Methylene groups copper catalysts

Various transition metals have been used in redox processes. For example, tandem sequences of cyclization have been initiated from malonate enolates by electron-transfer-induced oxidation with ferricenium ion Cp2pe+ (51) followed by cyclization and either radical or cationic termination (Scheme 41). ° Titanium, in the form of Cp2TiPh, has been used to initiate reductive radical cyclizations to give y- and 5-cyano esters in a 5- or 6-exo manner, respectively (Scheme 42). The Ti(III) reagent coordinates both to the C=0 and CN groups and cyclization proceeds irreversibly without formation of iminyl radical intermediates.The oxidation of benzylic and allylic alcohols in a two-phase system in the presence of r-butyl hydroperoxide, a copper catalyst, and a phase-transfer catalyst has been examined. The reactions were shown to proceed via a heterolytic mechanism however, the oxidations of related active methylene compounds (without the alcohol functionality) were determined to be free-radical processes. 

Copper Catalysts Direct oxidative functionalization of tertiary amines is of importance both enzymatically and synthetically. The combination of CuBr—TBHP has proved to be as an efficient system in the oxidative activation of sp3 C—H bonds adjacent to a nitrogen atom [10]. Various types of cross-dehydrogenative coupling (CDC) reactions have been developed, including compounds with activated methylene groups [11], indoles [12], and terminal alkynes (Scheme 11.2) [13]. Because 1,2,3,4-tetrahydroisoquinoline derivatives are important structure motifs of natural... 

Condensation Reactions.—Trost has reviewed the preparation and synthetic uses of cyclopropyldiphenylsulphonium ylides. The regioselectivity and chemospecificity of the cyclopentane and cyclopentenone annelation reactions have been examined. Whereas diphenylsulphonium methylide does not cyclopropanate simple, unactivated olefins such as tetramethylethylene, transfer of a methylene group from the ylide can be effected stereospecifically in the presence of a copper catalyst and this reaction may provide a model for biological cyclopropanations by the ylide derived from S-adenosyl-methionine. Attempts to catalyse a similar transfer to unactivated olefins using PdCl2 were not successful. ... 

---