The title compounds were synthesized from readily available quinolone and 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 a high chemoselectivity. Key to the success of the ring opening is the formation of a 4,5,5a-trihydrocyclobuta-2H-furan containing a strained bridgehead double bond which stems from the allenyl group tethered to the 4-position of the starting materials.

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。