Stereoselective reagent-controlled homologation of boronic esters with chiral carbenoids offers a programmable means to assemble complex molecules. To date, StReCH techniques capable of iteration have been directed to the installation of stereogenic centers bearing carbon-based substituents. We have discovered that a silicon-substituted Li-carbenoid of low configurational stability [lithio(dimethylphenyl)silylmethyl 2,4,6-triisopropylbenzoate] can be used to chain-extend boronic esters with good enantioselectivity in the presence of scalemic bisoxazoline ligands. The method differs from earlier stereospecific reagent-controlled homologation (s-StReCH) techniques in that stereochemistry emerges inductively as the boronate captures the carbenoid via a putative dynamic kinetic resolution process controlled by the chiral ligand. Given that the dimethylphenylsilyl group can be converted stereospecifically to a hydroxyl group, this finding constitutes an important step toward the realization of a StReCH manifold capable of producing stereochemically complex polyoxygenated molecules. Our ongoing efforts to improve on the efficiency of this 'i-StReCH' method and related studies to establish its scope, will be presented.

Enantioselective synthesis of alpha-(dimethylphenyl)silylalkylboronates via stereoinductive reagent-controlled homologation using a configurationally unstable silicon substituted lithium carbenoid

246th National Meeting (2013)

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