Chiral Cu(ii)-amino alcohol based complexes for asymmetric aza-Henry reaction of N-Ts imines?

Catalysis Science & Technology Pub Date: 2013-12-18 DOI: 10.1039/C3CY00774J

Abstract

A series of chiral dimeric ligands 1A–C, 2A–B, 3A–B and 4A derived from (S)/(R) 1,1′-bi(2-naphthol)-bis-aldehyde/piperazine-bis-aldehyde and various aminoalcohols viz., (1R,2S)-(?)-2-aminodiphenylethanol, (1S,2R)-(?)-2-aminodiphenylethanol, (1R,2S)-1-amino-2,3-dihydro-1H-inden-2-ol and (R)-valinol were synthesized. In situ generated complexes 1A–C–, 2A–B–, 3A–B–, 4A–Cu(II)/Cu(I) of dimeric chiral ligands with different copper salts were used as catalysts for the asymmetric aza-Henry reaction of a variety of N-tosylimines as substrates with different nitroalkanes at RT to afford good yields of aza-Henry products (80% with respect to the imines) with excellent enantioselectivity (ee > 99%) in 24 h with nitromethane and high syn selective products with excellent enantioselectivity with nitroethane. The dimeric chiral Cu(II) complex 1A–Cu(II) retained its performance at the gram level and was expediently recycled for a number of times. The enantio-pure aza-Henry product was further used for the synthesis of (S)-levamisole (an anthelminthic agent) in good yield and ee in three steps.

Graphical abstract: Chiral Cu(ii)-amino alcohol based complexes for asymmetric aza-Henry reaction of N-Ts imines
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