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Gas‐phase chemistry of acylium ions. Seven‐to‐five ring contraction of 1,3‐dioxepane and 1,3‐dioxep‐5‐ene
Author(s) -
Moraes Luiz Alberto B.,
Kotiaho Tapio,
Eberlin Marcos N.
Publication year - 1999
Publication title -
journal of mass spectrometry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.475
H-Index - 121
eISSN - 1096-9888
pISSN - 1076-5174
DOI - 10.1002/(sici)1096-9888(199906)34:6<670::aid-jms819>3.0.co;2-h
Subject(s) - chemistry , ene reaction , acetal , ring (chemistry) , exothermic reaction , ion , medicinal chemistry , stereochemistry , organic chemistry
As shown by pentaquadrupole triple‐stage mass spectrometric and 18 O‐labeling experiments, two seven‐membered cyclic acetals, 1,3‐dioxepane and 1,3‐dioxep‐5‐ene, fail to react by transacetalization with the gaseous acylium ions CH 3 C + O and (CH 3 ) 2 NC + O. Instead, a novel and less exothermic but more kinetically favored reaction, seven‐to‐five ring contraction, occurs predominantly, and to great extents with the most reactive acylium ion, (CH 3 ) 2 NC + O. 1,3‐Dioxepane yields O ‐acylated tetrahydrofurans; 1,3‐dioxep‐5‐ene yields O ‐acylated 2,5‐dihydrofurans. Copyright © 1999 John Wiley & Sons, Ltd.