Transannular 1,5-hydride shift in 5-hydroxycyclooctanone: an experimental and theoretical investigation.
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.
Rademacher
Paul
P
Institut für Organische Chemie, Universität Duisburg-Essen, 45117 Essen, Germany. paul.rademacher@uni-duisburg-essen.de
Mohr
Parveen Choudhary
PC