作者:Kenichi Somekawa、Tetsuro Shimo、Hiroyuki Yoshimura、Takaaki Suishu
DOI:10.1246/bcsj.63.3456
日期:1990.12
Sensitized photoreactions of two 2-pyrones with five unsaturated compounds were investigated. The reactions of 2-pyrones with electron-deficient ethylenes gave [4+2]cycloadducts (3) and [2+2]cycloadducts (4) across the C5–C6 double bonds in the 2-pyrones. On the other hand, reactions with an electron-donating ethylene, ethyl vinyl ether (2i), gave other kinds of [2+2]cycloadducts (5) and a [4+2]cycloadduct (6), site- and regio-selectively. These two kinds of reactions were inferred to start at the C-6 and C-4 positions of the 2-pyrones to give 3 or 4, and 5 or 6, respectively. The regioselectivity of 6 was opposite to that for a thermal [4+2]cycloadduct (7). The substituents on 2-pyrones also influenced the product-distribution and the triplet energy-level.
研究了两种 2-吡喃酮与五种不饱和化合物的敏化光反应。2-pyrones 与缺电子的乙烯反应,在 2-pyrones 的 C5-C6 双键上产生 [4+2]cycloadducts (3) 和 [2+2]cycloadducts (4)。另一方面,与乙烯(乙烯基乙醚 (2i))这种电子捐赠型乙烯反应,则会产生其他类型的 [2+2]cycloadducts (5) 和一种 [4+2]cycloadduct (6),具有位点和区域选择性。根据推断,这两种反应分别从 2-吡喃酮的 C-6 和 C-4 位置开始,得到 3 或 4,以及 5 或 6。6 的区域选择性与热[4+2]环加合物(7)的区域选择性相反。2-pyrones 上的取代基也会影响产物分布和三重能级。