- Efficient synthesis of α-branched purine-based acyclic nucleosides: Scopes and limitations of the method
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An efficient route to acylated acyclic nucleosides containing a branched hemiaminal ether moiety is reported via three-component alkylation of N-heterocycle (purine nucleobase) with acetal (cyclic or acyclic, variously branched) and anhydride (preferentially acetic anhydride). The procedure employs cheap and easily available acetals, acetic anhydride, and trimethylsilyl trifluoromethanesulfonate (TMSOTf). The multi-component reaction is carried out in acetonitrile at room temperature for 15 min and provides moderate to high yields (up to 88%) of diverse acyclonucleosides branched at the aliphatic side chain. The procedure exhibits a broad substrate scope of N-heterocycles and acetals, and, in the case of purine derivatives, also excellent regioselectivity, giving almost exclusively N-9 isomers.
- Dra?ínsky, Martin,Frydrych, Jan,Janeba, Zlatko,Slavětínská, Lenka Po?tová
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- Facile synthesis of acid-labile polymers with pendent ortho esters
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This work presents a facile approach for preparation of acid-labile and biocompatible polymers with pendent cyclic ortho esters, which is based on the efficient and mild reactions between cyclic ketene acetal (CKA) and hydroxyl groups. Three CKAs, 2-ethylidene-1,3-dioxane (EDO), 2-ethylidene-1,3-dioxolane (EDL), and 2-ethylidene-4- methyl-1,3-dioxolane (EMD) were prepared from the corresponding cyclic vinyl acetals by catalytic isomerization of the double bond. The reaction of CKAs with different alcohols and diols was examined using trace of p-toluenesulfonic acid as a catalyst. For the monohydroxyl alcohols, cyclic ortho esters were formed by simple addition of the hydroxyl group toward CKAs with ethanol showing a much greater reactivity than iso-propanol. When 1,2- or 1,3-diols were used to react with the CKAs, we observed the isomerized cyclic ortho esters besides the simple addition products. Biocompatible polyols, that is, poly(2-hydroxyethyl acrylate) (PHEA) and poly(vinyl alcohol) (PVA) were then modified with CKAs, and the degree of substitution of the pendent ortho esters can be easily tuned by changing feed ratio. Both the small molecule ortho esters and the CKA-modified polymers demonstrate the pH-dependent hydrolysis profiles, which depend also on the chemical structure of the ortho esters as well as the polymer hydrophobicity.
- Cheng, Jing,Ji, Ran,Gao, Shi-Juan,Du, Fu-Sheng,Li, Zi-Chen
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experimental part
p. 173 - 179
(2012/04/23)
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- Method of preparing optically active alpha -amino acids and alpha -amino acid derivatives
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PCT No. PCT/EP96/03984 Sec. 371 Date Apr. 30, 1998 Sec. 102(e) Date Apr. 30, 1998 PCT Filed Sep. 11, 1996 PCT Pub. No. WO97/10203 PCT Pub. Date Mar. 20, 1997The invention relates to a new process for the preparation of optically active amino acids and amino acid derivatives of the general formula (I), wherein *, X and R1 to R4 have the meaning given in the description. Starting from commercially obtainable (-)-menthol or (+)-menthol, the enantiomerically pure compounds of the formula (I) are obtained in high yields. The method is particularly suitable for the preparation of sterically demanding amino acids and amino acid derivatives.
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- Acetalization of α,β-unsaturated carbonyl compounds catalyzed by complexes of Pt(II)
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A class of cationic diphosphine complexes of Pt(II) are sufficiently Lewis acidic to catalyze the acetalization of aldehydes and ketones. α,β-Unsaturated substrates can be easily acetalized with ethylene glycol under mild conditions in high yield and avoiding side reactions leading to formation of undesired by-products arising from the nucleophilic addition to the carbon-carbon double bond conjugated to the carbonyl group. A comparison of the behavior of a Pt complex with respect to PTSA as catalysts under identical conditions shows the superior selectivity of the former in many cases.
