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%0 Thesis
%A Li, Sun
%T N-heterocyclic carbene catalyzed asymmetric cycloaddition/annulation reactions of enals and α-chloroaldehydes
%I RWTH Aachen University
%V Dissertation
%C Aachen
%M RWTH-2018-223520
%P 1 Online-Ressource (III, 118 Seiten) : Illustrationen
%D 2018
%Z Veröffentlicht auf dem Publikationsserver der RWTH Aachen University
%Z Dissertation, RWTH Aachen University, 2018
%X Since the first enantioselective carbon-carbon bond formations catalyzed by N-heterocyclic carbenes (NHCs) in the case of the benzoin condensation reported by Sheehan and Hunnemann in 1966 and the first enantioselective Stetter reaction developed by our group in the late eighties, the field of asymmetric NHC-organocatalysis has grown rapidly being now an important chapter of Lewis-base organocatalysis. During the reactions, the activation of the formed Breslow intermediate from α,β-unsaturated aldehyde and NHC was reported via three modes: homoenolate equivalent, azolium enolate equivalent and unsaturated acylazolium intermediate. In this thesis, three N-heterocyclic carbene catalyzed organocatalytic methodologies via homoenolate equivalents and azolium enolate equivalents have been presented.1. An new synthetic strategy for the asymmetric synthesis of five membered spiropyrazolones via N-heterocyclic carbene-catalyzed [3+2] annulations employing enals and unsaturated pyrazolones as substrates has been developed. The new protocol allows the flexible variation of all four substituents of the pharmaceutically important spiropyrazolones with moderrate to very good yields, in most cases excellent diastereoselectivities and good to excellent enantioselectivities.2. An N-heterocyclic carbene (NHC) catalyzed asymmetric [4+2] annulation of (E)-2-benzoyl-3-phenylacrylonitriles with α-chloroaldehydes has been developed. The protocol leads to 5-cyano-substituted dihydropyranones in good to exellent yields with excellent diastereo- and enantioselectivities (up to 93
%F PUB:(DE-HGF)11
%9 Dissertation / PhD Thesis
%R 10.18154/RWTH-2018-223520
%U https://publications.rwth-aachen.de/record/722321