Enantiospecific Total Synthesis and Absolute Configuration Assignment of Chabrolobenzoquinone H

Rizos S.R., Peitsinis Z.V., Koumbis A.E.

The total synthesis of cytotoxic meroditerpenoid naphthoquinone derivative chabrolonaphthoquinone B (1) in an enantiospecific manner is divulged using a chiral pool approach. The key step of our synthetic route is a modified Julia olefination between a sulfone-bearing aliphatic fragment and a Diels-Alder-derived aromatic aldehyde, leading to the stereoselective construction of the E-trisubstituted double bond.

Nazir M., Saleem M., Tousif M.I., Anwar M.A., Surup F., Ali I., Wang D., Mamadalieva N.Z., Alshammari E., Ashour M.L., Ashour A.M., Ahmed I., Elizbit, Green I.R., Hussain H.

Meroterpenoids are secondary metabolites formed due to mixed biosynthetic pathways which are produced in part from a terpenoid co-substrate. These mixed biosynthetically hybrid compounds are widely produced by bacteria, algae, plants, and animals. Notably amazing chemical diversity is generated among meroterpenoids via a combination of terpenoid scaffolds with polyketides, alkaloids, phenols, and amino acids. This review deals with the isolation, chemical diversity, and biological effects of 452 new meroterpenoids reported from natural sources from January 2016 to December 2020. Most of the meroterpenoids possess antimicrobial, cytotoxic, antioxidant, anti-inflammatory, antiviral, enzyme inhibitory, and immunosupressive effects.

Nguyen T., Mac H., Pham P.

An alternative catalytic strategy for the preparation of benzylmethacrylate esters, key intermediates in the synthesis of coenzyme Q10 and derivatives, was reported. This strategy avoided undesirable stoichiometric reduction/oxidation processes by utilizing the catalytic formation of allylarenes and then cross-metathesis to selectively form E-benzylmethacrylate esters with good yields (58–64%) and complete E-selectivity. The ester intermediates were reduced to common key benzylallylic alcohols (90–92% yield), which were subsequently used in the formal syntheses of coenzyme Q10 and one derivative.

Takahashi K., Ogura Y., Kuse M., Takikawa H.

ABSTRACT The first synthesis of phorbasin H, a diterpene carboxylic acid isolated from the sponge Phorbas gukulensis, was achieved using 1,4-trans-cyclohexanedimethanol and (S)-citronellal as starting materials. The data collected in this synthesis indicated the absolute configuration of the naturally occurring phorbasin H to be S.

Sakaine G., Smits G.

A formal total synthesis of pyrrolo[1,4]benzodiazepine anticancer antibiotic family member limazepine E is described. The synthesis features a stereoselective introduction of a trisubstituted double bond using novel sterically demanding Julia-Kocienski reagents, allowing the number of linear steps to be significantly reduced. The potential of the newly developed reagents has also been demonstrated by the formal total synthesis of barmumycin.

Blakemore P.R., Sephton S.M., Ciganek E.

Abstract The Julia–Kocienski olefination is a direct connective synthesis of alkenes via the addition of metalated aryl alkyl sulfones to carbonyl compounds. The activating aromatic group associated with the sulfone must possess electrophilic character, and alkene formation occurs via β‐alkoxy sulfone formation, transfer of the aryl group from sulfur to oxygen via a Smiles rearrangement, and then elimination of sulfur dioxide and an aryloxide anion from the resulting β‐aryloxy sulfinate anion. The olefination process itself and the methods used to prepare the requisite sulfone substrates are tolerant of a wide variety of functional groups, and a variety of alkene targets can be prepared. Stereoselectivity is dependent on the nature of the sulfone, the carbonyl compound, the activating aryl moiety, and the reaction conditions. This chapter describes theoretical and operational aspects of the Julia–Kocienski olefination such that the reader will be able to obtain optimal results in his/her own research. A detailed mechanistic overview is included to account for the factors that influence stereoselectivity and yield. Methods for introducing sulfone activators into fragments of interest, best practices for generating sulfone anions, and optimal strategies for targeting different classes of alkene targets are discussed. Functional group compatibilities, reaction variants, and a comparison to other methods of alkene synthesis are also presented. Tabular surveys are organized according to type of alkene synthesized, with an emphasis on the degree of substitution and the level of conjugation about the newly formed double bond. The literature is covered from the initial disclosure of the Julia–Kocienski olefination in 1991 to the first quarter of 2016.

