Topic
Annulation
About: Annulation is a research topic. Over the lifetime, 10152 publications have been published within this topic receiving 189701 citations.
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TL;DR: An enantioselective synthesis of pharmaceutically important spirobarbiturates has been achieved via spirocyclic chiral phosphine-catalyzed asymmetric [4 + 2] annulation of barbiturate-derived alkenes with allenoates.
80 citations
TL;DR: This protocol represents a new strategy to access α-imino gold carbenes, which corresponds to an unprecedented intermolecular transfer of N-acylimino nitrenes to ynamides, and proceeds with 100% atom economy, exhibits good functional group tolerance, and can be conducted in gram scale.
80 citations
TL;DR: A general synthetic methodology for palladium-catalyzed carbonylative annulation of o-alkynylphenol to construct 2-substituted-3-aroyl-benzo[b]furan is reported and could be applied to a wider selection of iodide substrates to generate desired products.
Abstract: We report here a general synthetic methodology for palladium-catalyzed carbonylative annulation of o-alkynylphenol to construct 2-substituted-3-aroyl-benzo[b]furan. On the basis of the results, this methodology could be applied to a wider selection of iodide substrates to generate desired products. In accordance with mechanistic studies, this process involves coordination of cationic and less hindered acyl palladium complexes with o-alkynylphenols to create a desired cascade triad (coordination, nucleophilic addition, and reductive elimination). Consistent with this mechanism, addition of 1 equiv of AgBF4 to palladium catalyst Pd(Ph3P)4 generates an ideal candidate for this unique transformation.
80 citations
TL;DR: The origin of stereoselectivity of NHC-catalyzed annulation reactions of ynals and stable enols was studied with Density Functional Theory and the data suggest that the C-C bond formation is the stereo-determining step.
Abstract: The origin of stereoselectivity of NHC-catalyzed annulation reactions of ynals and stable enols was studied with Density Functional Theory. The data suggest that the C–C bond formation is the stereo-determining step. Only the deprotonated pathway (containing an oxy-anion and overall neutral species) was found to give rise to discrimination of the competing stereoisomers. This is due predominantly to electrostatic repulsion of the β-stabilizing enolate functionality with the π-cloud of the aryl group in the NHC-catalyst.
80 citations
TL;DR: N-Heterocyclic carbene (NHC)-catalyzed highly enantioselective lactonization of modified enals with enolizable aldehydes, proceeding via the α,β-unsaturated acylazolium intermediates, results in the asymmetric synthesis of synthetically important 4,5-disubstituted dihydropyranones.
80 citations