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Enantioselective epoxidation of unfu...

Lee, Virgil James.

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Enantioselective epoxidation of unfunctionalized olefins catalyzed by threitol-strapped metalloporphyrins.

Record Type:	Electronic resources : Monograph/item
Title/Author:	Enantioselective epoxidation of unfunctionalized olefins catalyzed by threitol-strapped metalloporphyrins./
Author:	Lee, Virgil James.
Description:	138 p.
Notes:	Source: Dissertation Abstracts International, Volume: 53-09, Section: B, page: 4668.
Contained By:	Dissertation Abstracts International53-09B.
Subject:	Chemistry, Organic. -
Online resource:	http://pqdd.sinica.edu.tw/twdaoapp/servlet/advanced?query=9302238

Enantioselective epoxidation of unfunctionalized olefins catalyzed by threitol-strapped metalloporphyrins.
Lee, Virgil James.

Enantioselective epoxidation of unfunctionalized olefins catalyzed by threitol-strapped metalloporphyrins. - 138 p.

Source: Dissertation Abstracts International, Volume: 53-09, Section: B, page: 4668.

Thesis (Ph.D.)--Stanford University, 1992.

A family of strapped, chiral metalloporphyrins were prepared and studied as asymmetric epoxidation catalysts of unfunctionalized olefins. These catalysts were derived from the condensation of hydroxy-substituted porphyrins with (S,S)- or (R,R)-1,4-ditosylthreitol derivatives. The steric environments of these porphyrin systems are easily modified by forming various acetal or ketal derivatives at the 2,3-diol position of the threitol unit. This simple modification scheme permitted the first systematic study of asymmetric catalysis using chiral metalloporphyrin systems.Subjects--Topical Terms:

516206
Chemistry, Organic.

Enantioselective epoxidation of unfunctionalized olefins catalyzed by threitol-strapped metalloporphyrins.
LDR:03715nmm 2200313 4500 001 1840141
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008 130614s1992 eng d
035 $a (UnM)AAI9302238
035 $a AAI9302238
040 $a UnM $c UnM
100 1 $a Lee, Virgil James. $3 1928489
245 1 0 $a Enantioselective epoxidation of unfunctionalized olefins catalyzed by threitol-strapped metalloporphyrins.
300 $a 138 p.
500 $a Source: Dissertation Abstracts International, Volume: 53-09, Section: B, page: 4668.
500 $a Adviser: James P. Collman.
502 $a Thesis (Ph.D.)--Stanford University, 1992.
520 $a A family of strapped, chiral metalloporphyrins were prepared and studied as asymmetric epoxidation catalysts of unfunctionalized olefins. These catalysts were derived from the condensation of hydroxy-substituted porphyrins with (S,S)- or (R,R)-1,4-ditosylthreitol derivatives. The steric environments of these porphyrin systems are easily modified by forming various acetal or ketal derivatives at the 2,3-diol position of the threitol unit. This simple modification scheme permitted the first systematic study of asymmetric catalysis using chiral metalloporphyrin systems.
520 $a Two different types of mono-faced, threitol-strapped porphyrins were prepared: bridged and unbridged. Each of these systems have two threitol units spanning adjacent positions of tetrakis(2-hydroxyphenyl)porphyrin. In the bridged systems the threitol units are linked by an organic spacer that spans the center of the macrocycle.
520 $a The manganese(III) chloride derivatives of these mono-faced systems were studied as asymmetric epoxidation catalysts. These systems give moderate enantiomeric excesses (up to 61%) at low turnovers. The optical yields appear to reflect a fortuitous initial conformation of these catalysts in which the chloride ligand blocks the unsubstituted face of the porphyrin, forcing the reaction to occur within the chiral straps. Higher optical yields (up to 88% ee) are obtained with the bridged systems when bulky ligands are added to block the unhindered face of the catalysts. It is proposed that the stereochemical-defining interaction in epoxidation reactions with these mono-faced porphyrins occurs between the olefin substituents and the inner dioxolane oxygen atom of the threitol straps.
520 $a Four different bis-faced, threitol-strapped catalysts were prepared. These systems have two threitol units spanning adjacent positions of tetrakis(2,6-dihydroxyphenyl)porphyrin on each face of the porphyrin macrocycle. Iron(III) and manganese(III) chloride derivatives of these bis-faced systems were found to give moderate optical yields (up to 63% ee). The stereoselectivity with three of these systems is also believed to result from the interaction between the inner dioxolane oxygen atom of the threitol straps and the olefin substituents. However, a reversal in selectivity was observed when threitol ketals of 2,7-dimethylxanthone were used to prepared the porphyrin, reflecting a different approach of the olefin to the reactive site of the catalyst.
520 $a This study has produced one of the most effective asymmetric epoxidation catalysts for unfunctionalized olefins. The advantages that this system offers are that it is relatively easy to prepare and modify. The information gained from this study could lead to even more effective asymmetric epoxidation catalysts.
590 $a School code: 0212.
650 4 $a Chemistry, Organic. $3 516206
650 4 $a Chemistry, Inorganic. $3 517253
690 $a 0490
690 $a 0488
710 2 0 $a Stanford University. $3 754827
773 0 $t Dissertation Abstracts International $g 53-09B.
790 1 0 $a Collman, James P., $e advisor
790 $a 0212
791 $a Ph.D.
792 $a 1992
856 4 0 $u http://pqdd.sinica.edu.tw/twdaoapp/servlet/advanced?query=9302238