Asymmetric Total Synthesis of Dankasterones A and B and Periconiastone A Through Radical Cyclization

Abstract

We describe herein the assembly of the cis-decalin framework through radical cyclization initiated by metalcatalyzedh ydrogen atom transfer (MHAT), further applied it in the asymmetric synthesis of dankasterones Aa nd Ba nd periconiastone A. Position-selective C À Hoxygenation allowed for installation of the necessary functionality.Aradical rearrangement was adopted to create 13(14!8)abeo-8-ergostane skeleton. Interconversion of dankasterone Ba nd periconiastone Awas realized through biomimetic intramolecular aldol and retro-aldol reactions.T he MHAT-based approach, serves as an ew dissection means,i sc omplementary to the conventional ways to establish cis-decalin framework.

Fe-catalyzed Fukuyama-type indole synthesis triggered by hydrogen atom transfer

“… 7 Remarkably, Baran's Fe(acac) 3 /phenylsilane system has proved to be a useful methodology for both inter- and intramolecular reductive olefin coupling, 8 as well as a general protocol for construction of polycyclic frameworks. 9 By means of this catalysis system, a variety of SOMOphiles were further introduced as radical traps, achieving diverse olefin hydrofunctionalization such as hydroamination, hydrogenation, and the Minisci reaction. 10 …”

Divergent Synthesis of Skeletally Distinct Arboridinine and Arborisidine

“…In contrast to target‐oriented synthesis, diversity‐oriented synthesis aims to access a collection of natural products with appendage, functional group, stereochemical, or scaffold diversity [14] . We have been interested in the divergent synthesis of alkaloids [15] and rearranged steroids for some time [16] . With this synthetic logic in mind, we developed a unified strategy for both alkaloids by taking into consideration their hidden topological connection and hypothetical biosynthesis, eventually leading to a divergent synthesis of the skeletally distinct (±)‐arboridinine ( 1 ) and (±)‐arborisidine ( 2 ) from a similar core intermediate ( 4 ) as shown in Scheme 1 c.…”

Concise Synthesis of 9,11-Secosteroids Pinnigorgiols B and E

“…Rearranged steroid natural products, including secosteroids (in which at least one ring is cleaved) and abeo -steroids (in which there is at least one migrated C–C bond within the classic tetracyclic framework), have recently received considerable attention from synthetic chemists owing to the structural diversity and biological importance of these compounds. , Representative naturally occurring rearranged steroids include cyclopamine, glaucogenins, cortistatins, − nakiterpiosin, strophasterol A, cyclocitrinols, − pleurocins, swinhoeisterol, bufospirostenin A, dankasterones, and periconiastone A. , Two particularly challenging examples of such natural products are the 9,11-secosteroids pinnigorgiol B ( 1 ) and pinnigorgiol E ( 2 ) (Figure ), − which possess a unique tricyclo­[5,2,1,1]­decane framework with an embedded γ-diketone moiety. These compounds were isolated by Sung and co-workers from a Pinnigorgia coral species in 2016, along with a biogenetic precursor, pinnisterol E ( 3 ) .…”

“…1,2 Representative naturally occurring rearranged steroids include cyclopamine, 3 glaucogenins, 4 cortistatins, 5−13 nakiterpiosin, 14 strophasterol A, 15 cyclocitrinols, 16−18 pleurocins, 19 swinhoeisterol, 20 bufospirostenin A, 21 dankasterones, and periconiastone A. 20,22 Two particularly challenging examples of such natural products are the 9,11-secosteroids pinnigorgiol B (1) and pinnigorgiol E (2) (Figure 1), 23−25 which possess a unique tricyclo[5,2,1,1]decane framework with an embedded γ-diketone moiety. These compounds were isolated by Sung and co-workers from a Pinnigorgia coral species in 2016, along with a biogenetic precursor, pinnisterol E (3).…”

“…Treatment of 13 with 10% Rh/C in ethyl acetate enabled selective hydrogenation of the C22−C23 olefin, providing diene 21 in 96% yield. Li/NH 3 reduction of 21 gave rise to desired olefin 14 as the major product, along with the C7−C8 olefin (22) and 23 as minor products. Alternatively, hydrogenation of 13 over 10% Pd/C in MeOH furnished 23 in 71% yield.…”