Enantioselective reduction of α-substituted ketones mediated by the boronate ester TarB-NO2
作者:Scott Eagon、Nicholas Ball-Jones、Dustin Haddenham、Jaime Saavedra、Cassandra DeLieto、Matthew Buckman、Bakthan Singaram
DOI:10.1016/j.tetlet.2010.09.146
日期:2010.12
A facile and mild reduction procedure is reported for the preparation of chiral secondary alcohols prepared from α-substituted ketones using sodium borohydride and the chiral boronate ester (l)-TarB-NO2. Direct reduction of substituted ketones bearing Lewis basic heteroatoms generally provided secondary alcohols of only modest enantiomeric excess likely due to either competition between the target
据报道,使用硼氢化钠和手性硼酸酯(1)-TarB-NO 2由α-取代的酮制备手性仲醇的方法简便而温和。直接还原带有Lewis碱性杂原子的取代酮通常可提供仅适度对映体过量的仲醇,这可能是由于目标羰基与TarB-NO 2中Lewis酸性硼原子处的官能化侧链之间的竞争或α的增加的空间体积造成的-侧链。作为替代方法,使用TarB-NO 2合成这些底物通过两步程序,包括将α-卤代酮还原为手性末端环氧化物,然后通过各种亲核试剂打开区域选择性/区域特异性环氧化物。该方法提供了各种功能化的仲醇,包括β-羟基醚,硫醚,腈和胺,对映体过量为94%,收率最高为98%。