Enantioselective Syntheses of syn- and anti-β-Hydroxyallylsilanes Via Allene Hydroboration-Aldehyde Allylboration Reactions
摘要:
The kinetic hydroboration of allenylsilane 5 with ((d)Ipc)(2)BH at -40 degrees C provides allylborane 9Z with >= 12:1 selectivity. When the hydroboration is performed at temperatures above -40 degrees C, 9Z isomerizes to the thermodynamically more stable allylborane 9E with >20:1 selectivity. Subsequent treatment of 9Z or 9E with aldehydes at -78 degrees C provides syn- or anti-beta-hydroxyallylsilanes, 7 or 8, respectively.
Stereoselective Synthesis of γ-Substituted (<i>Z</i>)-Allylic Boranes via Kinetically Controlled Hydroboration of Allenes with 10-TMS-9-borabicyclo[3.3.2]decane
作者:Jeremy Kister、Amy C. DeBaillie、Ricardo Lira、William R. Roush
DOI:10.1021/ja905494c
日期:2009.10.14
Kineticallycontrolled hydroboration of allenes 8 and 14a-d with the readily accessible Soderquist borane 7, which is generated in situ from borohydride 6, constitutes a convenient and preparatively useful method for synthesis of (Z)-gamma-(substituted)allylboranes 9 and 15a-d. These allylboranes undergo highly diastereo- (> or = 90: 10) and enantioselective (typically 89-96% e.e.) allylboration reactions