Regio- and enantioselective synthesis of functionalized tetrahydroquinolines by palladium-catalyzed cyclization of 2-amidophenylmalonates with allylic bisacetates

A palladium-catalyzed cyclization of 2-amidophenylmalonates with allylic bisacetates is described. Tetrahydroquinolines having a vinyl group at the 3- or 2-position were produced, in which the regioselectivity of the resulting products was altered depending on the substituent on the amino group. The product was transformed to the azabicyclo[3.3.1]nonene via the ring-closing metathesis. Enantioselective reactions also successfully proceeded in the presence of (S)-BINAP to give the optically active tetrahydroquinoline with high enantioselectivity.     

Highly regioselective synthesis of substituted tetrahydroquinolines by palladium-catalyzed cyclization of substituted 2-amidophenylmalonates with 1,4-diacetoxybut-2-ene

The reaction of 2-amidophenylmalonates with 1,4-diacetoxybut-2-ene in the presence of a palladium catalyst is described. Substituted tetrahydroquinolines having a vinyl group at the 3- or 2-position were synthesized, in which the regioselectivities of the double allylic substitution reactions have been altered depending on the substituent on the amino group.     

Bisthioxanthylidene biscrown ethers as potential stereodivergent chiral ligands

The concept of bisthioxanthylidene biscrown ethers as potential stereodivergent chiral ligands in asymmetric synthesis is introduced. Substituted bisthioxanthylidenes may be chiral and can exist as stable enantiomers due to their folded structure. As a result, both a right-handed helix (P) and left-handed helix (M) are present in this type of molecule. This offers the unique possibility to construct two crown ether moieties, attached to the same molecule, of which one exhibits (P)-helicity and the other (M)-helicity. When the crown ether moieties differ in size they can be complexed selectively with a base containing a cation of appropriate diameter. In this manner the (P)-helix and the (M)-helix can be activated selectively to serve as a chiral environment for base catalyzed asymmetric synthesis. Thus, we envisioned the new concept of a single chiral ligand to separately synthesize two enantiomers of a chiral product just by varying the added base. For this purpose, four new bisthioxanthylidene monocrown ethers and two new bisthioxanthylidene biscrown ethers were synthesized. Two biscrowns and two monocrowns were separated into their respective enantiomers (HPLC) and optical data (UV and CD) were collected to ensure stability of enantiomers at ambient temperatures. Ion complexation of one mono- and two biscrown ethers with potassium and sodium cations was investigated.     

A stereodivergent approach to chiral nonracemic N-protected alpha,alpha-dialkylated amino acids

Menthyl carboxaldehyde is used as a chiral auxiliary to make quaternary amino acids of either configuration via a stereodivergent approach that includes an SN2' displacement by a cuprate reagent and a Curtius rearrangement as key steps.     

Efficient synthesis of racemic and chiral alkenyl sulfoxides by palladium-catalyzed Suzuki coupling

Alkenyl sulfoxide derivatives are obtained in high yields through a palladium-catalyzed Suzuki/Miyaura cross-coupling reaction of racemic and chiral 1-halo sulfoxides with aryl and alkenyl boronic acids. Chiral substrates react with no loss of optical purity and high optical yields. The reaction takes place with different palladium catalysts, such as Pd(PPh₃)₄ or Pd(OAc)₂/DABCO. Although nitrogen ligands like DABCO lead to an active palladium catalyst, they are less effective than the phosphine ones.     

A route to 2-substituted tetrahydroquinolines via palladium-catalyzed intramolecular hydroamination of anilino-alkynes

The cyclization of amino-alkynes 1 in which an amino group is attached to the aromatic ring, proceeded smoothly using a catalytic amount of Pd(PPh3)4 and benzoic acid in toluene at 120 degrees C, leading to the formation of the 2-substituted tetrahydroquinolines 2. An asymmetric variant of the reaction using the chiral palladium catalyst (prepared in situ by mixing Pd2(dba)3.CHCl3 and (R,R)-RENORPHOS) was also explored. The absolute configuration of the enantiomerically enriched tetrahydroquinolines, obtained in this way, was determined by converting them to the known compounds and was found to be R. The alkaloids such as (+/-)-galipinine, (+/-)-angustureine, and their optically active form were synthesized by using this reaction as a key step.     

