Asymmetric alkylation reactions of chiral imide enolates. A practical approach to the enantioselective synthesis of .alpha.-substituted carboxylic acid derivatives

A number of ethyl 4-(2-benzylalkyloxy)benzoates were prepared and their activity to induce precocious metamorphosis was evaluated in larvae of the silkworm, Bombyx mori, which was clearly recognized as a juvenile hormone (JH)-deficiency symptom. Ethyl 4-(2-benzylhexyloxy)benzoate (6) and its 2-benzylheptyloxy analog (7) were found to induce precocious metamorphosis at relatively low doses. Both enantiomers of 6 and 7 were prepared using a chiral auxiliary oxazolidinone. (S)-Enatiomers were more active than (R)-isomers at low doses of 0.1 and 1 mg, but at higher doses their activity was reversed. The activity of compound 6 could be fully counteracted by methoprene, a JH agonist, but not by the dietary administration of 20-hydroxyecdysone. The ester group was important in the ability to induce precocious metamorphosis. The (S)-enatiomer of 6 prolonged the duration of the instar and delayed the onset of cocoon spinning when applied to 5th instar larvae, suggesting that this compound might have JH-like activity as well as anti-JH activity.

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“…13) As a typical procedure, the synthesis of ethyl 4-[(R)-2-benzylhexyloxy]benzoate (6R) is outlined in Fig. 2(B).…”

Section: Synthesismentioning

confidence: 99%

Synthesis and anti-juvenile hormone activity of ethyl 4-(2-benzylalkyloxy)benzoates and their enantiomers

et al. 2007

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“…Nestes sistemas, empregam-se enolatos quirais onde a quelação com o metal fixa uma orientação entre o centro estereogênio e o sistema enolato (transferência de quiralidade intraanular forçada por quelação). 16,42 Os auxiliares de Evans foram obtidos, por exemplo, a partir de S-valina ou de (S)-ou (R)-fenilalanina ou (1S,2R)-norefedrina. O emprego das oxazolidinonas de Evans permitiu a obtenção de aldóis com altas diastereo e enantiosseletividades com possibilidade de acessar os diferentes aldóis pela escolha apropriada do indutor.…”

Section: Emprego De Auxiliares Quiraisunclassified

“…O emprego das oxazolidinonas de Evans permitiu a obtenção de aldóis com altas diastereo e enantiosseletividades com possibilidade de acessar os diferentes aldóis pela escolha apropriada do indutor. 42 Tais auxiliares foram e são ainda hoje, utilizados na obtenção de diversos produtos naturais, 43 sendo muito eficientes, principalmente, na obtenção de aldóis sin. (25) 50 Nestes sistemas catalíticos, quando se emprega a oxazolidinona como auxiliar quiral, obtém-se um dos adutos anti, enquanto que o aduto anti de configuração oposta pode ser acessado com o auxiliar de Crimmins (Esquema 23).…”

Section: Emprego De Auxiliares Quiraisunclassified

Aldol reactions

Martins¹

2009

Revista Virtual De Química

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Abstract:The aldol reaction is one of the most powerful tools for C-C bond formation in organic synthesis. The C-C bond is formed by a reaction between an enolizable carbonyl compound and a carbonyl compound acting as an electrophile to produce a β-hydroxycarbonyl compound named aldol. One or two stereocenters can be formed with stereochemical control. Since the β-hydroxycarbonyl unit is present in a variety of natural products, the aldol reaction has been used in the synthesis of several biologically important substances. In this work, some important aspects of this useful reaction like regiochemistry, stereochemistry and different methodologies introduced since its discovery will be addressed.Keywords: aldol; C-C bond formation; stereochemistry; regiochemistry; -hydroxycarbonyl compounds ResumoA reação aldólica é uma das ferramentas mais poderosas da síntese orgânica para a construção de ligações C-C. Esta ligação é formada através da reação entre uma substância carbonílica enolizável que age como nucleófilo e outra substância carbonílica que age como eletrófilo. Como resultado da reação, obtém-se um produto β-hidróxi-carbonilado que se denomina aldol. Um ou dois centros estereogênicos podem ser gerados com controle sobre os mesmos. Uma vez que a unidade β-hidróxi-carbonila está presente em vários produtos naturais, a reação aldólica foi empregada em diversas oportunidades na síntese de substâncias de importância biológica. Neste trabalho, são abordados fatores importantes no que concerne à reação aldólica tais como a estereoquímica e a regioquímica, bem como as diferentes metodologias introduzidas desde a sua descoberta.

