Synthesis, characterization and enantioselective free radical reductions of (1R,2S,5R)-menthyldiphenylgermane and its enantiomer
作者:Le Zeng、Dainis Dakternieks、Andrew Duthie、Tamara Perchyonok、Carl Schiesser
DOI:10.1016/j.tetasy.2004.06.020
日期:2004.8
5R)-Menthyldiphenylgermane and its enantiomer have been prepared in a few steps from germanium tetrachloride. The initial step in this sequence, namely the reaction between germanium tetrachloride and menthylmagnesium chloride, produces menthylgermanium trichloride, which is the exclusive product of this Grignard reaction, presumably due to the bulk of the menthyl group. When used at a low temperature
(1 R,2 S,5 R)-甲基二苯基锗烷及其对映异构体是由四氯化锗分几步制备的。此顺序的第一步,即四氯化锗与氯化薄荷基镁之间的反应,产生了氯化三薄荷基锗,这是格氏试剂的唯一产物,可能是由于薄荷基的体积较大。当在低温(-78°C)下使用并与路易斯酸(如镁盐)结合使用时,这些手性锗烷能够以高对映选择性,但以中等产率收率还原酯官能化的自由基。例如,(R在镁存在下,于-78°C下于甲苯中将2-溴萘酚乙酯与(1 R,2 S,5 R)-薄荷基二苯基锗烷在甲苯中反应,可得到15%收率和99%ee的萘普生乙酯。溴化物。在80°C下,(1 R,2 S,5 R)-薄荷基二苯基锗烷与伯烷基自由基反应,速率常数为1.02×10 6 M -1 s -1。动力学研究表明该反应的Arrhenius表达式为:log(k / M -1 s -1)=(11.1±0.4)-(34.6±3.1)/ θ,其中θ = 2.3