Novel Palladium-Catalyzed Acyloxylation/Cyclization of 2-(3′-Alkenyl)indoles

Pd-Catalyzed and ligand-enabled alkene difunctionalization via unactivated C-H bond functionalization

Palladium-catalyzed and ligand-enabled C-H functionalization methods have emerged as a powerful approach for the preparation of therapeutically important motifs and complex natural products. Olefins, owing to their natural abundance, have been extensively employed for the formation of C-C and C-X bonds and the generation of various heterocycles. Traditionally, activated as well as starting materials with preinstalled functional groups, and also halide substrates under transition metal catalysis, have been employed for olefin difunctionalization. However, strategies for employing unactivated C-H bond functionalization to achieve alkene difunctionalization have rarely been explored. A possible solution to this challenge is the application of bulky ligands which enhances the reductive elimination pathway and inhibits β-hydride elimination to selectively yield difunctionalized alkene products. This feature article summarizes the utilization of unreactive C-H bonds in the Pd-catalyzed and ligand-enabled difunctionalization of alkenes.

Enantioselective first total syntheses of the antiviral natural products xiamycins D and E

The enantioselective first total syntheses of marine pentacyclic indolosesquiterpenoids xiamycins D (4) and E (5) have been described for the first time to the best of our knowledge. The synthetic approach was designed to feature functionalization of enantiopure Wieland-Miescher ketone, Michael addition followed by Heck-type annulation/aromatization, regioselective sp³(C-H) activation, benzylic oxidation and diastereoselective reduction.

A concise total synthesis of sespenine, a structurally unusual indole terpenoid from Streptomyces

A ten-step (the longest linear sequence) total synthesis of sespenine was accomplished.

Palladium-Catalyzed Intermolecular Oxyarylation of Vinylacetates with Retention of an Alkenyl Moiety

Palladium-catalyzed intermolecular oxyarylation reaction of vinylacetates with retention of the double bond in the final product is developed. Under the optimized reaction conditions, the desired products of multisubstituted vinylesters could be obtained in moderate to high yields.

Total synthesis and antiviral activity of indolosesquiterpenoids from the xiamycin and oridamycin families

Indolosesquiterpenoids are a growing class of natural products that exhibit a wide range of biological activities. Here, we report the total syntheses of xiamycin A and oridamycins A and B, indolosesquiterpenoids isolated from Streptomyces. Two parallel strategies were exploited to forge the carbazole core: 6π-electrocyclization/aromatization and indole C2–H bond activation/Heck annulation. The construction of their trans-decalin motifs relied on two diastereochemically complementary radical cyclization reactions mediated by Ti(III) and Mn(III), respectively. The C23 hydroxyl of oridamycin B was introduced by an sp³ C–H bond oxidation at a late stage. On the basis of the chemistry developed, the dimeric congener dixiamycin C has been synthesized for the first time. Evaluation of the antiviral activity of these compounds revealed that xiamycin A is a potent agent against herpes simplex virus–1 (HSV-1) in vitro.

Using a single strategy to make a number of related intermediates is a useful strategy in the total synthesis. Here, the authors report the synthesis of a number of natural products, employing two diastereomerically complementary metal-catalyzed cyclizations as the key step to access a number of frameworks.

Copper promoted radical addition/cyclization of azobisisobutyronitrile with arylacrylamides: a convenient process to synthesize 3-(2′-cyano alkyl) oxindoles

A CuI promoted radical addition/cyclization of azobisisobutyronitrile with alkenes for the preparation of 3-(2′-cyano alkyl) oxindoles was developed.

Palladium(ii)-catalyzed direct alkenylation of dihydropyranones

A palladium(ii)-catalyzed direct alkenylation reaction of dihydropyranones was developed.

Transition-metal-free oxidative carboazidation of acrylamides via cascade C–N and C–C bond-forming reactions

A novel transition-metal-free oxidative carboazidation of acrylamides using inexpensive NaN₃ and K₂S₂O₈ was achieved, which not only provided an efficient method to prepare various N₃-substituted oxindoles, but also represented a novel strategy for C–N and C–C bond formation via a free-radical cascade process.

Copper-catalyzed bis-arylations of alkenes leading to oxindole derivatives

A simple and practical copper-catalyzed approach to oxindole derivatives by copper-catalyzed bis-arylation of N-alkyl-N-phenylacrylamides with diaryliodonium triflates has been developed under mild conditions, and the method is of tolerance towards some functional groups in the substrates.

Palladium-catalyzed dual C-H or N-H functionalization of unfunctionalized indole derivatives with alkenes and arenes

This review highlights the development of palladium-catalyzed C-H and N-H functionalization reactions involving indole derivatives. These procedures require unactivated starting materials and are respectful of the basic principle of sustainable chemistry tied to atom economy.

Copper-catalyzed intramolecular alkene carboetherification: synthesis of fused-ring and bridged-ring tetrahydrofurans

Fused-ring and bridged-ring tetrahydrofuran scaffolds are found in a number of natural products and biologically active compounds. A new copper-catalyzed intramolecular carboetherification of alkenes for the synthesis of bicyclic tetrahydrofurans is reported herein. The reaction involves Cu-catalyzed intramolecular addition of alcohols to unactivated alkenes and subsequent aryl C-H functionalization provides the C-C bond. Mechanistic studies indicate a primary carbon radical intermediate is involved and radical addition to the aryl ring is the likely C-C bond-forming mechanism. Preliminary catalytic enantioselective reactions are promising (up to 75% ee) and provide evidence that copper is involved in the alkene addition step, likely through a cis-oxycupration mechanism. Catalytic enantioselective alkene carboetherification reactions are rare and future development of this new method into a highly enantioselective process is promising. During the course of the mechanistic studies a protocol for alkene hydroetherification was also developed.

Palladium-catalyzed carbo-heterofunctionalization of alkenes for the synthesis of oxindoles and spirooxindoles

A palladium-catalyzed oxidative carbo-heterofunctionalization of aniline derivatives involving concomitant direct C-H functionalization and C-X bond formation was developed. By simply changing the reaction conditions (solvent and catalyst), either 3,3'-disubstituted oxindole or spirooxindole was accessible from the same starting material.