Scheme 1. 1,2-Dicarbonyl or monocarbonyl compounds directly serve as surrogates for diazo compounds in Mo-catalyzed deoxygenative cyclopropanation reactions.

The radical cascade reaction is considered as one of the most powerful methods to build molecular complexity. However, highly stereoselective intermolecular radical cascade reactions that can produce complex cyclic compounds bearing multiple stereocenters via visible-light-induced photocatalysis have been challenging yet desirable. Herein we report a facile and efficient synthesis of multi-substituted trans-fused hexahydrocarbazoles via a stereoselective intermolecular radical cascade reaction of readily available tryptophans and acrylamides enabled by visible-light-induced photoredox catalysis. The trans-fused hexahydrocarbazoles with up to five stereocenters including two quaternary ones can be accessed in up to 82% yield, >20/1 diastereoselectivity, and 96% ee. Interestingly, the tetrahydrocarbazoles are favorably formed when the reaction is performed under air. Moreover, by simply switching the starting material from tryptophans to ɤ-alkenyl substituted α-amino acids, this protocol can be further applied to the stereoselective syntheses of 1,3,5-trisubstituted cyclohexanes which are otherwise challenging to access. Preliminary mechanistic studies suggest that the reaction goes through radical addition cascade and radical-polar crossover processes.

The transition‐metal‐catalyzed cyclopropanation of alkenes by the decomposition of diazo compounds is a powerful and straightforward strategy to produce cyclopropanes, but is tempered by the potentially explosive nature of diazo substrates. Herein we report the Mo‐catalyzed regiospecific deoxygenative cyclopropanation of readily available and bench‐stable 1,2‐dicarbonyl compounds, in which one of the two carbonyl groups acts as a carbene equivalent upon deoxygenation and engages in the subsequent cyclopropanation process. The use of a commercially available Mo catalyst afforded an array of valuable cyclopropanes with exclusive regioselectivity in up to 90 % yield. The synthetic utility of this method was further demonstrated by gram‐scale syntheses, late‐stage functionalization, and the cyclopropanation of a simple monocarbonyl compound. Preliminary mechanistic studies suggest that phosphine (or silane) acts as both a mild reductant and a good oxygen acceptor that efficiently regenerates the catalytically active Mo catalyst through reduction of the Mo‐oxo complexes.