Synthesis of C-17-functionalized beyerane diterpenes. Synthesis of (–)-erythroxylol B, (–)-erythroxydiol A and (–)-benuol

Abstract

The title compounds 1, 2 and 3 became accessible from an appropriately functionalized podocarpenone 4 in short sequences of operations, in which the key step involves the toluene-psulfonic acid-induced rearrangement of 1 3-epimeric epoxides 6 and 7.The presence of a bridgehead hydroxymethyl group at C-13 is unique to some tetracyclic diterpenes of the beyerane group.' Erythroxylol B 1, isolated from Erythroxylon rnonogynurn, 2a erythroxydiol A 2, isolated from Erythroxylon monogynum,2a Helichrysum dendroideum,2b and Baccharis tola,2c and benuol3, isolated from Sideritis serrata,2d are some representative examples of beyeranes containing this characteristic moiety.? beyerane skeleton 1 R'=Me,R2=H 3 R' = Me, R2 = OH 2 R' = CHZOH, R2 = H 10 11 Qa X=OTs ii Scheme 2 12 13Puper 4/02765E

1H and13C NMR assignments and conformational analysis of some tetracyclic compounds with a bicyclo[4.2.0]octane ring system

“…Further support for this conformational assignment was derived from the comparison with the chemical shift of H-9 in some analogues in which ring C can only adopt a chair conformation. 6 The chemical shift of proton H-9 in 2b, 3b, 4b and 5b is also consistent with the twist conformations. However, the presence of an additional hydroxyl group at C-7 induces a shielding e †ect of ca.…”

Recent Advances in the Synthesis of Cyclobutanes by Olefin [2 + 2] Photocycloaddition Reactions

“…In the synthesis of ent -kaurane and beyerane diterpenoids, Baran and co-workers explored numerous methods to generate the quaternary stereogenic center at C8 of enone 178 but only the [2 + 2] photocycloaddition turned out to be successful . Related work was performed by Abad et al , Allene addition proceeded in the expected HH fashion to product 179 . The pyramidalization of the triplet state in a chairlike fashion , is likely responsible for the facial diastereocontrol.…”

Photochemische Reaktionen als Schlüsselschritte in der Naturstoffsynthese

“…Homoerythrina-Alkaloide (AE )-Erysotrin, [367] (AE )-Schelhammericin [368] und (AE )-3-Epischelhammericin. [368] Vollzieht sich die Umlagerung [370 ] von (+)-Quadron (278, Schema 73) durch Smith III et al [371] sowie von (À)-Erythroxylol B, [372] (À)-Erythroxydiol A [372] und (À)-Benuol durch Abad et al [372] Durch Spaltung der Bindung c (Schema 67) wird die zweifache C-C-Verknüpfung an dem photoangeregten Alken manifestiert. Eine oxidative Spaltung der Bindung führt zu einer 1,4-Difunktionalität, die vielfältig genutzt werden kann.…”