Álcoois quirais: métodos químicos e catalíticos de obtenção por redução assimétrica

Temba, Eliane S. C.; Oliveira, Ione Maria Ferreira de; Donnici, Cláudio Luis

doi:10.1590/s0100-40422003000100019

Cited by 5 publications

(5 citation statements)

References 55 publications

(67 reference statements)

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“…Note that we used boranes for what seems to be an unusual task: as a selective reducing agent for (activated) double bonds. Boranes are normally used for hydroboration-oxidation of double bonds or reduction of carbonyls [61,62]. But we have noted that, rather than reducing the carbonyl group of oxidized MBH adducts, the borane dimethyl sulfide complex reduces the double bond in a fully selective fashion.…”

Section: Resultsmentioning

confidence: 99%

Morita–Baylis–Hillman adducts as building blocks of heterocycles: a simple approach to 4-substituted pyrazolones, and mechanism investigation via ESI–MS(/MS)

et al. 2015

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We describe herein an efficient approach for the preparation of 4-substituted 2,3-dihydro-1H-pyrazol-3-ones starting from Morita-Baylis-Hillman adducts. These heterocycles were obtained in two or three steps as single isomers with moderate to good overall yields. One efficient and alternative methodology for the synthesis of a-methylb-ketoesters is also reported (up to 91 % yield). Additionally, the mechanism of formation of pyrazolones was investigated employing ESI-MS/MS reaction monitoring. Graphical abstract

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Section: Resultsmentioning

confidence: 99%

Morita–Baylis–Hillman adducts as building blocks of heterocycles: a simple approach to 4-substituted pyrazolones, and mechanism investigation via ESI–MS(/MS)

et al. 2015

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“…Os atropoisômeros enantiomericamente puros são amplamente utilizados em sínteses assimétricas catalisadas por metais [31][32][33][34] , promovendo a formação de complexos organometálicos quirais, através da indução de quiralidade por diferenciação termodinâmica do sítio reativo dos substratos durante a catálise [35][36][37] . Os principais atropoisômeros comercializados com esta finalidade são apresentados na Figura 11, com destaque para os enantiômeros do bifenilnaftol (BINOL) 32 e da bifenilfosfina (BINAP) 33,34 , que estão entre os ligantes quirais mais utilizados em síntese assimétrica.…”

Section: Uso Do Atropoisomerismo Em Reações Assimétricasunclassified

Atropoisomerismo: o efeito da quiralidade axial em substâncias bioativas

Santos¹,

Pinheiro²,

Sodero³

et al. 2007

Quím. Nova

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Recebido em 26/9/05; aceito em 30/3/06; publicado na web em 26/9/06 ATROPISOMERISM: THE EFFECT OF THE AXIAL CHIRALITY IN BIOACTIVE COMPOUNDS. Atropisomerism is a special kind of stereoisomeric relationship that arises from the freezing of a certain conformation of an organic molecule, associated with a high rotational barrier about a single covalent bond. Atropisomerism has been originally described in orto-functionalyzed biphenyl derivatives, but a lot of other organic functionalities can present this structural phenomenon, characterized by the presence of chiral properties in compounds that don't present classical stereogenic centers. Atropisomeric compounds, intermediates and catalysts have well-know importance in organic synthesis, but the influence of the axial chirality in substances able to modulate biological systems is still not very exploited in drug design and development. In this context, the present account describes the importance of this structural property in the medicinal chemistry of different classes of bioactive compounds or therapeutic agents, emphasizing how atropisomerism could affect the molecular recognition of a ligand or a prototype by the target bioreceptor.Keywords: atropisomerism; atropisomerism of drugs; stereoselective molecular recognition. INTRODUÇÃOO fenômeno conhecido como atropoisomerismo, denominação oriunda da palavra grega atropos (i.e. sem rotação), é atribuído a um tipo de estereoisomerismo característico de sistemas onde a rotação livre em torno de uma ligação simples é impedida, produzindo uma barreira energética suficientemente elevada, de modo a permitir o isolamento ou simplesmente a detecção dos diferentes rotâmeros, chamados atropoisômeros 1,2 . Este tipo de isomeria axial é caracterizada pela atividade ótica promovida por um eixo de ligação, não necessitando que a substância apresente carbono estereogênico como elemento de quiralidade. O fenômeno foi observado pela primeira vez por Christie e Kenner 3 , após a resolução dos atropoisômeros do ácido 6,6'-dinitro-2,2'-difênico 1, os quais não se mostraram interconversíveis à temperatura ambiente (Figura 1).A nomenclatura de substâncias que apresentam quiralidade axial pode ser atribuída como R ou S pela aplicação das regras de prioridade de Cahn-Ingold-Prelog 4,5 , conforme exemplificado na Figura 2. A partir da projeção da estrutura vista na direção do eixo de ligação do sistema bifenílico, deve-se definir a ordem de prioridade dos grupos funcionais, iniciando por aqueles mais próximos ao observador e, em seguida, atribuir a configuração absoluta R ou S com base no sentido da rotação produzida quando se caminha do substituinte de maior prioridade para o de menor prioridade. Apesar de ser opcional, a descrição da configuração absoluta de estereoisômeros atropoisoméricos deve ser acompanhada pela introdução do prefixo a, i.e. aR ou aS, visando distinguí-los de outros tipos de compostos oticamente ativos. De maneira alternativa, os compostos atropoisoméricos podem ser vistos como hélices e suas configurações descritas...

