Totalsynthese von ( + )−2′S,3′R‐Zoapatanol

Abstract

Aus Blattextrakten der mexikanischen Zoapatl-Pflanze Muntanoa tornentosa, die in der Volksmedizin als empfangnisverhiitendes Mittel eingesetzt werden, konnten die Oxepane 1-4 isoliert werden Die auljergewohnliche biologische Aktivitat und die ungewohnliche Struktur dieser Diterpenoide sowie neuere Verinutungen['], daS auch weitere Metaboliten zur Aktivitiit beitragen. animierten zu einer Vielzahl von T~talsynthesen'~~, von denen jedoch keine asymmetrisch verlluft. Neben der stereokontrollierten Synthese des Oxepangrundgerusts ist die korrekte Einfuhrung der exocyclischen Doppelbindung eine besondere Herausforderung. Wir berichten nun uber die erste asymmetrische Synthese von Zoapatanol 1, die diese beiden stereochemischen Probleme lost.

Total Synthesis of (+)‐(2′S,3′R)‐Zoapatanol Exploiting the B‐Alkyl Suzuki Reaction and the Nucleophilic Potential of the Sulfinyl Group

“…The physical characteristics of the synthetic sample were in excellent agreement with those reported in the literature 1. 5a, c…”

“…We disclose herein a stereoselective total synthesis of (+)‐ 1 taking advantage of the B ‐alkyl Suzuki cross‐coupling reaction for carbon–carbon bond formation and the nucleophilic potential of a sulfinyl group for carbon–oxygen bond formation. Retrosynthetic analysis (Scheme ) revealed that the oxepane ring in 5 could be constructed by a Williamson‐type ether synthesis from 6 , as demonstrated by Trost and co‐workers 5a. Compound 6 was envisaged as being accessible by a B ‐alkyl Suzuki reaction of an organoborane derived from terminal alkene 8 with the iodoalkene 7 .…”

“…Thus, two of the three key issues in the synthesis of zoapatanol had been addressed. The third, stereoselective construction of the oxepane ring, was also considered addressed since we were to follow the precedent set by Trost and co‐workers 5a. The cyclization precursor 28 was obtained by deprotection of the TBS group in 27 using pyridinium p ‐toluenesulfonate (PPTS) in methanol.…”

“…The cyclization precursor 28 was obtained by deprotection of the TBS group in 27 using pyridinium p ‐toluenesulfonate (PPTS) in methanol. Treatment of 28 with triflic anhydride in the presence of 2,6‐lutidine,19 according to Trost’s general method,5a selectively afforded the desired product 29 in 68 % yield.…”

Synthesis of Phytuberin. 4-endo-tet Acid-Catalyzed Cyclization of α-Hydroxy Epoxides

“…The rearrangement of β-hydroxy epoxides may also occur through the two possible 5- endo 7 or 4- exo cyclization modes. Some examples of cyclization of α-hydroxy epoxides via 3- exo - tet (Payne rearrangement) have been described, but the alternative 4- endo cyclization mode remains unknown.…”