Synthetic Exploitation of the Ring-Opening of 3,4-Dinitrothiophene. A Novel Access to 1,4-Dialkyl- and 1,4-Diaryl-2,3-dinitro-1,3-butadienes

(E,E)-1,4-Bis(diethylamino)-2,3-dinitro-1,3-butadiene (2a), obtained from the ring-opening of 3,4-dinitrothiophene, reacts with Grignard reagents in THF to give good yields of 1,4-disubstituted ( Et, cy-Hex, Ph ) 2,3-dinitro- 1, 3-butadienes (3a-c) having almost exclusively (E,E) configuration.