Mild and Efficient Deoxygenation of Epoxides with Bis(cyclopentadienyl)titanium(IV) Dichloride-Indium System

Abstract

The deoxygenation of epoxides to olefins is an important synthetic transformation in organic chemistry. Since the combination epoxidation/deoxygenation would provide a useful protection/deprotection sequence for the multiple bond, a variety of methods have been devised to accomplish the transformation. These include FeCl3/n-BuLi, 2 NaOH/ n-Bu4NBr, 3 Mo(CO)6, 4 SmI2, 5 Cp2TiCl2/Mg, 6 and dimethyl diazomalonate. However, many of these remain incompatible with other functional groups in the organic substrates and require expensive reagents and harsh reaction conditions. There still exist a need for the development of new efficient and readily available reagents for this conversion. The chemical reactivity of Cp2TiCl2/M system (M = Zn, Al, Mg, Sm) has been the subject of considerable interest and the reducing ability of these systems has been extensively studied. Because of the close resemblance of indium to magnesium and zinc in several respects, including first ionization potential, we considered that Cp2TiCl2/In system can be an efficient reagent for the deoxygenation of epoxides to olefins. Thus we have investigated the reactions of Cp2TiCl2/In system with various epoxides and found that epoxides can be rapidly deoxygenated to give the corresponding olefins in good to excellent yields (eq. 1). Herein we describe a new and efficient deoxygenation of a variety of epoxides to olefins with Cp2TiCl2/In system in THF under mild conditions. Due to the unique features of high