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Title:Diastereoselectivity of Organometallic Additions to Nitrones
Author(s):Chang, Zen-Yu
Doctoral Committee Chair(s):Coates, Robert M.
Department / Program:Chemistry
Degree Granting Institution:University of Illinois at Urbana-Champaign
Subject(s):Chemistry, Organic
Abstract:The diastereoselectivity of organometallic additions to nitrones bearing stereogenic substituents has been investigated. High and complementary diastereoselectivity was observed in the additions of Grignard reagents to nitrones (e.g. 62) bearing a potentially chelating $\beta$-alkoxy group on nitrogen. The high facial diastereoselectivity is explained by a simple chelation model which was supported(DIAGRAM, TABLE OR GRAPHIC OMITTED...PLEASE SEE DAI)by $\sp1$H NMR analysis of a nitrone-magnesium bromide complex (86). However, the opposite selectivity resulted from the reaction of methylmagnesium bromide with the corresponding silyl ether (68). N-Deoxygenation of N,N-dialkylhydroxylamine adducts was achieved by lithium-ammonium reduction of the hydroxylamino carbonates (90 and 95) and phosphates (114). N-Dealkylation by periodic acid cleavage of the resulting amino alcohols (91 and 96) and subsequent hydrolysis of the imine products provided non-racemic chiral amines. The optical purities of the amines were determined by HPLC analyses of their 3,5-dinitrobenzamide derivatives (94 and 97). The relative stereochemistry of selected hydroxylamine adducts was established by N-deoxygenation of the adducts to amines (115), by conversion of the adducts to primary amines, by periodate cleavage of a $\beta$-hydroxyhydroxylamine (118) and by various correlations. Low selectivity was observed in the organometallic additions to C-($\alpha$-alkoxy)nitrones (74-76). Organometallic additions to nitrones (70-71) prepared from carbohydrates were also surveyed but further experiments are necessary to explore the potential for chiral amine syntheses by this approach. Formation of tetrahydrooxadiazine dimers in the reactions of N-benzylidene-N-(1-arylalkyl)nitrones with methyllithium was also observed.
Issue Date:1988
Description:160 p.
Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 1988.
Other Identifier(s):(UMI)AAI8908646
Date Available in IDEALS:2014-12-15
Date Deposited:1988

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