Synthesis and photochromism of Δ2,2′-BI-(2H-1,4-benzothiazine)

Article abstract of DOI:10.1016/S0040-4020(01)97445-9

Δ^2,2′-Bi- (2H-1,4-benzothiazine) (4), the parent ring system of a group of amino-acid pigments (trichosiderins) from red hair and feathers, has been synthesized by a simple and novel method involving air oxidation of 2H-1,4-benzothiazine, generated in situ by treatment of 1-(o-aminophenylthio)-2,2-diethoxyethane (1). This procedure yields only the yellow trans-isomer 4, which in solution exhibits marked photochromism, being reversibly converted into the red unstable cis-form 5 on brief irradiation with sunlight.