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Type: Artigo de periódico
Title: Mannich-type reactions in the gas-phase: The addition of enol silanes to cyclic N-acyliminium ions
Author: Tomazela, DM
Moraes, LAB
Pilli, RA
Eberlin, MN
D'Oca, MGM
Abstract: The intrinsic gas-phase reactivity of cyclic N-acyliminium ions in Mannich-type reactions with the parent enol silane, vinyloxytrimethylsilane, has been investigated by double- and triple-stage pentaquadrupole mass spectrometric experiments. Remarkably distinct reactivities are observed for cyclic N-acyliminium ions bearing either endocyclic or exocyclic carbonyl groups. NH-Acyliminium ions with endocyclic carbonyl groups locked in s-trans forms participate in a novel tandem N-acyliminium ion reaction: the nascent adduct formed by simple addition is unstable and rearranges by intramolecular trimethylsilyl cation shift to the ring nitrogen, and an acetaldehyde enol molecule is eliminated. An NSi(CH3)(3)-acyliminium ion is formed, and this intermediate ion reacts with a second molecule of vinyloxytrimethylsilane by simple addition to form a stable acyclic adduct. N-Acyl and NN-diacyliminium ions with endocyclic carbonyl groups, for which the s-cis conformation is favored, react distinctively by mono polar [4(+) + 2] cycloaddition yielding stable, ressonance-stabilized cycloadducts. Product ions were isolated via mass-selection and structurally characterized by triple-stage mass spectrometric experiments. B3LYP/6-311G(d,p) calculations corroborate the proposed reaction mechanisms.
Country: EUA
Editor: Amer Chemical Soc
Rights: fechado
Identifier DOI: 10.1021/jo016382o
Date Issue: 2002
Appears in Collections:Artigos e Materiais de Revistas Científicas - Unicamp

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