A compound of formula (I)whereinn is 0 to 4R is ethyl or vinylR1 is hydrogen or (C1-6)alkyl,R2 is hydrogen or- cycloalkyl including (C3-6)cycloalkyl, or- unsubstituted (C1-6)alkyl, or- (C1-6)alkyl substituted by one or more of- hydroxy preferably one or two,- halogen,- (C3-6)cycloalkyl, orR1 is hydroxy and R2 is formyl.