Synthesis of Benzofuro[3,2-b]indol-3-one Derivatives via Dearomative (3 + 2) Cycloaddition of 2-Nitrobenzofurans and para-Quinamines

An efficient dearomative (3 + 2) cycloaddition of para-quinamines and 2-nitrobenzofurans has been developed. This reaction proceeds smoothly under mild conditions and affords a series of benzofuro[3,2-b]indol-3-one derivatives in good to excellent yields (up to 98%) with perfect diastereoselectivities (all cases > 20:1 dr). The scale-up synthesis and versatile derivatizations demonstrate the potential synthetic application of the protocol. A plausible reaction mechanism is also proposed to account for the observed reaction process. This work represents the first instance of the N-triggered dearomative (3 + 2) cycloaddition of 2-nitrobenzofurans.

Site-selective and stereoselective transformations on p-quinols & p-quinamines

The intermolecular transformation of simple substrates into highly functionalized scaffolds with multiple stereogenic centers is an attractive strategy in modern organic synthesis. Prochiral 2,5-cyclohexadienones, being stable and easily accessible, are privileged key building blocks for the synthesis of complex molecules and bioactive natural products. In particular, p-quinols and p-quinamines are important subclasses of cyclohexadienones, having both nucleophilic and electrophilic sites, and can undergo various intermolecular cascade annulations via formal cycloadditions and other transformations. This article highlights the recent developments of intermolecular transformations on p-quinols and p-quinamines along with plausible reaction mechanisms. We hope that this review will inspire the readers to explore the new potential applications of these unique prochiral molecules.

Synthesis of Benzofuran Derivates via a Gold-Catalyzed Claisen Rearrangement Cascade

A novel method toward a facile synthesis of diverse benzofuran derivates from easily obtained quinols and alkynyl esters has been reported. A gold-catalyzed intermolecular alkoxylation/Claisen rearrangement/condensation cascade was involved. The introduction of difluorodiphenylsilane as a water-trapping reagent in the reaction leads to a higher yield.

Highly Enantioselective Synthesis of [1,2,4]Triazino[5,4-a]isoquinoline Derivatives via (3 + 3) Cycloaddition Reactions of Diazo Compounds and Isoquinolinium Methylides

An array of chiral [1,2,4]triazino[5,4-a]isoquinoline derivatives were obtained in excellent yields (up to 98%) and with excellent enantioselectivities (up to 99% ee) via a new highly asymmetric (3 + 3) cycloaddition reaction of diazo compounds and isoquinolinium methylides, with a bifunctional chiral phase-transfer catalyst (PTC). Density functional theory calculations show that PTC has a bridge role in the deprotonation/protonation process. The obtained products were transformed into densely functionalized polycyclic heterocompounds with multiple stereocenters.

Rhodium-Catalyzed Azine-Directed C-H Amidation with N-Methoxyamides

Using N-methoxyamide reagents as an amide source, C-H amidation was realized at the ortho position of azine under the action of rhodium and boric acid. The method has mild reaction conditions, high atomic utilization, excellent yield, and wide adaptability to amidation reagents (both aromatic amides and fatty amides are applicable). Amide-substituted ketones can be obtained by a simple treatment and can be further transformed into bioactive substances. This provides a good supplement for the C-H bond amidation of aromatic rings.

Chiral Phosphoric Acid Catalyzed Asymmetric Desymmetrization of para-Quinamines with Isocyanates: Access to Functionalized Imidazolidin-2-one Derivatives

The development of enantioselective desymmetrization of para-quinamines with isocyanates catalyzed by chiral phosphoric acid is reported. The strategy provides concise access to functionalized imidazolidin-2-one derivatives in high yields and enantioselectivities under mild reaction conditions. Remarkably, this reaction could be performed on a gram scale using 5 mol % catalyst loading and the chiral imidazolidin-2-one derivatives could be easily transformed into valuable scaffolds without disturbing the enantiopurity, demonstrating the synthetic utility of this protocol.

[3 + 2] Cycloaddition of Nitrile Imines with Enamides: An Approach to Functionalized Pyrazolines and Pyrazoles

An efficient [3 + 2] cycloaddition of in situ generated nitrile imines with enamides has been established. A wide range of functionalized pyrazoline derivatives (53 examples) were obtained in moderate to good yields (up to 96%) under very mild conditions. This protocol features broad substrate scope, good functional group tolerance, and operational simplicity. Practical transformation of the products into useful pyrazoles via a one-pot process and the scalability of this protocol highlight the utility of this synthetic methodology.

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.