Enantioselective total synthesis of (+)-galbulin via organocatalytic domino Michael-Michael-aldol condensation

Recent Advance of Domino Michael Reaction in Natural Product Synthesis

Recent advances in the total syntheses of cyclic natural products and related compounds from 2005 to 2021, which employ domino Michael reactions as key steps, have been reviewed, focusing mainly on the domino Michael reactions catalyzed by organocatalysts.

Recent applications of asymmetric organocatalytic annulation reactions in natural product synthesis

The past two decades have witnessed remarkable growth of asymmetric organocatalysis, which is now a firmly established synthetic tool, serving as a powerful platform for the production of chiral molecules. Ring structures are ubiquitous in organic compounds, and, in the context of natural product synthesis, strategic construction of ring motifs is often crucial, fundamentally impacting the eventual fate of the whole synthetic plan. In this review, we provide a comprehensive and updated summary of asymmetric organocatalytic annulation reactions; in particular, the application of these annulation strategies in natural product synthesis will be highlighted.

Total Synthesis of (+)-Galbulin and Unnatural Lignans

The total synthesis of (+)-galbulin was achieved in 15% yield and 99% ee over eight steps from commercially available 4-veratraldehyde. The key steps include Meyer's asymmetric tandem addition to a chiral 2-oxazoline-substituted naphthalene, a Pd-catalyzed stereospecific decarboxylative γ-arylation, and a formal anti-Markovnikov hydromethylation. In addition, five unnatural lignans were synthesized using the same synthetic strategy.

Advances in the Asymmetric Total Synthesis of Natural Products Using Chiral Secondary Amine Catalyzed Reactions of α,β-Unsaturated Aldehydes

Chirality is one of the most important attributes for its presence in a vast majority of bioactive natural products and pharmaceuticals. Asymmetric organocatalysis methods have emerged as a powerful methodology for the construction of highly enantioenriched structural skeletons of the target molecules. Due to their extensive application of organocatalysis in the total synthesis of bioactive molecules and some of them have been used in the industrial synthesis of drugs have attracted increasing interests from chemists. Among the chiral organocatalysts, chiral secondary amines (MacMillan's catalyst and Jorgensen's catalyst) have been especially considered attractive strategies because of their impressive efficiency. Herein, we outline advances in the asymmetric total synthesis of natural products and relevant drugs by using the strategy of chiral secondary amine catalyzed reactions of α,β-unsaturated aldehydes in the last eighteen years.

Advances in the Synthesis of Lignan Natural Products

Lignans comprise a family of secondary metabolites existing widely in plants and also in human food sources. As important components, these compounds play remarkable roles in plants' ecological functions as protection against herbivores and microorganisms. Meanwhile, foods rich in lignans have revealed potential to decrease of risk of cancers. To date, a number of promising bioactivities have been found for lignan natural products and their unnatural analogues, including antibacterial, antiviral, antitumor, antiplatelet, phosphodiesterase inhibition, 5-lipoxygenase inhibition, HIV reverse transcription inhibition, cytotoxic activities, antioxidant activities, immunosuppressive activities and antiasthmatic activities. Therefore, the synthesis of this family and also their analogues have attracted widespread interest from the synthetic organic chemistry community. Herein, we outline advances in the synthesis of lignan natural products in the last decade.

Concise Synthesis of (+)-β- and γ-Apopicropodophyllins, and Dehydrodesoxypodophyllotoxin

Herein, we present an expeditous synthesis of bioactive aryldihydronaphthalene lignans (+)-β- and γ-apopicropodophyllins, and arylnaphthalene lignan dehydrodesoxypodophyllotoxin. The key reaction is regiocontrolled oxidations of stereodivergent aryltetralin lactones, which were easily accessed from a nickel-catalyzed reductive cascade approach developed in our group.

Total Syntheses and Biological Evaluation of (±)-Botryosphaeridione, (±)-Pleodendione, 4-epi-Periconianone B, and Analogues

The total syntheses of (±)-botryosphaeridione, (±)-pleodendione, (±)-hoaensieremodione, 4-epi-periconianone B, and their analogues have been accomplished for the first time. All the synthesized target compounds were screened in neural anti-inflammatory assays using LPS induced microglia cells (N9). Among them, compounds 1 and 21 were identified as potential lead compounds for further profiling.

Regioselectivity switch in chiral amine-catalysed asymmetric addition of aldehydes to reactive enals

A regioselectivity switch was realized in the chiral amine-catalysed asymmetric addition of aldehydes to reactive enals, and either aldol adducts or conjugate adducts were obtained in a stereoselective fashion.

Neighboring heteroatom effect unique to aqueous aldol reactions of water-insoluble substrates

The reactions of ketones and aldehydes in the presence of Li(+) and in the presence or absence of PTC mediated by water were performed to produce aldol products. Several advantages of the aqueous reactions over organic solvent-mediated ones have been demonstrated including higher yields, shorter reaction times, simpler purifications, and better functional group tolerance. Some reactions that do not take place in organic solvents have been realized in water. The successes are attributed to the neighboring heteroatom effect. In the aqueous aldol condensations, Li2CO3 was an efficient catalyst, and therefore base-liable groups such as epoxides, esters, and silyl groups could survive. For heteroaromatic ethanones, the aqueous aldol reactions were accomplished without PTC to give β-hydroxyketones in good yields. The water-mediated condensations of aldosyl hemiacetals with aromatic ketones led to a new carbohydrate-derived skeleton in quantitative yields. To some extent, this research has expanded the applicablities of aldol condensations and reactions.

Stereocontrolled syntheses of tetralone- and naphthyl-type lignans by a one-pot oxidative [3,3] rearrangement/Friedel-Crafts arylation

The development of a stereoselective one-pot oxidative [3,3] sigmatropic rearrangement/Friedel-Crafts arylation that provides enantioenriched benzhydryl compounds is reported. The utility of this new transformation is demonstrated by the concise synthesis of several tetralone- and naphthyl-type lignan natural products, many of which display anti-malarial activity.