Lewis acid catalyzed stereoselective hydrosilylation of ketones under the control of σ-π chelation
Lewis acid catalyzed stereoselective hydrosilylation of ketones under the control of σ-π chelation
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DOI：
10.1016/s0040-4020(02)00968-7
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发表时间：
2002-10-07
期刊：
影响因子：
2.1
通讯作者：
Yamamoto, Y
中科院分区：
文献类型：
--
作者：
Asao, N;Ohishi, T;Yamamoto, Y
在催化量的B（C_6 F_5）存在下，2-甲基-1-苯基-戊-1-酮与Et_3SiH的氢化硅烷化反应（3）得到反式产物，其相对于合成产物的优势稍大（顺式/反式=1：1.5）。相反，在β-位带有乙炔基的2-甲基-1-苯基-N-（4-炔-1-酮）的反应中立体选择性地获得了顺式产物（顺/反=7：1）。在B（C_6F_5）（3）催化的其它相关酮如α-甲基-β-炔基芳基酮和α-甲基-β-炔基烷基酮的反应中也观察到顺式选择性。在前一种情况下观察到的适度的反选择性可以用普通的Felkin-Anh模型来解释。另一方面，在后一种情况下的不寻常的顺式选择性可以通过R3 Si+的σ-π螯合来解释，其中羰基的孤对电子（σ）和炔的π-电子都与甲硅烷基离子配位。σ-π螯合对照对1，3-不对称诱导也有效。(C)2002爱思唯尔科技有限公司版权所有。
Hydrosilylation of 2-methyl-1-phenyl-pentan-1-one with Et3SiH in the presence of catalytic amounts of B(C6F5)(3) gave the anti-product with slight predominance over syn-product (syn/anti=1:1.5). In contrast, the syn-product was obtained stereoselectively in the reaction of 2-methyl-1-phenyl-pent-4-yn-1-one bearing an ethynyl group at the beta-position (syn/anti=7:1). The syn-selectivities were also observed in the B(C6F5)(3)-catalyzed reactions of other related ketones, such as alpha-methyl-beta-alkynyl aryl ketones and alpha-methyl-beta-alkynyl alkyl ketones. The moderate anti-selectivity observed in the former case can be explained by the ordinary Felkin-Anh model. On the other hand, the unusual syn-selectivity in the latter cases can be accounted for by the sigma-pi chelation by R3Si+, in which both the lone pair (sigma) of the carbonyl group and the pi-electrons of the alkyne coordinate to the silylium ion. The sigma-pi chelation control was also effective for the 1,3-asymmetric induction. (C) 2002 Elsevier Science Ltd. All rights reserved.