European Journal of Organic Chemistry

The cover picture shows a snapshot of the blooming canola field in Southwest China. The catalytic cycle illustrates the P,O-chelating and P-monodentate complexation modes of the hemilabile Aphos-Y with palladium(0) and the reductive elimination of the P,O-chelating palladium(II) species derived from an alkyl borinate and an alkenyl halide under mild conditions (K₃PO₄·3H₂O, THF/H₂O, r.t.). It is considered that switching between the P,O-chelating and P-monodentate complexation modes facilitates various steps in the whole catalytic cycle. The usefulness of the Aphos-Y–Pd(OAc)₂ catalyst in the “9-MeO-9-BBN variant” of the Suzuki–Miyaura cross-coupling reaction used for the total synthesis of complex natural products has been demonstrated. Details are discussed in the Short Communication by N. Ye and W.-M. Dai on p. 831 ff.

This article reviews the total syntheses of all four stereoisomers of 3-hydroxypipecolic acids 1–4 from 1996 to the present.

One ligand acts for two: Aphos-Y and Pd(OAc)₂ enable the cross-coupling of the 9-alkyl-9-MeO-9-BBN species formed from an alkyl iodide (step a: tBuLi, 9-MeO-9-BBN) and an alkenyl halide with excellent yield under mild conditions (step b: K₃PO₄·3H₂O, THF/H₂O, room. temp.). Aphos-Y substitutes two ligands, dppf and Ph₃As, popularly used in the “9-MeO-9-BBN variant” of Suzuki–Miyaura cross-coupling.

A detailed investigation of the modified Julia olefination of aromatic aldehydes shows that the elimination step occurs through a concerted antiperiplanar and synperiplanar mechanism in the case of anti-5 and syn-5, respectively. The high experimental E selectivity is thus explained by the fact that both syn and anti diastereomeric pathways lead preferentially to the (E)-alkene.

Substituted 3(2H)-furanones are synthesized in good to excellent yields by the palladium-catalyzed reaction of 4-chloroacetoactate with activated styrenes. The tandem reaction starts with Michael addition of an acetoacetate to the activated alkene followed by palladium-catalyzed ring closing of the primary adduct to form the furanone.

The one-pot conversion of proline derivatives into azanucleotide analogues has been achieved in good yields by a sequential radical decarboxylation/phosphorylation process. The stereoselectivity of the reaction can be controlled by using different oxygen and nitrogen substituents at C-4 and in this way the 2,4-cis/2,4-trans ratio can be shifted from 98:2 to 15:85.

Several synthetic approaches to an important water-soluble nitroxide antioxidant are described. Each provides the final product in a comparable overall yield, however, the copper-mediated cyanation of an aryl halide followed by hydrolysis employs the fewest steps and provides the greatest synthetic convenience.

We have found that the intramolecular oxidative coupling of N-arylenamines proceeds well in the presence of catalytic amounts of nBu₄NI (TBAI) using tert-butyl hydroperoxide as oxidant to afford the corresponding 1H-indole derivatives. This is one of the rare examples of TBAI-catalyzed C–C bond-forming CDC reactions.

A Cu-catalyzed C–N coupling reaction is described for the synthesis of pyridine-2-carbaldehyde N,N-diarylhydrazones by the arylation of hydrazones with aryl bromides/iodides, and the subsequent conversion of the hydrazones into N,N-diarylhydrazines by a transimination process with an aqueous solution of H₂NNH₂. The reaction features the use of CuI as catalyst without external ligands.

The use of ethynylated anilines as activated alkynes in cycloaddition–retroelectrocyclization reactions with tetracyanoethene and tetracyanoquinodimethane provides access to novel, highly electron-deficient polycyanobutadienes and unprecedented chromophores. Electrochemical studies show that the electron-accepting abilities are strongly enhanced upon elimination of the amino donor substituent.

We report the design, synthesis, and biological evaluation of N(1)-thiolan-2-ylated and C(5)-substituted ligands. The compounds were used to explore the molecular recognition properties of the methylerithritol sub-pocket of the substrate binding site in IspE proteins from Escherichia coli and Aquifex aeolicus, which are model enzymes for Plasmodium falciparum IspE, the causative agent of malaria.

A chloroacetate-caged fluorescein chemodosimeter (CACFC) employing a double molecular recognition mechanism was designed and synthesized to selectively detect cysteine (Cys) and homocysteine (Hcy) over glutathione (GSH) and other amino acids.