Takahashi K., Matsui M., Kuse M., Takikawa H.

Abstract Hymenoic acid, isolated from cultures of the fungus, Hymenochaetaceae sp., is a specific inhibitor of DNA polymerase λ. The first synthesis of (S)-(+)-hymenoic acid was achieved by starting from trans-1,4-cyclohexanedimethanol and methyl (R)-(−)-3-hydroxyisobutyrate, and Julia–Kocienski olefination was employed as the key step.

Knölker H., Kutz S., Schmidt A.

We describe the total synthesis of murrayafoline-B and seven carbazole-1,4-quinone alkaloids. A palladium(II)-catalyzed oxidative cyclization is used to construct the carbazole skeleton. Pyran annulation and oxidation provide pyrayaquinone-A, -B, and -C. DIBAL-H-promoted reductive ring opening of pyrano[3,2-a]carbazole precursors leads to the prenylated and geranylated carbazole-1,4-quinone alkaloids murrayaquinone-B, -C, -D, and -E and to murrayafoline-B.

Tan D., Xu Z., Chen H., Wu Y., You J.

The long-known furanoterpenes furospongin-1 and dihydrofurospongin-2 were synthesized for the first time using a chiral-pool-based route in an effort to secure the previous configurational assignments. The key C-11 stereogenic centre was taken from D-mannose, and the C-13 alkyl centre was installed exploiting the chirality of mannose. Due to deprotonation and/or enolization of the building blocks used, introduction of the furan moieties was problematic, and so some reactions had to be avoided. The trisubstituted alkene was most satisfactorily constructed using a Julia–Kocienski olefination in 1,2-dimethoxyethane, with the best (E)/(Z) ratio achieved using a secondary sulfone. The synthetic samples not only provided the first unequivocal piece of evidence for the C-13 configuration of both natural products, but also confirmed the absolute configuration at C-11 of furospongin-1.

Fujii M., Morimoto Y., Ono M., Akita H.

Lipase-catalyzed kinetic resolution of γ-cyclogeraniol by Candida antarctica lipase B yielded 23% of enantiomerically pure (S)-γ-cyclogeraniol. (+)-trixagol and (+)-luffarin-P were synthesized from the obtained (S)-γ-cyclogeraniol, and the absolute configuration of natural (+)-luffarin-P was determined to have an S configuration by our first synthesis of (S)-luffarin-P for the first time.

Sparling B.A., Tucker J.K., Moebius D.C., Shair M.D.

A general strategy for the synthesis of polycyclic polyprenylated acylphloroglucinols is described in which a scalable, Lewis acid catalyzed epoxide-opening cascade cyclization is used to furnish common intermediate 4. The utility of this approach is exemplified by the total syntheses of both ent-nemorosone and (+)-secohyperforin, which were each accomplished in four steps from this intermediate.

Lorente A., Gil A., Fernández R., Cuevas C., Albericio F., Álvarez M.

Lorente A., Albericio F., Álvarez M.

In our effort to gain further insight into the enantioselective synthesis of the structural core of phormidolides B and C, we have discovered the formation of a Z-trisubstituted double bond. Here, we describe a highly selective process that can be applied to our target following a strategy that is based on Julia–Kocienski olefination. The use of 1-(tert-butyl)tetrazolyl sulfone affords the construction of the Z-trisubstituted alkene with high efficiency and stereoselectivity.

Bilel H., Hamdi N., Zagrouba F., Fischmeister C., Bruneau C.

