Titanocene dichloride epoxides

Though the usual product of epoxide reductions is the alcohol (10-85), epoxides are reduced all the way to the alkane by titanocene dichloride and Et3SiH-BH3. ... 

Therefore, we derided to initiate a program directed towards the development of a tita-nocene-catalyzed epoxide opening [3c]. Since titanocene dichloride is formed in the stoichiometric reaction after the protic quench, the challenge to be met is the regeneration of the redox-active species in situ, the fundamental requirement for a catalytic reaction. This underlying problem is depicted in Scheme 12.12. 

The problem of diastereoselectivity in additions to cyclic radicals arising from the opening of bi- or tricyclic epoxides, e. g. cycloheptene oxide or norbornene oxide, has been addressed only recently [32], In the former case, reasonable selectivities can be obtained with titanocene dichloride (trans cis = 76 24), but excellent selectivities are observed with bis(tert-butyl)titanocene dichloride (transxis = 94 6), as shown in Scheme 12.17. 

Alcohols from epoxides. Free radical reaction using titanocene dichloride as an... 

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... 

Bai, D. Nian, G. Wang, G. Wang, Z. Titanocene Dichloride/KI An Efficient Catalytic System for Synthesis of Cyclic Carbonates from Epoxides and CO. Appl Or-ganometal. Chem. 2013, 27, 184-187. 

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