Target-oriented synthesis of functionalized pyrazolo-fused medium-sized N,S-heterocycles via Friedel–Crafts ring closure approach

Efficient and concise synthetic protocol to benzo- and pyrazolo-fused medium-sized N,S-heterocycles (e.g,. thiazocinones, thiazoninones, thiazecinones, thiecinones, and thioninones) is developed. The process involves the AlCl3/MeNO2, TfOH or polyphosphoric acid mediated cyclization of pyrazole-based carboxylic acids or esters into tricyclic ketones under mild conditions. The designed protocol offers easy access to biologically and pharmaceutically promising pyrazoles in good yields. The structure elucidation of all new compounds without stereochemical assignments has been carried out by spectral and elemental analysis.