Lewis acid catalyzed stereoselective hydrosilylation of ketones under the control of σ–π chelation
作者:Naoki Asao、Takeshi Ohishi、Kenichiro Sato、Yoshinori Yamamoto
DOI:10.1016/s0040-4020(02)00968-7
日期:2002.10
Felkin–Anh model. On the other hand, the unusual syn-selectivity in the latter cases can be accounted for by the σ–π chelation by R3Si+, in which both the lone pair (σ) of the carbonyl group and the π-electrons of the alkyne coordinate to the silylium ion. The σ–π chelation control was also effective for the 1,3-asymmetric induction.
在催化量的B(C 6 F 5)3存在下,将2-甲基-1-苯基-戊烷-1-酮与Et 3 SiH进行硅氢加成反应,得到的反产物略高于同产物(syn / anti = 1:1.5)。相反,在β位上带有乙炔基的2-甲基-1-苯基-戊-4-yn-1-one的反应中,立体选择性地获得了顺式产物(syn / anti= 7∶1)。所述顺式-selectivities也在B观察到的(C 6 ˚F 5)3-α-甲基-β-炔基芳基酮和α-甲基-β-炔基烷基酮等其他相关酮的催化反应。在前一种情况下观察到的适度的抗选择性可以用普通的Felkin–Anh模型来解释。另一方面,R 3 Si +的σ-π螯合可解释后一种情况下异常的顺选择性,其中羰基的孤对(σ)和π的电子炔与硅离子配位。σ-π螯合控制对1,3-不对称诱导也有效。