Asymmetric Synthesis of Spiro β-Lactamsviaa Squaramide- Catalyzed Sulfa-Michael Addition/Desymmetrization Protocol

Organocatalytic Desymmetric Spirocyclization of Enone-Tethered 2,5-Cyclohexadienone with Isoxazolines to Access Enantioenriched Spiro-Fused Scaffolds

Enantioselective desymmetric spirocyclization is a powerful tool for concisely generating intricate 3D molecular architectures from readily accessible substrates. Herein, we report an organocatalytic desymmetric spirocyclization of enone-tethered 2,5-cyclohexadienone with 3-arylisoxazol-5(4H)-one to access enantioenriched spiro-fused scaffolds featuring four consecutive stereogenic centers in high yields and excellent diastereo- and enantioselectivities. This protocol could proceed smoothly under parts per million-level organocatalyst loading. Furthermore, the reusability of the catalyst and various intriguing derivatizations of the title product highlight its synthetic utility.

NbCl5-catalyzed sulfa-Michael addition for constructing quaternary centers in enones

A novel NbCl5-catalyzed sulfa-conjugate addition has been developed to construct quaternary centers in various enones. This new method enables a range of functionalized thiols to access different β-sulfido carbonyl compounds bearing a quaternary center. 27 novel β-sulfido ketones have been obtained with moderate to excellent yields. The preparative scale reactions also proceed well, showing no decrease in yield. We further studied the mechanism by DFT calculations. This methodology is significant in sulfur chemistry, especially in sulfa-conjugate addition, giving a new pathway to add thiols to tri-substituted enones.

Asymmetric synthesis of spirocyclic isobenzofuranones via a squaramide-catalysed sulfa-Michael desymmetrisation reaction

Enantioselective synthesis of spirocyclohexenone isobenzofuranones has been achieved through an organocatalysed sulfa-Michael desymmetrisation reaction. A cinchona-derived squaramide effectively promotes the desymmetrisation of spirocyclic 2,5-cyclohexadienone isobenzofuranones via the controlled addition of various aryl thiols to generate two vicinal stereocenters with perfect diastereoselectivities and up to very good enantioselectivities.

NBS-mediated elimination of β-keto sulfides to access enones and dienones

A novel transformation of β-keto sulfides into enones has been developed. The new method facilitates an NBS-mediated elimination of sulfides to access both enones and dienones. 22 enone products were obtained in moderate to high yields. 4 different dienones were also prepared in 73%-93% yields. 7 different alkylthio motifs have been removed efficiently from β-keto sulfides. We also found that our transformation proceeds well in gram-scale reactions showing no decrease in yield. This methodology is significant in the research and application of sulfides, giving a new pathway to transform β-keto sulfides into enones.

Silver-Catalyzed Asymmetric Desymmetrization of Cyclohexadienones via Van Leusen Pyrrole Synthesis

A catalytic asymmetric desymmetrization of cyclohexadienones was accomplished via Van Leusen pyrrole synthesis in the presence of a chiral silver catalyst. The ready access to chiral-fused pyrrole derivatives is attributed to the identification of a suitable isocyanomethyl sulfone surrogate, NasMIC. The current Ag(I)-chiral phosphino-carboamide ligand system can be extended to the kinetic resolution of racemic cyclohexadienones, capitalizing on the differentiated reactivity of chiral quaternary complexes from AgSbF₆, chiral ligand (L*), cyclohexadienone, and NasMIC.

Recent advances in the asymmetric transformations of achiral cyclohexadienones

This review describes recent developments in the asymmetric transformations of achiral cyclohexadienones, including enantioselective desymmetrization of prochiral cyclohexadienones and kinetic resolution of racemic cyclohexadienones.

Synthesis of β- and γ-lactam fused dihydropyrazinones from Ugi adducts via a sequential ring construction strategy

A modular approach for the construction of β- and γ-lactam fused dihydropyrazinones from the readily available Ugi adducts has been described. The sequential construction of rings through base-mediated cycloisomerization followed by acid-mediated cyclization yielded β-lactam fused dihydropyrazinones. However, the Ugi-derived dihydropyrazinones afforded γ-lactam fused dihydropyrazinones under base-mediated cycloisomerization. The regioselectivity in the cycloisomerization reactions is explained on the basis of ring-strain. Substrate scope, limitations and mechanistic investigations through DFT-calculations have been explored.

Synthesis of Spiro-β-lactam-pyrroloquinolines as Fused Heterocyclic Scaffolds through Post-transformation Reactions

A sequential post-transformation of Ugi four-component reaction/nucleophilic substitution was developed for the synthesis of spiro-β-lactam-pyrroloquinolines. This method involves the Ugi-4CR of 2-chloro-3-formyl quinolines 1a-h, amines 2a-d, 2-chloroacetic acid 3, and isocyanides 4a, 4b for the synthesis of versatile precursors 5a-v. The Ugi adducts were intramolecularly cyclized under basic conditions through the sequential nucleophilic aromatic substitution (S_NAr)/second-order nucleophilic substitution (S_N2) reaction to give spiro-β-lactam-pyrroloquinoline scaffolds 6a-t. This approach is an efficient method for the synthesis of fused bioactive heterocyclic backbones containing quinoline, pyrrolidone, and β-lactam with high bond-forming efficiency.

Stereocontrolled transformations of cyclohexadienone derivatives to access stereochemically rich and natural product-inspired architectures

The last two decades or so have witnessed an upsurge in defining the art of designing complex natural products and nature-inspired molecules. Throughout these decades, fundamental insights into stereocontrolled, step-economic and atom-economical synthesis principles were achieved by the numerous synthetic accomplishments particularly in diversity-oriented synthesis (DOS). This has empowered the visualization of the third dimension in synthetic design and thus has resulted in a dramatic increase with today's diversity-oriented synthesis (DOS) at the forefront enabling access to diverse scaffolds with a high degree of stereochemical and skeletal complexity. To this end, a starting material-based approach is one of the powerful tools utilized in DOS that allows rapid access to molecular architectures with a high sp3 content. Skeletal and stereochemical diversity is often paramount for the selective modulation of the biological function of a complementary protein in the biological space. In this context, stereocontrolled transformation of cyclohexadienone scaffolds has positioned itself as a powerful platform for the rapid generation of stereochemically enriched and natural product-inspired compound collections. In this review, we cover multidirectional synthetic strategies that utilized cyclohexadienone derivatives as pluripotent building blocks en route for the construction of novel chemical space.

Enantioselective synthesis of 3-amino-hydrobenzofuran-2,5-diones via Cu(i)-catalyzed intramolecular conjugate addition of imino esters

The copper-catalyzed enantioselective intramolecular conjugate addition of imino esters for desymmetrization of cyclohexadienones was described, providing access to enantioenriched 3-amino-hydrobenzofuran-2,5-diones.

New development in the enantioselective synthesis of spiro compounds

In this review we summarize the latest developments in the enantioselective synthesis of spirocompounds. The most important organometallic and organocatalytic methodologies are highlighted.

Recent advances in β-lactam synthesis

During the past century, β-lactams have been identified as the core of penicillin and since then several strategies have been developed for their synthesis.

Organocatalytic enantioselective construction of isatin-derived N-alkoxycarbonyl 1,3-aminonaphthols via sterically encumbered hydrocarbon-substituted quinine-based squaramide

2-Adamantyl substituted quinine-squaramide catalyzed aza-Friedel–Crafts reaction of N-carbamate isatin ketimines with naphthol afforded chiral isatin-derived 1,3-aminonaphthols with excellent enantioselectivity up to greater than 99% and quantitative yield.