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

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