Arylsulfonylation-Triggered Cyclization of 3-Alkenyl Indoles Enabling Synthesis of Tetrahydro-γ-carboline

A visible-light promoted cyclization reaction of 3-alkenyl indole derivatives with arylsulfonyl chlorides as coupling partners has been developed, which afforded functionalized tetrahydro-γ-carbolines in good chemical yields. The reaction used 3-alkenyl indoles as radical acceptors and proceeded via the sequence of sulfonylation and intramolecular cyclization. The reaction was carried out under mild conditions and tolerated a wide range of substrates, which provides an efficient strategy for the synthesis of tetrahydro-γ-carboline derivatives.

Ag-Catalyzed Asymmetric Interrupted Barton-Zard Reaction Enabling the Enantioselective Dearomatization of 2- and 3-Nitroindoles

We disclose a Ag-catalyzed asymmetric interrupted Barton-Zard reaction of α-aryl-substituted isocyanoacetates with 2- and 3-nitroindoles, which enables the dearomatization of nitroindoles and hence offers rapid access to an array of optically active tetrahydropyrrolo[3,4-b]indole derivatives bearing three contiguous stereogenic centers, including two tetrasubstituted chiral carbon atoms with pretty outcomes (up to 99% yield, 91:9 dr, and 96% ee). The synthetic potential of the protocol was showcased by the gram-scale reaction and versatile transformations of the product.

Silver-Catalyzed Asymmetric Dearomatization of Electron-Deficient Heteroarenes via Interrupted Barton-Zard Reaction

Herein we report a catalytic asymmetric dearomatization reaction of electron-deficient heteroarenes with α-substituted isocyanoacetates through an interrupted Barton-Zard reaction. A range of optically active pyrrolo[3,4-b]indole derivatives was obtained in good yields (up to 97 %) with high stereoselectivities (up to >20:1 dr and 97 % ee), using a catalytic system consisting of a cinchona-derived amino-phosphine and silver oxide. This reaction features wide substrate scope and mild conditions, and provides a new strategy for developing asymmetric dearomatization reactions.

Recent developments on synthesis and biological activities of γ-carboline

γ-Carboline alkaloids are a family of natural and synthetic agents that have diverse bioactivities including antiviral, antibacterial, antifungal, antiparasitic, antitumor, anti-inflammatory, neuropharmacological activities and so on. They constitute an important class of pharmacologically active scaffolds that exhibit biological activity via diverse mechanisms. This review provides an update on the recent developments (2010-2017) in the synthesis and biological activities of these compounds. In cases where sufficient information is available, the mechanism and the structure-activity relationship (SAR) of biological activity are presented, and based on our expertise in the field and careful analysis of the recent literature, for the potential of γ-carboline alkaloids as medicinal drugs is proposed.

Catalytic Enolate Arylation with 3-Bromoindoles Allows the Formation of β-Carbolines

Synthesis of substituted β-carbolines was accomplished by utilizing the catalytic enolate arylation reaction of ketones in conjunction with several 3-bromoindole derivatives. Quenching of the arylation reaction in situ with an electrophile allowed ready incorporation of functionality at the carboline C-4 position in an efficient one-pot protocol.

Palladium-catalyzed α-arylation of carbonyls in the de novo synthesis of aromatic heterocycles

Aromatic heterocycles are a very well represented motif in natural products and have found various applications in chemistry and material science, as well as being commonly found in pharmaceutical agents. Thus, new and efficient routes towards this class of compound are always desirable, particularly if they expand the scope of chemical methodology or facilitate more effective pathways to complex substitution patterns. This perspective covers recent developments in the de novo synthesis of aromatic heterocycles via palladium-catalysed α-arylation reactions of carbonyls, which is itself a powerful transformation that has undergone significant development in recent years.

Controlling the ambiphilic nature of σ-arylpalladium intermediates in intramolecular cyclization reactions

The reactivity of main group organometallics, such as organolithium compounds (RLi) and Grignard reagents (RMgX), is quite straightforward. In these species the R group usually exhibits nucleophilic reactivity without any possibility of inducing electrophilic character. In contrast, in organopalladium complexes, researchers can switch the reactivity from electrophilic to nucleophilic relatively simply. Although σ-aryl and σ-vinylpalladium complexes are commonly used as electrophiles in C-C bond-forming reactions, recent research has demonstrated that they can also react with carbon-heteroatom multiple bonds in a nucleophilic manner. Nevertheless, researchers have completely ignored the issue of controlling the ambiphilic nature of such species. This Account describes our efforts toward selectively promoting the same starting materials toward either electrophilic α-arylation or nucleophilic addition reactions to different carbonyl groups. We could tune the properties of the σ-arylpalladium intermediates derived from amino-tethered aryl halides and carbonyl compounds to achieve chemoselective transformations. Therefore, chemists can control the ambiphilic nature of such intermediates and, consequently, the competition between the alternative reaction pathways by the adequate selection of the reaction conditions and additives (base, presence/absence of phenol, bidentate phosphines). The nature of the carbonyl group (aldehydes, ketones, esters, and amides) and the length of the tether connecting it to the aniline moiety also play an important role in the outcome of these processes. Our joint computational and experimental efforts to elucidate the reaction mechanism of these palladium-catalyzed transformations suggest that beyond the formation of the four-membered azapalladacycle, two major factors help to control the dual character of the palladium(II) intermediates derived from 2-haloanilines. First, their high nucleophilicity strongly modifies the interaction of the metal center with the carbonyl group. Second, the additive phenol exchanges the iodide ligand to give an arylpalladium(II) phenoxide complex, which has a beneficial effect on the arylation. The formation of this transient intermediate not only stabilizes the arylpalladium moiety, thus preventing the nucleophilic attack at the carbonyl group, but also assists the enolization reaction, which takes place in a more favorable intramolecular manner. The azapalladacycle intermediate is, in the words of J. R. R. Tolkien, "the one ring to bring them all and in the darkness to bind them." With this intermediate, we can easily achieve the synthesis of a variety of heterocyclic systems by selectively promoting electrophilic α-arylation or nucleophilic addition reactions from the same precursors.