Gold(I)-Catalyzed Hydrofunctionilzations of Allenes with Nitrogen and Oxygen Nucleophiles

Abstract

The importance of nitrogen-containing compounds in human life has drawn us to focus on the preparation of amine derivatives, combined with the limitations associated with traditional methods for the formation of C-N bonds has prompted us to develop new and efficient syntheses, of amine and ether derivatives and explore the mechanisms of the gold(I)-catalyzed reactions.A mixture of AuCl[P(t-Bu)2o-biphenyl] (5 mol %) and AgOTf (5 mol %) served as an effective catalyst for the intermolecular hydroamination of allenes with arylamines to form N-prenylaniline and N,N-diprenylaniline derivatives. This gold(I)-catalyzed protocol was effective for the formation of arylamines at non-forcing conditions with wide substrate scope in both allene and aniline, in high yields with good regioselectivity diastereoselectivity.The mechanism of the gold(I)-catalyzed hydroalkoxylation and hydroamination of alcohols and carbamates with allenes, catalyzed by AuIPrCl (IPr= 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidine) and AgOTf was investigated. The experimental rate laws for both reactions indicate first-order behavior in nucleophile and catalyst and zero-order behavior in catalyst. We propose an outer-sphere mechanism with turnover limiting protonolysis for the gold(I)-catalyzed hydrofunctionalization of allenes with alcohols or carbamates based on kinetic isotope effect, saturation behavior, and stereochemical analysis of hydroalkoxylation.The mechanism of gold(I)-catalyzed hydroamination of allenes with arylamines was examined. Specifically, we explored the hydroamination of 3-methy-1,2-butadiene with aniline catalyzed by AuCl[P(t-Bu)2o-biphenyl] (5 mol %) and AgOTf (5 mol %) in dioxane at 45 °C to form N-prenylaniline and N,N-diprenylaniline. The kinetics of this reaction were determined to be first-order in aniline, allene, and catalyst. We have concluded that the mechanism for the gold(I)-catalyzed intermolecular hydroamination of allenes with arylamines involves outer-sphere attack of aniline on the gold--allene complex based on stereochemical analysis of the hydroamination product from the reaction of an enantiomerically enriched allene, (R)-1-phenyl-1,2-butadiene, with 3-bromoaniline.