Metal‐ and Oxidant‐Free Electrosynthesis of Heterocycles from 1,2‐Diarylalkene Derivatives

Abstract

Synthesis of heterocycles from 1,2‐diarylalkene derivatives through electrosynthesis under metal‐ and oxidant‐free conditions has been discovered. Cathodic reduction of 2‐alkenylbenzoic acid or anodic oxidation of 2‐alkenylbenzamide, 2‐alkenylphenol and 2‐alkenylaniline leads to the formation of reactive radical intermediates which afford corresponding phthalide, isochroman‐1‐one, isoindolin‐1‐one, benzofuran, and indole in satisfying yields with good functional group tolerance. Interestingly, different chemoselectivities were found in different reaction solvents. Several mechanistic investigations including cyclic voltammetry studies and control experiments were carried out to elucidate the reaction mechanisms.

An Operationally Simple Approach to Indole Derivatives from 2-Alkenylanilines Utilizing an Oxidation–Intramolecular Cyclization–Elimination Sequence

“…Recently, methods avoiding the use of metals in cyclization have attracted much attention. A few notable examples are Scheme 1, the use of DDQ mediation, NIS mediation, selenium-catalyzed NFSI oxidation, and 3,5-dichlorobenozic acid catalysis with molecular oxygen as the oxidant [7][8][9][10][11][12][13]. Herein, we report an additional method to the metal-free C-H aminations listed above.…”

A Study of Alkene Disulfonoxylation

“…Relative to alkene dihydroxylation, [1][2][3] alkene disulfonoxylation remains less explored (Scheme 1). [4][5][6][7][8][9][10] As diols are often subsequently converted into the corresponding tosylates or mesylates, one step syntheses of such compounds from alkene starting materials would be desirable from the perspective of step economy and reagent waste. Existing protocols for disulfonoxylation [4][5][6][7][8][9][10] have greatly inspired this study and most employ the use of hypervalent iodine reagents, [11][12][13][14][15][16][17] which are convenient alternatives to toxic metals such as osmium.…”

Electrochemical reductive cascade cyclization of o-alkynylated derivatives for saturated amides/amines

“…This is subsequently protonated by the electrolyte to form the α-aminyl radical E . 15 The radical intermediate E undergoes further cathodic reduction via SET to generate the anion F, which subsequently protonated to furnish the final compound 2 . Similarly, under electrochemical conditions, 3a and 4a undergo cyclization in the presence of a base to yield quinazolinone G .…”