Dioxopyrrolines. LIII. Stereochemical Pathway of (2+2) Photocycloaddition Reaction of 4-Ethoxycarbonyl-5-phenyl-1H-pyrrole-2,3-dione to Cyclic Enol Trimethylsilyl Ethers.
作者:Takehiko SANO、Miyuki HIROSE、Yoshie HORIGUCHI、Fumiyuki KIUCHI、Yoshisuke TSUDA
DOI:10.1248/cpb.41.64
日期:——
The photocycloaddition reaction of the dioxopyrroline 1 to cyclic trimethylsilyloxy olefins was examined. The addition of 3-trimethylsilyloxy-1H-indene and 4-trimethylsilyloxy-1, 2-dihydronaphthalene occurred in a regio- and stereoselective manner to give the cis-anti-cis cyclobutanes 3 and 4, respectively. The stereochemical result supported the stereo-selection rule which states that the photocycloaddition of a very polar dioxopyrroline-olefin pair proceeds in an s+s manner via f favored O-endo-π-complex transition. On the other hand, the addition of 1-trimethylsilyloxy-cyclopentene and 1-trimethylsilyloxycyclohexene occurred less stereoselectively, proceeding predominantly in an s+a manner to give the adducts 5a, b, 6a, b, 7a, b, and 12. The results are consistent with the prediction of the stereo-selection rule obtained by assuming that these dioxopyrroline-olefin pairs are polar. The latter cases demonstrate that an incresed steric hindrance around the olefin moiety affects the polarity of enone-olefin pair in the transition state.
研究了二氧吡咯啉1与环状三甲基硅氧基烯烃的光环加成反应。3-三甲基硅氧基-1H-茚和4-三甲基硅氧基-1,2-二氢萘进行了区域选择性和立体选择性的加成反应,分别得到顺反顺式环丁烷3和4。立体化学结果支持立体选择规则,该规则指出非常极性的二氧吡咯啉-烯烃对的光环加成反应通过优先的O-endo-π-复合物过渡态以s+s方式进行。另一方面,1-三甲基硅氧基环戊烯和1-三甲基硅氧基环己烯的加成立体选择性较低,主要以s+a方式进行,得到加合物5a, b, 6a, b, 7a, b和12。结果与假设这些二氧吡咯啉-烯烃对为极性时得到的立体选择规则预测一致。后一种情况表明,烯烃部分周围的立体阻碍增加会影响过渡态中烯酮-烯烃对的极性。