ChemInform Abstract: Reactions of 1,3-Dipoles with Heterocycles. Part 8. Synthesis of 1,8a- Dihydro(1,2,4)triazolo(4,3-a)pyridines and Benzologues.
Abstract
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ChemInform Abstract
A facile route to hitherto unreported title compounds such as (III) ( 14 examples), (VIII) and (X) (4 examples each) is described based on the reaction of the C=N double bond of (I), (VII) and (IX) as heterodipolarophiles with diarylnitrilimines, which are generated in situ by dehydrodehalogenation of (II). This cycloaddition proceeds with complete regioselectivity and is in contrast to earlier reports in the literature. The ring cleavage of (IIIa) gives (IV), whose conversion back to (III) is carried out in Py containing NEt3. Anodic oxidation of the title compounds in aprotic medium yields the corresponding (1,2,4)triazolohetarenium perchlorates in yields which are similar or better than with chemical oxidants. The thermally initiated cycloreversion of (III) and (IX) is discussed.