- Nieddu, Enrico,Cataldo, Maurizio,Pinna, Francesco,Strukul, Giorgio
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p. 6987 - 6990
(2007/10/03)
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- Process for the production of 2-vinyl-1,3-dioxolane
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Process for the production of 2-vinyl-1,3-dioxolane reacting acrolein with ethylene glycol in the presence of a solid, acidic catalyst and recovery of the reaction mixture. Selectivity may be increased in comparison with known prior art processes by performing the reaction in the presence of a solid acidic catalyst at a temperature of below 50° C.; the reaction mixture, from which the catalyst has been removed, is treated by extraction using an organic solvent which substantially does not dissolve ethylene glycol and has a boiling point of above 130° C.; the two phases obtained on extraction are treated for recovery by distillation and recovered educts and the organic solvent are recycled.
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- Synthesis of 1,3-dioxolanes catalysed by AlPO4 and AlPO4-Al2O3: kinetic and mechanistic studies
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A number of aldehydes and ketones were easily and quantitatively converted to the corresponding 1,3-dioxolanes by the reaction with ethylene glycol over four synthetic amorphous AlPO4 and AlPO4-Al2O3 catalysts using acetonitrile as the solvent at different temperatures in the range 30-60 deg C without the formation of any by-product.The influence of the number of acid sites on the catalyst surface as well as the substituent effects of different carbonyl compounds studied can be evaluated through several isokinetic parameters obtained owing to the existence of a linearfree-energy relationship (LFER).The results obtained account for an intermediate in the transition state whose relative stability is determined by the resonance between the carbonyl group and their substituents, but its evolution is via a concerted process in two adsorption-desorption steps.
- Bautista, Felipa M.,Campelo, Juan M.,Garcia, Angel,Leon, Josefa,Luna, Diego,Marinas, Jose M.
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p. 815 - 822
(2007/10/02)
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- Acetals and Ethers. XVIII. Reaction Products of Prop-2-enal and But-2-enal with Mixture: n-Aliphatic Alcohol and Ethylene Glycol
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The direct condensation reaction of prop-2-enal or but-2-enal with mixture of n-aliphatic alcohol and ethylene glycol, in the presence of p-toluenesulphonic acid as catalyst, leads to a complex mixture of saturated, unsaturated, cyclic and linear acetals, moreover, 2-(2-alkoxy-alkyl)-1,3-dioxolanes are the main reaction products.The detailed investigations for n-butanol showed that unsaturated cyclic acetals: 2-vinyl-1,2-dioxolane 1a or 2-(1-propenyl)-1,3-dioxolane 1b, as well as unsaturated linear acetals: 1,1-dibutoxy-prop-2-en 2a or 1,1-dibutoxy-but-2-en 2b are intermediate reaction products.Additionally, it was found in final products presence of eight by-products: 5-butoxy-4a or 5-butoxy-7-methyl-1,4-dioxepane 4b, 1,1,3-tributoxypropane 5a or 1,1,3-tributoxybutane 5b, 2--6a or 2--1,3-dioxolane 6b, 5-(2-hydroxyethoxy)-7-methyl-1,4-dioxepane 7b, 1,3-dibutoxy-1-(2-hydroxyethoxy)-propane 8a or 1,3-dibutoxy-1-(2-hydroxyethoxy)-butane 8b, 1,1-dibutoxy-3-(2-hydroxyethoxy)-propane 9a or 1,1-dibutoxy-3-(2-hydroxyethoxy)-butane 9b, 3-butoxy-1,1-bis-(2-hydroxyethoxy)-propane 10a or 3-butoxy-1,1-bis-(2-hydroxyethoxy)-butane 10b, and 1-butoxy-1,3-bis-(2-hydroxyethoxy)-propane 11a or 1-butoxy-1,3-bis-(2-hydroxyethoxy)-butane 11b, respectively.
