substituted aroyl group such as benzoyl and the like the aroyl group may be substituted heteroaroyl group such as pyridyl carbonyl furyl carbonyl and the like the heteroaroyl group may be substituted and sulfonyl group such as methanesulfonyl benzenesulfonyl p toluenesulfonyl and the like the sulfonyl group may be substituted the substituents on r 1 r 2 and r 3 may be selected from cyano hydroxy nitro halogen atom such as fluorine chlorine or bromine substituted or unsubstituted group selected from c 1 c 8 alkyl such as methyl ethyl propyl butyl and the like the substituents of c 1 c 8 alkyl may be selected from halogen atom hydroxy nitro cyano amino phenyl or c 1 c 6 alkoxy groups amino mono or disubstituted amino group the substituents of the amino group may be selected from hydroxy or c 1 c 6 alkoxy groups alkanoyl group such as ethanoyl propanoyl butanoyl and the like c 1 c 6 alkoxy group such as methoxy ethoxy propyloxy butyloxy and the like aroyl group such as benzoyl and the like acyloxy group such as acetyloxy propanoyloxy butanoyloxy and the like aryl group such as phenyl naphthyl and the like the aryl group may be mono or disubstituted and the substituents may be selected from c 1.