Couphng reactions, transition metal catalyzed

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. 

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. 

As alkynyl halides are troublesome electrophilic partners in transition-metal-catalyzed cross-couphng reactions, variants involving alkynylmetals are often preferred to carry out C(sp)-C(sp ) and C(sp)-C(sp ) carbon-carbon bond formation. Among these variants, Pd-catalyzed alkynylation reactions using alkynylzincs are some of the most efficient and synthetically useful [167, 222). 

Metallocycles as intermediates in synthesis of heterocycles by transition metal-catalyzed couphng reactions under C—H bond activation 99AG(E)1698. 

The boryl groups installed on the aromatic polymers are useful synthetic intermediates for conversion to other polar functional groups. For example, they can be oxidized to give hydroxylated polymers and a variety of polar group-containing polymers via either direct functional group transformations or palladium-catalyzed Suzuki cross-coupHng reactions with appropriate phenyl bromides (Fig. 25). This transition metal-catalyzed polymer... 

A truly biomimetic route to alkaloids of the narciclasine type has not been published yet. Nevertheless, very interesting protocols for the coupling of the six-membered ring motifs have been employed in the preparation of these compounds. Transition metal-catalyzed couphng reactions play an important role in the preparation of Amaryllidaceae alkaloids, and Hudlicky s synthesis of narciclasine highlights this approach [171,172]. Keck utihzed radical reactions and... 

Lopez, S., Fernandez-Trillo, F., Midon, P., Castedo, L and Saa, C. (2006) Synthesis of marine polyacetylenes callyberynes A-C by transition-metal-catalyzed cross-couphng reactions to sp centers. J. Org. Chem., 71,2802-2810. 

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