Photochemical transformations of 3-alkyl-3-ferrocenylcyclopropenes

Photolysis of 3-ferrocenyl-3-methyl- and 3-fenocenyl-3-isopropylcyclopropen es was studied. Sensitized irradiation (triplet excitation) afforded [2+2]- cycloaddition products, vit., tricyclohexane derivatives. Direct irradiatio n (singlet excitation) of methyl-substituted ferrocenylcyclopropene gave ri se to 2-ferrocenylbut-1-en-3-yne and trans-2-ferrocenylbut-2-ene. The isopr opyl analog was converted into 1-ferrocenyl-4,4-dimethylcyclobutene. The re action of this cyclopropene with 2-ferrocenyl-3-methylbut-1-ene afforded 1, 3-diferrocenyl-3-isopropyl-6,6-dimethylcyclohexene. The latter compound and 3,6-diferrocenyl-3,6diisopropyltricyclo[3.1.0.0(2,4)]hexane were studied b y X-ray diffraction analysis. Possible reaction pathways are discussed.