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RING‐CHAIN TAUTOMERISM OF SUBSTITUTED HYDRAZONES. XI. SYNTHESIS OF 5,6‐DIHYDRO‐4H‐1,3,4‐OXADIAZINES

As we have shown in a number of papers of this series, 8-hydroxyalkylhydrazones are capable of equilibrium isomerization to perhydro-l,3,4-oxadiazines. The structures of the latter were confirmed unambiguously by spectral data (IR and PMR spectroscopy); however, chemical evidence for their presence in an equilibrium mixture has not yet been presented. Since tautomeric perhydro-l,3,4-oxadiazines contain a trisubstituted hydrazine fragment, it might have been expected that when no more than one substituent is present in the 2 position, they would be capable of undergoing oxidation in the same way as the similarly constructed hydrazines [2] to give compounds with a C=N bond -5,6-dihydro-4H-l,3,4-oxadiazines. Biologically active compounds have been found among representatives of this class of heterocycles (for example, see [3, 4]); however, the methods used to prepare them are not always sufficiently universal.