Regiochemical Trends in Intramolecular [2 + 2] Photocycloadditions of 6-(prop-2-enyl)cyclohex-2-enones and 5-(prop-2-enyl)cyclopent-2-enones
作者:Giuliano Cruciani、Paul Margaretha
DOI:10.1002/hlca.19900730208
日期:1990.3.14
cyclization becomes low enough so that lumiketone rearrangement to bicyclohexanones 6 and 3-isopropylcyclopent-2-enones 9 becomes competitive. Enones 9 undergo consecutive intramolecular [2 + 2] photocycloaddition to tricyclo[3.2.1.03,6]octan-2-ones 7 and to tricyclo[3.2.1.03,6]octan-7-ones 8, compounds 8 only being formed when R Me.
取代基(烯丙基侧链的C(6)处的XH,Me或F,烯丙基侧链的C(2')处的RH或Me)对6烯丙基环己基-2-烯酮1的光异构化(λ= 350 nm)的影响在MeCN中进行了研究。取代基X控制分子内[2 + 2]光环加合物形成的整体效率(Φ:Me> F> H),但不影响外环双键向烯酮CC键加成的方向。相比之下,丙-2-烯基(RH)被2-甲基丙-2-烯基(R Me)侧链取代会引起三环[3.3.1.0 2,7 ] nonan -6-one 4 vs 。三环[4.2,1.0 3,8 ]壬烷-7-酮(5)产品比率从100:0(RH)到大约2:1(R Me),但几乎与1到产品的相对转化率无关。对于C(6)-未取代的烯酮1aa和1ba(XH),环化的效率变得足够低,以至于双环己酮6和3-异丙基环戊-2-烯酮9的烯酮重排变得具有竞争力。烯酮9经历连续的分子内[2 + 2]光环加成反应到三环[3.2.1.0 3