Oxidative rearrangement of 2-substituted oxazolines. A novel entry to 5,6-dihydro-2H-1,4-oxazin-2-ones and morpholin-2-ones

Article abstract of DOI:10.1021/jo952144f

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 described. Yields are good to excellent (up to 94%) with the highest yields obtained for 2-arylmethyl- and 2-neopentyl-substituted oxazolines. This reaction provides convenient access to novel 5-aryl-substituted dihydrooxazinones in high yield. The latter compounds are important 'chiral glycine' synthons for asymmetric synthesis of α-amino acids. Since oxazolines are readily derived from carboxylic acids or their equivalents, this oxidative rearrangement constitutes an entry to synthesis of α-amino acids from carboxylic acids. A mechanism is proposed to account for the rearrangement involving a 'nitrilium to acylium' 1,2-migration.