title: Povarov reactions involving 3-aminocoumarins: synthesis of 1,2,3,4-tetrahydropyrido[2,3-c]coumarins and pyrido[2,3-c]coumarins.
abstract: Condensation of 3-aminocoumarin (5) with 4-nitrobenzaldehyde (8) afforded a 2-azadiene (9), which reacted with various electron-rich alkenes (10 examples) in the presence of Yb(OTf)3 to afford 1,2,3,4-tetrahydropyrido[2,3-c]coumarins. Yields were generally good, but the diastereomeric ratios were highly variable. The products arose through a formal [4 + 2] cycloaddition (inverse electron demand Diels-Alder reaction) followed by tautomerization. As such, these are examples of the Povarov reaction. A range of 1,2,3,4-tetrahydropyrido[2,3-c]coumarins was then synthesized using a three-component version of this reaction, which involves in situ formation of the 2-azadiene component. Some of these products were converted into the corresponding pyrido[2,3-c]coumarins upon treatment with various oxidants, the most effective of which proved to be nitrous gases.
authors.affiliation: Department of Chemistry, Memorial University, St. John's, NL, Canada A1B 3X7.
authors.forename: Amit A
authors.initials: AA
authors.lastname: Kudale
authors.forename: Jamie
authors.initials: J
authors.lastname: Kendall
authors.forename: David O
authors.initials: DO
authors.lastname: Miller
authors.forename: Julie L
authors.initials: JL
authors.lastname: Collins
authors.forename: Graham J
authors.initials: GJ
authors.lastname: Bodwell
mesh_terms: D049933:Aminocoumarins / Q000737:chemistry*; D001547:Benzaldehydes / Q000737:chemistry; D003374:Coumarins / Q000138:chemical synthesis*
chemical_list: D049933:Aminocoumarins; D001547:Benzaldehydes; D003374:Coumarins; C029915:4-nitrobenzaldehyde