Practical Syntheses of Enantiomerically Enriched γ-Lactones and γ-Hydroxy Ketones by the Alkylation of Pseudoephedrine Amides with Epoxides and Their Derivatives
摘要:
Pseudoephedrine amide enolates are shown to undergo efficient alkylation reactions with epoxides as electrophiles. Reactions with monosubstituted epoxides are subject to stereochemical matching such that the pairing leading to the 1,3-syn diastereomer is a highly selective, synthetically useful process, while the pairing forming the 1,3-anti diastereomer is not. Reactions with the 1,1-disubstituted epoxide isobutylene oxide are also highly diastereoselective and synthetically useful, but ethylene oxide exhibits poor diastereoselectivity. As an alternative to the use of ethylene oxide, 2-(tert-butyldimethylsilyloxy)ethyl iodide is shown to undergo highly diastereoselective and efficient alkylation reactions with pseudoephedrine amide enolates. Interestingly, epoxides and alkyl halides are found to attack opposite pi-faces of pseudoephedrine amide enolates. The products of each of these alkylation reactions are transformed efficiently into gamma-lactones by acidic hydrolysis and into methyl ketones by the addition of methyllithium. The methodology described provides useful procedures for the synthesis of enantiomerically enriched gamma-lactones and gamma-hydroxy ketones.
Total Syntheses of the Assigned Structures of Lituarines B and C
作者:Amos B. Smith、Matthew O. Duffey、Kallol Basu、Shawn P. Walsh、Hans W. Suennemann、Michael Frohn
DOI:10.1021/ja078293k
日期:2008.1.1
The first syntheses of the structuresassigned to the marine natural products lituarines B and C have been achieved via a highly convergent sequence. The structures comprise complex, highly oxygenated 25-membered macrolactones possessing a rare tricyclic spiroketal and a unique (E,Z)-dienamide side chain. Unfortunately, the spectral properties of the synthetic compounds did not match those reported
分配给海洋天然产物 lituarines B 和 C 的结构的首次合成是通过高度收敛的序列实现的。该结构包括复杂的、高度氧化的 25 元大环内酯,具有罕见的三环螺缩酮和独特的 (E,Z)-二烯酰胺侧链。不幸的是,合成化合物的光谱特性与天然 lituarines 的光谱特性不匹配。本通讯提供了 lituarines B 和 C 指定结构的全合成,以及支持结构指定的证据。