Asymmetric organocatalysts supported on vinyl addition polynorbornenes for work in aqueous media

Abstract

In an effort to identify novel polymer architectures suitable for the covalent supporting of catalysts, L-proline derivatives have been immobilized onto rationally designed vinyl addition polynorbornene (VA-PNB) resins through copper-catalyzed azide-alkyne cycloaddition (CuAAC) reactions. The fully saturated VA-PNB resins have been found to be optimal catalyst supports, the resulting proline-functionalized resins behaving as very active, easily recoverable and highly reusable organocatalysts for the asymmetric direct aldol reaction of benzaldehydes with ketones in aqueous media. The results show that the combination of modular, VA-PNB resins with proline derivatives and triazole linkers represents a promising strategy for the immobilization of organocatalytic species.

Vinylic Addition Polynorbornene as Support for N‐Heterocyclic Carbene Palladium Complexes: Use as Reservoir of Active Homogeneous Catalytic Species in C−C Cross‐Coupling Reactions

“…Vinylic addition polynorbornenes (VA‐PNBs, Figure ) have an aliphatic, robust backbone that has been successfully used as a scaffold to support N‐heterocyclic carbenes (NHCs), or proline‐based organocatalysts, as well as stannyl groups for their application as recyclable reagents in the Stille reaction . The saturated polymer backbone in VA‐PNBs has a clear advantage compared with ring‐opening metathesis polymerization (ROMP)‐PNBs (Figure ), especially in metal‐catalyzed reactions.…”

Vinylic Addition Polynorbornene in Catalysis

“…The efficiency of these functionalization reactions is generally high, and can be evaluated by elemental analysis of the residual bromo in the polymer and also by IR and NMR spectroscopy. The synthesis of the VA‐PNBs bearing azido groups is an interesting transformation since this opens the possibility of using azido‐alkyne cycloaddition reactions, a very useful click reaction, to anchor a variety of groups ,. VA‐PNB‐(CH 2 ) n Br materials are in a way analogues to the polystyrene resins with halobenzyl groups because of their versatility as starting materials.…”

Pursuing Chemical Efficiency by Using Supported Organocatalysts for Asymmetric Reactions under Aqueous Conditions

“…A small decrease in activity was encountered for catalyst 5 due to some leaching of the proline residue, whereas catalyst 7 showed comparable results for each reaction cycle and no leaching at all. The use of the robust polynorbonene resin as support, with a complete saturated structure, transparent to UV light, made these systems suitable candidates to be applied in photoorganocatalyzed reactions [60]. Using also a click reaction trans-4-hydroxyproline was grafted to commercially available mercapto-methylpolystyrene resin by means of a thiol-ene reaction, giving catalyst 8 ( Figure 2).…”