Pd-catalyzed diastereoselective allylation of aldehydes with 3-bromomethyl-5H-furan-2-one: stereoselective synthesis of β-(hydroxymethylaryl/alkyl)-α-methylene-γ-butyrolactones with a syn configuration

Diastereoselective allylation-based asymmetric total synthesis of 1,10-seco-guaianolides

A Cr(II)-mediated Nozaki-Hiyama allylation of aldehydes with functionalized chiral allylbromolactone paved the way to easily access β-hydroxy-aryl/alkyl-α-methylene-γ-butyrolactones in good yields with high diastereoselectivities. A subsequent undemanding translactonization was orchestrated in the efficient first asymmetric total synthesis of two 1,10-seco-guaianolides as a valuable extension of the strategy developed.

Synthesis of α-exo-Methylene-γ-butyrolactones: Recent Developments and Applications in Natural Product Synthesis

The α-exo-methylene-γ-butyrolactone moiety is present in a vast array of structurally diverse natural products and is often central to their biological activity. In this short review, we summarize new approaches to α-exo-methylene-γ-butyrolactones developed over the past decade as well as their applications in total synthesis.

1 Introduction

2 Approaches to α-exo-Methylene-γ-butyrolactones

2.1 Enantioselective Synthesis via Lactonization Approaches

2.2 Enantioselective Halolactonizations

2.3 Enantioselective Barbier-Type Allylation

2.4 C–H Insertion/Olefination Sequences

2.5 Alkene Cyclization

2.6 Strain-Driven Dyotropic Rearrangement

3 β-(Hydroxymethylalkyl)-α-exo-methylene-γ-butyrolactones

4 Applications in Total Synthesis

4.1 Sesquiterpene Lactones

4.2 Lignans

4.3 Other Monocyclic Natural Products

4.4 Choice of Methodology in Recent Total Syntheses

5 Summary and Outlook

Total Syntheses of Paraconic Acids and 1,10-seco-Guaianolides via a Barbier Allylation/Translactonization Cascade of 3-(Bromomethyl)-2(5H)-furanone

A palladium-catalyzed Barbier allylation/translactonization cascade reaction was established for the rapid construction of β,γ-disubstituted α-exo-methylene-γ-butyrolactone, an important motif in sesquiterpenes. Dimethyl zinc played significant roles in both steps for the umpolung of π-allylpalladium as a nucleophile and promoting a Lewis acid-mediated translactonization. This sequence showed a broad substrate scope and was further harnessed for the synthesis of two paraconic acids as well as the first protecting-group-free total synthesis of two 1,10-seco-guaianolides.

Selective synthesis of mono- and bis-butenolide α-aminomethyl adducts

The selective installation of α-methylamine residues at the butenolide core is described using α-bromomethylene-γ-butenolide and primary as well as secondary amines in methanol at 0 °C. The preparation of mono- and bis-butenolide α-adducts is described. Bis-γ-butenolide adducts as well as mono α-aminomethyl-γ-butenolides can be selectively obtained depending on the nature of the reacting primary amine. In contrast, the use of secondary amines allows two different pathways leading either to the expected amino derivatives or to the formation of a C-O bond.

Divergent synthesis and identification of the cellular targets of deoxyelephantopins

Herbal extracts containing sesquiterpene lactones have been extensively used in traditional medicine and are known to be rich in α,β-unsaturated functionalities that can covalently engage target proteins. Here we report synthetic methodologies to access analogues of deoxyelephantopin, a sesquiterpene lactone with anticancer properties. Using alkyne-tagged cellular probes and quantitative proteomics analysis, we identified several cellular targets of deoxyelephantopin. We further demonstrate that deoxyelephantopin antagonizes PPARγ activity in situ via covalent engagement of a cysteine residue in the zinc-finger motif of this nuclear receptor.

Deoxyelephantopin is a naturally occurring sesquiterpene lactone with known anticancer properties. Here, the authors synthesize deoxyelephantopins and a range of analogues including alkyne-tagged probes, using them to identify its cellular targets.

A novel visible light mediated radical cyclization of enol lactones: a concise method for fluorinated polycyclic lactone scaffolds

A novel visible light mediated cyclization of enol lactones with difluoroacyl arenes via a free radical tandem difluoroalkylation and C–C coupling of butenolides is presented. This strategy provides a facile approach to potential biological fluorinated γ-butyrolactones with excellent diastereoselectivity.

Diastereoselection during 1,2-addition of 3-bromomethyl-5H-furan-2-one to α-chiral aldehydes mediated by indium in aqueous and organic solvent systems: direct route to obtain optically active α-methylene-γ-butyrolactones

High chelation control or Felkin–Ahn selective allylic addition of2to α-hydroxyaldehydes or α-rigid aldehydes mediated by indium.

Asymmetric Synthesis of β-Substituted α-Methylenebutyro- lactones via TRIP-Catalyzed Allylation: Mechanistic Studies and Application to the Synthesis of (S)-(-)-Hydroxymatairesinol

Asymmetric allylation of (hetero)aromatic aldehydes by a zinc(II)-allylbutyrolactone species catalyzed by a chiral BINOL-type phosphoric acid gave β-substituted α-methylenebutyrolactones in 68 to >99% ee and 52-91% isolated yield. DFT studies on the intermediate Zn2+-complex - crucial for chiral induction - suggest a six-membered ring intermediate, which allows the phosphoric acid moiety to activate the aldehyde. The methodology was applied to the synthesis of the antitumour natural product (S)-(-)-hydroxymatairesinol.