Synthesis of carbon-14 labeled 4-bromo-2,7-dimethoxy-3H-phenothiazin-3-one

Two different syntheses of (5), one labeled with carbon‐14 in the quinonoid ring and the other in the phenyl ring are described. Treatment of p‐[U‐14C]benzoquinone with 2‐amino‐5‐methoxy benzenethiol yielded (7), which was methoxylated to provide a mixture of isomers (4a) and (8). Separation of isomers followed by bromination of (4a) gave (5a). Thiocyanation of p‐[U‐14C]anisidine provided (10), which was hydrolysed to give labeled aminothiol (3b); the latter was condensed with 2‐bromo‐6‐methoxy‐p‐benzoquinone to afford (5b).