Ionic Michael reaction

Scheme 72 Ionic liquid catalyzed Michael reaction...

The imidazolium-based ionic liquid [bmim][BF ] has been used as a catalyst in the aza-Michael reaction of various aliphatic amines to unsaturated compounds with different electron withdrawing groups in good yields as shown in Scheme 76. Water was used as the solvent in order to obtain up to 98% yield in 7 h. In the presented example, 95% yield in 7 h was achieved [198], The ionic liquid could be recovered and reused five times without loss of activity. 

A chiral phase transfer catalyst was dissolved in ionic liquid media for the enantioselective Michael reaction of dimethyl malonate with l,3-diphenylprop-2-en-l-one with K2CO3 203). The phase-transfer catalyst was a chiral quininium bromide (Scheme 20). The reaction proceeded rapidly with good yield and good enantioselectivity at room temperature in all three ionic liquids investigated, [BMIM]PF6, [BMIM]BF4 and [BPy]BF4. In the asymmetric Michael addition, the enantioselectivity or the reaction in [BPy]Bp4 was the same as in conventional organic solvents. 

The Michael reaction is the nucleophilic addition of a carbanion to ot,p-unsaturated carbonyl compounds. It is a useful way to make C-C and C-hetero atom bonds. Karodia s group studied the use of the ionic liquid ethyltri- -butylphosphonium tosylate ( -Bu3PEtOTs) as a solvent for... 

Michael Reactions in Ionic Liquids and Heterogeneous Catalysis... 

One synthesis approach towards y-hydroxylated ionic liquids is a Michael-type addition of a protonated ammonium salt to a a, /l-an sal uni led carbonyl compound such as methylvinyl ketone yielding an oxobutyl functionalized cation. Intrinsically unstable due to retro-Michael reaction, this OS could however be transformed by a heterogeneous catalyzed hydrogenation reaction yielding a hydroxyl functionalized TSIL [24] (Fig. 7). 

Recently, Wasserscheid and co-workers [103] introduced a complementary method for functionalized ionic liquid synthesis (11). In a one-pot, two step synthesis, the protonation of an imidazolium or pyridinium cation followed by a Michael-type addition to methyl vinyl ketone was reported. The only drawback is the limited thermal stability of the cations, which at moderately elevated temperatures undergo a retro-Michael reaction ... 

Table 1.3 Ionic-tagged pyrrolidines for the asymmetric Michael reaction under neat conditions or in water...

A similar dramatic influence of ionic liquid was also reported by Ranu s group in the Michael reaction of active methylene compounds with methyl vinyl ketone and methyl acrylate in the presence of an ionic liquid, 1-butyl-3-methylimidazolium hydroxide ([bmImjOH). Interestingly, open-chain 1,3-dicarbonyl compounds reacted with methyl vinyl ketone and chalcone to give the usual monoaddition products, whereas the same reactions with methyl acrylate or acrylonitrile provided exclusively bis-addition products (Scheme 5.55). 

Some more significant applications. Aldol reaction in ionic liquids is catalyzed by 0-silylserines. Michael reaction between malonitrile and chalcones proceeds without the usual catalysts using ionic liquids as reaction media, presumably the acidity of the carbon acid is enhanced/... 

The Michael reaction proceeds very efficiently in many ionic liquids. Traditionally, metal catalysts are used to promote the reaction, however, these catalysts are not necessary in ionic liquids. Xia et al. have found that amines reacts with ethyl or methyl acrylate in aqueous solutions of ionic liquids such as [BMIM][BF4] [202] to give the Michael product in up to 96% yield (Scheme 5.2-81). Similar reactions are also described by Yadav in [BMIMjlPFe] [203] where no catalyst is required. Unfortunately neither of these papers give an explanation of why the ionic liquids seem to catalyze the reaction. 

Scheme 5.2-84 The L-proline catalyzed Michael reaction in ionic liquids [208].

Other transformations similar to the Mannich reaction, such as a-amination and a-ojg amination share a similar ionic interaction resulting from hydrogen bonding between the amine-substituted electrophile and the stereodireeting earbo g late from proline, leading to excellent enantiofaeial discrimination (Figure 5.5). An exception is the Michael reaction with... 

