Portal de Periódicos da CAPES

Fluorinated Alcohols Enable Olefin Epoxidation by H 2 O 2 : Template Catalysis

2003; American Chemical Society; Volume: 68; Issue: 7 Linguagem: Inglês

10.1021/jo034087t

1520-6904

Sam P. de Visser, José Kaneti, Ronny Neumann, Sason Shaik,

Organic Chemistry Cycloaddition Reactions

Experimental observations show that direct olefin epoxidation by H(2)O(2), which is extremely sluggish otherwise, occurs in fluorinated alcohol (R(f)OH) solutions under mild conditions requiring no additional catalysts. Theoretical calculations of ethene and propene epoxidation by H(2)O(2) in the gas phase and in the presence of methanol and of two fluorinated alcohols, presented in this paper, show that the fluoro alcohol itself acts as a catalyst for the reaction by providing a template that stabilizes specifically the transition state (TS) of the reaction. Thus, much like an enzyme, the fluoro alcohol provides a complementary charge template that leads to the reduction of the barrier by 5-8 kcal mol(-)(1). Additionally, the fluoro alcohol template keeps the departing OH and hydroxyalkenyl moieties in close proximity and, by polarizing them, facilitates the hydrogen migration from the latter to form water and the epoxide product. The reduced activation energy and structural confinement of the TS over the fluoro alcohol template render the epoxidation reaction observable under mild synthetic conditions.