R3 may be hydrogen; substituted or unsubstituted alkyl of from 1 to about 6 carbon atoms such a those listed above for R1 and R2 ; substituted or unsubstituted aryl of from about 5 to about 10 carbon atoms such as phenyl, p-tolyl, m-chlorophenyl, p-methoxyphenyl, m-bromophenyl, o-tolyl, etc.; alkylthio or halogen;