Extended Lifetimes of Gold(III) Chloride Catalysts using Copper(II) Chloride and 2,2,6,6-Tetramethylpiperidine 1-Oxyl (TEMPO)

The turnovers of a gold(III) chloride catalyst were increased by 3,300% with the addition of several equivalents of 2,2,6,6-tetramethylpiperidine 1-oxyl (TEMPO) and catalytic amounts of copper(II) chloride. A three-component coupling reaction between piperidine, phenylacetylene, and benzaldehyde yielded a propargylic amine in quantitative conversions and isolated yields when gold(III) chloride was added in catalytic amounts, but the gold catalyst decomposed and had little to no reactivity when a second set of piperidine, phenylacetylene, and benzaldehyde was added after the reaction was complete. Thus, only one cycle was possible with gold(III) chloride. The addition of TEMPO and copper(II) chloride to reactions with gold(III) chloride maintained the catalytic activity of gold for up to 33 cycles. This result demonstrates a new way to greatly increase the turnovers of a gold(III) chloride catalyst with the addition of inexpensive, commercially available reagents.