Regio- and <i>endo</i>-Selective [2 + 2] Photocycloadditions of Homobenzoquinones with Ethyl Vinyl Ether
作者:Ken Kokubo、Yu-ichi Nakajima、Katsuyuki Iijima、Hiroshi Yamaguchi、Tatsuya Kawamoto、Takumi Oshima
DOI:10.1021/jo991749z
日期:2000.6.1
various meta- and para-substituted homobenzoquinones with ethyl vinyl ether gave the [2 + 2] photoadducts, tricyclic diones, regio- and endo-selectively and in good yields. The tricyclic skeleton has an anti-form built by the addition of ethyl vinyl ether from the less hindered side of homoquinones. All of the CH(3), Cl, Br, and CH(3)O substituents at the reacting C=C double bond afforded head-to-head
用乙基乙烯基醚辐照各种间位和对位取代的均苯醌,可选择性和高产率地产生[2 + 2]光加合物,三环二酮。三环骨架具有反形态,该形态是通过从同醌的受阻较小的一侧添加乙基乙烯基醚而建立的。在反应的C = C双键处的所有CH(3),Cl,Br和CH(3)O取代基主要提供头对头(HH)加成。在CH(3),Cl和Br的情况下,乙氧基位于内位,而CH(3)O取代基则与外显异构体形成1/5的混合物。还发现,Br取代的[2 + 2]加合物会发生容易的骨架重排,转化为对位取代的二氢-邻苯醌单甲基化物衍生物和对位取代的二氢苯并呋喃衍生物,可能受到原位生成的HBr的影响。烯基高苯并醌的分子内[2 + 2]光环加成反应得到四环二酮。