Recent examples of the three component reaction: imino-phosphoranes/isocyanates/heteroarenes(imines) are described. The uracil (1) affors with O-methyl-e-caprolactim ether and isocyanates the pyrimido-[4',5':4,5]pyrimido[6,1-a]azepines (6a-c) and with benzylideneaniline (8) the pyrimido[4,5-d]pyrimidines (9a-d), while azodicarboxylate gives the isofervenuline, pyrimido[4,5-e][1,2,4]triazine (11). Furthermore, pyrimido[4,5-d]-pyrimidine (15) is obtained via 14 from 1, N-phenylbenzimidoyl chloride (13), and phenylisocyanate, while the tautomeric mixture 17A ⇄ 17B results from treatment of 6-aminouracil (16) with 13; interception with dimethyl acetylene-dicarboxylate give the pyrido[2,3-d]pyrimidine (19)
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Wamhoff et al. (1993) studied this question.