Highly Enantioslective Synthesis of Multisubstituted Polyfunctional Dihydropyrrole via an Organocatalytic Tandem Michael/Cyclization Sequence

Highly Diastereoselective Synthesis of 2,3-Dihydropyrroles via Formal [4 + 1] Annulation Reaction of α,β-Unsaturated Imines and in Situ Generated Pyridinium Ylide

We report a cascade approach for the synthesis of 2,3-dihydropyrroles derivatives via a formal [4 + 1] annulation reaction of α,β-unsaturated imines with in situ generated pyridinium ylides. Importantly, this protocol is compatible with diverse substituted imines as well as pyridinium ylides, constructing 2,3-dihydropyrroles with excellent yield and selectivity. Thereafter, the Merrifield resin-supported pyridinium ylide as a potential C1 synthon was also employed in our strategy and reused several times, resulting in products with excellent yield and diastereoselectivity.

Enantioselective organocatalyzed one-pot synthesis of N-phenyl thioether-tethered tetrasubstituted dihydropyrrole-3-carbaldehydes

An efficient method for the asymmetric one-pot synthesis of N-phenyl thioether-tethered tetrasubstituted chiral 4,5-dihydropyrrole-3-carbaldehydes have been developed using readily available benzothiazolium salts and α,β-unsaturated aldehydes as starting materials in the presence of the chiral organocatalyst (R)-diphenylprolinol trimethylsilyl ether. The protocol afforded various functionally enantioenriched chiral tetrasubstituted 4,5-dihydropyrrole-3-carbaldehydes in high yields, with excellent enantio- and diastereoselectivity (≤90% yield, ≤98% ee, and >20 : 1 d.r.). This asymmetric one-pot reaction starts with the reaction of azomethine ylides with dipolarophiles to yield pyrrolo-thiazine-2-carbaldehydes as intermediates. Subsequently, the electrophile alkyl halide is attacked by the sulfur atom of the intermediate, followed by C-S bond cleavage (ring-opening), which furnishes the desired chiral tetrasubstituted 4,5-dihydropyrroles.

Dehydroabietane-type bifunctional organocatalysts in asymmetric synthesis: recent progress

Dehydroabietane-type bifunctional organocatalysts derived from rosane-type diterpenes of dehydroabietic acid (DHAA) and dehydroabietylamine (DA) have been utilized in a wide variety of highly enantioselective reactions. Since one well-documented review exclusively reported on the development of terpene-derived bifunctional thioureas in asymmetric organocatalysis in 2013, fragmentary progress on the dehydroabietane-type bifunctional thioureas and squaramides has been mentioned in other reviews. In this mini-review, we systematically analyze and reorganize the published literature on dehydroabietane-type bifunctional organocatalysts in the recent decade according to the type of catalysts. Our aim is for this review to provide helpful research information and serve as a foundation for further design and application of rosin-based organocatalysts.

Atom-Economical Syntheses of Dihydropyrroles Using Flavin-Iodine-Catalyzed Aerobic Multistep and Multicomponent Reactions

Herein, we report facile, atom-economical syntheses of multisubstituted 2,3-dihydropyrroles using flavin-iodine-catalyzed aerobic oxidative multistep transformations of chalcones with β-enamine ketones or 1,3-dicarbonyl compounds and amines. Exploiting coupled flavin-iodine catalysis, the multistep reaction, including C-C and C-N bond formation, is promoted only by the consumption of O₂ (1 atm), thus allowing aerobic oxidative synthesis that generates green H₂O as the only waste.

Modular Synthesis of Polar Spirocyclic Scaffolds Enabled by Radical Chemistry

Herein, we report a highly modular strategy to access spirocyclic scaffolds from abundant starting materials, i.e., cyclic ketones and α-amino or oxamic acids. The sequence proceeds through a straightforward Knoevenagel condensation, followed by a domino Giese-type reaction/base-mediated cyclization process, to deliver a broad scope of polar spirocyclic scaffolds in good to excellent yields. The products can be readily diversified, thus increasing the versatility of our method to gain rapid access to libraries of potential druglike molecules.

Chiral Quaternary Ammoniums Derived from Dehydroabietylamine: Synthesis and Application to Alkynylation of Isatin Derivatives Catalyzed by Silver

Abietic acid and its derivatives have broadly been used in fine chemicals and are renewable resources. Its inherent chiral rigid tricyclic phenanthrene skeleton is unique. Its utilities in asymmetric catalysis remain to be explored. A series new amide-type chiral quaternary ammoniums bearing dehydroabietylamine were designed, and prepared by two convenient steps. Acylation of dehydroabietylamine with bromoacetyl chloride afforded amide holding bromoacetyl group in higher yields using triethyl amine as base. Subsequent quaternization reaction gave the desired amide-type chiral quaternary ammoniums. The new chiral quaternary ammoniums can be used as phase-transfer catalyst (PTC) for the transition metal-catalysed alkynylation of isatin derivatives.

Multi-component syntheses of 2-pyrrolines and organocatalytic asymmetric syntheses of functionalized chiral 2-pyrrolines

The atom-economical synthesis of 2-pyrrolines has been achieved by carrying out the multi-component tandem [2 + 2 + 1] annulation of commercially available starting materials, namely, an aldehyde, glycine ester hydrochloride, and benzoylacetonitrile.

Chiral Thioureas-Preparation and Significance in Asymmetric Synthesis and Medicinal Chemistry

For almost 20 years, thioureas have been experiencing a renaissance of interest with the emerged development of asymmetric organocatalysts. Due to their relatively high acidity and strong hydrogen bond donor capability, they differ significantly from ureas and offer, appropriately modified, great potential as organocatalysts, chelators, drug candidates, etc. The review focuses on the family of chiral thioureas, presenting an overview of the current state of knowledge on their synthesis and selected applications in stereoselective synthesis and drug development.

