Electrochemical Dearomative Dihydroxylation and Hydroxycyclization of Indoles

Metal-free electrochemical dihydroxylation of unactivated alkenes

Herein, a metal-free electrochemical dihydroxylation of unactivated alkenes is described. The transformation proceeds smoothly under mild conditions with a broad range of unactivated alkenes, providing valuable and versatile dihydroxylated products in moderate to good yields without the addition of costly transition metals and stoichiometric amounts of chemical oxidants. Moreover, this method can be applied to a range of natural products and pharmaceutical derivatives, further demonstrating its synthetic utility. Mechanistic studies have revealed that iodohydrin and epoxide intermediate are formed during the reaction process.

The Total Synthesis of Raistrickindole A

The total synthesis of raistrickindole A has been achieved, thereby confirming the proposed structure as an N-hydroxylated DKP. In the first but less selective approach, the DKP was built up by cyclization of a diastereoisomerically mixed N-hydroxylated dipeptide. In the second approach, the same DKP was constructed stereoselectively by the intramolecular Mitsunobu reaction of a hydroxamic acid. The synthesis was completed by a stereoselective oxidative cyclization.

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.

The eco-friendly electrosynthesis of trifluoromethylated spirocyclic indolines and their anticancer activity

A method for the electrochemical diastereoselective oxytrifluoromethylation of indoles was developed for the eco-friendly synthesis of CF₃-containing spirocyclic indolines. The cascade reaction comprised anodic oxidation to obtain CF₃ radicals, the addition of radicals to indoles, and intramolecular spirocyclization. The reaction system without external chemical oxidants could easily be scaled up. Antiproliferation assays of these CF₃-substituted spirocyclic indolines exhibited their promising activities and selectivities toward several types of cancer cells, including Huh-7, A549, and cisplatin-resistant cancer cells (A549/DDP).

Electrochemical Benzylic C-H Functionalization with Isocyanides

We report the challenging direct carbamoylation or cyanation of benzylic C(sp³)-H bonds with an isocyanide via an electrochemical process giving rise to structures that are encountered in several biologically relevant compounds and drugs. This transformation proceeds under mild conditions without the need for any external oxidant and avoids the necessity to start from a prefunctionalized benzylic substrate or the deployment of the cation pool method. The anodic oxidation of the benzylic position and the subsequent addition of the isocyanide lead to the formation of a C-C bond and to a nitrilium cation that hydrolyzes to yield α-aryl acetamide derivatives, whereas the elimination of a t-butyl cation delivers α-aryl acetonitrile derivatives.

Photons or Electrons? A Critical Comparison of Electrochemistry and Photoredox Catalysis for Organic Synthesis

Redox processes are at the heart of synthetic methods that rely on either electrochemistry or photoredox catalysis, but how do electrochemistry and photoredox catalysis compare? Both approaches provide access to high energy intermediates (e.g., radicals) that enable bond formations not constrained by the rules of ionic or 2 electron (e) mechanisms. Instead, they enable 1e mechanisms capable of bypassing electronic or steric limitations and protecting group requirements, thus enabling synthetic chemists to disconnect molecules in new and different ways. However, while providing access to similar intermediates, electrochemistry and photoredox catalysis differ in several physical chemistry principles. Understanding those differences can be key to designing new transformations and forging new bond disconnections. This review aims to highlight these differences and similarities between electrochemistry and photoredox catalysis by comparing their underlying physical chemistry principles and describing their impact on electrochemical and photochemical methods.

Electrochemical oxidative dearomatization of 2-arylthiophenes

Herein we report a green and sustainable electrochemical oxidative dearomatization of 2-arylthiophenes. The variation of substitution patterns affords easy access toward both the C2/C3 and C2/C5 difunctionalized dearomative products. The...

Electrochemical Enantioselective Dihydroxylation Reaction of N-Alkenyl Nucleobases for the Construction of Chiral Acyclic Nucleosides

A simple and sustainable KI-mediated electrochemical enantioselective dihydroxylation reaction of N-alkenyl nucleobases was developed for the first time in an undivided cell. A series of chiral acyclic nucleosides bearing two...

Dearomatization Reactions of Indoles to Access 3D Indoline Structures

This Account summarizes our involvement in the development of dearomatization reactions of indoles that has for origin a total synthesis problematic. We present the effort from our group to obtain 3D-indolines scaffold from the umpolung of N-acyl indoles via activation with FeCl3 to the oxidative spirocyclizations of N-EWG indoles and via the use of electrochemistry.

1 Introduction

2 Activation of N-Acyl Indoles with FeCl3

2.1 Hydroarylation of N-Acyl Indoles

2.2 Difunctionalization of N-Acyl Indoles

3 Radical-Mediated Dearomatization of Indoles for the Synthesis of Spirocyclic Indolines

4 Electrochemical Dearomatization of Indoles

4.1 Direct Electrochemical Oxidation of Indoles

4.2 Indirect Electrochemical Oxidation of Indoles

5 Conclusion