Visible-Light-Induced Radical Cascade [4 + 2]/[4 + 2] Cycloaddition of Underexplored N‑Acryloyl Indoles To Access Dihydropyrido[1,2‑a]‑indolones

TL;DR

A new visible-light-driven chemical reaction creates complex indolone structures using N-acryloyl indoles and N-hydroxyphthalimide esters.

Contribution

A novel radical cascade [4+2]/[4+2] cycloaddition method for synthesizing dihydropyrido[1,2-a]indolones is introduced.

Findings

The reaction forms four new C–C bonds and causes dearomatization of an indole ring.

The mechanism involves two N-acryloyl indole molecules in a radical cascade.

Scale-up and derivatization demonstrate the method's synthetic utility.

Abstract

We report a visible-light-mediated radical cascade [4
+ 2]/[4 +
2] cycloaddition of simple N-acryloyl indoles and N-hydroxyphthalimide esters, which provides a streamlined
route to structurally complex dihydropyrido­[1,2-a]-indolones. The reaction features a sequence of four consecutive
radical additions involving two N-acryloyl indole
molecules, which forges four new C–C bonds and induces dearomatization
of one indole ring. The proposed mechanism is supported by observations
of [4 + 2] cycloaddition byproducts and additional control experiments.
The synthetic utility of this method is demonstrated by the scale-up
reaction and downstream derivatizations.

Figures