TfOH-Catalyzed Intramolecular Annulation of 2-(Aryl)-Phenyl-Substituted p-Quinone Methides under Continuous Flow: Total Syntheses of Selaginpulvilin I and Isoselagintamarlin A

1,6-Conjugate addition of in situ generated aryldiazenes to p-quinone methides

Herein we report a transition-metal free, base-mediated 1,6-conjugate addition of aryldiazenes to para-quinone methides (p-QMs). Arylhydrazines were used for the in situ generation of aryldiazenes using a base-mediated protocol in the presence of air as the oxidant. The 1,6-conjugate addition of aryldiazenes to para-quinone methides via a radical mechanism is followed by an oxidative rearrangement to furnish the desired product, arylhydrazones. Interestingly, our synthetic protocol results in the formation of an aryldiazene radical, which undergoes 1,6-conjugate addition with p-QMs to furnish the arylhydrazones.

A HMPA-H2O mediated oxygenative carbocyclization of 2-alkynylphenyl-substituted p-quinone methides to indenones

Herein, we report a transition-metal and base-free protocol to access a wide range of functionalized indenone derivatives through a HMPA-H2O-mediated oxygenative annulation of 2-alkynylphenyl-substituted p-quinone methides. This method worked effectively for most of the p-QMs investigated and the corresponding indenone derivatives were obtained in moderate to good yields. This methodology was further extended to the formal synthesis of one of the resveratrol based natural products, (±)-isopaucifloral F.

Cu(I)-Catalyzed Three-Component Annulation for the Synthesis of 3-Acyl Imidazo[1, 5-a]Pyridines from 2-Pyridinyl-Substituted p-Quinone Methides, Terminal Alkynes, and TsN3 Using O2 as the Oxygen Source

Currently, most conventional methods to achieve imidazo[1,5-a]pyridines have limitations for the synthesis of 3-acyl imidazo[1,5-a]pyridines. Herein, a novel and efficient Cu(I)-catalyzed three-component annulation method for the synthesis of valuable 3-acyl imidazo[1,5-a]pyridines by the reaction of 2-pyridinyl-substituted p-QMs, terminal alkynes, and TsN3 in the presence of O2 under mild conditions have successfully been developed. The investigation indicated that molecular oxygen (O2) and TsN3, respectively, serving as oxygen and nitrogen sources, were essential for the successful completion of the reaction system.

Eosin Y-catalyzed reductive homocoupling of para-quinone methides under visible-light

In this manuscript, we demonstrate a visible-light driven dimerization of para-quinone methides using eosin Y catalyst via a reductive homocoupling process. This mild and operationally simple methodology was found to be compatible with a variety of differently substituted para-quinone methides and a broad range of tetra-arylethane derivatives were obtained in moderate to good yields (47%-87%).

An Open-Air Palladium-Catalyzed Stereoselective O-Glycosylation of Glycals via in-situ Generation of gem-Disubstituted Methanols from p-Quinone Methides

We devised a palladium-catalyzed α-stereoselective glycosylation that incorporates oxygen via in-situ generation of gem-disubstituted methanols from p-quinone methides to access 2,3-unsaturated gem-diarylmethyl O-glycosides under open-air atmosphere at room temperature. Advantages of this environmentally friendly strategy include the absence of additives and ligands, using water as the green source of oxygen, mildest, operationally simple, exhibiting a wide functional group tolerance, and compatibility with a variety of glycal progenitors in appreciable yields. A mechanistic study has been verified via H2 18 O labeling, which validates that water (moisture) is a sole source of oxygen.

Construction of heterocycle-fused tetrahydrocarbazoles through a formal [3 + 3]-annulation of 2-indolylmethanols with para-quinone methides

A metal-free approach for the synthesis of tetrahydroindolo[2,3-b]carbazoles has been developed through an acid-mediated one-pot [3 + 3]-annulation of 2-indolylmethanols and 3-indolyl-substituted para-quinone methides. This operationally simple protocol allowed us to prepare many unsymmetrical tetrahydroindolo[2,3-b]carbazoles in good to excellent yields with a broad substrate scope. This concept was also elaborated to the synthesis of tetrahydrothieno[2,3-b]carbazoles and tetrahydrothieno[3,2-b]carbazoles.

Atom-Economic Synthesis of Unsymmetrical gem-Diarylmethylthio/Seleno Glycosides via Base Mediated C(O)-S/Se Bond Cleavage and Acyl Transfer Approach of Glycosylthio/Selenoacetates

Herein, we invented the Cs₂CO₃-mediated atom economic method that streamlines the scission of the C(O)-S/Se bond involving the in situ generation of an anomeric thiolate/selenolate anion, which reacted with p-QMs to yield novel unsymmetrical gem-diarylmethylthio/seleno glycosides while retaining the anomeric stereochemistry. Notably, the key features of this protocol involve unprecedented long-range acyl transfer (from S/Se to O), thus affording acylation of the final product which is not yet reported by classical methods. This straightforward protocol offers a mild, short reaction time, synthetically simple approach, and compatibility with 8 types of sugar along with phenylthio/benzylseleno esters.

Multicomponent Synthesis of S-Benzyl Dithiocarbamates from para-Quinone Methides and Their Biological Evaluation for the Treatment of Alzheimer's Disease

Multicomponent synthesis of biologically relevant S-benzyl dithiocarbamates from para-quinone methides, amines, and carbon disulfide are described under catalyst and additive-free conditions. The reactions proceeded at room temperature in a short span of time with excellent yields. One of the synthesized compounds, 3e showed considerable acetylcholinesterase (AChE) inhibitory (51.70 + 5.63% at 20 μm) and antioxidant (63.52 ± 1.15 at 20 μm) activities.