Reductive aminations of ketones and aldehydes using borane–pyridine

Pelter, Andrew; Rosser, Richard M.; Mills, Stuart

doi:10.1039/p19840000717

Cited by 125 publications

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“…Sodium triacetoxyborohydride (NaBH 3 (OAc)) 6 has also been employed, but mostly in non-protic solvents, since in methanol or water it reduces the carbonyl groups, decomposes, and gives flammable subproducts. 7 Pyridine borane (Pyr-BH 3 ) [8][9][10] was the most representative aminoborane employed, but it is unstable, and decomposes causing fire; even explosions were reported.…”

Section: Introductionmentioning

confidence: 99%

Usage of α-picoline borane for the reductive amination of carbohydrates

Navarro¹,

Stortz²

2011

Arkivoc

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, to recognize their achievements in organic chemistry and their contributions in the development of the field in Argentina AbstractThe reaction of reductive amination, widely used for carbohydrates, was reviewed in our lab, especially in the context of the analytical determination of carbohydrate enantiomers. The best conditions for the technique have been evaluated, showing that under optimal working conditions it is possible to use α-picoline borane as a reducing agent instead of sodium cyanoborohydride without affecting the selectivity or the yield. The main reason for the variation of the technique was that, in the presence of acetic acid, secondary epimeric products were produced with α-picoline borane due to an Amadori rearrangement. This new modification assures lower toxicity, and thus a more environmental-friendly reaction system. Preparative scale synthesis can also be efficiently made with this reducing reagent.

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Section: Introductionmentioning

confidence: 99%

Usage of α-picoline borane for the reductive amination of carbohydrates

Navarro¹,

Stortz²

2011

Arkivoc

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“…Além disto, apesar da formação de aminas terciárias a partir de aminas secundárias e iminas 135 , análises por CG-EM não registraram a presença destes produtos competitivos em reduções de amidas secundárias por boranos 136 . Assim, por estes resultados, pode-se propor que, no caso de amidas, a redução não deve proceder via formação de cátion imino 137,138 . (43) Considerando que as amidas e boranos contendo grupos substituintes pouco volumosos não apresentam restrições estéricas significativas para interações intramoleculares de nitrogênio e borano ligado ao oxigênio (Figura 3), pode ser proposta que a hidrogenólise da ligação carbono-oxigênio no intermediário tetraédrico ocorra por ataque nucleofílico intramolecular de hidretos (Equação 44).…”

Section: Figura 4 Etapas Da Transferência De Hidretos (A) E (B) Naunclassified

Redução de amidas por boranos

2002

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Recebido em 27/3/01; aceito em 25/7/01 REDUCTION OF AMIDES BY BORANES. Despite the fact that boranes are frequently used in amide reductions, the reaction mechanisms of the involved are note well known. This work presents the results of a bibliographic search on probable amide reduction mechanisms and an analysis of the existing literature. Steric and electronic effects were considered in light of reactivity since it could be concluded that the formation of intermediates and products depends mainly on the substitution patterns of both the boron and nitrogen atoms. Otherwise, results described in the literature for the reactions of boranes, sodium borohydride, lithium aluminum hydride, alkylboranes or haloboranes with others functional groups such as carboxylic acids, esters, ketones and alkenes were analysed with the aim to obtain something about the N-substituted amide reactions employing boranes.Keywords: amides; reactivity of boranes; reduction. INTRODUÇÃOAmidas estão envolvidas em vários processos químicos e bioló-gicos e têm sido empregadas em diversas classes de medicamentos como hipnóticos (zolpidem, zopiclone e acecarbromal), anticonvulsantes (carbamazepina, felbamato e progabida), tranqüilizan-tes (metilprilona e glutetimida), relaxantes musculares (alildietilacetamida, valnoctamida e oxanamida) e antivirais (AZT e ribavirin) 1-3 . Além disto, as amidas são empregadas também na síntese de agentes radiofarmacêuticos em medicina nuclear 4 .De um modo geral, as propriedades químicas e biológicas das amidas estão relacionadas com a ordem da ligação carbono-nitrogê-nio, a qual expressa a deslocalização eletrônica entre os heteroátomos, sendo influenciada por fatores estéricos e eletrônicos dos grupos substituintes presentes tanto no nitrogênio quanto no carbono carbonílico. Devido à deslocalização eletrônica, essa ligação (denominada também de ligação peptídica) apresenta um alto grau de rigidez, com barreiras de energia rotacional variando entre 50 e 100 kJ/mol 5,6 . A rigidez da ligação carbono-nitrogênio proporciona uma planaridade ao grupo amido em peptídeos e proteínas, a qual, somada aos efeitos de ligações de hidrogênio intramoleculares, determina formas estruturais helicoidais (Figura 1).Nos processos químicos, as reduções de amidas têm sido muito empregadas no desenvolvimento de metodologias para formação de aminas, substâncias também importantes quimicamente 8 . Os procedimentos utilizados para reduções de amidas podem ser agrupados em quatro tipos: reações eletroquímicas; reações com metais; reduções nucleofílicas e reduções eletrofílicas.As reações eletroquímicas e aquelas envolvendo metais são dependentes das condições de reação 9,10 , podendo levar à formação competitiva entre aminas, aldeídos ou álcoois [11][12][13][14][15][16][17] . As reduções nucleofílicas, empregando principalmente boro-hidreto de sódio (NaBH 4 ), hidreto de lítio e alumínio (LiAlH 4 ) e seus derivados 18-28 , proporcionam, além de aminas, a formação de outros produtos de reação. Assim, tris-(dialquilamino)-alumino-hidreto...

