title: A formal [3 + 3] cycloaddition reaction. Improved reactivity using alpha,beta-unsaturated iminium salts and evidence for reversibility of 6pi-electron electrocyclic ring closure of 1-oxatrienes.
abstract: A detailed account regarding a formal [3 + 3] cycloaddition method using 4-hydroxy-2-pyrones and 1,3-diketones is described here. This formal cycloaddition reaction or annulation reaction is synthetically useful for constructing 2H-pyranyl heterocycles. The usage of alpha,beta-unsaturated iminium salts is significant in controlling competing reaction pathways to give exclusively 2H-pyrans. Most significantly, experimental evidence is provided to support the mechanism of this reaction that involves a sequential Knoevenagel condensation and a reversible 6pi-electron electrocyclic ring-closure of 1-oxatrienes.
authors.affiliation: Department of Chemistry, University of Minnesota, Minneapolis, Minnesota 55455, USA.
authors.forename: Hong C
authors.initials: HC
authors.lastname: Shen
authors.forename: Jiashi
authors.initials: J
authors.lastname: Wang
authors.forename: Kevin P
authors.initials: KP
authors.lastname: Cole
authors.forename: Michael J
authors.initials: MJ
authors.lastname: McLaughlin
authors.forename: Christopher D
authors.initials: CD
authors.lastname: Morgan
authors.forename: Christopher J
authors.initials: CJ
authors.lastname: Douglas
authors.forename: Richard P
authors.initials: RP
authors.lastname: Hsung
authors.forename: Heather A
authors.initials: HA
authors.lastname: Coverdale
authors.forename: Aleksey I
authors.initials: AI
authors.lastname: Gerasyuto
authors.forename: Juliet M
authors.initials: JM
authors.lastname: Hahn
authors.forename: Jia
authors.initials: J
authors.lastname: Liu
authors.forename: Heather M
authors.initials: HM
authors.lastname: Sklenicka
authors.forename: Lin-Li
authors.initials: LL
authors.lastname: Wei
authors.forename: Luke R
authors.initials: LR
authors.lastname: Zehnder
authors.forename: Craig A
authors.initials: CA
authors.lastname: Zificsak
mesh_terms: D000475:Alkenes / Q000737:chemistry; D002384:Catalysis; D002625:Chemistry, Organic / Q000379:methods*; D018360:Crystallography, X-Ray; D003500:Cyclization; D007097:Imines / Q000737:chemistry; D007202:Indicators and Reagents; D007659:Ketones / Q000737:chemistry*; D009682:Magnetic Resonance Spectroscopy; D015394:Molecular Structure; D010084:Oxidation-Reduction; D011714:Pyrans / Q000138:chemical synthesis*; D011753:Pyrones / Q000737:chemistry*; D012492:Salts / Q000138:chemical synthesis; D013237:Stereoisomerism
chemical_list: D000475:Alkenes; D007097:Imines; D007202:Indicators and Reagents; D007659:Ketones; D011714:Pyrans; D011753:Pyrones; D012492:Salts