Related Experiment Video
Updated: Aug 21, 2026

Facile Preparation of (2Z,4E)-Dienamides by the Olefination of Electron-deficient Alkenes with Allyl Acetate
Published on: June 21, 2017
Diradical Character of Cyclic Allenes Enables Their Thermal (2 + 2) Cycloadditions
Noah W Gilbertson1, Allison T Hands1, Jacob P Sorrentino1
1Department of Chemistry and Biochemistry, University of California, Los Angeles, California90095, United States.
None:
(2 + 2) Cycloadditions are a versatile transformation often employed in the synthesis of cyclobutanes. Such cycloadditions usually require the use of light or another synthetic workaround, given that thermal (2 + 2) cycloadditions are orbital symmetry-forbidden for unstrained all-suprafacial transition states. A unique type of (2 + 2) cycloaddition involves transient strained cyclic allenes, which proceed readily at ambient temperature without external stimuli. In the present study, computations and experiments show that the feasibility of these cycloadditions is tied to the inherent diradical character of the cyclic allenes. Moreover, comparative stereochemical transfer experiments for Diels-Alder and (2 + 2) cycloadditions are consistent with strained cyclic allenes having both closed- and open-shell character, thus rendering them diradicaloids. This study is expected to prompt the further strategic use of diradicaloids for the assembly of complex scaffolds.
More Related Videos
09:35Preparation of a Corannulene-functionalized Hexahelicene by Copper(I)-catalyzed Alkyne-azide Cycloaddition of Nonplanar Polyaromatic Units
Published on: September 18, 2016
07:50Efficient Synthesis of All-Carbon Quaternary Centers via the Conjugate Addition of Functionalized Monoorganozinc Bromides
Published on: May 26, 2019
Related Concept Videos
Cycloaddition Reactions: Overview
Cycloaddition Reactions: MO Requirements for Thermal Activation
[4+2] Cycloaddition of Conjugated Dienes: Diels–Alder Reaction
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.
Electrophilic 1,2- and 1,4-Addition of X2 to 1,3-Butadiene
Electrophilic Addition to Alkynes: Halogenation
Halogenation is another class of electrophilic addition reactions where a halogen molecule gets added across a π bond. In alkynes, the presence of two π bonds allows for the addition of two equivalents of halogens (bromine or chlorine). The addition of the first halogen molecule forms a trans-dihaloalkene as the major product and the cis isomer as the minor product. Subsequent addition of the second equivalent yields the tetrahalide.