Nucleophilic arylation

Although a C—CN bond is normally strong, one or two cyano groups in TCNE can be replaced easily, about as easily as the one in an acyl cyanide. The replacing group can be hydroxyl, alkoxyl, amino, or a nucleophilic aryl group. Thus hydrolysis of TCNE under neutral or mildly acidic conditions leads to tricyanoethenol [27062-39-17, a strong acid isolated only in the form of salts (18). 

The principal mechanisms for the nucleophilic arylation by aromatic halides... 

Hayashi et al. and Miyaura et al. have reported that far less nucleophilic aryl- and alkenyl-boronic acids can react with a variety of enones in the presence of a BINAP-rhodium catalyst to give adducts with high enantiopurity in general (Scheme 8D.5) [13], The one pot procedure, involving the hydroboration of alkynes as the first step (R = alkenyl), was achieved in the presence of amines without affecting the enantioselectivity [13]. 

Meisenheimer complex (Section 16.7) an intermediate formed in the nucleophilic aryl substitution reaction of a base with a nitro-substituted aromatic ring. 

Both the addition step and the elimination step can afTect the overall rate of a nucleophilic aryl substitution reaction, but the first step is generally rate-limiting. Thus, any factor that makes the eaihonyl group more easily attacked by a nucleophile favura the reacdon. 

The conversion of trifluoromethylphenyl halide 4 is almost quantitative (90-100 %), in heterogeneous (Pd/C), as well as in homogeneous conditions [(Ph3)4Pd, bipyPdCl2, (Ph3P)2PdCl2] (Scheme 2). However, the product of the nucleophilic arylation is formed only in very low yield, in both palladium(O) and palladium(II) catalysis. On the other hand, whatever the complex used, the formation of the reduction product, the trifluoromethylbenzene, is important, even with apparently a moderate yield (which can be explained by a partial loss of trifluoromethylbenzene, a highly volatile product Any other aromatic product apart 6 and 7 cannot be detected in the reaction mixture). 

Readily available nucleophilic aryl Grignard compounds can be coupled with aryl halide electrophiles to give unsymmetrical biaryls in the presence of Ni, Co, V, Ti, Cu, Cr, Fe, Pd and T1 salts [34] (Scheme 41). 

Nucleophiles other than OH also give stereospecific additions at alkenes. The acetylacetonate ion adds to co-ordinated cis- or trans-C J z in [Pd(CsH5)-(PPh3)(CHD=-CHD)]+ to give [Pd(C5H5)(PPh3) CHDCHDCH(COMe)2 ] by fra 5-addition, and the overall c/j-diamination of alkenes has been achieved by rraAZ5-aminopalladation of alkenes followed by oxidative amination in which the amine displaces the oxidized palladium by an 5 n2 displacement so that there is inversion at the Pd-bound carbon atom. Other carbon-centred nucleophiles (aryl, alkyl, or methoxycarbonyl) had previously been shown to add cis to alkenes, presumably by prior co-ordination at the metal. 

An additional nucleophilic arylation accounts for the final TeArg product ... 

In a significant recent development, Masahito Ochiai and coworkers synthesized aryl-A -bromanes from BrFj and a nucleophilic aryl donor such as an arylsilane or arylstannane ... 

Rhodium has been successfully used in a range of Suzuki-Miyaura type reactions. Satoh and Miura have reported the Suzuki-Miyaura-type cross-coupling of arylboron compounds with aryl halides in the presence of a rhodium-based catalyst system to produce the corresponding biaryls (Scheme 13.21). They also found, unexpectedly, that when employing benzonitrile as substrate under similar reaction conditions a multiple arylation is observed, in which nucleophilic arylation on the cyano group and subsequent ortho arylation via C-H bond cleavage is involved. 

The chiral induction for the nitrostyrene Michael addition can be explained using the similar model (Figure 2.12). The nucleophilic aryl group coordinated to the Pd nitrostyrene is ds to the oxazoline. The... 

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