OXIDATIVE REARRANGEMENT OF 2-SUBSTITUTED OXAZOLINES - A NOVEL ENTRY TO 5,6-DIHYDRO-2H-1,4-OXAZIN-2-ONES AND MORPHOLIN-2-ONES

A novel synthesis of 5,6-dihydro-2H-1,4-oxazin-2-ones by SeO2-promoted oxidative rearrangement of 2-alkyl- and 2-(arylmethyl)oxazolines is d escribed. Yields are good to excellent; (up to 94%) with the highest y ields obtained for 2-arylmethyl- and 2-neopentyl-substituted oxazoline s. This reaction provides convenient access to novel 5-aryl-substitute d dihydrooxazinones in high yield. The latter compounds are important ''chiral glycine'' synthons for asymmetric synthesis of a-amino acids. Since oxazolines are readily derived from carboxylic acids or their e quivalents, this oxidative rearrangement constitutes an entry to synth esis of a-amino acids from carboxylic acids. A mechanism is proposed t o account for the rearrangement involving a ''nitrilium to acylium'' 1 ,2-migration.