Oxidation organocopper compounds

Since isolable organocopper) 11) compounds do not apparently exist, it is rather surprising that oxidation of the cuprate CdI+[(CF3)2Cu ] (prepared in situ) with thiuram disulfide affords (CF3)2Cu "S2CNEt2 (see Eqn. 1 in Scheme 1.6), the first and so far only example of an organocopper compound with the copper atom in the trivalent oxidation state. The structure of this compound was unambiguously proven by an X-ray crystal structure determination (see Fig. 1.2) [37]. 

While a large number of studies have been reported for conjugate addition and Sn2 alkylation reactions, the mechanisms of many important organocopper-promoted reactions have not been discussed. These include substitution on sp carbons, acylation with acyl halides [168], additions to carbonyl compounds, oxidative couplings [169], nucleophilic opening of electrophilic cyclopropanes [170], and the Kocienski reaction [171]. The chemistry of organocopper(II) species has rarely been studied experimentally [172-174], nor theoretically, save for some trapping experiments on the reaction of alkyl radicals with Cu(I) species in aqueous solution [175]. 

Although organocopper compounds are established for various organosyn-thetic transformations and simple Cu salts are widely apphed in organic syntheses [1,2], conventional applications of Cu in oxidation or oxygenation catalysis have largely been limited to a co-catalytic role. The most promi-... 

Copper oxides, salts, and organocopper compounds find extensive use in industry and commerce. Some of the more important compounds are summarized ... 

The thermal decomposition of aryl- and vinylcopper compounds is an alternative method of obtaining dimeric products from organocopper compounds. Both methods have been used extensively by Kauffmann and co-workers 153-164). Thermal decomposition of organocopper compounds of the type ZN=C(R)—CHRCu affords suitable precursors for a variety of 1,4-diketones. Thermal decomposition is not applicable to all organocopper compounds (see Section III,B,3). Various oxidations and dimerizations are listed in Table V. 

The facile iodination of organocopper compounds (79) is a useful reaction for the characterization of intermediate copper compounds which are formed by addition or insertion reactions 61, 223, 294, 304). Bromine has also been used 223, 294), but the yields may be low ( 15%) compared with iodolysis, because of bromine s ability to function as an oxidant 223). 

Since then, experiments have been reported which indicate that (1) organocopper compounds will couple with aryl halides (2) arylcopper compounds can be oxidatively and thermally dimerized (3) arylcopper compounds are intermediates in the Ullmann reaction (4) organocopper compounds are intermediates in copper-catalyzed decarboxylations and (5) copper-promoted coupling reactions are not restricted to aromatic halides. The copper(I) oxide-promoted coupling reactions, however, have still to yield firm evidence of a copper intermediate. 

Ebert, G. W., RIeke, R. D. Preparation of aryl, alkynyl, and vinyl organocopper compounds by the oxidative addition of zerovalent copper to carbon-halogen bonds. J. Org. Chem. 1988, 53,4482-4488. 

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