# A focus on substituents effect in the force-promoted disrotatory ring-opening of cis-cyclobutenes

## TL;DR

The study explores how substituents affect the disrotatory ring-opening of cis-cyclobutenes under mechanical force.

## Contribution

The novel finding is that substituents near the scissile bond stabilize the diradical pathway, accelerating the reaction.

## Key findings

- Substituents close to the scissile bond stabilize the diradical character of the disrotatory pathway.
- This stabilization accelerates the mechanochemical ring-opening of cis-cyclobutenes.
- Mechanical activation reveals symmetry-forbidden pathways not accessible through conventional methods.

## Abstract

Symmetry-forbidden reactions are notoriously difficult to investigate as they are typically overshadowed by the corresponding symmetry-allowed pathway. Mechanical activation allows access to reaction pathways disfavoured using other methods of activation, such as the symmetry-forbidden disrotatory ring-opening of substituted cis-cyclobutenes. In a recent publication, Bowser, et al. have studied the effects of various substituents on this reaction using atomic force microscopy and computational analysis (B. H. Bowser, C. L. Brown, J. Meisner, T. B. Kouznetsova, T. J. Martínez and S. L. Craig, Chem. Sci., 2025, https://doi.org/10.1039/D5SC00253B). The largest effect is observed with substituents close to the scissile bond having the ability to stabilise the diradical character of the disrotatory ring-opening reaction pathway.

Bowser et al. have shown that substituents stabilising the diradical character of the symmetry-forbidden disrotatory pathway accelerate the mechanochemical ring-opening of cis-cyclobutenes (Chem Sci., 2025, https://doi.org/10.1039/D5SC00253B).