Metal carbonyl derivatives, oxidative coupling

The oxidative coupling of other organometallic derivatives of alkynes has been reported. For example, when metal carbonyl derivatives 30, formed by mixing... 

The main use of CF3SO3H in synthetic inorganic chemistry reported to date has been in preparation of binary compounds which are themselves triflates or of complexes derived from those triflates. HSO3F has been used similarly in the generation of fluorosulfates and of fluorosulfato-complexes but it has also been the medium of choice, particularly when coupled with the oxidant S206F2, in the generation and characterisation of many homopolyatomic cations and transition metal carbonyl cations, as will be shown in Sec. 11.3.4. 

Finally, Nikishin and coworkers have reported that the mediated oxidations of doubly activated methylene compounds can be used to synthesize cyclopropane derivatives (Scheme 17) [30]. Reactions using dimethyl malonate, ethyl cyanoacetate, and malononitrile were studied. Metal halides were used as mediators. When the activated methylene compound was oxidized in the absence of a carbonyl compound, three of the substrate molecules were coupled together to form the hexasubstituted product. Interestingly, when the ethyl cyanoacetate substrate was used the product was formed in a stereoselective fashion (18b). In an analogous reaction, oxidation of the activated methylene compounds in the presence of ketones and aldehydes led to the formation of cyclopropane products that had incorporated the ketone or aldehyde (20). In the case of 19a, the reactions typically led to a mixture of stereoisomers. 

Hypervalent iodine reagents have successfully been employed in the oxidative functionalization of enolizable carbonyl compounds over the years [6]. This methodology has allowed the construction of diverse C-C bonds in the context of heterocychc synthesis and has enriched the otherwise rare repertoire of such chemistry. Zhao, Du, and coworkers [37] have recendy realized a metal-free PIFA-mediated synthesis of 3-hydroxy-2-oxindoles 34 and spirooxindoles 35 starting from anilide derivatives 33 (Scheme 8 (1)). These processes showcase an oxidative cross coupling between an aromatic carbon and a pendant aliphatic carbon, followed by further oxidative hydroxylation or spirocycUzation. Later, the authors extended the same concept to achieve C(sp )-C(sp ) bond formation, where anilide derivatives possessing terminal enol functionality underwent PIDA-... 

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