Highly Stereoselective Assembly of Polycyclic Molecules from 1,6-Enynes Triggered by Rhodium(III)-Catalyzed C–H Activation

Catalyst-Controlled Diastereoselective Synthesis of Bridged [3.3.1] Bis(Indolyl)-Oxanes and Oxepanes via Desymmetrization of Bis(Indolyl)-Cyclohexadienones

A catalyst-controlled divergent synthesis of bridged [3.3.1] bis(indolyl)-oxanes and cis-[6.7] fused bis(indolyl) oxepanes via diastereoselective desymmetrization of bis(indolyl)-cyclohexadienones is presented for the first time. The reaction is highly atom- and step-economic, furnishing sp³-rich functionalized bis(indolyl) derivatives in good to excellent yields with wide substrate scope. The reaction proceeds through Friedel-Crafts alkylation followed by catalyst-controlled selective C-C bond formation/rearrangement. Gram scale synthesis and synthetic utility to generate bis(indolyl) alkaloid-like molecular diversity were also illustrated.

Catalytic Friedel-Crafts Alkylative Desymmetrization of Cyclohexa-2,5-dienones: Access to Linear and Bridged Polycyclic Pyrroles and 3-Arylpyrroles

A catalytic [3 + 2]-cycloaddition/Friedel-Crafts alkylative desymmetrization strategy has been developed for the stereoselective construction of linear and bridged polycyclic pyrroles from alkynylcyclohexa-2,5-dienones. This strategy was further explored for the synthesis of 3-arylpyrroles under Brønsted acid catalysis. Reaction is highly chemo-, regio-, and stereoselective and is compatible with wide range of functionalized cyclohexa-2,5-dienones/pyrroles (>51 examples, ≤98% yields). Gram-scale synthesis and synthetic utility of the products have also been demonstrated to showcase the robustness of present method.

Rapid Construction of Hexacyclic Indolines via the Ru(II)-Catalyzed C-H Activation Initiated Cascade Cyclization of Phenidones with Enynones

A highly efficient cascade cyclization of phenidones and enynones has been developed via a Ru(II)-catalyzed C-H activation initiated indole formation/Diels-Alder reaction/iminium ion cyclization sequence, which afforded hexacyclic indolines as single diastereomer in good to excellent yields with a broad substrate scope under mild conditions. The reaction features the simultaneous generation of five new chemical bonds and four new rings in one pot, providing a rapid and concise approach toward polycyclic indoline alkaloids and their analogues.

Synthesis of Indole-Fused Oxepines via C-H Activation Initiated Diastereoselective [5 + 2] Annulation of Indoles with 1,6-Enynes

A rhodium-catalyzed diastereoselective formal [5 + 2] annulation of indoles with cyclohexadienone-containing 1,6-enynes has been established via indole 2,3-difunctionalization. The reaction, probably proceeding through tandem indole C2-H alkenylation and intramolecular Friedel-Crafts alkylation relay, provides rapid construction of indole-fused oxepines in good to excellent yields with a broad substrate scope. This method also features concomitant construction of cis-hydrobenzo[b] oxepine scaffolds, a core unit found in numerous natural products of important biological activities.

Ru(II)-catalyzed allenylation and sequential annulation of N-tosylbenzamides with propargyl alcohols

We hereby report Ru(ii)-catalyzed C(sp2)-H allenylation of N-tosylbenzamides to access multi-substituted allenylamides. Furthermore, the allenylamides were converted to the corresponding isoquinolone derivatives via base mediated annulation. The current protocol features low catalyst loading, mild reaction conditions, high functional group compatibility and desired scalability. The unique functionality of the afforded allenes allowed further transformations to expand the practicality of the protocol.

Transition-Metal Catalyzed Stereoselective Desymmetrization of Prochiral Cyclohexadienones

The development of transition-metal catalyzed enantioselective and diastereoselective transformations has contributed many advances in the field of synthetic organic chemistry. Particularly, stereoselective desymmetrization of prochiral cyclohexadienones represents a powerful strategy for accessing highly functionalized and stereochemically enriched scaffolds, which are often found in biologically active compounds and natural products. In recent years, several research groups including our group have made a significant progress on transition-metal catalyzed stereoselective desymmetrizations of 2,5-cyclohexadienones. In this account, we will provide an overview of the recent developments in this area employing Pd, Cu, Rh, Au, Ag, Ni, Co, and Mn-catalysts.

