The Direct Asymmetric Vinylogous Aldol Reaction of Furanones with α-Ketoesters: Access to Chiral γ-Butenolides and Glycerol Derivatives

Asymmetric Construction of α,γ-Disubstituted α,β-Butenolides Directly from Allylic Ynoates Using a Chiral Bifunctional Phosphine Ligand Enables Cooperative Au Catalysis

A highly efficient construction of chiral γ-substituted α-allyl-α,β-butenolides with up to >99% enantiomeric excess from readily available allylic ynoates is realized. In this asymmetric gold catalysis, the cationic gold(I) catalyst featuring a bifunctional phosphine ligand enables a four-step cascade which permits the conversion of a diverse array of allylic ynoates into valuable chiral α,γ-disubstituted α,β-butenolides.

Copper-Catalyzed Asymmetric Oxidative Desymmetrization of 2-Substituted 1,2,3-Triols

Asymmetric oxidative desymmetrization of 2-substituted glycerols has been achieved by using a new chiral bisoxazoline ligand/copper catalyst system with 1,3-dibromo-5,5-dimethylhydantoin and MeOH. The present transformation smoothly proceeds with readily accessible 2-(hetero)aryl- and alkyl-substituted glycerols and provides straightforward access toward various glycerate derivatives in good to high yields with high enantioselectivities. The synthetic utility of the present protocol was demonstrated by the transformation of the optically active glycerol into a glyceraldehyde derivative.

Synthesis of artemisinin-piperazine-furan ether hybrids and evaluation of in vitro cytotoxic activity

For the first time, eight novel artemisinin-piperazine-furane ether hybrids (5a-h) were efficiently synthesized and investigated for their in vitro cytotoxic activity against some human cancer and benign cells. The absolute configuration of hybrid 5c was determined by X-ray crystallographic analysis. Hybrids 5a-h exhibited more pronounced growth-inhibiting action on hepatocarcinoma cell lines than their parent dihydroartemisinin (DHA) and the reference cytosine arabinoside (ARA). The hybrid 5a showed the best cytotoxic activity against human hepatocarcinoma cells SMMC-7721 (IC₅₀ = 0.26 ± 0.03 μM) after 24 h. Furthermore, hybrid 5a also showed good cytotoxic activity against human breast cancer cells MCF-7 and low cytotoxicity against human breast benign cells MCF-10A in vitro. We found the cytotoxicity of hybrid 5a did not change when tumour cells absorb iron sulfate (FeSO₄); thus, we conclude the anti-tumour mechanism induced by iron ions (Fe²⁺) is unclear.

Facile syntheses of tetrahydroquinolines and 1,2-dihydroquinolines via vinylogous cascade hydride transfer/cyclization

The medicinally significant 3-monosubstituted tetrahydroquinolines and 1,2-dihydroquinolines were controllably constructed via redox-neutral vinylogous cascade condensation/[1,5]-hydride transfer/cyclization in EtOH.

New Developments of the Principle of Vinylogy as Applied to π-Extended Enolate-Type Donor Systems

The principle of vinylogy states that the electronic effects of a functional group in a molecule are possibly transmitted to a distal position through interposed conjugated multiple bonds. As an emblematic case, the nucleophilic character of a π-extended enolate-type chain system may be relayed from the legitimate α-site to the vinylogous γ, ε, ..., ω remote carbon sites along the chain, provided that suitable HOMO-raising strategies are adopted to transform the unsaturated pronucleophilic precursors into the reactive polyenolate species. On the other hand, when "unnatural" carbonyl ipso-sites are activated as nucleophiles (umpolung), vinylogation extends the nucleophilic character to "unnatural" β, δ, ... remote sites. Merging the principle of vinylogy with activation modalities and concepts such as iminium ion/enamine organocatalysis, NHC-organocatalysis, cooperative organo/metal catalysis, bifunctional organocatalysis, dicyanoalkylidene activation, and organocascade reactions represents an impressive step forward for all vinylogous transformations. This review article celebrates this evolutionary progress, by collecting, comparing, and critically describing the achievements made over the nine year period 2010-2018, in the generation of vinylogous enolate-type donor substrates and their use in chemical synthesis.

Deconjugated butenolide: a versatile building block for asymmetric catalysis

Deconjugated butenolides have emerged as a popular synthon for the enantioselective synthesis of γ-lactones. This review provides a comprehensive overview on the catalytic asymmetric reactions of deconjugated butenolides reported till date.

