Creation through Immobilization: A New Family of High Performance Heterogeneous Bifunctional Iminophosphorane (BIMP) Superbase Organocatalysts

Abstract

An immobilized chiral bifunctional iminophosphorane superbase organocatalyst has been developed and applied in a range of challenging enantioselective reactions. A unique feature of this novel catalytic system is that the final step creation of the iminophosphorane occurs at the point of immobilization. The utility of the immobilized catalyst system was demonstrated in the nitro-Mannich reaction of ketimines as well as the conjugate addition of high pKa 1,3-dicarbonyl pro-nucleophiles to nitrostyrene. Catalyst recycling was also demonstrated.

Chiral Iminophosphoranes—An Emerging Class of Superbase Organocatalysts

“…In most cases, application of the catalyst 50 a ensured high yields and enantiomeric excesses of the products (Scheme , conditions A). Interestingly, comparable results in terms of yields and enantioselectivities were obtained for the immobilized catalyst 52 (Scheme , conditions B) 23. Importantly, catalyst 52 could be easily recovered after the reaction by a simple filtration and reused up to 11 times without significant influence either on its catalytic activity or on the enantiomeric enrichment of the products obtained as demonstrated for the nitro‐Mannich reaction.…”

“…Very recently, Dixon and co‐workers developed an analogue of the catalysts 50 immobilized on a solid support (Scheme ) 23. Immobilization of the catalyst chiral scaffold was performed employing polystyrene‐supported (PS) triphenyl phosphine 51 as a substrate in the Staudinger‐type reaction with the azide 48 a .…”

“…The Michael addition of active methylene compounds 56 or 58 to β‐nitrostyrene 55 was also studied in the presence of polystyrene‐supported bifunctional iminophosphorane catalyst 52 (Scheme ) 23. It was found that 52 promoted the reaction efficiently with both α‐substituted dimethyl malonates 56 and β‐ketoamides 58 .…”

Organocatalysts for enantioselective synthesis of fine chemicals: definitions, trends and developments

“…This resulted in highly active, selective, recoverable solid catalysts, which were employed in the Michael addition reaction depicted in Figure 19. Some other successful examples of enantioselective transformations by immobilised organocatalysts are reported in the very recent literature [92][93][94][95].…”

Chelating P2‐Bis‐phosphazenes with a (R,R)‐1,2‐Diaminocyclohexane Skeleton: Two New Chiral Superbases

“…Goldys et al. presented the immobilization of a chiral phosphazene superbase . This system is capable of catalyzing the nitro‐Mannich reaction of ketimines and conjugate addition reactions between acidic 1,3‐dicarbonyl pro‐nucleophiles and nitrostyrene.…”