fused pyrazole synthesis by n-n bond formation: The pyrazolo [5,1-b] benzothiazole system

Treatment of (benzothiazol-2-yl)acetone oxime 1 with excess trifluoroacetic anhydride (TFAA) at room temperature produces 2-methyl-3-trifluoroacetylpyrazoIo[5, l-Z\u3e ]benzothiazole 11 in 71-92 % yield depending on the purity of the oxime. Compound 11 is reduced by NaBHi to the corresponding alcohol 12 and hydrolyzed to the corresponding carboxylic acid 13 under alkaline conditions. Other reagents commonly used to promote Beckmann rearrangement of oximes cause only decomposition of 1 to intractable materials. © 2011 by Walter de Gruyter GmbH & Co. All rights reserved