α,β-Unsaturated acyl ammonium species as reactive intermediates in organocatalysis: an update

Abstract

α,β-Unsaturated acyl ammonium species are versatile intermediates that have been applied in a variety of transformations including Michael additions, domino reactions and cycloadditions.

Rice straw ash extract/glycerol: an efficient sustainable approach for Knoevenagel condensation

“…It is well known that, under harsher thermodynamically controlled conditions, a second enolate generated from 1,3-cyclohexanedione (2b) could follow the conjugated addition with the a,b-unsaturated Knoevenagel product, decreasing the concentration of 2b to attack the benzaldehyde 1a and affecting the yield of the reaction to afford the desired product 4a. 65,66 However, switching the temperature to 50 1C (Scheme 1b), the desired product 4a was obtained with an 88% yield (Table 1, entry 7).…”

Isothiourea-catalyzed formal enantioselective conjugate addition of benzophenone imines to β-fluorinated α,β-unsaturated esters

“…12,13 In previous work, we and others have demonstrated a range of enantioselective Michael-addition processes of in situ generated α,β-unsaturated acyl ammonium species. 14,15 Building on these precedents, we report herein the formal isothiourea-catalyzed enantioselective addition of 2-hydroxybenzophenone imines to β-fluorinated α,β-unsaturated para -nitrophenyl esters via an α,β-unsaturated acyl ammonium intermediate, giving products in up to 98 : 2 er (Scheme 2c).…”

Achiral Cp*Rh(III)/Chiral Lewis Base Cooperative Catalysis for Enantioselective Cyclization via C–H Activation

“…Chiral Lewis base catalysts, such as tertiary amines (pyridines, quinuclidines, and isochalcogenureas (ICUs)) or N-heterocyclic carbenes (NHCs), can activate α,β-unsaturated carbonyl compounds to form a chiral α,β-unsaturated acyl ammonium (or azolium) intermediate. This intermediate can undergo enantioselective bond-forming reactions at the β-position and carbonyl group with various nucleophiles (Scheme e). − Our reaction design based on this well-documented activation mechanism is shown in Scheme f. A metallacycle intermediate is generated via the C–H activation of a benzylamine derivative by a Cp*Rh catalyst.…”