Organisch Chemisches Institut , Westfälische Wilhelms-Universität Münster , Corrensstraße 40 , 48149 Münster , Germany.
Org Lett. 2019 Dec 6;21(23):9724-9728. doi: 10.1021/acs.orglett.9b03882. Epub 2019 Nov 20.
An operationally simple one-pot protocol has been developed to enable the conversion of diversely substituted cinnamic acid derivatives into angularly-fused dihydrocoumarins (up to 94%). Inspired by coumarin biosynthesis, this reaction cascade harnesses photochemical alkene isomerization enabled by energy transfer catalysis using inexpensive thioxanthen-9-one (TX) under irradiation at 402 nm. Subsequent lactonization generates the heterocyclic core prior to a second photosensitization event to induce a [2 + 2] cycloaddition, again mediated by TX. The tetracyclic products are generated efficiently, and proof of the structure was established by X-ray crystallography. Mechanistic investigations, including structural probes and NMR reaction monitoring, support the postulated order of events. The study underscores the synthetic value of inexpensive small-molecule organic photocatalysts in the generation of structural complexity via sequential π-bond activation.
已经开发出一种操作简单的一锅法协议，可将各种取代的肉桂酸衍生物转化为角形稠合的二氢香豆素（高达 94%）。受香豆素生物合成的启发，该反应级联利用廉价的噻吨酮-9-酮（TX）通过能量转移催化进行光化学烯烃异构化，在 402nm 照射下进行。随后内酯化在第二次光致敏化事件之前生成杂环核心，以诱导[2+2]环加成，再次由 TX 介导。四环产物的生成效率高，并通过 X 射线晶体学证明了结构的合理性。包括结构探针和 NMR 反应监测在内的机理研究支持所提出的事件顺序。该研究强调了廉价小分子有机光催化剂在通过顺序π键活化生成结构复杂性方面的合成价值。
