Synthetic Access to the Class of 3‐Amino‐4‐Cyano‐Substituted Thiophenes

The synthesis of 1,1‐dibromo‐3,4,4‐trichloro‐2‐cyano‐1,3‐butadiene ( 3 ) provides a selective access to the new class of 3‐amino‐4‐cyano‐thiophenes 2 . The unique push–pull substitution pattern of 2 allows a chemoselective modification in the 2 and 5 positions. Derivatization of 2 is accomplished by selective S ‐oxidation of the vinylsulfanyl unit. Substitution of the resulting vinylsulfinyl group of 14 by halogen nucleophiles led to dihalothiophenes 16 and 17 in good yields. A subsequent selective dehalogenation in the 2 and 5 positions is accomplished, leaving the 3,4‐push–pull unit untouched. The new 2,5‐dihalothiophenes, as well as the 2,5‐unsubstituted thiophene 20 , are interesting monomers for the preparation of highly conducting polythiophenes.