Investigations of the reaction of pentacovalent oxaphosphlenes with isocyanates. Synthetic and mechanistic aspects

The reaction of the pentacovalent oxaphospholene 1 with isocyanates to prod uce the heterocycle 2 was followed by NMR in order to delineate the mechani sm. The addition of 1 and 2 eq. of an isocyanate to 1 indicated very fast f ormation of 2 long-lived species that slowly rearranged to product. Cross-o ver experiments using 2 different isocyanates indicated the very fast forma tion of a statistical mixture of all 4 products 4-7, Kinetic analysis of th e data was performed.