Azides imidoyl

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... 

Part A Tetrazoles (233) via imidoyl azides (232) from precursor (231) (Scheme 36) ... 

The addition of azide ion to nitriles remains the main synthetic route to 5-substituted tetrazoles. The distinction between this approach and the imidoyl azide route (Section 4.17.9.1.1) is blurred... 

The most likely explanation is as outlined in Scheme 3. Following a well-known stereoelectronic effect , wherein addition of nucleophiles to triple bonds places the developing new lone pair trans to the incoming nucleophile, a fast addition of azide ion to the diazonium ion would give the Z-diazoazide (21) which cannot form a pentazole. This is analogous to the stable imidoyl azide of tetrazole chemistry. Rapid loss of N2 from this produces the first N2 evolution. 

Azido-tetrazole tautomerism is also observed for partially hydrogenated azoles and even for monocyclic tetrazoles. The latter (258, X = NR ) may exist in equilibrium with an acyclic imidoyl azide... 

Tetrazoles from imidoyl azides and related substrates 371... 

Another example is the photoreaction of tctrazolo[ 1,5- ]pyrimidinc 14 with aromatic compounds in the presence of trifluoroacetic acid (TFA) to give 2-(2-, 3-, and 4-substituted anilino)pyrimidines together with 2-aminopyridine and biphenyl or diarylmethanes. Here the key intermediate is also the 2-pyrimidylnitrenium ion originating from the photochemical decomposition of an imidoyl azide. This ion, depending on the reaction conditions, is present either in the singlet or triplet state and this governs the composition of the products (Scheme 11) <1998JP0478>. 

Cyclization of imidoyl azides 150 into 1,5-disubstituted tetrazoles 5 (Equation 10) is widely used both in the laboratory and on an industrial scale. Imidoyl azides form in situ in the course of various multistage processes, and sometimes in the multicomponent reactions (MCRs). The problems related to generation of imidoyl azides and also to electrocyclization of these intermediates into 1-mono- and 1,5-disubstituted tetrazoles are of crucial importance for the tetrazole chemistry. These problems are traditionally treated at length in basic reviews <1984CHEC(4)791, 1996CHEC-II(5)621>. The traditional methods for the synthesis and cyclization of imidoyl azides into tetrazoles were broadly employed and further refined in more recent works <1997MI1375>. Several new methods based on this approach have also been developed. 

The traditional method for generation of imidoyl azides 150 consists of treating the appropriate imidoyl chlorides 492 with HN3 or NaN3 (Scheme 59). 

The replacement of the halogen in the imidoyl chloride by an azide group with subsequent cyclization of the intermediate imidoyl azide 150 into 1,5-disubstituted tetrazole 5 can be performed under PTC conditions < 1996S 1428>. This procedure avoids contact with HN3 solutions and also removes the problem of the low solubility of HN3 salts in organic solvents. It is important that in this procedure the losses due to hydrolysis of imidoyl chlorides... 

The problems of the formation of 5-substituted-l-acylated tetrazoles from the corresponding imidoyl azides have been considered <2000JOC7284>. Dabbagh and Lwowski studied the isomerization of 5-substituted-l-acylated tetrazoles into 2-acylated derivatives. 

The substitution of the halogen in the cyclic imidoyl chloride, like 2-chloropyridine, with azide leads to the intermediate formation of an imidoyl azide 497 that further undergoes cyclization into a fused tetrazole 14 (Scheme 61) <2004SOS(13)861>. 

Both cyclic imidoyl chlorides and cyclic imidoyl bromides have been used as starting materials for generating and further cyclization of intermediate imidoyl azides into the corresponding fused tetrazoloazines. Thus, treating 4-methyl-3,5,6-tribromopyridazine with NaN3 in a mixed solvent (THF-DMSO) at room temperature led to 3,5-diazido-4-methyl[l,5- ]tetrazolopyridazine 502 (45% yield) <20040BC1782>. 

One of the classical methods for the generation of imidoyl azides as precursors to mono- and disubstituted tetrazoles is based on reactions of amidrazoles with sodium nitrite. This procedure developed by Kaufmann et al. in the middle of thel960s <2004SOS(13)861> has found an extension and advancement in recent studies. By this method, 5-hydrazino-3-methyl-l-phenyl-l//-pyrazolo[4,3-< ][l,2,4]triazine 503 through a cyclic imidoyl azide 504 was converted into 5-phcnyl-l //-pyra/olo[4,3-<,]tetrazolo[4,5- tria/inc 505 (Scheme 64) <2005JCX151>. 

The procedure developed by Elmorsy has been adjusted to the synthesis of 1,5-disubstituted tetrazoles from secondary amides <2000CHE878, 2004RJ0443, 2004RJ01528, 2004RJ01532>. By analogy with the mechanism in Scheme 65, the formation of 1,5-disubstituted tetrazoles 5 from the secondary amides may be presented as going through an intermediate imidoyl azides 150 (Scheme 66). 

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