A novel phosphine-catalyzed, highly enantioselective umpolung addition of trifluoromethyl ketimines to Morita-Baylis-Hillman carbonates was developed and it provides facile access to optically active trifluoromethyl amines with a chiral tertiary stereocenter under mild reaction conditions. The salient features of this reaction include general substrate scope, mild reaction conditions, good yields, high enantioselectivity, ease of scale-up to gram scale, and further transformations of the products.
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http://dx.doi.org/10.1002/anie.201607918 | DOI Listing |
Chemistry
January 2025
Central University of Gujarat, School of Chemical Sciences, Sector 30, 382030, Gandhinagar, INDIA.
The selective synthesis of 4-alkyl/aryl-3H-1,2-dithiole-3-thione in THF and water-dependent switchable product ketothioamide is demonstrated. The presented method describes explicitly the synthesis of the extremely rare positional isomer 4-alkyl/aryl-3H-1,2-dithiole-3-thione, a unique structure distinct from another positional isomer, 5-alkyl/aryl-3H-1,2-dithiole-3-thione. The unique umpolung of the nitromethyl group is exploited for solvent selective nucleophilic sulfur and amine addition.
View Article and Find Full Text PDFPolarity reversal, or "umpolung", is a widely acknowledged strategy to allow organic functional groups amenable to react in alternative ways to the usual preference set by their electronic features. In this article, we demonstrate that cyclohexyne umpolung, realized through complexation to zirconocene, makes the small strained cycloalkyne amenable to C-F bond functionalisation. Such strong bond activation chemistry is unprecedented in "free" aryne and strained alkyne chemistry.
View Article and Find Full Text PDFJ Am Chem Soc
January 2025
Institute of Organic Chemistry, University of Leipzig, 04103 Leipzig, Germany.
The enantioselective synthesis of 1,4-dicarbonyl compounds continues to pose a significant challenge in organic synthesis, and a catalytic process which generates two adjacent stereogenic centers with full stereochemical control is lacking until now. The 1,4-relationship of the functional groups requires an Umpolung strategy as one of the α-carbonyl positions has to be inverted into an electrophilic center to react with a normal enolate. We report herein the highly enantio- and diastereoselective addition of silyl ketene acetals toward electrophilic 1-azaallyl cations to furnish chiral 4-hydrazonoesters, which are masked 1,4-dicarbonyl compounds.
View Article and Find Full Text PDFChem Rec
December 2024
School of Pharmacy and Food Engineering, Wuyi University, Jiangmen, 529020, China.
N-heterocyclic carbene (NHC) organocatalysis has been developed as a powerful tool in modern synthetic chemistry. NHC catalytic activation of ynals and alkynoic acid derivatives provided versatile reactions that involve acetylenic Breslow and/or acylazolium as key intermediates, and diverse transformations have been established for access to molecules with unique skeletons in efficient fashions. Herein we summarize the recent achievements in NHC-catalyzed reactions involving acetylenic Breslow and/or acylazolium intermediates.
View Article and Find Full Text PDFAngew Chem Int Ed Engl
January 2025
Department of Organic Chemistry, Indian Institute of Science, Bangalore, 560012, India.
The umpolung of aldimines using N-heterocyclic carbenes (NHCs) is less explored compared to the established polarity reversal of aldehydes. Described herein is an NHC-catalyzed imine umpolung /6π-electrocyclization cascade, which leads to the atom- and pot-economic synthesis of biologically important dihydrochromeno indoles. For the first time, the nucleophilic aza-Breslow intermediates have been intercepted with unactivated alkynes.
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