Diastereoselectivity of Organometallic Additions to Nitrones
Chang, Zen-Yu
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https://hdl.handle.net/2142/70420
Description
Title
Diastereoselectivity of Organometallic Additions to Nitrones
Author(s)
Chang, Zen-Yu
Issue Date
1988
Doctoral Committee Chair(s)
Coates, Robert M.
Department of Study
Chemistry
Discipline
Chemistry
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(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.
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