Reaction Mechanism of Organocatalytic Michael Addition of Nitromethane to Cinnamaldehyde: A Case Study on Catalyst Regeneration and Solvent Effects
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Reaction Mechanism of Organocatalytic Michael Addition of Nitromethane to Cinnamaldehyde: A Case Study on Catalyst Regeneration and Solvent EffectsFecha de publicación
2017-12Editor
American Chemical SocietyCita bibliográfica
Świderek, K., Nödling, A. R., Tsai, Y. H., Luk, L. Y., & Moliner, V. (2018). Reaction Mechanism of Organocatalytic Michael Addition of Nitromethane to Cinnamaldehyde: A Case Study on Catalyst Regeneration and Solvent Effects. The Journal of Physical Chemistry A, 122(1), 451-459.Tipo de documento
info:eu-repo/semantics/articleVersión de la editorial
https://pubs.acs.org/doi/abs/10.1021/acs.jpca.7b11803Versión
info:eu-repo/semantics/publishedVersionPalabras clave / Materias
Resumen
The Michael addition of nitromethane to cinnamaldehyde has been computationally studied in the absence of a catalyst and the presence of a biotinylated secondary amine by a combined computational and experimental ... [+]
The Michael addition of nitromethane to cinnamaldehyde has been computationally studied in the absence of a catalyst and the presence of a biotinylated secondary amine by a combined computational and experimental approach. The calculations were performed at the density functional theory (DFT) level with the M06-2X hybrid functional, and a polarizable continuum model has been employed to mimic the effect of two different solvents: dichloromethane (DCM) and water. Contrary to common assumption, the product-derived iminium intermediate was absent in both of the solvents tested. Instead, hydrating the C1–C2 double bond in the enamine intermediate directly yields the tetrahedral intermediate, which is key for forming the product and regenerating the catalyst. Enamine hydration is concerted and found to be rate-limiting in DCM but segregated into two non-rate-limiting steps when the solvent is replaced with water. However, further analysis revealed that the use of water as solvent also raises the energy barriers for other chemical steps, particularly the critical step of C–C bond formation between the iminium intermediate and nucleophile; this consequently lowers both the reaction yield and enantioselectivity of this LUMO-lowering reaction, as experimentally detected. These findings provide a logical explanation to why water often enhances organocatalysis when used as an additive but hampers the reaction progress when employed as a solvent. [-]
Proyecto de investigación
Generalitat Valenciana (PROMETEOII/2014/ 022) ; Wellcome Trust (200730/ Z/16/Z and 202056/Z/16/Z); National Institutes of Health (R01 GM065368); Universitat Jaume I (P1·1B2014-26); Ministerio de Educación, Cultura y Deporte (PRX17/00166); Ministerio de Economía y Competitividad (CTQ2015-66223-C2); Leverhulme Trust (RPG-2017-195).Derechos de acceso
Copyright © 2017 American Chemical Society
info:eu-repo/semantics/openAccess
info:eu-repo/semantics/openAccess
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