Synthesis, spectroscopic characterization, and in vitro antimicrobial activity of fused pyrazolo[4′,3′:4,5]thieno[3,2-d]pyrimidine

4-Amino-3-methyl-1-phenyl-1H-thieno[2,3-c]pyrazole-5-carboxamide (1), which had been previously synthesized according to literature, was used for synthesizing pyrazolothieno-pyrimidine (2) in the presence of triethyl orthoformate and acetic acid. Chlorination of the latter compound upon reflux with phosphorus oxychloride afforded the chloropyrazolothienopyrimidine (3), which underwent heterocyclization reaction with sodium azide to produce the tetrazolo-pyrazolothienopyrimidine (6). The chloropyrimidine (3) reacted with hydrazine hydrate to give the hydrazinopyrimidine derivative (4), which in turn underwent intramolecular condensation reactions with various 1,3-dicarbonyl compounds, namely ethyl acetoacetate, ethyl benzoylacetate, ethyl cyanoacetate, acetylacetone, diethyl malonate, and ethyl (ethoxymethylene) cyanoacetate, yielding new pyrazolyl pyrazolothienopyrimidine ring systems. Also triazolopyrazolothieno-pyrimidines and benzylidene Schiff's base compounds were obtained as a result of the reactions with carbon disulfide in pyridine and benzaldehyde, respectively. The chemical structures of the newly synthesized compounds were elucidated using elemental and spectroscopic analyses (FT-IR, ¹H-NMR, ¹³C-NMR, and mass spectroscopy). Some of the synthesized compounds possess high antibacterial and antifungal activities.