Synthetic Study Aiming at the Tricyclic Core of 12-epi-JBIR-23/24

First Stereoselective Total Synthesis of Marliolide-(4R,5R,3E)-4-hydroxy-5-methyl-3-tetradecylidenedihydrofuran-2(3H)-one and Vittarilide-B: A Unified Strategy Utilizing a Chiral Pool Approach

The first stereoselective total synthesis of the natural products Marliolide-(4R,5R,3E)-4-hydroxy-5-methyl-3-tetradecylidenedihydrofuran-2(3H)-one (1) and Vittarilide-B (1b) has been accomplished using a carbohydrate-based approach starting from d-glucose. The synthesis of Marliolide-(4R,5R,3E)-4-hydroxy-5-methyl-3-tetradecylidenedihydrofuran-2(3H)-one (1) was achieved in 13 steps with an overall yield of 6.5%, featuring key transformations such as reduction, Wittig olefination, TEMPO-mediated oxidation, isomerization, and debenzylation. Vittarilide-B (1b) was synthesized in 18 steps with an overall yield of 8.8%, involving crucial steps like inversion, radical-mediated lactonization, Steglich esterification, and deprotection. The synthesis of Marliolide (1) led to the discovery of a notable isomerization phenomenon, where the Z -isomer was converted to the E -isomer during the oxidation step using BAIB and TEMPO. Various reaction conditions were investigated for this isomerization process, with the TEMPO-mediated reaction consistently providing the best results. The synthesis of Vittarilide-B (1b) required the inversion of stereochemistry at the C-2 position of the common intermediate 6b, followed by a sequence of steps to obtain the final product. The analytical data for both synthetic Marliolide-(4R,5R,3E)-4-hydroxy-5-methyl-3-tetradecylidenedihydrofuran-2(3H)-one (1) and Vittarilide-B (1b) were consistent with the data reported for the natural compounds. This work demonstrates the efficiency of using readily available chiral pool materials like d-glucose in the stereoselective synthesis of complex natural products and provides a foundation for further exploration of their biological activities and potential therapeutic applications.

Natural epoxyquinoids: isolation, biological activity and synthesis. An update

Epoxyquinoids are of continuing interest due to their wide natural distribution and diverse biological activities, including, but not limited to, antibacterial, antifungal, anticancer, enzyme inhibitory, and others. The last review on their total synthesis was published in 2017. Since then, almost 100 articles have been published on their isolation from nature and their biological profile. In addition, the review specifically considers synthesis, including total and enantioselective, as well as the development of shorter approaches for the construction of epoxyquinoids with complex chemical architecture. Thus, this review focuses on progress in this area in order to stimulate further research.

Enolates ambushed - asymmetric tandem conjugate addition and subsequent enolate trapping with conventional and less traditional electrophiles

Metal enolates are useful intermediates and building blocks indispensable in many organic synthetic transformations. Chiral metal enolates obtained by asymmetric conjugate additions of organometallic reagents are structurally complex intermediates that can be employed in many transformations. In this review, we describe this burgeoning field that is reaching maturity after more than 25 years of development. The effort of our group to broaden possibilities to engage metal enolates in reactions with new electrophiles is described. The material is divided according to the organometallic reagent employed in the conjugate addition step, and thus to the particular metal enolate formed. Short information on applications in total synthesis is also given.