Aryl diazonium salts, triazoles, and

Grimshaw, J., Photochemistry of Aryl Diazonium Salts, Triazoles and Tetrazoles. In Horspool, W. M., Lenci, F. (eds), CRC Handbook of Organic Photochemistry and Photobiology, 2nd edn, CRC Press LLC, Boca Raton, FL, 2004, Chapter 43, pp. 1 17. 

Photochemistry of Aryl Diazonium Salts, Triazoles and Tetrazoles... 

Daidone and co-workers cyclized the diazonium salt derived from N-pyrazolylbenzamide 173 to obtain, in addition to other products, a small amount of pyrazolodiazocine, 174 (R = Ph) (80JHC1409). Rahman condensed 3-chloro-4-aryl-1,2,4-triazoles with N-methylanthranilic acid to afford triazoles 175 (R = H, Me R = Me). Conversion of this compound to the acid chloride, followed by cyclization with aluminum chloride,... 

The nitrosamine (121) and especially diazonium salts (122) prepared from it, as well as their alkyl and aryl derivatives, are important synthetic intermediates (b-76MI4i200, p. 325). For conditions that decide between nitrosamine function or diazotization see (73jcS(P1)13S7). At room temperature or in concentrated hydrochloric acid nitrosamines derived from triazoles are unstable, and their decomposition products include chlorotriazoles (63LA(665)144) 5-nitrosamino-3-phenyl-l,2,4-triazole affords the 5-bromo compound with hydrobromic acid at 0 °C and reacts violently with hydroiodic acid (05lA(343)i). Thermal arylation with triazole nitrosamines is possible (73jcs(pi)i357). 

Two pathways for the preparation of 1,4-dihydropyridazine derivatives were envisaged. According to the first, dimethyl 3-oxopentane-l,5-dioate (dimethyl acetone-1,3-dicarboxylate) (1) was treated in ethanol and sodium acetate at 0 °C with acidic aqueous diazonium salts, prepared from aromatic or heteroaromatic amines, to give hydrazones 69 in 35-94% yields. They were next treated with DMFDMA in dichloromethane at room temperature to form the (dimethylamino) methylidene derivatives 70 as intermediates, which immediately cyclized into dimethyl 1 -(hetero)aryl-4-oxo-l, 4-dihydropyridazine-3,5-dicarboxy-lates 71 in 72-94% yields, except for 71 (R=lH-l,2,4-triazol-3-yl), which was obtained in 35% yield (08ZN(63b)407) (Scheme 23). 

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