Enantioselective photochemical reactions of 2-pyridones in solution

[GRAPHICS] Two key photochemical reactions of prochiral 2-pyridones were studied in th e presence of a chiral host. The [4 + 4]-photocycloaddition with cyclopenta diene (CpH) proceeded smoothly and with high enantioselectivity (84-87% eel . The absolute configuration of the endo-diastereoisomer was established by Xray crystallography. The electrocyclic [4 pi]-ring closure to 3-oxo-2-aza bicyclo[2.2.0]-5-hexenes occurred with lower enantioselectivity (20-23% ee at -20 degreesC). The velocity of the latter reaction slowed significantly with decreasing temperature.