Synthesis of amino acid derivatives of 5-alkoxy-3,4-dihalo-2(5H)-furanones and their preliminary bioactivity investigation as linkers

A series of amino acid derivatives are successfully synthesized via a metal-free C-N coupling reaction of 5-alkoxy-3,4-dihalo-2(5H)-furanones and amino acids. Their structures are well characterized with ¹H NMR, ¹³C NMR, ESI-MS and elemental analysis. As potential linkers of the 2(5H)-furanone unit with other drug moieties containing a hydroxyl or amino group, the effect of amino acids is investigated by comparison with other 2(5H)-furanone compounds by constructing C-O/C-S bonds. The preliminary results of the biological activity assay by the MTT method on a series of cancer cell lines in vitro reveal that the introduction of amino acids basically has no toxic effect. This can lead to these 2(5H)-furanone derivatives being further well-linked with other bioactive moieties with amino or hydroxy groups as expected. Thus, the biological activity assay gives a direction for the design of bioactive 2(5H)-furanones based on these amino acid linkers.

A Sequential Pd-AAA/Cross-Metathesis/Cope Rearrangement Strategy for the Stereoselective Synthesis of Chiral Butenolides

A practical and highly enantio- (up to 94:6 er) and diastereoselective (up to >20:1 dr) synthesis of γ-butenolides bearing two adjacent stereogenic centers is reported featuring a sequential direct palladium-catalyzed asymmetric allylic alkylation/( E)-selective cross-metathesis/[3,3]-sigmatropic Cope rearrangement from readily available α-substituted (5 H)-furan-2-ones.

Stereoconvergent 1,4-Addition Reaction of 5H-Oxazol-4-ones with E,Z Isomeric Mixture of Alkylidene β-Ketoesters Catalyzed by Chiral Guanidines

A 1,4-addition reaction of 5H-oxazol-4-ones to alkylidene β-ketoesters, which was catalyzed by using chiral guanidines via a dynamic kinetic resolution process that involved geometric isomerization of the alkylidene β-ketoesters, was developed. This method allowed using E,Z isomeric mixture of various acyclic alkylidene β-ketoesters to obtain the products stereoselectively. The relation between the geometry and the stereoselectivity of products was investigated, and the derivatization of the products to the corresponding α-acyl-γ-lactone was performed.

Catalytic asymmetric formal γ-allylation of deconjugated butenolides

A formal γ-allylation of deconjugated butenolides is reported based on a two-step sequence consisting of a catalytic diastereo- and enantioselective vinylogous nucleophilic addition to vinyl sulfones and Julia-Kocienski olefination. This highly modular approach delivers densely functionalized butenolides containing a quaternary stereogenic centre in excellent yield with high enantioselectivity.

Phosphine catalyzed δ-carbon addition and isomerization of alkynones to ketimines: the preparation of 1,3-diene substituted dihydroquinazolinones and 3-aminooxindoles

A novel strategy of the phosphine catalyzed addition of alkynones to ketimines for the synthesis of α-amino diene derivatives has been developed for the first time, thus providing diene incorporating α-amino products in moderate to excellent yields.

Catalytic Asymmetric Synthesis of Butenolides and Butyrolactones

γ-Butenolides, γ-butyrolactones, and derivatives, especially in enantiomerically pure form, constitute the structural core of numerous natural products which display an impressive range of biological activities which are important for the development of novel physiological and therapeutic agents. Furthermore, optically active γ-butenolides and γ-butyrolactones serve also as a prominent class of chiral building blocks for the synthesis of diverse biological active compounds and complex molecules. Taking into account the varying biological activity profiles and wide-ranging structural diversity of the optically active γ-butenolide or γ-butyrolactone structure, the development of asymmetric synthetic strategies for assembling such challenging scaffolds has attracted major attention from synthetic chemists in the past decade. This review offers an overview of the different enantioselective synthesis of γ-butenolides and γ-butyrolactones which employ catalytic amounts of metal complexes or organocatalysts, with emphasis focused on the mechanistic issues that account for the observed stereocontrol of the representative reactions, as well as practical applications and synthetic potentials.

A Simple Tetraminocalix[4]arene as a Highly Efficient Catalyst under "On-Water" Conditions through Hydrophobic Amplification of Weak Hydrogen Bonds

The simple tetraminocalix[4]arene 1, which contains weak H-bond-donor NH₂ groups, is reported to be a highly efficient organocatalyst for the Vinylogous Mukaiyama Aldol Reaction (VMAR) of 2-(trimethylsilyloxy)furan 5 with α-ketoesters 6 a-l under "on-water" conditions owing to the hydrophobic amplification of weak H-bond interactions. The catalytic efficiency of calixarene catalyst 1 was shown to be closely related to its recognition abilities towards the reactants 5 and 6 through a multipoint recognition model. The proposed model provided good explanations for the differences on the reaction rate acceleration and on the stereoselectivity observed with different substrates.

