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@PHDTHESIS{Li:722321,
      author       = {Li, Sun},
      othercontributors = {Enders, Dieter and Albrecht, Markus},
      title        = {{N}-heterocyclic carbene catalyzed asymmetric
                      cycloaddition/annulation reactions of enals and
                      α-chloroaldehydes},
      school       = {RWTH Aachen University},
      type         = {Dissertation},
      address      = {Aachen},
      reportid     = {RWTH-2018-223520},
      pages        = {1 Online-Ressource (III, 118 Seiten) : Illustrationen},
      year         = {2018},
      note         = {Veröffentlicht auf dem Publikationsserver der RWTH Aachen
                      University; Dissertation, RWTH Aachen University, 2018},
      abstract     = {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 $93\%$ yield, >20:1 d.r. and $99\%$ ee).3. A highly
                      diastereo- and enantiostereoselective synthesis of bicyclic
                      dihydropyrano thiazoles combining a thiazole and δ-lactone
                      skeleton via NHC-catalyzed [4+2] annulations of 5-alkenyl
                      thiazolones and α-chloroaldehydes has been developed. The
                      heterocyclic products are formed via azolium enolate
                      intermediates in good yields with high diastereo- and
                      enantistereoselecties.},
      cin          = {152110 / 150000},
      ddc          = {540},
      cid          = {$I:(DE-82)152110_20140620$ / $I:(DE-82)150000_20140620$},
      typ          = {PUB:(DE-HGF)11},
      doi          = {10.18154/RWTH-2018-223520},
      url          = {https://publications.rwth-aachen.de/record/722321},
}