Asymmetric alcoholysis of 2-phenyl-5(4H)-oxazolones by the catalytic mixture of cyclo[(S)-His-(S)-Phe] with chiral auxiliaries

Some derivatives of dipeptides containing a His residue catalyzed the ring opening of 2-phenyl-4-benzyl-5(4H)oxazolone by methanol. The mixture of cyclo[(S)-His-(S)-Phe] (CHP) with chiral auxiliaries which possess both a hydrogen-bond donor and a hydrogen-bond acceptor was a more effective and enantioselective catalyst than the CHP alone. The influence of racemic and the two enantiomerically pure auxiliaries on the cyclo[(S)-His-(S)Phe]-catalyzed alcoholysis of the 5(4H)-oxazolone was different. A mixture of CHP with L-diisopropyl tartrate catalyzed the enantioselective ring opening of 2-phenyl-4-benzyl-5(4H)-oxazolone by methanol, ethanol and n-butanol, preferentially affording the N-benzoyl-L-phenylalaninates (20-39% e.e.). (C) 2000 Elsevier Science Ltd. All rights reserved.