Synthesis and Structural Characterization of Stable Organogold(I) Compounds. Evidence for the Mechanism of Gold-Catalyzed Cyclizations

Abstract

The vast majority of homogeneous Au-catalyzed reactions have exploited the propensity of Au to activate unsaturated carbon-carbon bonds as electrophiles. It is generally assumed that a nucleophile attacks a gold-activated carbon-carbon multiple bond to give an alkenyl Au intermediate, notwithstanding the fact that these intermediates are hitherto unknown. We have obtained room temperature stable gamma-lactone gold(I) complexes through the reaction of cationic Au(I) reagents with allenoates, under mild conditions. The reactions of one such complex with electrophiles yielded the expected products of Au-catalyzed cyclizations. These results furnish experimental evidence for the mechanism of Au-catalyzed cyclizations.

Unique distal size selectivity with a digold catalyst during alkyne homocoupling

“…No additional 31 P peaks were found during oxidation, which suggests that phosphine ligands are not detached during reaction, at least at a measurable rate, and that transmetallation (if occurs) and reductive elimination are much faster processes than gold(I) oxidation since no phosphine intermediates are detected. These results indicate that the oxidation of the phosphine follows the oxidation of gold(I) to gold(III), and when the former occurs the active acetylide gold species decompose to O ¼ PPh 3 , free terminal alkyne and gold 19,20 .…”

Stabile cyclische Carbene und verwandte Spezies jenseits der Diaminocarbene

“…[ [110] Komplex 20 erinnert an Komplexe, wie sie jüngst von Hammond et al [111] und GagnØ et al [112] bei der goldkatalysierten Cyclisierung von Allenoaten bzw. der intramolekularen Hydroarylierung von Allenen isoliert wurden.…”

Expanding the frontier of gold-catalyzed cyclizations and rational ligand design.

“…A major breakthrough occurred in 2008 while investigating the reactivity of allenoates to afford γ-lactones; our group discovered the formation of stable organogold(I) complexes. 46 This important discovery supported the postulated mechanism of gold catalysis at the time, providing the first experimental evidence to support the mechanism of Au-catalyzed reactions of carbon-carbon multiple bonds, including alkynes/allenes/alkenes.…”

“…The chemistry of the oxonium ions formed from alkynylic aldehydes or ketones by mediation of transition metals, Lewis acids, Brønsted acids, or even electrophiles such as iodine, has attracted a lot of attention because these intermediates could undergo both inter-and intramolecular cycloadditions to carbon-carbon multiple bonds to give products of synthetic importance. 22,36,81, Because of our continuous interest in gold catalysis, 5,11,13,38,46,[124][125][126][127][128][129][130] we subjected compound 2-1a to gold catalysis and found that the reaction, using AuCl as the catalyst, cleanly furnished cyclopentenyl ketone 2-2a, an intramolecular-oxygen-transferred product, in excellent yields after only 5 min at room temperature (Scheme 18).…”