ISSN:
0170-2041
Keywords:
Nitrilimines
;
[1,2,4]Triazolopyridines
;
1,3-Dipolar cycloadditions
;
Chemistry
;
Organic Chemistry
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
Notes:
Reactions of 1,3-Dipoles with Heterocycles, 8. - Synthesis of 1,8a-Dihydro[1,2,4]triazolo[4,3-a]pyridines and BenzologuesThe C,N double bond of pyridine, quinoline and isoquinoline as heterodipolarophile react with diarylnitrilimines 2, generated in situ by dehydrohalogenation of N-phenylbenzhydrazonoyl chlorides 1, in a cycloaddition with complete regioselectivity. A facile route to hitherto unreported 1,3-diaryl-1,8a-dihydro[1,2,4]triazolo[4,3-a]pyridines 3, 1,3-diaryl-3,3a-dihydro[1,2,4]triazolo[4,3-a]quinolines 4, and 1,3-diaryl-1,10b-dihydro[1,2,4]triazolo[3,4-a]isoquinolines 5 has been developed. In a similar way, cycloadditions are carried out with C-ethoxy-carbonyl- and C-acetyl-N-phenylnitrilimines. The ring cleavage of 3 in acidic medium yields the corresponding [(arylhydrazono)methyl]pyridinium chlorides 7. The conversion of the open-chain products back to 3 has been carried out in pyridine containing triethylamine. Anodic oxidation of 3-5 in aprotic medium affords the [1,2,4]triazolohetarenium perchlorates 9-11. The yields in such reactions are either similar or better than with chemical oxidants. The thermally initiated cycloreversion of 3 and 5 is discussed, judging from the facts that the thermolysis afford 2:1 cycloadducts.
Additional Material:
7 Tab.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/jlac.1992199201147
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