The first reverse regioselective intermolecular annulation of aryl substituted 2-acetylenic ketones with O-substituted N-hydroxybenzamides or acrylamides followed by tandem cyclization via ruthenium-catalyzed C–H activation, is reported.

Rhodium-catalyzed asymmetric hydrogenation of alkyne-tethered cyclohexadienones enables highly regio- and enantioselective reductive cyclization to afford cis-hydrobenzofurans and cis-hydroindoles in high yields. Desymmetrization of 1,3-diyne-tethered cyclohexadienones was also explored, wherein the intramolecular coordination of a Rh complex with the cyclohexadienone ring induces exclusive regioselectivity. Mechanistic studies including hydrogen–deuterium crossover experiments suggested that hydrogen activation is the rate-determining step for tandem reductive cyclization. Moreover, this highly practical and atom-economical transformation has tolerance to many functional groups with a broad range of substrate scope, allowing further transformations to expand the structural complexity of the bicyclic scaffolds.

Cp*Co(III)-catalyzed C-H functionalization cascade of N-methoxyamides with alkynedione has been reported for the synthesis of indolizidine scaffolds under redox-neutral conditions. The reaction displays broad functional group tolerance along with excellent yield. The reaction proceeds with kinetically relevant C-H bond activation through carboxylate assistance with excellent diastereoselectivity and complete opposite selectivity with respect to alkyne insertion.

A Rh(I)-catalyzed highly stereoselective desymmetrization of 2-alkynylbenzaldehyde-tethered cyclohexadienones triggered by intramolecular Huisgen-type [3+2] cycloaddition has been developed. This method enables convergent construction of complex epoxy-bridged polycyclic ring systems with five...

An unconventional Ag­(I)-catalyzed intramolecular cyclopropanation of prochiral alkyne-tethered cyclohexadienones has been developed using simple perchloric acid as an external oxidant. The transformation involves the formation of a perchloryloxy vinyl-silver species, which then proceeds through either intramolecular conjugate addition or an α-oxo silver carbene pathway to yield cyclopropane fused tricyclic enones with high diastereoselectivity. In the case of C-tethered cyclohexadienones, the reaction proceeds further via acid mediated semipinacol-type rearrangement to give complex and highly strained tricyclo­[3.3.1.0]­nonanediones. This cascade annulation has wide functional-group tolerance and broad substrate scope. Late-stage functionalization of estrone was also demonstrated with excellent diastereoselectivity.