Tandem 6π-Azatriene Electrocyclization of Fused Amino-cyclopentenones: Synthesis of Functionalized Pyrrolo- and Indolo-quinoxalines

Abstract

A tandem 6π-azacyclization approach for the synthesis of diversified pyrrolo/indolo­[1,2-a]­quinoxalines from amino-cyclopentenones has been developed. The reaction proceeds through a trifluoroacetic-acid-mediated 6π-electrocyclization and concomitant opening of the cyclopentenone ring. The advantageous features of the developed chemistry include transition-metal-free conditions, operational simplicity, and a broad substrate scope. Further X-ray crystallographic studies confirm the assigned structures of the fused heterocycles.

Recent Examples in the Synthesis and Functionalization of C−H Bonds in Pyrrolo/Indolo [1,2‐a]Quinoxalines

“…In 2021, Verma and co-workers developed a method for synthesis of 4-(2-acyl)phenyl pyrrolo[1,2-a]quinoxalines derived from 6π-electrocyclization of amine-substituted indenones. [26] Brønsted acid was pivotal to the transformation, with trifluoroacetic acid was superior to analogous acetic acid and other mineral inorganic acids. Scope of pyrrolo[1,2-a]quinoxalines included substituted cyclopentaquinolinones, cyclopentapyridinones, and indenones (Scheme 28).…”

Crystal structure, DFT studies, Hirshfeld surface and energy framework analysis of 4-(5-nitro-thiophen-2-yl)-pyrrolo [1, 2-a] quinoxaline: A potential SARS-CoV-2 main protease inhibitor

“…Methods to synthesize pyrrolo [1,2-a] quinoxalines often involve the use of functionalized aniline precursors [20] , transition metal catalysts [21] , [22] , [23] , and harsh reaction conditions. We aimed to develop a simple method that avoids the use of expensive transition metal catalysts and dangerous oxidizers.…”

DBU‐Promoted 6π‐Azaelectrocyclization and Hydrogen‐Migration to Prepare 6‐Alkyl Pyridine N‐Oxides from N‐Vinyl‐α,β‐Unsaturated Nitrones

“…6π-Azaelectrocyclization, [6] one of the well-known concerted pericyclic reactions, represents an elegant annulation approach for the synthesis of N-heterocycles and has attracted great interest in the synthesis of pyridines, [7] quinoxalines and quinolines, [8] and azepines. [9] Some of these strategies have been successfully applied in the total synthesis of natural products and biologically active molecules.…”