A NEW AND EFFICIENT SYNTHESIS OF IMIDAZO[1,5-A]PYRIDINE DERIVATIVES BY A TANDEM AZA-WITTIG ELECTROCYCLIC RING-CLOSURE OF N-VINYLIC PHOSPHAZENES

Imidazo[1,5-a]pyridines 1 are prepared by reaction of N-vinylic phosph azene 3, obtained from phosphorus ylide 5 and 2-cyanopyridine 4, with aldehydes. Formation of fused heterocycles 1 can be explained through aza-Wittig reaction of phosphazene 3, followed by 1,5-electrocyclic ri ng closure of the resulting aldimines 2. Phosphazene 3 undergoes pyrid o annelation by reaction with Diethyl Ketomalonate to give isoquinolin e derivative 9.