Department of Chemistry, BMC, Uppsala University, Uppsala, Sweden.
Chem Asian J. 2013 May;8(5):974-81. doi: 10.1002/asia.201201178. Epub 2013 Mar 7.
In this study, we investigate the effect of the electrophiles and the nucleophiles for eight catalysts in the catalytic SN 1 type substitution of alcohols with different degree of activation by sulfur-, carbon-, oxygen-, and nitrogen-centered nucleophiles. The catalysts do not show any general variance in efficiency or selectivity with respect to the alcohols and follow the trend of alcohol reactivity. However, when it comes to the nucleophile, the eight catalysts show general and specific variances in the efficiency and selectivity to perform the desired substitution. Interestingly, the selectivity of the alcohols to produce the desired substitution products was found to be independent of the electrophilicity of the generated carbocations but highly dependent on the ease of formation of the cation. Catalysts based on iron(III), bismuth(III), and gold(III) show higher conversions for S-, C-, and N-centered nucleophiles, and Bi(III) was the most efficient catalyst in all combinations. Catalysts based on rhenium(I) or rhenium(VII), palladium(II), and lanthanum(III) were the most efficient in performing the nucleophilic substitution on the various alcohols with the O-centered nucleophiles. These catalysts generate the symmetrical ether as a by-product from the reactions of S-, C-, and N-centered nucleophiles as well, resulting in lower chemoselectivity.
在这项研究中，我们研究了亲电试剂和亲核试剂对 8 种催化剂的影响，这些催化剂在硫、碳、氧和氮中心亲核试剂的催化 SN1 型醇取代反应中具有不同程度的活化。催化剂对醇的效率或选择性没有表现出任何一般的变化规律，而是遵循醇反应性的趋势。然而，当涉及到亲核试剂时，这 8 种催化剂在效率和选择性方面表现出一般和特定的变化，以进行所需的取代。有趣的是，发现醇产生所需取代产物的选择性与生成的碳正离子的亲电性无关，但高度依赖于阳离子的形成难易程度。基于铁(III)、铋(III)和金(III)的催化剂对 S-、C-和 N-中心亲核试剂显示出更高的转化率，而 Bi(III)在所有组合中是最有效的催化剂。基于铼(I)或铼(VII)、钯(II)和镧(III)的催化剂在各种醇与 O-中心亲核试剂的亲核取代反应中表现出最高的效率。这些催化剂也会从 S-、C-和 N-中心亲核试剂的反应中生成对称醚作为副产物，导致较低的化学选择性。
