Synthetic studies on tricyclic diterpenoids: convenient synthesis of 16-arylisopimaranes
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RIGINAL PAPER
Synthetic studies on tricyclic diterpenoids: convenient synthesis of 16‑arylisopimaranes Marya A. Gromova1 · Yurii V. Kharitonov2 · Tatyana V. Rybalova2 · Elvira E. Shults2 Received: 31 July 2020 / Accepted: 10 November 2020 / Published online: 20 November 2020 © Springer-Verlag GmbH Austria, part of Springer Nature 2020
Abstract A series of 16-arylisopimaranes has been synthesized by palladium-catalyzed arylation of the corresponding tricyclic diterpenoid isopimaric acid or its methyl ester in the presence of silver carbonate. No ligand was essential for the formation of new type optically active styrene derivatives. Good-to-excellent yields were obtained with good chemical tolerance. Silver carbonate enhanced the rate of the reaction. The use of cesium carbonate as the base requires an increase in reaction time and need for increasing amounts (2 mol%) of the palladium salt. The cross-coupling reaction proceeds with the formation of 16-arylisopimaranes with the (E)-type geometry of the double bond. Several transformations on the aryl substituent were carried out. The structure of target compounds was confirmed by X-ray diffraction study. Graphic abstract
Keywords Natural products · Terpenoids · Cross-coupling reactions · Selectivity
Introduction Resin acids are a family of naturally occurring diterpenoids, which were found as main chemical components in tree resins and are therefore highly abundant commodities. Therefore, isopimaric acid (1) and methyl isopimarate (2) are readily available and versatile tricyclic diterpenoids Electronic supplementary material The online version of this article (https://doi.org/10.1007/s00706-020-02713-3) contains supplementary material, which is available to authorized users. * Elvira E. Shults [email protected] 1
Novosibirsk State Pedagogical University, Novosibirsk 630126, Russia
Novosibirsk Institute of Organic Chemistry, Novosibirsk 630090, Russia
2
well represented in the resin of conifers of the genera Pinus, Larix, and Picea [1, 2]. A wide range of biological and pharmaceutical properties such as antibacterial [3–5], anti-viral [6], and anti-inflammatory [7] activities was reported for isopimaric acid. Indeed, derivatization of these natural products has been a topic of interest over the last decades. Several functionalizations of the pimarane diterpenoid core included oxidative [8–13] and isomeric [14] transformations, in addition to several modifications of the carboxyl group [15–22], were carried out. Recently, we reported the successful Wacker oxidarion of methyl isopimarate with the formation of methyl 15-oxo-15,16-dihydroisopimarate and subsequent generating in situ 15-oxo-16-formyldihydroisopimarate [23]. Using this approach to the terminal double-bond modification, we synthesized oxazoles and β-carbolines with a diterpenic moiety [23, 24]. Methods relying on the derivatization of the terminal double bond of pimarane core are limited
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and based on the preliminary isomerization of
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