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: Interestingly, a detailed investigation of the catalytically active palladium species pointed toward a dual role of the NHC acting as an organocatalyst and forming a novel mixed ligand Pd/NHC/phosphine complex, which represents a new class of chiral palladium catalyst.
Abstract: A comprehensive investigation of the mechanism of the highly enantioselective Pd(PPh3)4/NHC-catalyzed annulation of vinyl benzoxazinanones and enals has been conducted. A study of reaction orders supports the postulated cooperative catalysis. Interestingly, a detailed investigation of the catalytically active palladium species pointed toward a dual role of the NHC acting as an organocatalyst and forming a novel mixed ligand Pd/NHC/phosphine complex. The catalytically active Pd/NHC/phosphine complex represents a new class of chiral palladium catalyst. Remarkably, phosphine plays a crucial role in this transformation. These complexes could be characterized by X-ray crystallographic analysis and employed as catalysts for the enantioselective [4 + 1] annulation reaction of vinyl benzoxazinones and sulfur ylides in good yields and good enantioselectivities.
142 citations
TL;DR: The enantioselective synthesis of pyrazolone-fused spirocyclohexadienones was demonstrated by the reaction of α,β-unsaturated aldehydes with α-arylidene pyrazolinones under oxidative N-heterocyclic carbene (NHC)catalysis.
Abstract: The enantioselective synthesis of pyrazolone-fused spirocyclohexadienones was demonstrated by the reaction of α,β-unsaturated aldehydes with α-arylidene pyrazolinones under oxidative N-heterocyclic carbene (NHC)catalysis. This atom-economic and formal [3+3] annulation reaction proceeds through a vinylogous Michael addition/spiroannulation/dehydrogenation cascade to afford spirocyclic compounds with an all-carbon quaternary stereocenter in moderate to good yields and excellent ee values. Key to the success of the reaction is the cooperative NHC-catalyzed generation of chiral α,β-unsaturated acyl azoliums from enals, and base-mediated tandem generation of dienolate/enolate intermediates from pyrazolinones.
142 citations
TL;DR: In this article, the redox-neutral annulation of alkynes by differently decorated nitrones set the stage for a step-economical access to indoles with ample substrate scope.
Abstract: The redox-neutral annulation of alkynes by differently decorated nitrones set the stage for a step-economical access to indoles with ample substrate scope. The redox-neutral C–H/N–O functionalization process proceeded through kinetically relevant C–H activation by carboxylate assistance, and displayed an excellent site- and regio-selectivity with unsymmetrical nitrones and alkynes.
142 citations
TL;DR: The straightforward and efficient synthesis of naphtho[1,8-bc]pyran derivatives and related polycyclic compounds is achieved by the rhodium-catalyzed oxidative coupling of 1-naphthols or other phenolic and alcoholic substrates with alkynes.
Abstract: The straightforward and efficient synthesis of naphtho[1,8-bc]pyran derivatives and related polycyclic compounds is achieved by the rhodium-catalyzed oxidative coupling of 1-naphthols or other phenolic and alcoholic substrates with alkynes. In these annulation reactions, the hydroxy groups effectively act as the key function for the regioselective CH bond cleavage.
142 citations
TL;DR: The authors show the electrocatalytic cross-coupling of phenols and indoles to generate biologically relevant benzofuroindolines in high yields.
Abstract: Intermolecular [3 + 2] annulation is one of the most straightforward approaches to construct five membered heterocycles However, it generally requires the use of functionalized substrates An ideal reaction approach is to achieve dehydrogenative [3 + 2] annulation under oxidant-free conditions Here we show an electrooxidative [3 + 2] annulation between phenols and N-acetylindoles under undivided electrolytic conditions Neither external chemical oxidants nor metal catalysts are required to facilitate the dehydrogenation processes This reaction protocol provides an environmentally friendly way for the selective synthesis of benzofuroindolines Various N-acetylindoles bearing different C-3 and C-2 substituents are suitable in this electrochemical transformation, furnishing corresponding benzofuroindolines in up to 99% yield Electrochemical oxidation provides a green alternative to the use of hazardous chemical oxidants and forcing conditions Here, the authors show the electrocatalytic cross-coupling of phenols and indoles to generate biologically relevant benzofuroindolines in high yields
142 citations