Efficient Control of the Diastereoselectivity and Regioselectivity in the Singlet-Oxygen Ene Reaction of Chiral Oxazolidine-Substituted Alkenes by a Remote Urea NH Functionality:  Comparison with Dimethyldioxirane and m-Chloroperbenzoic Acid Epoxidations

The singlet-oxygen ene reaction and the epoxidation by DMD of chiral oxazolidine-substituted alkenes, equipped with a free urea NH functionality and a conformationally fixed double bond, proceed in high like diastereoselectivity (up to >95:5); also a high regioselectivity was found for the 1O2 en...

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Bibliographic Details
Published in:Journal of the American Chemical Society 2001-08, Vol.123 (30), p.7228-7232
Main Authors: Adam, Waldemar, Peters, Karl, Peters, Eva-Maria, Schambony, Simon B
Format: Article
Language:English
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Summary:The singlet-oxygen ene reaction and the epoxidation by DMD of chiral oxazolidine-substituted alkenes, equipped with a free urea NH functionality and a conformationally fixed double bond, proceed in high like diastereoselectivity (up to >95:5); also a high regioselectivity was found for the 1O2 ene reaction. Capping of the free NH functionality by methylation erases this like selectivity for both oxidants and significantly reduces the regioselectivity in the ene reaction. These data demonstrate effective hydrogen bonding between the remote urea NH functionality and the oxidant that favors the like attack on the C−C double bond. For 1O2, the hydrogen bonding in the exciplex results in preferred hydrogen abstraction from the alkyl group cis to the directing urea functionality.
ISSN:0002-7863
1520-5126
DOI:10.1021/ja010463k