European Journal of Organic Chemistry

The aza-Darzens reaction (younger sibling of the homonymous epoxidation process) has recently burgeoned as a practical method for aziridinations of imines. This Microreview summarizes the pertinent features and recent developments of the reaction.

Vinyl selenides can be easily obtained through nucleophilic substitution of the corresponding halides by using PhSeZnCl in THF as well as in water suspension. Retention of the olefin geometry is generally observed. A mechanism involving the zinc atom has been studied by DFT calculations.

Aquatic reaction of thioamidinium salts and 2-aminophenol, 2-aminothiophenol, and o-phenylenediamine was successfully employed for the synthesis of benzoxazole, benzothiazole, and benzimidazole derivatives, respectively. The method represents apromising alternative as an environmentally safe synthesis of 2-aryl-substituted benzazoles, which are extremely important compounds in medicinal and industrial chemistry.

The unusual downfield NMR shifts of the proton resonances of the inclusion complex of acridine orange (AO) with cucurbit[7]uril (CB[7]) were the net result of large downfield shifts arising from the deaggregation of AO aggregates followed by small upfield shifts resulting from the inclusion of AO in the CB[7] cavity.

The hydrogen-bond properties of five-membered nitrogen heterocycles are reported. These compounds were found to act either as very weak π bases or strong imino or amino bases, depending on theimmediate surrounding of the nitrogen atom. The individual hydrogen-bond basicity of the pyrrolinic and pyridinic nitrogen atoms of myosmine derivatives have been determined.

The asymmetric conjugate addition of trialkylaluminium to oxacyclic substrates in the presence of a copper catalyst with phosphoramidite ligands allows the simultaneous formation of two stereocenters.The addition occurs syn to the bridging oxygen atom, and the corresponding products were obtained in good yields and with good to excellent enantioselectivities.

Mono- and diphosphanyltriazines with a variety of substituents on the triazine ring were selectively synthesized from cyanuric chloride by the one-pot step-by-step reaction. Polymer-supported and water-solubleligands can be obtained by the same procedure. Phosphanyltriazine Pd complexes are active catalysts in the Mizorogi–Heck reaction and the Suzuki–Miyaura coupling.

We have developed a novel and efficient method for the synthesis of various 1,4-dihydroquinoline derivatives from o-halobenzaldehyde and a wide range of β-enaminones with the use of a Pd(OAc)₂/DABCOcatalytic system. Noteworthy, the catalytic system was employed in the C–N cross-coupling reaction for the first time and showed outstanding performance.

Cyclopentene derivatives can be obtained by a Lewis-acid-catalyzed protocol in good yield from readily accessible (arylmethylene)cyclopropanes 1 and bis(4-alkoxyphenyl)methanol (2) under mild conditions.

The synthesis of new thiosugar scaffolds containing unsaturated carbonyl systems – namely 5-thiopyranose-fused butenolides and a 1-eno-5-thiopentopyran-3-ulose – from easily available starting furan-3-uloseswas accomplished. Methods used included the introduction of sulfhydryl groups at C-5 on appropriate furanose intermediates and took advantage of furanose–pyranose conversion.

A general method for the determination of the configurations of large polypropionates, based on NMR spectroscopic investigation of intact molecules, is proposed. The procedure, an extension of Kishi's original¹³C NMR UDB approach based on a statistical process, was applied to the stereochemical determination of different pentads and hexads.

The Fmoc/phenoxyacetyl, Fmoc/levulinoyl and Fmoc/allyloxy carbonyl pairs have been studied as potential orthogonal ester protecting groups for vicinal diols. Selective access to the 3-hydroxy group or the 4-hydroxy group of glucosamine has been investigated.

Several new δ-(polyfluoroalkyl)-δ-hydroxy-α-amino acids were synthesized startingfrom corresponding 6-(polyfluoroalkyl)pyrones.

Tethered (η¹:η⁶-phosphanoarene)ruthenium complexes, such as 5, are efficient catalyst precursors (up to 5000 turnovers!) for the highly regioselective synthesis ofMarkovnikov vinyl esters 1 through the addition of carboxylic acids to terminal alkynes.

Facile entry to the [4.3.3]propellane structure through a tandem radical cyclization reaction of a dienyne set the stage forstereoselective epoxide formation followed by stereospecific Lewis acid catalyzed ring contraction to an oxygenated modhephene structure and led to the total synthesis of (–)-13-acetoxymodhephene and (+)-14-acetoxymodhephene.

A flexible common approach for the synthesis of sphingofungins E and F is reported. Steric effects of 2-substituents in diastereoselective dihydroxylations of (E)-2-hydroxymethyl-2,3-alkenoates were observed, and control over the configurations of quaternary stereocenters in α-substituted amino acids through adjustment of oxidation states was achieved.

Probed with silicon: Chirality at Si induces decent diastereoselectivity in the B(C₆F₅)₃-catalyzed carbonyl reduction whereas no stereoinduction is observed in the related imine reduction. Mechanisms of action are suggested for the irreversible, stereochemistry-determining hydride transfer from a borohydride. Moreover, an unsual 1,6-reduction with a borohydride is disclosed for a sterically congested ketone.

Gold(III)-catalysed reactions of alleneamides give benzazepines in the presence of nucleophiles. This sequential process may follow two different reaction pathways, and these are discussed. Metal coordination tothe allene and addition of NuH to give 3, which can decompose into other products and also form 4, is postulated as the best explanation for these results.

Heptamethine merocyanines containing a nucleofugal chlorine atom react with aromatic and heteroaromatic thiols with formation of ramified dyes. The reactivity differs from that of analogous cationic cyanines and is consistent with a S_NAr addition–elimination pathway. The stability of the new dyes is significantly improved as a result of the elongation of the polymethine chain.

A short and stereoselective synthetic pathway to synthesize cyclopropane aminoacids derived from proteinogenic α-amino acids or analogues has been developed.