- Synthesis and easy aromatisation of 5-substituted 6-(alkylthio)-2-methoxy-2,3-dihydropyridines. A new approach to the pyridine ring
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Reaction of lithiated methoxyallene, 1-ethoxyethoxyallene, 1-(methylthio)propyne and 2-butyne with methoxymethyl isothiocyanate, MeOCH2N=C=S followed by methylation affords the imidothioates H2C=C=C(R)C(SMe)=NCH2OMe [R=Me, OMe, OCH(Me)OEt, SMe]. Rearrangement to the fully conjugated systems H2C=CH-C(R)=C(SMe)-N=CHOMe and subsequent electrocyclisation of these compounds leads to the 5-substituted 6-(methylthio)-2-methoxy-2,3-dihydropyridines with good to excellent yields. In the presence of acidic catalysts or by heating at elevated temperatures these dihydropyridines eliminate methanol to afford 3-substituted 2-(methylthio)pyridines. The aroma compound 2-(methylthio)-3-pyridinol was obtained by acid-catalysed treatment of 3-(1-ethoxyethoxy)-2-(methylthio)pyridine.
- Nedolya, Nina A.,Schlyakhtina, Nataly I.,Klyba, Lyudmila V.,Ushakov, Igor A.,Fedorov, Sergei V.,Brandsma, Lambert
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- 1,3-Dipolar Character of Six-membered Aromatic Rings. Part 55. 3-Hydroxypyridine-2-thiones: Betaines, Cycloadditions, and Other Reactions
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1-Methyl-2-methylthio-3-oxidopyridinium, 2-allylthio-1-methyl-3-oxidopyridinium, and 1--2-methylthio-3-oxidopyridinium undergo 1,3-dipolar cycloaddition to electron-deficient alkenes giving azabicyclooctene adducts having 1-alkylthio substituents.Quaternisation and tropone formation are investigated. 3-Hydroxypyridine-2-thione is cycloalkylated between sulphur and oxygen by substituted 1,1-dichloromethanes and certain α-haloacetyl chlorides. 1-(2-Pyridylmethyl)-3-oxidopyridinium gives azabicyclooctene cycloadducts with electron-deficient alkenes.The stereochemistry of all cycloadducts is deduced from the n.m.r.spectra.
- Katritzky, Alan R.,Grzeskowiak, Nicholas E.
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p. 2345 - 2389
(2007/10/02)
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