Herein we report the synthesis of substituted indolizidines and related N-fused bicycles from simple saturated cyclic amines through sequential C–H and C–C bond functionalizations. Inspired by the Norrish–Yang Type II reaction, C–H functionalization of azacycles is achieved by forming α-hydroxy-β-lactams from precursor α-ketoamide derivatives under mild, visible light conditions. Selective cleavage of the distal C­(sp2)–C­(sp3) bond in α-hydroxy-β-lactams using a Rh-complex leads to α-acyl intermediates which undergo sequential Rh-catalyzed decarbonylation, 1,4-addition to an electrophile, and aldol cyclization, to afford N-fused bicycles including indolizidines. Computational studies provide mechanistic insight into the observed positional selectivity of C–C cleavage, which depends strongly on the groups bound to Rh trans to the phosphine ligand.

A combined experimental and mechanistic study of the chemoselective hydroboration of carbonyls by the paramagnetic bis-amido Mn­[SMeNSMe]2 complex (1) is described. The catalyst allows for room-temperature hydroboration of carbonyls at low catalyst loadings (0.1 mol %) and reaction times (<30 min). A series of mechanistic studies highlight the significance of bifunctional amido bis­(thioether) ligand L to the success of the reaction, insight otherwise difficult to attain in paramagnetic systems. Kinetic studies using variable time normalization analysis revealed no unusual reaction kinetics, indicating the absence of side reactions. A borylated analogue of L was observed and characterized via mass spectrometry. Density functional theory (DFT) calculations showed that thioether hemilability of L is crucial during catalysis for providing the active coordinating site. Also, the frequently proposed Mn–H intermediate was found not to be the active species responsible for catalysis. Instead, an inner-sphere reaction pathway with carbonyl coordination to the metal center and amido-promoted B–H reactivity is proposed to be operative.

The selective transition-metal-mediated activation of C­(sp2)–H bonds of allenes is a formidable challenge because of the competitive, intrinsic reactivity of cumulated double bonds. Herein, we report a Pd-catalyzed C–H alkenylation of electronically unbiased allenes, affording penta-1,2,4-triene products in up to 94% yield. A picolin­amide directing group enables the formation of putative allenyl-pallada­cycles, which subsequently participate in a turnover-limiting Heck-type reaction with electron-deficient alkene coupling partners. This mechanistic proposal is consistent with experimental and computational investigations. Additionally, we report for the first time the use of picolin­amide N,O-acetals as readily removable auxiliaries for C–H activation reactions, allowing the efficient alkenylation of allenyl carbinol derivatives. Successful removal of the directing groups without affecting the reactive penta-1,2,4-triene substructure of the products is demonstrated.