Highly Stereoselective Iodolactonization of 4,5-Allenoic Acids-An Efficient Synthesis of 5-(1′-Iodo-1′(<i>Z</i>)-alkenyl)-4,5-dihydro-2(3<i>H</i>)-furanones
作者:Xinpeng Jiang、Chunling Fu、Shengming Ma
DOI:10.1002/chem.200801363
日期:2008.10.29
In this paper, it is reported that the efficient iodolactonization of 4,5-allenoic acid with I2 in cyclohexane in the presence or absence of K2CO3 afforded 5-(1'-iodo-1'(Z)-alkenyl)-4,5-dihydro-2(3H)-furanones highly stereoselectively. However, the reaction of axially optically active 4,5-allenoic acids (R)-(-)-5 a and (R)-(-)-5 b with I2 afforded the corresponding products with a serious loss of chirality
在本文中,据报道,在存在或不存在K2CO3的条件下,在环己烷中用I2对4,5-烯丙酸进行有效的碘内酯化,可得到5-(1'-碘-1'(Z)-烯基)-4,5 -dihydro-2(3H)-呋喃酮具有高度立体选择性。然而,轴向旋光的4,5-烯丙酸(R)-(-)-5a和(R)-(-)-5b与I 2的反应提供了具有严重手性损失的相应产物。通过在Cs2CO3存在下用N-碘琥珀酰亚胺在CH2Cl2中进行碘内酯化解决了这个问题。然而,Z / E的选择性较低。通过随后的Sonogashira偶联动力学拆分,可以制备纯的光学活性Z产物。底物与起始4,5-烯丙酸的3位上的取代基反应得到反式4,5-二取代的γ-丁内酯是唯一的产品。4,5-烯丙酸(S)-(+)-1 l,(R)-(-)-1 l和(S)-(+)-1 m的反应在3处具有中心手性不管丙二烯部分的轴向手性如何,-位置提供的反式产物具有非常高的对映体纯度和高达98:2的Z