The ruthenium-catalyzed cross-metathesis of eugenol derivatives with electron deficient olefins is reported. It is shown that in the presence of ruthenium catalysts, eugenol and its O-protected derivatives have a high tendency to undergo carbon–carbon double bond migration before and after metathesis leading to the formation of conjugated styrene derivatives. The addition of 1,4-benzoquinone suppresses these isomerization reactions and provides an efficient access to new polyfunctional phenol derivatives upon cross-metathesis of the biosourced eugenol with acrylates, acrylonitrile and acrylamides.

Cai Z., Yongpruksa N., Harmata M.

The first total synthesis of buddledone A was accomplished in seven steps from methyl ethyl ketone (MEK). The key step in the sequence featured an 11-membered ring formation by ring-closing metathesis.

Selka A., Abidli A., Schiavo L., Jeanmart L., Hanquet G., Lubell W.D.

Starting materials for sustainable total synthesis often come from the chiral pool: carbohydrates, cyclitols, amino acids, and terpenes. In the terpene family, (–)‐sclareol has served as a sustainable, readily available, and versatile chiral building block for the synthesis of numerous natural products. (–)‐Sclareol possesses a unique structure that has consequently promoted its integration as a core framework within various structurally complex and biologically active substances, including sesquiterpenoids, diterpenoids, and sesterterpenoids. In fact, (–)‐sclareol has facilitated access to diverse synthetic key intermediates, promoting the sustainable synthesis of several natural products. Herein, a critical and comprehensive review is presented covering the recent trends in sustainable total syntheses and the chiral pool approaches with emphasis on the synthesis of natural products through diverse synthetic routes employing (–)‐sclareol as chiral educt. Additionally, newly developed catalysts and synthetic protocols using (–)‐sclareol amongst their substrates scope are also analyzed and discussed in this review.

Antonova Alexandra S., Zubkov Fedor I.

Catalytic olefin metathesis using Hoveyda-Grubbs type ruthenium complexes is a powerful tool for creating complex molecules possessing a variety of practically useful properties. This method is also applied for obtaining modern polymer materials from low-demand petroleum products. Among all ruthenium complexes containing five- or six-membered chelate rings, the commercially available HG-II catalyst is the most common. In addition, other Hoveyda-Grubbs type complexes, which include a Het→Ru donor–acceptor bond in the chelate ring, often exhibit metathesis activity equal to or superior to that of HG-II. This review considers second-generation N-heterocyclic ruthenium carbene Hoveyda-Grubbs type complexes with donor–acceptor bonds such as O→Ru, S→Ru, Se→Ru, N→Ru, P→Ru and Hal→Ru in the chelate ring. Methods of preparation, analysis of stability and catalytic activity of such complexes are compared, and examples of the application of these organometallic ruthenium derivatives in the synthesis of practically relevant products are provided. The literature from 2010 to 2023 is summarized, making this review useful for a broad audience of chemists working in heterocyclic and organometallic chemistry, as well as practitioners involved in the production of catalysts and polymers.The bibliography includes 174 references.

Cheng-Sánchez I., Moya-Utrera F., Sarabia F.

Ouzounthanasis K.A., Rizos S.R., Koumbis A.E.

AbstractJulia‐Kocienski olefination, a coupling reaction between a carbonyl component and a sulfone partner, has emerged as a powerful synthetic tool in the preparation of several organic compounds. A number of interesting examples involving particularly the preparation of trisubstituted alkenes along with important observations regarding the stereoselectivity of those reactions have been recently reported. This reviewing work covers the literature for the period 2016–2022 and describes in a comprehensive way the progress and developments of Julia‐Kocienski olefination application in the synthesis of trisubstituted alkenes which serve as precursors of natural products and their analogs as well of pharmaceutically interesting/biologically important compounds. Moreover, key methodology results dealing with the investigation of the optimum conditions and stereoselectivities and new modifications and approaches are discussed.