SYNTHESIS OF CYCLIC ACYLATED ENAMINO ESTERS FROM ENOL LACTONES, 4-KETO AMIDES, AND 5-HYDROXY LACTAMS

Enol lactones react with an amine to give either a keto amide or a hydroxy lactam under mild conditions. Subsequent dehydration with p-toluenesulfonic acid (PTSA) gives a cyclic acylated enamino ester in good yield (Tables 1 and 2, Schemes 2 and 4). The key prostaglandin analog precursor 18 and the gly-gly dipeptide analogs 26a and 26b were prepared using the reported conditions. Acetylation of the chloro hydroxy lactam 31, prepared from the chloro enol lactones 29, followed by elimination of acetic acid gave the chloro acylated enamino esters 28.