Stereoselective reactions of a thioester butanediacetal with various electrophiles
| Autor: | Adam Drop, Hubert Wojtasek, Bożena Frąckowiak-Wojtasek |
|---|---|
| Rok vydání: | 2014 |
| Předmět: |
chemistry.chemical_classification
Stereochemistry Organic Chemistry Silyl enol ether Alkylation Thioester Medicinal chemistry Catalysis Inorganic Chemistry chemistry.chemical_compound chemistry Hexamethylphosphoramide Electrophile Stereoselectivity Physical and Theoretical Chemistry Alkyl Methyl iodide |
| Zdroj: | Tetrahedron: Asymmetry. 25:1396-1400 |
| ISSN: | 0957-4166 |
| Popis: | The reactions of the lithium enolate of S -ethyl (2 R ,5 R ,6 R )-5,6-dimethoxy-5,6-dimethyl-[1,4]-dioxane-2-carbothioate were investigated in the presence or absence of hexamethylphosphoramide (HMPA). Fluorination gave a single isomer with a much better yield than for the corresponding methyl ester. Alkylation with alkyl halides strongly depended upon their structure. Without HMPA, only methyl iodide reacted with moderate yield and gave a single isomer. In the presence of HMPA, all of the alkyl halides reacted almost quantitatively (81–98% yield) with moderate stereoselectivity and preferentially gave products with the alkyl chain attached at the equatorial position. The silyl enol ether obtained from the thioester had the opposite geometry to that obtained from the methyl ester, which thus explains the difference in stereoselectivity between these two compounds. |
| Databáze: | OpenAIRE |
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