Between 2011 and 2012 Schitzer et al. introduced the sulfate anion of the ionic compounds 31 (Figure 11.5) as a catalyst for the asymmetric aldol" " and Michael reactions in the ionic liquid [bmim][NTf2] (buthyl-methyl-imidazolium bis-trifluorosulfonylimide), with good yields but only moderate... 

Figure 11.5 Ionic organocatalysts 31 for the asymmetric aldol and Michael reactions in ionic liquids.

Methods for the synthesis of central hydroisoquinolines or pyrrolo-hydroisoquinoHnes of manzamine A can be classified into 11 types of reactions (1) intermolecular Diels-Alder reaction, (2) intramolecular Diels-Alder reaction, (3) photochemical reaction, (4) radical reaction, (5) ionic cyclization, (6) intramolecular Michael reaction, (7) intramolecular Maimich reaction, (8) intramolecular [3 + 2] cycloaddition, (9) intermolecular [3 + 2] cycloaddition, (10) Pauson-Khand reaction, and (11) eneyne metathesis. 

Verma AK, Attri P, Chopra V, Tiwari RK, Chandra R (2008) Triethylammonium acetate (TEAA) a recyclable inexpensive ionic liquid promotes the chemoselective aza- and thia-michael reactions. Monatsh Chem 139 1041-1047... 

Xu LW, Li JW, Zhou SL, Xia CG (2004) A green, ionic liquid and quaternary ammonium salt-catalyzed aza-Michael reaction of a,p-ethylenic compounds with amines in water. New J Chem 28 183-184... 

Catalyst 5-Hydroxypentylammonium acetate (5-HPAA reusable task-specific ionic liquid) Keywords Alkyl/aryl/heteroaryl aldehydes, nitromethane, trialkylphosphites, 5-HPAA, solvent-free, room temperature, one-pot tandem Henry-Michael reaction, multicomponent reaction, terminal vinylphosphonates... 

Previous works have shown that metallic iodide activated bismuth(lll) chloride efficiently catalyzes the Mukaiyama aldol and Michael reactions. Moreover, it has been shown that ultrasound activates significantly the catalytic power of these metallic halide systems [32a]. Interestingly, the use of these catalytic systems proved to be particularly remarkable in the case of the synthesis of functional furan derivatives [24c, 32b]. The use of Bi(OTf)3 xH20 has also been reported for these reactions [32c-e]. The Mukaiyama aldol reaction in an ionic liquid such as [Bmim][BF4] proceeds smoothly with silyl enolates and a catalytic amount of Bi(0Tf)3 %H20 [32d,e]. Various silyl enolates and aldehydes were tested. Moderate to very good yields of P-hydroxy ketones were obtained. 

Since the Petasis boronic-Michael reaction generally requires prolonged stirring at room temperature for 24 h or more, some studies have been devoted to acceleration of this process. Ionic liquids have been shown to be convenient solvents, shortening the reaction times down to 3-4 h at room temperature [19].The recovered ionic liquid was re-used up to five times without loss of activity. In some cases, microwave activation has been shown to achieve acceptable conversion within short reaction times [20]. 

The direct application of unmodified aldehydes in catalytic Michael additions can be severely hindered due to the presence of undesirable intermolecular self-aldol reactions (Hagiwara, Komatsubara et al. 2001 Hagiwara, Okabe et al. 2001). Barbas and co-workers achieved the first direct catalytic asymmetric Michael reaction between unmodified aldehydes and nitroolefins. The usage of an (S)-2-(morphohnomethyl) pyrrolidine catalyst in 20 % furnished the Michael addition products in 72 % enantioselectivity, 12 1 diastereoselectivity and 78 % yield (Betancort and Barbas 2001 Betancort, Sakthivel et aL 2004 Mosse, Andrey et al. 2006). The utilization of the ionic hquid tagged catalysts 25 and 26 in the Michael reactions of frans- -nitrostyrenes to aldehydes resulted in high yields but... 

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