Cycloheptabenzothiazines and Their Diazine Analogues. 1- Formation and Reactions of Cycloheptabenzothiazines

Article abstract of DOI:10.1246/bcsj.58.165

2-Chlorotropone reacted with o-aminobenzenethiol to give 2-(o-aminophenylthio)tropone, which readily cyclized in dilute methanolic HCl to afford the title benzothiazine(9).Although 9 was stable under basic conditions, its N-methyl cation reversibly afforded the ring-opened 2-tropone in alkali.Oxidation of 9 with hydrogen peroxide in methanol underwent a rearrangement reaction to afford (exclusively) phenothiazine and its 1-formyl derivative.A similar H2O2 oxidation of 10-methoxycyclohepta<1,4>benzothiazine gave mainly methyl phenothiazine-1-carboxylate and 3-formyl-1-methoxy phenothiazine.Further oxidation of these products with hydrogen peroxide yielded their S-oxides and S,S-dioxides.The reactivities of these cycloheptabenzothiazines are discussed in connection with those of the O- and N-analogues.