Epoxide openings electron transfer

Enantiomerically pure bis-Gp derivatives with chiral Gp ligands have been used with success in the catalytic enantioselective opening of meso-epoxides via electron transfer (see Section 4.05.8). The structural features are of relevance for the understanding of activity and selectivity of these complexes in diastereoselective reactions and for the design of novel catalysts. A comparison of the structure of three of these bis-Gp Ti derivatives (Scheme 481) in the solid state and in solution determined by X-ray crystallography and NMR methods indicated that the structures in the crystal and in solution are the same, and that applications of these complexes in catalysis can de discussed on the basis of crystallographic data.1114 In a similar study, the 1-methylcyclohexyl-Cp, 1-butyl-1-methylbutyl-Cp, and cyclohexyl-Cp titanocene dichlorides (Scheme 481) have been prepared and their molecular structures compared. The use of these three compounds in radical addition reactions has been studied.1115... 

Stoichiometric Opening of Epoxides by Electron Transfer 435 Titanocene-Catalyzed Epoxide Opening 439 Titanocene-Catalyzed Reductive Epoxide Opening to Alcohols 439... 

Opening of Epoxides via Electron Transfer from Low-Valent Metal Complexes... 

Reductive ring opening of epoxides in radical reactions in presence of titanocenes as electron transfer catalysts 98SL801. 

Reductive C-C Bond Formation after Epoxide Opening via Electron Transfer... 

Epoxide Opening by Single Electron Transfer Birch Conditions and Radical Anions... 

Since the seminal contributions by Nugent and RajanBabu the field of reductive C - C bond formation after epoxide opening via electron transfer has developed at a rapid pace. Novel catalytic methodology, enantio- and stereoselective synthesis and numerous applications in the preparation of biologically active substances and natural products have evolved. In brief, a large repertoire of useful and original reactions is available. These reactions are waiting to be applied in a complex context ... 

The proposed mechanism includes a reductive epoxide opening, trapping of the intermediate radical by a second equivalent of the chromium(II) reagent, and subsequent (3-elimination of a chromium oxide species to yield the alkene. The highly potent electron-transfer reagent samarium diiodide has also been used for deoxygenations, as shown in Scheme 12.3 [8]. 

Scheme 12.22. Concept for enantioselective meso epoxide opening by electron transfer.

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