Intramolecular Electron Transfer Reactions Catalyzed by α-Oxo and β-Oxo Substituents in the 1-Chlorobicycloheptane System

Article abstract of DOI:10.1021/jo00109a035

Efficient intramolecular ET catalysis in S_RN1 reactions was observed when a carbonyl group is present in 1-chlorobicyclo<2.2.1>heptane in the α or β position. 1-Chloro-3,3-dimethyl-2-oxobicyclo<2.2.1>heptane (1) and 4-chloro-1,7,7-trimethyl-2-oxobicyclo<2.2.1>heptane (4) reacted with diphenylphosphide ion (Ph2P(1-)) as nucleophile in liquid ammonia under photostimulation to give the substitution products in good yields, together with very small amounts of the reduction product.The substitution products were not observed in dark conditions, and the photostimulated reactions were inhibited by p-dinitrobenzene.These reactions are proposed to proceed via the S_RN1 mechanism.In competition experiments, the reactivity ratio of 1 to 4 was 2.8, whereas the ratio of 1-chloro-3,3-dimethyl-2-oxobicyclo<2.2.2>octane (8) to 4 was 1:1.On the other hand, 1-chloro-2-methylene-3,3-dimethylbicyclo<2.2.1>heptane (7) was unreactive under these experimental conditions.It then seems to follow that when there is a carbonyl group in these bicyclic compounds, in the α or β position, they react by the S_RN1 mechanism, and the overall reactivity is similar, but when the C=O is replaced by a C=C, the substrate did not react in these experimental conditions.These results are in agreement with MO calculations, in which the LUMO of compounds 1, 4, and 8 belongs to the ?^* MO of the C=O group, with similar energies, and is lower than the ?^* MO of 7.