membered monocyclic heteroaromatic ring containing from 4 to 5 carbon atoms and from 1 to 2 hetero atoms selected from the group consisting of oxygen nitrogen or sulfur among the preferred heteroaromatic groups are included thiopenyl thioazole pyridinyl furanyl etc the term u201c hydroxy lower alkyl u201d means a lower alkyl group as defined above which is substituted preferably monosubstituted by a hydroxy group the term u201c lower alkylene u201d designates a divalent saturated straight or branch chain hydrocarbon substituent containing from one to six carbon atoms the term u201c cyclo lower alkylene u201d designates a cyclo lower alkenyl substituent which is a divalent unsubstituted 3 to 6 membered saturated carbocyclic hydrocarbon ring among the preferred cycloalkylene substituents are cyclopropenyl and cyclobutenyl the term u201c lower alkanoyloxy lower alkylene u201d designates a lower alkylene substituent substituted preferably monosubstituted with a lower alkanoyloxy group where lower alkanoyloxy is defined as above the term u201c lower alkoxy lower alkylene u201d denotes a lower alkylene substituent as designated hereinbefore substituted preferably monosubstituted with a lower alkoxy group where lower alkoxy is defined as above the term u201c hydroxy lower alkylene u201d designates a lower alkylene substituent substituted preferably monosubstituted with a hydroxy group the term u201c lower alkoxy lower alkyl u201d means a lower alkyl substituent as.