While organocatalyzed domino reactions or "organocascade catalysis" developed into an important tool in synthetic chemistry during the past decade, the utility of N-heterocyclic carbenes (NHCs) as catalysts in domino reactions has only received growing attention in the past three years. Taking into account the unique activation modes of the substrates by NHC catalysts, it is often difficult to distinguish between a single chemical transformation and a sequential one-pot transformation. Therefore, herein we present a critical consideration of domino, cascade, and tandem catalysis in the case of NHC catalysts and highlight recent publications in this area.

Teaming up: The title reaction has been developed to deliver the product α‐alkylidene‐γ‐butyrolactones as single diastereomers with up to 98 % ee (see scheme; Ts=4‐toluenesulfonyl). The enantioselective process is catalyzed by 1, which contains both Lewis base and Brønsted acid moieties.

A new triazolium salt derived N-heterocyclic carbene catalyses an asymmetric cross-benzoin-type reaction of heteroaromatic aldehydes and various trifluoromethyl ketones in good to excellent yields (69-96%) and moderate to good enantioselectivities (ee = 39-85%). Up to 99% ee can be achieved by recrystallisation.

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.

Keywords: Domino reactions / Umpolung / Michael addition / Organocatalysis / CarbenesPolyfuncionalized cyclopentanones with three contiguous stereogenic centers were formed in good to excellent yields and stereoselectivities by utilizing a secondary amine/N-heterocyclic carbene catalytic system in the reaction of β-oxo Results and DiscussionWe were intrigued by the possibilities of utilizing dual catalytic systems and hence envisioned that β-oxo sulfones A, which are known substrates [8,9] for the organocatalytic Michael addition, might undergo a Michael/cross-benzoin [10] cascade reaction with enals B to form, via the Michael adducts C, polyfunctionalized cyclopentanones D bearing three contiguous stereogenic centers (Scheme 1). Since the reaction of β-oxo carbonyl compounds with alde- [a] Institute