Cyclobutene photochemistry. Reinvestigation of the photochemistry of cis- and trans-tricyclo[6.4.0.02,7]dodec-1-ene

The direct photolyses of cis- and trans-tricyclo[6.4.0.0 2,7 ]dodec-1-ene in hydrocarbon solution have been reinvestigated with 193-nm, 214-nm, and broad-band UV (>200 nm) light sources. The two compounds undergo competitive stereospecific fragmentation (yielding cis- or trans-cyclododec-7-en-1-yne, respectively) and ring opening (yielding 1,1'-bicyclohexenyl). The observation of 1,1'-bicyclohexenyl formation from both cyclobutene isomers differs from the results of a previous study of the photochemistry of these compounds, which concluded that only the cis isomer undergoes ring opening upon photolysis in solution, presumably via a disrotatory electrocyclic pathway. The present results verify the conclusions of several recent studies that the photochemical ring opening of alkylcyclobutenes in general proceeds nonstereospecifically