Visible Light‐mediated, Iodine‐catalyzed Radical Cascade Sulfonylation/Cyclization for the Synthesis of Sulfone‐containing Coumarin under Photocatalyst‐free Conditions

Stereoselective Synthesis of Biology-Oriented Pentacyclic Pyrrolo[2,1-a]isoquinoline Scaffolds by Photoredox-Induced Radical Annulations

We report a visible-light photoredox-induced stereoselective radical 1,3-dipolar cycloaddition between tetrahydroisoquinolines and coumarin derivatives, providing a platform for the efficient synthesis of pseudo-natural-inspired fused pentacyclic scaffolds. Using this protocol, a diverse range of valuable fused pentacyclic pyrrolo[2,1-a]isoquinolines were efficiently obtained in moderate to good yields and excellent diastereoselectivities. Mechanistic investigations including radical control experiments and light on/off studies indicated that the reaction underwent a visible-light induced radical process. The insights gained from our studies are expected to advance general efforts toward the green synthesis of biology-oriented pseudo-natural products and heterocyclic skeletons.

Photoinduced Radical Annulations of Tetrahydroisoquinoline Derivatives with 2-Benzothiazolimines: Highly Diastereoselective Synthesis of Fused Hexahydroimidazo[2,1-a]isoquinolines

We report herein a photoinduced radical 1,3-dipolar cycloaddition between the 2-benzothiazolimines and tetrahydroisoquinoline derivatives with an organo-photocatalyst. A variety of benzothiazole-based hexahydroimidazo[2,1-a]isoquinoline architectures with great synthetic value were conveniently and efficiently constructed in moderate to good yields and excellent diastereoselectivities with highly tolerant functional groups. Moreover, the practicality and utility of this protocol were demonstrated by scale-up synthesis and facile elaboration. Preliminary mechanistic investigations indicated that the reaction proceeded via a visible-light-induced radical 1,3-dipolar cycloaddition pathway. This finding is expected to stimulate a more extensive exploration of the green and concise synthesis of structurally diverse heterocyclic molecules in the synthetic community.

Visible-light-induced C-S bond formation in the synthesis of 2,4-disubstituted thiazoles through cascade difunctionalization of acetophenone: a greener approach

A groundbreaking approach has been developed for synthesizing 2,4-disubstituted thiazoles using an eco-friendly and metal-free approach. This novel method utilizes methyl aryl ketones, N-bromo-succinimide (NBS), and thioamides in water as a green reaction medium under visible light irradiation. Using NBS as a bromine source, the reaction takes place through an in situ α-bromination method. This approach does not require any catalyst, which makes it exceptionally beneficial for the environment. The advantages of this efficient approach are manifold and include the use of greener conditions, absence of metals, easy isolation of products, cost-effectiveness, non-toxicity, and reliance on renewable energy sources like visible light. Moreover, this technique offers higher product purity and excellent yield, enhancing itsappeal.

Visible-Light-Induced Tandem Radical Brominative Addition/Cyclization of Activated Alkynes with CBr4 for the Synthesis of 3-Bromocoumarins

A visible-light-induced tandem radical brominative addition/spiro-cyclization/1,2-ester migration of activated alkynes with CBr₄ is developed. This protocol features good functional group tolerance, operational simplicity, and mild reaction conditions without the use of catalysts and external additives, providing easy access to valuable 3-bromocoumarins in generally high yields.

Visible-Light-Mediated Three-Component Cascade Sulfonylative Annulation

Visible-light-promoted cascade radical cyclization for the synthesis of sulfonylated benzimidazo/indolo[2,1-a]iso-quinolin-6(5H)-ones has been reported. The reaction provides transition-metal-free and expeditious access to sulfonylated polyaromatics. The use of sodium metabisulfite as a SO₂ surrogate and the rapid generation of molecular complexity using a three-component photochemical protocol are the salient features of this reaction manifold.