Lithium Wurtz-type coupling

Wurtz-type couplings have also been observed upon sonication of lithium in the presence of both organic halides (yields 36-73%) (218) and chlorosilanes or chlorostannanes (yields 42-94%) [Eq. (42)] (219). 

Many other metals, in addition to magnesium, lithium and copper, promote Wurtz-type couplings. In most cases cross-couplings are not possible and the methods are only of value in producing homo-coupled dimers. Reagents which do permit cross-coupling reactions are normally very limited in either the type of halide used for preparation of the metal derivative, or the halide to be cross-coupled, or both. 

Metallocarbenes have been implicated in the iridium-catalysed isomerization of branched hydrocarbons, such as that of 2-methylpentane (1) to 3-methylpentane (3). Studies with C-labelled (1) support a mechanism which proceeds via (2) as intermediate. Polymer-bound triphenylphosphine-lithium diorganocuprates may offer advantages in the Wurtz-type coupling of alkyl halides, in that work-up is easier and the product is not contaminated with residual tertiary phosphine. However, yields in general are comparable with those from the corresponding homogeneous reagents. ... 

These results are corroborated by Boudjouk and Han s study of the equivalent lithium-mediated reaction [94, 95] with both trialkyltin and silicon coupounds. Nevertheless, the cross-coupling reaction occurs faster than Wurtz-type coupling in this case, and products were uncontaminated by... 

Several new syntheses of vinylsilanes have been described. Tris(trimethyl-silyl)aluminium undergoes 5yn-addition to alkynes alternatively the same -isomers can be obtained by photochemical isomerisation of Z-1-alkenyl-silanes. Other methods described involve treatment of the lithium salts of hydrazones with trimethylsilyl chloride, Wurtz-type coupling with vinyl bromides, and reaction of acetylenes with a silyl-copper reagent followed by an electrophile. Using the hydrazone method, a route has been devised for 1,2-carbonyl transposition within ketones (Scheme 17). ... 

Wurtz-Type Coupling of Chlorosilanes with Alkali Metals 464 Wurtz-type coupling of monochlorosilane with lithium 465 Wurtz-type coupling of dichlorosilane with lithium 465 Wurtz-type coupling of two kinds of chlorosilanes with lithium 466... 

Synthesis of Cyclotetrasilane-Fused Octasilacuneane 487 Wurtz-type coupling of 1,1-di-tert-butyl-1,2-dichloro-2,2-diphenyldisilane with lithium 487... 

Wurtz-type coupling of monochlorosilane with lithium (18)... 

Wurtz-type coupling of dichlorosilane with lithium (19)... 

Wurtz-type coupling of two kinds of chlorosilanes with lithium (20,21)... 

Wurtz-tYpe coupling of 2,2-di-tert-butyl-1-chloro-1,1-diphenyldisilane with lithium (34)... 

Osborne, A. G., Glass, K. J., Staley, M. L. Ultrasound-promoted coupling of heteroaryl halides in the presence of lithium wire. Novel formation of isomeric bipyridines in a Wurtz-type reaction. Tetrahedron Lett. 1989, 30, 3567-3568. 

An alternative to produce H-H arranged PIB is the coupling via the Wurtz-Fittig reaction. This is the coupling of alkyl halides by the treatment with metallic sodium or other metals such as lithium and zinc. However, this type of reaction results in substantially branched polymers with a comparatively low molecular weight (19). 

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