Lewis Acid-Driven Meyer-Schuster-Type Rearrangement of Yne-Dienone

Developed herein is a Cu(II)-catalyzed Meyer-Schuster-type rearrangement of alkyne-tethered cyclohexadienone for the construction of m-enone-substituted phenols. The reaction involves an uncommon 5-exo-trig 1,6-enyne cyclization of alkyne-tethered-cyclohexadienone, aromatization-triggered C-O bond cleavage, and an electrocyclic 4π-ring-opening of oxetene intermediate. This atom-efficient transformation provides access to a wide range of synthetically important α-(m-substituted phenol)-α,β-unsaturated ketones, featuring a broad scope with labile functional group tolerance. The gram-scale demonstration makes this transformation synthetically viable. The synthetic application of α,β-unsaturated ketones is also showcased.

Electrochemical synthesis of versatile ammonium oxides under metal catalyst-, exogenous-oxidant-, and exogenous-electrolyte-free conditions

An electrochemical oxidative cross-coupling reaction between 2.5-substituted-pyrazolin-5-ones and ammonium thiocyanate has been developed, which resulted in a series of unprecedented cross-coupling products under metal catalyst-, exogenous-oxidant-, and exogenous-electrolyte-free conditions. It is worth noting that since the resulting cross-coupling products are nearly insoluble in MeCN, the pure product could be afforded without silica gel column purification. In addition, the prepared ammonium oxides are versatile building blocks for synthesizing functionalized pyrazole derivatives.

One-Pot Preparation of 9,10-Dihydrophenanthrenes Initiated by Rhodium(III)-Catalyzed C-H Activation and Relay Diels-Alder Reaction

An efficient one-pot synthesis of multisubstituted 9,10-dihydrophenanthrenes from easily available 2-arylazaarenes and cyclohexadienone-tethered terminal alkynes (1,6-enynes) has been successfully achieved. This domino reaction proceeded smoothly through Cp*Rh(III)-catalyzed C-H activation, direct protonation of alkenyl-Rh intermediates, intramolecular Diels-Alder reaction, alkene isomerization, subsequent ring-opening aromatization, and acetylation. This strategy was pot-economical and tolerated a wide range of functional groups. Moreover, the potent anticancer activities against HepG2 cells were observed for these artificial 9,10-dihydrophenanthrene derivatives.

The oxidative coupling between benzaldehyde derivatives and phenylacetylene catalyzed by rhodium complexes via C-H bond activation

This paper reports the use of rhodium (Rh) catalysts for the oxidative coupling reaction between phenylacetylene and benzaldehyde derivatives via C-H bond activation. These reactions were catalyzed by Rh(l-amino acid)(cod) (the l-amino acid is l-phenylalanine, l-valine or l-proline; cod is 1,5-cyclooctadiene) to obtain chromones in 12.7–88.3% yield. These new Rh catalysts have excellent activity for the coupling reaction between phenylacetylene and different benzaldehyde derivatives. It was found that the electronic effects of the benzaldehyde derivative substituent affected the reaction yield, which is in accordance with the proposed mechanism.

K2S2O8-promoted direct thiocyanation of pyrazolin-5-ones with ammonium thiocyanate at room temperature

A facile and efficient approach for the direct thiocyanation of pyrazolin-5-ones under mild conditions has been established for the first time.

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.

Rh(III)-Catalyzed C–H Bond Activation for the Construction of Heterocycles with sp3-Carbon Centers

Rh(III)-catalyzed C–H activation features mild reaction conditions, good functional group tolerance, high reaction efficiency, and regioselectivity. Recently, it has attracted tremendous attention and has been employed to synthesize various heterocycles, such as indoles, isoquinolines, isoquinolones, pyrroles, pyridines, and polyheterocycles, which are important privileged structures in biological molecules, natural products, and agrochemicals. In this short review, we attempt to present an overview of recent advances in Rh(III)-mediated C–H bond activation to generate diverse heterocyclic scaffolds with sp3 carbon centers.

Pyrazolone: a powerful synthon for asymmetric diverse derivatizations

This feature article reports recent advances in the asymmetric diverse derivatizations of the pyrazolone scaffold.