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Regiodivergent Photocyclization of Dearomatized Acylphloroglucinols: Asymmetric Syntheses of (−)-Nemorosone and (−)-6-epi-Garcimultiflorone A

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posted on 19.06.2019, 00:00 authored by Saishuai Wen, Jonathan H. Boyce, Sunil K. Kandappa, Jayaraman Sivaguru, John A. Porco
Regiodivergent photocyclization of dearomatized acylphloroglucinol substrates has been developed to produce type A polycyclic polyprenylated acylphloroglucinol (PPAP) derivatives using an excited-state intramolecular proton transfer (ESIPT) process. Using this strategy, we achieved the enantioselective total syntheses of the type A PPAPs (−)-nemorosone and (−)-6-epi-garcimultiflorone A. Diverse photocyclization substrates have been investigated leading to divergent photocyclization processes as a function of tether length. Photophysical studies were performed, and photocyclization mechanisms were proposed based on investigation of various substrates as well as deuterium-labeling experiments.