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.

Pd(II)-catalyzed annulation of terminal alkynes with 2-pyridinyl-substituted p-quinone methides: direct access to indolizines.

A Pd-catalyzed direct method has been developed to access 1,3-disubstituted indolizines. This reaction proceeds through a regiospecific annulation of terminal alkynes with 2-pyridinyl-substituted p-quinone methides and, in most of the cases, the desired 1,3-disubstituted indolizines were obtained in moderate to good isolated yields. The control experiments suggested that the reaction does proceed through a substrate-controlled regiospecific formal [3 + 2]-annulation pathway.

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

In this article, we describe a convenient method to access 9-aryl fluorene derivatives through a TfOH-catalyzed intramolecular 1,6-conjugate arylation of 2-(aryl)-phenyl-substituted p-quinone methides (QMs) under continuous flow using the microreaction technique. This method was found to be very effective for most of the p-QMs, and the corresponding 9-aryl fluorene derivatives were obtained in moderate to excellent yields. Moreover, this protocol was further elaborated to the first total syntheses of selaginpulvilin I and isoselagintamarlin A.

Construction of Oxygen- and Nitrogen-based Heterocycles from p-Quinone Methides.

In the last few years, there has been an explosive growth in the area of para-quinone methide (p-QM) chemistry. This boom is actually due to the unique reactivity pattern of p-QMs, and also their remarkable synthetic applications. In fact, p-QMs serve as synthons for unsymmetrical diaryl- and triarylmethanes, and also for the construction of diverse range of carbocycles and heterocycles. In the last few years, a wide range of structurally complex heterocyclic frameworks could be accessed through the synthetic transformations of structurally modified stable p-QMs. Therefore, the main focus of this review article is to cover the recent advancements in the transition-metal, Lewis acid and base-catalyzed/mediated synthetic transformations of the stable p-quinone methides (p-QMs) to oxygen- and nitrogen-containing heterocycles.

1,6-Hydroolefination and Cascade Cyclization of p-Quinone Methides with Styrenes: Total Synthesis of (±)-Isopaucifloral F.

A Lewis acid-catalyzed intermolecular 1,6-hydroolefination of p-quinone methides with styrenes leading to vinyl diarylmethanes and indenes has been developed. This protocol was also elaborated to the total synthesis of (±)-isopaucifloral F. Besides, interestingly, the reaction between 2-alkynylated p-quinone methides and styrenes provided a straightforward access to dihydrobenzo[ a]fluorene derivatives in one pot with 100% atom-economy.

Tandem One-Pot Approach To Access 1,2,3-Triazole-fused Isoindolines through Cu-Catalyzed 1,6-Conjugate Addition of Me3SiN3 to p-Quinone Methides followed by Intramolecular Click Cycloaddition.

A Cu-catalyzed one-pot approach has been developed for the synthesis of 1,2,3-triazole-fused tricyclic heterocycles. This tandem approach actually involves the 1,6-conjugate addition of Me3SiN3 to o-alkynylated p-quinone methides followed by an intramolecular [3+2]-cycloaddition reaction. This protocol allowed us to access a wide range of 1,2,3-trazole-fused isoindoline derivatives in moderate to good yields.

Exploring Gold Catalysis in a 1,6-Conjugate Addition/Domino Electrophilic Cyclization Cascade: Synthesis of Cyclohepta[ b]indoles.

An effective method for the construction of the structurally complex fused cyclohepta[ b]indole core has been developed through an intermolecular 1,6-conjugate addition of indoles to 2-alkynyl p-quinone methides followed by an intramolecular electrophilic cyclization under oxophilic and alkynophilic gold catalysis.