Stereocontrol in radical Mannich equivalents for aminosugar synthesis: haloacetal and 2-(phenylthio)vinyl tethered radical additions to α-hydroxyhydrazones
作者:Gregory K. Friestad、Tao Jiang、Gina M. Fioroni
DOI:10.1016/j.tet.2008.10.013
日期:2008.12
silicon-tethered ethynyl group to the CN bond of hydrazones, affording anti-hydrazino alcohols with a trans-2-(phenylthio)vinyl substituent. The one-pot process occurs under neutral, tin-free radical conditions, and offers stereocontrol which is complementary to the haloacetal method. Synthetic utility of the radical Mannich concept is demonstrated in a brief asymmetric synthesis of N-trifluoroacetyl-l-daunosamine
曼尼希加成反应的两种自由基当量的立体控制研究为氨基糖合成应用提供了新的见解。在第一种方法中,卤代乙缩醛的加成反应(上野-斯托克反应)扩展到二羟基hydr ,导致加合物具有出乎意料的3-表位-1-柔松胺构型。与不存在该取代基的相比,相邻的α-苄氧基取代基引起立体控制的显着逆转。建议用邻近偶极排斥来解决非对映选择性。在第二种方法中,自由基加成环化与苯硫酚和治疗用氟化导致从硅-拴系的乙炔基非对映选择性基团转移到腙的CN键,得到的抗-肼基醇与一反式-2-(苯硫基)乙烯基取代基。一锅法过程在中性,锡自由基条件下进行,并提供立体控制,这是卤代缩醛方法的补充。自由基曼尼希概念的合成效用在由非手性前体短暂合成N-三氟乙酰基-1-daunosamine中得到了证明。