Sequential Energy Transfer Catalysis: A Cascade Synthesis of Angularly-Fused Dihydrocoumarins
Tomáš Neveselý1, Constantin G Daniliuc1, Ryan Gilmour1
1Organisch Chemisches Institut , Westfälische Wilhelms-Universität Münster , Corrensstraße 40 , 48149 Münster , Germany.
Abstract:
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 E → Z 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.
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