Theoretical and experimental NMR studies of the Swern oxidation of methyl 6¦Á,7¦Â-dihydroxyvouacapan-17¦Â-oate
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- 作者：Fl¨¢vio Jos¨¦ L. dos Santos ; Ant?nio Fl¨¢vio de C. Alcantara ; Dalton L. Ferreira-Alves and Dorila Pil¨®-Veloso
- 关键词：Swern oxidation ; Furanoditerpenes ; α ; diketones ; α ; hydroxyketones ; NMR analysis ; HF and DFT calculations
- 刊名：Structural Chemistry
- 出版年：2008
- 出版时间：August, 2008
- 年：2008
- 卷：19
- 期：4
- 页码：625-631
- 全文大小：311.6 KB
文摘
This work describes the synthesis of new derivatives of 6α,7β-dihydroxyvouacapan-17β-oic acid (1) employing the Swern method for the oxidation of C-6 and C-7 of methyl 6α,7β-di-hydroxyvouacapan-17β-oate (2) and the formation of methyl 6,7-dioxovouacapan-17β-oate (3). NMR structural studies associated with theoretical calculations of reaction intermediates and products are also reported. The mixture of methyl 7β-hydroxy-6-oxovouacapan-17β-oate (4; 21 % ) and methyl 6α-hydroxy-7-oxovouacapan-17β-oate (5; 79 % ) was the product from the first step of the oxidation of 2. The lower energy of 5, calculated by HF/6-31G* and DFT/BLYP/6-31G* methods, reinforces the thermodynamic control proposed for the reaction. After further Swern oxidation of the mixture of 4 and 5, the isomeric form methyl 6-hydroxy-7-oxovouacap-5-en-17β-oate (6) was obtained. Theoretical calculations indicate a lower energy for the mono-enol 6 than the 1,2-diketo 3 and the other mono-enol methyl 7-hydroxy-6-oxovouacap-7-en-17β-oate (7).