Supramolecular carbohydrate scaffold-catalyzed synthesis of tetrahydroquinolines

Natural supramolecular carbohydrate scaffold-catalyzed synthesis of tetrahydroquinoline derivatives by the reaction of aromatic amine and cyclic enol ether in excellent yield with high diastereoselectivity has been developed. Carbohydrates, cellulose, and starch were converted into their sulfonic acid derivative and these scaffolds exhibit efficient catalytic properties, along with excellent cost effectivity and recyclability.     

A facile one-pot synthesis of N-substituted tetrahydroquinolines

An uncatalyzed one-pot synthesis of N-substituted tetrahydroquinolines was achieved in good yields by the reaction of quinoline and alkyl/acyl halides with Hantzsch dihydropyridine ester under mild reaction conditions.     

A stereodivergent,two-directional synthesis of stereoisomeric C-linked disaccharide mimetics

Dipyranones, such as 1,2-bis[(2R,3S,6S)-3-hydroxy-6-methoxy-3-oxo-6H-pyran-2-yl]ethane, were exploited as templates for the synthesis of some novel C-linked disaccharide analogues. Efficient methods, such as stereoselective reduction and dihydroxylation, were developed for two-directional functionalisation of these templates. Peracetylated derivatives of ten stereoisomeric disaccharide analogues [acetic acid 4,5-diacetoxy-6-methoxy-[(3',4',5'-triacetoxy-6'-methoxytetrahydropyran- 2'-yl)ethyl]tetrahydropyran-3-yl esters] were synthesised from a virtual library of 136 compounds; furthermore, an additional eight stereoisomers could have been synthesised simply by using the enantiomeric ligand in the enantioselective step. The ability of (2S,3S,4R,5R,6R)-6-methoxy-2-[2'-((2'R,3'R,4'S, 5'R,6'S)-3',4',5'-trihydroxy-6'-methoxytetrahydropyran-2'-yl) ethyl]tetrahydropyran-3,4,5-triol to bind to the repressor protein, LacI, was estimated to be similar to that of isopropyl-beta-thiogalactoside. The disaccharide mimetics were concluded to be a new and interesting class of C-linked disaccharide mimetics with promising, though largely unstudied, biological activity.     

Three component synthesis of oxa-bridged tetracyclic tetrahydroquinolines

Bridged tetracyclic tetrahydroquinoline is synthesized by a novel one-pot three component condensation of an ortho-amino cinnamate, alpha-isocyano acetamide and an aldehyde.     

2.2]Paracyclophane-derived chiral P,N-ligands: design, synthesis, and application in palladium-catalyzed asymmetric allylic alkylation

With the idea of tuning structural flexibility and rigidity, several [2.2]paracyclophane-derived P,N-ligands were designed and synthesized. A full investigation of the relationship between the ligands' structures and their abilities to induce asymmetry in palladium-catalyzed asymmetric allylic alkylations of malonates with 1,3-diphenyl 2-propenyl acetate was carried out, and high yields and enantioselectivities (i.e., 99% yield, 97% ee) were observed while using ligands bearing matched planar and central chirality.     

A regio- and stereodivergent synthesis of vic-amino alcohols

A regio- and stereodivergent synthesis of vic-amino alcohols starting from vinylepoxides is described. The developed strategy focuses on the propensity of vinylepoxides and vinylaziridines to be ring-opened at the allylic position by suitable nucleophiles and makes use of reactions that perform such tasks selectively with either retention or inversion of configuration.     

Imino Diels-Alder reactions: One-pot synthesis of tetrahydroquinolines

<正>An efficient synthesis of tetrahydroquinoline derivatives is reported via three component coupling reactions of aldehydes and anilines with various dienophiles in the presence of a catalytic amount of perchloric acid adsorbed on silica gel(HClO_4-SiO_2) under mild reaction conditions.     

