Polystyrene copolymer supported by substituted (1R,2R)-1,2-diphenylethane-1,2-diamine-copper(II) complexes: a recyclable catalyst for asymmetric Henry reactions

Abstract

Herein described the preparation of swelling pearl-like copolymer styrene—4-vinylbenzyl chloride cross-linked by means of tetra(ethylene glycol)-bis(4-vinylbenzyl)ether (200–800μm). The pearl-like polymer was used to anchor (1R,2R)-1-amino-2-(2,3-dihydro-1H-isoindole-2-yl)-1,2-diphenylethane by a covalent bond; the product was subsequently transformed into the corresponding complex with Cu(II) acetate. The synthesized catalyst was used for the catalysis of the Henry reaction of functionalized aldehydes with nitromethane in ethanol. The reactions proceeded in a polymeric matrix of the swelling catalyst at a rate comparable with the rates of reactions in a homogeneous medium. The corresponding functionalized 2-nitroethanols were formed in quantitative yields (20°C, 24h) with enantiomeric excess values of up to 96%. The catalyst was recycled five times without losing its effectiveness with regard to the yield and enantioselectivity; only a partial mechanical degradation of the polymeric matrix occurred due to stirring.