The NorrishâYang cyclisation of a prochiral
imidazolidinone which was conducted in the presence of a chiral host
afforded enantiomerically enriched (up to 26% ee)
1,3-diazabicyclo[3.3.0]octanones in good yields (73â86%) with a
distinct preference for the exo-diastereoisomer (dr =
77/23â90/10).
single-crystal X-ray crystallography of its chiral N-methoxyphenylacetyl derivative 15a. In a similar fashion, the absolute configurations of the endo products 12b and ent-12b were established. The N-2-oxoethylimidazolidinone 5, which crystallized in a chiral space group, was irradiated in the solidstate. At low levels of conversion, the product 9a/ent-9a was formed with high enantiomeric excess (78%