Evaluation of possible intramolecular [4+2] cycloaddition routes for assembling the central tetracyclic core of the potent marine antiinflammatory agent mangicol A
摘要:
A plan for enantioselective construction of the mangicol A framework by means of intramolecular Diels-Alder cycloaddition is outlined. First to be assembled is the enantiopure cyclopentenecarboxylic acid 16. Of the several approaches targeting the 1,3-diene component 56, only that involving palladium-catalyzed enyne cyclization proved successful. Following the coupling of 16 to 56, we were unable to bring about any detectable level of (4 pi+2 pi) cycloaddition. Activation of the diene by incorporation of an OSiEt3 substituent on a terminal sp(2)-hybridized center likewise proved unsuccessful. Further facilitation was sought in the form of cyclopentenonecarboxylate 66. However, thermal activation, Lewis acid catalysis, and high-pressure conditions proved ineffective and did not lead to C-C bond formation. These studies serve to underscore the extent to which steric complications can complicate matters and the extent to which they must be skirted to arrive at the title compound. (c) 2006 Elsevier Ltd. All rights reserved.
Evaluation of possible intramolecular [4+2] cycloaddition routes for assembling the central tetracyclic core of the potent marine antiinflammatory agent mangicol A
摘要:
A plan for enantioselective construction of the mangicol A framework by means of intramolecular Diels-Alder cycloaddition is outlined. First to be assembled is the enantiopure cyclopentenecarboxylic acid 16. Of the several approaches targeting the 1,3-diene component 56, only that involving palladium-catalyzed enyne cyclization proved successful. Following the coupling of 16 to 56, we were unable to bring about any detectable level of (4 pi+2 pi) cycloaddition. Activation of the diene by incorporation of an OSiEt3 substituent on a terminal sp(2)-hybridized center likewise proved unsuccessful. Further facilitation was sought in the form of cyclopentenonecarboxylate 66. However, thermal activation, Lewis acid catalysis, and high-pressure conditions proved ineffective and did not lead to C-C bond formation. These studies serve to underscore the extent to which steric complications can complicate matters and the extent to which they must be skirted to arrive at the title compound. (c) 2006 Elsevier Ltd. All rights reserved.
Mono- and Bis-Acrolein Derivatives by Reliable and Efficient One-Step Methylenation of Aldehyde Precursors
作者:Leo Paquette、Kallol Basu、Jonathan Richards
DOI:10.1055/s-2004-834866
日期:——
A series of aldehydes carrying different functional groups was transformed directly into the α-methylene derivatives. Dialdehydes behaved comparably at both active sites. When keto aldehydes are involved, excellent levels of chemoselectivity are observed, with the ketone substructures exhibiting no sign of reactivity.
Evaluation of possible intramolecular [4+2] cycloaddition routes for assembling the central tetracyclic core of the potent marine antiinflammatory agent mangicol A
作者:Stefan Pichlmair、Manuel de Lera Ruiz、Kallol Basu、Leo A. Paquette
DOI:10.1016/j.tet.2005.11.096
日期:2006.5
A plan for enantioselective construction of the mangicol A framework by means of intramolecular Diels-Alder cycloaddition is outlined. First to be assembled is the enantiopure cyclopentenecarboxylic acid 16. Of the several approaches targeting the 1,3-diene component 56, only that involving palladium-catalyzed enyne cyclization proved successful. Following the coupling of 16 to 56, we were unable to bring about any detectable level of (4 pi+2 pi) cycloaddition. Activation of the diene by incorporation of an OSiEt3 substituent on a terminal sp(2)-hybridized center likewise proved unsuccessful. Further facilitation was sought in the form of cyclopentenonecarboxylate 66. However, thermal activation, Lewis acid catalysis, and high-pressure conditions proved ineffective and did not lead to C-C bond formation. These studies serve to underscore the extent to which steric complications can complicate matters and the extent to which they must be skirted to arrive at the title compound. (c) 2006 Elsevier Ltd. All rights reserved.