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

Article abstract of DOI:10.1039/c3cy00774j

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. The Royal Society of Chemistry.