ABSTRACT
Tetrahydrotetrazoles are five-membered-ring heterocycles containing four contiguous saturated nitrogen atoms. Very few examples of such compounds have been reported in the literature. Our previous attempt at the synthesis of a member of this class of compound suggested that the N-N bonds may be more labile than expected. This finding raised the question as to whether the structures of any of the previously reported tetrahydrotetrazoles had been properly assigned. We have reproduced the synthesis of a reported tetrahydrotetrazole, namely 1,2-di-tert-butyl 3-phenyl-1H,2H,3H,10bH-[1,2,3,4]tetrazolo[5,1-a]isoquinoline-1,2-dicarboxylate, C25H30N4O4, and have now confidently confirmed its structure via X-ray crystallography. However, while sufficiently stable in the crystal phase, we discovered that it remains very labile in solution (having a half-life of only 15â min at 20â °C in CDCl3). A tentative reaction pathway for its dissociation based on 1H NMR spectral evidence is provided.
ABSTRACT
Tetrahydrotetrazoles are a little-explored class of five-membered heterocycles with four contiguous singly-bonded N atoms. Recent work in our labs has demonstrated that urazole radicals are amenable to N-N bond formation via radical combination to form such a chain of four N atoms. Previously described 1,1-bis-urazole compounds appeared to be convenient precursors to the target tetrazoles via their oxidation to intermediate urazole diradicals, which upon N-N bond formation would complete the tetrazole framework. While oxidation proceeded smoothly, the novel 10-membered octaaza heterocycle 7,7,18,18-tetraacetyl-4,10,15,21-tetraphenyl-1,2,4,6,8,10,12,13,15,17,19,21-dodecaazapentacyclo[17.3.0.02,6.08,12.013,17]docosan-3,5,9,11,14,16,20,22-octone, C42H32N12O12, was obtained (36% yield) instead of the expected tetrazole product, as confirmed by X-ray crystallography. Calculations at the (U)B3LYP/6-311G(d,p) level of theory suggest that the desired tetrazoles have weak N-N bonds connecting the two urazole units.