An unexpected valence bond isomerization to the heteroaromatic ring system: [1,2,3]triazolo[4,5-d]pyridazine

Abstract

The arylazo substituted salt 2 when treated with a base underwent a valence bond isomerization to yield a derivative of the heteroaromatic ring system, [1,2,3]triazolo[4,5-d]pyridazine (4). Scheme 1 (a) Ar = 4-ClC 6 H 4 -, (b) Ar = 4-NO 2 C 6 H 4 -, (c) Ar = 4-CH 3 OC 6 H 4 -.Fig. 1 A molecular diagram 9 of 4b with the numbering of atoms. Anisotropic displacement parameters represent 50% probabilities.

Condensed 1,2,3-triazoles (review)

“…Treatment of the arylazopyridazo[1,2,4]triazine tetrafluoroborate 43 with strong bases leads to the formation of the corresponding base, which undergoes a Bolton-Katritzky rearrangement to [1,2,3]triazolo-[4,5-d]pyridazine 44 [35]. …”

Cyclizations to new azolopyridazines and related ring systems

“…We have found that dipolar cyclizations, Michael additions and some other interesting transformations due to the zwitterionic character can be realized [5,6]. As a continuation of these studies we have investigated the reactivity of 7 toward aryldiazonium salts [7]. The rapid appearance of a deep red color of the reaction mixture indicated that most possibly an azo coupling took place, and structure analysis of the red crystals (8) isolated from the reaction mixture provided satisfactory support for this assumption.…”