ABSTRACT
Several excellent reviews dealing with various aspects of
β
,
γ
-enone photochemistry have appeared.
A good historical background on the photoreactions of
β
,
γ
-enones is described by Schuster.
In principle,
β
,
γ
-enones can undergo photoreactions that are characteristic of carbonyl and olefinic chromophores, such as photoreduction, epimerization and
cis,trans-
isomerization, [2+2]-cycloaddition, etc. They also undergo two unique reactions as
a result of interaction between the alkene and carbonyl chromophore. In general, it has been observed that sensitized irradiation of
β
,
γ
-enones induces a 1,2-acyl migration that results in the formation of cyclopropyl conjugated ketones of type
, a reaction also known as oxa-di-
π
-methane rearrangement because of its analogy to the di-
π
-methane (Zimmerman) rearrangement. The direct irradiation of
β
,
γ
- enones leads to formation of enones of type
as a result of 1,3-acyl migration (Scheme 1).
