Gold‐Catalyzed Cyclopenta‐ and Cycloheptannulation Cascades: A Stereocontrolled Approach to the Scaffold of Frondosins A and B

Gold(I)-catalyzed enantioselective cycloaddition reactions

“…A possible mechanism would involve a gold-mediated 1,2-acyloxy migration of the propargyl ester to generate a gold–carbene species III which cyclopropanates a C–C double bond of the diene to form a cis -cyclopropane intermediate IV . A subsequent gold-catalyzed Cope rearrangement through a boat-like transition state would deliver the cis -2,3-disubstituted cycloheptenyl acetates of type 5 (Scheme 3) [43]. …”

Gold‐Catalyzed Reaction of ortho‐Alkynylarylaldehydes with Conjugated Dienes: An Efficient Access to Highly Strained Tetracyclic Bridgehead Olefins

“…This approach would not only allow rapid and unprecedented accesst oh ighly strained polycyclic bridgehead olefins, but would also furtherh ighlight the potential of gold catalysis for the generation of structural complexity from simple startingm aterials. [9] o-Alkynylbenzylaldehyde 4a [10] and conjugated diene 5a [11] were initially chosen as model substrates for our study (Scheme 3). We were aware that their reaction in the presence of ag old catalyst might lead to some selectivity issues.…”

Platinum-Catalyzed α,β-Unsaturated Carbene Formation in the Formal Syntheses of Frondosin B and Liphagal

“…1a,2 Liphagal has been found to have human phosphatidylinositol-3-kinase (PI3K) α -selective inhibitory activity; 1b,3 compounds that modulate the PI3K signaling pathway may have therapeutic potential in the treatment of autoimmune disorders, cancer, and cardiovascular disease. Their interesting architectures coupled with their potential to serve as leads in the search for therapeutics have inspired numerous groups to undertake total syntheses of both frondosin B 4 and liphagal. 1b,5 …”

“…We evaluated different ligand systems and found that inclusion of Feringa’s phosphor-amidite 14 provided the best results, with a 74% isolated yield of chromatographically inseparable tetracycles 6aa and 12 , in a 2.5:1 ratio. 15 These compounds could be separated after the acid-mediated isomerization 4i to conjugated benzofurans 13 and 14 . 16 The syntheses of tetracycle 6aa , and subsequently tetracycle 13 , represent a formal total synthesis of frondosin B; demethylation affords the natural product.…”

“…16 The syntheses of tetracycle 6aa , and subsequently tetracycle 13 , represent a formal total synthesis of frondosin B; demethylation affords the natural product. 4a,b,g,i,k …”