A Short Synthesis of Enantiomeric Phytoprostanes B1 Type I

Synthesis
DOI: 10.1055/s-0029-1216883



Abstract

The synthesis of both enantiomers of phytoprostane B type I from 3-[(dimethoxyphosphoryl)methyl]cyclopent-2-enone is reported. It consists of three steps including regioselective alkylation of the substrate at C(2) with methyl 8-bromooctanoate, subsequent Horner reaction with enantiomeric O-benzoyl-protected α-hydroxybutanals and final methanolysis. This affords the product in 25% overall yield.
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© Georg Thieme Verlag Stuttgart ˙ New York

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Studies on the Reaction of Diimines with Thiourea: Synthesis and Solvent-Induced cis/trans-Isomerization of 1,3,5-Triazinane-2-thiones

Synthesis
DOI: 10.1055/s-0029-1216884



Abstract

The reaction of ,′-bis(arylmethylidene)arylmethane diimines with thiourea under reflux in methanol was studied. The reaction gave a diastereomeric mixture of 4,6-disubstituted 1,3,5-triazinane-2-thiones in good yields. Two diastereoisomers of 4,6-diphenyl-1,3,5-triazinane-2-thione were detected in a solution of CDCl by NMR analysis. According to the NMR studies, the -dia­stereoisomer undergoes a solvent-induced /-isomerization process, producing the -diastereoisomer in DMSO. The stereochemistry of the -diastereoisomer was determined by X-ray crystallographic analysis.
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© Georg Thieme Verlag Stuttgart ˙ New York

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Synthesis and Chemoselective N- and O-Alkylation of Thiadiazolopyrimidine Nucleosides and Uridines

Synthesis
DOI: 10.1055/s-0029-1216882



Abstract

A facile and selective N- or O-alkylation of 4-β--ribofuranosyl[1,2,5]thiadiazolo[3,4-]pyrmidine-5,7(4,6)-dione as well as uridines was accomplished via bimolecular base alkylation or bimolecular nucleophilic substitution reaction controlled by the reagents. In the presence of 18-crown-6 and anhydrous KCO, the highly chemoselective O-methylation was performed using dimethyl carbonate (DMC) in DMF at 22-25 ˚C, i.e. the 2′,3′--isopropylidene derivatives of 4-β--ribofurnosyl[1,2,5]thiadiazolo[3,4-]pyrmidine-5,7(4,6)-dione, uridine, and 5-bromouridine, underwent only the primary alcoholic O-methylation reaction without affecting the NH group of the pyrimidne ring. The novel N-alkylated derivatives of 4-β--ribofurnosyl[1,2,5]thiadiazolo[3,4-]pyrmidine-5,7(4,6)-dione were also prepared using the appropriate alkyl halides with a base.
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© Georg Thieme Verlag Stuttgart ˙ New York

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Synthesis of Highly Substituted Pyridines via a One-Pot, Three-Component Cascade Reaction of Malononitrile with Aldehydes and S-Alkylisothiouronium Salts in Water

Synlett
DOI: 10.1055/s-0029-1217529



Abstract

A novel methodology for the synthesis of 2-amino-4-aryl(alkyl)-6-sulfanyl pyridine-3,5-dicarbonitriles via a one-pot, three-component reaction of structurally diversified aldehydes with various -alkylisothiouronium salts and malononitrile in water has been developed. Utilization of -alkylisothiouronium salts as thiol equivalents greatly broadens the application of the current method, and also makes the reaction more environmentally friendly.
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© Georg Thieme Verlag Stuttgart ˙ New York

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Efficient Synthesis of 3-Alkoxy-4,4-difluoropiperidines

Synlett
DOI: 10.1055/s-0029-1217533



Abstract

Fluorinated piperidines bearing an additional functional group at the heterocyclic ring are important building blocks for use in agrochemical or pharmaceutical chemistry. Therefore, for the first time 3-alkoxy-4,4-difluoropiperidines were synthesized by deoxofluorination of 3-alkoxy-4-piperidinones with morpholinosulfur trifluoride and were selectively N- and O-deprotected. In ­addition, the oxidation of 4,4-difluoro-3-hydroxy-1-trifluoroacetylpiperidine resulted in the interesting 4,4-difluoro-3,3-dihydroxypiperidine.
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© Georg Thieme Verlag Stuttgart ˙ New York

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Synthesis of the First Thiazolidine-Condensed Five-, Six-, and Seven-Membered Heterocycles via Cyclization of Vinylogous N-Acyliminium Ions

Synlett
DOI: 10.1055/s-0029-1217532



Abstract

Synthesis of new thiazolidine-fused five-, six-, and seven-membered heterocycles through vinylogous -acyliminium ion-cyclization sequence, involving positions 3 and 4 of the thiazolidine ring, is described. The formation of bicyclic products, arising by generally disfavored 5--trig cyclization initiated by sulfur atom acting as a nucleophile, indicates the preparative value of this method.
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© Georg Thieme Verlag Stuttgart ˙ New York

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Scope and Limitations of Samarium Diiodide Induced Cyclizations of Alkenyl-Substituted γ-Keto Esters to Benzannulated Cyclooctanol Derivatives

Synlett
DOI: 10.1055/s-0029-1217520



Abstract

A series of γ-keto esters bearing various alkenyl substituents were synthesized and subjected to samarium diiodide mediated 8-- ketyl-alkene coupling reactions. Highly substituted benzannulated cyclooctanol derivatives were obtained in good yields and with moderate to excellent stereoselectivities. The obtained results demonstrate the influence of steric and electronic factors on the regio- and stereoselectivity of ketyl-alkene cyclizations. Stilbenyl-substituted derivatives can cyclize either to cyclooctanol or to cycloheptanol derivatives depending on the substitution pattern at the carbonyl group.
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© Georg Thieme Verlag Stuttgart ˙ New York

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Synthesis of Substituted Pyranopyrazoles under Neat Conditions via a Multicomponent Reaction

Synlett
DOI: 10.1055/s-0029-1217526



Abstract

A simple and efficient synthesis of pyranopyrazoles in good yields via a four-component reaction between an aromatic aldehyde, hydrazine hydrate, ethyl acetoacetate and malononitrile under neat conditions is described.
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© Georg Thieme Verlag Stuttgart ˙ New York

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Platinum- and Palladium-Catalyzed Sequential Reactions: Regioselective Synthesis of 9-Fluorenylidenes from 9-Ethynylfluoren-9-yl Carboxylates and Furans

Synlett
DOI: 10.1055/s-0029-1217531



Abstract

The transformation of 9-acyloxy-9-ethynylfluorene and furans with platinum and palladium co-catalysts gave 9-fluor­enylidenes in excellent yields with high regioselectivity in a one-pot manner.
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© Georg Thieme Verlag Stuttgart ˙ New York

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Synthesis of Furo[3,4-c]furanones via DDQ Treatment of Furo[3,4-c]pyranone Derivatives

Synlett
DOI: 10.1055/s-0029-1217525



Abstract

A new method for the synthesis of 4,6-disubstituted furo[3,4-]furanones is described. The title compounds are obtained by simple treatment of furo[3,4-c]pyranones with DDQ; furo[3,4-]furanones are obtained in moderate yields. A possible mechanism for the conversion is discussed.
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© Georg Thieme Verlag Stuttgart ˙ New York

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