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Asymmetric Organocatalyzed Aza‐Henry Reaction of Hydrazones: Experimental and Computational Studies
Author(s) -
Sonsona Isaac G.,
AlegreRequena Juan V.,
MarquésLópez Eugenia,
Gimeno M. Concepción,
Herrera Raquel P.
Publication year - 2020
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.202000232
Subject(s) - nitroaldol reaction , chemistry , enantioselective synthesis , catalysis , reaction mechanism , computational chemistry , elementary reaction , kinetic isotope effect , protonation , organocatalysis , organic chemistry , kinetics , physics , ion , deuterium , quantum mechanics
Abstract The first asymmetric catalyzed aza‐Henry reaction of hydrazones is presented. In this process, quinine was used as the catalyst to synthesize different alkyl substituted β‐nitrohydrazides with ee up to 77 %. This ee was improved up to 94 % by a further recrystallization and the opposite enantiomer can be obtained by using quinidine as the catalyst, opening exciting possibilities in fields in which the control of chirality is vital, such as the pharmaceutical industry. Additionally, experimental and ab initio studies were performed to understand the reaction mechanism. The experimental results revealed an unexpected secondary kinetic isotope effect (KIE) that is explained by the calculated reaction pathway, which shows that the protonation of the initial hydrazone and the C−C bond forming reaction occur during a concerted process. This concerted mechanism makes the catalysis conceptually different to traditional base‐promoted Henry and aza‐Henry reactions.