Ketene-acetylene [2+2] cycloadditions: cyclobutenone and/or oxete formation?

Koch, R. and Wentrup, C. (2004) Ketene-acetylene [2+2] cycloadditions: cyclobutenone and/or oxete formation?. Organic & Biomolecular Chemistry, 2 2: 195-199. doi:10.1039/b309549e


Author Koch, R.
Wentrup, C.
Title Ketene-acetylene [2+2] cycloadditions: cyclobutenone and/or oxete formation?
Journal name Organic & Biomolecular Chemistry   Check publisher's open access policy
ISSN 1477-0520
Publication date 2004
Sub-type Article (original research)
DOI 10.1039/b309549e
Open Access Status Not Open Access
Volume 2
Issue 2
Start page 195
End page 199
Total pages 5
Place of publication Cambridge, United Kingdom
Publisher Royal Society of Chemistry
Language eng
Abstract The [2 + 2] cycloaddition of monosubstituted acetylenes to ketene has been studied by ab initio (G2(MP2,SVP) and DFT (B3LYP/6-31Gd)) methods. The activation barrier decreases with increasing electron-donating ability of the acetylene substituent, and it can be roughly correlated with the energy of the acetylene HOMO. The addition to the C=C bond of ketene (giving cyclobutenones) is preferred for the less electron-rich acetylenes, but for the most electron rich ones (X = NH2 and NMe2) the addition to the C=O bond (giving oxetes) becomes competitive, with activation barriers as low as ca. 45 ( 30) kJ mol(-1) for the two computational methods used. The cyclobutenones and oxetes can undergo ring opening to vinylketenes and acylallenes, respectively. Furthermore, the latter two compounds can interconvert by a 1,3-shift of the substituent X. The acylallenes become thermodynamically more stable than the vinylketenes for pi-(lone pair) donating substituents X, and the 1,3-shift barrier also decreases, to ca. 130 kJ mol(-1) for X = NMe2. In contrast, the 1,3-shifts of CH3 and H have very high barriers.
Keyword Chemistry, Organic
Vinylketene-acylallene Rearrangement
Electrocyclic Ring Openings
Density-functional Theory
Ab-initio
Pseudopericyclic Reactions
Theoretical Predictions
Conjugated Ketenes
Ynamines
Imidoylketene
(aminoethynyl)metallations
Q-Index Code C1

Document type: Journal Article
Sub-type: Article (original research)
Collections: Excellence in Research Australia (ERA) - Collection
School of Chemistry and Molecular Biosciences
 
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Created: Wed, 19 Sep 2007, 18:44:02 EST