https://cyberleninka.org/article/n/132565.pdf

Discovery and resupply of pharmacologically active plant-derived natural products: A review.

With the exception of palladium-catalyzed cross-couplings, no other group of reactions has had such a profound impact on the formation of carbon-carbon bonds and the art of total synthesis in the last quarter of a century than the metathesis reactions of olefins, enynes, and alkynes. Herein, we highlight a number of selected examples of total syntheses in which such processes played a crucial role and which imparted to these endeavors certain elements of novelty, elegance, and efficiency. Judging from their short but impressive history, the influence of these reactions in chemical synthesis is destined to increase.

Metathesis Reactions in Total Synthesis

Catalytic olefin metathesis--through which pairs of C = C bonds are reorganized--transforms simple molecules to those that are complex and precious. This class of reactions has noticeably enriched chemical synthesis, which is the art of preparing scarce molecules with highly desirable properties (for example, medicinal agents or polymeric materials). Research in the past two decades has yielded structurally well-defined catalysts for olefin metathesis that are used to synthesize an array of molecules with unprecedented efficiency. Nonetheless, the full potential of olefin metathesis will be realized only when additional catalysts are discovered that are truly practical and afford exceptional selectivity for a significantly broader range of reactions.

The remarkable metal-catalysed olefin metathesis reaction

The use of photochemical transformations is a powerful strategy that allows for the formation of a high degree of molecular complexity from relatively simple building blocks in a single step. A central feature of all light-promoted transformations is the involvement of electronically excited states, generated upon absorption of photons. This produces transient reactive intermediates and significantly alters the reactivity of a chemical compound. The input of energy provided by light thus offers a means to produce strained and unique target compounds that cannot be assembled using thermal protocols. This review aims at highlighting photochemical transformations as a tool for rapidly accessing structurally and stereochemically diverse scaffolds. Synthetic designs based on photochemical transformations have the potential to afford complex polycyclic carbon skeletons with impressive efficiency, which are of high value in total synthesis.

Photochemical Approaches to Complex Chemotypes: Applications in Natural Product Synthesis

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Euphorbia Diterpenes: Isolation, Structure, Biological Activity, and Synthesis (2008–2012)

Total synthesis of ingenol, a diterpene isolated from the genus Euphorbia, was accomplished on the basis of the novel key reactions. The highly strained ingenane skeleton was constructed through an intramolecular cyclization reaction of an acetylene dicobalt complex followed by a rearrangement reaction of an epoxy alcohol. The C(3),C(4),C(5)-triol moiety was introduced by a stereoselective double dihydroxylation reaction of a diene having C(2)−C(3) and C(4)−C(5) double bonds.

Total synthesis of ingenol.

Methylenecyclopentane annulation via formal [3 + 2] cycloaddition reaction

A new method for methylenecyclopentane annulation via formal [3+2] cycloaddition reaction was developed. Under the influence of Lewis acids, enol ethers and vinylsulfides were treated with I-(alkylthio)-2-(trimethylsilylmethyl)allyl esters 1a or 1b to afford methylenecyclopentanes in good yields. The reaction proceeds with almost complete regioselectivity as well as high stereoselectivity.

Yoshinori Takahashi

Papers

Total synthesis of ingenol.

Methylenecyclopentane annulation via formal [3 + 2] cycloaddition reaction

Methylenecyclopentane Annulation via Formal (3 + 2) Cycloaddition Reaction.