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Type: Artigo de periódico
Title: Stereoselective addition of chiral titanium enolates to 5-substituted five-membered oxocarbenium ions
Author: Pilli, Ronaldo A.
Riatto, Valéria B.
Abstract: The sterochemical outcome of the addition of chiral titanium enolates to gamma-lactols derived from (S)-glutamic acid were examined. When 5-substituted gamma-lactols were treated with chiral titanium enolates of N-acetyl-, N-propionyl-, N-bromoacetyl- and N-phenylacetyl oxazolidin-2-ones, only two diastereoisomers were obtained, revealing complete facial control by the chiral titanium enolate while the oxocarbenium ion facial discrimination was dependent on the nature of the enolate R³ substituent. After desilylation with aqueous HF/CH3CN, LiBH4 reduction allowed the efficient preparation of the corresponding trans-2,5-disubstituted tetrahydrofuran diols and recovery of the chiral auxiliary.
O curso estereoquímico da adição de enolatos de titânio quirais a gama-lactóis derivados do ácido (S)-glutâmico foi investigado. Quando gama-lactóis 5-substituídos foram tratados com enolatos de titânio quirais derivados de N-acetil-, N-propionil-, N-bromoacetil- e N-fenilacetil oxazolidin-2-onas somente dois diastereoisômeros foram obtidos, revelando um completo controle facial pelo enolato de titânio, enquanto que a discriminação facial do íon oxocarbênio mostrou-se dependente da natureza do grupo R³ do enolato. Dessililação com HF/CH3CN aquoso, seguida de redução com LiBH4, forneceu eficientemente dióis tetraidrofurânicos trans-2,5-dissubstituídos e recuperação do auxiliar quiral.
Subject: oxocarbenium ions
chiral titanium enolates
trans-2,5-disubstituted tetrahydrofurans
Editor: Sociedade Brasileira de Química
Rights: aberto
Identifier DOI: 10.1590/S0103-50532008000300030
Date Issue: 1-Jan-2008
Appears in Collections:Unicamp - Artigos e Outros Documentos

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