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 gamma-boryl substituted syn-beta-alkoxy- or syn-beta-amino-homoallylic alcohols is developed. Pt-catalyzed regioselective diboration of alkoxyallene or aminoallene with B(2)pin(2) occurred at the terminal alkene unit of the allene to give (Z)-gamma-alkoxy- or (Z)-gamma-amino-beta-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.