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Title:Scope and stereochemistry of carbon-carbon bond formation via addition of carbon nucleophiles to nitrones
Author(s):Tao, Ming
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 scope and stereochemistry of nucleophilic addition of Grignard reagents and silyl ketene acetals to acyclic and cyclic nitrones have been studied. A 4:1 selectivity favoring axial addition was observed in the reactions of cis-3,5-dimethyl-2,3,4,5-tetrahydropyridine N-oxide with both methyl and phenyl Grignard reagents and the silyl ketene acetal of t-butyl acetate. However, similar additions of carbon nucleophiles to 4-t-butyl-2,3,4,5-tetrahydropyridine N-oxide afforded only the trans isomer from axial addition in moderate yields (60-68%). The stereoselectivity in these endocyclic nitrone additions can be explained by a stereoelectronic effect which favors axial approach of the nucleophile. Acyclic nitrones reacted with crotyl Grignard reagent to give different diastereoselectivity depending on the substrates. Syn-anti selectivities ranging from 7:1 to 1:3 were observed in the reactions of acyclic nitrones with E-silyl ketene acetals of t-butyl propionate. The addition of Grignard reagents to nitrones of glyoxylate esters provides a direct method for the preparation of N-($\alpha$-hydroxylamino) esters. The scope of this addition reaction was surveyed with a diversity of substrates and nucleophiles. Primary, secondary, tertiary, vinyl, and aryl Grignard reagents generally gave good yields (55-81%) in the nitrone addition reactions. High diastereoselectivity (13-15:1) was observed in Grignard addition to nitrones of (1R, 2S, 5R)-phenylmenthyl esters. The facial bias of the reaction can be explained by a chelation model. N-Deoxygenation of N,N-dialkylhydroxylamines was achieved by reduction with trivalent phosphorus reagents via desulfurization of their thionocarbonate derivatives. The mechanism of the desulfurization reaction has been studied by a double labelling experiment provide an intermolecular pathway. Alternatively, reduction of the N,N-dialkylhydroxylamine adducts was accomplished by either lithium-ammonia or catalytic hydrogenation of their hydroxyamino carbonates. N-Deoxygenation of silyl ketene acetal adducts was effected by catalytic hydrogenation using palladium as a catalyst.
Issue Date:1992
Rights Information:Copyright 1992 Tao, Ming
Date Available in IDEALS:2011-05-07
Identifier in Online Catalog:AAI9215895
OCLC Identifier:(UMI)AAI9215895

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