New Synthetic Protocols for the Preparation of Unsymmetrical Bisindoles

Stereospecific Synthesis of Unprotected, α,β-Disubstituted Tryptamines and Phenethylamines from 1,2-Disubstituted Alkenes via a One-Pot Reaction Sequence

Unprotected, α,β-disubstituted tryptamines and phenethylamines are obtained by a one-pot, metal-free sequence that proceeds by the in situ formation of aziridinium salts followed by Friedel-Crafts reaction with electron-rich (hetero)arenes. Both steps are facilitated by hexafluoroisopropanol as the solvent. The one-pot sequence was effective for diversely substituted indoles and 1,3,5-trimethoxybenzene, for cyclic and acyclic alkenes, and proceeded in a stereospecific fashion for both (E)- and (Z)-1,2-disubstituted alkenes. Moreover, one-pot morpholine addition to an aziridinium salt provided a diamine.

Syntheses and medicinal chemistry of azepinoindolones: a look back to leap forward

Nitrogen-containing heterocyclic scaffolds constitute nearly 75% of small molecules which favorably act as drug candidates. For the past few decades, numerous natural and synthetic indole-based scaffolds have been reported for their diverse pharmacological profiles. In particular, indole-fused azepines, termed azepinoindolones, have come under the radar of medicinal chemists owing to their synthetic and pharmacological importance. A plethora of literature reports has been generated thereof, which calls for the need for the compilation of information to understand their current status in drug discovery. Accumulating reports of evidence suggest that compounds containing this privileged scaffold display their cytotoxic effects via inhibition of kinase, topoisomerase I, mitochondrial malate dehydrogenase (mMDH), and tubulin polymerization and as DNA minor groove binding agents. Herein, we endeavor to present a closer look at the advancements of various synthetic and derivatization methods of azepinoindolone-based compounds. We have further extended our efforts to discuss the pharmacological effects of azepinoindolones in the whole range of medicinal chemistry as anti-Alzheimer, anticancer, anti-inflammatory, antidiabetic, antileishmanial, and antipyranosomal agents and as drug delivery vectors. Our analysis of recent advances reveals that azepinoindolones will continue to serve as potential pharmaceutical modalities in the years to come and their substantial pool of synthetic methods will be ever expanding.

An approach to unsymmetrical 3,3′-diindolylmethanes through Pd-catalyzed cascade Heck cyclization of allenamides and o-ethynylanilines

A highly efficient synthesis of unsymmetrical 3,3′-diindolylmethanes has been developed by palladium-catalyzed cascade Heck/cyclization reaction.

Selectivity Control in Gold-Catalyzed Hydroarylation of Alkynes with Indoles: Application to Unsymmetrical Bis(indolyl)methanes

Gold-catalyzed hydroarylation of unactivated alkynes with indoles have previously been reported to proceed with double indole addition to produce symmetrical bis(indolyl)methanes (BIMs). We demonstrate for the first time that the selectivity of the gold-catalyzed reaction can be fully switched to allow for isolation of the vinylindole products instead. Furthermore, this selective reaction can be utilized to synthesize the more difficult to access unsymmetrical BIMs from readily available starting materials.

Zn(OTf)2-catalyzed access to symmetrical and unsymmetrical bisindoles from α-keto amides

Zn(OTf)2-catalyzed synthesis of 3,3'-bisindolyl acetamides from α-keto amides is developed. Both aromatic α-keto amides substituted with electron-donating as well as -withdrawing groups and aliphatic α-keto amides are well tolerated to provide symmetrical bisindoles in moderate to excellent yields. The chemoselective bisindolylation of the keto group of α-keto amides in the presence of a simple keto functionality is successfully achieved in good yields. The transformation is further extended to the synthesis of challenging unsymmetrical bisindoles by treating indolyl α-hydroxy amides with substituted indoles. The unsymmetrical bisindoles are isolated in good to excellent yields.

Cu(I)-Catalyzed Enantioselective Friedel-Crafts Alkylation of Indoles with 2-Aryl-N-sulfonylaziridines as Alkylating Agents

A highly enantioselective Friedel-Crafts alkylation of indoles with N-sulfonylaziridines as alkylating agents has been developed by utilizing the complex of Cu(CH3CN)4BF4/(S)-Segphos as a catalyst. A range of optically active tryptamine derivatives are obtained in good to excellent yields and enantioselectivities (up to >99% ee) via a kinetic resolution process.

Exploiting the σ-phylic properties of cationic gold(i) catalysts in the ring opening reactions of aziridines with indoles

Gold(i) species catalyze the ring opening reactions of aziridines with indoles as nucleophiles for the synthesis of tryptamines and pyrroloindolines.

Iridium-catalyzed direct synthesis of tryptamine derivatives from indoles: exploiting n-protected β-amino alcohols as alkylating agents

The selective C3-alkylation of indoles with N-protected ethanolamines involving the "borrowing hydrogen" strategy is described. This method provides convenient and sustainable access to several tryptamine derivatives.

Synthesis and Preliminary Biological Study of Bisindolylmethanes Accessed by an Acid-Catalyzed Hydroarylation of Vinylindoles

An acid-catalyzed hydroarylation reaction of vinyl indoles is reported, which tolerates a wide range of heterocycles as the exogenous nucleophile such as indoles, pyrroles, and indolizines. The method rapidly accesses the biologically relevant bisindolylmethane scaffold in good to excellent yields. Evaluation of the biological activity of several synthesized analogues reveals cytotoxic activity against and selectivity for the MCF-7 breast cancer cell line.

A general copper-catalyzed sulfonylation of arylboronic acids

A general copper-catalyzed method for the sulfonylation of arylboronic acids with sulfinate salts is described. A variety of alkyl-aryl, diaryl, and alkyl-heteroaryl sulfones were synthesized in good yield.