A compound of formula (I) wherein n is 0 to 4； R is ethyl or vinyl； R 1 is hydrogen or (C 1-6 )alkyl, R 2 is hydrogen or - cycloalkyl including (C 3-6 )cycloalkyl, or - unsubstituted (C 1-6 )alkyl, or - (C 1-6 )alkyl substituted by one or more of - hydroxy； preferably one or two, - halogen, - (C 3-6 )cycloalkyl, or R 1 is hydroxy and R 2 is formyl.
