Stereoselective total synthesis of (.+-.)-subergorgic acid, a new type of angular triquinane sesquiterpene

Photochemische Reaktionen als Schlüsselschritte in der Naturstoffsynthese

“…Weitere Anwendungen dieser [2+2]-Photocycloaddition/ Fragmentierung finden sich in der Synthese der (AE )-Giberrilinsäure [358] sowie als modifizierte Varianten in der Synthese von (+)-3-Deoxyaphidicolin [359] und (AE )-Subergorginsäu-re. [360] Die direkte Nutzung eines Allen-[2+2]-Photocycloaddukts beschrieben Schreiber et al in der Synthese des (AE )-Periplanons B (282). [245,361] Ausgehend vom Diastereomerengemisch 279 der regioselektiven [2+2]-Photocycloaddition wurde nach Addition von Vinylmagnesiumbromid eine Oxy-Cope-Umlagerung durchgeführt, die das Cyclobuten 280 ergab.…”

Synthesis of a Highly Functionalized Triquinane: Studies Towards a Total Synthesis of Subergorgic Acid and Its Analogues

“…The phenyl thionocarbonates (20) and (21), required by Robins' procedure, were prepared in 76% and 71% yield, respectively, from the reaction between the corresponding alcohols (18) and (19) and phenyl chlorothionoformate, in the presence of DMAP [23,24]. The phenyl thionocarbonates (20) and (21) were reduced to the triquinane (13) in refluxing benzene with tributyltin hydride and a small amount of AIBN, as a radical initiator. The overall yield for the three step deoxygenation procedure via the phenyl thionocarbonate (20) was 60% (58% via (21)) (Scheme 1).…”

“…Two consecutive column chromatographies (3 cm × 15 cm silica gel columns, eluting the first column with petroleum ether, and the second column with 5:1 petroleum ether/Et 2 O) of the material thus obtained gave a colorless oil. The crude product thus obtained was distilled (80°C/0.1 mm Hg) to provide 425 mg (87%) of the alkene (13 …”

“…The naturally occurring triquinanes (±)-∆ 9(12) -capnellene [10], (±)-penta-lenene [11], (±)-methyl cantabrenonate [12] and (±)-methyl epoxycantabronate [12] have already been prepared via routes in which the described annulation sequence played a key role. Several synthetic approaches to subergorgic acid (2) (Figure 1) have appeared in the literature [13][14][15][16]. The principal difficulty encountered in the synthesis of subergorgic acid is related to the unusual functionality present in the molecule as compared with other silphiperfolanes.…”

The Application of Cyclobutane Derivatives in Organic Synthesis

“…It is noteworthy that the yield was especially high in the case of lactam derivatives. In the first stereoselective total synthesis of (±)-subergorgic acid, reductive β-fragmentation was employed 29 . Mesylate 69 was reduced by NaBH 4 at room temperature and the corresponding aldehyde 70 was reduced further in situ to yield the alcohol 71 in 74% yield.…”