Ohno Hiroaki, Mizutani Tsuyoshi, Kadoh Yoichi, Aso Akimasa, Miyamura Kumiko, Fujii Nobutaka, Tanaka Tetsuaki
Graduate School of Pharmaceutical Sciences, Kyoto University, Sakyo-ku, Kyoto 606-8501, Japan.
J Org Chem. 2007 Jun 8;72(12):4378-89. doi: 10.1021/jo0700528. Epub 2007 May 10.
Thermal [2 + 2] cycloaddition of allenes with an additional multiple bond is described. By simply heating the allenenes or allenynes having a three-atom tether in an appropriate solvent such as dioxane or DMF, the distal double bond of the allenic moiety regioselectively participates in the cycloaddition to form bicyclo[4.2.0]oct-5-ene derivatives in good to excellent yields. In all the reactions of allenenes, the olefin geometry was completely transferred to the cycloadducts. While the reaction of terminal allenes afforded bicyclic cyclobutane derivatives as a single isomer, the cycloaddition of some internal allenes with axial chirality yielded a diastereomeric mixture of cycloadducts. These results are in good accordance with the stepwise mechanism through a biradical intermediate with a coplanar allyl radical.
描述了丙二烯与额外多重键的热[2 + 2]环加成反应。通过在适当的溶剂（如二氧六环或N,N-二甲基甲酰胺）中简单加热具有三原子连接链的丙二烯或烯炔，丙二烯部分的远端双键区域选择性地参与环加成反应，以良好至优异的产率形成双环[4.2.0]辛-5-烯衍生物。在丙二烯的所有反应中，烯烃的几何构型完全转移到环加成产物中。虽然末端丙二烯的反应生成了作为单一异构体的双环环丁烷衍生物，但一些具有轴向手性的内丙二烯的环加成反应产生了环加成产物的非对映体混合物。这些结果与通过具有共平面烯丙基自由基的双自由基中间体的逐步机理高度一致。
