The formal syntheses of (+)-prelaureatin (1) and (+)-laurallene (2), halogenated eight-membered-ring ethers, are described. The key step of our strategy relies on diastereoselective construction of a trans-alpha,alpha'-disubstituted oxocene structure through a Brook rearrangement-mediated [3 + 4] annulation with acryloylsilane 9 and 6-oxa-2-cycloheptenone derivative 22'.
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General Synthetic Approach for the Laurencia Family of Natural Products Empowered by a Potentially Biomimetic Ring Expansion.
J Am Chem Soc
May 2019
Department of Chemistry , University of Chicago, 5735 South Ellis Avenue , Chicago , Illinois 60637 , United States.
The Laurencia family of C-acetogenins is Nature's largest collection of halogenated natural products, with many of its members possessing a brominated 8-membered cyclic ether among other distinct structural elements. Herein, we demonstrate that a bromonium-induced ring expansion, starting from a common tetrahydrofuran-containing bicyclic intermediate and using the highly reactive bromenium source BDSB (EtSBr·SbClBr), can lead to concise asymmetric total syntheses of microcladallenes A and B, desepilaurallene, laurallene, and prelaureatin. Key advances in this work include (1) the first demonstration that the core bromonium-induced cyclization/ring-expansion can be initiated using an enyne with an internal ether oxygen nucleophile, (2) that reasonable levels of stereocontrol in such processes can be achieved both with and without appended ring systems and stereogenic centers, (3) that several other unique chemoselective transformations essential to building their polyfunctional cores can be achieved, and (4) that a single, common intermediate can lead to five different members of the class encompassing two distinct 8-membered cyclic ether ring collections.
View Article and Find Full Text PDFFormal total syntheses of (+)-prelaureatin and (+)-laurallene by diastereoselective brook rearrangement-mediated [3 + 4] annulation.
J Org Chem
June 2010
Department of Synthetic Organic Chemistry, Graduate School of Medical Sciences, Hiroshima University, 1-2-3 Kasumi, Minami-Ku, Hiroshima 734-8553, Japan.
The formal syntheses of (+)-prelaureatin (1) and (+)-laurallene (2), halogenated eight-membered-ring ethers, are described. The key step of our strategy relies on diastereoselective construction of a trans-alpha,alpha'-disubstituted oxocene structure through a Brook rearrangement-mediated [3 + 4] annulation with acryloylsilane 9 and 6-oxa-2-cycloheptenone derivative 22'.
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