Couphng reactions, transition metal

For example, the sensitive imidoyl chloride moiety at the C-3 position of the pyrazinone scaffold is known to vmdergo Stille reactions with a variety of tetraaryltin reagents, generating the corresponding 3-substituted pyrazi-nones (Scheme 10) [26]. Furthermore, the transition-metal-catalyzed stannyl-ation at the C-3 position is also documented in the hterature, in view of cross-couphng with a variety of alkyl and (hetero)aryl hahdes [26]. However, this strategy is completely restricted to the C-3 position, while the Cl atom of C-5 position was found to be inert under these conditions. 

Recent trend in the synthesis of olefinic pheromones is the use of transition metal-catalyzed cross couphng reaction for carbon-carbon bond formation. Scheme 8 summarizes a synthesis of the termite trail marker pheromone, (3Z,6Z)-3,6-dodecadien-l-ol (2) by Oehlschlager [19]. The key-step is the palladium-catalyzed cross-couphng of allyhc chloride A and alkenylalane B. 

This observation opens up a new possibility in the formation of C - O bonds for the already comphcated oxygenation reactions of organic substrates, i.e., the non-innocent behavior of the olefin in open-shell transition metal olefin complexes can allow a direct radical couphng of dioxygen with the coordinated olefin. 

Aliphatic iodides, and especially secondary and tertiary representatives, are subject to hydride ehmination and are not generally useful substrates in transition metal catalysed coupling reactions. The last reaction in Scheme 14 [31], for instance, cannot be executed using current transition metal-based technology. In contrast, vinyl and aryl iodides, which are superb partners in many classical metal-induced couphng reactions, are very poor substrates in the present radical process because of the high energy of vinyl and aryl radicals. The two methods thus nicely complement each other. 

Kahn BE, Rieke R (1988) Carbonyl couphng reactions using transition metals, lanthanides, and actinides. Chem Rev 88 733... 

Adjustable coordination properties Ionic liquids have the potential to be polar yet weaMy coordinating toward transition metal complexes they may enhance reaction rates involving cationic electrophilic intermediates When they contain coordinating anions (e.g., Cl ) they may stabilize anionic transition metal intermediates (e.g., Pd Heck couphng catalysis)... 

Polysilanes (or polysilylenes) are usually prepared by the Wurtz-type couphng reaction of dichlorodialkylsilanes or, alternatively, via a transition metal-catalyzed dehydrogenation of dialkylsilanes both approaches often exhibit difficulties in terms of controlling the molecular weight and chain-structure, however. Nonetheless, by using masked silylene monomers (l-phenyl-7,8-disilabicyclo[2.2.2]octa-2,5-dienes), a series of novel, well-defined linear poly(silylene)s (M /Mn 1.3) was successfully obtained via an anionic ROP (Scheme 5.11) [147-150]. 

Transition metal-catalyzed reductive acylation, coupHng, amination, and cycHzation reactions of oximes and their derivatives 13CJ066. Transition-metal-catalyzed synthesis of aromatic ketones via direct C—H bond activation 12S677. 

For recent reviews on the Mizoroki-Heck reaction, see (a) Alonso, F., Beletskaya, I.P. and Yus, M. (2005) Non-conventional methodologies for transition-metal catalysed carbon-carbon coupling a critical overview. Parti theHeckie ction.Tetrahedron,61,11771-835 (b) Erase, S. and de Meijere, A. (2004) Cross-couphng of organyl halides with alkenes the Heck reaction, in... 

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