Abstract
A novel one‐step ‘Inverse Indigo Synthesis’ of the Δ2,2′‐bi(3,4‐dihydro‐3‐oxo‐2H‐1, 4‐benzothiazine) chromophore is described. Structure, substitution reactions, mechanism of formation, colour and other relevant properties of this system have been investigated in relation to known thioindigos. A synthesis of the basic skeleton of one of the ‘Trichosiderins’, the colouring matters of human red hair, is reported.