Structural and solvent effects on the mechanism of base-induced rearrangement of epoxides to allylic alcohols
A combined experimental and computational study is presented which explores the influence of structure and solvent on the base-catalyzed isomerization of cyclopentene- and cyclohexene oxides. Cyclohexene oxide is known to rearrange via a syn beta-elimination in nonpolar solvents. Cyclopentene oxide instead undergoes alpha-elimination to a carbenoid intermediate in nonpolar solvents due to the unusual acidity of the alpha-proton, not because of an unfavorable conformation. In HMPA, cyclopentene oxide undergoes beta-elimination. To explore the origins of this mechanistic change, deuterium-labeled cis-4-tert-butylcyclohexene oxide was rearranged in HMPA and was found to react via anti beta-elimination, as presumably do cyclopentene oxide and other epoxides.
Morgan
KM
Department of Chemistry, College of William & Mary, P.O. Box 8795, Williamsburg, Virginia 23187, and Department of Chemistry and Biochemistry, San Francisco State University, San Francisco, California 94132, USA.
Gronert
S