Stereo- and regiocontrol in intermolecular [2+2] cycloadditions between diarylketenes and allenamides to access substituted α-methylenecyclobutanones.

The development of intermolecular [2+2] cycloadditions between allenamides and diarylketenes is described. α-Aryldiazo arylketones are employed as ketene precursors that react smoothly with allenamides in the presence of a P(C6F5)3 promoter. High diastereoselectivity (dr > 20 : 1) with endo-regioselectivity can be achieved when two aryl groups of ketenes have opposite electronic properties. The role of P(C6F5)3 is to increase the reaction yields, but also enhancing stereoselectivity.

Reactions of thioalkynes with diarylketenes via [3+2]-annulation versus benzannulation using Au and P(C6F5)3 catalysts.

Two catalytic annulations of non-symmetric diarylketenes with thioalkynes are described using gold and phosphine catalysts respectively. We employed α-aryldiazo ketones to generate gold-π-ketenes, ultimately yielding azulen-1-one derivatives. With the same reactants, we utilized P(C6F5)3 to increase the yields of 1-naphthols, notably with a complete regioselectivity.

Gold Catalysts Can Generate Nitrone Intermediates from a Nitrosoarene/Alkene Mixture, Enabling Two Distinct Catalytic Reactions: A Nitroso-Activated Cycloheptatriene/Benzylidene Rearrangement.

Gold-catalyzed reactions of cycloheptatrienes with nitrosoarenes yield nitrone derivatives efficiently. This reaction sequence enables us to develop gold-catalyzed aerobic oxidations of cycloheptatrienes to afford benzaldehyde derivatives using CuCl and nitrosoarenes as co-catalysts (10-30 mol %). Our density functional theory calculations support a novel nitroso-activated rearrangement, tropylium → benzylidene. With the same nitrosoarenes, we developed their gold-catalyzed [2 + 2 + 1]-annulations between nitrosobenzene and two enol ethers to yield 5-alkoxyisoxazolidines using 1,4-cyclohexadienes as hydrogen donors.

Gold-Catalyzed Iminations of Terminal Propargyl Alcohols with Anthranils with Atypical Chemoselectivity for C(1)-Additions and 1,2-Carbon Migration.

This work reports gold-catalyzed iminations of terminal propargyl alcohols with anthranils or isoxazoles to yield E-configured α-amino-2-en-1-ones and -1-als with complete chemoselectivity. These catalytic iminations occur exclusively with C(1)-nucleophilic additions on terminal alkynes, in contrast to a typical C(2)-route. For 3,3-dialkylprop-1-yn-3-ols, a methyl substituent is superior to long alkyl chains as the 1,2-migration groups toward α-imino gold carbenes. For secondary prop-1-yn-3-ols, phenyl, vinyl, and cyclopropyl substituents are better than hydrogen as the migrating groups, obviating typical gold carbene reactions. DFT calculations have been performed to rationalize the observed C(1)-regioselectivity and the preferable cyclopropyl migration based on gold carbene pathways.