Synthesis of enantiopure functionalized β-alkoxy γ-amino aldehydes by a new internal redox ring cleavage of carbohydrate-derived 1,2-oxazines

N-Methylation of 3,6-dihydro-2H-1,2-oxazines such as syn-1 or anti-1 followed by treatment with triethylamine smoothly furnished enantiopure beta-alkoxy gamma-amino aldehydes syn-2 and anti-2 in excellent yields. This mild N-O bond cleavage may be classified as internal redox process. Similar transformations of related 1,2-oxazines led to the expected compound anti-6 or to protected 4-amino hexose derivative 10. Starting from syn-2 or anti-2 condensation with hydrazine afforded new pyrazole derivatives syn-11 and anti-11 with stereodefined and protected amino diol side chain. Heterocycles syn-12 and syn-13 were prepared from syn-2 by condensation with 2-aminoimidazole or 2-aminobenzimidazole, respectively.