Grob fragmentation of norbornyl α-diketones: a route to α-ketoenols and aromatic compounds.
J Org Chem
; 76(9): 3320-8, 2011 May 06.
Article
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| MEDLINE
| ID: mdl-21413814
An efficient acid-catalyzed Grob fragmentation of symmetrical and asymmetrically substituted norbornyl α-diketones to the corresponding six-membered α-ketoenols is reported. The regio- and stereochemical outcome of the Grob fragmentation of C2 mono- and disubstituted α-diketones was investigated. A single regioisomer resulting from a favorable half-chair intermediate was normally observed. A departure from the normal course was noticed for C2 disubstituted α-diketones possessing an exo-methyl and an endo-methoxycarbonyl derivative, giving the opposite regioisomers due to initial formation of the hemiketal. The bromo analogues of the C2 disubstituted α-diketones furnished an unusual byproduct, which appears to have been formed through highly reactive fused four-membered bicyclo[2.2.0]hexane intermediates. A plausible mechanistic proposal involving the gem-dihalo intermediate, which in one case was actually isolated as its BF(2)-complex, is outlined. The fragmentation protocol was applied to various norbornyl substrates including bis-α-diketone derivatives. The methodology was successfully utilized for the synthesis of substituted aromatic compounds.
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1
Colección:
01-internacional
Base de datos:
MEDLINE
Idioma:
En
Revista:
J Org Chem
Año:
2011
Tipo del documento:
Article
País de afiliación:
India
Pais de publicación:
Estados Unidos