A convenient synthesis of 2-oxazolin-5-ones and related compounds via amide cyclization
Acid catalyzed cyclization of diamides 3 leads to 2-oxazolin-5-ones of type 2 in high yield (Scheme 2). Resolution of racemic oxazolinone 2b is accomplished by reaction with (S)-phenylalanin dimethylamide ((S)-5) to yield a diastereomeric mixture of triamides 6 (Scheme 3) and cleavage of the diastereomers with HCl in toluene (cf. also Scheme 4). In an analogous reaction, monothio- and dithio-diamides 10, 12 and 14 have been cyclized to 2-thiazolin-5-ones 11, 2-thiazolin-5-thiones 13, and 2-oxazolin-5-thiones 15, respectively (Schemes 5 and 6).