Triplet ketone sensitizers are of central importance within the realm of photochemical transformations. Although the radical-type character of triplet excited states of diaryl ketones suggests the viability for triggering hydrogen-atom transfer (HAT) and single-electron transfer (SET) processes, among others, their use as multifaceted catalysts in C-C bond-formation via sp C-H functionalization of alkane feedstocks still remains rather unexplored. Herein, we unlock a modular photochemical platform for forging C( sp)-C( sp) and C( sp)-C( sp) linkages from abundant alkane sp C-H bonds as functional handles using the synergy between nickel catalysts and simple, cheap and modular diaryl ketones. This method is distinguished by its wide scope that is obtained from cheap catalysts and starting precursors, thus complementing existing inner-sphere C-H functionalization protocols or recent photoredox scenarios based on iridium polypyridyl complexes. Additionally, such a platform provides a new strategy for streamlining the synthesis of complex molecules with high levels of predictable site-selectivity and preparative utility. Mechanistic experiments suggest that sp C-H abstraction occurs via HAT from the ketone triplet excited state. We believe this study will contribute to a more systematic utilization of triplet excited ketones as catalysts in metallaphotoredox scenarios.

A base-mediated protocol that allows for the site-selective sp 2 C−H silylation of azines is described. This method is distinguished by its mild conditions, simplicity and excellent site-selective modulation for a diverse set of azines, even in the context of late-stage functionalization, while exhibiting orthogonal reactivity with classical silylation reactions.

Two classes of phosphine-catalyzed addition/cycloaddition domino reactions of β'-acetoxy allenoate 1 have been developed. The reaction of 1 with 2-acyl-3-methyl-acrylonitrile 2 readily occurs to give 2-oxabicyclo[3.3.1]nonane 3, furnishing the β'-addition/[4 + 4] cycloaddition domino sequence. In this sequence, β'C of allenoate 1 is an electrophilic center, and its β'C and γC serve as a 1,4-dipole. When the other reaction partner is switched to 2-acyl-3-(2-pyrrole)-acrylonitrile 8, a γ-addition/[3 + 2] cycloaddition domino reaction is instead observed, in which allenoate 1 exhibits dual electrophilic reactivity of γC and 1,3-dipole chemical behavior of βC and β'C. Furthermore, both of these two asymmetric variants have also been achieved with up to 93% ee. The domino reactions presented in this report are valuable for highly stereoselective construction of complex structures under mild reaction conditions.

Under mild conditions (room temperature, 80 psi of H2) Cp*Rh­(2-(2-pyridyl)­phenyl)H catalyzes the selective hydrogenation of the CC bond in α,β-unsaturated carbonyl compounds, including natural product precursors with bulky substituents in the β position and substrates possessing an array of additional functional groups. It also catalyzes the hydrogenation of many isolated double bonds. Mechanistic studies reveal that no radical intermediates are involved, and the catalyst appears to be homogeneous, thereby affording important complementarity to existing protocols for similar hydrogenation processes.