Synthetic exploitation of the ring-opening of 3,4-dinitrothiophene, VIII -Access to 4,5-dinitro-1,3,5,7-octatetraene systems

The reactions between 1,4-bis(diethylamino)-2,3-dinitro-1,3-butadiene (2), easily obtainable by ring-opening of 3,4-dinitrothiophene with diethylamine , and 2-substituted vinylmagnesium bromides gave good yields of the 4,5-din itro-1,3,5,7-octatetraene derivatives 3a-e. With 1-phenylmagnesium bromide, conversely, only 3,4-dinitro-1,4-diphenyl-1,3,5-cyclooctatriene (4f) was o btained. From the unsubstituted dinitrooctatetraene 3a both the octatriene cycloisomer 4a and the valence tautomer of the latter (6a) could be isolate d and characterized The results obtained evidence an unfavourable effect of the two nitro groups on the cycloisomerization process of the octatetraene system.