A Combined Experimental and Theoretical Study on the Reaction Mechanism and Molecular Structure of 4-(Diphenylamino)-3-iodo-2(5H)-furanone

The simultaneous α-iodination and Nβ-arylation mechanism of 5-alkyloxy-4-phenylamino-2(5H)-furanone by (diacetoxyiodo)benzene was investigated by means of density functional theory (DFT) with B3LYP/6-31G*//LANL2DZ, selecting 4-(diphenylamino)-5-methyloxy-3-iodo-2(5H)-furanone as the calculation model. In addition, the effect of solvent on the reaction pathway was investigated using the Polarisable Continuum Model (PCM). Good agreement was found between the computational and the experimental results. Furthermore, single crystals of 4-(diphenylamino)-5-ethoxy-3-iodo-2(5H)-furanone were grown by slow evaporation technique. The molecular structure analysis was performed by single crystal X-ray analysis and theoretical calculations using a semi-empirical quantum chemical method and DFT/B3LYP methods with a LANL2DZ as basis set.

A One-Pot Tandem Strategy in Catalytic Asymmetric Vinylogous Aldol Reaction of Homoallylic Alcohols

Reported is a rationally-designed one-pot sequential strategy that allows homoallylic alcohols to be employed in a catalytic, asymmetric, direct vinylogous aldol reaction with a series of activated acyclic ketones, including trifluoromethyl ketones, γ-ketoesters, and α-keto phosphonates, in high yields (up to 95%) with excellent regio- and enantio-selectivity (up to 99% ee). This modular combination, including Jones oxidation and asymmetric organocatalysis, has satisfactory compatibility and reliability even at a 20 mmol scale, albeit without intermediary purification.

Thermodynamically driven, syn-selective vinylogous aldol reaction of tetronamides

A stereoselective vinylogous aldol reaction of N-monosubstituted tetronamides with aldehydes is described.

Organocatalytic asymmetric conjugate addition of diaryloxazolidin-2,4-diones to nitroolefins: an efficient approach to chiral α-aryl-α-hydroxy carboxylic acids

The first asymmetric conjugate addition of diaryloxazolidin-2,4-diones to nitroolefins using an l-threonine-based tertiary amine-urea catalyst has been developed.

Enantioselective direct vinylogous aldol-cyclization cascade reaction between β,γ-unsaturated amides and o-quinones

The first enantioselective vinylogous reaction with 1,2-dikeones as aldol donors has been developed to provide chiral spirocyclic dihydropyranones.

Hg/Pt-catalyzed conversion of bromo alkynamines/alkynols to saturated and unsaturated γ-butyrolactams/lactones via intramolecular electrophilic cyclization

Convenient and general Hg(ii)/Pt(iv) catalyzed syntheses of γ-butyrolactams and α,β-unsaturated γ-butyrolactones/lactams are described via intramolecular electrophilic cyclizations of bromoalkynes with tosylamino and hydroxyl tethers. The reaction features the use of wet solvents, the exclusion of any base and additive, mild conditions and practical yields. We also synthesised few chiral lactams through this pathway. Additionally, it is shown that the NHTs group distanced further from the homopropargylic position assists regioselective bromoalkyne hydration to yield useful α-bromoketones. Furthermore, Boc protected bromo homo propargyl amines undergo 6-endo-dig cyclization through Boc oxygen to give bromomethylene substituted oxazinones.

An asymmetric allylic alkylation reaction of 3-alkylidene oxindoles

An efficient asymmetric allylic alkylation reaction with respect to 3-alkylidene oxindoles and racemic MBH carbonate has been achieved.

Highly enantioselective direct allylic alkylation of butenolides with Morita–Baylis–Hillman carbonates catalyzed by chiral squaramide-phosphine

Asymmetric vinylogous allylic alkylation of β,γ-butenolides with Morita–Baylis–Hillman carbonates has been developed to construct γ,γ-disubstituted butenolides containing adjacent quaternary and tertiary chiral centers.

A convenient enantioselective decarboxylative aldol reaction to access chiral α-hydroxy esters using β-keto acids

We show a convenient decarboxylative aldol process using a scandium catalyst and a PYBOX ligand to generate a series of highly functionalized chiral α-hydroxy esters. The protocol tolerates a broad range of β-keto acids with inactivated aromatic and aliphatic α-keto esters. The possible mechanism is rationalized.