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“…Concerning the synthesis of (3R,4R,5R)-2 and (3S,4S,5S)-2, we envisaged the epoxy alcohol 10 [8], the most suitable building block, because it contains already the C 5 skeleton of the final tetrahydropyranol, and it is known in the literature that the nucleophilic attack on this kind of epoxy alcohols should proceed regioselectively affording precursors with the same configuration as our target molecules [9] (Scheme 3). However, we found that the synthesis of 10 in enantiomerically pure form suffers two main drawbacks: i) the access to both enantiomers of the alcohol I is not straight forward and requires a considerable effort; it can mainly be prepared through the use of Evans chiral-auxiliary chemistry [10], reduction of the O-protected derivate of the methyl l-hydroxyisobutyrate and methyl d-hydroxyisobutyrate [11], or by an enzymatic resolution of the racemic alcohol I [12]; ii) the Swern oxidation of I to give the aldehyde II on large scale is not apparently practicable due to the aldehyde epimerization [13]. Alternatively, we found that the enzymatic resolution of the racemic epoxy alcohol 10, by acetylation with vinyl acetate in CHCl 3 catalyzed by lipase-PS [14], gave the access to both enantiomers of 10 with higher optical-rotation values than those reported in literature and excellent ee values To improve the ring-closure protocol of alcohols 14, instead of the Ts, the I leaving group was tested.…”

Section: Preparation Of Four Stereoisomers Ofmentioning

confidence: 99%

Enzyme-Mediated Preparation of the Enantiomerically Enriched Isomers of the Odorous Tetrahydropyranyl AcetatesJasmal® andJessemal®, and Their Olfactory Evaluation

Abate

Brenna

Fronza

et al. 2006

C&B

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All four stereoisomers of the fragrance Jasmal of structure 3,4,5,6-tetrahydro-3-pentyl-2H-pyran-4-yl acetate were prepared by enzymatic resolutions of the corresponding alcohols. The absolute configurations were unambiguously determined by comparison with the enantiomer (3R,4S)-1 prepared from l-tartaric acid. The four stereoisomers of the fragrance Jessemal of structure 3-butyl-5-methyl-3,4,5,6-tetrahydro-2H-pyran-4-yl acetate were obtained starting from the epoxy alcohol 10, which was obtained in an optically pure state by enzymatic resolution of the racemic mixture. The olfactory evaluations of all stereoisomers are reported. 1 H-NMR Conformational analysis of diastereoisomers (3RS,4RS,5RS)-2 and (3RS,4SR,5RS)-2 is also reported.

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Asymmetric alkylation reactions of chiral imide enolates. A practical approach to the enantioselective synthesis of .alpha.-substituted carboxylic acid derivatives

Cited by 1,056 publications

References 2 publications

Synthesis and anti-juvenile hormone activity of ethyl 4-(2-benzylalkyloxy)benzoates and their enantiomers

Synthesis and anti-juvenile hormone activity of ethyl 4-(2-benzylalkyloxy)benzoates and their enantiomers

Aldol reactions

Enzyme-Mediated Preparation of the Enantiomerically Enriched Isomers of the Odorous Tetrahydropyranyl AcetatesJasmal® andJessemal®, and Their Olfactory Evaluation

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