The development of the transition metal-catalyzed allylic substitution reaction is dominated by “soft” stabilized nucleophiles, rather than “hard” unstabilized nucleophiles. This striking dichotomy can presumably be ascribed to the high reactivity of the hard nucleophiles, which often promotes unproductive reaction pathways. Although benzyl-motifs are ubiquitous in several bioactive molecules, for example aliskiren, indinavir <i>etc</i>. the utilization of “hard” unstabilized benzyl organometallics is particularly challenging because of their decreased rate of reductive elimination, which is further exasperated by the formation of the Wurtz-type homocoupling product. This presentation will describe a highly regioselective allylic alkylation of “hard” benzylzinc nucleophiles in the presence of a rhodium(III) catalyst. Importantly, this method utilizes bench stable and commercially available rhodium(III) chloride as a catalyst, in the absence of an exogenous ligand. This seminar will also outline the development of a diastereoselective variant, which permits both acyclic and cyclic allylic carbonates bearing a homoallylic stereocenter to undergo benzylation with high levels of diastereocontrol. Hence, this approach provides a rare example of 1,2-stereoinduction in transition metal-catalyzed allylic substitution.

Regio- and diastereoselective rhodium-catalyzed allylic substitution with unstabilized benzyl nucleophiles

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ACS Fall 2022

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