Mild and Expedient Asymmetric Reductions of α,β-Unsaturated Alkenyl and Alkynyl Ketones by TarB-NO<sub>2</sub> and Mechanistic Investigations of Ketone Reduction
作者:Scott Eagon、Cassandra DeLieto、William J. McDonald、Dustin Haddenham、Jaime Saavedra、Jinsoo Kim、Bakthan Singaram
DOI:10.1021/jo101530f
日期:2010.11.19
yields up to 99%. In the case of α,β-unsaturated alkenyl ketones, α-substituted cycloalkenones were reduced with up to 99% ee, while more substituted and acyclic derivatives exhibited lower induction. For α,β-ynones, it was found that highly branched aliphatic ynones were reduced with optimal induction up to 90% ee, while reduction of aromatic and linear aliphatic derivatives resulted in more modest enantioselectivity
据报道,制备对映体纯度高的手性烯丙基和炔丙基醇的方法轻而易举。在最佳条件下,TarB-NO 2和NaBH 4在25°C下于1 h内将炔基和烯基酮还原,生成对映体过量的手性炔丙基和烯丙基醇,收率高达99%。在α,β-不饱和烯基酮的情况下,α-取代的环烯酮的还原度最高可达99%ee,而更多被取代和无环的衍生物则显示出较低的诱导率。对于α,β-炔酮,发现高支化的脂族炔酮在最高达90%ee的情况下以最佳诱导被还原,而芳族和线性脂族衍生物的还原导致更适度的对映选择性。使用(升源自(l)-酒石酸的)-TarB-NO 2试剂,我们通常获得具有(R)构型的高度对映体富集的手性烯丙基和炔丙基醇。由于先前的模型和饱和类似物预测的(S)构型的炔丙基产物的减少,因此进行了一系列新的机理研究,以确定过渡态芳族,烯基和炔基酮的可能取向。