()-α-Boryl-crotylboron reagents -selective alkene isomerization and application to stereoselective syntheses of ()-δ-boryl--homoallylic alcohols.

Stereoselective synthesis of ()-α-boryl-crotylboronate is developed. Ni-catalyzed -selective alkene isomerization of α-boryl substituted homoallylboronate provided the targeted ()-crotylboronate with high selectivity. Stereoselective addition of the novel crotylboron reagent to aldehydes gave ()-δ-boryl-substituted -homoallylic alcohols with excellent diastereoselectivities. The vinyl boronate unit in the products can be directly used for a subsequent C-C bond-forming transformation as illustrated in the synthesis of the C fragment of the natural products nannocystin A and nannocystin Ax.