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 β-alkoxy γ-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.
将 3,6-二氢-2H-1,2-噁嗪(如 syn-1 或 anti-1)进行 N-甲基化,然后用
三乙胺处理,就能以极好的收率顺利制得对映纯δ-²-烷氧基δ-³-
氨基醛 syn-2 和 anti-2。这种温和的 N-O 键裂解可归类为内部氧化还原过程。相关的 1,2-噁嗪类化合物经过类似的转化后,可得到预期的化合物 anti-6 或受保护的 4-
氨基己糖衍
生物 10。从 syn-2 或 anti-2 开始,与
肼进行缩合,可得到具有立体定向和受保护
氨基二元醇侧链的新
吡唑衍
生物 syn-11 和 anti-11。由 syn-2 通过与
2-氨基咪唑或
2-氨基苯并咪唑缩合,分别制备出了杂环 syn- 12 和 syn-13。