Iminophosphorane-mediated annelation of a pyridine ring into a preformed pyridine one: Synthesis of naphthyridine, pyrido[1,2-c]pyrimidine and pyrido[1,2-c]quinazoline derivatives

Article abstract of DOI:10.1016/S0040-4020(01)81234-5

Aza Wittig-type reaction of iminophosphoranes 2 and 6, prepared from 4- and 3-formylpyridines by sequential treatment with ethyl azidoacetate and triphenylphosphine, with isocyanates leads to 2,7-naphthyridine 4, 1,7-naphthrydine 7 and 2,6-naphthyridine 8