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

Abstract

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-<i>epi</i>-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.