Azides, imidoyl synthesis

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 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). 

In 1991, Duncia et al. reported on the synthesis of 1,5-disubstituted tetrazoles from secondary amides and azidotrimethylsilane under the conditions of the Mitsunobu reaction <1996CHEC-II(4)621>. The Mitsunobu protocol was successfully applied to the conversion of AT(cyanoethyl)amide into tetrazole 510. The tetrazole ring in this event forms by the cyclization of an imidoyl azide (not shown in the scheme) whose precursor is the phosphonium imidate 509 (Scheme 67) <2000JME488>. 

Disubstituted tetrazoles 751 are most often prepared by the cyclization of imidoyl azides 750. The traditional method for generation of imidoyl azides 750 consists of treating the appropriate imidoyl chlorides 749 with HN3 or NaN3 (Scheme 323) numerous other methods for the synthesis of imidoyl azides and their cyclization to tetrazoles have also been reported . 

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