Halides, aryl, arylation coupling with enolate anions

Another reaction that cannot be an SN2, because of the impossibility of carrying it out on an aryl halide, is the displacement from the aryl bromide 7.187. The mechanism is an Sr jI reaction (see p. 147), involving an electron transfer from the enolate 7.186 to the halide 7.187. The radical anion 7.189 loses the bromide ion to give the aryl radical 7.190, and this couples with the radical 7.188 derived from the nucleophile to give the ketone 7.191.252 The m-mcthyl group shows that the reaction did not take place by way of a benzyne. 

A nickel-catalyzed ene cyclization (sec. 11.13) has been reported that uses Ni(cod)2- The reaction proceeds by initial formation of a ac-allylnickel complex, which facilitates the intramolecular ene reaction with an allylic amine unit. l jt-Allylnickel complexes can be used in coupling reactions with both aryl and alkyl halides. Enolate anions react with nickel(O) reagents to form a complex that subsequently couples to aryl iodides. Semmelhack s final step in the synthesis of cephalotaxinone (446) treated 445 with Ni(cod)2 to... 

Deprotonation. After iV,iV-diethyl-l-lithiovinylcarbamate, which is obtained by a deprotonation process (with r-BuLi as base), is converted into the organozinc reagent, it can be used to couple with aryl halides (e.g., bromides) and triflates in the presence of (dppf)PdClj to afford the enol carbamates of the acetophenones. The overall transformation can be considered an anionic equivalent of Friedel-Crafts acylation. ... 

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