Stereoselective Syntheses of γ‑Boryl Substituted syn-β-Alkoxy- and syn-β-Amino-homoallylic Alcohols via a Regio- and Stereoselective Allene Diboration and Aldehyde Allylboration Reaction Sequence

Diastereoselective synthesis of γ-boryl substituted syn-β-alkoxy- or syn-β-amino-homoallylic alcohols is developed. Pt-catalyzed regioselective diboration of alkoxyallene or aminoallene with B2pin2 occurred at the terminal alkene unit of the allene to give (Z)-γ-alkoxy- or (Z)-γ-amino-β-boryl substituted allylboronates with high selectivities. Addition of the allylboronates to aldehydes followed by protection of the resulting secondary hydroxyl group gave TES-protected syn-1,2-diols and syn-1,2-amino alcohols with high diastereoselectivities. The vinyl-Bpin group in the products is a useful handle for further transformations.