Stoichiometric and catalytic inter- and intramolecular hydroamination of terminal alkynes by frustrated Lewis pairs.

Abstract

Frustrated Lewis pairs (FLPs) based on sterically encumbered anilines and the Lewis acid B(C6 F5 )3 were found to react with terminal alkynes effecting intermolecular hydroamination affording iminium alkynylborate species of the form [RPhNC(R')Me][R'CCB(C6 F5 )3 ]. In these cases, the reagent ratio of borane, aniline, and alkyne is 1:1:2. These reactions could also be performed in an intramolecular fashion by using anilines with alkynyl substituents effecting cyclization reactions. The use of 10 mol % B(C6 F5 )3 under a H2 atmosphere provides a one-pot synthesis of the pyrrolidine 12, the piperidines 13-15, the azepane 16, the isoindoline 17, and the benzoxazine 18.