atoms, an alkylthio group having 1 to 5 carbon atoms, an alkylsulfonyl group having 1 to 5 carbon atoms, or a group of the formula R3 CONH- (where R3 is an alkyl group having 1 to 5 carbon atoms); n is an integer of 0 to 5; R1 is hydrogen, an alkyl group having 1 to 5 carbon atoms, a phenyl group, a group of the formula --(A)--COOR4 [where R4 is hydrogen, an alkyl group having 1 to 5 carbon atoms,