Rapid intramolecular 1,4-hydride transfer across a rigid 4-hydroxycycloheptanone

Abstract

The n.m.r. spectrum of the sodium salt (4; R = Na) was found to be temperature dependent and this behaviour has been associated with a rapid degenerate rearrangement involving intramolecular hydride transfer from alkoxide to carbonyl. Dynamic ¹³C n.m.r. measurements gave a barrier of 13.7 (4 °C) kcal mol^–1 for the rearrangement. A much slower competing process leading to the hemiacetal (5) was also found. The X-ray crystal structure of (4; R =p-nitrobenzoyl) has been determined and the ketonic carbonyl shows some pyramidalization.