Homo-coupling, alkenyl halide

Nickel-bpy and nickel-pyridine catalytic systems have been applied to numerous electroreductive reactions,202 such as synthesis of ketones by heterocoupling of acyl and benzyl halides,210,213 addition of aryl bromides to activated alkenes,212,214 synthesis of conjugated dienes, unsaturated esters, ketones, and nitriles by homo- and cross-coupling involving alkenyl halides,215 reductive polymerization of aromatic and heteroaromatic dibromides,216-221 or cleavage of the C-0 bond in allyl ethers.222... 

The relatively vigorous reaction conditions required to effect vinyl substitution by heteroaryl halides under the influence of Pd-catalysis may lead to homo-coupling. The dominating reaction path in attempted alkenyl-ations of 4-iodopyrimidines was the formation of 4,4 -bipyrimidines (19) (Scheme 4 Section II.A.2). In reactions of 4-iodopyrimidines with a Pd-catalyst at 160°C, near-quantitative yields of the 4,4 -bipyrimidine were obtained (79CPB193). Also, in the reaction of 2-iodo-4-methylquinoline with Pd(OAc)2 as added catalyst, a major reaction path led to 4,4 -dimethyl-2,2 -biquinoline (Scheme 2 Section II.A.2.) (82CPB3647). 

These transition elements are Fe, Co, Ni, Pd, Cu and Ag. These metal catalysts have respective characteristics. For example, the representative catalytic actions are as follows silver is for alkyl-alkyl homo-coupling, copper is for cross-coupling, nickel and iron are for cross-coupling containing unsaturated halides such alkenyl and aryl halides [56]. These basic reaction examples are shown in eqs. (4.28)-(4.32) [55,56]. Kumada el al. synthesized many compounds as ligands which have... 

Negishi and his co-workers have described a new synthetic route to 1,5-dienes (or 1,5-enynes) which is particularly suitable for the construction of head-to-tail coupled isoprene units. The key step involves a regio- and stereo-selective palladium-catalysed cross-coupling of homoallylic (or homopropargylic) organozinc compounds with alkenyl halides (e.g. Scheme 95) homo-coupling... 

Homo-coupling involving alkenyl halides has been performed efficiently using an electro-assisted nickel-complex catalysis [23], This coupling reaction can even work with simple aliphatic substrates to give the corresponding dimeric products [21,24],... 

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