PHOTOISOMERIZATION AND FRAGMENTATION OF VINYLIDENECYCLOALKANES AND SPIRO(2.N)CYCLOPROPENES (N=3-5) IN THE FAR-ULTRAVIOLET (185 NM)
The photochemistry of four-six membered ring vinylidenecycloalkanes and, additionally, the ground and excited state chemistry of a homologous series of spiro 2.n alk-1-enes (n = 3-5) were studied. The allenes were found to undergo excited state, 1,2-H migration on 185 nm photolysis to produce isomeric spirocyclopropenes ((PHI) = 0.016-0.034) and ethynylcycloalkanes ((PHI) = 0.011-0.019). Vinylmethylenes are discussed as potential intermediates. Isomeric 1-vinylcycloalkenes ((PHI) = 0.005) were also formed, presumably via carbene intermediates which undergo 1,4-H shifts. Depending on the structure of allene reactant, additional products were formed. For example photofragmentation of six and five-ring vinylidenecycloalkanes produced corresponding methylenecycloalkanes at short wavelength, 185 nm, but not at longer wavelength 228 nm. In the case of four and five-ring homologs, ring expansion to 3-methylenecycloalkenes was also important. Indication of the exocyclic allenic system and cyclobutane ring was significant for vinylidenecyclobutane, as evidenced by facile ((PHI) = 0.14) photochemical cleavage to ethylene and butatriene; in contrast pyrolysis produced 1,2-dimethylenecyclobutane. Comparison between ground and excited state chemistry of spirocyclopropenes revealed striking differences, photolysis at 185 nm led to isomerization to corresponding allenes ((PHI) = 0.10-0.15) and ethynylcycloalkanes ((PHI) = 0.07-0.17) for n = 3-5. For n = 4,5 1-vinylcycloalkenes were also photoproducts ((PHI) = 0.03). Photoextrusion of ethylene was the most efficient process ((PHI) = 0.46) of spiro 2.3 hex-1-ene, suggestive of spirocyclic interaction of cyclobutane ring and cyclopropene double bond. In contrast, pyrolysis of spirocyclopropenes (n = 3-4) gave high yields of ethynylcycloalkanes to the exclusion of isomeric allenes; 1-vinylcycloalkene was also formed for n = 4. Loss of ethylene was not observed in the ground state for spiro 2.n hex-1-ene.
YEN, YAO-PIN, "PHOTOISOMERIZATION AND FRAGMENTATION OF VINYLIDENECYCLOALKANES AND SPIRO(2.N)CYCLOPROPENES (N=3-5) IN THE FAR-ULTRAVIOLET (185 NM)" (1985). Dissertations (1962 - 2010) Access via Proquest Digital Dissertations. AAI8604965.