Differences in thermal and photochemical product distributions of spiro[2.4] hept-I -ene reflect state selective reactivity of So and S, vinylcarbene intermediates. ... The singlet photochemistry of cyclopropenes has continued to attract interest,lP5 although efforts have largely been devoted to examples bearing substituents to provide a chromophore accessible at long wavelengths (h >220 nm). Such substituents as phenyl, vinyl, or acyl on C(3) divert reactivity towards ...