A synthesis of N -(1 H -pyrazol-5-yl)-1,3,4-thiadiazol-2(3 H )-imines from nitrile imines and Erlenmeyer thioazlactones

Erlenmeyer thioazlactones are reacted with hydrazonoyl chlorides in the presence of Et 3 N to afford functionalized N -(1 H -pyrazol-5-yl)-1,3,4-thiadiazol-2(3 H )-imines in excellent yields. This strategy is based on a domino double 1,3-dipolar cycloaddition reaction of nitrile imines to Erlenmeyer thioazlactones, followed by the elimination of carbon monoxide and phenylmethanthiol from the initially formed cycloadducts. This method provides fast access to a variety of structurally diverse N -(1 H -pyrazol-5-yl)-1,3,4-thiadiazol-2(3 H )-imines. The structure of a typical product was established by X-ray crystallography. Graphic abstract