Transition-metal catalysts containing gold present new opportunities for chemical synthesis, and it is therefore not surprising that these complexes are beginning to capture the attention of the chemical community. Cationic phosphine-gold(i) complexes are especially versatile and selective catalysts for a growing number of synthetic transformations. The reactivity of these species can be understood in the context of theoretical studies on gold; relativistic effects are especially helpful in rationalizing the reaction manifolds available to gold catalysts. This Review draws on experimental and computational data to present our current understanding of homogeneous gold catalysis, focusing on previously unexplored reactivity and its application to the development of new methodology.

F. Dean Toste received his B.Sc. and M.Sc. degrees in chemistry from the University of Toronto where he worked with Prof. Ian W. J. Still. In 1995, he began his doctoral studies at Stanford University under the direction of Professor Barry M. Trost. Following postdoctoral studies with Professor Robert H. Grubbs at Caltech, he joined the faculty at the University of California, Berkeley, in 2002, and was promoted to Associate Professor in 2006. Current research in his group is aimed towards the design of catalysts and catalytic reactions and the application of these methods to chemical synthesis.

A triphenylphosphinegold(I)-catalyzed cyclopropanation of olefins using propargyl esters as gold(I)-carbene precursors is reported. This reaction provided the basis for the use of a DTBM-SEGPHOS gold(I) complex as a catalyst in the enantioselective (up to 94% ee) preparation of vinyl cyclopropanes with high cis-selectivity.

The importance of cyclopentenones as building blocks for organic synthesis continues to inspire the development of general methods for their stereoselective preparation. [1][2][3] In 1984, Rautenstrauch reported that palladium(II) complexes catalyzed the isomerization of 1-ethynyl-2-propenyl acetates (1) to cyclopentenones (eq 1). 4 This reaction and related rearrangements 5 are proposed to proceed through a metal carbene intermediate, such as 2, arising from a 1,2-acetate migration. While the Rautenstrauch rearrangement provided an efficient route to cyclopentenones, it was limited to the preparation of achiral cyclopentenones substituted at the 2 and 3 positions (eq 1). On the basis of recent examples of gold(I)-catalyzed cyclizations of enynes, 6 we hypothesized that these catalysts might afford an increase in the scope of this reaction and allow the preparation of chiral cyclopentenones.In light of our previous success employing Ph 3 PAuOTf in methylene chloride for carbon-carbon bond formation, 6b,7 we chose this catalyst system in preliminary studies of the rearrangement (eq 2). To develop catalysts that would permit the synthesis of chiral cyclopentenones, we initiated our investigation with a substrate (4) containing a trisubstituted olefin. We were pleased to find that rearrangement of 4, catalyzed by 5 mol % Ph 3 PAuOTf in methylene chloride, did afford desired cyclopentenone 5, however, in only 30% yield. Examination of the effect of solvent on the reaction revealed that acetonitrile produced the desired adduct with a marked improvement in yield. The yield was further improved by changing the ester from acetate to pivaloate. 8 With optimized reaction conditions in hand, we set out to define the scope of the cyclopentenone synthesis. The reaction is highly tolerant of substitution at the acetylenic position of the 1-ethynyl-2-propenyl pivaloates (Table 1). In addition to unsubstituted alkynes, the gold(I)-catalyzed reaction proceeded smoothly with substrates containing aryl-(entry 2), alkyl-(entry 3), and vinyl-substituted alkynes (entry 4). Cyclization of the latter produced exo-methylene cyclopentenone 13 after isomerization of the iso-propenyl group into conjugation with the ketone. The reaction also showed excellent scope with respect to substitution on the olefin. Specifically, 1,1-disubstituted (entries 1-4), 1,2-disubstituted (entry 5), and cyclic (entries 6 and 7) alkenes participated in the cyclization. Rearrangement of styrenyl substrates 14 and 18 afforded 3-phenylcyclopentenones 15 and 19 as a result of olefin isomerization into conjugation with the aryl group.A 1:1 diastereomeric mixture of 20, derived from (S)-(-)-perillaldehyde, underwent Au-catalyzed isomerization to produce bicyclic enone 21 as a 1:1 mixture of diastereomers (eq 3). We envisioned two scenarios to account for this diastereoselectivity: the stereochemistry of the starting ester is lost in generating a carbene-like intermediate (such as 2) that undergoes subsequent cyclization with no selectivity, or the stereochemist...

Substituted pyrroles were prepared by a gold(I)-catalyzed acetylenic Schmidt reaction of homopropargyl azides. The reaction allows for regiospecific substitution at each position of the pyrrole ring under mild conditions. A mechanism in which azides serve as nucleophiles toward gold(I)-activated alkynes with subsequent gold(I)-aided expulsion of dinitrogen is proposed.