Lewis acid-mediated β-selective hydrocarboxylation of α,α-diaryl- and α-arylalkenes with R3SiH and CO2
作者:Shinya Tanaka、Yuuki Tanaka、Masafumi Chiba、Tetsutaro Hattori
DOI:10.1016/j.tetlet.2015.04.090
日期:2015.6
alpha,alpha-Diarylalkenes are successfully hydrocarboxylated with Et3SiH and CO2 with the aid of Et3SiB(C6F5)(4) or EtAlCl2/Ph3SiCl to give carboxylic acids with a carboxy group at the beta-position to the aryl groups. The EtAlCl2/Ph3SiCl-mediated reaction is also applicable to various alpha-arylalkenes. H-1 NMR analysis of a mixture of EtAlCl2, Ph3SiCl, and Et3SiH strongly suggests the formation of a mu-H complex, [Ph3Si-H-SiEt3](+) AlEtCl3-, which is an equivalent of R3Si+ ions, while Et3SiB(C6F5)(4) is an ion pair with a Et3Si+ ion. Therefore, in these reaction systems, a siloxycarbonylium, R3Si-O-C O+, is considered to be a common electrophile, the addition of which to the substrate, followed by trapping of the resulting cationic species with Et3SiH seems to afford the desired acid after aqueous workup. (C) 2015 Elsevier Ltd. All rights reserved.