New Chiral Thiophene−Salen Chromium Complexes for the Asymmetric Henry Reaction

Abstract

Chiral thiophene-salen chromium complexes were investigated in their monomeric form as soluble catalysts in the enantioselective Henry reaction of several aldehydes. The anodic polymerization of one complex led to an insoluble powder that was successfully used as a heterogeneous catalyst for the transformation of 2-methoxybenzaldehyde with enantiomeric excesses up to 77%. The polymerized catalyst was recovered and also recycled in an original multisubstrate procedure.

Nanostructured Catalysts for the Aldol, Knoevenagel, and Henry Reactions

“…By using anodic electropolymerization, Zulauf et al 87 complex into insoluble solid polymeric material containing active metal-salen catalytic groups (polythiophene containing Cr-salen complexes) (Figure 7.17). The authors then showed that this material in a powder form can serve as a heterogeneous catalyst and catalyze the Henry reaction between 2-methoxybenzaldehyde and nitromethane at 20 • C. The catalytic reaction gave an isolated yield of approximately 100% within 24 h of reaction time (Figure 7.17).…”

Recyclable Stereoselective Catalysts

“…The resulting polymer 82 (Fig. 1.36 ) was then applied to the hetero Diels -Alder reaction [152] between Danishefsky ' s diene and heptanal and the Henry reaction [153] . In both cases, the catalyst immobilization proved to be a bit detrimental for the reaction enantioselectivity.…”

Chemical-promoted oxidative polymerization of modified-cobalt salen complexes, efficient catalysts for the dynamic HKR

“…2 In this context, we have described an electrochemical oxidative procedure leading to the synthesis of linear polymers that possessed the chiral metallic salen moiety in the main chain. Tested as insoluble heterogeneous catalysts, they could promote diverse carbon-carbon or carbon-heteroatom bond formation in hetero Diels-Alder reactions, 4 in nitroaldol transformations, 5 in dialkylzinc addition to aldehydes, or in the ring-opening of epoxides with various nucleophiles. Tested as insoluble heterogeneous catalysts, they could promote diverse carbon-carbon or carbon-heteroatom bond formation in hetero Diels-Alder reactions, 4 in nitroaldol transformations, 5 in dialkylzinc addition to aldehydes, or in the ring-opening of epoxides with various nucleophiles.…”