Efficient route for the synthesis of 3,4-cycloalkoxy-2,5-diethoxycarbonyl-thiophenes obtained with bulky alkyl dibromides using trialkylamines as base-solvent

New reaction conditions were investigated for dialkylizing diethyl 3,4-dihydroxy-2,5-thiophenedicarboxylate with sterically hindered alkyl-dibromides, using as reaction system DMF-trialkylamine or only the trialkylamine as base-solvent. This methodology produced the corresponding 3,4-cycloalkoxy-2,5-diethoxycarbonyl-thiophene derivatives faster and with better yields than those reported previously for K2CO3-DMF. Experiments were performed with triethylamine, tripropylamine, and tributylamine. Tributylamine produced the best results in a general reaction with alkyl-bromides. Aromatic amines like N,N-dimethylaniline, N-methyldiphenylamine, and triphenylamine failed to react at all. Reactions using only the tributylamine as base-solvent demonstrated that DMF is not necessary as a solvent to obtain good yields.