A conceptually new method for synthesis of tetrasubstituted thiophenes in two steps from trans-2-aroyl-3-aryl-cyclopropane-1,1-dicarboxylates and 1,4-dithiane-2,5-diol has been developed. It involves AlCl3-mediated [3+3] annulation of the cyclopropane-derived 1,3-zwitterionic intermediates with in situ generated mercaptoacetaldehyde, followed by DBU-induced rearrangement of the resulting tetrahydrothiopyranols. The target thiophenes are produced in 55-82% yields.
Activated donor-acceptor cyclopropanes underwent formal [3 + 2] cycloaddition with nitriles in the presence of SnCl(4). The product 1-pyrrolines were isolated as single cis-diastereomers in moderate to good yields.
Domino synthesis of tetrasubstituted thiophenes is described from 1,3-enynes and mercaptoacetaldehyde using DABCO at room temperature via a Michael addition, 5-exo-dig carboannulation, and oxidation sequence under air. The broad substrate scope and mild reaction conditions are significant practical features.
trans-2-Aroyl-3-arylcyclopropane-1,1-dicarboxylates upon treatment with aluminiumA C H T U N G T R E N N U N G (III) chloride (AlCl 3 ) underwent ring-opening, fragmentation, recombination and lactonization to give highly substituted 2-pyrones. Alternatively, when treated with titanium(IV) chloride (TiCl 4 ), the cyclopropane diesters underwent a Nazarov cyclization to afford 1-indanones with high diastereoselectivity.
trans-2-Aroyl-3-aryl-cyclopropane-1,1-dicarboxylates when treated with arylhydrazines in refluxing EtOH gave dihydropyrazoles, whereas with hydrazines in refluxing AcOH, they formed cyclopropane-fused pyridazinones. Although in both cases the corresponding hydrazones are formed initially, the former case involves a subsequent 5-exo-tet nucleophilic ring-opening, and the later, a 6-exo-trig nucleophilic attack by the other hydrazone nitrogen. The products are obtained in moderate to excellent yields with complete regio-and diastereoselectivity.
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