Intermolecular hydrogen binding of a chiral host and aprochiral imidazolidinone: enantioselective Norrish–Yang cyclisationin solution

The Norrish–Yang 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 (73–86%) with a distinct preference for the exo-diastereoisomer (dr = 77/23–90/10).