CO/CO and NO/NO coupling at a hidden frustrated Lewis pair template

Abstract

N-Allyltetramethylpiperidine is readily isomerized to the corresponding enamine by treatment with catalytic amounts of B(C₆F₅)₃. It adds HB(C₆F₅)₂ at the nucleophilic enamine carbon atom to form a C/B Lewis adduct. This reacts with two molar equivalents of carbon monoxide by selective head to tail coupling to give a five-membered C₂O₂B heterocycle. In contrast the enamine/HB(C₆F₅)₂ Lewis pair reacts with two molar equiv. of nitric oxide by head to head coupling. This reaction probably proceeds via equilibrium with the corresponding vicinal N/B Lewis pair. Most products were characterized by X-ray diffraction.