The total synthesis and characterization of ammonium-salt-tagged IMesAuCl complexes is described. Moreover, we have demonstrated their catalytic activity and recyclability in cycloisomerization reactions of allenic and acetylenic alcohols in water. The water-soluble gold catalysts can be stabilized by the addition of LiCl.

A new and efficient one-pot synthesis of 2,5-dihydrofurans from propargyloxiranes and arylboronic acids takes advantage of sequential rhodium-gold catalysis. The transformation proceeds with center-to-axis-to-center chirality transfer and tolerates a wide variety of electron-accepting or electron-withdrawing substituents at the arylboronic acid, as well as cyclic or acyclic propargyloxiranes.

The purpose of this study is to point out the synthetic utility of a new class of Michael acceptors (nitrodienes and nitroenynes). The highly enantioselective organocatalytic Michael addition of carbonyl compounds to these functionalized nitroolefins has been carried out in the presence of (S)-diphenylprolinol silyl ether to achieve some interesting building blocks in high selectivities. The adducts thus obtained can be easily converted by taking advantage of the corresponding unsaturated carbon-carbon bond. In presence of the double bond, metathesis or electrophilic activation could be carried out whereas in the presence of the triple bond electrophilic activation could be conducted. We thus focused on a gold-catalyzed cyclization of the bis-homopropargylic alcohol to afford the corresponding substituted tetrahydrofuran. Then, we also demonstrated that organic and gold catalysts were compatible in a one-pot process. Indeed, we developed a one-pot enantioselective organocatalytic Michael addition to a nitroenyne followed by a gold-catalyzed acetalization/cyclization to achieve tetrahydrofuranyl ethers in high diastereo- and enantioselectivities with excellent yields.

The stereoselective gold-catalyzed 6-endo cyclization ofvarious β-hydroxyallenes in the presence of N-iodosuccinimide affords iodinated dihydropyrans in good yield. Subsequent functionalization by palladium-catalyzed cross coupling opens an access to α-hydroxyallenes that are converted in a second gold-catalyzed cyclization into furopyrans which occur in various natural products.

We report the first example of a tandem kinetic resolution/cycloisomerization of racemic allenic acetates in the presence of Burkholderia cepacia lipase (PS Amano SD) and catalytic amounts of chloroauric acid (HAuCl₄) which affords 2,5-dihydrofurans, as well as unreacted starting material, in one pot with high enantiomeric excess and moderate to good yield.

A stereoselective synthesis of conjugated bis(α-hydroxyallenes) by copper-mediated S_N2′-substitution is described. Their silver- or gold-catalyzed cycloisomerization affords highly functionalized 2-allenyl-substituted 2,5-dihydrofurans and bis(2,5-dihydrofurans) under axis-to-center chirality transfer.

A new catalytic method for the synthesis of α-hydroxyallenes is described. Efficient S_N2′ substitution of propargylic dioxolanones has been achieved with a copper(I)/P(OBu)₃ catalyst using Grignard reagents as the nucleophiles. The reaction tolerates a wide variety of propargylic dioxolanones, the corresponding primary and secondary α-hydroxyallenes are obtained in good to excellent yields and excellent diastereoselectivity. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)

Nine α-hydroxyallenes 1/3 were cyclized to the corresponding 2,5-dihydrofurans 2/4 with complete axis-to-center chirality transfer in the presence of 1 mol% of AuBr₃ using [BMIM] [PF₆] as solvent at room temperature. The gold catalyst/ionic liquid system is air-stable and recyclable. The leaching of the gold catalyst upon extraction of the product is extremely low (0.03% after five runs).