No abstract

Two series of sterically encumbered gold(I)-acyclic diaminocarbene (ADC) complexes were prepared by reaction of mono-and dialkylamines with gold-bound 2-mesitylphenyl isocyanide (monomesityl series) and 2,6-dimesitylphenyl isocyanide (dimesityl series). X-ray crystal structures and solution 1 H NMR data showed that the ADC-gold complexes adopt major rotameric conformations with the bulky biaryl/terphenyl group and one alkyl group located syn to gold. This engenders substantial steric hindrance at the metal, as evidenced by percent buried volume (%V bur ) parameters of 35.7 -37.2 for the monomesityl series and 46.4 -52.4 for the dimesityl series. Modest out-of-plane distortions of the ADC N-substituents in the dimesityl series were attributed to attractive CH•••π interactions between alkyl groups and mesityl rings on the basis of dispersion-corrected density functional theory calculations. Gold-catalyzed regiodivergent domino cyclization/hydroarylation reactions of a 1,6-enyne with indole revealed that the bulky biaryl/terphenyl substituents of the ligands exert a strong influence on product selectivity, with the bulkier dimesityl ADC-Au catalysts inducing a shift away from the cyclopropane-fused product toward the normally disfavored alkene product. Incorporation of a yet bulkier bis(2,6-diisopropylphenyl)-substituted terphenyl moiety into the ADC led to a gold catalyst that provided exclusive selectivity for the alkene product. Computational modeling suggested that bulky terphenyl groups hinder attack at the a carbon in the initially formed organogold intermediate, allowing steric effects to override the intrinsic electronic preference for the cyclopropane product. File list (3) download file view on ChemRxiv Slaughter_Encumbered_ADC-Au_Preprint.pdf (2.05 MiB) download file view on ChemRxiv Slaughter_Encumbered_ADC-Au_SuppInfo_Preprint.pdf (4.44 MiB)

We report carbon-hydrogen acetoxylation of nondirected arenes benzene and toluene, as well as related functionalization with pivalate and 2-ethylhexanoate ester groups, using simple copper(II) [Cu(II)] salts with over 80% yield. By changing the ratio of benzene and Cu(II) salts, 2.4% conversion of benzene can be reached. Combined experimental and computational studies results indicate that the arene carbon-hydrogen functionalization likely occurs by a nonradical Cu(II)-mediated organometallic pathway. The Cu(II) salts used in the reaction can be isolated, recycled, and reused with little change in reactivity. In addition, the Cu(II) salts can be regenerated in situ using oxygen and, after the removal of the generated water, the arene carbon-hydrogen acetoxylation and related esterification reactions can be continued, which leads to a process that enables recycling of Cu(II).

A tandem reaction initiated by Au(I)-catalyzed C1-C5 cyclization of enediynes bearing an internal carboxy nucleophile has been developed, providing a distinctive methodology for the assembly of fused indenes including indeno[1,2-c]isochromen-5(11H)-ones and indeno[1,2-b]pyran-2(5H)-ones. A mechanism involving the concerted formation of the five- and six-membered rings was proposed.

Gold(i) catalyzes domino homodimerization of o-alkynylbenzaldehydes via a sequence of 6-endo-dig-cyclization, amine addition, and [4+2] cycloaddition involving two bicyclic intermediates. The resulting products integrate medicinally relevant 1,2-dihydronaphthalene and isochromene moieties into a single amine-substituted tetracyclic framework.