Modular chiral selenium-containing oxazolines: synthesis and application in the palladium-catalyzed asymmetric allylic alkylation

A new series of modular chiral selenium-containing oxazolines has been synthesized from inexpensive and commercially available l-serine and l-aspartic acid. These new compounds were evaluated as chiral ligands in the palladium-catalyzed asymmetric allylic alkylation reaction, furnishing the product in high enantiomeric excess, using Cs₂CO₃/CH₂Cl₂ as the base/solvent system.     

An efficient route for the synthesis of chiral conduritol-derivative carboxamides via palladium-catalyzed aminocarbonylation of bromocyclohexenetetraols

A family of chiral conduritol-derivative carboxamides was synthesized through palladium-catalyzed aminocarbonylation of diastereoisomeric bromocyclohexenetetraols, previously prepared through biotransformation of bromobenzene by mutant strains of Pseudomonas putida F39/D.The coupling reactions of bromocyclohexenetetraols with CO and different amines, such as tert-butylamine, aniline, and piperidine, were performed in the presence of in situ generated Pd(0)/PPh₃ catalyst. The methodology was applied to the corresponding iodo-cyclohexenetetraol derivative, using (L)-alanine and (L)-valine methyl ethers as N-nucleophiles. The resulting carboxamides were obtained in highly chemoselective reactions, isolated, and fully characterized.     

A stereodivergent synthesis of beta-hydroxy-alpha-methylene lactones via vinyl epoxides

A catalytic diastereoselective sulfonium ylide epoxidation of aldehydes furnished original vinyl epoxides, having an MBH backbone. These highly functionalized building blocks were used for a formal synthesis of the antibiotic conocandin, and opened up a stereodivergent route towards beta-hydroxy-alpha-methylene lactones, core units of naturally occurring compounds. Under acidic conditions, the oxiranes were mainly transformed, with moderate to good yields, into trans beta-hydroxy-alpha-methylene lactones. On the other hand, a user-friendly palladium-catalysed CO2 insertion and cyclisation sequence gave the cis beta-hydroxy-alpha-methylene lactone counterparts along with an interesting cis-trans equilibration of the pi-allyl intermediates.     

Three-component, stereoselective palladium-catalyzed synthesis of functionalized bicyclopentanoids

1,5-Cyclooctadiene can be stereoselectively transformed into a substituted bicyclo[3.3.0]octane ring system under palladium catalysis with concomitant formation of three carbon-carbon bonds. Reaction with an aryl iodide or triflate and malonate gives an exo-endo product, while the reaction with a malonate in the presence of oxygen affords a bis-endo adduct.     

Novel chiral P,N-ferrocene ligands in palladium-catalyzed asymmetric allylic alkylations

Novel chiral P,N-ferrocene ligands, 1-diphenylphosphino-1′-oxazolinylferrocenes, were prepared from ferrocene via 1,1′-bis(tributylstannyl)ferrocene and 1-diphenylphosphino-1′-methoxycarbonylferrocene as intermediates, and with this new kind of ligand up to 91% ee with 99% chemical yield was afforded for the palladium-catalyzed allylic alkylation of 1,3-diphenyl-2-propenyl acetate with dimethylmalonate anion. The complexation behavior of this kind of ligand with dichlorobis(acetonitrile)palladium and bis(μ-chloro)(1,3-diphenyl-η³-allyl)dipalladium was investigated.     

Facile synthesis of axially chiral styrene-type carboxylic acids via palladium-catalyzed asymmetric C–H activation

A novel method by a one-step introduction of axial chirality and sterically hindered group has been developed for facile synthesis of axially chiral styrene-type carboxylic acids. With the palladium-catalyzed C–H arylation and olefination of readily available cinnamic acid established, this transformation demonstrated excellent yield, excellent stereocontrol (up to 99% yield and 99% ee), and broad substrate scope under mild conditions. The axially chiral styrene-type carboxylic acids produced have been successfully applied to Cp*Co^III-catalyzed asymmetric C–H activation reactions, indicating their potential as chiral ligands or catalysts in asymmetric synthesis.

Palladium-catalyzed asymmetric C–H functionalization to yield axially chiral styrene-type carboxylic acids is described, in which axial chirality and sterically hindered group were incorporated in one-step.