New chemistry of alkynyl trifluoroborates under transition metal catalyst-free conditions

Abstract

Alkynyl trifluoroborates, when compared with conventional alkynyl metal reagents, exhibit unique properties and reactivities, including weak basicity, high intrinsic nucleophilicity and good oxidative stability. Often, boron coordination of Lewis bases (alcohols, amines and nitrogen-containing heteroarenes) renders rate acceleration in new bond formation and excellent regioselectivity. The boron coordination is capitalized not only in alkynylation of an array of conventional carbon electrophiles, but also in new types of cycloaddition reactions. The beta-substitution of trifluoroborate on ynones significantly reduces electrophilicity of Michael acceptors, enabling them to act as chemoselective dielectrophiles. The review covers several new types of methodologies based on of alkynyl trifluoroborates under transition metal-free conditions: undirected alkynylation of carbon electrophiles, oxidative alkynylation of alkenes via radical-polar crossover, boron-directed alkynylation and cycloaddition, and annulation reactions of ynone trifluoroborates. We also discuss green and sustainable aspects of the novel chemistry offered by robust alkynylborons.