2H‐1,4‐benzothiazines from the reaction of 2‐aminoethanethiol with nascent 4‐methyl‐o‐benzoquinone

Abstract 4‐Methyl‐o‐benzoquinone, generated oxidatively, reacts readily with 2‐aminoethanethiol giving 5‐hydroxy‐7‐methyl‐1,3,4‐dihydro‐2H‐1,4‐benzothiazine (I) or 5‐oxo‐7‐methyl‐8‐(2‐hydroxy‐4‐methylphenoxy)‐3,5‐dihydro‐2H‐1,4‐benzothiazine (VIII), depending on the conditions under which the reaction is performed. Chemical and spectral (uv, ir, nmr and ms) evidence for the assigned structures, as well as the course of the above mentioned reaction is described. A study of the behaviour of compound VIII in the presence of acids and alkalies is also reported.