Related Experiment Video
Updated: Jun 21, 2026

Photogeneration of N-Heterocyclic Carbenes: Application in Photoinduced Ring-Opening Metathesis Polymerization
Published on: November 29, 2018
The photochemical C2-C6 cyclization of enyne-allenes: interception of the fulvene diradical with a radical clock ring
Götz Bucher1, Atul A Mahajan, Michael Schmittel
1Lehrstuhl für Organische Chemie II, Ruhr-Universität Bochum, Universitätsstrasse 150, D-44801 Bochum, Germany. goebu@chem.gla.ac.uk
Abstract:
The mechanism of the photochemical C(2)-C(6) cyclization of enyne-allenes has been studied through radical clock, intramolecular kinetic isotope effect, and laser flash photolysis (LFP) experiments as well as density functional theory (DFT) and ab initio computations. While the photochemical cyclization of enyne-allenes 1 and 2 furnished ene and Diels-Alder products without any cyclopropyl ring opening, that of 3 carrying the ultrafast diphenylcyclopropylcarbinyl radical clock afforded products derived from cyclopropyl ring opening. Laser flash photolysis (LFP) studies on enyne-allene 3 point to an allene triplet excited state (transient A) as a primarily formed short-lived (tau = 430 ns) intermediate. In addition, we have obtained evidence for the formation of a diphenylmethyl-type diradical (transient C, tau = 1.0 micros) resulting from ring opening of a diphenylcyclopropane ring. C subsequently undergoes a surprisingly slow (tau = 1.0 micros) 1,6-hydrogen shift leading to the stable 1,3-diene 6.
More Related Videos
10:10Application of Elemental Lanthanides in the Selective C-F Activation of Trifluoromethylated Benzofulvenes Providing Access to Various Difluoroalkenes
Published on: July 28, 2018
09:12[(DPEPhos)(bcp)Cu]PF6: A General and Broadly Applicable Copper-Based Photoredox Catalyst
Published on: May 21, 2019
Related Concept Videos
Photochemical Electrocyclic Reactions: Stereochemistry
Selection Rules: Photochemical Activation
Thermal and Photochemical Electrocyclic Reactions: Overview
Diels–Alder Reaction Forming Cyclic Products: Stereochemistry
[4+2] Cycloaddition of Conjugated Dienes: Diels–Alder Reaction
Cycloaddition Reactions: MO Requirements for Photochemical Activation
Thermal Electrocyclic Reactions: Stereochemistry
Selection Rules: Thermal Activation
Conjugated systems containing an even number of π-electron pairs undergo a conrotatory ring closure. For example, thermal electrocyclization of (2E,4E)-2,4-hexadiene, a conjugated diene containing two π-electron pairs, gives trans-3,4-dimethylcyclobutene.