Asymmetric Henry reactions of aldehydes with various nitroalkanes catalyzed by copper(II) complexes of novel chiral N ‐monoalkyl cyclohexane‐1,2‐diamines

A number of novel chiral diamines 3 , (1 R ,2 R )‐ N ‐monoalkylcyclohexane‐1,2‐diamines, were designed and synthesized from trans ‐cyclohexane‐1,2‐diamine and applied to the catalytic asymmetric Henry reaction of benzaldehyde and nitromethane to provide β‐nitroalcohol in high yield (up to 99%) and good enantiomeric excess (up to 89%). By using ligand (1 R ,2 R )‐ N 1 ‐(4‐methylpentan‐2‐yl)cyclohexane‐1,2‐diamine ( 3g ), the reaction was optimized in terms of the metal ion, temperature, solvent and base. Further experiments indicated that the complex, 3g –Cu(OAc) 2 , was an efficient catalyst in the asymmetric Henry reaction between different aldehydes and nitromethane, and the desired products have been obtained with high chemical yields (up to 99%) and high enantiomeric excess (up to 93%). The optimized catalyst promoted the diastereoselective Henry reaction of various aldehyde substrates and nitroalkane, which gave the corresponding anti ‐selective adduct with up to 99% yield and 83:17 anti / syn selectivity. Upon scaling up to gram quantities, the β‐nitroalcohol was obtained in good yield (96%) with excellent selectivities (93% ee ). The chiral induction mechanism was tentatively explained on the basis of a previously proposed transition‐state model. Copyright © 2014 John Wiley & Sons, Ltd.