Related Experiment Video
Updated: May 5, 2026

A Novel Technique for Generating and Observing Chemiluminescence in a Biological Setting
Published on: March 9, 2017
Visible-Light-Mediated Rose Bengal- or [Ru(bpy)3]2+-Catalyzed Radical [4 + 2] Cycloaddition: An Efficient Route to
Cody Bishir1, Abbey Hubbard1, Liangyong Mei1
1Department of Chemistry and Biochemistry, University of North Florida, Jacksonville, Florida 32224, United States.
Abstract:
A visible-light-induced Rose Bengal- or [Ru(bpy)3]2+-catalyzed radical [4 + 2] cycloaddition of redox-active indole N-hydroxyphthalimide esters with electron-deficient alkenes has been developed. This base-free protocol provides a facile and powerful route for the synthesis of functionalized and biologically significant tetrahydrocarbazoles under mild conditions. On one hand, when an organic photocatalyst-Rose Bengal was employed under green light, the desired tetrahydrocarbazoles were obtained in up to 82% yield. On the other hand, the reaction yield increased to up to 93% in the presence of [Ru(bpy)3Cl2]·6H2O under blue light. The success of the gram-scale and transformation experiments, as well as the photopromoted radical [5 + 2] cycloaddition further highlight the practicality and robustness of this protocol. Mechanistic studies also support the generation of a crucial alkyl radical intermediate.
Related Concept Videos
Halogenation of Alkenes
Consider the bromination of cyclopentene. Molecular bromine is polarized in the proximity of the π electrons of cyclopentene. An electrophilic bromine atom adds across the double bond, forming a cyclic bromonium ion intermediate.
Photochemical Electrocyclic Reactions: Stereochemistry
Selection Rules: Photochemical Activation
Cycloaddition Reactions: Overview
Benzene to 1,4-Cyclohexadiene: Birch Reduction Mechanism
Cycloaddition Reactions: MO Requirements for Thermal Activation
Cycloaddition Reactions: MO Requirements for Photochemical Activation

