Conditions of the Dieckmann condensation of alkyl 2-(N-methyl-N-(alkoxycarbonylmethyl)sulfamoyl)benzoates

Abstract

The Dieckmann condensation of alkyl 2-(N-methyl-N-(alkoxycarbonylmethyl)sulfamoyl)benzoates IIIa-IIIe with various bases affords alkyl 4-hydroxy-2-methyl-2 H -1,2-benzothiazine-3-carboxylate 1,1-dioxides IVa-IVe which are intermediates in the synthesis of antiinflammatory drug piroxicam. The yields of benzothiazines IVa-IVe depend mostly on the nature of a base, reaction temperature and solvent used for these condensations. Hitherto undescribed esters IIIb-IIIe were synthesized and their structures were confirmed by 1 H and 13 C NMR, and mass spectra.