Phenazines shifts

The NMR spectrum of quinoxaline has been measured in CDCI3 and the chemical shift values are as shown in (16) (69JA6381). Curiously, C NMR spectra of phenazine and its derivatives have been recorded in benzene solution and the chemical shift values quoted relative to benzene however, for consistency the values in (17) are quoted relative to TMS. 

Phenazines and their derivatives are known to be biologically significant molecules, particularly in the field of photodynamic therapy. A recent example of the preparation of red-shifted azine dyes potentially useful for photodynamic therapy was reported <1999JHC25>. 

The H NMR spectra of quinoxaline and its monosubstituted derivatives have been reported <67JCS(B)l24l>, and those of di- and trisubstituted quinoxalines have also been measured <68JCS(C)1274>. The spectra of a number of phenazine derivatives have been reported <66CPB419>. The H NMR solvent shifts in acetone, carbon tetrachloride and cyclohexane have been measured for the parent pyrazine, quinoxaline and phenazine <86BCJ1650>. For the last two compounds the NMR spectra of both for the neutral and the acidic species are reported <91BCJ2668>. 

Becker et al. discovered the formation of alkyl-shifted phenazines 138 versus the anticipated 9-membered triazaorthocyclophane 139 when treating halotriaryl derivatives 140 with potassium diisopropylamide (Scheme 68) (13JOC3532). The reaction passes through an aryne intermediate, but the exact mechanism is still unclear. 

Reaction of chlorotriaryl derivatives with potassium diisopropylamide have been reported to give alkyl-shifted phenazine derivatives by either intramolecular nucleophilic attack on an aryne intermediate leading to a zwitterionic intermediate and alkyl transfer via a 5-endo-tet process or via a Smiles rearrangement (Scheme 193). ... 

---