Enantioselective Total Synthesis of Cyathin A₃

Abstract

The cyathins are a unique group of diterpenoids produced by the bird's nest fungi Cyathus helenae, C. africanus, and C. earlei In Section 2.2, the enantioselective Diels-Alder reaction of quinone 106 and diene 105 is presented. This reaction is effectively catalyzed by a carefully iii prepared Mikami catalyst. It was carried out on a preparative scale to give the chiral building block 108. The absolute configuration of the Diels-Alder adduct 108 was determined by NMR and X-ray analysis.

Photochemische Reaktionen als Schlüsselschritte in der Naturstoffsynthese

“…Als synthetisches ¾quivalent für Propylen oder Keten dient in der [2+2]-Photocycloaddition mitunter Allen. Anwendungen finden sich in den Synthesen von (AE )-Atisin, [293] (À)-Annotinin, [294] (AE )-Allocyathin B 3 , [295] (À)-Cyathin A 3 , [296] (AE )-Heliannuol D [297] und (AE )-Pentalenen. [298] Weitere intermolekulare Zugangswege zum racemischen und zum enantiomerenreinen Kelsoen (216) [299] wurden ebenso beschrieben wie eine der oben gezeigten Strategie folgende Synthese des strukturell verwandten (À)-Sulcatin G. [300] Ein alternativer Zugang zu (AE )-Kelsoen (216) bediente sich der intramolekularen Cu-katalysierten [2+2]-Photocycloaddition (Schema 57).…”

Substrate‐Controlled, Phosphine‐Catalyzed Domino Reactions of Activated Conjugated Dienes: Highly Diastereoselective Synthesis of Bicyclic Skeletons

“…Polycyclic dihydrofuran skeletons are widespread among various natural products of important biological activities [10] and also serve as very useful precursors for the construction of molecular complexity such as (À)-himandrine [11] and cyathin A 3 . [12] At present, however, the formation of the bicyclic dihydrofuran framework generally involves building a second five-or six-membered ring onto a preformed dihydrofuran moiety in several steps, which dramatically weakens the overall efficiency. Cyclopentenyl phosphoranes may serve as ligands in the synthesis of many inorganic and organic complexes.…”

7-6-5 Tricarbocyclic Diterpenes

“…5.18 appears the tricyclic diterpenes with a 7-6-5 system not synthesized until now. Synthesized cyathanes are (AE)-allocyathin B 2 and (+)-erinacine A [160,161], (AE)-allocyathin B 2 [162,163], (+)-allocyathin B 2 [164,165], (AE)-sarcodonin G [68], (AE)-allocyathin B 3 [166][167][168], (À)-cyathin A 3 [168,169], (À)-erinacine B [170], (À)-erinacine E [171], (À)-scabronine G [172], (+)-cyanthiwigin U [173], (+)-cyanthiwigin W [173], (À)-cyanthiwigin Z [173], (+)-cyanthiwigin AC [174], and (À)cyanthiwigin F [175]. Until 2009, cyathane syntheses have been collected in the excellent reviews of Wright and Whitehead [3] and Enquist and Stoltz [4].…”