Enantioselective photocyclisation reactions of 2-aryloxycyclohex-2-enones mediated by a chiral copper-bisoxazoline complex
作者:Verena Edtmüller、Alexander Pöthig、Thorsten Bach
DOI:10.1016/j.tet.2017.05.005
日期:2017.8
The photocyclisation of the title compounds leads upon direct irradiation at λ = 366 nm in dichloromethane solution to racemic cis-2,3,4a,9b-tetrahydro-1H-dibenzofuran-4-ones (nine examples, 37–74% yield). Since it was found that the substrates show a significant bathochromic absorption shift upon treatment with EtAlCl2, it was attempted to perform the reactions enantioselectively in the presence of
标题化合物的光环化作用是在二氯甲烷溶液中以λ= 366 nm的直接照射导致外消旋的顺式-2,3,4a,9b-四氢-1 H-二苯并呋喃-4-酮(9个实例,产率37-74%) 。由于发现在用EtAlCl 2处理时底物显示出显着的红移吸收位移,因此试图在手性路易斯酸的存在下对映选择性地进行反应。Cu(ClO 4)2 ·6H 2 O和双恶唑啉配体的络合物具有最佳的对映选择性(最高ee为60%))。据报道对映选择性光环化有两种方法。第一种方案是基于在λ= 368 nm(LED)处直接照射,催化剂负载量为50 mol%,它以26–76%的收率提供了22–40%ee的产物。第二种方案适用于富含电子的2-芳氧基环己-2-烯酮(31-62%收率,29-46%ee),并依赖于噻吨酮(50 mol%)在λ= 419 nm处的敏化作用。