Asymmetric Dearomatization/Cyclization Enables Access to Polycyclic Chemotypes

Abstract

Enantioenriched, polycyclic compounds were obtained from a simple acylphloroglucinol scaffold. Highly enantioselective dearomatization was accomplished using a Trost ligand-palladium(0) complex. A computational DFT model was developed to rationalize observed enantioselectivities and revealed a key reactant-ligand hydrogen bonding interaction. Dearomatized products were used in visible light-mediated photocycloadditions and oxidative free radical cyclizations to obtain novel polycyclic chemotypes including tricyclo[4.3.1.01,4]decan-10-ones, bicyclo[3.2.1]octan-8-ones and highly-substituted cycloheptanones.

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

“…However, under the optimized conditions for type A PPAP scaffolds, photocyclization of 25 afforded the de Mayo-type cycloaddition product 26 as a single diastereomer in 24% yield (Scheme ). We had previously observed 26 to be a product of visible light-mediated photocycloaddition of 25 resulting from triplet energy transfer . In a similar manner, photoirradiation of the dearomatized prenyl derivative 27 afforded the related product 28 in 13% yield along with rearomatized product 29 (17%).…”

Modular Total Syntheses of Hyperforin, Papuaforins A, B, and C via Gold(I)-Catalyzed Carbocyclization

“…Other PPAPs such as papuaforins A, B, and C ( 2 - 4 ) isolated from Hypericum papuanum found in Papua New Guinea possess modest antibacterial properties activity . The structural complexity of PPAPs combined with their therapeutic profiles have stimulated the genesis of numerous synthetic strategies . These strategies culminated in the successful syntheses of various PPAPs including hyperforin ( 1 ), nemorosone ( 5 ), and garsubellin A ( 6 ) .…”

Controlling Isomerization Selectivity in Chiral, Photochromic N,C-Chelate Organoboron Systems with Extended π-Conjugation

“…Unlike ground state (thermal) reaction pathways, which are readily influenced by steric and electronic considerations of the reacting components, controlling the outcome of excited-state processes tends to be more difficult given the highly reactive/​transient nature of the intermediates that are involved . Nevertheless, it is still possible to develop useful and selective photochemical transformations that yield desirable products, as exemplified by various well-known organic reactions (e.g., Norrish and DeMayo), and recent advances in photochromic materials science (e.g., diarylethenes, spiropyrans, and fulgides). With respect to the design of new main-group based molecular switches, we have been extensively studying the photoreactivity of tetracoordinate N,C-chelate organoboron compounds (Scheme a; A / B ), which undergo aryl insertion into a B–C Ph bond upon exposure to UV light, generating intensely colored azaborata­bis­norcaradiene (borirane) isomers ( C/D ) .…”