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Asymmetric catalytic epoxidations of...

Zhang, Wei.

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Asymmetric catalytic epoxidations of simple olefins.

Record Type:	Electronic resources : Monograph/item
Title/Author:	Asymmetric catalytic epoxidations of simple olefins./
Author:	Zhang, Wei.
Description:	242 p.
Notes:	Source: Dissertation Abstracts International, Volume: 52-11, Section: B, page: 5837.
Contained By:	Dissertation Abstracts International52-11B.
Subject:	Chemistry, Organic. -
Online resource:	http://pqdd.sinica.edu.tw/twdaoapp/servlet/advanced?query=9211057

Asymmetric catalytic epoxidations of simple olefins.
Zhang, Wei.

Asymmetric catalytic epoxidations of simple olefins. - 242 p.

Source: Dissertation Abstracts International, Volume: 52-11, Section: B, page: 5837.

Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 1991.

Two types of chiral (salen)Mn(III) complexes, either cationic or neutral, were synthesized by complexation of the corresponding chiral salen ligands with manganese salt. Neutral Mn(III) salen complexes were prepared from the ligands and Subjects--Topical Terms:

516206
Chemistry, Organic.

Asymmetric catalytic epoxidations of simple olefins.
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035 $a (UnM)AAI9211057
035 $a AAI9211057
040 $a UnM $c UnM
100 1 $a Zhang, Wei. $3 1043738
245 1 0 $a Asymmetric catalytic epoxidations of simple olefins.
300 $a 242 p.
500 $a Source: Dissertation Abstracts International, Volume: 52-11, Section: B, page: 5837.
500 $a Adviser: E. N. Jacobsen.
502 $a Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 1991.
520 $a Two types of chiral (salen)Mn(III) complexes, either cationic or neutral, were synthesized by complexation of the corresponding chiral salen ligands with manganese salt. Neutral Mn(III) salen complexes were prepared from the ligands and $\ rm Mn(OAc)\sb2{\cdot}4H\sb2O $ via in situ aerial oxidation of the corresponding (salen)Mn(II) species. This approach circumvents the manipulation of highly air sensitive Mn(II) salen intermediates. The use of commercially available bleach solution as the oxidant greatly increases the practical value of this asymmetric epoxidation process.
520 $a High enantioselectivities in alkene epoxidation, especially for cis-disubstituted olefins, has been achieved through a rational sequence of ligand modifications. A mechanism involving side-on approach of alkene to a Mn(V)-oxo intermediate accounts for the sense and degree of asymmetric induction with various types of olefins, and it provides a guideline for improving catalyst design.
520 $a Electronic environment of the catalyst can dramatically affect the enantioselectivity of olefin epoxidation. Sterically non-biasing substituents were shown in the epoxidation of 2,2-dimethylchromene to effect a difference in $\ Delta\Delta{\rm G}{\sp\ne} $ of 2.0 Kcal/mol, corresponding to a range in ee's from 22% to 96%. Increases in selectivity due to electron donating substituents are attributed to a more product-like transition structures in the ee-determining olefin oxidation step.
520 $a Different reaction mechanisms are proposed for alkyl-substituted and aryl-substituted alkenes. Epoxidation of alkyl-substituted olefins is very likely to be a concerted oxygen transfer process, while a stepwise reaction mechanism is indicated with aryl-substituted olefins.
520 $a A convenient and very inexpensive catalyst synthesis, a simple and practical epoxidation procedure, good catalyst turnovers, and high levels of asymmetric induction render the (salen)Mn(III) epoxidation system superior to any other catalytic or stoichiometric asymmetric processes for unfunctionalized olefins reported thus far. Widespread application of these catalysts may be foreseen.
590 $a School code: 0090.
650 4 $a Chemistry, Organic. $3 516206
690 $a 0490
710 2 0 $a University of Illinois at Urbana-Champaign. $3 626646
773 0 $t Dissertation Abstracts International $g 52-11B.
790 1 0 $a Jacobsen, E. N., $e advisor
790 $a 0090
791 $a Ph.D.
792 $a 1991
856 4 0 $u http://pqdd.sinica.edu.tw/twdaoapp/servlet/advanced?query=9211057