Pressure control of diastereodifferentiating [2 + 2] photocycloaddition of (E)-stilbene to chiral fumarate upon direct and charge-transfer excitation.

The geometry (donor-acceptor distance) and association constant of the ground-state CT complex were considerably affected by applied pressure, thus enhancing the reaction rate and the adduct yield particularly upon CT excitation, but the diastereoselectivity did not show any substantial change at elevated pressures in both excitation modes.