3,4‐Dihydro‐2‐phenyl‐2<i>H</i>‐pyrano[2,3‐<i>b</i>]pyridines. Novel aza analogs of flavans

Bargar, Thomas M.; Wilson, Timothy J.; Daniel, John K.

doi:10.1002/jhet.5570220624

Cited by 15 publications

(1 citation statement)

References 10 publications

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“…The crude product was purified by distillation to give a colorless oil; yield: 0.841 g (75%); bp 72-75°C (12 mbar) [Lit. 30…”

Section: -Chloro-2-methoxypyridine (3g) 29mentioning

confidence: 99%

Noncryogenic Synthesis of Functionalized 2-Methoxypyridines by Halogen-Magnesium Exchange Using Lithium Dibutyl(isopropyl)magnesate(1-) and Lithium Chloride

Struk¹,

Sośnicki²

2012

Synthesis

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2-Methoxypyridines functionalized in the 3-, 5-, or 6-position and 2,6-dimethoxypyridines functionalized in the 3-position were prepared from the corresponding bromo or iodo analogues by using lithium dibutyl(isopropyl)magnesate(1-) and lithium chloride under noncryogenic conditions. The procedure was optimized in terms of the choice between two magnesates and the presence or absence of lithium chloride in the reaction medium.The functionalized 2-alkoxypyridine ring is a common structural motif that is present in many organic compounds that exhibit a broad spectrum of biological activities. 1 Functionalized 2-methoxypyridines are particularly valuable examples of such derivatives because, apart from their biological activities, 2 they are also useful in synthesis. Transformation of 2-methoxypyridines into Nsubstituted 3 or N-unsubstituted 4 2-pyridones or replacement of the 2-methoxy substituent by chlorine by using phosphoryl chloride 5 followed by cross-coupling reactions 6 permits the preparation of hundreds of derivatives containing a pyridine ring, including alkaloids 7 and pharmacophores. 8 Moreover, the 2-methoxy group of 2-methoxypyridine can be directly replaced by an aryl moiety in a cross-coupling reaction. 9Halogen-metal exchange in a bromo-or iodo-substituted pyridine, followed by reaction with an electrophile, is a useful method for the functionalization of the pyridine ring. The most common synthetic approach of this type involves the use of organolithium compounds as exchange reagents; however, these reactions must be performed at low temperatures, typically between -78 and -65°C. 10 In the case of organomagnesium compounds, Grignard derivatives, particularly isopropylmagnesium chloride, 11 or its complex with lithium chloride 12 can be used. In the past decade, increasing attention has been paid to the use of magnesate complexes of the type [R 3 Mg]Li as halogenmagnesium exchange reagents; these complexes are relatively stable at temperatures between -10°C and 0°C. 13 Magnesate reagents have been used in the functionalization of substituted pyridines, 13c-k,t,x,aa among other reactions. Other promising candidates for use as stable halogen-exchange reagents include zincate 'ate' complexes. Recently, dilithium tetrabutylzincate and its complex with N,N,N¢,N¢-tetramethylethylenediamine have been used in the chemoselective zincation of bromopyridines at room temperature. 14 In our recent study on the application of magnesates in synthesis, we introduced the use of lithium allyl(dibutyl)magnesate(1-) as a powerful allylating agent, useful in nucleophilic addition reactions of 2-(thio)pyridones. 15 Recently, we also presented some preliminary results on the use of lithium tributylmagnesate(-1) as an exchange reagent for the noncryogenic 5-functionalization of 2-methoxypyridine, starting from the 5-bromo-substituted analogue. 16 Here, we report further studies on the functionalization of 5-bromo-2-methoxypyridine by halogenmagnesium exchange and the extension of this reaction to 6-bromo-and 3-iodo-su...

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“…The crude product was purified by distillation to give a colorless oil; yield: 0.841 g (75%); bp 72-75°C (12 mbar) [Lit. 30…”

Section: -Chloro-2-methoxypyridine (3g) 29mentioning

confidence: 99%

Noncryogenic Synthesis of Functionalized 2-Methoxypyridines by Halogen-Magnesium Exchange Using Lithium Dibutyl(isopropyl)magnesate(1-) and Lithium Chloride

Struk¹,

Sośnicki²

2012

Synthesis

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Heck reactions of aryl halides with alk‐1‐en‐3‐ol derivatives catalysed by a tetraphosphine–palladium complex

Berthiol

Doucet

Santelli

2006

Applied Organom Chemis

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cis,cis,cis-1,2,3,4-Tetrakis(diphenylphosphinomethyl)cyclopentane-[PdCl(C 3 H 5 )] 2 efficiently catalyses the Heck reaction of alk-1-en-3-ol with a variety of aryl halides. In the presence of hex-1-en-3-ol or oct-1-en-3-ol, the β-arylated carbonyl compounds were selectively obtained. Turnover numbers up to 84 000 can be obtained for this reaction. Linalool and 2-methylbut-3-en-2-ol led regio-and stereoselectively to the corresponding (E)-1-arylalk-1-en-3-ol derivatives. A minor electronic effect of the substituents of the aryl bromide was observed. Quite similar reaction rates were generally observed in the presence of activated aryl bromides such as bromoacetophenone and deactivated aryl bromides such as bromoanisole, indicating that, with these alkenols and this catalyst, the oxidative addition of aryl bromides to palladium is not the rate-limiting step. It should be noted that this reaction also proceeds with sterically very congested aryl bromides such as 9-bromoanthracene or 2,4,6-triisopropylbromobenzene or with a vinyl bromide. On the other hand, low yields were obtained with aryl chlorides.

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ChemInform Abstract: 3,4‐Dihydro‐2‐phenyl‐2H‐pyrano[2,3‐b]pyridines. Novel Aza Analogs of Flavans.

Bargar¹,

Wilson²,

Daniel³

1986

Chemischer Informationsdienst

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3,4‐Dihydro‐2‐phenyl‐2H‐pyrano[2,3‐b]pyridines. Novel aza analogs of flavans

Cited by 15 publications

References 10 publications

Noncryogenic Synthesis of Functionalized 2-Methoxypyridines by Halogen-Magnesium Exchange Using Lithium Dibutyl(isopropyl)magnesate(1-) and Lithium Chloride

Noncryogenic Synthesis of Functionalized 2-Methoxypyridines by Halogen-Magnesium Exchange Using Lithium Dibutyl(isopropyl)magnesate(1-) and Lithium Chloride

Heck reactions of aryl halides with alk‐1‐en‐3‐ol derivatives catalysed by a tetraphosphine–palladium complex

ChemInform Abstract: 3,4‐Dihydro‐2‐phenyl‐2H‐pyrano[2,3‐b]pyridines. Novel Aza Analogs of Flavans.

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