Synthesis and Homologation of an Azetidin-2-yl Boronic Ester with α-Lithioalkyl Triisopropylbenzoates.

An α-boryl azetidine, obtained by α-lithiation-borylation of N-Botc azetidine, undergoes reaction with α-triisopropylbenzoyloxy organolithiums to give homologated boronic esters that can be further oxidized, homologated, arylated, and deprotected to give a range of α-substituted azetidines. Scalemic α-boryl azetidine-α-triisopropylbenzoyloxy organolithium pairings show stereospecific reagent control, providing access to either diastereomeric series of homologated boronic esters with very high er's.