| abstract |
A process for the preparation of a compound (I) ##STR1## wherein R is a hydroxyl protecting group which comprises isomerising a compound of formula (I) wherein R is a hydroxyl protecting group by reacting the compound of formula (I) with a sterically hindered organic base in the presence of a Lewis acid and a compound of forumula (III) ##STR2## wherein R 1 and R 2 each independently represent cyano, COR 5 or COR 2 R 6 or R 1 and n R 2 together with the carbon atom to which they are attached from a C═O group; n R 5 represents alkyl, cycloalkyl, amino, alkylamino, dialkyl amino or optionally substituted phenyl or phenylalkyl group; n R 6 represents alkyl, cycloalkyl or optionally substituted phenyl or phenylalkyl group; n R 3 and R 4 represent each independently hydrogen, alkyl, alkoxy or optionally substituted phenyl group. |