Asymmetric nitro-Mannich reaction

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. 

The catalytic asymmetric nitro Mannich-type reaction using the complex Yb, K, and binaphthol gives the best result (see Eq. 4.141).206 The reaction conditions are important to get a good ee, where nitromethane is added very slowly over 27 h. 

K. Yamada, S. J. Harwood, H. Groger, M. Shibasaki, The First Catalytic Asymmetric Nitro-Mannich-Type Reaction Promoted by a New Heterobimetallic Complex, Angew. Chem, 1999, 38, 3504-3506. 

Catalytic asymmetric nitro-Mannich-type reactions have also been introduced very recently by the groups of Shibasaki [37] and Jorgensen [38,39]. 

The catalytic asymmetric nitroaldol reaction was extended to a direct catalytic asymmetric nitro-Mannich-type reaction promoted by hetero-bimetallic catalysts (Scheme 2) [53-55] or by EtjNBOX-Cu complexes [56]. These topics are reviewed in Chap. 28.2. 

A direct catalytic asymmetric Mannich reaction using unmodified ketones was reported using cooperative catalysis of a AlLibis((i )-binaphthoxide) complex ((.R)-ALB) and La(0Tf)3-nH20 [27,28]. It was also reported that enantiose-lective and diastereoselective catalytic nitro-Mannich reactions of N-phosphi-noylimines proceeded smoothly using the complex of ALB and ferf-BuOK [29, 30] [(Eq. (5)]. 

For example, an effective procedure for the synthesis of LLB (where LL = lanthanum and lithium) is treatment of LaCls 7H2O with 2.7 mol equiv. BINOL dilithium salt, and NaO-t-Bu (0.3 mol equiv.) in THF at 50 °C for 50 h. Another efficient procedure for the preparation of LLB starts from La(0-/-Pr)3 [54], the exposure of which to 3 mol equiv. BINOL in THF is followed by addition of butyllithium (3 mol equiv.) at 0 C. It is worthy of note that heterobimetallic asymmetric complexes which include LLB are stable in organic solvents such as THF, CH2CI2 and toluene which contain small amounts of water, and are also insensitive to oxygen. These heterobimetallic complexes can, by choice of suitable rare earth and alkali metals, be used to promote a variety of efficient asymmetric reactions, for example nitroaldol, aldol, Michael, nitro-Mannich-type, hydrophosphonylation, hydrophosphination, protonation and Diels-Alder reactions. A catalytic asymmetric nitroaldol reaction, a direct catalytic asymmetric aldol reaction, and a catalytic asymmetric nitro-Mannich-type reaction are discussed in detail below. 

These rare earth-containing heterobimetallic complexes can be utilized for a variety of efficient catalytic asymmetric reactions, as shown in Sch. 13, and quite recently we have succeeded in realizing the first example of a catalytic asymmetric nitro-Mannich-type reaction using the newly developed heterobimetallic complex 71 (Table 17) [72]. 

Scheme 10 A catalytic asymmetric 5yn-selective nitro-Mannich reaction promoted by heterobimetallic Cu/Sm/dinucleating Schiff base complexes...

On the basis of ESl-MS observation as well as positive nmilinear effects of this system, we assumed that p-oxo-p-aiyloxy-trimer complex is the most enantiose-lective active species (Fig. 3). Therefore, Sm50(0-/Pr)i3 with a well-ordered structure would have beneficial effects for the formation of desired trimer species. Postulated catalytic cycle of the reaction based on the initial rate kinetic studies and kinetic isotope effect studies is shown in Fig. 4. In this catalyst system, both Cu and Sm are essential. We assume that the cooperative dual activation of nitroalkanes and imines with Cu and Sm is important to realize the syn-selective catalytic asymmetric nitro-Mannich-type reaction. The Sm-aryloxide moiety in the catalyst would act as a Brpnsted base to generate Sm-nitronate. On the other hand, Cu(ll) would act as a Lewis acid to control the position of iV-Boc-imine. Among possible transition states, the sterically less hindered TS-1 would be more favorable. Thus, the stereoselective C-C bond formation via TS-1 followed by protonation with phenolic proton affords syn product and regenerates the catalyst. 

Scheme 10 Anti-selective catalytic asymmetric nitro-Mannich-type reaction with a Yb/K hetero-bimetallic catalyst...

Very recently. Barber et al. reported a tandem reaction combining bifunctional urea and Au(I) salt for the asymmetric synthesis of valuable tetrahydropyridine derivatives [80]. This reaction consisted of a urea-promoted nitro-Mannich reaction of an alkyne-tethered secondary nitroalkane to N-Boc-protected imines and an Au(I) complex-catalyzed intramolecular hydroamination and isomerization (Scheme 9.75). Notably, since the inherent Lewis basic tertiary amine-tethered urea would deactivate the Au catalyst, the reaction system was acidified by additional DPP before addition of an Au catalyst to ensure the success of the overall process. 

Ph (SbFe)2 Ph Ph TIO OTf Ph 84 Scheme 14 Catalytic asymmetric aza-Henry (nitro-Mannich-type) reactions... 

List B, Lerner RA, Barbas CF 3rd (2000) Proline-catalyzed direct asymmetric aldol reactions. J Am Chem Soc 122 2395-2396 List B, Pojarliev P, Martin HJ (2001) Efficient proline-catalyzed Michael additions of unmodified ketones to nitro olefins. Org Lett 3 2423-2425 List B, Pojarliev P, Biller WT, Martin HJ (2002) The proline-catalyzed direct asymmetric three-component Mannich reaction scope, optimization, and application to the highly enantioselective synthesis of 1,2-amino alcohols. J Am Chem Soc 124 827-833... 

An all organic catalyst system 38 has been reported by the Maruoka group for directing asymmetric additions of oxindole enolates derived from 36 to nitro-aUcenes 37 under phase-transfer conditions [26] (Scheme 10). The methodology was extended to the synthesis of a tetrahydropyrroloindole scaffold bearing two chiral centers. Asymmetric Michael and Mannich reactions of 3-aryloxindoles directed by chiral phosphonium salt phase-transfer catalysts have been described by the same group [27]. 

Cobb, A.J.A., Shaw, D.M., Longbottom, D.A., Gold, J.B. and Ley, S.V. (2005) Organocatalysis with proline derivatives improved catalysts for the asymmetric Mannich, nitro-Michael and aldol reactions. Org. Biomol. Chem., 3, 84. 

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