Divergent Total Synthesis of Euphoranginol C, Euphoranginone D, ent‐Trachyloban‐3β‐ol, ent‐Trachyloban‐3‐one, Excoecarin E, and ent‐16α‐Hydroxy‐atisane‐3‐one

Abstract

A divergent synthetic approach to biogenetically related diterpenoids such as ent-kauranes, ent-trachylobanes, ent-beyerane, and ent-atisane has been developed. The unified synthetic route involves the De Mayo reaction to rapidly generate the bicyclo[3.2.1]-octane moiety of ent-kaurane. The key reactions also include bioinspired nucleophilic cyclopropanation generating the [3.2.1.0 2,7 ]-tricyclic core of ent-trachylobane and regioselective cyclopropane fragmentation furnishing ent-beyerane and ent-atisane through the nucleophilic attack and protonation of the cyclopropane ring. This strategy enables the asymmetric total syntheses of six diterpenoids from the commercially available geraniol.

Sequential Visible Light‐Induced Reactions Using Different Photocatalysts: Transformation of Furans into 2‐Pyridones via γ‐Lactams Using a New Ring Expansion Reaction

“…For the analogous all carbon variant (X=Y=C, Figure 1A), while cationic rearrangements are well established, [14] a limited number of radical triggered ring expansions are known [15] . The analogous nucleophilic opening is extremely rare [16] . However, when concentrating our focus on the heterocyclic variant where X=N, our searches found no known ring expansions.…”

Dynamische kinetische Sensibilisierung von β‐Dicarbonyl‐verbindungen – Zugang zu mittelgroßen Ringen durch eine De‐Mayo‐artige Ringerweiterung

“…Seit ihrer Entdeckung wurde diese Transformation in zahlreichen Totalsynthesen angewandt, was ihr großes synthetisches Potenzial hervorhebt. [5,6,11] Voraussetzung für diesen Reaktionsweg ist die Erzeugung des 1,2-Diradikals durch direkte Anregung des Enol-tautomers. Daher sind die klassische De-Mayo-Reaktion [10] und ihre formalen synthetischen Äquivalente [12] in der Regel auf solche Substrate beschränkt, bei denen das Enol-Tautomer überwiegend in Lösung vorliegt, da die Anregung des Keto-Tautomers zu seinem n-π*-Triplett-Zustand die gewünschte Cycloaddition verhindert und zu unerwünschter Nebenreaktivität führen kann.…”

Divergent Total Synthesis of Euphoranginol C, Euphoranginone D, ent‐Trachyloban‐3β‐ol, ent‐Trachyloban‐3‐one, Excoecarin E, and ent‐16α‐Hydroxy‐atisane‐3‐one

“…The structure of 7 was unambiguously determined through X-ray analysis. [14] Better yield was obtained later by using 0.6 equivalents 1n HCl (aq) after stirring for 5 h. This procedure may serve as an example of nucleophilic displacement in the formation of cyclopropanes. Moving forward, reduction of the highly sterically hindered C11 ketone was achieved under drastic Wolff-Kishner conditions by stirring at 210 8C for 50 h. Using the same procedure described above, pentacyclic trachylobanes ent- To access ent-beyerane and ent-atisane, we explored the regioselective cyclopropane fragmentation of trachylobane (Scheme 3 B).…”

“…Eventually, we found that BF 3 •2 AcOH [13] gave ent-kaurene-type 14 and ent-phyllocladene-type [2e] 15 in a one pot reaction, and the structures were unambiguously confirmed by X-ray analysis. [14] It is noteworthy that the treatment of intermediate 14' with BF 3 •2 AcOH resulted in its C9 epimerization via an oxonium intermediate. In parallel, the De Mayo reaction was attempted on substrate epi-9, affording C9-epi-kaurane-type 16 as the single isomer.…”