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.

Oxytrofalcatin Puzzle: Total Synthesis and Structural Revision of Oxytrofalcatins B and C.

The previously reported structures of oxytrofalcatins B and C possess a benzoyl indole core. However, following synthesis and NMR comparison of both the proposed structure and the synthesized oxazole, we have revised the structure of oxytrofalcatins B and C as oxazoles. The synthetic route developed herein can further our understanding of the biosynthetic pathways that govern the production of natural 2,5-diaryloxazoles.

One-Pot Synthesis of Core Structure of Shewanelline C Using an Azidoindoline.

The unprecedented synthesis of the indolines bearing N3-quinazolin-2,4-dione moiety using an AZIN is reported. The concise synthesis features the tandem Staudinger/chemo-selective aza-Wittig/cyclization sequence of AZINs with isatoic anhydride by a one-pot protocol.

First Total Synthesis of Reassigned Echinosulfonic Acid D.

Echinosulfonic acid D, a sponge metabolite whose structure was recently reassigned, was synthesized for the first time. The key step is the double indolization of dimethylbarbituric acid using the umpolung indole reagent, followed by a hydrolysis/decarboxylation/esterification sequence.

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.

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-Nß 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.

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

Enamines undergo α-indolization with ammonium salts in the presence of Et3N to form α-indolylketones. This is the first example of transition metal-, oxidant-, and fluorous solvent-free α-indolization of ketones. Key to the success of this convenient protocol was the use of in situ generated electrophilic indole species, as well as the use of enamines as a ketone enolate equivalent.

Revisiting 2-Alkoxy-3-bromoindolines: Control C-2 vs. C-3 Elimination for Regioselective Synthesis of Alkoxyindoles.

The regioselective synthesis of both 2- and 3-alkoxyindoles from a common intermediate, 2-alkoxy-3-bromoindolines (ROBIN), is described. The 2-alkoxyindoles are obtained by a base-promoted regioselective elimination of HBr from ROBIN, whereas the synthesis of 3-alkoxyindoles is achieved by a silver-mediated alkoxylation followed by an acid-promoted elimination of alkoxide. This key elimination features the complete regioselectivity and no need for catalysts, that makes it have potential synthetic applications. Furthermore, this protocol is user friendly because ROBIN is able to be prepared from commercially available indoles and is a bench-stable easy-to-handle crystalline substrate, thus allowing the concise synthesis of a variety of both 2- and 3-alkoxyindoles.

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

2,3-Dimethoxyindolines (DiMeOINs) have emerged as a latent electrophile in indium-catalyzed SNAr reactions. They are easily obtained from commercially available indoles and allowed access to 3-substituted indoles. The reaction proceeds via SNAr reactions of in situ generated 3-methoxyindoles. Formation of C2-substituted indoles was also possible utilizing the C2-nucleophilicity of DIMeOIN. Our protocol is user friendly as DiMeOIN is a bench-stable easy-to-handle crystalline reagent.