Related Experiment Video
Updated: Jun 19, 2026

Isolating Free Carbenes, their Mixed Dimers and Organic Radicals
Published on: April 19, 2019
Dötz benzannulation reactions: heteroatom and substituent effects in chromium Fischer carbene complexes
J Oscar C Jimenez-Halla1, Miquel Solà
1Institute of Computational Chemistry, University of Girona, Campus Montilivi, 17071 Girona, Catalonia, Spain.
Abstract:
We have carried out a theoretical investigation of the Dötz reaction between acetylene and a series of chromium Fischer-type carbenes [(CO)(5)Cr=C(X)R] with different representative substituents (R=CH=CH(2), Ph) and heteroatom ligands (X=OH, NH(2), OCH(3), N(CH(3))(2)) by using density functional theory with the B3LYP functional. We have studied the Dötz and chromahexatriene mechanisms of benzannulation and also the reaction mechanism leading to cyclopentannulation. For the benzannulation, it was found that the most likely mechanism in the case of vinylcarbenes is the chromahexatriene route, whereas for phenylcarbenes, the Dötz route via a ketene intermediate is clearly the most favorable. The reactions leading to the cyclopentannulated and benzannulated products are more exothermic with vinylcarbenes than with phenylcarbenes and also more exothermic with alkoxycarbenes than with aminocarbenes. The relative stability of the cyclopentannulated products as compared with the benzannulated products increases for bulkier X substituents and on going from alkoxy- to aminocarbenes. The kinetic data concurs with the experimental product distribution found for vinylcarbenes, by which mainly benzannulated products are obtained, and dimethylaminophenylcarbenes, which lead exclusively to cyclopentannulated adducts.
More Related Videos
19:58Palladium N-Heterocyclic Carbene Complexes: Synthesis from Benzimidazolium Salts and Catalytic Activity in Carbon-carbon Bond-forming Reactions
Published on: July 30, 2017
10:52Line Shape Analysis of Dynamic NMR Spectra for Characterizing Coordination Sphere Rearrangements at a Chiral Rhenium Polyhydride Complex
Published on: July 27, 2022
Related Concept Videos
Electrophilic Aromatic Substitution: Chlorination and Bromination of Benzene
Benzene to 1,4-Cyclohexadiene: Birch Reduction Mechanism
Reactions at the Benzylic Position: Halogenation
Electrophilic Aromatic Substitution: Fluorination and Iodination of Benzene
Reactions at the Benzylic Position: Oxidation and Reduction
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.