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URN: urn:nbn:de:bsz:25-opus-61462
URL: http://www.freidok.uni-freiburg.de/volltexte/6146/


Litvinov, Alexander E.

Ortho-diphenylphosphanylbenzoyl-directed Palladium catalyzed allylic substitution with soft nucleophiles

Ortho-Diphenylphosphanylbenzoyl-dirigierte Palladium-katalysierte allylische Substitution mit weichen Nucleophilen

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Kurzfassung in Englisch

Palladium catalyzed allylic substitution with soft nucleophiles is a valuable synthetic method. So far problematic is the control of regiochemistry which usually prefers substitution at the less hindered allyl terminus. In the course of this project we wanted to learn how the o-DPPB catalyst-directing group being a part of the substrate can alter intrinsic regio- and stereochemical preferences.
Only a few attempts have been reported in literature, which tried to employ directing effects in palladium catalyzed allylic substitution in order to tune regioselectivity. Having great experience with ortho-diphenylphosphanylbenzoyl (o-DPPB) group as a directing leaving group for copper mediated allylic substitution, we decided to study the application of the o-DPPB group for palladium catalyzed allylic substitution with soft nucleophiles.
In orienting experiments it was found that o-DPPB is not suitable as a directing leaving group for palladium catalyzed allylic substitution, since no effect on regioselectivity could be observed. These preliminary results led us explore substrates with o-DPPB acting as a sole directing group with carbonates or acetates as allylic leaving groups.
A series of allylic carbonates were synthesized and studied in palladium catalyzed allylic substitution with soft nucleophiles. Scope and limitations of the reaction were investigated. The reactions showed high regioselectivity in favour of the SN2 product which was obtained in good yield and excellent levels of chirality transfer.
Allylic substitution with non-directing substrates (CH or P(O) instead of P-atom) proved the role of the o-DPPB group as a directing group in these reactions. Non-directing substrates led either to considerably lower selectivity or side reactions.
Additionally, the same substrates were explored in copper-mediated allylic substitution. Interestingly, cis-alkenes were formed following an anti-SN2'-substitution pathway, which again results from a directing effect of the substrate-bound o-DPPB group.
In conclusion, the o-DPPB system can be used as a directing group for palladium catalyzed allylic substitution with soft nucleophiles as well as for copper-mediated allylic substitution with hard nucleophiles to regulate regio- and stereoselectivity of the reaction and to allow for excellent levels of chirality transfer from the substrate to the product.


Kurzfassung in Englisch

Palladium catalyzed allylic substitution with soft nucleophiles is a valuable synthetic method. So far problematic is the control of regiochemistry which usually prefers substitution at the less hindered allyl terminus. In the course of this project we wanted to learn how the o-DPPB catalyst-directing group being a part of the substrate can alter intrinsic regio- and stereochemical preferences.
Only a few attempts have been reported in literature, which tried to employ directing effects in palladium catalyzed allylic substitution in order to tune regioselectivity. Having great experience with ortho-diphenylphosphanylbenzoyl (o-DPPB) group as a directing leaving group for copper mediated allylic substitution, we decided to study the application of the o-DPPB group for palladium catalyzed allylic substitution with soft nucleophiles.
In orienting experiments it was found that o-DPPB is not suitable as a directing leaving group for palladium catalyzed allylic substitution, since no effect on regioselectivity could be observed. These preliminary results led us explore substrates with o-DPPB acting as a sole directing group with carbonates or acetates as allylic leaving groups.
A series of allylic carbonates were synthesized and studied in palladium catalyzed allylic substitution with soft nucleophiles. Scope and limitations of the reaction were investigated. The reactions showed high regioselectivity in favour of the SN2 product which was obtained in good yield and excellent levels of chirality transfer.
Allylic substitution with non-directing substrates (CH or P(O) instead of P-atom) proved the role of the o-DPPB group as a directing group in these reactions. Non-directing substrates led either to considerably lower selectivity or side reactions.
Additionally, the same substrates were explored in copper-mediated allylic substitution. Interestingly, cis-alkenes were formed following an anti-SN2'-substitution pathway, which again results from a directing effect of the substrate-bound o-DPPB group.
In conclusion, the o-DPPB system can be used as a directing group for palladium catalyzed allylic substitution with soft nucleophiles as well as for copper-mediated allylic substitution with hard nucleophiles to regulate regio- and stereoselectivity of the reaction and to allow for excellent levels of chirality transfer from the substrate to the product.


SWD-Schlagwörter: Palladium , Homogene Katalyse
Freie Schlagwörter (deutsch): dirigierende Gruppe , Tsuji-Trost Reaktion
Freie Schlagwörter (englisch): directing group , Tsuji-Trost reaction
Institut: Institut für Organische Chemie und Biochemie
Fakultät: Fakultät für Chemie, Pharmazie und Geowissenschaften
DDC-Sachgruppe: Chemie
Dokumentart: Dissertation
Erstgutachter: Breit, Bernhard (Prof. Dr.)
Sprache: Englisch
Tag der mündlichen Prüfung: 10.12.2008
Erstellungsjahr: 2008
Publikationsdatum: 12.12.2008
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