Acridine salt intermediate

Photoaddition of nucleophiles to heterocycles is often observed.1 Irradiation of acridine and its quaternary salt in ethanol produced 9,9 -bisacridan (151) as the major product besides a little acridan and 9a-hydroxyethylacridan.207 The reaction mechanism is most likely a hydrogen abstraction from the alcohol by the excited molecule, followed by competitive radical combination to yield 151. Irradiation of an aqueous solution of alloxan monohydrate and its derivatives produces an alloxantin-type dimer (152 R = H, Me, Et) by combination (at the 5-position) of a radical intermediate.208... 

The copper-catalyzed cascade annulation of nitriles, diaryliodonium salts, and alkynes was recently described by Chen and coworkers. N-Arylation of the nitrile resulted in an V-arylnitrilium intermediate, which was trapped by the aUcyne and subsequently underwent electrophilic annulation to yield substituted quinolines (Scheme 6d) [107]. The concept was later varied to reach polycyclic quinolines, quinazolines, quinazolinimine, and acridine scaffolds [108—110], A similar cascade reaction delivered iminobenzoxazines by N-aiylation of ort/io-cyanoanilides followed by C-O cyclization [111], and the reactimi of nitriles with [1,1-biphenyl]-derived iodonium salts resulted in phenanthiidines [112]. The corresponding C-arylation cascade reactions are discussed in Sect. 4.3. 

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