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

Abstract

A number of novel chiral diamines 3, (1R,2R)‐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 (1R,2R)‐N1‐(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.

Synthesis and Catalytic Application of Two Mononuclear Complexes Bearing Diethylenetriamine Derivative Ligand

“…Therefore, Complex 1 with 20 mol% Et3N as the co-catalyst was selected as the optimum one. Moreover, there was a close relationship between the yield and the nature of the reaction solvent [32][33][34]. The reaction could be carried out in some aprotic solvents such as THF, CH2Cl2, and toluene, and only moderate yields were obtained (Entries 19-21).…”

Carboxylate ion dependency in the Cu(II) catalysed asymmetric Henry reaction: Structural characterisation of a tridentate Schiff base complex containing a coordinated carboxylic acid

“…Calculations and x‐ray structures of precursor square planar Cu(L 2 )(OAc) 2 complexes are consistent with this postulate. As a result, this process has been widely quoted as the most likely mechanism in related works involving Cu(II) complexes of bidentate ligands …”

Asymmetric catalysis in direct nitromethane-free Henry reactions

“…Some of the few monometal-catalyzed anti -selective asymmetric Henry reactions were achieved using Gou's chiral N -monoalkyl cyclohexane-1,2-diamine ligand L15 43 and Breuning's chiral bispidine ligand L16. 44 These reactions gave products with anti / syn ratios of 6.1 : 1 and enantioselectivity above 90% ee ( Scheme 25 ).…”