Godenschwager Peter F, Collum David B
Department of Chemistry and Chemical Biology, Baker Laboratory, Cornell University, Ithaca, New York 14853-1301, USA.
J Am Chem Soc. 2008 Jul 9;130(27):8726-32. doi: 10.1021/ja800250q. Epub 2008 Jun 17.
Lithium hexamethyldisilazide (LiHMDS) in triethylamine (Et 3N)/toluene is shown to enolize acyclic ketones and esters rapidly and with high E/ Z selectivity. Mechanistic studies reveal a dimer-based mechanism consistent with previous studies of LiHMDS/Et 3N. E/ Z equilibration occurs when <2.0 equiv of LiHMDS are used. Studies of the aldol condensation and Ireland-Claisen rearrangement of the resulting Et 3N-solvated enolates show higher and often complementary diastereoselectivities when compared with analogous reactions in THF. The Et 3N-solvated enolates also display a marked (20-fold) acceleration of the Ireland-Claisen rearrangement with evidence of autocatalysis. A possible importance of amine-solvated enolates is discussed.
已表明，在三乙胺（Et₃N）/甲苯中的六甲基二硅基锂（LiHMDS）能快速使无环酮和酯烯醇化，且具有高E/Z选择性。机理研究揭示了一种基于二聚体的机理，这与之前对LiHMDS/Et₃N的研究一致。当使用少于2.0当量的LiHMDS时会发生E/Z平衡。对所得Et₃N溶剂化烯醇盐的羟醛缩合反应和爱尔兰-克莱森重排反应的研究表明，与在四氢呋喃中的类似反应相比，其非对映选择性更高，且往往具有互补性。Et₃N溶剂化烯醇盐还显示出爱尔兰-克莱森重排反应有显著（20倍）加速，并伴有自催化的证据。讨论了胺溶剂化烯醇盐可能的重要性。
