The photochemistry of several bridgehead phenyl ketones has been investigated. Bicyclo[2.2.2]octyl, 1-adamantyl, and 1- and 3-homoadamantyl phenyl ketones undergo efficient photochemical α-cleavage in benzene solution, whereas bicyclo[3.2.1]octyl and bicyclo[2.2.1]heptyl phenyl ketones do not. The rates for α-cleavage of ketones 1-4 are dependent upon bi- and tricycloalkane structure in a manner similar to that previously reported for the thermolysis of bridgehead peresters. The rate constant for α-cleavage is accelerated for 1- or 3-homoadamantyl vs. tert-butyl, but retarded by the smaller bicyclic ring systems. The kinetic results are indicative of an early transition state with polar character for photochemical α-cleavage. Quantum yields for product formation are larger for the bridgehead ketones than for pivalophenone owing to a decreased cage effect. The photoreduction of these ketones has also been investigated.
ASJC Scopus subject areas
- Organic Chemistry