Ring Contraction of a Pinacolatoboryl Group To Form a 1,2-Oxaboretane Ring: Reaction of Unsymmetrical Diborane(4) with 2,6-Dimethylphenyl Isocyanide

An unsymmetrical diborane(4), pinB-BMes2, reacted with 2,6-dimethylphenyl isocyanide to give a spirocyclic 1,2-oxaboretane or isocyanide-coordinated boraalkene. The former product formed via ring contraction of the pinacolatoboryl group. DFT calculations revealed the ring contraction proceeded via a carbocationic intermediate. This new degradation pathway from the Bpin group would provide important information in Bpin-related chemistry.