Internal alkyne regio- and chemoselectivity using a zwitterionic [(NHC)Au(I)] catalyst in a silver-free alkyne hydration reaction

Abstract

An alkyne hydration of terminal and internal alkynes is reported using a zwitterionic NHC Au catalyst, (BNHC)Au(SMe2) (1), in the absence of silver and Brønsted acid additives. The hydration demonstrates good regioselectivity in alkyne hydration and chemoselectivity for internal alkynes vs. terminal. In addition, (1) performs a propargyl alcohol hydration to predominantly form α-hydroxy methyl ketone over the more common Meyer-Schuster rearrangement product. While complex (1) is active without silver additives, addition of AgSbF6 increases reaction rate and decreases selectivity for internal alkyne hydration over terminal substrates. To our knowledge, the rate enhancement of (1) by AgSbF6 is the first such demonstration of a silver effect for a “halide-free” Au catalyst.