Double “Open and Shut” Transformation of γ-Carbolines Triggered by Ammonium Salts: One-Pot Synthesis of Multiheterocyclic Compounds

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.

Asymmetric Organocatalyzed Cyclization Cascade Reactions of 3,3-Difluoro-2-aryl-3H-indoles and Enamides

The direct functionalization of β-C(sp2)-H bonds in enamides has garnered increasing attention within the realm of organic synthesis. However, these remarkable advancements are predominantly dependent on transition metals; limited success has been achieved via organocatalytic catalysis. Herein, we report a CPA-catalyzed β-C(sp2)-H functionalization of enamides cascade intramolecular cyclization to synthesize the chiral dihydropyrimido[1,6-a]indoles bearing gem-difluoromethylene. Moreover, this methodology enables the synthesis of diverse chiral dihydropyrimido[1,6-a]indoles with outstanding enantioselectivities in moderate to high yields.

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.

Crystal structure of 2-hydroxy-1-tosylindolin-3-yl- 2-naphthoate, C26H21N1S1O5

C26H21N1S1O5, monoclinic, P21/c (no. 14), a = 7.623(3) Å, b = 25.617(12) Å, c = 11.775(5) Å, β = 100.073(8)°, V = 2264.2(17) Å3, Z = 4, R gt (F) = 0.0470, wR ref (F 2) = 0.1365, T = 298(2) K.

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.

Synthesis and stability of 1-aminoalkylphosphonic acid quaternary ammonium salts

An effective protocol for the quaternization of simple 1-aminoalkylphosphonic acids under basic conditions using Me2SO4 as a convenient alkylating agent is reported. During the course of the reaction, phosphonic acid quaternary ammonium derivatives, along with their corresponding monoesters are formed. Subsequent direct acidic hydrolysis of the crude reaction mixture leads to the desired novel N,N,N-trialkyl-N-(1-phosphonoalkyl)ammonium salts with overall yields of up to 88%. The developed protocol is general in scope and the products are purified by simple crystallization to give stable solids. Novel quaternary ammonium salts bearing a phosphonic group are generally unreactive in acidic and alkaline media. However, some of them undergo Hofmann elimination and substitution reactions in the presence of a base.

Rapid access to indole-fused bicyclo[2.2.2]octanones by merging the umpolung strategy and molecular iodine as a green catalyst

One-pot synthesis of indole-fused bicyclo[2.2.2]octanones from DiMeOIN and 2-cyclohexen-1-one is accomplished under an iodine catalyst. The simple and metal-free conditions provide a practical tool to construct Csp3-rich complex molecules via coupling cyclization.

A metal-, oxidant-, and fluorous solvent-free synthesis of α-indolylketones enabled by an umpolung strategy

We have developed the first transition metal-, oxidant-, and fluorous solvent-free α-indolization of ketones using ammonium salts and enamines.

Selective direct C–H polyfluoroarylation of electron-deficient N-heterocyclic compounds

An efficient protocol of C2-selective direct C–H polyfluoroarylation of six-membered N-heterocyclic compounds with polyfluorobenzoic acid via corresponding N-methyl quaternary ammonium salts.

2,3-Dimethoxyindolines: a latent electrophile for SNAr reactions triggered by indium catalysts

An unprecedented utilization of 2,3-dimethoxyindolines (DiMeOINs) as a latent electrophile in regioselective In-catalyzed aromatic substitutions has been reported.

Three-Component Approach to Pyridine-Stabilized Ketenimines for the Synthesis of Diverse Heterocycles

Ketenimines are versatile synthetic intermediates capable of performing novel transformations in organic synthesis. They are normally generated in situ due to their inherent instability and high level of reactivity. Herein, we report pyridine-stabilized ketenimine zwitterionic salts, which are prepared through click chemistry from readily accessible alkynes and sulfonyl azides. To demonstrate their synonymous reactivity to ketenimines, these salts have been utilized in a cascade sequence to access highly functionalized quinolines including the core structures of an antiprotozoal agent and the potent topoisomerase inhibitor Tas-103.

Revisiting Furodiindolines: One-Pot Synthesis of Furodiindolines Using Indole 2,3-Epoxide Surrogates and Their Synthetic Applications

Furodiindolines have emerged as versatile intermediates in various transformations, which are easily obtained from indole 2,3-epoxide surrogates via a one-pot procedure and allowed access to heterocyclic compounds with structural diversity and complexity. Four types of transformations from the furodiindolines have been achieved: (i) dehydrative rearrangement to afford 2,3'-biindoles, (ii) hydrolysis/cyclization to give 3,4-disubstituted quinolines, (iii) ring-opening/cyclization to give pyrroloindolines, and (iv) aminal cleavage to give a 3,3-disubstituted 2-oxindole.