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.
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.
Shen
Hong C
HC
Department of Chemistry, University of Minnesota, Minneapolis, Minnesota 55455, USA.
Wang
Jiashi
J
Cole
Kevin P
KP
McLaughlin
Michael J
MJ
Morgan
Christopher D
CD
Douglas
Christopher J
CJ
Hsung
Richard P
RP
Coverdale
Heather A
HA
Gerasyuto
Aleksey I
AI
Hahn
Juliet M
JM
Liu
Jia
J
Sklenicka
Heather M
HM
Wei
Lin-Li
LL
Zehnder
Luke R
LR
Zificsak
Craig A
CA
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
D000475:Alkenes; D007097:Imines; D007202:Indicators and Reagents; D007659:Ketones; D011714:Pyrans; D011753:Pyrones; D012492:Salts