Bis(amino)cyclopropenylidenes as Organocatalysts for Acyl Anion and Extended Umpolung Reactions

Abstract

Scheme 2. Preparation of bis(amino)cyclopropenium salts 1 and 3.

Bis(amino)cyclopropenylidene-Catalyzed 1,6-Conjugate Addition of Aromatic Aldehydes to para-Quinone Methides: Expedient Access to α,α′-Diarylated Ketones

“…This observation clearly suggests that the formation of 4a is reversible under the standard reaction conditions. 25 The observation of benzoin and retrobenzoin reactivity with this catalyst is in contrast to observations by Gravel and co-workers; 13,14 however, the reaction conditions were different in their case. The reversible formation of 4a was further confirmed by a crossover experiment, in which the homobenzoin 4a (as an aldehyde equivalent) was treated with 2.3 equiv of 5 under standard conditions.…”

Functionalized cyclopentenes through a tandem NHC-catalyzed dynamic kinetic resolution and ambient temperature decarboxylation: mechanistic insight and synthetic application

“…1 N -Heterocyclic carbenes (NHC) have emerged as powerful class of organic catalysts that can be used to construct important structural motifs, bioactive molecules, and natural products. 2 Our group and others have shown that NHCs react with aldehydes to generate catalytically competent enolate, 3 homoenolate, 4 and acyl anion intermediates, 5 which have been trapped with various electrophiles. In 2012, we reported the first NHC-catalyzed dynamic kinetic resolution (DKR) of α-substituted-β-ketoesters (1) to furnish bicyclic β-lactones (2) and cyclopentenes (3) (Scheme 1 eq.…”

An Overview on the N-Heterocyclic Carbene-Catalyzed Aza-Benzoin Condensation Reaction

“…Efforts to develop non five-membered nitrogen-containing heterocyclic carbenes have been rather limited as a consequence of the success of NHCs. However, bis(amino)-cyclopropenylidenes (BACs), the smallest aromatic rings containing a carbene center, have recently been employed in some intriguing applications [33,34]. Easily prepared in a one-pot reaction, BACs, likewise NHCs, catalytically induce acyl anion reactivity in aldehydes.…”