Palladium-catalysed 5-endo-trig allylic (hetero)arylation

Access to CF3-benzofulvenes via palladium-catalyzed cascade arylation/Trost-Oppolzer cyclization/double-bond isomerization

Herein, we demonstrated a Pd-catalyzed cascade reaction that involves arylation, Trost-Oppolzer type Alder ene reaction, and double bond isomerization using the 4-(2-alkynylphenyl)-allylcarbonates and aryl boronic acids. This cascade process delivers a wide array of distinctive functionalized CF3-benzofulvenes in good yields with high stereoselectivity (E). A single palladium catalyst orchestrates the two individual reactions in a single operation. Trost-Oppolzer type Alder ene reaction is the key in this transformation, also called a rare acid-free iso-Nazarov type cyclization.

Modular Total Synthesis of the 5/5-Spirocyclic Spiroindimicins

Total syntheses of the 5/5-spirocyclic indoline alkaloids (±)-spiroindimicins B, C, D, E, F, and G have been achieved via a modular approach. Our route features direct coupling of halogenated pyrrolemetal and isatin partners, Suzuki coupling to append the indole unit, Lewis acid-mediated spirocyclization, and divergent functionalization to give various family members. These syntheses are concise (six or seven steps from commercial materials) and highly amenable to analogue synthesis.

C(sp3)–H Activation Enabled by (η3-Indolylmethyl)palladium Complexes: Synthesis of Monosubstituted Tetrahydrocarbazoles

The synthesis of monosubstituted tetrahydrocarbazoles is achieved via the palladium-catalyzed formal [4+2] cycloaddition of 2-alkyl-3-indolylmethyl carbonates and monosubstituted olefins. The transformation demonstrates an unusual C(sp3)–H activation enabled by (η3-indolylmethyl)palladium complexes. The regioselectivity is found to be dependent on the nature of the substituent across the olefin component. Elaborate mechanistic studies are performed, and the synthetic utility of the products is also demonstrated.

Pd-Catalyzed Nazarov-Type Cyclization: Application in the Total Synthesis of β-Diasarone and Other Complex Cyclopentanoids

We describe the palladium-catalyzed Nazarov-type cyclization of easily accessible (hetero)arylallyl acetates to pentannulated (hetero)arenes. This method provides ready access to various types of bi-, tri-, tetra-, and pentacyclic cyclopentanoids under neutral conditions. The synthetic utility is further demonstrated in the first total synthesis of β-diasarone and several other complex cyclopentanoids relevant to medicinal chemistry and materials science.

Palladium-Catalyzed Aminomethylative Oppolzer-Type Cyclization of Enynes: Access to Aminomethylated Benzofulvenes

A novel palladium-catalyzed Oppolzer-type cyclization reaction aided by the aminomethyl cyclopalladated complex has been developed, which provides rapid access to functionalized benzofulvenes with excellent stereoselectivity. The corresponding products can undergo Diels-Alder reaction with maleimides, providing a series of complex polycyclic compounds with excellent regio- and stereoselectivities.

Synthesis of Spiroindenyl-2-Oxindoles through Palladium-Catalyzed Spirocyclization of 2-Bromoarylamides and Vinyl Bromides

An expeditious approach to the construction of spiroindenyl-2-oxindoles was developed via a palladium-catalyzed spirocyclization reaction of 2-bromoarylamides with vinyl bromides. The reaction formed spiropalladacycles as the intermediates via carbopalladation and the C–H functionalization of 2-bromoarylamides. The spiropalladacycles reacted with vinyl bromides to form spiroindenyl-2-oxindoles. A Heck process rather than vinylic C–H functionalization was involved in the reaction.

Lewis acid-catalyzed [3 + 2] annulations of oxindole based spirocyclic donor-acceptor cyclopropanes with ynamides

[3 + 2] annulations of oxindole based spirocyclic donor-acceptor cyclopropanes and ynamides catalyzed by copper triflate have been developed for the synthesis of biologically important spirocyclopenteneoxindoles. These reactions tolerated a wide scope of substrates and provided the desired products in good to high yields (up to 90%) with up to >40 : 1 diastereoselectivities under mild conditions.

Total synthesis of (+)-spiroindimicin A and congeners unveils their antiparasitic activity

The spiroindimicins are a unique class of chlorinated indole alkaloids characterized by three heteroaromatic rings structured around a congested spirocyclic stereocenter. Here, we report the first total synthesis of (+)-spiroindimicin A, which bears a challenging C-3′/C-5′′-linked spiroindolenine. We detail our initial efforts to effect a biomimetic oxidative spirocyclization from its proposed natural precursor, lynamicin D, and describe how these studies shaped our final abiotic 9-step solution to this complex alkaloid built around a key Pd-catalyzed asymmetric spirocyclization. Scalable access to spiroindimicins A, H, and their congeners has enabled discovery of their activity against several parasites relevant to human health, providing potential starting points for new therapeutics for the neglected tropical diseases leishmaniasis and African sleeping sickness.

Spiroindimicins A and H have been synthesized for the first time via a key palladium-catalyzed spirocyclization. Access to these alkaloids and several congeners has allowed the discovery of their antiparasitic properties.

Hypothesis-Driven Palladium-Catalyzed Transformations for the Construction of New Molecular Architectures

The development of new synthetic protocols to access diverse molecular scaffolds from readily available starting compounds is of significance in both academia and industry. Towards this, the catalysis by transition metals has been employed as a powerful tool to access molecules with broad structural and functional diversity. An overview of the recent literature manifested the tremendous potential of transition metal-catalyzed processes in advancing organic synthesis in a new direction. This account compiles new conceptual advancements in the palladium-catalyzed Alder-ene type cycloisomerization reactions, C-H functionalizations, and one-pot multicatalytic processes, which have become essential tools to access new classes of molecules.

Palladium-Catalyzed Aminomethylation and Cyclization of Enynol to O-Heterocycle Confined 1,3-Dienes

The rational tuning of the electrophilicity of the allylpalladium intermediates enables the regioselectively intramolecular 1,2-addition of enynol in the presence of aminal. This aminomethylation and cyclization reaction via C-N bond activation and intramolecular nucleophilic addition provides a rare example for the synthesis of O-containing heterocycle-confined 1,3-dienes, which is of synthetic potential for further derivatization. The method possesses broad substrate generality as well as functional group compatibility and efficiently affords a wide range of desired products with 5-, 6-, and 8-membered O-containing heterocycles with various functional groups.

Palladium-catalysed annulative allylic alkylation for the synthesis of benzannulated heteroarenes

A conceptually novel intramolecular allylic alkylation strategy is developed for the synthesis of carbazoles and dibenzothiophenes.

Palladium-Catalyzed Intramolecular Alder-Ene Type Cycloisomerization Reactions

An overview of the recent literature on palladium-catalyzed intramolecular Alder-ene (IMAE) reaction of a variety of 1,n-unsaturated systems is presented. The reaction which was first reported by Trost and Lautens provided an efficient alternative to the thermal or Lewis acid catalyzed cycloisomerizations involving ene-type reaction. The IMAE cyclization of enynes and dienes has emerged as an important area and found significant applications in building up of complex molecular architectures and in the synthesis of several bioactive natural products. Since highly impactful reviews on this subject have covered the literature till 2015, this article focuses on summarizing the works subsequent to 2015.