Caged trans-4-hydroxy-2-nonenal.

[reaction: see text] A caged 4-hydroxy-2-nonenal (4-HNE) has been prepared and its photochemistry investigated. Upon photolysis, 1 releases 4-HNE in up to 100% yield. From these photolyses, 4-HNE could be isolated in up to 91% yield. 4-HNE is produced under either aerobic or anaerobic conditions. The caging strategy does not require prior preparation of 4-HNE and, therefore, represents a three-step synthetic route to the bioactive enal in 48% overall yield.