Stereodivergent Synthesis of 1,4-Dicarbonyl Compounds through Sulfonium Rearrangement: Mechanistic Investigation, Stereocontrolled Access to γ-Lactones and γ-Lactams, and Total Synthesis of Paraconic Acids

Although simple γ-lactones and γ-lactams have received considerable attention from the synthetic community, particularly due to their relevance in biological and medicinal contexts, stereoselective synthetic approaches to more densely substituted derivatives remain scarce. The in-depth study presented herein, showcasing a straightforward method for the stereocontrolled synthesis of γ-lactones and γ-lactams, builds on and considerably expands the stereodivergent synthesis of 1,4-dicarbonyl compounds by a ynamide/vinyl sulfoxide coupling. A full mechanistic and computational study of the rearrangement was conducted, uncovering the role of all of the reaction components and providing a rationale for stereoselection. The broad applicability of the developed tools to streamlining synthesis is demonstrated by concise enantioselective total syntheses of (+)-nephrosteranic acid, (+)-rocellaric acid, and (+)-nephromopsinic acid.

Expeditious access to cis-β-aryl, γ-alkyl disubstituted (±)-γ-butyrolactones via nickel-hydride catalysis

The 1,4-reduction of β- and γ-substituted butenolides using 5 mol% of NiCl2·6H2O and NaBH4 in MeOH for rapid access to cis-β,γ-disubstituted γ-butyrolactones is described. The reaction was selective for cis-products, which were obtained in good to excellent yields. This study showcased the influence of steric hindrance and angle strain on the diastereoselectivity outcome of conjugate reductions facilitated by in situ generated nickel-hydride.

Nickel Carbene-Mediated One-Carbon Homologative γ-Butyrolactonization

In this report, we present a highly efficient approach for the synthesis of β,γ-disubstituted γ-butyrolactone motifs. This newly developed strategy is based on the combination of a diastereoselective aldol and a nickel carbene-mediated γ-butyrolactonization and uses an effective intramolecular ring closure to rapidly access a range of functionalized chiral γ-butyrolactones. This single-step approach was applied to produce straightforward asymmetric syntheses of (-)-talaumidin methyl ether, (+)-veraguensin, and (+)-dubiusamine A and a formal synthesis of (+)-phaseolinic acid as one of the shortest syntheses disclosed to date.

The Cloke-Wilson rearrangement of aroyl-substituted donor-acceptor cylopropanes containing arylethyl donors

The chemistry of donor-acceptor (D-A) cyclopropanes containing alkyl donors has been scantily investigated. In the present work, we have synthesized new D-A cyclopropanes containing arylethyl donors and explored their reactivity in the presence of Lewis acids. Upon treatment with SnCl₄, these cyclopropanes underwent the Cloke-Wilson rearrangement to yield 3,4,5-trisubstituted γ-butyrolactones in good yields with high diastereoselectivity.

Phylogenetic Studies and Metabolite Analysis of Sticta Species from Colombia and Chile by Ultra-High Performance Liquid Chromatography-High Resolution-Q-Orbitrap-Mass Spectrometry

Eleven species of lichens of the genus Sticta, ten of which were collected in Colombia (S. pseudosylvatica S. luteocyphellata S. cf. andina S. cf. hypoglabra, S. cordillerana, S. cf. gyalocarpa S. leucoblepharis, S. parahumboldtii S. impressula, S. ocaniensis) and one collected in Chile (S. lineariloba), were analyzed for the first time using hyphenated liquid chromatography with high-resolution mass spectrometry. In the metabolomic analysis, a total of 189 peaks were tentatively detected; the analyses were divided in five (5) groups of compounds comprising lipids, small phenolic compounds, saturated acids, terpenes, and typical phenolic lichen compounds such as depsides, depsidones and anthraquinones. The metabolome profiles of these eleven species are important since some compounds were identified as chemical markers for the fast identification of Sticta lichens for the first time. Finally, the usefulness of chemical compounds in comparison to traditional morphological traits to the study of ancestor–descendant relationships in the genus was assessed. Chemical and morphological consensus trees were not consistent with each other and recovered different relationships between taxa.

