Source:http://linkedlifedata.com/resource/pubmed/id/15352115
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| Predicate | Object |
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| rdf:type | |
| lifeskim:mentions | |
| pubmed:issue |
17
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| pubmed:dateCreated |
2004-9-7
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| pubmed:abstractText |
At the 6-311G* level of theory, DFT methods predict that the rearrangement of 1,4-dihydroxy-5-methylpentadienyl cation 1 (R = Me) to protonated trans-3-hydroxy-2-methylcyclopent-4-en-1-one 2, an intermediate step in the Piancatelli reaction or rearrangement of furfuryl carbinols to trans-2-alkyl(aryl)-3-hydroxycyclopent-4-en-1-one, is a concerted electrocyclic process. Energetic, magnetic, and stereochemical criteria are consistent with a conrotatory electrocyclic ring closure of the most stable out,out-1 isomer to afford trans-2. Although the out,in-1 isomer is thermodynamically destabilized by 6.84 kcal mol(-1), the activation energy for its cyclization is slightly lower (5.29 kcal mol(-1) versus 5.95 kcal mol(-1)). The cyclization of the isomers of 1 with the C1-hydroxy group inwards showed considerably higher activation energies than their outwards counterparts. in,out-1, although close in energy to out,out-1 (difference of 1.57 kcal mol(-1)) required about 10 kcal mol(-1) more to reach the corresponding transition structure. The value measured for the activation energy of in,in-1 (17.32 kcal mol(-1)) eliminates the alternative conrotatory electrocyclization of this isomer to provide trans-2. Geometric scrambling by isomerization of the terminal C1--C2 bond of 1 is also unlikely to compete with electrocyclization. The possibility to interpret the 1-->2 reaction as a nonpericyclic cationic cyclization was also examined through NBO analysis, and the study of bond lengths and atomic charges. It was found that the 1-->2 concerted rearrangement benefits from charge separation at the cyclization termini, an effect not observed in related concerted electrocyclic processes, such as the classical Nazarov reaction 3-->4 or the cyclization of the isomeric 2-hydroxypentadienyl cation 5.
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| pubmed:language |
eng
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| pubmed:journal | |
| pubmed:status |
PubMed-not-MEDLINE
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| pubmed:month |
Sep
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| pubmed:issn |
0947-6539
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| pubmed:author | |
| pubmed:issnType |
Print
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| pubmed:day |
6
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| pubmed:volume |
10
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| pubmed:owner |
NLM
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| pubmed:authorsComplete |
Y
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| pubmed:pagination |
4324-33
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| pubmed:dateRevised |
2009-8-4
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| pubmed:year |
2004
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| pubmed:articleTitle |
Theoretical study of the electrocyclic ring closure of hydroxypentadienyl cations.
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| pubmed:affiliation |
Departamento de Química Orgánica, Facultade de Química, Universidade de Vigo, 36200, Vigo, Spain.
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| pubmed:publicationType |
Journal Article
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