Introduction of small, unfunctionalized alkyl groups (e.g. methyl) into a specific C–H bond in an organic compound is among the toughest challenges in organic synthesis and often requires reagents which are toxic, expensive or both. This task becomes even trickier when the resulting C–C bond formation leads to the generation of a stereocenter. Controlling absolute stereochemistry at this newly formed stereocenter poses a challenge of different dimension. Elimination of small and stable molecules during or after the bond formation event can be viewed as an effective strategy for installing small and unfunctionalized alkyl groups into a C–H bond, even enantioselectively. During the past few years, our research group have adopted this strategy for accomplishing this intricate task. In this process we have also developed a number of reactions for controlling stereochemistry at a stereogenic center remote from the reaction site. We have developed alkylative desymmetrizations of prochiral 2,2-disubstituted cyclopentene-1,3-diones (1)1and meso-norbornenoquinones (2)2using nitroalkanes as the alkyl source (Scheme 1). These reactions are catalysed by tertiary amino(thio)urea derivatives and proceed via C(sp2)−H alkylation. Scheme 1: Enantioselective C(sp2)–H alkylations In addition, we have developed the direct enantioselective C(sp3)−H allylic alkylation of 4-methyl coumarin derivatives (3) under Lewis base catalysis3 and Ir-catalysis (Scheme 2).4 Scheme 2: Enantioselective C(sp3)–H allylations

Catalytic enantioselective C(sp2)–H and C(sp3)–H alkylation: From organocatalysis to transition metal catalysis

2019 Fall National Meeting

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