A DFT study of the enantioselective reduction of oxime ethers promoted by chiral spiroborate esters

Abstract

Mechanisms of borane reduction of the (E)-acetophenone O-methyl oxime catalyzed by the easily prepared and stable spiroborate ester 1, derived from diphenylvalinol has been reported for the first time using density functional theory. Two reaction pathways are investigated at the B3LYP/6-31G(d,p) level of theory. The calculated results reveal that this reaction is accomplished via four steps. All the reactants, products, transition states, and intermediates have been optimized at the B3LYP/6-31G (d,p) level. The analysis of these results reveals that one pathway is more energetically favorable than the other, and its associated product is in good agreement with the experimental result. The solvent effect has been further considered at the B3LYP/6-31G(d,p) level in the solvent THF using the PCM model, and the results indicate that it has no great influence on the enantioselectivity of this reduction. (C) 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2012National Natural Science Foundation of China [20972130, 21072178]; Henan Province (Innovation Specialist Projects

Reduction of Oximes and Hydrazones: Asymmetric and Diastereoselective Approaches

“…Finally, the reduction of amide functionality of 17 into the corresponding secondary amine gave calcimimetic analogues 18 in modest to good yields [40]. The mechanism of the asymmetric borane-mediated reduction of (E)-acetophenone O-methyloxime using chiral spiroborate ester 2 was proposed and supported by chemical calculations at the DFT level [41]. Two possible pathways were considered in this study and the more energetically favourable is outlined in Scheme 5.…”

“…At this stage, a hydride is transferred to the prochiral center of C=N double bond by the Si face, determining the observed stereoselectivity. Intermediate IV undergoes a [2+2] cycloaddition reaction to form the four-membered ring present in V. A sequential two bond cleavage releases the catalyst and VII, which gives the chiral amine after work-up [41]. Inspired by the success of spiroborate esters in the asymmetric reduction of oximes, Anandhan and co-workers described the synthesis of triazole-based dendrimers supported spiroborate esters and explored their behaviour in the asymmetric reduction of (E)-Obenzyloximes.…”