期刊
CHEMISTRY-A EUROPEAN JOURNAL
卷 19, 期 45, 页码 15248-15260出版社
WILEY-V C H VERLAG GMBH
DOI: 10.1002/chem.201302330
关键词
allenamides; cycloaddition; density functional calculations; gold; reaction mechanisms
资金
- Spanish MINECO [SAF2010-20822-C02-01/02, 2010 CSD2007-00006, CTQ2011-23336]
- ERDF funds
- Xunta de Galicia [INCITE09209084PR, GRC2010/12]
- Fundacao para a Ciencia e Tecnologia (FCT, Portugal)
- POPH/FSE [SFRH/BD/60214/2009]
- Fundação para a Ciência e a Tecnologia [SFRH/BD/60214/2009] Funding Source: FCT
The mechanism of the gold-catalyzed intermolecular cycloaddition between allenamides and 1,3-dienes has been explored by means of a combined experimental and computational approach. The formation of the major [4+2] cycloaddition products can be explained by invoking different pathways, the preferred ones being determined by the nature of the diene (electron neutral vs. electron rich) and the type of the gold catalyst (AuCl vs. [IPrAu](+), IPr=1,3-bis(2,6-diisopropylphenyl)imidazole-2-ylidene). Therefore, in reactions catalyzed by AuCl, electron-neutral dienes favor a concerted [4+3] cycloaddition followed by a ring contraction event, whereas electron-rich dienes prefer a stepwise cationic pathway to give the same type of formal [4+2] products. On the other hand, the theoretical data suggest that by using a cationic gold catalyst, such as [IPrAuCl]/AgSbF6, the mechanism involves a direct [4+2] cycloaddition between the diene and the gold-activated allenamide. The theoretical data are also consistent with the observed regioselectivity as well as with the high selectivity towards the formation of the enamide products with a Z configuration. Finally, our data also explain the formation of the minor [2+2] products that are obtained in certain cases.
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