Phenanthridine halogenation

Halogenations of quinoline, isoquinoline, acridine, and phenanthridine will be discussed here. Reaction usually occurs in a homocyclic fused ring rather than in the 7r-deficient pyridine moiety, especially in acidic media. Relatively mild conditions suffice, but under more vigorous regimes radical involvement can result in heteroring halogenation. Substituents are able to modify reactivity and regiochemistry. 

Although, predictably, C-6 of the phenanthridine ring is susceptible to nucleophilic attack, until recently only qualitative reactivity data were available. New examples of both direct substitutions (hydride ion extrusion) and nucleophilic replacements, notably of halogen atoms, have been reported since the last review.6... 

Aminative replacement in compounds other than those bearing halogen atoms are uncommon, but 6-aminophenanthridine is easily prepared by heating 6-phenoxyphenanthridine with urea296 and 6-anilinophenanthridine has been obtained by the action of aniline on the 6-phenoxy compound.268 The formation of 6-anilinophenanthridine from phenanthridine iV-oxide and phenyl isocyanate probably proceeds via an initial 1,3-dipolar addition, followed by nucleophilic substitution and decarboxylation (Scheme 4).309... 

Electroreduction of l-(4-fluorophenyl)-5-(2-halogenophenyl)tetrazoles (89), when the halogen substituent is Cl, Br or I, leads to cleavage of the carbon-halogen bond to give a phenyl radical (equation 52). Competition then follows between intramolecular radical substitution giving 7-fluorotetrazolo[l,5-f]phenanthridine (90). Further reduction of the... 

Charge-transfer (C-T) bands have been located in the spectra of solutions of phenanthridine in 1,2-dimethoxyethane containing bromine solutions containing up to a 2 1 mole ratio of halogen to base were examined, but the structure of the species involved is not clear. Phenanthridine satisfies the conditions necessary for both n and tt- donation and n donation is apparently involved in the charge-transfer interaction with iodine. The equilibrium constant for this reaction has been determined spectrophotometrically, but the claimed correlation (for a series of A -heteroaromatic bases) between values (in 50% ethanol) and these C-T equilibrium constants appears to be an unsatisfactory one and in any case lacks theoretical justification, since it is doubtful whether dissociation constants provide, in general, an accurate measure of w-ionization potentials. In particular, the excellent correlation in the case of phenanthridine is probably fortuitous, since the authors report that w-halogen interactions are markedly sensitive to steric factors which are almost... 

Conformational equilibria of amines and aminoacids have been studied in low-temperature matrix under UV or IR irradiation." Amine-imine tautomerism and formation of a radical was observed from adenine. New studies on the aniline excited states has evidenced the role of Rydberg states. A re-examination of the Oilman reaction has demonstrated that this is an electron transfer process. The photo-cyclization of halogenated (iodine is by far to be preferred) N-ben lani-lines to phenanthridine has been studied with particular attention at the preparative value and the tolerance of alko)q, dio)q methylene and halogen substituents, to which it was found to be quite tolerant. ... 

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