Base-induced cycloaddition of tosylmethyl or (tert-butoxycarbonyl)methyl isocyanide to 1,4-disubstituted 2,3-dinitro-1,3-butadienes. Access to 2,3-disubstituted 4-ethynylpyrroles

Abstract The reactions of 1,4-disubstituted 2,3-dinitro-1,3-butadienes 1a-g in THF with isocyanides XCH 2 NC (TosMIC, X = tosyl; TBICA, X = COOBu t ) and DBU furnish good to moderate yields of 2,3-disubstituted 4-ethynylpyrroles 5a-g or 6a-g . In the reaction of 1g with TosMIC and DBU the nitrovinyl pyrrole 7g and the 3,3′-dipyrrole 4g are also isolated as by-products. A mechanism involving sequential base-induced addition, elimination and cyclization steps is advanced to account for the formation of the isolated products.