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Type: Artigo de periódico
Title: The gas-phase Meerwein reaction
Author: Moraes, LAB
Eberlin, MN
Abstract: A systematic investigation of a novel epoxide and thioepoxide ring expansion reaction promoted by gaseous acylium and thioacylium ions is reported. As ab initio calculations predict, and O-18-labeling and MS3 pentaquadrupole experiments demonstrate, the reaction proceeds by initial O(S)-acylation of the (thio)epoxides followed by rapid intramolecular nucleophilic attack that results in three-to-five-membered ring expansion, and forms cyclic 1,3-dioxolanylium, 1,3-oxathiolanylium, or 1,3-dithiolanylium ions. This gas-phase reaction is analogous to a condensed-phase reaction long since described by H. Meerwein (Chem. Ber. 1955, 67, 374), and is termed as "the gas-phase Meerwein reaction"; it occurs often to great extents or even exclusively, but in some cases, particularly for the most basic (thio)epoxides and the most acidic (thio)acylium ions, proton transfer (eventually hydride abstraction) competes efficiently, or even dominates. When (thio)epoxides react with (thio)acylium ions, the reaction promotes O(S)-scrambling; when epoxides react with thioacylium ions and the adducts are dissociated, it promotes S/O replacement. An analogous four-to-six-membered ring expansion also occurs predominantly in reactions of trimethylene oxide with acylium and thioacylium ions.
Subject: epoxides
acylium ions
thioacylium ions
ion-molecule reactions
mass spectroscopy
Country: Alemanha
Editor: Wiley-v C H Verlag Gmbh
Citation: Chemistry-a European Journal. Wiley-v C H Verlag Gmbh, v. 6, n. 5, n. 897, n. 905, 2000.
Rights: fechado
Identifier DOI: 10.1002/(SICI)1521-3765(20000303)6:5<897
Date Issue: 2000
Appears in Collections:Unicamp - Artigos e Outros Documentos

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