Tetrazole Dimroth rearrangement

The imidoyl azide-tetrazole ring-chain isomerism of tetrazoles develops into a wide-ranging example of the Dimroth rearrangement in the thermal behavior of substituted 5-aminotetrazoles <84JHC627>. An example with 5-hydrazinotetrazoles is shown in Scheme 10 <88BSB543>. The reaction... 

An ab initio study of the Dimroth rearrangement of 5-amino-1,2,3,4-tetrazole (338) to 339 led to the conclusion that in the vapor phase the ratedetermining step was not ring-chain isomerism, but was either the Z-E isomerism around the C=N double bond or the 1,3-sigmatropic shift of the proton (82JHC943) (Scheme 104). 

Tetrazoles.—a-Azido-oximes, R C(N3)=NOH, cyclize to l-(acyloxy)tetrazoles (661) when treated with acid chlorides RCOCl. The action of hydrazoic acid on unsymmetrical carbodi-imides PhN=C=NR (R = alkyl) leads to l-phenyl-5-(alkylamino)tetrazoles (662) at 200 °C, these undergo a Dimroth rearrangement to yield the l-alkyl-5-anilino-isomers (663)/ ° (Diphenylmethyl)tetrazoles (664) are produced in the reaction of iV-aryl-diphenylketenimines Ph2C=C=NAr with hydrazoic acid/ Diethoxy disulphide, (EtO)2S2, dehydrogenates AW -dianil-inothiourea to dehydrodithizone (665). Diformazyl has been shown to be the betaine (666)/ ... 

Several classes are known. Dimroth-type rearrangements occur by ring opening and reclosure so that one ring atom changes places with an exocyclic atom. The rearrangement of 5-phenylaminothiatriazole to l-phenyl-5-mercaptotetrazole in basic solution is reversible (Scheme 74). As the anion, the tetrazole system is the more stable whereas as the neutral species, the thiatriazole is more stable... 

An interesting synthesis of these C-nucleosides utilized the easily accessible 5-(j3-D-ribofuranosyl)tetrazoles 235 as masked C-glycosyl-diazometh-ane. Reacting 235 with 2-chloro-3-nitropyridine gave a mixture of 1,2,4-triazolo[4,3-fl]pyridin-3-yl (236) and l,2,4-triazolo[l,5-a]pyridin-2-yl (237) C-nucleosides. The latter (237) resulted from thermally induced Dimroth-like rearrangement of the former (236) (86MI9) (Scheme 70). Compounds 236 and 237 possess considerable cytotoxic effect (86MI9). 

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