Synthesis of thieno[3,4-b]pyrrole derivatives based on the reaction of 1-methyl-2-nitromethylenepyrrolidine with isothiocyanates

The reaction of 1-methyl-2-nitromethylenepyrrolidine with arylisothiocyanates in the presence of a base was found to proceed at the 3-СН2 group of the nitroenamine followed by further cyclization to afford 4-R-imino-1-methyl-1,2,3,4-tetrahydro-6H-thieno[3,4-b]pyrrol-6-one oximes. Under analogous conditions, alkylisothiocyanates add to 1-methyl-2-nitromethylenepyrrolidine giving 1-methyl-2-nitromethylenepyrrolidine-3-carbothioic acid amides, and no cyclization was observed. A tentative mechanism for the formation of thieno[3,4-b]pyrrolе derivatives is proposed.