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Methanolysis of 1‐aryl‐1,2‐epoxycyclohexanes in the condensed and in the gas phase: importance of the substituent for the reaction mechanism
Author(s) -
Crotti Paolo,
Di Bussolo Valeria,
Macchia Franco,
Favero Lucilla,
Pineschi Mauro,
Lucarelli Laura,
Roselli Graziella,
Renzi Gabriele
Publication year - 2005
Publication title -
journal of physical organic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.325
H-Index - 66
eISSN - 1099-1395
pISSN - 0894-3230
DOI - 10.1002/poc.845
Subject(s) - chemistry , substituent , aryl , adduct , medicinal chemistry , catalysis , stereoselectivity , reaction mechanism , gas phase , acid catalysis , stereochemistry , computational chemistry , organic chemistry , alkyl
The stereoselectivity of a series of 1‐aryl‐1,2‐epoxycyclohexanes substituted on the phenyl group was determined in acid methanolysis in the condensed phase (0.2 N H 2 SO 4 –MeOH) and in the reaction with MeOH in the gas phase under catalysis by a gaseous Brønsted acid (D 3 + ). The results obtained show the presence of a clear Hammett‐type dependence of the syn / anti adduct ratio on the Brown σ + of the substituent on the phenyl group, thus confirming the validity of the ion–dipole pair mechanism in order to rationalize the stereochemical behavior of 2‐aryloxiranes in opening reactions under acidic conditions. Only in the cases of the p ‐OMe‐ and p ‐NO 2 ‐substituted epoxides, does an S N 1 and an S N 2 process, respectively, appear to be involved. Copyright © 2004 John Wiley & Sons, Ltd.