Demonstration of Woodward-Hoffmann behavior in the pulsed, infrared laser induced reaction of cis-3,4-dichlorocyclobutene

The pulsed, infrared laser induced reaction of cis-3,4-dichlorocyclobutene has been demonstrated to produce cis,-trans-1,4-dichloro-1,3-butadiene as the only detectable product even though the reaction system was not at thermal equilibrium. This is the isomer predicted by the Woodward-Hoffmann rules of conservation of orbital symmetry for a thermally allowed, ground-state, conrotatory ring opening. Even at relatively short laser pulses, reaction via a higher energy, nonallowed channel or biradical intermediate could not be made competitive within the experimental detection limit