coumarin derivatives by a cascade reaction (12 examples, 90–98% yield). The cascade comprised a [2+2] photocycloaddition which occurred upon sensitized irradiation at λ = 420 nm (or direct UV irradiation at λ = 366 nm) and a subsequent acid-catalyzed ring-opening reaction. A variety of substituents are compatible with the conditions and a 3-alkyl group in the coumarin (or quinolone) is crucial to achieve
通过级联反应,由容易获得的
喹诺酮和
香豆素衍
生物合成标题化合物(12个实例,收率90-98%)。级联包含[2 + 2]光环加成,该加成发生在λ= 420 nm的敏化辐射(或λ= 366 nm的直接紫外线辐射)和随后的酸催化开环反应中。多种取代基与条件相容,
香豆素(或
喹诺酮)中的3-烷基对于实现高
化学选择性至关重要。开环成功的关键是形成一个4,5,5a-三氢环丁2 H-
呋喃,它含有一个应变的桥头双键,该双键源于拴在起始材料4位上的烯基。