Enantioselective synthesis of unsubstituted and 3-substituted-4-aroyl-δ-lactones. Easy way to enantiopure bicyclic lactone systems

Article abstract of DOI:10.1016/0040-4020(96)00542-X

Michael addition of lithiated chiral aminonitriles 1a,b to α,β-unsaturated lactone 2 afforded (4R)-aroyl-δ-lactones 8a,b with a ee value ≤99%. Michael addition/subsequent α alkylation process gave the corresponding (3S)-substituted-(4R)-aroyl-δ-lactones 9-10a, 9b with a ee value of 66 up to 87% and 11-12a with high enantiomeric purity the ee being ≤99%. The absolute configuration of the Michael adduct 7a was established by X-ray analysis and as a result that of all the other compounds was assigned. Lewis acid catalyzed cyclization of (3S,4R)-12a provided the enantiomerically pure hydroxy bicyclic lactone (4aR,5S,8aS)-13a.