Enantioselective photochemical reactions of 2-pyridones in solution.
[reaction: see text] Two key photochemical reactions of prochiral 2-pyridones were studied in the presence of a chiral host. The [4 + 4]-photocycloaddition with cyclopentadiene (CpH) proceeded smoothly and with high enantioselectivity (84-87% ee). The absolute configuration of the endo-diastereoisomer was established by X-ray crystallography. The electrocyclic [4pi]-ring closure to 3-oxo-2-azabicyclo[2.2.0]-5-hexenes occurred with lower enantioselectivity (20-23% ee at -20 degrees C). The velocity of the latter reaction slowed significantly with decreasing temperature.
Bach
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Fachbereich Chemie, Philipps-Universität Marburg, Hans-Meerwein Str., 35032 Marburg, Germany. thorsten.bach@ch.tum.de
Bergmann
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H
Harms
K
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