Entwicklung von Carben-katalysierten asymmetrischen intermolekularen Stetter-Reaktionen und direkt gekreuzter intermolekularer Benzoin-Reaktionen

A new chiral triazolium based carbene precatalyst was synthesized and successfully employed in the asymmetric intermolecular Stetter reaction. The resulting 1,4-diketones were obtained in moderate to excellent yields (49-98%) and good enantioselectivities (56-78% ee). For several Stetter products the enantiomeric excess could be enhanced by a single recrystallization up to 99% ee. Examination of the reaction course revealed that the corresponding 1,4-diketones are generated via two coupled catalytic cycles. A direct intermolecular cross-benzoin reaction catalyzed by an N-heterocyclic carbene has been developed. The cross-coupling of aromatic aldehydes and trifluoromethyl ketones results in alpha-hydroxy-alpha-trifluoromethyl ketones bearing a quaternary stereocenter with excellent chemoselectivity and good to excellent yields (64-99%). This method could be enhanced to a nucleophilic acylation of trifluoromethyl ketimines via the employment of various furan-2-carbaldehydes in the presence of a carbene precatalyst. The corresponding alpha-amino-alpha-trifluoromethyl ketones could be obtained in moderate to very good yields (32-87%) via this method. A novel chiral bifunctional N-heterocyclic carbene precatalyst could be generated in high yields starting from the commercially available and inexpensive chiral source L-pyroglutamic acid. This structure represents the first combination of a N-heterocyclic carbene precatalyst with a broensted acidic thioureafunction. The developed precatalyst was tested in the intermolecular benzoin condensation of benzaldehyde, showing promising initial results.

Grantor dc:publisher

Mainz

Year dc:date

2010

Author dc:creator

• Henseler, Alexander

Contributors dc:contributor

• Enders, Dieter

• info:eu-repo/classification/ddc/540
• Heterocyclische Carbene <-N>
• Organokatalyse
• Stetter-Reaktion
• Benzoin-Kondensation
• Asymmetrische Synthese
• Chemie
• N-heterocyclic carbenes
• organocatalysis
• Stetter reaction
• benzoin reaction
• asymmetric synthesis

Statement dc:rights

• info:eu-repo/semantics/openAccess

Language dc:language

ger

Identifier

https://publications.rwth-aachen.de/search?p=id:%22RWTH-CONV-113917%22

OAI record oai:identifier

https://publications.rwth-aachen.de/oai2d?verb=GetRecord&metadataPrefix=oai_dc&identifier=oai%3Apublications.rwth-aachen.de%3A51646