Reactivity and Mechanism of a Mechanically Activated anti-Woodward-Hoffmann-DePuy Reaction.

Mechanical forces, applied via covalent polymer mechanochemistry, have been used to bias reaction pathways and activate otherwise inaccessible reactions. Here, single-molecule polymer mechanochemistry is used to induce the disrotatory outward ring opening of a cis-dialkyl substituted syn-chloro-gem-chlorofluorocyclopropane, in violation of the Woodward-Hoffmann-DePuy (WHD) rule. The forces required to trigger the anti-WHD pathway on the ∼100 ms time scale of the experiment are about 200 pN greater than those involved in the WHD favored process (1290 vs 1500 pN). The kinetics are complemented by tension trapping experiments that suggest that the reaction proceeds along a reaction pathway that generates substantial diradicaloid character.