Triazenes cyclization

In the case of a vinyl azide substituted with a keto group, triazene cyclization occurs with the carbonyl group of the azide and not with that of the ylide (Scheme 111).381... 

A related triazole synthesis utilizes phosphorous ylids, such as 264. The initially formed triazenes cyclize with elimination of triphenylphosphine oxide. The reaction proceeded sluggishly with phenyl azide, but good results have been obtained with acyl or sulphonyl azides. Tosyl azide and 264 yielded 98% of the 1-tosyl-triazole 265. The tosyl group could be removed by solvolysis in boiling ethanol... 

Kimball. D.B. Herges. R. Haley. M.M. Two unusual, competitive mechanisms for (2-ethynylphenyl)triazene cyclization Pseudocoarctate versus pericyclic reactivity. 

The copper-free protocols for alkynylation of organyl halides have been used for some applications where copper traces are not welcome. The initial findings came independently from Cassar (submitted January 17, 1975) and Heck (submitted January 8, 1975). ° For example, the alkynylation of haloaryltriazenes proceeds in the absence of copper-catalysts very smoothly (Scheme 5-124). Upon treatment with acids, these alkynyl triazenes cyclize to the corresponding cinnolines. °° ... 

To this end, the diazoimidazole carboxamide compound 32 was transformed first by methylamine to the methyl-triazene derivative 39, which was reacted with 11 (". -phosgene to give the desired product 40 <2002JME5448>. In another approach, 32 was directly cyclized to the bicyclic product by using 1 C-labeled methyl isocyanate. This route allowed the synthesis of both the C-2-labeled 40 and the (7-methyl-labeled samples 41 <1997JLR371, 2002JME5448> (Scheme 13). 

Tetrazoles from cyclization of tetrazenes, triazenes, and formazans... 

There are two general ring syntheses available for the preparation of 3-substituted l,2,3-benzotriazin-4(3//)-ones, namely, (i) diazotization of anthranilamide and its derivatives and (ii) cyclization of 1-alkyl- or 1-aryl-3-(o-carbalkoxy)triazenes, and both reactions have been studied in considerable detail. 3-Substituted l,2,3-benzotriazin-4(3//)-ones have also been obtained by alkylation and acylation of l,2,3-benzotriazin-4-one these last reactions are discussed separately (see Section II, C, 3). 

Halocinnolines can be prepared by treatment of polystyrene-bound (2-alkynyl-phenyl)triazenes with hydrogen chloride or hydrogen bromide (Entry 6, Table 15.27). This reaction involves the initial release of 2-alkynylphenyldiazonium salts into solution, which then cyclize to the halocinnolines. The corresponding 4-hydroxycinnolines are obtained as by-products in variable amounts. Hydrogen fluoride or hydrogen iodide do not lead to the formation of cinnolines [324]. 

Based on the postulate that 5-hydroxytriazolines can exist in equilibrium with the open-chain triazene compounds in solution (Scheme 66),259,261-264 one can envisage the cyclization of an appropriately substituted triazene to a triazoline. Thus the cyclization of a ketotriazene to a 5-hydroxytriazoline has been demonstrated (Scheme 105).258... 

When the azide is strongly electron withdrawing (R = formate, benzoyl,304 or substituted vinyl381), the betaine (44) does not cyclize to a triazoline it gives the triazene (45) or adds another molecule of the ylide to give 47. In solution,... 

Substituted 1,2,3-triazole 1-oxide 448 can be prepared by N-oxidation of 1-substituted 1,2,3-triazoles 457, by N-alkylation of 1-hydroxy-1,2,3-triazoles 443, by cyclization of triazene 1-oxides 460, or by rearrangement of 2-substituted 1,2,3-triazole 1-oxides 445 (R=PMB). Finally, base-mediated ring opening of pyrimidinediones 463 offers a route to 464. 

Aryl-l-(a-cyanoethyl)-triazene 1-oxides 460 upon treatment at room temperature for 0.5h with catalytic or equimolar amounts of KOH in methanol solution cyclize to give 3-aryl-4-amino-5-methyl-l,2,3-triazole 1-oxides 461. The triazenes are synthesized by reaction of 4-nitroben-zenediazonium tetrafluoroborate with N-cyanomethylhydroxyamine 459 (1992BAU1895) (Scheme 133). 

According to Butler, acyclic systems other than imidoyl azides that may be cyclized to tetrazoles include substituted tetrazenes, some triazenes, and formazanes <1984CHEC(4)791, 1996CHEC-II(4)621 Examples of these reactions and of the corresponding products 6, 10, and 525-528 are shown in Scheme 75 <1996CHEC-II(4)621>. 

May and Moody (52) have reported a full account of their Diels-Alder cycloaddition route to ellipticine (1) and isoellipticine (27) (Scheme 10). Conversion of indole (50) to 3-indole-2-propionic acid (56) with lactic acid was followed by a Plieninger cyclization to the pyranoindole 57. Reaction of 57 with 3,4-pyridyne (59), as generated from triazene 58, afforded equal amounts of ellipticine (1) and isoellipticine (27). Although the overall yield of 1 from indole is only 3%, the sequence involves only three steps. 

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