CONDENSATION-REACTIONS OF (1E,3E)-4-AMINO-3-CYANO-4-METHOXY-1-PHENYL-2-AZABUTADIENE AND ELECTROCYCLIZATIONS OF DIAZATRIENES

(1E,3E)-4-Amino-3-cyano-4-methoxy-1-phenyl-2-azabutadiene (2) reacts with 2-methoxypropene in refluxing methylbenzene in the presence of catalytic pyridinium p-toluenesulfonate (PPTS) to give 2-cyano-5,5-dimethyl-3-methoxy-6-phenyl-4,5-dihydro-1,4-diazabenzene (5). Similarly, 2-aza-1,3-butadiene 2 reacts with triethyl orthoformate and triethyl orthobenzoate to give 3-cyano-2-methoxy-5-phenyl-1,4-diazabenzene (6) and 2-cyano-3-methoxy-5,6-diphenyl-1,4-diazabenzene (7), respectively. The PPTS-catalyzed reaction of 2 with triethyl orthoacetate gives 2-cyano-3-methoxy-5-methyl-6-phenyl-1,4-diazabenzene (8) and 2-cyano-5-ethoxy-3-methoxy-5-methyl-6-phenyl-4,5-dihydro-1,4-diazabenzene (9). Phenylmethanal and (2-thienyl)methanal react with 2-aza-1,3-butadiene 2 to give 5-methoxy-2,3-diphenyl-1,4-diazabenzene (17) and 5-methoxy-2-phenyl-3-(2-thienyl)-1,4-diazabenzene (18), respectively. Diazatrienes (enediimines) are proposed as the intermediates undergoing six pi-electron electrocyclizations to 1,4-diazabenzenes (dihydropyrazines, pyrazines, and pyrazinecarbonitriles).