Biomimetic Total Synthesis of the Rubiginosin Meroterpenoids

Abstract

Total synthesis of the Rhododendron meroterpenoids rubiginosins A and G, which both contain unusual 6−6−6−4 ring systems, has been achieved using a bioinspired cascade approach. Stepwise synthesis of these natural products, and the related 6−6−5−4 meroterpenoids fastinoid B and rhodonoid B, from naturally occurring chromene precursors is also reported.Rhododendron plants are a rich source of stereochemically complex, polycyclic meroterpenoids. Among the various possible scaffolds, the 6−6−6−4 ring system (Figure 1a) is

Pd-Catalyzed Formal [3 + 3] Heteroannulation of Allylic gem-Diacetates: Synthesis of Chromene-Based Natural Products and Exploration of Photochromic Properties

“…Chromenes (or benzopyrans) are important substructures owing to their occurrence in an array of bioactive natural products, medicinally relevant compounds, and photochromic materials . These scaffolds are traditionally assembled under acidic or basic conditions from appropriate precursors, but their synthesis under neutral conditions is less explored .…”

Diastereoselective construction of tetracyclic chromanes via a triply annulative strategy

“…7 The lack of efficient approaches for the assembly of the corresponding tetracyclic skeletons is possibly attributed to their structural complexity and rigidity. 8 Therefore, the development of a direct catalytic synthetic approach to stereoselectively access chromane-containing tetracyclic compounds from readily available starting materials remains a highly desirable field of research.…”

On the Erosion of Enantiopurity of Rhodonoids via Their Asymmetric Total Synthesis

“… Subsequently, the same research group isolated rhodonoids C–G ( 3–7 , respectively) from the same plant . The intriguingly fused structures of rhodonoid natural products immediately attracted the attention of the synthetic community, and elegant total syntheses were accomplished by George’s research team − and Tang and Hsung’s joint research team . Notably, both research teams utilized a biomimetic strategy that exploits the chemical reactivity of the chromene core in accessing the racemic mixture of the target compounds.…”

“…In that regard, the isolation of rhodonoids with an eroded ee caught our attention, especially with respect to their biogenesis. Previous synthetic studies − hinted that chromene derivative 8 is the biosynthetic precursor that undergoes diverse modes of (oxidative) cyclization to forge the distinct rhodonoid frameworks (Scheme ). We hypothesized that the erosion of ee during rhodonoid biosynthesis originates from the reversible electrocyclic ring opening of the chiral chromene core (Scheme ).…”