Stereoselective aldol condensation of 3,4-dihydro-3-oxo-2H-1,4-benzothiazines: X-ray determination of the aldol stereostructure

3,4-Dihydro-2-methyl-3-oxo-2 H -1,4-benzothiazines ( 1 ) give erythro -stereoselective aldol condensation. The stereochemistry was determined by single crystal X-ray diffraction. The aldol condensation takes place under kinetic control. The reasons for the observed stereoselectivity are discussed.