Monophenylborane: synthesis and use in hydroborations

Monophenylborane was generated in situ by the addition of acid to lithium phenyiborohydride. Methanesuifonic acid was found to be the acid of choice. The reaction was performed in the presence of alkenes to give dialkylphenylboranes, which were found to be very unstable under the reaction conditions and prone to disproportionation.

A series of representative alkenes were hydroborated with monophenylborane. This borane was found to be a highly selective hydroborating agent. Unfortunately, the instability of phenylborane seriously limits its applicability in hydroboration reactions.