Heterogeneous Mannich reaction

The use of water in Mannich reactions is counterintuitive since it is supposed to shift to the left the imine formation reaction. However, as in the case of aldol reactions catalysed by species 3-12 (Table 1.1), the success is due to the biphasic heterogeneous conditions adopted - all three components of the Mannich reaction and the catalyst forming an organic phase where the process takes place, the water/organic interphase providing a local environment rich in free OH bonds that can co-activate the substrate. ... 

LLC networks containing catalytic headgroups have also been shown to be useful for heterogeneous Lewis acid catalysis. The Sc(III)-exchanged cross-linked Hu phase of a taper-shaped sulfonate-functionalized LLC monomer has been shown to be able to catalyze the Mukaiyama aldol and Mannich reactions [115] with enhanced diastereoselectivity. This Sc(III)-functionalized Hu network affords condensation products with syn-to-anti diastereoselectivity ratios of 2-to-l, whereas Sc(III) catalysts in solution or supported on amorphous polymers show no reaction diastereoselectivity at all. 

Lee, A., Kim, W., Lee, J., Hyeon, T., Kim, B.M. 2004. Heterogeneous asymmetric nitro-Mannich reaction using a bis(oxazoline) ligand grafted on mesoporous silica. Tetrahedron Asymmetry 15( 17) 2595-2598. 

Gold derivatives have also been found to facilitate the Mannich reaction.Thus, the heterogeneous catalyst, gold supported on nanocrystalline Ce02 or Zr02, was found to accelerate the reaction of aldehyde 26, amine 54, and acetylide 55 to produce 56, with a turn-over number (TON) 50-fold greater than the homogeneous variation. 

Keywords Substituted amines, amines, a,p-unsaturated alkenes, ZrOCla-SHaO/montmorillon-ite KIO, heterogeneous catalysis, solvent-free, room temperature, Mannich reaction, Michael addition... 

Scheme 10.16 Heterogeneous photocatalysis for CDC nitro-Mannich reactions.

Another approach undertaken by Lin and co-workers towards heterogeneous catalysis involved doping metal-organic frameworks (MOFs) with the metal complex chromophores (Figure 10.3). The authors incorporated Ru and Ir complexes U.2L and H2L , respectively, into porous Zr604(0H)4(bpdc)s (bpdc =para-biphenyldicarbo)ylic acid) frameworks to produce MOF-1 and MOF-2, respectively, which were used in nitro-Mannich reactions of THIQ derivatives (Scheme 10.16). Conversions were generally lower for MOF-1 and MOF-2 than for cross-linked polymers or their monomeric counterparts however, these catalysts could be readily filtered off and re-used for subsequent reactions. For example, N-phenyl THIQ was subjected three times to the photocatalyzed nitro-Mannich reaction in the presence of MOF-2, which provided consistent conversions (57-59%) for each run. 

Finally, it is worth mentioning a heterogeneous series of papers covering syntheses unrelated to the schemes illustrated in the present section. They deal mainly with condensation reactions, for example, the formation of cyclic acetals that were described in Sec. A.l." Moreover, cyclic Mannich bases may be formed by mutual condensation of functional groups present in the aminomethylation product. - - In other cases the participation of additional molecules of formaldehyde is necessary in order to produce a sufficiently stable ring derivative. ... 

Dong et al. reported the preparation of a novel Brbnsted acid-surfactant-combined halogen-free ionic liquid [DDPA][HSO ] that bears a propane sulfonic acid group in an acyclic dimethyldodecylammonium cation (Fig. 12.69) [42] and its use in the heterogeneous catalysis procedure of one-pot three-component Mannich-type reaction in aqueous media. 

K. Arya, U. C. Rajesh, D. S. Rawat, Green Chem. 2012, 14, 3344—3351. Proline confined FAU zeolite heterogeneous hybrid catalyst for the synthesis of spiroheterocycles via a Mannich type reaction. 

Quite recently, cross-linked dendrimer was also found to be a good support for Sc(III) catalyst [101]. The resultant material could be used in water as a catalyst for three-component Mannich-type reactions and Mukaiyama aldol reactions. A simple immobilization method of Sc species by using montmorillonite as a support has also been reported recently [102]. This method provides a highly active heterogeneous catalyst for Michael reactions under aqueous or solvent-free conditions. 

The heterobimetallic catalytic system using the amide-based ligand as a platform was extended to the diastereo- and enantioselective nitro-Mannich-type reaction. In an initial attempt using the heterogeneous heterobimetallic Nd/Na for the reaction of benzaldehyde-derived N-Boc imine and nitroethane exhibited poor stereoselectivity, likely because the coordination mode of N-Boc imine is different... 

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