Formal One Carbon Deletion of Indoline Hemiaminals under Tautomeric Control to Access 2-Aminobenzyl Compounds

Unprecedented tert-BuOK-mediated one carbon deletion of indoline hemiaminals has been achieved. This novel protocol provides an efficient synthetic tool for the construction of 2-aminobenzyl compounds with high chemoselectivity. In addition, functionalized 2-aminobenzyl compounds are difficult to make, for which few limited means of access currently exist. The key to success is the use of in situ generated Heyns rearrangement products (α-amino carbonyl compounds) as precursors for formal one carbon deletion.

Switchable synthesis of 3-aminoindolines and 2'-aminoarylacetic acids using Grignard reagents and 3-azido-2-hydroxyindolines

The switchable synthesis of 3-aminoindolines and 2'-aminoaryl acetic acids from the same substrates, 3-azido-2-hydroxyindolines, was developed through denitrogenative electrophilic amination of Grignard reagents. The key to success is the serendipitous discovery that the reaction conditions, including solvents and reaction temperature, can affect the chemoselectivity. It is noteworthy that isotope-labeling experiments revealed the occurrence of the aziridine intermediate in the production of 2'-aminoaryl acetic acids.

On Demand Synthesis of C3-N1' Bisindoles by a Formal Umpolung Strategy: First Total Synthesis of (±)-Rivularin A

In this work, a straightforward synthesis of C3-N1' bisindolines is achieved by a formal umpolung strategy. The protocols were tolerant of a wide variety of substituents on the indole and indoline ring. In addition, the C3-N1' bisindolines could be converted to C3-N1' indole-indolines and C3-N1'-bisindoles. Also, we have successfully synthesized (±)-rivularin A through a biomimetic late-stage tribromination as a key step.

Unveiling a Strategy for Ring Opening of Epoxides: Synthesis of 2-Hydroxyindolinylidenes Using α-Ester Sulfoxonium Ylides

The untapped potential of α-carbonyl sulfoxonium ylides in epoxide ring-opening reactions has been a notable gap in current research, with such reactivity predominantly associated with the highly reactive dimethylsulfoxonium methylide. This study introduces an innovative approach wherein an epoxide indole, formed in situ from 2-hydroxyindoline-3-triethylammonium bromide, undergoes reaction with α-ester sulfoxonium ylides. The outcome is the efficient synthesis of a range of 2-hydroxyindolin-3-ylidenes, demonstrating favorable yields (41-81%) and Z/E ratios from 4:1 to those of exclusive Z isomers. Additionally, the photophysical properties of the synthesized indolinylidenes are explored, along with their derivatization using various nucleophiles under acid catalysis.

Aluminum-Catalyzed Cross Selective C3–N1′ Coupling Reactions of N-Methoxyindoles with Indoles

C3–N1′ bond formation of bisindoles has been a great challenge due to the intrinsic reactivity of indoles as both C3 and N1-nucleophilic character. Herein, we demonstrate an C3–N1′ cross-coupling reaction of indoles using N-methoxyindoles as N-electrophilic indole reagents in the presence of Lewis acid. The bisindoles generated in this transformation are latent C3-nucleophile, allowing them to be used as strategic intermediates in sequential C3–N1′–C3′–N1″ triindole formations. The potential synthetic usefulness of this sequential transformation was highlighted upon application to the construction of C3–N1 looped polyindoles.

Gold-Catalyzed Cascade Reaction of 2-Alkynyl Aryl Azides with Enecarbamates for Direct Synthesis of α-(3-Indolyl)ketones

α-(3-Indolyl)ketones are essential building blocks for the generation of biologically active molecules. We described a new method for the direct assembly of α-(3-indolyl)ketones through the cascade reaction of 2-alkynyl aryl azides with enecarbamates, in which the in situ generated α-imino gold carbene intermediate was trapped by enecarbamate to achieve umpolung reactivity of indole at the 3-position.

Indole Editing Enabled by HFIP-Mediated Ring-Switch Reactions of 3-Amino-2-Hydroxyindolines

This work reports the novel reactivity of hemiaminal as a precursor for indole editing at the multi-site. The HFIP-promoted indole editing of indoline hemiaminals affords 2-arylindoles through a ring-switch sequence. The key to success of this transformation is to use a cyclic hemiaminal as an α-amino aldehyde surrogate under transient tautomeric control. This transformation features mild reaction conditions and good yields with broad functional group tolerance. The utility of this transformation is presented through the one-pot protocol and the synthesis of isocryptolepine.

Synthesis of 2-monosubstituted indolin-3-ones by cine-substitution of 3-azido-2-methoxyindolines

We report herein the formal cine-substitution/hydrolysis of 3-azidoindole intermediates generated from 3-azido-2-methoxyindolines (AZINs). This protocol enables the introduction of both various carboxylic acid and alcohol into indolin-3-ones at the C2-position,...

cis-3-Azido-2-methoxyindolines as safe and stable precursors to overcome the instability of fleeting 3-azidoindoles

Use of 3-azidoindoles in organic synthesis remains a difficult task owing to their instabilities. Herein, we report a general and concise approach for tackling this problem by using 3-azidoindole surrogates. The surrogates are bench-stable, presumably due to the observed intramolecular O-N_β bonding. The resultant fleeting intermediates undergo capturing in situ to afford 3-substitued indoles through formal ipso-substitution of the azide group by nucleophiles. In these investigations, we found that the fleeting 3-azidoindoles show a C3-electrophilic character for the first time.

Synthesis of α-substituted indolylacetamide using acetonitriles as acetamide enolate equivalents through O-transfer reactions

We introduce readily available ammonium hemiaminals as O-transfer reagents and commercially available acetonitriles as a primary amide enolate precursor. The combination serves as an amide enolate equivalent, thereby providing one-pot access to α-substituted indolylacetamides. A broad substrate scope and good functional group tolerance as well as gram-scale synthesis make this protocol highly attractive. Mechanistic experiments suggest that the cyano group is trapped by a hydroxy group of hemiaminals en route to the desired primary amides under metal-free conditions.