Recent advances in the synthesis of 2,3-dihydropyrroles

This review summarizes the advances in the synthesis of 2,3-dihydropyrroles with an emphasis on recent developments or important seminal contributions.

Asymmetric Michael Addition of Malononitrile with Chalcones via Rosin-Derived Bifunctional Squaramide

A rosin-derived bifunctional squaramide catalyzed asymmetric Michael addition of malononitrile with chalcones was discovered. This protocol provides a methodology for the facile synthesis of chiral γ-cyano carbonyl compounds in high yields and enantioselectivities (up to 99% yield and 90% ee) with a lower catalyst loading (0.3 mol%). The predominant R-configured adducts were obtained by this organocatalystic reaction, according to the experimental findings.

Advances in Rosin-Based Chemicals: The Latest Recipes, Applications and Future Trends

A comprehensive review of the publications about rosin-based chemicals has been compiled. Rosin, or colophony, is a natural, abundant, cheap and non-toxic raw material which can be easily modified to obtain numerous useful products, which makes it an excellent subject of innovative research, attracting growing interest in recent years. The last extensive review in this research area was published in 2008, so the current article contains the most promising, repeatable achievements in synthesis of rosin-derived chemicals, published in scientific literature from 2008 to 2018. The first part of the review includes low/medium molecule weight compounds: Especially intermediates, resins, monomers, curing agents, surfactants, medications and biocides. The second part is about macromolecules: mainly elastomers, polymers for biomedical applications, coatings, adhesives, surfactants, sorbents, organosilicons and polysaccharides. In conclusion, a critical evaluation of the publications in terms of data completeness has been carried out with an indication of the most promising directions of rosin-based chemicals development.

One-Pot Multicomponent Mechanosynthesis of Polysubstituted trans-2,3-Dihydropyrroles and Pyrroles from Amines, Alkyne Esters, and Chalcones

An efficient and practical one-pot multicomponent reaction of amines with alkyne esters and chalcones promoted by I₂/PhI(OAc)₂ has been developed under solvent-free ball-milling conditions to afford a variety of polysubstituted trans-2,3-dihydropyrroles in moderate to good yields. The present method features a short reaction time, mild reaction conditions, broad substrate scope, and feasibility of large-scale synthesis. Intriguingly, this protocol can also furnish the corresponding synthetically more attractive pyrroles with the addition of an oxidant in a one-pot way.

Chemoselective synthesis of m-teraryls through ring transformation of 2H-pyran-2-ones by 2-(1-arylethylidene)-malononitriles

Base mediated chemoselective synthesis of m-teraryls was carried out by the reaction of 2H-pyran-2-ones and 2-(1-arylethylidene)malononitriles.

A nordehydroabietyl amide-containing chiral diene for rhodium-catalysed asymmetric arylation to nitroolefins

A non-covalently interacting, phellandrene derived, nordehydroabietyl amide-containing chiral diene was developed in rhodium catalysed asymmetric arylation.

α,α-Dicyanoolefins: versatile substrates in organocatalytic asymmetric transformations

α,α-Dicyanoolefins have emerged as versatile reactants, finding use as vinylogous nucleophiles, Michael acceptors and dienophiles in a variety of organic reactions.

Efficient and practical synthesis of enantioenriched 2,3-dihydropyrroles through gold-catalyzed anti-Markovnikov hydroamination of chiral homopropargyl sulfonamides

A direct gold-catalyzed anti-Markovnikov hydroamination of chiral homopropargyl sulfonamides has been developed. A range of enantioenriched 2,3-dihydropyrroles are readily accessed by utilizing this approach.

Synthesis of functionalized 2-vinyl-2,3-dihydropyrroles and 3-methylene-1,2,3,4-tetrahydropyridines by palladium-catalyzed cyclization of β-enaminocarbonyl compounds with allylic bisacetates

Palladium-catalyzed reactions of β-enaminocarbonyl compounds with 1,4-diacetoxybut-2-ene and 2-methylene-1,3-propanediol diacetate are described.

Development of four-component synthesis of tetra- and pentasubstituted polyfunctional dihydropyrroles: free permutation and combination of aromatic and aliphatic amines

We previously reported the novel efficient proton/heat-promoted four-component reactions (4CRs) of but-2-ynedioates, two same/different primary amines, and aldehydes for the synthesis of tetra- and pentasubstituted polyfunctional dihydropyrroles. If aromatic and aliphatic amines were used as reagents, four different series of products should be obtained via the permutation and combination of aromatic and aliphatic primary amines. However, only three/two rather four different series of tetra-/pentasubstisuted dihydropyrroles could be prepared via the proton/heat-promoted 4CRs. Herein, Cu(OAc)2·H2O, a Lewis acid being stable in air and water, was found to be an efficient catalyst for the 4CR synthesis of all the four different series of tetra-/pentasubstisuted dihydropyrroles. The copper-catalyzed 4CR could produce target products at room temperature in good to excellent yields. Interestingly, benzaldehyde, in addition to being used as a useful reactant for the synthesis of pentasubstituted dihydropyrroles, was found to be an excellent additive for preventing the oxidation of aromatic amines with copper(II) and ensuring the sooth conduct of the 4CRs for the synthesis of tetrasubstituted dihydropyrroles with aryl R(3). In addition, salicylic acid was found to be needed to increase the activities and yields of the copper-catalyzed 4CRs for the synthesis of petasubstituted diyhydropyrroles. On the basis of experimental results, the enamination/amidation/intramolecular cyclization mechanism was proposed and amidation is expected to be the rate-limited step in the copper-catalyzed 4CRs.