Metal groups electrophile cross-coupling

Transition metal catalysed cross-coupling reactions of organometalUc reagents containing Zn, Si, Mg, Sn or B with organic electrophiles in the presence of group 8-10 metals, notably Ni and Pd, are routinely the method of choice, both in academia and industry, for the preparation of C-0, C-S, C-H, C-N and C-C bonds [1]. 

To make the transformation even more useful, different carbon electrophiles should be connected sequentially in a stepwise manner. For this purpose, a transition-metal-catalyzed cross-coupling reaction opened the way. As shown in Scheme 22, cinnamyl chloride is treated with bis(iodozincio)methane (3) in the presence of palladium catalyst with various phosphine ligands. Phosphine ligands, having an electron-withdrawing group, such as tris[3,5-bis(trifluoromethyl)phenyl]phosphine and tris(2-furanyl)phosphine, show excellent results47. 

Cross-coupling reactions of ArCOAr. Reaction of Yb(0) with diaryl ketones changes the reactivity of the carbonyl group from electrophilic to nucleophilic. Thus in the presence of this lanthanoid metal, diaryl ketones couple with other ketones, nitriles, and epoxides to give pinacols, a-hydroxy ketones, and 1,3-diols, respectively, via the intermediate a. 

Attempts to bring about cross coupling of different allylic halides invariably led to mixtures suggesting exchange of the allylic units before coupling. This problem in synthesis is better solved by cross coupling of an allylic halide and an allylic derivative of a main group metal. However, electrophilic alkylation of )) -allyl-NiBr dimers by simple alkyl halides is successfiil (equations 130 and 131). 

A cross-coupling reaction can be partially defined by equation (1), where Nu is a carbon (or heteroatom) nucleophile see Nucleophile), R X is an electrophilic substrate, X is a halogen or other appropriate leaving group, and M is a metal or metalloid. At first glance, it would appear that simple nucleophihc substitution reactions should fall under this definition. However, what makes the cross-coupling chemistry special is its ability to perform transformations that cannot be accomplished with simple substitution chemistry. 

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