1.2.3- Triazines cyclopropenyl azides

Cyclopropenyl azides (350), the obvious precursors to cyclopropenylnitrene and hence possibly azetes by ring expansion of the latter, give 1,2,3-triazines on heating or irradiation (78HC(33)5). 

Thermolytic rearrangement of 1,2,3-trisubstituted cyclopropenyl azides constitutes the only proven method at present for the preparation of monocyclic 1,2,3-triazines, and both the generality and validity of the procedure have been established. Thus, a substantial number of derivatives of the type 2, R = alkyl, aryl, have now been prepared, and X-ray crystallographic analysis has confirmed the structures of the products (see Section II, D, 2). Thermolysis of triarylcyclopropenyl... 

The rearrangement of cyclopropenyl azides (396) is used for the synthesis of monocyclic 1,2,3-triazines (397) (73JOC3149, 79CB1514). However, the most general method is the oxidation of N-aminopyrazoles (398) with lead tetraacetate or variety of other oxidants (92AHC(53)85). 

Three atom ring-expansion of cyclopropenyl azides and diazo-compounds provides a useful route to triazines and pyridazines respectively 278). 

In the reaction of the phosphanyl-substituted cyclopropenylium ion 12 with azide, an isomeric mixture of the covalent-bonded cyclopropenyl azides 13 and 14 was isolated, which was then thermally converted to the 1,2,3-triazine derivative 15. 

The second method for the synthesis of monocyclic aromatic 1,2,3-triazines 2 by ring enlargement is the rearrangement of cyclopropenyl azides i78-86"89-"7- 124 (cf. Houben-Weyl, Vol. E 17d, p2849), by heating them neat,78-89,117-118 in methanol,86 89 dimethylformamide,89 benzene,86119 toluene,86 xylene,88-120 or dichloromethane.87 121 The only limitation to this method seems to be the availability of the cyclopropenylium salts as starting materials for the cyclopropenyl azides. Cyclopropenyl azides may be generated in situ from a cyclopropenylium salt and sodium or potassium azide.86 89... 

Mass spectrometric studies of the 1,2,3-triazines formed have shown that, in all cases, the substituent with the highest electron-donating capacity is located in the 5-position of the formed 1,2,3-triazine, even when the starting cyclopropenyl azide is a mixture of two isomers. 

There are two general synthetic methods for 1,2,3-triazines which belong to this section. The first, reported in 1960 <60TL19>, is the thermal rearrangement of a cyclopropenyl azide (115) (Equation... 

Without additional reagents 1,2,3-Triazines from cyclopropenyl azides... 

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