Metallfreie formale oxidative C‐C‐Kupplung durch In‐situ‐Erzeugung einer elektrophilen Enoloniumspezies

Abstract

Viele moderne organische Synthesen nutzen die intrinsische, natürliche Polarität der chemischen Bindungen und reaktiven Zentren der Substrate. Die Entwicklung unkonventionell polarisierter Synthone ist daher eine wünschenswerte Strategie, weil somit neuartige retrosynthetische Schritte in der Synthese komplexer Strukturen zugänglich gemacht werden können. Während die Umpolung von Carbonylzentren eine gängige Strategie ist, finden sich in der Literatur nur wenige Berichte über die Polaritätsumkehr der α‐Position von Carbonylen. Wir stellen hier die Entwicklung einer neuen elektrophilen Enoloniumspezies und ihre Anwendung in der chemoselektiven, metallfreien oxidativen C‐C‐Kupplung vor.

Efficient One‐Pot Multifunctionalization of Alkynes en Route to α‐Alkoxyketones, α‐Thioketones, and α‐Thio Thioketals by using an Umpolung Strategy

“…Other functional groups,s uch as amide, hydroxyl, ester and sulfonyl,a re compatible with the transformationa nd the correspondingp roducts were obtained with good yields (16)(17)(18)(19)(20)(21). Pleasingly,a sr evealed in Ta ble 2, we found ab road range of alkynes possessing various functional groups readilyp articipate in this two-steps one-pot reactionw ith moderate to excellent yields.…”

“…[10] Hashmi reported earlier that the N-alkenoxypyridinium intermediates generated from protonation of electron-rich phenoxyethynes were likewise electrophilic. [12][13][14][15][16] We believe that the N-alkenoxypyridiniums alts that show unconventional umpolung activity should be distinctive building blocks for other important chemicalt ransformations. [12][13][14][15][16] We believe that the N-alkenoxypyridiniums alts that show unconventional umpolung activity should be distinctive building blocks for other important chemicalt ransformations.…”

Triflic Anhydride (Tf2O)-Activated Transformations of Amides, Sulfoxides and Phosphorus Oxides via Nucleophilic Trapping

“…In their first disclosure of amide umpolung chemistry, they reported a conceptually new strategy that achieved polarity inversion at the α-position of N-benzyl amides 37a for the synthesis of 1,4-dihydroisoquinolin-3(2H)-ones (indolin-2-ones) 37b employing Tf2O and 2,6-lutidine-N-oxide (LNO) (Scheme 37). 69 This approach judiciously utilized an aryl group of the N-benzyl amide motif on 37a as a second nucleophile resulting in an intramolecular formal oxidative C-C coupling reaction under metal-free conditions. This method allowed various linear and branched amides to form the desired products 37c-37f via C-C coupling reaction; it also tolerated different functional groups such as ketones, esters, nitriles, alkenes, sulfonamides, and halides.…”

Highlights from the 53rd EUCHEM conference on stereochemistry, Bürgenstock, Switzerland, May 2018

“…"The sulfoxide is activated faster than you can say Ilan Marek" Nuno Maulide The second talk before lunch titled "The simplicity of rearrangements: sulfur and other heteroatoms" was delivered by Prof. Nuno Maulide (University of Vienna) who introduced variations on the theme of umpolung, or polarity reversal, not at a carbonyl carbon, but rather α to it. 7 Prof. Maulide started with the activation of amides with N-oxides to generate an enolonium equivalent. 8 He then described the perceptive study his group carried out, which allowed them to harness this discrete electrophile to develop a unique route to 1,4-dicarbonyl compounds.…”