Phenanthridines from biphenyls

Isocyanides, which are isoelectronic with carbon monoxide, can undergo insertion reactions to provide Af-containing heterocycles. In 2013, Yu and coworkers [46] developed a photoredox catalytic, somophilic isocyanide insertion (HAS) yielding 6-alkylated phenanthridine derivatives from biphenyl isocyanide and electron-deficient bromides (Eq. (13.14)). Interestingly, when ethyl bromoflu-oroacetate or ethyl bromodifluoroacetate were used as the substrate [47], a subsequent decarboxylation efficiently produced mono- and difluoromethylated phenanthridine derivatives (Eq. (13.15)). 

Methods of synthesis of the phenanthridine system reported up to 1950 have been surveyed in an article by Walls.7 Since the later5 of the two reviews mentioned above did not include synthetic work and the earlier article4 dealt largely with the ring closure of 2-acylamino-biphenyls, an attempt has been made here to cover the synthetic literature from 1950 while largely restricting the discussion of properties to material not dealt with by Eisch and Gilman.5... 

Phenanthridines are obtained from 2,2 -disubstituted biphenyls in which the substituents react intramolecularly to form the heterocyclic ring. The oldest examples of syntheses of this type involve Hofmann65 and Curtius66- 67 reactions on biphenic acid, and have been explained... 

The phenanthridine can be obtained from the reduction and dehydration of phenan-thridone, which is easily prepared from the cyclization of (9-biphenyl isocyanante with AICI3. In addition, the coupling between nitrile and biphenyl carbocation generated from ortho-disLZomum biphenyl salt is also a good method for phenanthridine (i.e., the Ritter Reaction). ... 

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