Photochemical reactions are powerful tools to construct complex molecular scaffolds in organic synthesis. Among these transformations, intramolecular photochemical reaction cascades initiated by ortho-photocycloadditions (ortho-PCA) have been subject to extensive studies in our research group. While we had investigated a tandem transformation on salicylate substrates initially, we were able to extend the scope of this reaction to a variety of indanone substrates (A). Irradiation of such indanone substrates provided access to highly complex fused ring systems which can be applied in total synthesis (B). With this key step we could rapidly access the core structure of protoilludane natural products in a single operation. Chiral resolution of the obtained photo product 1 through a CBS-reduction-oxidation sequence and 10 subsequent transformations were performed to present the first total synthesis of (+)-atlanticone C (2). Fascinated by the power of this photochemical method for synthetic applications we are investigating whether substrate variation may allow quick assembly of further highly oxidized sesquiterpene natural products. Along these lines, we are currently developing methods for novel Brønsted acid activated and ortho-PCA initiated cascade reactions which provide access to further complex ring systems (C).

Accessing high structural complexity: Reaction cascades initiated by intramolecular ortho-photocycloadditions

ACS Spring 2022

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