Chemistry

The diagnostic values of the following three spectral criteria for the configuration of N-acyl-a,b-dehydroa-amino acid esters were examined: (i) the proton at the b-position at the double bond of a Z-isomer is shielded if compared with the respective E-isomer (d Z b hd E b ); (ii) the proton at the nitrogen atom is shielded in a Z-isomer in comparison with the corresponding E-isomer (d Z NH hd E NH ); and (iii) changing of the solvent from CDCl 3 to deuterated trifluoroacetic acid (TFA) causes shielding of the H b vinylic proton of an E-isomer or deshielding of the respective proton of the Z-isomer (d E CDCl 3 id E TFA or d Z CDCl 3 hd Z

Alkyl-propenyl and aryl-propenyl ethers are interesting substrates for, among others, synthesis of heterocyclic systems [1], cycloaddition reactions [2] and are thoroughly investigated monomers and co-monomers . Isomerization of allyl to propenyl ethers is also the key step of protection and following deprotection of amino and hydroxyl groups . The most convenient method of propenyl ether synthesis consists in isomerization of appropriate, easy to synthetize, allyl ethers. The following have been used as isomerization catalysts: bases

The results of double-bond migration in alkyl allyl and allyl silyl ethers catalyzed by ruthenium complexes [RuClH(CO)(PPh 3 ) 3 ] and in situ forming catalytic system {[RuCl 2 (cod)] x } with hydride and a phosphine) are presented. The conversion of allyl to 1-propenyl ethers is quantitative. The mechanism of double-bond migration has been investigated on deuterated reagents. It has been proved that the reaction is consistent with hydride mechanism, which encompasses addition and elimination of Ru H and intermolecular exchange of hydrogen. We are presenting the first literature description of the direct recycling investigation of ruthenium catalyst for double-bond migration. The recycling has been investigated on model reaction of isomerization of 1,4-diallyloxybutane with [RuClH(CO)(PPh 3 ) 3 ]. It has been shown that fivefold recycle of the catalyst was successful. In the recycling investigation it has been found that the highest activity loss occurred after first use of the catalyst.

A hexadentate ligand built on an amine-bis(phenol) skeleton with an aminal, self-immolative moiety is presented. Synthesis of the ligand is convenient and relatively high yielded. Moreover, it enables synthesis of many derivatives, both in the amino-phenol and aminal fragment (various heterocycles). Once the final hexadentate ligand is synthesized via the Katritzky reaction, it becomes prone to hydrolysis. Bioactivation by beta-galactosidase cleaves the glycosylic bond and a spontaneous collapse of the aminal fragment occurs, thus leading to a pentadentate chelate. This bioactivation has been shown for pyrazole, 1,2,4 triazole and benzotriazole derivatives.

A convenient and highly selective method of synthesis of (E)-N-aryl-N-(1-propenyl)ethanamides via isomerization of respective N-allyl-N-arylethanamides catalyzed by [RuClH(CO)(PPh3)3] has been described. N-Allyl-N-arylethanamides have been obtained by allylation of respective N-arylethanamides under PTC conditions. It is proposed that the observed selectivity of the double bond migration to (E)-enamides is due to the interaction of the arene ring with the Ru atom in the transition state.Graphic

This review provides a literature survey of the double-bond migration in O-allyl systems catalyzed by transition metal complexes: allyl aryl, allyl alkyl ethers, cyclic ethers, such as 2,5-dihydrofurane and cyclic acetals, e.g. 4,7-dihydro-1,3-dioxepine derivatives and allyl silyl ethers. The most frequently used catalysts are ruthenium and rhodium phosphine complexes, but other compounds, such as palladium halides, cobalt and iron carbonyls, are also presented. Also, isomerization of allyl carboxylates is mentioned. Recently double-bond migration reactions have been coupled with ring closing metathesis in a tandem reaction in both (one-pot or two-step) ways, and this is also reviewed. The specific aspects of double-bond migration mechanisms in O-allyl systems are presented. Stereoselectivity (E/Z products), as a key parameter of double-bond migration, resulting from steric factors or the possibility of chelating coordination of isomerized molecule, is discussed in the article. The advantages of transition metal complexes applied for double-bond migration catalysis are presented.

