Sara Morales, Fernando G. Guijarro, Inés Alonso, José Luis García Ruano*, and M. Belén Cid*
Department of Organic Chemistry, Universidad Autónoma de Madrid, Cantoblanco, 28049 Madrid, Spain
ACS Catal., 2016, 6, pp 84–91
DOI: 10.1021/acscatal.5b01726
Publication Date (Web): November 12, 2015
Abstract:
The formation of nitrones by direct condensation between equimolecular amounts of N-substituted hydroxylamine hydrochlorides and aromatic or aliphatic aldehydes is efficiently promoted by pyrrolidine in a matter of minutes under very mild conditions in almost quantitative yields after a simple filtration through a short pad of silica gel. According to theoretical, spectroscopic, and experimental studies, this success is due to the ability of pyrrolidine to liberate the hydrochloride of the hydroxylamine and catalyze the reaction via iminium activation ion. Moreover, a cooperative pyrrolidine/pyrrolidinium chloride effect facilitates several steps of the catalytic cycle through proton transfer without hampering the nucleophilicity of the hydroxylamine by protonation.
Keywords: nitrone preparation; iminiumactivation; cooperative; DFT calculations; pyrrolidine/pyrrolidinium
The formation of nitrones by direct condensation between equimolecular amounts of N-substituted hydroxylamine hydrochlorides and aromatic or aliphatic aldehydes is efficiently promoted by pyrrolidine in a matter of minutes under very mild conditions in almost quantitative yields after a simple filtration through a short pad of silica gel. According to theoretical, spectroscopic, and experimental studies, this success is due to the ability of pyrrolidine to liberate the hydrochloride of the hydroxylamine and catalyze the reaction via iminium activation ion. Moreover, a cooperative pyrrolidine/pyrrolidinium chloride effect facilitates several steps of the catalytic cycle through proton transfer without hampering the nucleophilicity of the hydroxylamine by protonation.
Keywords: nitrone preparation; iminiumactivation; cooperative; DFT calculations; pyrrolidine/pyrrolidinium
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