Durch N‐heterocyclische Carbene katalysierte Dominoreaktionen

Abstract

Während sich die organokatalytischen Dominoreaktionen (auch Organokaskadenkatalysen genannt) im letzten Jahrzehnt zu einem wichtigen Hilfsmittel in der Synthesechemie entwickelt haben, fand die Anwendung von N‐heterocyclischen Carbenen (NHCs) als Katalysatoren in Dominoreaktionen erst in den letzten drei Jahren zunehmend Beachtung. Unter Berücksichtigung der besonderen Aktivierungsmodi der Substrate durch die NHC‐Katalysatoren ist eine Unterscheidung zwischen einer einzelnen chemischen Transformation und einer sequenziellen Eintopfreaktion schwierig. Das Ziel dieses Kurzaufsatzes besteht darin, die Domino‐, Kaskaden‐ und Tandemkatalyse in Gegenwart von NHC‐Katalysatoren kritisch zu betrachten und jüngste Publikationen auf diesem Gebiet vorzustellen.

Recent Progress in Organocatalytic Asymmetric Domino Transformations

“…action led to the formation of enantioenriched 3,3'-thiopyrrolidonyl spirooxindoles 411 in excellent yields, dr and ee values.T he catalytic model mentioned earlier [133,136] could possibly also be operative in this case,a st he protection of the 9-OHg roup of the catalyst with an OBn group resulted in ac omplete loss of the enantioselectivity in this reaction. [162] Xu, Wang, and co-workers developed an asymmetric domino allylic alkylation/cyclization reactionb etween 3-hydroxyoxindoles 412 and Morita-BaylisHillmanc arbonates 413 to affords pirooxindoles 414 bearing the a-methylene-g-butyrolactone motif (Scheme 106).…”

Characterization of the Key Intermediates of Carbene‐Catalyzed Umpolung by NMR Spectroscopy and X‐Ray Diffraction: Breslow Intermediates, Homoenolates, and Azolium Enolates

“…The diene moiety is virtually planar, with a torsion angle C2-C6-C21-C22 of 177.4(3)8. The lengths of the two C=C bonds are 1.362(4) (C2=C6) and 1.356(3) (C21=C22), whereas the length of the connecting C-C single bond (C6-C21) amounts to 1.424 (3) . As in the case of the 2,2-diamino enols 3 a, 3 c, and 3 e, the crystal packing of the diamino dienol 3 g did not indicate the involvement of the hydroxy group in hydrogen bonding (see the Supporting Information).…”

“…[3][4][5] In Seebachs terminology, the aldehyde undergoes a 1 -d 1 umpolung. [6] Postulated in 1958, [1,2] the first successful generation of diamino enols from aldehydes and carbenes, and their characterization by in situ NMR spectroscopy was reported by us in 2012.…”

N‐Heterocyclic Carbene Catalyzed [4+3] Annulation of Enals and o‐Quinone Methides: Highly Enantioselective Synthesis of Benzo‐ε‐Lactones

“…[3] In the last decade, the N-heterocyclic carbene (NHC) catalyzed annulation reactions emerged as powerful methods for various heterocycles. [7] In 2004, Bode et al and Glorius et al independently reported the pioneering NHC-catalyzed [3+2] annulation of enals with aldehydes to give g-butyrolactones (Scheme 1 a). [8] Then, g-lactams were synthesized by reaction with imines.…”