The reaction of 3-aminodiphenylamine (I) with ethyl chloroformate (A) gives ethyl 3-anilinocarbanilate (II), which is cyclized by heating with S and I2 to yield ethyl phenothiazine-2-carbamate (III). The condensation of (III) with 3-chloropropionyl chloride (B) in refluxing toluene affords ethyl 10-(3-chloropropionyl)phenothiazine-2-carbamate (IV), which is finally condensed with refluxing morpholine (C).