Two stereoisomeric ketones, endo-and exo-(2-hydroxy-[2.2. 2] bicyclo-5-en-1-yl)-phenyl methanone (endo-2 and exo-2) were synthesized via a Lewis acid catalyzed Diels–Alder reaction. Both compounds were tested in terms of their efficiency as photoinitiators for radical polymerization. Whereas the exo isomer serves as a good photoinitiator, the curing efficiency is poor in the case of the endo derivative. CIDNP investigations and product ...