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.