Enantioselective Catalysis of Ketoester-ene Reaction of Silyl Enol Ether to Construct Quaternary Carbons by Chiral Dicationic Palladium(II) Complexes

Catalytic Enantioselective Aldol Reactions of Pyruvates as Nucleophiles with Chlorinated and Fluorinated Aldehydes and Ketones

Reactions of pyruvates as nucleophiles under catalytic conditions are difficult to control without the use of enzymes as catalysts. Here, enantioselective aldol reactions of pyruvates with chlorinated and fluorinated aldehydes and ketones under organocatalytic conditions, in which pyruvates act as nucleophiles, are reported. Based on analyses of self-aldol reactions of pyruvates in the presence of model catalysts, catalysts of the desired cross aldol reactions were developed. Using the primary amine-derived catalyst, the desired aldol products, i.e., γ-chlorinated alkyl or γ-fluorinated alkyl group-substituted γ-hydroxy α-ketoesters, were obtained in good to high yields with high enantioselectivities.

Enantioselective vinylogous Mukaiyama aldol reaction of α-ketoesters under bifunctional organocatalysis

A highly enantioselective vinylogous Mukaiyama aldol reaction to ketoesters catalysed by a hydrogen-bond-donor-based bifunctional organocatalyst is presented. The addition of silyloxy dienol ether gives rise to multifunctional chiral tertiary alcohols bearing a versatile α,β-unsaturated aldehyde with excellent enantiocontrol.

Recent Advances in the Development of Macrolide Antibiotics as Antimicrobial Agents

The chemical modification of natural products has been a major method in the discovery and synthesis of new macrolide antibiotics (MA) to treat a variety of infectious diseases. However, a lot of MA obtained in the above methods are no longer effective, because the bacteria quickly develop their resistance to these new macrolides, which has become a great threat to successful treatment of infectious diseases, such as infections of the respiratory system and urinary system. In this paper, total synthetic methods for MA that include erythromycin A (ERY), azithromycin (AZM), the clinical candidate solithromycin (CEM-101), as well as 14-membered and 15-membered azaketolides have been systematically reviewed on the basis of the literature reported previously. The total synthetic methods we describe here helps to accelerate the discovery of newer MA to deal with the serious problem of bacterial resistance.

Autocatalyzed three-component cyclization of polyfluoroalkyl-3-oxo esters, methyl ketones and alkyl amines: a novel approach to 3-alkylamino-5-hydroxy-5-polyfluoroalkylcyclohex-2-en-1-ones

A new one-pot reaction between polyfluoroalkylated 3-oxo esters, methyl ketones and primary or secondary alkyl amines is reported as an efficient approach to 3-alkylamino-5-hydroxy-5-polyfluoroalkylcyclohex-2-en-1-ones. The scope of three-component cyclization and its plausible mechanism are discussed. The described protocol makes it possible to vary the functional substituents in 2, 3 and 5 positions of carbocycles. Anhydrous conditions are necessary for the productive synthesis of aminocyclohexenones, whereas in the presence of water the competitive formation of alkyl ammonium salts of keto hydroxy carboxylates is observed. Dehydration of the aminocyclohexenones was effectively used for the synthesis of 3-alkylamino-5-trifluoromethylphenols, some of which exhibited moderate antifungal activities against eight pathogenic fungal strains.

Asymmetric "Acetylenic" [3+2] Cycloaddition of Nitrones Catalyzed by Cationic Chiral PdII Lewis Acid

Highly enantioselective [3+2] cycloaddition of ynones and nitrones has been developed. Very bulky ligand, DTBM-SEGPHOS, was used for an effective asymmetric induction over distal reaction centers on the linear ynone dipolarophile and for prevention of Pd^II catalyst deactivation by coordination of the nitrones. The reaction has wide scope of substrates in both ynones and nitrones.

Copper-catalyzed asymmetric methylation of fluoroalkylated pyruvates with dimethylzinc

The catalytic asymmetric methylation of fluoroalkylated pyruvates is shown with dimethylzinc as a methylating reagent in the presence of a copper catalyst bearing a chiral phosphine ligand. This is the first catalytic asymmetric methylation to synthesize various α-fluoroalkylated tertiary alcohols with CF₃, CF₂H, CF₂Br, and n-C _n F_2n+1 (n = 2, 3, 8) groups in good-to-high yields and enantioselectivities. Axial backbones and substituents on phosphorus atoms of chiral phosphine ligands critically influence the enantioselectivity. Moreover, the methylation of simple perfluoroalkylated ketones is found to be facilitated by only chiral phosphines without copper.

