Synthesis of tricyclic spirophosphoranes via reaction of 2-(4,5-dihydrofuran-3-yl)-N-phenyl-1,3,2-oxazaphospholidine with C,N-diarylnitrile imines

Unique tricyclic compounds with a five-coordinate phosphorus atom shared by three rings, 7-aryl-3′,5-diphenyl-3,5-dihydro-2H-spiro[1,2-oxaphospholo[2,3-d][1,2,4]diazaphosphinine-8,2′-[1,3,2]oxazaphospholidines], have been synthesized for the first time via reaction of 2-(4,5-dihydrofuran-3-yl)-3-phenyl-1,3,2-oxazaphospholidine with C,N-diarylnitrile imines. Presumably, these compounds are formed via a three-step process including generation of P+-C=N-N− dipolar ion, intramolecular N−→C= cyclization with simultaneous opening of the dihydrofuran ring, and closure of oxaphospholane ring.