Carboxyketenes, methyleneketenes, vinylketenes, oxetanediones, ynols, and ylidid ketenes from Meldrum's acid derivatives

George, Lisa, Wong, M. and Wentrup, Curt (2007) Carboxyketenes, methyleneketenes, vinylketenes, oxetanediones, ynols, and ylidid ketenes from Meldrum's acid derivatives. Organic & Biomolecular Chemistry, 5 9: 1437-1441. doi:10.1039/b702518a


Author George, Lisa
Wong, M.
Wentrup, Curt
Title Carboxyketenes, methyleneketenes, vinylketenes, oxetanediones, ynols, and ylidid ketenes from Meldrum's acid derivatives
Journal name Organic & Biomolecular Chemistry   Check publisher's open access policy
ISSN 1477-0520
Publication date 2007-03-26
Year available 2007
Sub-type Article (original research)
DOI 10.1039/b702518a
Open Access Status Not Open Access
Volume 5
Issue 9
Start page 1437
End page 1441
Total pages 5
Place of publication Cambridge, United Kingdom
Publisher Royal Society of Chemistry
Collection year 2008
Language eng
Abstract It has been documented that 5-methylene-Meldrum's acid derivatives ( 1, 12) and their enols ( 2, 13) can undergo fragmentation to malonic anhydrides ( 4, 19), carboxyketenes ( 3, 16) and methyleneketene ( 5, 21, 35), as well as cyclization to pyrrole-3-one and thiophene-3-one derivatives 11a, b ( but not furan-3-ones 11c) under the conditions of. ash vacuum thermolysis (FVT). Here we report theoretical calculations at the B3LYP/6-311 + G(2d, p) and G3X(MP2) levels of theory, which allow a rationalization of these observations. The calculated activation barriers for these reactions are all of the order of 37 - 40 kcal mol(-1). Hydroxyacetylenes ( alkynols) 7 are sometimes observed in FVT reactions of Meldrum's acid derivatives. Their formation is now explained as an FVT reaction of the carboxyketenes (e.g. 3 -> 7 and 32 -> 34) with a calculated activation barrier of ca. 39 kcal mol(-1). The cyclization of alkylamino- and alkylthio-substituted methyleneketenes 8a, b to pyrrolone and thiophenone derivatives 11a, b is found to be energetically very feasible under FVT conditions, and even in some cases in solution, with activation barriers of 33 - 39 kcal mol(-1). This cyclization takes place via the fleeting ylidic ketene intermediates 9a, b, 25, and 37a, b, which exist in very shallow energy minima. Alkoxy-substituted methyleneketenes 8c do not cyclize in this manner due to the rather high, but in principle not impossible, activation barriers for the initial 1,4-H shifts to the ylidic ketenes 9c ( ca. 47 kcal mol(-1)).
Q-Index Code C1
Q-Index Status Confirmed Code

Document type: Journal Article
Sub-type: Article (original research)
Collections: 2008 Higher Education Research Data Collection
School of Chemistry and Molecular Biosciences
 
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Created: Sat, 15 Mar 2008, 00:41:59 EST by Darryl Greensill on behalf of School of Chemistry & Molecular Biosciences