title: Mechanistic intricacies of gold-catalyzed intermolecular cycloadditions between allenamides and dienes.
abstract: 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.
authors.affiliation: Departament de Química, Universitat Autònoma de Barcelona, 08193 Bellaterra, Barcelona (Spain).
authors.forename: Sergi
authors.initials: S
authors.lastname: Montserrat
authors.forename: Hélio
authors.initials: H
authors.lastname: Faustino
authors.forename: Agustí
authors.initials: A
authors.lastname: Lledós
authors.forename: Jose L
authors.initials: JL
authors.lastname: Mascareñas
authors.forename: Fernando
authors.initials: F
authors.lastname: López
authors.forename: Gregori
authors.initials: G
authors.lastname: Ujaque
keywords: allenamides; cycloaddition; density functional calculations; gold; reaction mechanisms