- Plasecki, Andrzej
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p. 579 - 586
(2007/10/02)
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- Acetals and Ethers. XII. Reaction Products of Prop-2-enal with 1,2- and 1,3-Diols
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2-(Hydroxyalkoxyethyl)-substituted cyclic acetals (1; 2; 3a - 3d; 4a - 4d), derivatives of 1,3-dioxolane or 1,3-dioxane have been obtained in a p-toluenesulphonic acid-catalysed reaction of prop-2-enal with an excess of ethylene, propylene-1,2, trimethylene, or butylene-1,3 glycol.Respective 2-vinyl-1,3-dioxolanes or 2-vinyl-1,3-dioxanes were the intermediate products.The products of the reaction involving propylene-1,2 and butylene-1,3 glycols were mixtures of cis- and trans-2,4-disubstituted-1,3-dioxolanes and cis- and trans-2,4-disubstituted-1,3-dioxanes.The structure of HOROCH2CH2- substituents at C-2 atom of 1,3-dioxacyclane ring has been proved through 2,4-dinitrophenylhydrazone derivatives of the corresponding aldehydes HOROCH2CH2CHO that, however, could not be isolated as individual compounds.
- Piasecki, Andrzej,Burczyk, Bogdan
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p. 543 - 554
(2007/10/02)
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- α-Alkoxyallylation of Activated Carbonyl Compounds. A Novel Variant of the Michael Reaction
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Enolic or readly enolizable carbonyl compounds undergo α-alkoxyallylation upon reaction with acetals of α,β-enals or ethoxyallene at temperatures ranging from 200 deg C to ambient.Whereas reactions of the highly enolic or acidic carbonyl compounds (endocyclic β-diketones, α-cyano ketones, α-nitro carbonyl compounds, and α-hydroxy-methylene derivatives) occurred simply upon heating, alkylation of the less acidic exocyclic β-diketones and β-keto esters was best carried out in the presence of 1 mol percent of Ni(acac)2 as a catalyst.Pyridinium p-toluenesulfonate was employed as a catalyst for alkylations with acrolein ethylene acetal.Although ethoxyallylation of acylic substrates (e.g., ethyl acetoacetate, diethyl malonate, and ethyl cyanoacetate) with acrolein diethyl acetal proved to be slow, these and related alkylations could be conviently accomplished by use of the corresponding α-hydroxymethylene derivatives.Unsaturated acetals bearing a methyl or phenyl substituent at C-2 can be employed for alkoxyallylation, but the reaction appears to be incompatible with a methyl group at C-3.The mechanism of these reactions probably involves either direct C-allylation of the carbonyl compound on the γ-position of an alkoxyallyl carbocation intermediate or an indirect pathway via O-allylation at the α-position of the carbocation followed by Claisen rearrangement.
- Coates, Robert M.,Hobbs, Steven J.
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p. 140 - 152
(2007/10/02)
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- Hydroboration. 57. Hydroboration with 9-Borabicyclononane of Alkenes Containing Representative Functional Groups
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The hydroboration of alkenes containing representative functional groups was examined with 9-borabicyclononane (9-BBN) in order to extend the hydroboration reaction for the preparation of functionally substituted organoboranes.Terminal alkenes containing a remote functional group are hydroborated with a remarkable regioselectivity (>=98percent terminal), producing the corresponding stable organoboranes. 9-BBN hydroborates the allylic derivatives so as to place boron essentially on the terminal carbon atom (>=97percent).The directive effect is further enhanced (>=99percent) in the case of β-methylallyl derivatives.The hydroboration of crotyl derivatives attaches boron predominantly at the 2-position, followed by an elimination-rehydroboration sequence.However, crotyl alcohol can be protected against elimination as the tert-butyl or tetrahydropyranyl ethers.The hydroboration-oxidation of ethyl crotonate involves a series of elimination, hydroboration, and condensation processes.In the vinyl, crotyl, and isobutenyl systems, the mesomeric effect of the substituent favors the placement of boron at the β-position, while the inductive effect favors the α-position, with the former effect predominating in most cases.Acyclic β-substituted organoboranes undergo rapid elimination.Nonpolar solvents and lower reaction temperatures decrease the rate of elimination.However, those derived from cyclic vinyl derivatives are relatively stable under neutral conditions, undergoing facile elimination in the presence of a base.
- Brown, Herbert C.,Chen, Jackson C.
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p. 3978 - 3988
(2007/10/02)
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