Coupling, reactions, isocyanide complexes

Reductive coupling reactions, titanium complexes Carbon monoxide insertion, titanium complexes Acetylene insertion, titanium complexes Carbon dioxide insertion, titanium complexes Isocyanide insertion, titanium complexes Carbonylatlon, titanium alkyls... 

Early findings by Suzuki and co-workers [109] showed that the palladium-catalyzed iminocarbonylative cross-coupling reaction between 9-alkyl-9-BBN derivatives, t-butylisocyanide, and arylhalides gives access to alkyl aryl ketones 132 after hydrolysis of the corresponding ketimine intermediates 131. Presumably, the concentration of free isocyanide is kept to a minimum by its coordination with the borane. Formation of an iminoacylpalladium(II) halide 130 by insertion of isocyanide to the newly formed arylpalladium complex followed by a transmetallation step afford the ketimine intermediates 131 (Scheme 8.52). 

Another type of unique coupling reaction was reported by Jones and coworkers [87]. The low-valent ruthenium phosphine complex RuH2(dmpe)2 catalyzed intramolecular insertion of isocyanide into the benzyl C-H bond of 2,6-xy-lylisonitrile under thermal conditions (Eq. 59). Their finding provided a new route to the synthesis of indoles. 

Among MCRs, the Ugi reaction is a powerful three- or four-component coupling reaction with isocyanide as one of the reactants to construct multiple bonds in complex molecules. Applications of Ugi reactions in total synthesis are rather rare. One of the most advanced examples is the use in the total synthesis of ecteinascidin 743 48 by Fukuyama and coworkers, as depicted in Scheme 6.5 [22]. 

The unusual complex tetrakis(tert-butyl isocyanide)di-/i-chloro-di palladium(I) chlorobenzene has been prepared by Otsuka et al The preparation utilized a novel coupling reaction between bis(rert-butyl isocyanide)palladium(O) and cis-bis(rert-butyl isocyanide)dichloro-palladium(II) in cold chlorobenzene. Although the reported yield for the final step of this synthesis was good (70%), the preparation of the precursor bis(tert butyl isocyanide)palladium(O) from (i7 -allylX> cyclopenta-dienyl)palladium is time-consuming and is accomplished in only S0% yield. We have developed a greatly improved preparation of the title complex (chlorobenzene-free), which utilizes readily available Pd(0) and Pd(II) compounds as starting materials, namely bis(dibenzylideneacetone)palladium(0), [Pd(dba)2], and trans-bis(benzonitrile)dichloropalladium(II). In addition, since full details of the preparation of Pd(dba)2 have not been reported, we give a complete account of the preparation here.H... 

Another type of complex in which Tc C bonds predominate is the seven-coordinate complex [Tc(CNR)gX] + (398) (R = variety of organic groups X = C1, Br). The compounds are easily prepared in good yield by reaction of the Tc complex [Tc(CNR)6] " with Br2 or CI2 in acetonitrile. Attempts to introduce a bipy ligand as well led to dealkylation of the isocyanide to give the seven-coordinate complex [Tc(CNR)5(CN)X]+ (399). Reductive coupling of the coordinated isocyanides was attempted, but the reduction of Tc to Tc was the only reaction." ... 

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