Isomerization of N-allylamides catalyzed by ruthenium and rhodium complexes to corresponding 1-propenyl derivatives is described. The first catalytic system containing a precursor ({[RuCl2(1,5-COD)]x}), tris(2,4-di-t-butylphenyl)phosphite and CaH2 for highly (Z)-selective isomerization of allylamides is presented. It has been shown that the double bond migration catalyzed by the investigated catalytic systems occurs according to the hydride mechanism. The participation of ortho-metallation from precursor and triphenylphosphine in the formation of hydride complex has been proved. It is proposed that the observed (Z)-selectivity of the isomerization of some allylamides is the result of the steric effect in the transition state. The application of siliceous mesoporous cellular foams for an effective removal of the catalyst from the post-reaction mixture is described.Isomerization of N-allylamides (R1CON(R2)allyl) catalyzed by ruthenium and rhodium complexes has been studied. The first catalytic system containing a precursor ({[RuCl2(1,5-COD)]x}), tris(2,4-di-t-butylphenyl)phosphite and CaH2 for highly (Z)-selective isomerization of allylamides is presented. It is suggested that the observed (Z)-selectivity of the isomerization of some allylamides is the result of the steric effect in the transition state.

The X-ray structure of a diacetal with a 16-membered macrocyclic loop, which was obtained as a product of the condensation of methyl a-D-mannopyranoside and 1,4-bis(2-formylphenoxy)butane is presented together with polymeric compounds resulting from polycondensation; a similar polymer was formed in the reaction of methyl 2,3:4,6-di-O-salicylidene-a-D-mannopyranoside with 1,4-dibromobutane.

Reactions of S Ã/allyl systems (allyl sulphides of R Ã/SÃ/allyl type, where R 0/Et, allyl, Ph, Me 3 C, Ph 3 C, as well as of allyl phenyl sulphoxide, allyl phenyl sulphone, 2,5-dihydro-1,1-dioxothiophene) with [RuClH(CO)(PPh 3 ) 3 ] and other ruthenium compounds have been investigated. Double-bond migration was observed in the case of allyl trityl sulphide, allyl t -butyl sulphide and both sulphones, that is, where co-ordinating properties of sulphur were not too strong. High-yielded syntheses of (E )-and (Z )-R Ã/SÃ/ CH Ä/CHCH 3 (R 0/Me 3 C, Z :E0/96:4 and Ph 3 C, Z :E0/92:8), (E )Ã/Ph Ã/S(O 2 ) Ã/CH Ä/CHCH 3 and 2,3-dihydro-1,1-dioxothiophene from respective allyl systems are described. The binuclear Ru complex, formed in the model reaction of allyl phenyl sulphide with [RuClH(CO)(PPh 3 ) 3 ] has been isolated and its structure has been resolved. The mechanism of the reaction between S Ã/allyl systems and [RuClH(CO(PPh 3 ) 3 ] is proposed. #

The isomerisation of N-allyl-N-arylethanamides having a general formula of AcN(Ar)allyl (Ar=YC6H4 where Y=H; o-, m-, p-OMe; o-, p-Br, Cl, Me, O2N; Ar=1- and 2-naphthyl) catalysed by ruthenium complexes—mostly by [RuClH(CO)(PPh3)3] has been studied. N-Allyl-N-arylethanamides were obtained by allylation of respective N-arylethanamides in the PTC conditions (excess of allyl chloride, 50% aq. NaOH, NBu4+HSO4−). The products of isomerisation (reaction conditions: 0.5% mol [RuClH(CO)(PPh3)3], 120 °C, 2–16 h) were mostly or practically solely (E)-N-aryl-N-(1-propenyl)ethanamides. It is proposed that the observed selectivity of the double bond migration to (E)-enamides is a result of the interaction of the arene ring with the Ru atom in the transition states. Quantum calculations (PM5 method) done for N-allyl-N-arylethanamides and for (E)- and (Z)-N-aryl-N-(1-propenyl)ethanamides (aryl=YC6H4 where Y=H; o-, m-, p-OMe; o-, p-Br, Cl, Me, O2N) as well as results of isomerisation of AcN(R)allyl (R=H or cyclohexyl) amides support this assumption. Moreover, the impact of substituents in YC6H4N(Ac)allyl and solvents on the rate of the double bond migration has been studied. The structure of the complexes forming in the course of the reaction and the reaction mechanism are also discussed.Isomerisation of N-allyl-N-arylethanamides (MeCON(AR)allyl) catalysed by [RuClH(CO)(PPh3)3] has been studied. It is suggested that the observed selectivity of the double bond migration to (E)-enamides is the result of the interaction of the arene ring with the Ru atom in the transition states. Quantum calculations (PM5 method) done for N-allylamides and for the enamides support this assumption.

