Abstract
1‐Alkynyl allenyl sulfides H2C=C=CHSC≡ CR1 (R1 = CH3, C2H5), prepared from alkynethiolates LiSC≡CR1 and propargyl bromide in liquid ammonia, rearrange at room temperature to thioketenes HC≡CCH2C(R1)=C=S. These can be trapped by amines R22NH (R2 = C2H5, C3H7) to give the acetylenic thioamides H≡CCH2CH(R1)C(=S)NR22 in fair to good yields. Potassium tert‐butoxide in liquid ammonia causes cyclization of the thioamides to 2‐dialkylamino‐3,5‐dialkylthiophenes. The same thiophenes are obtained by simply heating the thioamides in hexamethylphosphoric triamide.