The aldol reaction using aldehyde-derived silyl enolates as nucleophiles with aromatic aldehydes chemoselectively proceeded in the presence of silyl triflate and 2,2'-bipyridyl to produce β-siloxy aldehydes, while the aliphatic aldehydes were completely recovered. The unprecedented chemoselectivities depend on the reactivities of the pyridinium-type intermediates derived from the aromatic and aliphatic aldehydes.
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Oxygenated Cyclopentenones via the Pauson-Khand Reaction of Silyl Enol Ether Substrates.
Org Lett
April 2022
Department of Pure and Applied Chemistry, University of Strathclyde, 295 Cathedral Street, Glasgow G1 1XL, Scotland, U.K.
We report here the application of silyl enol ether moieties as efficient alkene coupling partners within cobalt-mediated intramolecular Pauson-Khand reactions. This cyclization strategy delivers synthetically valuable oxygenated cyclopentenone products in yields of ≤93% from both ketone- and aldehyde-derived silyl enol ethers, incorporates both terminal and internal alkyne partners, and delivers a variety of decorated systems, including more complex tricyclic structures. Facile removal of the silyl protecting group reveals oxygenated sites for potential further elaboration.
View Article and Find Full Text PDFRhodium-Catalyzed β-Dehydroborylation of Silyl Enol Ethers: Access to Highly Functionalized Enolates.
Org Lett
December 2021
State Key Laboratory of Chemo/Biosensing and Chemometrics, Advanced Catalytic Engineering Research Center of the Ministry of Education, College of Chemistry and Chemical Engineering, Hunan University, Changsha, Hunan 410082, P. R. China.
An efficient rhodium-catalyzed β-dehydroborylation of aldehyde-derived silyl enol ethers (SEEs) with bis(pinacolato)diboron (Bpin) is disclosed. The borylation reactions proceeded well with alkyl- and aryl-substituted SEEs, affording a wide array of valuable functionalized β-boryl silyl enolates with high efficiency and excellent stereoselectivity. Moreover, the borylated products, through versatile carbon-boron bond transformations, were readily converted into diverse synthetically useful molecules, including α-hydroxy ketones, functionalized SEEs, and -difunctionalized aldehydes.
View Article and Find Full Text PDFMetal-Free Hydrosilylation of Ketenes with Silicon Electrophiles: Access to Fully Substituted Aldehyde-Derived Silyl Enol Ethers.
Chemistry
June 2021
Institut für Chemie, Technische Universität Berlin, Straße des 17. Juni 115, 10623, Berlin, Germany.
Little-explored hydrosilylation of ketenes promoted by main-group catalysts is reported. The boron Lewis acid tris(pentafluorophenyl)borane accelerates the slow uncatalyzed reaction of ketenes and hydrosilanes, thereby providing a convenient access to the new class of β,β-di- and β-monoaryl-substituted aldehyde-derived silyl enol ethers. Yields are moderate to high, and Z configuration is preferred.
View Article and Find Full Text PDFStereoselective Sc(OTf) -Catalyzed Aldol Reactions of Disubstituted Silyl Enol Ethers of Aldehydes with Acetals.
Angew Chem Int Ed Engl
June 2021
Schulich Faculty of Chemistry, Technion-, Israel Institute of Technology, Technion City, Haifa, 3200009, Israel.
Facile and modular access to stereodefined disubstituted aldehyde-derived silyl enol ethers allowed their successful application in a stereoselective aldol reaction affording the products with excellent yields and diastereomeric ratios. The counter-intuitive stereochemical behavior of this Mukaiyama-aldol reaction is accounted for by a non-classical open transition state.
View Article and Find Full Text PDFStereoselective Access to Fully Substituted Aldehyde-Derived Silyl Enol Ethers by Iridium-Catalyzed Alkene Isomerization.
Angew Chem Int Ed Engl
September 2020
Schulich Faculty of Chemistry, Technion-Israel Institute of Technology, Technion City, Haifa, 3200009, Israel.
An in situ generated cationic Ir-catalyst isomerizes simple allylic silyl ethers into valuable, fully substituted aldehyde-derived silyl enol ethers. Importantly, by judicious choice of substrate, either of the two possible stereoisomers of a given enolate derivative is accessible with complete stereoselectivity. One-pot isomerization-aldol and isomerization-allylation processes illustrate the synthetic utility of this method.
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