| abstract |
The intermediate products of formula (II): <IMAGE> R' = especially H or optionally substituted alkyl, alkenyl, alkynyl, aryl or aralkyl, hydroxyl, tetrahydropyranyl, tert-butoxy, optionally esterified carboxyl, amino, mono- or dialkylamino, tritylamino, chloroacetamido, trifluoroacetylamino, trichloroethoxycarbonylamino, halogen or trialkylsilyl, R2 = methyl or ethyl, and process for their preparation. |