Asymmetric borane reduction of ketones catalyzed by<i>N</i>-hydroxyalkyl-<i>l</i>-menthopyrazoles
作者:Choji Kashima、Yoshihiro Tsukamoto、Kohei Higashide、Hiroyuki Nakazono
DOI:10.1002/jhet.5570370449
日期:2000.7
N-(hydroxyalkyl)pyrazoles and borane formed boric ester complex, in which the remaining borane was stabilized by the adjacent nitrogen of thr pyrazole ring. The borane complex derived from the chiral pyrazoles such as 3-phenyl-l-menthopyrazole reduced p-methylacetophenone (21) enantioselectively. When (2′S)-2-(2′-phenyl-2′-hydroxyethyl)-3-phenyl-l-menthopyrazole ((2′S)-10b) was used, 21 was reduced into (
N-(羟烷基)吡唑与硼烷的等摩尔混合物形成硼酸酯络合物,其中剩余的硼烷被吡唑环的相邻氮原子稳定。衍生自手性吡唑的硼烷络合物,例如3-苯基-1-薄荷基吡唑,对映体选择性还原对甲基苯乙酮(21)。当使用(2 'S)-2-(2'-苯基-2'-羟乙基)-3-苯基-1-薄荷基吡唑((2 'S)-10b)时,将21还原为(S)-p-。甲基苯基-1-乙醇(22)的化学和光学收率中等。由于制备的不便和较低的光学收率,使用N-(α-羟烷基)吡唑对硼烷的对映体选择性还原酮是没有希望的。