The coupling of O-pivaloyl benzhydroxamic acids with donor/acceptor diazo compounds provides iso-indolones in high yield. The reaction tolerates a broad range of benzhydroxamic acids and diazo compounds including substituted 2,2,2-trifluorodiazo ethanes. Mechanistic experiments suggest that C–H activation is turnover limiting and irreversible, while insertion of the diazo compound favors electron deficient substrates.

An efficient enantioselective approach to form trans lactams and cis lactones in up to 98 % yield with greater than 99 % ee, and greater than 20:1 d.r. using simple aliphatic aldehydes has been developed. The process involves a new pathway to generate enolate intermediates from aliphatic aldehydes by oxidation and deprotonation. NHC=N‐heterocyclic carbene, Ts=4‐toluenesulfonyl.

Photoredox catalysis can be used to manipulate the redox state of a transition metal complex leading to the desired reactivity. While powerful, obviating the role of the second catalyst would be attractive from the perspective of simplifying the protocol and using visible light to uncover unexpected, enabling reactivity. Herein we report that Co-acetylides, formed in situ, are photoactive complexes that undergo ligand-to-metal charge transfer using visible light. The net transformation uses air-stable Co­(II) complexes as precatalysts and induces Co­(I) chemistry. The acetylide is an electron reservoir forming the Co­(I) but accepting the electron back at the end of the catalytic cycle. The electronic nature of the acetylide leads to either on–off behavior or simply initiates catalysis, depending on electronics.

The ability to exert spatial and temporal control over a transition-metal catalyst offers diverse opportunities for the fabrication of functional materials. Using an external stimulus such as visible light to toggle a catalyst between an active and dormant state has proven to be an effective approach for controlled, radical methodologies. Outside of radical bond formation, there is a dearth of evidence that suggests traditional transition metal catalysis can similarly be controlled with visible light energy. Many cobalt complexes that catalyze the [2+2+2] cycloaddition are assisted by UV photolysis, but strict photocontrolled methods are unattainable due to high levels of thermally driven reactivity. Herein, we disclose the first light-controlled, cobalt-catalyzed [2+2+2] cycloaddition via a dual cobalt and photoredox catalyst manifold. We demonstrate the power of this method with a spatially and temporally resolved technique for arene formation using photolithography.