Our synthetic approach toward fasicularin is presented. Key steps in this construction are a siloxy-epoxide semipinacol rearrangement, a B-alkyl Suzuki reaction and an intramolecular S(N)2 reaction.
An asymmetric formal synthesis of fasicularin (1) is described. This natural product, isolated from the extracts of the marine invertebrate Nephteis fasicularis, has shown modest cytotoxicity towards Vero cells. Fasicularin is among only two members of the cylindricinefamily of natural products, along with lepadiformine (2), to possess a trans A-B ring junction. Key steps of this approach to 1 involve
Investigations of α-Siloxy−Epoxide Ring Expansions Forming 1-Azaspirocyclic Ketones
作者:Gregory R. Dake、Michaël D. B. Fenster、Mélissa Fleury、Brian O. Patrick
DOI:10.1021/jo049356+
日期:2004.8.1
The construction of 1-azaspirocyclic cycloalkanones using a siloxy-epoxide semipinacol ring expansion process was examined. Functionalized 1-azaspiro[5.5]undecan-7-ones (1-azaspirocyclic cyclohexanones) proceeded in high chemical yields with complete diastereoselectivity using titanium tetrachloride as the Lewis acid promoter. The formation of functionalized 6-azaspiro[5.4]-decan-1-ones (1-azaspirocyclic cyclopentanones) proceeded in high chemical yield with little diastereoselectivity. Modification of reaction parameters such as the Lewis acid promoter or the nature of the silyl ether allowed for the preferential formation of either ("anti" or "syn" 1,2 alkyl shift) diastereomeric product. An explanation for the different reactivity profiles between the cyclobutanol silyl ethers and cyclopentanol silyl ethers is provided.
Construction of Azaspirocyclic Ketones through α-Hydroxyiminium Ion or α-Siloxy Epoxide Semipinacol Rearrangements
作者:Michaël D. B. Fenster、Brian O. Patrick、Gregory R. Dake
DOI:10.1021/ol0160708
日期:2001.6.1
[GRAPHICS]Semipinacol-type rearrangements to produce azaspirocyclic ketones are presented. The yields and stereoselectivities of these reactions range from 67-94% yield and 2.8:1 to 1:0 diastereoselectivity, respectively.