title: Cycloaddition Reactions of Indanedioneketene with Electron-Rich Dienophiles: An Experimental and a Theoretical Study.
abstract: Thermal decomposition of the phenyliodonium ylide of lawsone gives rise to a highly reactive cyclic α,α'-dioxoketene, indanedioneketene, which reacts with electron-rich dienophiles such as enol ethers to afford [4 + 2] cycloadducts. The initially formed 2,3-dihydro-2-alkoxy-indeno[1,2-b]pyrano-4,5-diones are labile compounds since through an opening of the pyranone ring upon heating they easily tautomerize to alkoxyallylidene-indenedione derivatives and under acid-catalysis they are additionally transformed to 2-(1,3-dihydroxyallylidene)-1H-indene-1,3(2H)-dione or by loss of alcohol to indeno[1,2-b]pyran-4,5-diones. A DFT study explains the polar nature of the cycloaddition reaction, the observed reactivity and suggests a possible mechanism operating in these reactions.
authors.affiliation: Laboratory of Organic Chemistry, School of Chemistry, Faculty of Sciences, Aristotle University of Thessaloniki , 54124 Thessaloniki, Greece.
authors.forename: Elizabeth
authors.initials: E
authors.lastname: Malamidou-Xenikaki
authors.affiliation: Laboratory of Organic Chemistry, School of Chemistry, Faculty of Sciences, Aristotle University of Thessaloniki , 54124 Thessaloniki, Greece.
authors.forename: Spyros
authors.initials: S
authors.lastname: Spyroudis
authors.affiliation: Laboratory of Organic Chemistry, School of Chemistry, Faculty of Sciences, Aristotle University of Thessaloniki , 54124 Thessaloniki, Greece.
authors.forename: Erifili
authors.initials: E
authors.lastname: Tsovaltzi
authors.affiliation: Laboratory of Applied Quantum Chemistry, School of Chemistry, Faculty of Sciences, Aristotle University of Thessaloniki , P.O. Box 135, 54124 Thessaloniki, Greece.
authors.forename: Evangelos G
authors.initials: EG
authors.lastname: Bakalbassis