Asymmetric esterification of ketenes catalyzed by an N-heterocyclic carbene
作者:Xiao-Na Wang、Hui Lv、Xue-Liang Huang、Song Ye
DOI:10.1039/b815139c
日期:——
The chiral N-heterocycliccarbene precursor 2, derived from L-pyroglutamic acid, was found to be an efficient precatalyst for the enantioselective esterification of alkylarylketenes with benzhydrol to give the corresponding esters in good yields with good to high enantioselectivities (up to 95% ee).
Four new cyclopropane-based bisoxazolines were synthesized and applied to cobalt-catalyzed cross-coupling reactions between racemic alpha-bromo esters and aryl Grignard reagents. The reaction afforded a series of chiral alpha-arylalkanoic esters with high yields and good enantioselectivities (up to 93% yield, 92:8 er). This research focuses on the cross-coupling between racemic alpha-bromopropanoate and p-isobutylphenyl Grignard reagent's which provides ibuprofen ester efficiently. Furthermore, ibuprofen ester 7e was transformed into (S) -ibuprofen (99:1 er) via hydrolysis and recrystallization. (C) 2016 Elsevier Ltd. All rights reserved.