Rh-catalysed divergent synthesis of polysubstituted pyrroles from α,β-unsaturated ketones via selective single or double insertion of isocyanides

Abstract

A novel divergent synthetic method for polysubstituted pyrroles from isocyanides and α,β-unsaturated ketones in the presence of a rhodium catalyst and bis(pinacolato)diboron (B₂pin₂) is described here. The selectivity for 1,2,4-trisubstituted pyrroles as a single insertion product and 2-imidoyl-1,3,5-trisubstituted pyrroles as a double insertion product was controlled by the reaction temperature and concentration of the isocyanide. After acidic hydrolysis, 2-imidoylpyrroles were isolated as 2-formylpyrroles, which are naturally abundant and synthetically useful structural motifs. The results of deuterium-labelling experiments suggested that the catalytic cycle involved rhodium hydride intermediates.