The reaction of 3-substituted-4-hydroxyroxy-2H-1,2-be~othiazine 1,l-dioxides with aryl isocyanate under different equivalents of strong base NaH was studied. Seventeen of new derivatives were obtained whose structures were characterized by ' H NMR, IR, MS, elementary analysis and FeCls test.
Keywords
Benzothiazine dioxides, reaction, aryl isocyanate, synthesis 3-Substituted-4-hydroxy-2H-1,2-benzothiazine 1,l-dioxides ( l a -c ) , which were firstly reported by Abe and co-workers,' had several reactive sites and could react with many compounds to provide various derivatives the majority of which showed good biological activities. 2-5 In this paper we studied the reaction of this kind of compounds la-c with aryl isocyanates (Scheme l), the reports on which had not been found. Compounds la-c reacted with ArNCO in the presence of one equivalent of NaH to give main product 2a-h. If using two equivalents of NaH the reactive products were 3a-h (main) and 2a-h. Treating l a with 3 equivalents of NaH, the main product obtained was 4a(X=H).
The structures of compounds 2a-h, 3a-h and 4a were characterized by lH NMR, IR, MS, elementary analysis and FeC13 test.
Compounds l a -c included two functional groups: hydroxy group (OH) and amino group (NH). When la-c reacted with ArNCO under 1 eq. of NaH, since the acidity of the OH group is stronger than that of the NH group, the OH group firstly reacted with NaH to transform the intermediate anions A which reacted with ArNCO and then acidified to obtain the OH-addition products 2a-h. Their NMR spectra showed no peak of the OH group and a new singlet at SH 9.6-9.8 ppm (DMCO-c& as solvent) or 11.3-11.9 ppm (DMSO-& as solvent) for -CONHPh. Their IFt spectra and the negative FeC13 test also proved the disappearance of the OH group. When l a -c