title: Transannular 1,5-hydride shift in 5-hydroxycyclooctanone: an experimental and theoretical investigation.
abstract: 1H NMR measurements have shown that eight out of twelve methylene hydrogen atoms of 5-hydroxycyclooctanone (1HK) are exchanged for deuterium atoms under acidic and basic conditions. For the reaction in 7.9 M DCl/D2O, an activation energy Ea = 19.2 +/- 0.4 kcal mol(-1) is found. In order to explain these findings, a degenerate transannular 1,5-hydride shift is essential, and this reaction has been analyzed by quantum chemical calculations. Hydride transfer takes place via a tight transition state with a six-membered ring. The activation barrier is lowest in the presence of base. The molecular conformation of the eight-membered ring in the transition state resembles that of the starting structure. It is unlikely that solvent molecules such as water participate in the formation of the transition state.
authors.affiliation: Institut für Organische Chemie, Universität Duisburg-Essen, 45117 Essen, Germany. paul.rademacher@uni-duisburg-essen.de
authors.forename: Paul
authors.initials: P
authors.lastname: Rademacher
authors.forename: Parveen Choudhary
authors.initials: PC
authors.lastname: Mohr