Enantioselective Friedel–Crafts alkylations catalysed by well-defined iridium and rhodium half-sandwich complexes
作者:Daniel Carmona、María Pilar Lamata、Antonio Sánchez、Fernando Viguri、Luis A. Oro
DOI:10.1016/j.tetasy.2011.05.003
日期:2011.4
Aqua-complexes (S-M,R-C)-[C-p*M((R)-prophos)(H2O)][SbF6](2)(M = Rh 1, Ir 2) catalysed the alkylation of alpha,beta-unsaturated aldehydes with aromatics and heteroaromatics but in some cases, mixtures of products were obtained. Complexes 1 and 2 were also used to activate nitroalkenes for the Friedel-Crafts alkylation of a variety of aromatics and heteroaromatics, in particular, 1,3,5-trimethoxybenzene. For this substrate, the monoalkylated adduct was obtained in quantitative yield with enantioselectivities of up to 73% ee being achieved. The intermediate catalyst/nitroalkene was isolated and characterized and the complex catalyst/adduct was detected spectroscopically. From these data a plausible catalytic cycle is proposed. (C) 2011 Elsevier Ltd. All rights reserved.