, -A-, -B- and R are as defined above in the presence of a base.