Two pairs of rare naturally occurring 4-hydroxy-4-methyl-2,5-heptanedione derivatives from the red alga Chondria crassicaulis

Two pairs of rare naturally occurring racemic lipids, (±)-4,7-dihydroxy-4-methyl-2,5-heptanedione (1), and (±)-7-butoxy-4-hydroxy-4-methyl-2,5-heptanedione (2) were isolated from the red alga Chondria crassicaulis Harv. The structures of the racemic mixtures of 1 and 2 were elucidated by detailed spectroscopic techniques, including 1D and 2D NMR (¹H and ¹³C NMR, ¹H-¹H COSY, HSQC, and HMBC) as well as mass spectrometry and optical rotation experiments, and by comparison with data for related known analogs. This is the first report of naturally occurring 4-hydroxy-4-methyl-2,5-heptanedione derivatives. Antifungal, PTP1B inhibitory, and receptor tyrosine kinase inhibitory activities of these two compounds were investigated. The results showed that compounds 1 and 2 exhibited good selective inhibition against RET tyrosine kinase activity with IC₅₀ values of 9.56 and 8.93 μM, respectively. Compound 1 also displayed moderate antifungal activity against Cryptococcus neoformans (32609), showing a MIC₈₀ value of 32 μg/ml.

A platform for the discovery of new macrolide antibiotics

The chemical modification of structurally complex fermentation products, a process known as semisynthesis, has been an important tool in the discovery and manufacture of antibiotics for the treatment of various infectious diseases. However, many of the therapeutics obtained in this way are no longer effective, because bacterial resistance to these compounds has developed. Here we present a practical, fully synthetic route to macrolide antibiotics by the convergent assembly of simple chemical building blocks, enabling the synthesis of diverse structures not accessible by traditional semisynthetic approaches. More than 300 new macrolide antibiotic candidates, as well as the clinical candidate solithromycin, have been synthesized using our convergent approach. Evaluation of these compounds against a panel of pathogenic bacteria revealed that the majority of these structures had antibiotic activity, some efficacious against strains resistant to macrolides in current use. The chemistry we describe here provides a platform for the discovery of new macrolide antibiotics and may also serve as the basis for their manufacture.

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.

Catalytic Asymmetric Synthesis of Tertiary Alcohols and Oxetenes Bearing a Difluoromethyl Group

The catalytic asymmetric ene reaction with difluoropyruvate as an electrophile in the presence of a dicationic palladium complex is shown. This is the reliable and practical catalytic asymmetric synthesis for various α-CF2H tertiary alcohols in high yields and enantioselectivities. The reaction with isobutene can be catalyzed efficiently under solvent-free conditions with low catalyst loading (up to S/C 2000). Furthermore, difluoropyruvate is applicable to the [2 + 2] cycloaddition reaction in high yields and enantioselectivities.

Catalytic hetero-ene reactions of 5-methyleneoxazolines: highly enantioselective synthesis of 2,5-disubstituted oxazole derivatives

An efficient catalytic asymmetric hetero-ene reaction of 5-methyleneoxazolines with 1,2-dicarbonyl compounds (including α-ketoesters and glyoxal derivatives) was realized using Ni(II)-N,N'-dioxide complexes as the catalysts. It provides a rapid, high yielding (up to 99%) route for the preparation of 2,5-disubstituted oxazole derivatives in a highly enantioenriched form (up to >99% ee) under mild conditions.

Catalyst-free formation of 1,4-diketones by addition of silyl enolates to oxyallyl zwitterions in situ generated from α-haloketones

Here we report an efficient and practical method for the preparation of 1,4-diketones by direct coupling of α-haloketones with silyl enolates at room temperature. No catalysts were required in our protocol.

A catalytic asymmetric carbonyl–ene reaction of β,γ-unsaturated α-ketoesters with 5-methyleneoxazolines

A catalytic asymmetric carbonyl–ene reaction of β,γ-unsaturated α-ketoesters with 5-methyleneoxazolines was accomplished. The process was based on the utilization of a chiral N,N′-dioxide/Mg^II catalyst, providing the desired products with excellent outcomes.

Enantioselective catalytic transannular ketone-ene reactions

Highly enantio- and diastereoselective transannular ketone-ene reactions are catalyzed by a new chromium(III) triflate tridentate Schiff base complex. Electronically unactivated keto-olefins undergo heteroene reactions at ambient temperature to afford enantioenriched bicyclic alcohols, common structural motifs in natural products. The kinetic resolution of a configurationally stable planar-chiral cyclodecenone is also described.

Enantioselective intramolecular aldehyde α-alkylation with simple olefins: direct access to homo-ene products

A highly selective method for the synthesis of asymmetrically substituted carbocycles and heterocycles from unactivated aldehyde-olefin precursors has been achieved via enantioselective SOMO-catalysis. Addition of a catalytically generated enamine radical cation across a pendent olefin serves to establish a general asymmetric strategy toward the production of a wide range of formyl-substituted rings with alkene transposition. Conceptually, this novel mechanism allows direct access to "homo-ene"-type products.

Catalytic asymmetric synthesis of stable oxetenes via Lewis acid-promoted [2+2] cycloaddition

A highly enantioselective and atom-economical [2 + 2] cycloaddition of various alkynes with trifluoropyruvate using a dicationic (S)-BINAP-Pd catalyst has been established. This is the first enantioselective synthesis of stable oxetene derivatives, whose structure has been clarified by X-ray analysis. This catalytic process offers a practical synthetic method for oxetene derivatives (catalyst loading: up to 0.1 mol %), which can serve as novel chiral building blocks for pharmaceuticals and agrochemicals and can also be transformed into a variety of enantiomerically enriched CF(3)-substituted compounds with high stereoselectivity.