Reactions of uracils. 21. Zwitterionic heteropolycyclic uracils by a novel three-component reaction: Iminophosphorane, isocyanate, heteroarene

Article abstract of DOI:10.1021/jo00077a013

The novel three-component reaction of (uracil-6-ylimino)phosphorane 1, isocyanate 2, and (substituted) pyridines gives, in a one-pot procedure, a variety of new pyrido[1',2':3,4]pyrimido[4,5-d]pyrimidines 3-11. The zwitterionic ground state of these new ring systems is i.a. established by means of solvatochromism, Hammett correlations, NMR, and X-ray analysis. Replacement of the pyridine by isoquinoline and phthalazine gives access to the novel ring systems pyrimido[4',5':4,5]pyrimido[6,1-a]isoquinoline and -phthalazine, which are formed as dihydro derivatives (14, 15) or as zwitterions (13, 17), depending on the reaction conditions. Oxidative cleavage of the phthalazine 15 in nitrobenzene affords the pyrimido[4,5-d]pyrimidines 16.