Metal‐Free Formal Oxidative C−C Coupling by In Situ Generation of an Enolonium Species

Abstract

Much contemporary organic synthesis relies on transformations that are driven by the intrinsic, so-called "natural", polarity of chemical bonds and reactive centers. The design of unconventionally polarized synthons is a highly desirable strategy, as it generally enables unprecedented retrosynthetic disconnections for the synthesis of complex substances. Whereas the umpolung of carbonyl centers is a well-known strategy, polarity reversal at the α-position of a carbonyl group is much rarer. Herein, we report the design of a novel electrophilic enolonium species and its application in efficient and chemoselective, metal-free oxidative C-C coupling.

Organocatalytic Oxidative Functionalizations of Alkynes

“…This could be trapped with N‐ benzoylhydroxylamine 31 into XV , then subsequent [3,3]‐sigmatropic rearrangement afforded 32 with α‐aryl group bearing a 2‐amino group . Alternatively, the keteniminium ion could be trapped with 2,6‐lutidine‐ N ‐oxides into XVI , then intramolecular attack of N‐ benzyl group occurred to afford 34 . Some anionic nucleophiles were found to be compatible with this reaction conditions .…”

Synthesis of N-Alkylpyridin-4-ones and Thiazolo[3,2-A]pyridin-5-ones Through Pummerer-Type Reactions

“…Proposed reaction mechanisms for either normal or interrupted Pummerer reaction between 4-fluoropyridines with activated sulfoxides are shown in Scheme 5, which are essentially the same as our previous report for the synthesis of N-alkylpyridin-2-ones from 2-fluoropyridines. [35] It should be noted that, due to their low nucleophilicity, 2fluoropyridine [53][54][55][56][57][58] and 2-chloropyridine [59][60][61][62][63] were widely used as acid scavengers in reactions involving triflic anhydride activation of sulfoxides or amides. Therefore, our use of electron-deficient pyridines as nucleophiles in Pummerer-type reactions is still very rare.…”

Mechanistic Pathways in Amide Activation: Flexible Synthesis of Oxazoles and Imidazoles

“…14 Therein, the formation of a latent electrophilic enolonium species ( I ) enabled intramolecular nucleophilic attack on the α-position of a selectively activated amide, generating tetrahydroisoquinolinones.…”