An asymmetric synthesis of enantiopure chair and twist trans-cyclooctene isomers
摘要:
A pair of enantiopure chair and twist trans-cyclooctenes isomers were prepared by regioselective Sharpless asymmetric dihydroxylation of the central olefin of (E)-1,5,9-dectriene triene, with subsequent ring-closing metathesis to form an enantiomerically pure cis-cyclooctene. Epoxidation and ring-opening with lithium diphenylphosphide gives after oxidation two diastereomeric hydroxyphosphine oxides. Separate syn-elimination of these diastereomers gives enantiomerically pure chair and twist trans-cyclooctenes. A discussion of the molecular motion required to achieve the chair and twist isomers is discussed with reference to the X-ray crystal structure obtained for the hydroxyphosphine oxide leading to the chair trans-cyclooctene. (C) 2004 Elsevier Ltd. All rights reserved.
Intermolecularhydroacylation between salicylaldehydes 1, 26−40 and 1,4-penta- or 1,5-hexadienes 4−13 by Rh-catalyst proceeded under mild reaction conditions to give a mixture of iso- and normal-hydroacylated products 14−25, 41−55, and 57−60. In the hydroacylationreaction, chelation of both salicylaldehyde and diene to the Rh-complex plays a crucial role. The ratio of iso- and normal-hydroacylated
intermediates. N-Iodosuccinimide (NIS) effectively worked as an activator of the double bonds in the substrates and the silyl enol ether. Application to an expedient synthesis of the adjacent bis-tetrahydrofuran core of Annonaceousacetogenins with a cis/threo/cis relative stereochemistry is also described.
The most efficient method for the synthesis of the trans/threo/trans-bis(tetrahydrofuran) (THF) ring unit was established, and the first total synthesis of (−)-asimilobin and its diastereomer was then accomplished in twelve and fourteen steps, respectively, from trans-1,5,9-decatriene, by a convergentroute with a Wittig reaction as the key step. By virtue of these synthetic results, the absolute configuration
[reaction: see text] Rh-Catalyzed intermolecularhydroacylation between salicylaldehydes and 1,5-hexadienes proceeded under remarkably mild reaction conditions to afford a mixture of iso- and normal-hydroacylated products in good yields. The experiments using deuterated salicylaldehyde-d revealed that "double chelation" of salicylaldehyde and 1,5-hexadiene to Rh-complex played vital roles in the catalytic
Stereocontrolled construction of the trans-tetrahydrofuran units in Annonaceous acetogenins
作者:Shi-Kai Tian、Zhi-Min Wang、Jian-Kang Jiang、Min Shi
DOI:10.1016/s0957-4166(99)00259-1
日期:1999.7
the construction of trans-tetrahydrofuran (THF) unit from trans-1,5,9-decatriene was successfully developed by means of Sharpless AD reactions and oxidative cyclizations catalyzed by Co(modp)2 under an oxygen atmosphere. Based on this new synthetic strategy, the trans-mono-THF unit, trans-bis-THF unit and trans-tris-THF unit in Annonaceous acetogenins were smoothly obtained.