Transition‐metal free synthesis of 2‐pyrones by [3 + 3] annulation of cyclopropenones and sulfur ylides

Abstract

A simple and efficient synthesis for 2‐pyrones by [3 + 3] annulation of cyclopropenones and sulfur ylides in the presence of triethyl amine as a base has been developed featuring transition‐metal free conditions, high yields, and excellent functional group compatibility. Using this process, a variety of 2‐pyrones were prepared in good to excellent yields.

Base- and sulfur-promoted oxidative lactonization of chalcone-acetate Michael adducts: access to pyran-2-ones

“…6 Consequently, considerable efforts have been devoted to developing effective synthesis. Notable examples include the reaction of diarylcyclopropenones with sulfonium ylides, 7 sulfoxonium ylides, 8 sulfur ylides, 9 β-ketoethers, 10 α-bromoketones, 11 and α-ammoniumketones. 12 Along with the involvement of a strong base 9–11 or an expensive Rh catalyst, 8 the significant drawbacks of these methods are the use of diarylcyclopropenone substrates, which require multistep syntheses.…”

“…Notable examples include the reaction of diarylcyclopropenones with sulfonium ylides, 7 sulfoxonium ylides, 8 sulfur ylides, 9 β-ketoethers, 10 α-bromoketones, 11 and α-ammoniumketones. 12 Along with the involvement of a strong base 9–11 or an expensive Rh catalyst, 8 the significant drawbacks of these methods are the use of diarylcyclopropenone substrates, which require multistep syntheses. Moreover, control of regiochemistry for nonsymmetrical diarylcyclopropenone substrates remains an unsolved challenge.…”

Recyclable Polymer Supported DMAP Catalyzed Cascade Synthesis of α-Pyrones

“…43 Annulation reactions of cyclopropenones with either α-haloketones or activated sulfur ylides have been reported by several groups (Scheme 1d). 45,46 On the other hand, 5H-oxazol-4-one is one of the strategic C-center pronucleophiles and serves as a potential surrogate of α-hydroxy carboxylic acid. 51 Oxazolones have been extensively used in many asymmetric transformations yielding structurally diverse scaffolds.…”

“…Moreover, natural 2-pyrones exhibit a huge array of biological activities with enormous therapeutic significance, such as telomerase inhibitory, HIV protease inhibitory, anti-inflammatory, antifungal, antibacterial, antimicrobial, anti-influenza, neurotoxic, cytotoxic, and cardiotonic effects . In addition, they serve as important synthons for constructing complex molecules. , Considering the significant biological importance and synthetic potential of α-pyrones, development of efficient methods for such an ambitious framework has attracted much attention. , Synthetic strategies leading to 2-pyrones with metal catalyzed reactions include ring expansion, annulations, − cycloadditions, , C–H activations, , and coupling reactions. − Traditional approaches − on the organocatalytic pathways majorly rely on reactions of α-halocarbonyls through ammonium/sulfur ylides − and NHC. − Among representative recent findings, Tiwari and Chen groups independently disclosed carbene-catalyzed reaction of α-haloaldehydes (Scheme a–b). − Very recently, Jin and Zhang developed a base promoted cascade reactions of dithiomalonate/α-halothioester with β,γ-unsaturated α-keto esters (Scheme c) . Annulation reactions of cyclopropenones with either α-haloketones or activated sulfur ylides have been reported by several groups (Scheme d). , …”