Syntheses for 2‐hydroxy‐2H‐1,4‐benzothiazin‐3(4H)‐one derivatives as thio analogues of natural hemiacetals

Reductive cyclizations of methyl 2‐(2‐nitrophenylthio)acetate 2 by means of electrochemistry or by catalytic hydrogenation have been used as key steps in the syntheses of the hemiacetals 2‐hydroxy‐2H‐1,4‐benzothiazin‐3(4H)‐one 10 and its 4‐hydroxy derivative 9 representing thio analogues of allelo chemicals found in Gramineae and Acanthaceae. In contrast to its natural counterpart 2,4‐dihydroxy‐2H‐1,4‐benzoxa‐zin‐3(4H)‐one hydroxamic acid 9 did not undergo degradation by extrusion of formic acid.