π-Insertion Reactions of Benzynes into P=N and P=S Double Bonds

The π-insertion reactions of in situ generated benzynes into the P=N bonds of N-benzyl and N-aryl iminophosphoranes and the P=S bonds of phosphane sulfides have been examined by using the Kobayashi benzyne precursors, (2-trimethylsilyl)phenyl triflates. The reactions with iminophosphoranes afforded (2-aminophenyl)phosphonium triflates under mild conditions, most probably by a [2+2]/retro [2+2] cycloaddition sequence and further N-protonation by the solvent (CH3CN) or N-phenylation by a second molecule of benzyne. The final products of the analogous reactions with P-OCH3-substituted iminophosphoranes were the respective (2-aminophenyl)phosphane oxides, as result of a final O-demethylation event of the putative phosphonium triflate. The reactions with phosphane sulfides involve a final S-phenylation step to yield (2-phenylthio)phenylphosphonium salts.