Umpolung Reaction Research Articles

Carbonyl Umpolung Reactivity of Enals: NHC-Catalyzed Synthesis of Aldol Products via Epoxide Ring Opening

A novel one-pot N-heterocyclic carbene catalyzed synthesis of aldol products and their application to a facile and highly cis-selective synthesis of tetrahydropyran-4-ones is reported. The protocol involves carbonyl umpolung reactivity of enals in which the carbonyl carbon attacks nucleophilically on electrophilic terminal epoxides, regioselectively, to afford aldol adducts in good to excellent yields.

ChemInform Abstract: Titanium and Zirconium Mediated or Catalyzed Umpolung Reactions

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

N-Heterocyclic Carbene-Catalyzed Cross-Coupling of Aldehydes with Arylsulfonyl Indoles

3-(1-Arylsulfonylalkyl)indoles as electrophiles in the N-heterocyclic carbene-catalyzed umpolung reaction of aldehydes were realized for the first time. This intermolecular Stetter-type reaction features the commercially available catalyst and mild reaction conditions, providing alpha-(3-indolyl) ketone derivatives in high yields for a wide range of substrates.

Intramolecular Anodic Olefin Coupling Reactions: Using Radical Cation Intermediates to Trigger New Umpolung Reactions

Anodic electrochemistry is a powerful tool for generating radical cation intermediates and initiating new cyclization reactions. Like most electrochemical reactions, the transformations involve umpolungs. In this review, recent studies examining the intramolecular coupling of radical cations derived from enol ethers, vinyl sulfides, and ketene acetals with carbon, oxygen, and nitrogen trapping groups are discussed to highlight their synthetic potential.

Stereoselective Synthesis of Amphidinolide T1

A highly stereoselective total synthesis of amphidinolide T1 is achieved using Sharpless asymmetric epoxidation, base-induced epoxide opening, radical cyclization, diastereoselective reduction followed by allylation, Evans methylation, base-induced reductive elimination, umpolung reaction, chemoselective oxidation, and regioselective macrolactonization.

Understanding the mechanism of the N-heterocyclic carbene-catalyzed ring-expansion of 4-formyl-β-lactams to succinimide derivatives

The mechanism of the N-heterocyclic carbene (NHC)-catalyzed ring-expansion of 4-formyl-β-lactams to succinimides has been studied using DFT methods at the B3LYP/6-31G ∗∗ level. The first step is the nucleophilic attack of NHC to the aldehyde to yield the zwitterionic intermediate, which by a proton-transfer process affords the Breslow intermediate. The lactam N–C breaking bond in this intermediate yields an enol-amidate, which by a keto–enol type equilibrium becomes the ketone form. The subsequent ring-closure achieved by the nucleophilic attack of the amidate to carbonyl carbon allows the formation of the five-membered ring. Finally, elimination of NHC affords the succinimide. Analysis of the nucleophilicity index correctly explains the behaviors of the NHCs and the Breslow intermediates in the umpolung reactivity of aldehydes.

Umpolung of halide reactivity: efficient (diacetoxyiodo)benzene-mediated electrophilic α-halogenation of 1,3-dicarbonyl compounds

An efficient high-yielding (diacetoxyiodo)benzene-mediated alpha-halogenation of 1,3-dicarbonyl compounds utilising titanium tetrahalides as the halide source has been developed.

Titanium and Zirconium Mediated or Catalyzed Umpolung Reactions

Titanium and Zirconium Mediated or Catalyzed Umpolung Reactions

Umpolung Reactivity of Difluoroenol Silyl Ethers with Amines and Amino Alcohols. Application to the Synthesis of Enantiopure α-Difluoromethyl Amines and Amino Acids

Difluoroenol silyl ethers, produced in situ from acylsilanes and CF3TMS, react as electrophiles with amines to give difluoroimines, via the corresponding hemiaminal adduct, as evidenced by 19F NMR spectroscopy. Reaction with (R)-phenylglycinol led to 2-difluoromethyloxazolidines. After separation of the diastereomers, reduction with LAH and Strecker-type synthesis gave enantiopure alpha-difluoromethylamines and alpha-difluoromethyl-alpha-amino acids, respectively.

