1,2-Epoxycyclo-octanes: effect of unsaturation on the course of ring opening and rearrangement with acids

Abstract

The products from the reactions of 1,2-epoxycyclo-octane (I), 3,4-epoxycyclo-octene (II), and 5,6-epoxycycloocta-1,3-diene (III) with a number of acids in ethereal solution have been studied. It is found that the ratio of intramolecular-isomerisation reactions to ring-opening processes involving incorporation of external nucleophile, increases with increasing degree of unsaturation in the substrate. Particular attention is paid to the reaction of (III), and it is suggested that the isomerisation to cyclo-octa-2,4-dienone may involve the first example of a 1,6-sigmatropic shift in a pentadienyl cation.