Gold-Catalyzed Oxidation of Thioalkynes To Form Phenylthio Ketene Derivatives via a Noncarbene Route.

Gold-catalyzed oxidations of thioalkynes with 8-methylquinoline oxides afford 2-phenylthioketenes that can be trapped efficiently with alcohols. The synthetic utility is manifested by terminal and internal thioalkynes over a wide scope, bearing esters, ketones, alkyl, and oxime substituents. Our density functional theory calculations suggest that gold-catalyzed oxidations of terminal and internal thioalkynes with 8-methylquinoline oxides generate gold-bound ketene intermediates without the intermediacy of α-oxo gold carbene.

Gold-Catalyzed Oxidative Hydrative Alkenylations of Propargyl Aryl Thioethers with Quinoline N-Oxides Involving a 1,3-Sulfur Migration.

This work reports gold-catalyzed oxidative alkenylations of quinoline N-oxides with propargyl aryl thioethers to afford 3-hydroxy-1-alkylidenephenylthiopropan-2-one via a 1,3-sulfur group migration. The mechanism of this reaction is postulated to involve an α-oxo gold carbene intermediate followed by formation of a four-membered sulfonium ring that is ring-opened by one H2O to form a gold enolate. A final condensation of this enolate with a second quinoline N-oxide delivers an alkenylation product accompanied by a 1,3-sulfur shift.

Gold-catalyzed (4+3)-annulations of 2-alkenyl-1-alkynylbenzenes with anthranils with alkyne-dependent chemoselectivity: skeletal rearrangement versus non-rearrangement.

Two distinct (4+3)-nitroxy annulations between 1,5-enynes and anthranils have been developed to access tetrahydro-1H-benzo[b]azepine derivatives; the chemoselectivity varies with the types of alkynes. Terminal alkyne substrates deliver benzo[b]azepine derivatives via a novel skeletal rearrangement while internal 1,5-enynes afford products without a rearrangement process. To elucidate the mechanism of rearrangement, we performed 13C- and 2H-labeling experiments to identify the gold-containing isobenzofulvene intermediates, but their formation relies on the presence of anthranils.

Gold-catalyzed oxidative couplings of two indoles with one aryldiazo cyanide under oxidant-free conditions.

Gold-catalyzed oxidative couplings of two indoles and one α-cyano gold carbene to form bis(indolyl)methane derivatives are described. Two different indoles are compatible with these reactions to provide reasonable yields. A plausible mechanism is postulated to rationalize the experimental data including product distributions, D2O labeling, and the significant effects of gold catalysts and cyano groups.

Gold-catalyzed [3+2]-annulations of α-aryl diazonitriles with ynamides and allenamides to yield 1-amino-1H-indenes.

Gold-catalyzed [3+2]-annulations of α-aryl diazonitriles with ynamides and allenamides yield 1-amino-1H-indenes in two distinct pathways; the success of these annulations relies on the high electrophilicity of α-cyano arylgold carbenes to activate an ionic pathway.

Gold-catalyzed 1,2-iminonitronation of electron-deficient alkynes with nitrosoarenes to afford α-imidoyl nitrones.

Gold-catalyzed 1,2-iminonitronation of propiolate derivatives with nitrosoarenes to give α-imidoyl nitrones is described; this new reaction is applicable to diverse propiolate derivatives and nitrosoarenes.