摘要:
Three new syn-11-substituted pentacycloundecan-8-ones 1a-c (X = CN, CO2CH3, C6H5) have been synthesized and evaluated for photochemical reactivity in the context of the development of a force field methodology for evaluation of Norrish Type II reactions. None of these compounds underwent significant intramolecular hydrogen abstraction reactions or showed evidence for interactions between the excited alkanone and the proximate methylene hydrogens. The absence of isotope effect in the fluorescence of the deuteriated analogue of 1a provides strong evidence that there are no radiationless processes involving the proximate hydrogens that deactivate the singlet state of this ketone. A novel photostimulated interaction between alkanone singlet states and a ''remote'' cyano group was observed and rationalized in terms of dynamic processes during the excited state lifetime. Evidence is presented for competing long-range and contact interactions between singlet aryl rings and ground-state carbonyl groups. syn-11-tert-Butylpentacycloundecanone (2) was prepared and found to be photochemically unreactive as a consequence of a large increase in steric energy associated with formation of the transition structure.