d with one or more lower alkyl containing 1 to 4 carbon atoms, halogen, lower alkoxy containing 1 to 4 carbon atoms, nitro, amino, dialkylamino, trifluoromethyl or a thiophenyl radical; R7 is R1 other than H or the radical R6 COO--; and R1 represents hydrogen or a straight-chain or branched lower alkyl containing 1 to 4 carbon atoms or benzyl. 28.