Synthesis and antimicrobial investigation of benzo[b] thiophene heterocycles

3-Chloro benzothiophene-2-carbonylchloride 1 was converted to ethyl 3-chloro-1-benzothiophene-2-carboxylate 2. The compound 1 and 2 were then converted into 3-chlorobenzothiophene-2-carboxyhydrazide 3. The compound 3 on stirring with substituted acetophenones at reflux temp produced various 3-chloro-N-[1-phenylethylidene]-1-benzothiophene 2-carbohydrazides 4a-c, which underwent smooth cyclization in presence of DMF and POCl3 to give various 1-[(3-chloro-1-benzothien-2-yl) carbonyl]-5-(phenyl)-1H-pyrazole-3-carboxaldehydes 5a-c. Refluxing 3 with various benzoic acids in presence of POCl3 produced various 2-(3-chloro-1-benzothien-2-yl)-5-phenyl-1,3,4-oxadiazoles 6a-g. The structures of newly synthesized compounds were elucidated on the basis of elemental analysis, IR, H-1 NMR, C-13 NMR and mass spectral data and have been screened for antimicrobial activities.