Studies On The Reactions Of α-formyl Ketene Dithioacetals And Methyl Isocyanides: The Regiodivergent Construction Of Polysubstituted Pyrroles And Furans

Pyrrole and furan derivatives are important five-membered heterocycles, which are thecore structure of many nature products and pharmaceuticals. Efficient synthesis of highlysubstituted pyrrole and furan derivatives has attracted extensive attentions. In recent years,although many synthetic methods have been reported, few of them allow the regiodivergentconstruction of a diverse array of furans and pyrroles from common starting materials.Methyl isocyanides are active synthons for the synthesis of heterocycles. The carbonatom of the isocyano group could react either of electrophiles or nucleophiles with goodselectivity. Combined with the acidity of the-C-H bond, methyl isocyanides could involvein various tandem reactions for the construction of heterocycles, such as pyrroles and oxzolesetc., for examples, the Barton–Zard and van Leusen pyrrole syntheses.Our group has been engaged in ketene dithioacetal chemistry for over twenty years.Various carbo/hetero-cycles have been produced with ketene dithioacetals as the usefulintermediates. In this thesis, we describe the selective construction of a diverse array offive-membered heterocycles from the readily available α-formyl ketene dithioacetals andmethyl isocyanides controlled by the choice of suitable catalysts/promoters. Thus,5-alkylthio-pyrroles,4-alkylthiocarbonyl-pyrroles and2-alkylthio-4-tosyl-furans have beenprepared, selectively, in a single operation from common precursors. The structures of thesefive-membered heterocycles have been verified by NMR spectra, high-resolution mass spectraand single crystal analyses. The mechanisms of these new reactions are also investigated indetails.