摘要:
A simple and efficient regiospecific synthesis of 6-trifluoromethyl-1H-pyrazolo[3,4-b]pyridines has been achieved in excellent yields via a three-component reaction between 2-hydrazinobenzothiazoles, alpha-cyanoacetophenones and trifiuoromethyl-beta-diketones under solvent-free conditions. This method was found to be more convenient than the classical stepwise solvent mediated process, which furnished not only the opposite regioisomer i.e. 4-trifluoromethyl-1H-pyrazolo[3,4-b]pyridines (50-60%) but also an undesired amide, 5-acetylamino-1-(benzothiazol-2'-yl)-3-phenyl-1H-pyrazole as a side product. The structure of the two regioisomers was established with certainty on the basis of rigorous analysis of H-1, C-13, F-19-NMR spectral data and (H-1-C-13) gs-HMQC, (H-1-C-13) gs-HMBC experiments. (C) 2012 Elsevier B.V. All rights reserved.