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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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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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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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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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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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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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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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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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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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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