Seven new alkaloids including tryptoquivaline K (1) and fumiquinazolines K–P (2–7), bearing a rare 1-aminocyclopropane-1-carboxylic acid residue, together with six known compounds, were isolated from the sponge-associated fungus Aspergillus sp. The structures of the new compounds were assigned by spectral analysis, and their absolute configurations were determined by calculations.

A study of chemoselective gold(I)-catalysed cycloaddition of propargyl acetals or esters with alkenes and indoles showed them to follow two different pathways. Whereas the esters underwent cyclopropanation, the acetals showed two important features: (i) the favoured pathway is an atypical [2+3] cycloaddition, and (ii) these complexes showed significantly higher reactivities than the ester counterparts.

We report the synthesis of spiroketals by a sequence of enol ether synthesis and cyclization. The enol ethers were prepared from lactones by a Julia olefination, and the starting chiral lactone was prepared from an industrial intermediate. This route allows the synthesis of naturally occurring and biologically interesting spiroketals, including SPIKET-P and a spiroketal from Bactrocera species.

The synthesis of a new series of amino acid-appended ethylenedithiotetrathiafulvalene or dimethyltetrathiafulvalene cores reveals three characteristic hydrogen-bonding types of interactions that effectively direct self-assembly in the solid state.

Photochemical reactions of phthalimide derivatives 5, 9 and 10 afford different polycyclic rearrangement products as a function of irradiation conditions.

A protecting-group-free approach to the title compounds has been developed. Starting from the hetero-Diels–Alder adduct of ethyl 2-nitrosoacrylate and ethyl vinyl ether, two isomeric terminal dienes were prepared, which, upon RCM followed by dihydroxylation and catalytic Raney Ni hydrogenation, led to the target compounds, which are of significant biological interest.

A facile and solvent-free synthesis of γ-aryl-substituted vinylphosphonates and diethyl (diarylmethyl)phosphonates has been developed under mild conditions. The reaction was performed with inexpensive FeCl₃ and easily accessible α-hydroxyphosphonates and unactivated arenes. In this atom-economic approach, hard-to-achieve allylphosphonate cations are stabilized through extended conjugation.

An efficient methodology has been developed for the synthesis of tetrahydroquinolines in good yields and with excellent diastereoselectivity. The reaction between α-allylic anilines and aldehydes proceeds through an imino-ene cyclization that is mediated by boron trifluoride–diethyl ether.

Ene–diyne systems possessing 1- and 2-azulenyl groups at the periphery, were prepared by Sonogashira–Hagihara reactions. The redox behavior of the ene–diyne compounds was examined by cyclic voltammetry and differential pulse voltammetry. Significant color changes of the ene–diyne derivatives were observed by visible spectroscopy under electrochemical reduction conditions.

Isoquinolin-1-ones and related fused-ring heterocycles have been prepared from N-Boc-protected (β-arylethyl)carbamates. The N-Boc-carbamates were first converted into isocyanates by using the reagents Tf₂O and 2-chloropyridine. These isocyanates were then subjected to in situ intramolecular Friedel–Crafts-type reaction to give the products in good yields and with high regioselectivities.

Ruthenium-catalyzed cycloaddition of symmetric disubstituted alkynes bearing two thiosugar units and azide-containing carbohydrate scaffolds afforded multivalent thiolactosides. A tetravalent glycoconjugate based on a trehalose scaffold displayed the best multivalent effect on binding to plant lectin, peanut agglutinin.

Original NPN Cu^I catalysts: Phospha-amidinates form Cu^I complexes whose structure and behavior strongly depend on the substituents at phosphorus (mononuclear 1 for R = tBu, dinuclear 2 for R = Ph). The complexes have been evaluated in catalytic aziridination. Dinuclear complex 2 proved to be a robust and efficient catalyst for the aziridination of alkenes.

We have developed a one-pot methodology for the synthesis of alkyl arylvinyl sulfides in good to excellent yields, free of any metal/ligand systems and from malodorous and air-sensitive alkyl thiols. This procedure uses commercially available potassium thioacetate, low temperatures, and short reaction times.

Electron-rich aromatic compounds react in aqueous media by PET with R_fX to render substitution products in reasonable yields. The proposed mechanism is a homolytic aromatic substitution, followed by ET and (PT) steps, in the absence of base; radical cations of the substrates are formed in the initiation step. The reaction is compared with radical and electrophilic aromatic substitutions.