Formation of an aryl-carbon bond by a nucleophilic substitution is limited to activated substituted aromatics and strong nucleophiles (SN2Ar path) or to good electron donors (SRN1 process). Aryl SN1 reactions forming new Ar-C bonds have now emerged as a convenient alternative and can be easily accomplished by reaction of phenyl cations (in their triplet state) with various nucleophiles (olefins, (hetero)arenes). These cations, thermally almost unaccessible, can be generated by photocleavage both from electron-rich phenyl chlorides, fluorides, mesylates, triflates and phosphates and from benzenediazonium salts. Some of these Ar-C bond forming reactions can be considered photochemical alternatives to metal catalyzed cross coupling reactions.
Keywords: photochemical behaviour, nucleophiles, triplet phenyl cations, fragment heterolitically, aryl-oxygen bond
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