A variety of 3-substituted benzisoxazoles were reduced with hydrogen using the chiral ruthenium catalyst, RuCl(p-cymene)[(R,R)-(S,S)-PhTRAP]}Cl. The ruthenium-catalyzed hydrogenation proceeded in high yield in the presence of an acylating agent, affording a-substituted o-hydroxybenzylamines with up to 57% ee. In the catalytic transformation, the N–O bond of the benzisoxazole substrate is reductively cleaved by the ruthenium complex under the hydrogenation conditions. The C–N double bond of the resulting imine is saturated stereoselectively through the PhTRAP–ruthenium catalysis. The hydrogenation produces chiral primary amines, which may work as catalytic poisons, however, the amino group of the hydrogenation product is rapidly acylated when the reaction is conducted in the presence of an appropriate acylating agent, such as Boc2O or Cbz-OSu.
使用手性
钌催化剂 RuCl(p-cymene)[(R,R)-(S,S)-Ph
TRAP]}Cl 用
氢气还原了多种 3-取代的苯并
异噁唑。在酰化剂存在的情况下,
钌催化的氢化反应以较高的产率进行,可得到 a-取代的邻羟基
苄胺,ee 值高达 57%。在催化转化过程中,苯并
异噁唑底物的 N-O 键在氢化条件下被
钌络合物还原裂解。通过 Ph
TRAP
钌催化,生成的
亚胺的 C-N 双键立体选择性地饱和。然而,当反应在适当的酰化剂(如 Boc2O 或 Cbz-OSu)存在下进行时,氢化产物的
氨基会迅速酰化。