Synthesis of 2 H ‐1,4‐thiazin‐3(4 H )‐one 1‐oxide and 2 H ‐1,4‐thiazin‐3‐(4 H )‐one 1,1‐dioxide, structural analogs of uracil

The synthesis of 1,4‐thiazine 1‐oxide and 1,1‐dioxide analogs of the antibiotic emimycin is described. Reaction of methylthioglycolate with 1‐bromo‐2,2‐diethoxyethane gave methyl (2,2‐diethoxyethylthio)acetate ( 2 ). Treatment of 2 with methanolic ammonia followed by cyclization furnished 2 H ‐1,4‐thiazin‐3(4 H )‐one ( 5 ). Oxidation of 5 with m ‐chloroperoxybenzoic acid converted it to 2 H ‐1,4‐thiazin‐3(4 H )‐one 1‐oxide ( 6 ). Oxidation of 2 with potassium permanganate, followed by treatment with methanolic ammonia, and cyclization gave 2 H ‐1,4‐thiazin‐3(4 H )‐one 1,1‐dioxide.