Abstract
Some pyridinium 1-[[(2-substituted ethy)thio]thiocarbonyl]aminides (4a-h) were prepared in moderate yields by the reactions of N-unsubstituted pyridinium aminides (2a-e) with carbon disulfide and ethyl acrylate (3a) or acrylonitrile (3b). The S-alkylations of these aminides 4a-h with bromoacetonitrile (5a) or ethyl bromoacetate (5b) at room temperature and the subsequent treatment of the resulting pyridinium salts with 1, 8-diazabicyclo[5.4.0]undec-7-ene (DBU) and then with chloranil at 0°C gave the corresponding 2-[(2-substituted ethyl)thio]pyrazolo[1, 5-a]pyridine derivatives (6a-p) in 40-75% yields. The β-eliminations of the 2-substituents in these pyrazolo[1, 5-a]pyridines 6a-p with potassium tert-butoxide in N, N-dimethylfomamide (DMF) proceeded smoothly to provide the title compounds, pyrazolo[1, 5-a]pyridine-2-thiols (7a-j), in good yields along with the release of 3a, b.
