Catalyst-free regioselective synthesis of fused 11H-benzo[5,6][1,4]thiazino [3,4-a]isoindol-11-ones and benzo[b]indeno[1,2-e][1,4]thiazin-11 (10aH)-ones targeting bacterial and fungal microbes

A nucleophilic addition/substitution followed by cyclization reaction of 2-bromo-2-(2/3-substitutedphenyl)-1H- indene-1,3(2H)-diones/2,5-dibromo-2-(2/3/4-substitutedphenyl)-1H-indene-1,3(2H)-diones 4a-g and 5substituted-2-aminothiophenols 7a-e under catalyst -free conditions in presence of eco-friendly solvent was carried out for the regioselective synthesis of 11H-benzo[5,6][1,4]thiazino[3,4-a]isoindol-11-ones 8a-l and benzo[b]indeno[1,2-e][1,4]thiazin-11(10aH)-ones 9a-g in excellent yields. Structural elucidation of the synthesized compounds is accomplished by physical and spectral analysis data (FTIR, NMR (1H & 13C), 2D NMR, and HRMS) and single -crystal X-ray crystallography. All the titled derivatives were screened for their in vitro antimicrobial activity through the serial dilution technique. Amongst them, 8a against S. aureus, 8d against E. coli, 9f against C. albicans and 8i against A. niger were found to be most active in relation to standard reference Ciprofloxacin and Fluconazole, respectively. The investigational findings suggest that the synthesized compounds have the potential to serve as promising leads for the subsequent development of highly effective antimicrobial candidates.