Nucleophilic Substitution of Aromatic Chlorides

Although chlorobenzene is rather inactive in usual reactions, its activity is enhanced by complex formation, and two products are formed by the reaction of stabilized carbanions on the complexed chlorobenzene 207, depending on the conditions [44], The anion of a-methy l propionitrile reacts at the meta position at —78 °C, and the mete-substituted product 208 is obtained by oxidation with I2. However, equilibration (rearrangement) of the carbanion occurs at 25 °C, because the attack of the carbanion is reversible, and the substitution product 209 of the chlorine is obtained. The fluorobenene 210, coordinated by Cr(CO)3, is very reactive. Reaction of y-butyrolactone to the o-lithiated fluorobenzene 211 gives rise to the alkoxide 212, which displaces the fluoride intramolecularly to give the cyclic ether 213 [52], In other words, the complex 211 can be regarded as the 1,2-dipolar synthon 214. However, Cr(CO)3-complexed aromatic bromide and iodide can not be used for the nucleophilic substitution. 

Although as described in Section 3.1.1.1, oxidative addition of chlorobenzene to Pd(0) is difficult, chlorobenzene 207, coordinated by Cr(CO)3, undergoes the facile oxidative addition to Pd(0). Then alkene insertion (Heck reaction) [53] and coupling 

The coordination of Cr(CO)3 does not activate aryl chloride sufficiently for Williamson diaryl ether formation to occur. Smooth formation of aryl ether 222 proceeds by reacting the easily prepared arene-Ru complex 220 of the highly functionalized aryl chloride with phenol 219. Decomplexation of 221 by irradiation gives 222, and the product is used for the synthesis of the BCF rings of ristocetin A [57], 

---