Characterization of Methylenepropenylidenecyclohexadiene Derivatives and Their Competing 1,6-Electrocyclic Reaction and 1,7-Hydrogen Shift at Room Temperature

1,2-Dihydronaphthalene-1,4-dicarbonitrile and its 1- and 2-benzyl- derivs. open upon photoexcitation to yield methylenepropenylidenecyclohexadienes (e.g., I, X = CN). The last compds., the spectra of which have been measured by flash photolysis, undergo 1,6-electrocyclic ring closure (rate 4 s-1 for the unsubstituted deriv.) and, when possible, 1,7-hydrogen shift (rate 400 s-1 for the 1-benzyl deriv.).