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“…The introduction of the nitrogen atom to the aldehyde, together with reduction is, in a formal sense, similar to the well-known reductive anim a tions of aldehydes by amines in the presence of so dium cyanohydroborate [7] or pyridine-borane [8].…”

Section: -Omentioning

confidence: 99%

The Direct Synthesis of Secondary Amides from Aldehydes; A Novel General Redox Procedure Mediated by Iodotrichlorosilane (ITCS)

Elmorsy

Badawy

Nour

et al. 1994

Zeitschrift Für Naturforschung B

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A unique, general redox process for the preparation of secondary amides by the interac tion, of aldehydes with nitriles in the presence of two equivalents of iodotrichlorosilane (ITCS) is described and possible pathways are discussed.Iodotrichlorosilane (ITCS) [1] may be generated by the interaction of sodium iodide with tetrachlorosilane [2]. For reactions, the mixture of so dium iodide with tetrachlorosilane in solvents such as dichlorom ethane or acetonitrile may be used in stead of isolated ITCS. So far, the organic chemi stry of ITCS has received little attention, the only previously recorded reaction being that of ether cleavage [3]. We have recently shown [4] that acetats and ketals are efficiently cleaved by ITCS to yield the parent carbonyl compounds under an hydrous conditions. We have also shown that sim ple aldehydes react with simple aromatic and ali phatic nitriles to give secondary amides in a unique redox reaction [1]. The reaction takes a different course and gives unsaturated iminoaldehydes when acrylonitrile is used [5]. Simple ketones do not react in the usual conditions but a,/?-unsaturated ketones either give allylic secondary amides or are reduced at the double bond [6].We now report in detail on the production of sec ondary amides from aldehydes. We first came across this reaction when exploring the functionality that would withstand the ether cleavage. With this in mind, we subjected 4-methoxybenzaldehyde to re action with ITCS in dichloromethane, using aceto nitrile as a cosolvent. To our surprise, for demethylation with ITCS is a facile process [2], there was no 4-hydroxybenzaldehyde in the product but, instead, the reaction gave N-(4-methoxybenzyl)acetamide (II), in which the acetonitrile unit had been incor porated and the aldehyde reduced (Scheme 1).

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Reductive aminations of ketones and aldehydes using borane–pyridine

Cited by 125 publications

References 0 publications

Usage of α-picoline borane for the reductive amination of carbohydrates

Usage of α-picoline borane for the reductive amination of carbohydrates

Redução de amidas por boranos

The Direct Synthesis of Secondary Amides from Aldehydes; A Novel General Redox Procedure Mediated by Iodotrichlorosilane (ITCS)

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