Electrochemistry and Umpolung Reactions: New Tools for Solving Synthetic Challenges of Structure and Location

Electrochemistry is a powerful tool for initiating new umpolung reactions. In this paper, two examples are provided. One demonstrates the use of electrochemistry for reversing the polarity of known functional groups and triggering carbon-carbon bond formation. The second demonstrates the use of electrochemistry for reversing the polarity of a chemical reagent, a technique that allows for spatially locating synthetic transformations on addressable chips.

Efficient, Two‐Step Synthesis of N‐Substituted Nortropinone Derivatives.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.

Stereospecific Side Chain Activation in Cyclobutadiene–Fe(CO)3 Chemistry: A Theoretical and Experimental Study on the Structure and Configurational Stability of Cationic, Radical and Anionic Intermediates

AbstractThe configurational stability of reactive intermediates (cation, radical and anion) derived from ethylcyclobutadiene–Fe(CO)3 by formal abstraction of a hydride, a hydrogen atom or a proton from the pseudobenzylic position was investigated. Density functional calculations (Becke3lyp) predicted that all these reactive intermediates can be regarded as planar chiral structures having a significant configurational stability. The racemization barriers were calculated to be 38.8 kcal mol–1 for the cationic, 16.9 kcal mol–1 for the radical and 44.8 kcal mol–1 for the anionic intermediate. In an experimental part of the study, derivatives of the 1‐hydroxyethyl‐substituted complex, which was enantioselectively prepared by CBS reduction of the acetyl complex, were subjected to SN1‐type as well as single‐electron‐transfer‐driven umpolung reactions. The observed stereospecificity of these transformations (retention of configuration) is in accordance with the predicted configurational stability of the involved reactive intermediates. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)

Cover Picture: Exploration of meso‐Substituted Formylporphyrins and Their Grignard and Wittig Reactions (Eur. J. Org. Chem. 23/2007)

AbstractThe cover picture shows the synthesis of formylporphyrins by Umpolung reactions that use 1,3‐dithian‐2‐ylporphyrins as masked synthons. This method offers a new pathway for the preparation of free‐base and metallo formylporphyrins under mild conditions. Grignard and Wittig reactions have been performed to demonstrate the wide range of applications for formylporphyrins. Details are discussed in the article by M. O. Senge et al. on p. 3833 ff.

Efficient, two-step synthesis of N-substituted nortropinone derivatives

We describe a novel strategy for the synthesis of N-substituted nortropinone derivatives starting from tropinone. The key step of our synthesis is a reactivity umpolung of tropinone, which yields 8,8-dimethyl-3-oxo-8-azonia-bicyclo[3.2.1]octane iodide (IDABO) as a stable and convenient synthetic equivalent of cycloheptadienone.

Synthesis of 3‐Alkylcoumarins from Salicylaldehydes and α,β‐Unsaturated Aldehydes Utilizing Nucleophilic Carbenes: A New Umpoled Domino Reaction

AbstractStarting from salicylaldehydes and α,β‐unsaturated aldehydes, a new coumarin synthesis in ionic liquids is presented. The key feature is the generation of N‐heterocyclic carbenes (NHC) and an Umpolung reaction. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)

Investigating organocatalytic reactions: mass spectrometric studies of a conjugate umpolung reaction

An organocatalyzed conjugate umpolung reaction has been studied in detail using electrospray mass spectrometry, which allows to support the catalytic cycle by intercepting intermediates.

Umpolung Reactivity of Alkenyl Fischer Carbene Complexes, Copper Enolates, and Electrophiles.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.

Recent Advances in Aryl C‐Glycoside Synthesis

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.

Umpolung Reactivity of Alkenyl Fischer Carbene Complexes, Copper Enolates, and Electrophiles

Umpolung Reactivity of Alkenyl Fischer Carbene Complexes, Copper Enolates, and Electrophiles

Umpolung Reactivity of Alkenyl Fischer Carbene Complexes, Copper Enolates, and Electrophiles

Copper makes the difference: An umpolung reactivity of Michael acceptors is observed when alkenyl carbene complexes react with copper ketone enolates and electrophiles. This reaction allows the straightforward synthesis of functionalized three-component coupling products in a completely regio- and diastereoselective way.