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Theoretical study on mechanism of cinchona alkaloids catalyzed asymmetric conjugate addition of dimethyl malonate to β-nitrostyrene

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Abstract

The mechanism and enantioselectivity of the asymmetric conjugate addition of dimethyl malonate to β-nitrostyrene catalyzed by cinchona alkaloid QD-4 as organic catalyst are investigated using density function theory and ab initio methods. Six different reaction pathways, corresponding to the different approach modes of β-nitrostyrene to dimethyl malonate are considered. Calculations indicate that the reaction process through a dual-activation mechanism, in which the tertiary amine of cinchona alkaloid QD-4 first works as a Brønsted base to promote the activation of the dimethyl malonate by deprotonation, and then, the hydroxyl group of QD-4 acts as Brønsted acid to activate the β-nitrostyrene. The rate-determining step is the proton transfer process from the tertiary amine of QD-4 to α-carbon of β-nitrostyrene. The comparison of the mechanisms and energies of the six reaction channels enable us to learn the fact that QD-4 has good catalytic activities for the system, and implies C9[BOND]OH in QD-4 may not be involved in the activation. These calculation results account well for the observations in experiments. © 2014 Wiley Periodicals, Inc.

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