Issue 34, 2020

Stereoretention in styrene heterodimerisation promoted by one-electron oxidants

Abstract

Radical cations generated from the oxidation of C[double bond, length as m-dash]C π-bonds are synthetically useful reactive intermediates for C–C and C–X bond formation. Radical cation formation, induced by sub-stoichiometric amounts of external oxidant, are important intermediates in the Woodward–Hoffmann thermally disallowed [2 + 2] cycloaddition of electron-rich alkenes. Using density functional theory (DFT), we report the detailed mechanisms underlying the intermolecular heterodimerisation of anethole and β-methylstyrene to give unsymmetrical, tetra-substituted cyclobutanes. Reactions between trans-alkenes favour the all-trans adduct, resulting from a kinetic preference for anti-addition reinforced by reversibility at ambient temperatures since this is also the thermodynamic product; on the other hand, reactions between a trans-alkene and a cis-alkene favour syn-addition, while exocyclic rotation in the acyclic radical cation intermediate is also possible since C–C forming barriers are higher. Computations are consistent with the experimental observation that hexafluoroisopropanol (HFIP) is a better solvent than acetonitrile, in part due to its ability to stabilise the reduced form of the hypervalent iodine initiator by hydrogen bonding, but also through the stabilisation of radical cationic intermediates along the reaction coordinate.

Graphical abstract: Stereoretention in styrene heterodimerisation promoted by one-electron oxidants

Supplementary files

Article information

Article type
Edge Article
Submitted
01 Jun 2020
Accepted
12 Aug 2020
First published
17 Aug 2020
This article is Open Access

All publication charges for this article have been paid for by the Royal Society of Chemistry
Creative Commons BY-NC license

Chem. Sci., 2020,11, 9309-9324

Stereoretention in styrene heterodimerisation promoted by one-electron oxidants

X. Zhang and R. S. Paton, Chem. Sci., 2020, 11, 9309 DOI: 10.1039/D0SC03059G

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