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17.2.1.2.2.2 Method 2: From Annulated Pyrazol-N-amines

DOI: 10.1055/sos-SD-017-00353

Döpp, H.; Döpp, D.Science of Synthesis, (200417293.

The amination of indazoles with hydroxylamine-O-sulfonic acid affords indazol-1- and 2-amines, which are are oxidized to the same 1,2,3-benzotriazines 298 (Scheme 85).[‌141‌] This procedure provides the most efficient syntheses of 1,2,3-benzotriazine and its 4-methyl and 4-phenyl derivatives. However, the preparation of the highly reactive parent 1,2,3-benzotriazine must be carried out by the slow addition of the 3-unsubstituted indazol-1- or 2-amine to lead(IV) acetate in a dry solvent, in the presence of calcium oxide, to minimize the attack of nucleophiles formed during the oxidation upon the triazine ring. With 4- or 5-nitroindazol-1- or 2-amines, no 1,2,3-benzotriazines are obtained.[‌141‌] 15N-Labeling experiments show that in the oxidation of 3-methoxyindazol-1-amine with lead(IV) acetate the N-amino group forms the central nitrogen (N2) of the 4-methoxy-1,2,3-benzotriazine.[‌60‌] 4-Methyl-[‌165‌] and 4-benzyl-1,2,3-benzotriazines[‌450‌,‌521‌] are prepared by the oxidation of the corresponding indazol-2-amines in the presence of freshly activated calcium oxide.

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