The preparatively important catalytic opening of epoxides to β-titanoxy radicals via single-electron transfer (SET) is described. These radicals can be reduced to alcohols or participate in C−C bond-forming reactions. A key step in the catalytic cycle is the conceptually novel protonation of titanium−oxygen and −carbon bonds. Our method combines the advantages of radical reactions, e.g., high functional
Dramatic rate acceleration in titanocene catalyzed epoxide openings: cofactors and Lewis acid cocatalysis
作者:Andreas Gansäuer、Harald Bluhm
DOI:10.1039/a805246h
日期:——
High synthetic efficiency concerning yield and catalytic turn-over in intermolecular C–C bond forming reactions of radicals derived from epoxides can be achieved by means of hydrogen bonding with cofactors or by Lewis acid cocatalysis.
A Direct Synthesis of γ-, δ-, and ε-Lactones Utilizing SmI<sub>2</sub>-induced Barbier-type Reaction in the Presence of Hexamethylphosphoric Triamide (HMPA)
By using an efficient reduction system of SmI2-THF-HMPA, the coupling reaction of β-, γ, or δ-bromoesters with carbonyl compounds was completed within a minute at room temperature affording γ-, δ-, or e-lactones, respectively, in good yields. Cp2ZrCl2 was also found to be effective for the coupling with ketones.