Of aza analogues

The main reaction of this type has been the reductive cyclization of nitropyridine derivatives carrying an o-amino ester or o-aminocarbonyl substituent. These cyclize in situ via the o-diamino derivative to give pyridopyrazines of known constitution, either for establishment of structure of products obtained in the ambiguous Isay synthesis (see Section 2.15.15.6.1), or in the synthesis of aza analogues of biologically active molecules. 

Much effort has been devoted to the study of the electronic spectra of aza analogues of pyridine (pyridazine, pyrimidine, pyrazine, sym. (l,3,5-)triazine, and sym. (l,2,4,5-)tetrazine) as well as of derivatives of all these compounds. Most of these absorption spectra are similar to those of the parent compounds, except for a band corresponding to the n -> it transition which appears in the long-wavelength... 

The long-wavelength absorption bands exhibited by solutions of methiodides of aza analogues of benzenoid hydrocarbons have been attributed to the presence of charge-transfer complexes.01 There is a correlation between the excitation energies of the bands and the calculated electron affinity of the cations, in agreement with the delocalized rather than the localized model of the excited state in the charge-transfer complex.91... 

The stilbene-to-dihydrophenanthrene photocyclization and the application of this reaction to nitrogen-containing systems has been reviewed in detail. Cyclization of aza-analogues of 9-styrylphenanthrene has also been reported. The related photochemical dehydrocyclization of anilides of heterocyclic car-... 

The aromaticity of aza-analogues of benzene is high and not differentiated. This conclusion is qualitatively in line with resonance energies computed for reactions with proton transfer." " ... 

From the results of the httempted syntheses of aza-analogues of penicillins and cephalosporins, it is clear that the real breakthrough is still ahead in this particular Held. 

Huskic, M., D. Vanderzande, and J. Gelan. 1999. Synthesis of aza-analogues of polyjisothia-naphthene). Synth Met 99 143. 

Scheme 8.64 Synthesis of aza analogues of podophyiiotoxin (249a) and etoposide (249b).

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