Microwave-assisted regioselective olefinations of cyclic mono- and di-ketones with a stabilized phosphorus ylide
作者:Jinlong Wu、Dan Li、Huafeng Wu、Lijie Sun、Wei-Min Dai
DOI:10.1016/j.tet.2005.12.060
日期:2006.5
4-cyclohexanediones with the ylide at 190 °C for 20 min in MeCN afforded the exocyclic olefins in >94:6 isomer ratios. On the other hand, the same reactions carried out at 230 °C for 20 min in the presence of 20 mol % DBU furnished the endocyclic olefins in >83:17 isomer ratios. The base-mediated isomerization of the exocyclic olefins into the endocyclic isomers was primarily driven by thermodynamic stability of the
在控制的微波加热下,许多环状的单酮和二酮与(carbethoxyethidene)三苯基磷芳烷进行区域选择性烯烃化反应。4-取代的环己酮或1,2-和1,4-环己二酮与ylide在MeCN中在190°C下进行Wittig反应20分钟,得到的外环烯烃的异构体比率> 94:6。另一方面,在20mol%DBU的存在下在230℃下进行20分钟的相同反应提供了> 83:17异构体比率的内环烯烃。碱介导的环外烯烃异构化成环内异构体主要是由产物的热力学稳定性驱动的,并且研究了环结构对去共轭作用的影响。