One-pot mild and efficient synthesis of [1,3]thiazino[3,2-a]indol-4-ones and their anti-proliferative activityElectronic supplementary information (ESI) available: Copies of NMR (1H & 13C) spectra of synthesized compounds 10, 17, and 19-34. See DOI: 10.1039/c9ob00500e

A base mediated environmentally benign one-pot efficient methodology has been developed for the synthesis of [1,3]thiazino[3,2- a ]indol-4-ones using indoline-2-thiones and propiolate esters in aqueous medium. The conjugate addition of thiones first results in ethyl (3-(indol-2-yl)thio)acrylates in situ , which subsequently undergoes intramolecular cyclization to produce indole-fused thiazin-4-ones in good to excellent yields. The cytotoxic screening of the synthesized compounds using MTT assay revealed the anti-proliferative nature of these frameworks against triple negative breast cancer cell lines with the highest activity emanating from 4 H -[1,3]thiazino[3,2- a ]indol-4-one and 8-methyl-2-propyl-4 H -[1,3]thiazino[3,2- a ]indol-4-one compounds. One-pot synthesis of [1,3]thiazino[3,2- a ]indol-4-one frameworks is developed in aqueous medium and the anti-proliferative activity of the synthesized compounds is evaluated against two triple negative breast cancer cell lines.