A compound of the formula: ##STR35## wherein R1 is C1 C6 lower alkyl, C1 C6 alkylthio, C6 C10 aryl, C7 C16 arylalkyl, C6 C10 arylthio, C7 C16 arylalkylthio, cyano, C1 C6 perfluorinated {TAIL ~ lower alkyl}, or ##STR36## wherein {HEAD ~ R} is a chain of 1 5 carbon atoms; and R2, R3, and R4 are each independently: 
A compound of the formula : # # STR35 # # wherein R1 is C1 C6 lower alkyl , C1 C6 alkylthio , C6 C10 aryl , C7 C16 arylalkyl , C6 C10 arylthio , C7 C16 arylalkylthio , cyano , C1 C6 perfluorinated { TAIL ~ lower alkyl } , or # # STR36 # # wherein { HEAD ~ R } is a chain of 1 5 carbon atoms ; and R2 , R3 , and R4 are each independently :
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