Gold(i)-catalyzed formation of dihydroquinolines and indoles from N-aminophenyl propargyl malonates

Enantioselective Synthesis of α-Quaternary Isochromanes by Oxidative Aminocatalysis and Gold Catalysis

A novel strategy that combines oxidative aminocatalysis and gold catalysis allows the preparation of chiral α-quaternary isochromanes, a motif that is prevalent in natural products and synthetic bioactive compounds. In the first step, α-branched aldehydes and propargylic alcohols are transformed into α-quaternary ethers with excellent optical purities (>90 % ee) via oxidative umpolung with DDQ and an amino acid-derived primary amine catalyst. Subsequent gold(I)-catalyzed intramolecular hydroarylation affords the isochromane products with retention of the quaternary stereocenter. A second approach explores the use of allylic alcohols as reaction partners for the oxidative coupling to furnish α-quaternary ethers with generally lower enantiopurities. Stereoretentive cyclization to isochromane products is achieved via intramolecular Friedel-Crafts type alkylation with allylic acetates as a reactive handle. A number of synthetic elaborations and a biological study on these α-quaternary isochromanes highlight the potential applicability of the presented method.

Copper-Catalyzed Cascade Cyclization of Indolyl Homopropargyl Amides: Stereospecific Construction of Bridged Aza-[n.2.1] Skeletons

Catalytic cycloisomerization-initiated cascade cyclizations of terminal alkynes have received tremendous interest, and been widely used in the facile synthesis of a diverse array of valuable complex heterocycles. However, these tandem reactions have been mostly limited to noble-metal catalysis, and are initiated by an exo-cyclization pathway. Reported herein is an unprecedented copper-catalyzed endo-cyclization-initiated tandem reaction of indolyl homopropargyl amides, where copper catalyzes both the hydroamination and Friedel-Crafts alkylation process. This method allows the practical and atom-economical synthesis of valuable bridged aza-[n.2.1] skeletons (n=3-6) with wide substrate scope, and excellent diastereoselectivity and enantioselectivity by a chirality-transfer strategy. Moreover, the mechanistic rationale for this novel cascade cyclization is also strongly supported by control experiments, and is distinctively different from the related gold catalysis.

A one pot three-component reaction for the preparation of dihydroquinolines with two different ketones and aromatic amines

A three component reaction with two different ketones and aromatic amines was firstly investigated. The difference in reactivity between ordinary ketones and ketone esters allowed for the production of 1,2-DHQs efficiently. The possible Skraup reaction with 2 equiv. of the same ketones was prohibited due to the fast formation of imines.

Gold catalysed synthesis of 3-alkoxyfurans at room temperature

3-Alkoxyfurans can be readily prepared from aldehydes via a gold-catalysed cyclisation of propargylic alcohols bearing an acetal unit.

Alkyne hydroarylation with Au N-heterocyclic carbene catalysts

Mono- and dinuclear gold complexes with N-heterocyclic carbene (NHC) ligands have been employed as catalysts in the intermolecular hydroarylation of alkynes with simple unfunctionalised arenes. Both mono- and dinuclear gold(III) complexes were able to catalyze the reaction; however, the best results were obtained with the mononuclear gold(I) complex IPrAuCl. This complex, activated with one equivalent of silver tetrafluoroborate, exhibited under acidic conditions at room temperature much higher catalytic activity and selectivity compared to more commonly employed palladium(II) catalysts. Moreover, the complex was active, albeit to a minor extent, even under neutral conditions, and exhibited lower activity but higher selectivity compared to the previously published complex AuCl(PPh(3)). Preliminary results on intramolecular hydroarylations using this catalytic system indicate, however, that alkyne hydration by traces of water may become a serious competing reaction.

Gold versus silver catalyzed intramolecular hydroarylation reactions of [(3-arylprop-2-ynyl)oxy]benzene derivatives

The scope and the generality of gold versus silver catalyzed intramolecular hydroarylation reactions of 3-[(3-arylprop-2-ynyl)oxy]benzene derivatives in terms of rings substitution were investigated. Only products deriving from 6-endo cyclization were exclusively formed. The features of substituents had a considerable effect on the reaction outcome in the presence of silver catalysis, whereas gold catalysis revealed a unique blend of reactivity and selectivity and represented the only choice for the intramolecular hydroarylation reaction of the starting substrates bearing electron deficient arenes.

Recent advances in the gold-catalyzed additions to C-C multiple bonds

C-O, C-N and C-C bonds are the most widespread types of bonds in nature, and are the cornerstone of most organic compounds, ranging from pharmaceuticals and agrochemicals to advanced materials and polymers. Cationic gold acts as a soft and carbophilic Lewis acid and is considered one of the most powerful activators of C-C multiple bonds. Consequently, gold-catalysis plays an important role in the development of new strategies to form these bonds in more convenient ways. In this review, we highlight recent advances in the gold-catalyzed chemistry of addition of X-H (X = O, N, C) bonds to C-C multiple bonds, tandem reactions, and asymmetric additions. This review covers gold-catalyzed organic reactions published from 2008 to the present.

Gold(I)-catalyzed formation of furans by a Claisen-type rearrangement of ynenyl allyl ethers

A series of ynenyl allyl ethers were rearranged into polysubstituted furans in the presence of a gold(I) catalyst. It is proposed that the transformation involves a Claisen-type rearrangement that allows the efficient creation of quaternary centers under mild experimental conditions.