One-bond Couplings not Involving Hydrogen

The dynamics of bimolecular C-Li exchange in several allylic lithium compounds with ligands tethered at C2 has been investigated by Fraenkel et alF by the use of the Li-C couplings yielding the thermodynamic data of this process. 

The products of the reaction of ketones with lithium hexamethyldisilazide have been studied by Collum and co-workers by an extensive use of the Li and NMR spectroscopy Vun couplings have been found to be particularly useful. 

Both Jlic and Jun couplings have been observed by Sott et alP in the spectra of isotopically labelled mixed complexes formed by the lithium salt of acetonitrile (LiCH2CN) and the chiral lithium amides, Li-( S)-N-(2-methoxybenzyl)-l-amino-1 -phenyl-2-ethoxyethane and Li-(S)-N-isopropyl-2-amino-1 -pheny 1-3-methoxypropane, providing crucial information on their structures. 

A J7LiSn coupling of ca. 560 Hz observed by Fukawa et al. in the Li and ii7/u9sn NMR spectra of the tris(di-tert-butymethylsilyl)stannyllithium-benzene 

A clear correlation between Jbp and Vcp couplings has been observed by Schmidbaur and co-workers in a series of trivinylphosphineboranes (CH2 = CH)3PBX3 (X = H, Cl, Br, I) and interpreted in terms of the influence of the electronegativity of the substituent. 

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The formation of a C-C bond resulting from the coupling of two C-H bonds is a particularly attractive target, since the only formal by-product would be hydrogen, or water in an oxidative system. However, substantial hurdles impede the conception of a catalytic arene cross-coupling process that does not involve any substrate pre-activation at all. Aside from issues of reactivity and regioselectivity, the prevention of homo-coupling is a key factor for the development of this important class of reaction. The catalyst must be able to react with one arene in the first step of the catalytic cycle and then invert its selectivity in the second step to react exclusively with a different arene (Scheme 29). 

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