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Title:The total syntheses of (+)-crotanecine, (-)-hastanecine and (-)-rosmarinecine utilizing the tandem (4+2)/(3+2) cycloadditions of nitroalkenes
Author(s):Thorarensen, Atli
Doctoral Committee Chair(s):Denmark, Scott E.
Department / Program:Chemistry, Organic
Discipline:Chemistry, Organic
Degree Granting Institution:University of Illinois at Urbana-Champaign
Degree:Ph.D.
Genre:Dissertation
Subject(s):Chemistry, Organic
Abstract:A short and efficient asymmetric synthesis of the pyrrolizidine necine base (${-}$)-hastanecine is described. The key reaction in the synthesis is a sequential inter (4+2) /inter (3+2) cycloaddition. The Lewis acid promoted (4+2) cycloaddition between 2-acyloxy nitroalkene 90 and chiral vinyl ether (+)-28 afforded a nitronate which underwent facile (3+2) cycloaddition with dimethyl maleate. The resulting nitroso acetal (${-}$)-96 had all the required stereocenters for (${-}$)-hastanecine. The critical unmasking of the nitroso acetal (${-}$)-96 employed a hydrogenolytic cleavage to give the 1-azabicyclo (3.3.0) octane skeleton of (${-}$)-hastanecine.
(${-}$)-Rosmarinecine 42 is the necine base portion of the pyrrolizidine alkaloid (${-}$)-rosmarinine. (${-}$)-Rosmarinecine is a representative of that group of pyrrolizidines which bear a cis relationship between adjacent stereocenters C(1), C(7) and C(7a) in addition to a highly oxygenated skeleton. (${-}$)-Rosmarinecine has been synthesized in 8 steps and 14.8% overall yield, as an illustration of a general approach for the construction of pyrrolizidines bearing this stereochemical feature. The key step in the asymmetric synthesis is a Lewis acid-promoted, tandem inter (4+2) /intra (3+2) cycloaddition between a fumaroyloxynitroalkene 165 and a chiral vinyl ether (${-}$)-29.
Numerous alkaloids contain (+)-crotanecine 36 as it necine constituent. (+)-Crotanecine which is an all cis substituted necine has been prepared in 10 steps and 10.2% overall yield. The key steps in the asymmetric synthesis is a Lewis acid-promoted, tandem inter (4+2) /intra (3+2) cycloaddition between a fumaroyloxynitroalkene 165 and a chiral propenyl ether (${-}$)-222 and a solvolytic elimination of a mesylate to install the unsaturation at C(6)-C(7).
Issue Date:1996
Type:Text
Language:English
URI:http://hdl.handle.net/2142/19961
ISBN:9780591199413
Rights Information:Copyright 1996 Thorarensen, Atli
Date Available in IDEALS:2011-05-07
Identifier in Online Catalog:AAI9712459
OCLC Identifier:(UMI)AAI9712459


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