Concise Stereoselective Synthesis of β-Hydroxy-γ-lactones: (4R,5R)-4-Hydroxy-γ-decalactone from the Japanese Orange Fly and Enantiomers of Arachnid Harvestmen Isolates

The naturally occurring (4R,5R)-4-hydroxy-γ-decalactone from the Japanese orange fly and the antipode of (4S,5R)-4-hydroxy-γ-dodecalactone from the harvestmen arachnid and their stereoisomers are synthesized from the chiral pool material d-glucono-δ-lactone in a few steps. The one-pot conversion of the latter to γ-vinyl-β-hydroxy-γ-lactone, cross-metathesis with requisite olefin, and hydrogenation enabled the synthesis of syn-lactones in just a two-pot operation. An additional efficient Pd-catalyzed allylic isomerization of γ-vinyl-β-hydroxy-γ-lactone led to the anti-lactones in high yields.

Synthesis of disubstituted γ-butyrolactones and spirocyclopropanes via a multicomponent reaction of aldehydes, Meldrum's acid and sulfoxonium ylides

An efficient synthesis of disubstituted γ-butyrolactones and spirocyclopropanes via multicomponent reaction of aldehydes, Meldrum's acid and sulfoxonium ylides has been developed.

An efficient enantioselective approach to multifunctionalized γ-butyrolactone: concise synthesis of (+)-nephrosteranic acid

A short, efficient and novel approach for multifunctionalized γ-butyrolactone paraconic acids and its application to the total synthesis of (+)-nephrosteranic acid from readily available PMB (R)-glycidyl ether as a starting material are described. Key transformations include asymmetric Michael addition catalyzed by chiral diphenylprolinol silyl ether and stereoselective α-methylation.

Stereoselective Sequential Spirocyclopropanation/Cloke-Wilson Rearrangement Reactions for Synthesis of trans-β,γ-Disubstituted γ-Butyrolactones Using Alkylidene Meldrum's Acid and Benzyl Halides

The stereoselective sequential spirocyclopropanation/Cloke-Wilson rearrangement reactions have been developed to synthesize γ-butyrolactones using alkylidene Meldrum's acids and benzyl halides. The DBU-promoted spirocyclopropanation was carried out efficiently at room temperature to generate trans-isomeric spirocyclopropyl Meldrum's acid, and the following stereospecific thermal decarboxylative Cloke-Wilson rearrangement afforded trans-γ-butyrolactones. A variety of aromatic and aliphatic Meldrum's acid derived olefins and benzyl halides were tolerated. Various trans-β,γ-disubstituted γ-butyrolactones were produced with moderate to good overall yields from 46 to 96% and excellent diastereoselectivities.

Asymmetric Multifunctional Modular Organocatalysis: One-Pot Direct Strategy to Enantiopure α,β-Disubstituted γ-Butyrolactones

A simple and efficient approach to enantioenriched α,β-disubstituted γ-butyrolactones has been developed through multifunctional modular organocatalysis in a highly enantioselective (>99% ee) and diastereoselective (>30:1) manner following a one-pot sequential Michael-hemiacetalization-oxidation reaction. The catalytic process has great substrate compatibility, and the products have been transformed to synthetically useful molecules. The methodology has also been applied to the formal synthesis of (+)-Pilocarpine.

Stereodivergent Synthesis of Chiral Paraconic Acids via Dynamic Kinetic Resolution of 3-Acylsuccinimides

A direct N-heterocyclic carbene (NHC) catalysis of maleimides with alkyl aldehydes is established for the synthesis of 3-acylsuccinimides. The first dynamic kinetic resolution of 3-acylsuccinimides is accomplished through asymmetric transfer hydrogenation. These two catalytic methodologies are utilized for the synthesis of each enantiomer of trans-paraconic acids in three steps and cis-paraconic acids in four steps with good yields and high stereoselectivities. This stereodivergent synthetic methodology is applied for the synthesis of seven bioactive paraconic acid natural products.