Nitration of thienothiophenes

Similarly, acetylation of thieno[3,2-6]thiophene (2) afforded 2-acetyl-thieno[3,2-6]thiophene, which was converted into methyl n-hexyl ketone by desulfurization with Raney nickel. Oxidation of 2-acetylthieno-[3,2-i]thiophene followed by nitration gave 5-nitrothieno[3,2-6]-thiophene-2-carboxylic acid. Decarboxylation of the latter furnished 2-nitrothieno[3,2-ft]thiophene identical with the compound obtained by direct nitration of thienothiophene 2 [Eq. (60)]. 

Nitration of thienothiophenes 1 and 2 occurs at position 2. Challenger et a/.i8.2 -22.26 showed that concentrated nitric acid in acetic anhydride furnished 2-nitrothieno[2,3-fr]thiophene (205) and 2-nitrothieno[3,2-6]-thiophene, respectively. The latter was converted into the 2,5-dinitro compound wiA more nitric acid. ... 

Nitration of thienothiophenes 1 and 2 with Cu(N0j)2-3H20 in acetic anhydride afforded the 2-nitro compounds in 30% and 56% yields, respectively. Gas-liquid chromatography showed the presence of 3-nitrothienol3,2-b]thiophene (up to 0.9%) and 3-nitrothieno[2,3-6]-thiophene (3-5%) in the crude reaction products. ... 

Nitration of thienothiophenes (3) and (7) has been carried out under several different conditions, leading mainly to 2-nitro derivatives (76) and (77). Acetyl nitrate (HNO3/AC2O), nitric-acetic acid mixture and copper nitrate/acetic anhydride have been used. 

AC2O/S11CI4), and nitration [Cu(N03)2] of thienothiophenes 1 and 2. He recently also studied the effect of the a-substitution (with halogen, CH3, SCHj, CN, NO2, COCH3, and COOH groups) on the chemical shifts of protons. He observed a good correlation between the shifts, reactivity constants, F (the field effect), and R (the resonance effect). ... 

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