Synthesis, characterization and antimicrobial investigation of new piperidinyl tetrahydrothieno[2,3-c]isoquinolines

Herein, we describe the synthesis of novel piperidinyl thieno tetrahydroisoquinolines attached or fused to other new heterocycles. The diazotization of the previously synthesized pyrrolyl carbohydrazide 1 followed by several reactions with ethanol, aniline and heterocyclization after boiling in dry xylene under Curtius rearrangement conditions yielded the corresponding carbamate, phenyl urea and pyrazino derivatives 3–5. Furthermore, the condensation of 1 with various aromatic aldehydes and ethyl acetoacetate afforded the consistent Schiff's bases 6a-c and 7. The ring closure of the ethyl butanoate ester 7 furnished pyrazolyl compound 8 after heating in an ethanolic sodium ethoxide solution. Moreover, the nucleophilic addition of the carbohydrazide 1 to carbon disulfide in pyridine produced oxadiazolyl thione 9 which was reacted with ethyl chloroacetate to give ethyl sulfanyl acetate ester 10. The assignments of the chemical structures of these new heterocycles were confirmed by using elemental and spectral analysis. Alternatively, selected compounds were examined for antibacterial and antifungal screening. The results revealed highly promising influences against the nominated pathogenic strains.