András Dobó

Anomalous Zemplén deacylation reactions of α- and β-d-mannopyranoside derivatives

Abstract Reaction of mono-, di-, and trisaccharide derivatives of methyl β- d - and octyl β- d -mannopyranosides bearing ester groups at isolated and non-isolated positions on the same molecule, under Zemplen conditions (catalytic amount of sodium methoxide in methanol) gave partially deacylated compounds, in which the O -acyl groups were retained at isolated sites. In the case of one disaccharide, all the benzoyl groups remained intact at the reducing end, while all the acetyl functions were removable from the nonreducing end. In another case, both isolated ester groups at positions 2 and 4 were retained at the reducing end. The isolated 2- O -acyl groups on methyl α- d -mannopyranoside compounds were more labile than on the corresponding β-mannosides under the same conditions. The mechanism of the reaction may be different for ester groups at isolated or non-isolated positions. In the latter case, acyl migration may take place and carry acyl groups into a less hindered position.

Synthesis of D-glucose-based Azacrown Ethers with phosphinoxidoalkyl side chains and their application to an enantioselective reaction

Five chiral α-D-glucose-based monoaza-15-crown-5 ethers with phosphinoxidoalkyl side chains of one to five carbon atoms (5a–e)have been synthesised. The cation binding ability of the new lariat ethers was evaluated bythe picrate extraction method. The substituents at the nitrogen atom were not a major influenceon the cation extraction ability of the azacrown ether; the compounds showed, however, a significant asymmetric induction as phase transfer catalysts in the Michael addition of2-nitropropane to chalcone (95% ee).

Diels-Alder reaction of (2,4,6-trialkylphenyl)phospholes with N-phenylmaleimide

2,4,6-Trialkylphenylphospholes 3a (R=Me), 3b (R=i–Pr) and 3c (R=t–Bu), with increasing flattening at phosphorus and hence with increasing electron delocalisation, underwent the Diels-Alder reaction with N-phenylmaleimide to give predominantly cycloadducts 4a–c with the trialkylphenyl substituents anti to the phosphanorbornene double bond. With increasing aromaticity, the cycloaddition was slower. The stereostructure of the products (6 and 7) obtained after oxidation was confirmed by stereospecific 2JPC NMR couplings and by an independent synthesis.

One-pot transformation of cyclic phosphine oxides to phosphine–boranes by dimethyl sulfide–borane

Different types of cyclic phosphine oxides, such as tetrahydrophosphole oxide 1, phosphabicyclo[3.1.0]hexane 3-oxide 8 and phosphabicyclo[2.2.1]heptene 7-oxides 10 and 12 were efficiently converted to phosphine–boranes 2, 9, 11 and 13, respectively, under relatively mild conditions by reaction with 4.4 equivalents of dimethyl sulfide–borane. The more strained hetero-ring the starting phosphine oxide (in general 16) has, the easier to accomplish the change in the P-function, that takes place through the corresponding phosphine intermediate (20). It is noteworthy that the imide carbonyl groups in starting materials 10 and 12 were fully reduced by the borane to give 11 and 13 respectively.

The reaction of 1-(2,4,6-trimethylphenyl)-1,2-dihydrophosphinine 1-oxides with dimethyl acetylenedicarboxylate; a [4+2] or a [2+2] cycloaddition?

The reaction of dimethyl acetylenedicarboxylate (DMAD) with 3- and 5-methyl-1-aryl-1,2-dihydrophosphinine oxides (6a and 6b, respectively) obtained by the two-step ring enlargement of 2,5-dihydro-1H-phosphole oxide 4 followed different routes. Isomer 6a entered into a [4+2] cycloaddition with DMAD giving, although in low yield, phosphabicyclooctadiene 7, while 6b reacted with the acetylene moiety according to a recently discovered [2+2] protocol to afford spirocyclic oxaphosphete 8. The reaction of isomers 6a and 6b with N-phenylmaleimide under forcing conditions furnished the expected Diels–Alder cycloadducts (10a and 10b, respectively). Hence, depending on the reactant, isomer 6b displayed a dual reactivity.

Phosphorylation of Amines by the UV-light Mediated Fragmentation of a 2-Phosphabicyclo[2.2.2]octene 2-Oxide

Irradiation of the title compound 1 at 254 nm in the presence of alkylamines or dialkylamines leads to the formation of phosphinic amides 3 and 4, respectively.

Synthesis and Cation Binding Ability of the Phosphonoalkyl- and Phosphinoylalkyl Derivatives of Monoaza-18-Crown-6

Azacrown ethers with phosphonoalkyl-and phosphinoylalkyl side chains of two to five carbonatoms (2–4, 7 and 5–6, 8,respectively) were synthesized in acceptable yields.The cation binding ability of the new lariat etherswas evaluated by the picrate extraction method.Introduction of the P-functionalised N-substituentresulted in a decrease in the cation extractionability in most cases, but the discrimination betweenthe cations examined was, in some instances,significantly increased.

Separation and identification of nonylphenylethylene oxide oligomers by high-performance liquid chromatography with UV and mass spectrometric detection

Nonylphenylethylene oxide surfactants were separated on an alumina column using an ethylene oxide-n-hexane mixture as the mobile phase, and UV and MS detection. Several well separated, large peaks and some small, partly separated peaks were detected. It was found that the main fractions elute log-equidistantly and they correspond to the nonylphenylethylene oxide oligomers with a given number of ethylene oxide units, and the small peaks contain isomers, probably surfactants with different positions of the nonylgroup at the phenyl ring. The method validation showed no significant differences between the intra-day and inter-day values of the area percentages and their standard deviations, showing the good reproducibility of the determination of the area percentages during at least three consecutive days. Significant differences were found between the intra-day and inter-day values of the standard deviation of the retention times, which indicates that the determination of the retention time is less reproducible than that of the area percentages.