Synthesis and mechanism of formation of novel 2,5-dihydro-2,5-diimino-3,4-di[(N,N-dimethylamino)methylideneamino]pyrroles and 5-amino-3,4-di[(N,N-dimethylamino)methylideneamino]-2H-2-iminopyrroles

Formation of 5-amino-3,4-di[(N, N-dimethylamino)methylideneamino]-2H-2-iminopyrroles 3 from the reaction of (Z)-N-1-(2-amino-1,2-dicyanovinyl)-N-2-substituted-formamidines 1 with dimethylformamide diethyl acetal has been shown to occur by initial formation of (Z)-N-1-{1,2-dicyano-2-[(N,N-dimethylamino)methylideneamino]vinyl} formamidines 8 (isolated), followed by base catalysed cyclisation and imidazole ring opening by dimethylamine. The kinetic product of the ring opening reaction is the 2,5-diimino-2,5-dihydropyrrole derivatives 11, which have been isolated and characterized spectroscopically and by a single crystal X-ray analysis on the R = Ph derivative. In solution at room temperature the N-aryl derivatives undergo a rapid Dimroth rearrangement to give the thermodynamically more stable isomer 3, but compound 11 (R = Me) is much more stable in solution.