Coupling Reaction of Enol Derivatives with Silyl Ketene Acetals Catalyzed by Gallium Trihalides
作者:Yoshihiro Nishimoto、Yuji Kita、Hiroki Ueda、Hiroto Imaoka、Kouji Chiba、Makoto Yasuda、Akio Baba
DOI:10.1002/chem.201602150
日期:2016.8.8
cross‐coupling reaction between enol derivatives and silyl ketene acetals catalyzed by GaBr3 took place to give the corresponding α‐alkenyl esters. GaBr3 showed the most effective catalytic ability, whereas other metal salts such as BF3⋅OEt2, AlCl3, PdCl2, and lanthanide triflates were not effective. Various types of enol ethers and vinyl carboxylates as enol derivatives are amenable to this coupling
GaBr 3催化烯醇衍生物与甲硅烷基烯酮缩醛之间发生交叉偶联反应,得到相应的α-烯基酯。GaBr 3表现出最有效的催化能力,而其他金属盐(例如BF 3 OEt 2,AlCl 3,PdCl 2和镧系三氟甲磺酸盐)无效。各种类型的烯醇醚和羧酸乙烯酯作为烯醇衍生物都适合这种偶联。与甲硅烷基乙烯酮缩醛的反应范围也很宽。我们通过NMR光谱法成功地观察到烷基镓中间体,提示了GaBr 3之间涉及抗碳藻糖基化的机理,烯醇衍生物和甲硅烷基烯酮乙缩醛,然后从烷基镓中进行顺-β-烷氧基消除。根据动力学研究,使用乙烯基醚和羧酸乙烯酯的反应限制周转步骤分别涉及顺-β-烷氧基消除和抗羰基镓化反应。因此,离去基团对反应的进行有重要影响。理论计算分析表明,适度的镓路易斯酸将有助于烷基镓中间体的柔性构象变化,并有助于在β-烷氧基消除过程中裂解碳氧键,这是反应中的周转限制步骤。在乙烯基醚和甲硅烷基乙烯酮缩醛之间。