Synthesis of thieno[2,3‐ e ]‐1,2,4‐triazines

3‐Methylmercapto‐5‐oxo‐6‐vinyl‐ and 2‐methyl‐3‐mercapto‐5‐oxo‐6‐vinyl‐2,5‐dihydro‐1,2,4‐triazines were readily converted into the corresponding thieno[2,3‐ e ]‐1,2,4‐triazine in one step by the action of phosphorus pentasulfide in pyridine. 4‐Methyl‐3‐mercapto‐5‐oxo‐4,5‐dihydro‐1,2,4‐triazine is only converted into the 5‐thioxo analog and no thiophene ring product was obtained under the same conditions. Thieno[2,3‐ e ]‐1,2,4‐triazines were also more efficiently obtained by the action of phosphorus petnasulfide in pyridine on the appropriate 6‐acylmethyl‐3‐mercapto‐5‐oxo‐2,5‐dihydro‐1,2,4‐triazine.