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“…[ 4,5 ] These compounds can exhibit important applications in the medicinal and fine chemistry fields or act as precursors of products for this purpose. [ 6–11 ]…”

Section: Introductionmentioning

confidence: 99%

“…[4,5] These compounds can exhibit important applications in the medicinal and fine chemistry fields or act as precursors of products for this purpose. [6][7][8][9][10][11] Diethylzinc is one of the most common organometallic reagents used in enantioselective alkylations, due to its accessibility and low reactivity, which increases when coordination with ligands occurs. [12,13] Although the study of this particular reaction is the subject of extended bibliography, focused on the synthesis of several classes of ligands and evaluation of their catalytic performances, they are often associated with long and expensive synthetic sequences and a narrow range of aromatic aldehydes as substrates.…”

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confidence: 99%

Deciphering the mechanism behind efficient enantioselective ethylation with thiazolidine‐based amino alcohols

Tavares

Cacho

Costa

et al. 2021

Applied Organom Chemis

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Taking advantage of the opposite chirality of two privileged starting materials, l‐cysteine and d‐penicillamine, a wide range of thiazolidine‐based amino alcohols was synthesized. l‐Cysteine derivatives were more efficient chiral inductors than the d‐penicillamine ones, with ee up to 92% in the enantioselective ethylation of benzaldehyde. The scope of the best catalyst was evaluated using several aromatic, heteroaromatic, and aliphatic aldehydes, providing excellent (S)‐enantioselectivities. Given the opposite chirality of the l‐cysteine and d‐penicillamine thiazolidines, it was expected that the use of one or the other type of derivative as ligand would allow the formation of opposite configurations of the alkylated product. However, whereas the l‐cysteine thiazolidines predominantly gave the (S) form of the alkylated product, the d‐penicillamine ones led to both configurations. The significant difference in the stereochemical outcome of this reaction when catalyzed by the two types of ligands prompted us to investigate the reasons behind such results. Extensive quantum chemical calculations were performed in order to identify the transition state structures by which the enantioselective ethylation of benzaldehyde in the presence of these type of amino alcohols can proceed. An alternative path for the rate‐determining step was also explored and found decisive for the rationalization of the experimental outcomes. It was observed that the type of ligand dictates the accessible reaction paths for the formation of the chiral product, which ultimately determine the balance between the two possible configurations.

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Álcoois quirais: métodos químicos e catalíticos de obtenção por redução assimétrica

Cited by 5 publications

References 55 publications

Morita–Baylis–Hillman adducts as building blocks of heterocycles: a simple approach to 4-substituted pyrazolones, and mechanism investigation via ESI–MS(/MS)

Morita–Baylis–Hillman adducts as building blocks of heterocycles: a simple approach to 4-substituted pyrazolones, and mechanism investigation via ESI–MS(/MS)

Atropoisomerismo: o efeito da quiralidade axial em substâncias bioativas

Deciphering the mechanism behind efficient enantioselective ethylation with thiazolidine‐based amino alcohols

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