Preparation of 3,4-di-t-butylthiophene 1-imide and its N-substituted derivatives

Treatment of 3,4-di-t-butylthiophene 1-oxide with (CF3CO)2O or (CF3SO2)2O, followed by reaction with RSO2NH2, ROC(O)NH2, or RCONH2 furnished a series of 1-imino derivatives of 3,4-di-t-butylthiophene, which carry an electron-withdrawing substituent on the imino nitrogen atom. Treatment of an imino derivative (substituent on the nitrogen atom=CO2tBu) with CF3CO2H gave the corresponding aminosulfonium salt, whose deprotonation led to the N-unsubstituted parent 1-imide derivative.