Unusual Reactivity of (Vinylimino)phosphoranes and Their Utility in the Preparation of Pyridine and Dihydropyridine Derivatives

Molina, Pedro; Pastor, Aurelia; Vilaplana, M. J.

doi:10.1021/jo960940v

Cited by 42 publications

(26 citation statements)

References 14 publications

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“…Dihydropyridines 96, formed through the addition of a second molecule of phosphazene 88, has been also previously observed [32,42]. Dihydropyridines 96, formed through the addition of a second molecule of phosphazene 88, has been also previously observed [32,42].…”

Section: N-vinylic Phosphazenes With -Unsaturated Carbonyl Compoundmentioning

confidence: 71%

N-Vinylic Phosphazenes. A Useful Tool for the Synthesis of Acyclic and Heterocyclic Compounds

Palacios¹,

Aparicio²,

Rubiales³

et al. 2006

COC

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The synthesis and reactivity of the N-vinylic phosphazene derivatives is the subject of this review. The first part gives a survey of different methodologies for the preparation of N-vinylic phosphazenes. These N-vinylic phosphazenes can be prepared either, by Staudinger reaction of N-vinylic azides with phosphines, or by reaction of phosphorus ylides and nitriles. The second part covers the high synthetic potential of these N-vinylic phosphazenes as valuable building blocks in preparative organic synthesis. N-Vinylic phosphazenes can be used as starting materials for the preparation of enamines by hydrolysis under basic or acidic conditions, and can be transformed into aminophosphonium salts by treatment with hydrogen halides or acyl halides. However, the most important synthetic application of N-vinylic phosphazenes is their use for the construction of carbon-nitrogen double bonds by means of aza-Wittig reaction with carbonyl compounds. This aza-Wittig reaction of N-vinylic phosphazenes has been widely applied for the preparation of simple and functionalized 2-aza-1,3-butadienes. These 2-azadienes are excellent starting materials for the construction of acyclic and heterocyclic compounds, and more elaborated polycyclic derivatives. Also the reactivity of N-vinylic phosphazenes with cumulene double bonds as carbon dioxide, carbon disulfide, isocyanates, isothiocyanates, ketenes and triple bonds, and the use of this process for the synthesis of acyclic and cyclic derivatives has been reviewed.

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Section: N-vinylic Phosphazenes With -Unsaturated Carbonyl Compoundmentioning

confidence: 71%

N-Vinylic Phosphazenes. A Useful Tool for the Synthesis of Acyclic and Heterocyclic Compounds

Palacios¹,

Aparicio²,

Rubiales³

et al. 2006

COC

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“…The efficient synthesis of symmetrical dihydropyridines 5 here described from enaminophosphonium salts 3 provides an easy approach to the preparation of these kind of compounds, avoiding the use of high temperatures (160 ºC). 30 Different behavior has been observed in the reaction of enaminophosphonium salts 3 with α,β-unsaturated ketones 7. Dihydropyridines 9 are obtained by an enamine alkylation of enaminophosphonium salts 3 onto the β-carbon of the carbonyl compound and intramolecular aza-Wittig reaction of resulting phosphazenes.…”

Section: Reaction Of Enamino-phosphonium Salts 3 With Ketonesmentioning

confidence: 99%

Regioselective synthesis of dihydropyridines and pyridines derived from β-aminoacids from N-vinylic phosphazenes

Palácios¹,

Herrán²,

Alonso³

et al. 2007

Arkivoc

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“…Enaminonas diidropiridínicas do tipo E2 (n=2) podem ser obtidas por tratamento de iminofosforil-enonas com aldeídos aromáti-cos a 160 o C em uma reação do tipo aza-Wittig 126 . O mesmo produto pode ser obtido em condições mais brandas, pela conversão prévia do intermediário reativo em seu sal de enamino-fosfônio, por tratamento com HCl 127 (Esquema 26).…”

Section: Outras Reaçõesunclassified

Síntese de enaminonas

Ferraz¹,

Pereira²

2004

Quím. Nova

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Recebido em 18/9/02; aceito em 13/6/03 SYNTHESIS OF ENAMINONES. The general term "enaminone" is applied to any compound bearing the conjugated system N-C=C-C=O. Enaminones are typical capto-dative ethylenes, showing particular properties due to π-electron delocalization. Their reactivity can be predicted by structural patterns of substitution, conformation and configuration, making them versatile synthetic building blocks. In this review, a variety of methods for the synthesis of enaminones is described. The methods were divided into condensation of amines to β-dicarbonyl compounds, addition of amines to α,β-unsaturated carbonyl compounds, condensation between carbonyl compounds and N-unsaturated functions and other methods, covering the period from 1993 to 2001.Keywords: β-enamino ketones; β-enamino esters; methods of preparation. INTRODUÇÃOO termo geral "enaminona" refere-se a qualquer composto que apresente o sistema conjugado N-C=C-C=O. Enaminonas são compostos β-enamino carbonílicos, derivados de β-dicetonas, β-ceto ésteres e outros compostos β-dicarbonílicos. Os representantes mais comuns desta classe são β-enamino cetonas e β-enamino ésteres, também chamados de amidas vinílogas e carbamatos ou uretanas vinílogas, respectivamente; denominações como "β-aminoenona", "acilvinilamina" e "acilenamina" também são encontradas na literatura.Compostos deste tipo são considerados etilenos capto-dativos típicos, devido ao efeito mesomérico dos substituintes acil e amino sobre a ligação dupla (o que também é denominado efeito "pushpull" de elétrons) 1 . A deslocalização de elétrons π, decorrente deste efeito, tem como conseqüência uma notável polarização destes carbonos olefínicos (como se pode constatar pelos seus deslocamentos químicos de 13 C não usuais) 2 , conferindo a estes compostos uma natureza reativa distinta de seus correlatos estruturais enamina e enona (pela estabilização de seus estados de transição polares) 3 . O efeito mesomérico em enaminonas também é responsável pela coexistência de isômeros conformacionais e configuracionais, devido à restrição rotacional de ligações σ (aumento do caráter π das ligações N-C e C-CO) e à atenuação da barreira de isomerização da dupla ligação olefínica (caráter π diminuído) 4 , esta última podendo ocorrer até mesmo à temperatura ambiente 5 . Quatro formas isoméricas (Esquema 1) são possíveis, e a predominância e a interconversão entre elas dependem de diversos fatores estruturais. O tipo e o volume de substituintes em enaminonas acíclicas podem favorecer uma determinada forma isomérica, em razão de uma menor tensão estrutural ou de uma maior planaridade para conjugação de elétrons π 6,7 . O tautomerismo imino-enamina também pode favorecer o equilíbrio conformacional 8 , e o isômero cis-s-cis pode ser estabilizado por ponte de hidrogênio intramolecular (R 1 = H) [9][10][11] . A isomeria conformacional também é observada para o grupo amino (R 1 ≠ R 2 ), cuja restrição rotacional se intensifica proporcionalmente ao grau de conjugação no sistema enaminona 12 (neste caso a ...

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Unusual Reactivity of (Vinylimino)phosphoranes and Their Utility in the Preparation of Pyridine and Dihydropyridine Derivatives

Cited by 42 publications

References 14 publications

N-Vinylic Phosphazenes. A Useful Tool for the Synthesis of Acyclic and Heterocyclic Compounds

N-Vinylic Phosphazenes. A Useful Tool for the Synthesis of Acyclic and Heterocyclic Compounds

Regioselective synthesis of dihydropyridines and pyridines derived from β-aminoacids from N-vinylic phosphazenes

Síntese de enaminonas

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