The kinetics and mechanism of the reaction between [PtI 3 (AsPh 3 )] Ϫ and pyridine in acetonitrile solvent has been studied by use of stopped-flow spectrophotometry. Substitution of iodide trans to arsine is irreversible under the conditions used and takes place via parallel direct and solvolytic pathways. By comparing the rate constants of the direct pathway with literature values of the corresponding phosphine and stibine complexes the following trans effect series can be obtained: Ph 3 Sb > Ph 3 P > Ph 3 As. The crystal and molecular structures of reactant and product have been determined. Based on Pt-I distances for the investigated arsine complex and literature data for the corresponding phosphine and stibine complexes the following trans influence series was derived: Ph 3 P ≥ Ph 3 As > Ph 3 Sb. To the best of our knowledge this is the first comparison of all the three heavier pnictogens as donor atoms using strictly analogous complexes with identical cis-ligands.

A method for the synthesis of N-aryl-C-nitroazoles is presented. A coupling reaction between variously substituted arylboronic acids and 3(5)-nitro-1H-pyrazole catalyzed by copper salt has been carried out in methanol in the presence of sodium hydroxide to afford the desired N-aryl-C-nitroazoles in good yields. This synthetic route has also been successfully applied to obtain N-phenyl derivatives of 4-nitropyrazole, 2-nitroimidazole, 4(5)-nitroimidazole and 3-nitro-1,2,4-triazole.

The results of double-bond migration in allyl aryl ethers catalysed by ruthenium complexes, mainly by [RuClH(CO)(PPh 3) 3 ] have been presented. The conversion of allyl to 1-propenyl ethers is quantitative. High E/Z selectivity of some 1-propenyl ethers has been achieved by the application of [RuCl 2 (COD)] x + PR 3 catalytic system (also with addition of inorganic hydrides). An explanation of E/Z selectivity control based on transition state of ␤-elimination has been proposed. The results are supplemented with elements of coordination effects of reactants, solvent influence and catalyst activity on chosen models. Separation of the 1-propenyl ethers might be achieved by simple techniques-distillation or crystallization. Moreover, it has been shown that less stable products, such as (4-aminophenyl) (1-propenyl) ether, might be separated from the reaction mixture using functionalized siliceous mesoporous cellular foams.

Reactions of S Ã/allyl systems (allyl sulphides of R Ã/SÃ/allyl type, where R 0/Et, allyl, Ph, Me 3 C, Ph 3 C, as well as of allyl phenyl sulphoxide, allyl phenyl sulphone, 2,5-dihydro-1,1-dioxothiophene) with [RuClH(CO)(PPh 3) 3 ] and other ruthenium compounds have been investigated. Double-bond migration was observed in the case of allyl trityl sulphide, allyl t-butyl sulphide and both sulphones, that is, where coordinating properties of sulphur were not too strong. High-yielded syntheses of (E)-and (Z)-R Ã/SÃ/ CH Ä/CHCH 3 (R 0/Me 3 C, Z :E0/96:4 and Ph 3 C, Z :E0/92:8), (E)Ã/Ph Ã/S(O 2) Ã/CH Ä/CHCH 3 and 2,3-dihydro-1,1-dioxothiophene from respective allyl systems are described. The binuclear Ru complex, formed in the model reaction of allyl phenyl sulphide with [RuClH(CO)(PPh 3) 3 ] has been isolated and its structure has been resolved. The mechanism of the reaction between S Ã/allyl systems and [RuClH(CO(PPh 3) 3 ] is proposed.

Ethers P 0150 Highly Selective Isomerization of Allyloxyalcohols to Cyclic Acetals or 1-Propenyloxyalcohols.-Depending on the type of ruthenium (or rhodium) catalyst, allyloxy alcohols undergo double-bond migration in the presence of hydride complexes to give propenyloxy alcohols with (Z)-isomers predominating. In the presence of non-hydride complexes, cyclization to cyclic acetals is observed.-(URBALA, M.; KUZNIK*,

Addition of alcohols and phenols to O-allyl compounds (allyl ethers and acrolein acetals), catalyzed by [RuCl 2 (PPh 3) 3 ], was examined. Intramolecular addition of an OH group, leading to the formation of cyclic acetals and orthoesters, was also investigated. As a result, a new, selective and convenient method for the synthesis of symmetrical and unsymmetrical (mixed) acetals and orthoesters was developed.

We report a new approach for the synthesis of new chiral synthons in which two unsaturated sugars are linked via a glycosidic bond. The di-unsaturated disaccharide can be further functionalized using effective, highly selective methods and used in convergent syntheses of relatively complex glycoconjugates. Our approach utilizes in situ generation of active glycosyl donors via Ferrier-type rearrangement under phase-transfer conditions and subsequent reaction with a nucleophile.