Iterative stereospecific reagent-controlled homologation of pinacol boronates by enantioenriched α-chloroalkyllithium reagents

Reaction of pinacol boronates with putative enantioenriched alpha-chloroalkyllithium species, generated in situ from homochiral alpha-chloroalkylsulfoxides by sulfoxide ligand exchange with t-BuLi in PhMe at -78 degrees C, gave chain-extended boronic ester products with generally excellent stereochemical fidelity. Iteration of this stereospecific reagent-controlled homologation (StReCH) process enabled the programmed synthesis of all four stereoisomers of a stereodiad-containing model system (4-benzyl-1,6-diphenylhexan-2-ol) with er >= 97:3 in all cases.