Direct access to 1,4-benzothiazine 4,4-dioxides and 4-oxides via a domino reaction

The domino reactions of 2-fluoro benzensulfonyl acetonitrile and alpha-chloro oximes in the presence of Cs2CO3 in aprotic high boiling point solvents have been achieved to provide isoxazole-fused 4H-1,4-benzothiazine-4,4-dioxides via an unprecedented transition metal-free one-pot addition/cyclization process. The tunable synthesis of either isoxozolo-1,4-benzothiazin-4-oxides or their precursor 5-aminoisoxazoles can be controlled depending on the solvent selection. The observed products were characterized by means of (IR, 1H, C-13 NMR and HRMS) and physical methods. (C) 2017 Elsevier Ltd. All rights reserved.