Michael ionic liquid

NEW Green chemistry promotes environmentally sound chemistry. Passages in the text created in consultation with Michael Cann and new end-of-chapter exercises are accompanied by a (IT). Topics include ionic liquids (Chapter 5), supercritical C02 (Chapter 8), yttrium in paint (Chapter 12), chelates as a substitute for chlorine bleach (Chapter 16), and transesterification (Chapter 19). 

Thiolates, generated in situ by the action of ammonium tetra-thiomolybdate on alkyl halides, thiocyanates, and disulfides, undergo conjugate addition to a, (1-unsaturatcd esters, nitriles, and ketones in water under neutral conditions (Eq. 10. II).29 Conjugate addition of thiols was also carried out in a hydrophobic ionic liquid [bmim]PF6/water-solvent system (2 1) in the absence of any acid catalyst to afford the corresponding Michael adducts in high to quantitative yields with excellent 1,4-selectivity under mild and neutral conditions (Eq. 10.12). The use of ionic liquids helps to avoid the use of either acid or base catalysts... 

A basic ionic liquid, l-methyl-3-butylimidazolium hydroxide ([bmIm]OH) and l-butyl-3-methyl-methylimidazolium tetrafluoroborate ([bmim]BF4), has been introduced as a catalyst and reaction medium for the Markovnikov addition of imidazoles 116 to vinyl esters 115 under mild conditions to give imidazoesters 117 <06JOC3991 06TL1555>. A series of (nitroimidazolyl)succinic esters and diacids were prepared from the Michael-type addition of the nitroimidazole to the a,P-unsaturated ester <06S3859>. 

In 2002, Leadbeater and Torenius reported the base-catalyzed Michael addition of methyl acrylate to imidazole using ionic liquid-doped toluene as a reaction medium (Scheme 6.133 a) [190], A 75% product yield was obtained after 5 min of microwave irradiation at 200 °C employing equimolar amounts of Michael acceptor/donor and triethylamine base. As for the Diels-Alder reaction studied by the same group (see Scheme 6.91), l-(2-propyl)-3-methylimidazolium hexafluorophosphate (pmimPF6) was the ionic liquid utilized (see Table 4.3). Related microwave-promoted Michael additions studied by Jennings and coworkers involving indoles as heterocyclic amines are shown in Schemes 6.133 b [230] and 6.133 c [268], Here, either lithium bis(trimethylsilyl)amide (LiHMDS) or potassium tert-butoxide (KOtBu) was em-... 

In a related study, the group of Bazureau applied their polyethylene glycol-grafted ionic liquid phases (ILPs) to the preparation of 2-thioxotetrahydropyrimidinones [105], After the initial formation of acrylate-bound ILPs utilizing acryloyl chloride in refluxing dichloromethane, several primary amines were attached in a Michael addi-... 

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. 

In 2006, Xu and Xia et al. revealed the catalytic activity of commercially available D-camphorsulfonic acid (CS A) in the enantioselective Michael-type Friedel-Crafts addition of indoles 29 to chalcones 180 attaining moderate enantiomeric excess (75-96%, 0-37% ee) for the corresponding p-indolyl ketones 181 (Scheme 76) [95], This constitutes the first report on the stereoselectivity of o-CSA-mediated transformations. In the course of their studies, the authors discovered a synergistic effect between the ionic liquid BmimBr (l-butyl-3-methyl-l/f-imidazohum bromide) and d-CSA. For a range of indoles 29 and chalcone derivatives 180, the preformed BmimBr-CSA complex (24 mol%) gave improved asymmetric induction compared to d-CSA (5 mol%) alone, along with similar or slightly better yields of P-indolyl ketones 181 (74-96%, 13-58% ee). The authors attribute the beneficial effect of the BmimBr-D-CSA combination to the catalytic Lewis acid activation of Brpnsted acids (LBA). Notably, the direct addition of BmimBr to the reaction mixture of indole, chalcone, d-CSA in acetonitrile did not influence the catalytic efficiency. 

A systematic investigation of the effect of Cl impurity was reported for a metal-catalyzed Michael addition of acetylacetone to methyl vinyl ketone in [BMIM]BF4 (77(5). The time required for the completion of the reaction was used as a measure of the effect of Cl . With a Ni(acac)2.2H20 catalyst, the Michael addition was completed in 2, 5, and 9h when the ionic liquid contained 0, 0.62, and 1.62% CP, respectively. 

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. 

On the basis of encouraging work in the development of L-proline-DMSO and L-proline-ionic liquid systems for practical asymmetric aldol reactions, an aldolase antibody 38C2 was evaluated in the ionic liquid [BMIM]PF6 as a reusable aldolase-ionic liquid catalytic system for the aldol synthesis of oc-chloro- 3-hydroxy compounds (288). The biocatalytic process was followed by chemical catalysis using Et3N in the ionic liquid [BMIM]TfO at room temperature, which transformed the oc-chloro-(3-hydroxy compounds to the optically active (70% ee) oc, (3-epoxy carbonyl compounds. The aldolase antibody 38C2-ionic liquid system was also shown to be reusable for Michael additions and the reaction of fluoromethylated imines. 

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... 

Figure 1.4 Dr. Michael Zaworotko from Saint Mary s University in Halifax, Nova Scotia. He was a visiting professor at the U.S. Air Force Academy in 1991, where he first prepared many of the water-stable ionic liquids popular today.

Ni, B., Zhang, Q. and Headley, A.D. (2007) Functionalized chiral ionic liquid as recyclable organocatalyst for asymmetric Michael addition to nitrostyrenes. Green Chem., 9 (7), 737-739. 

Michael Reactions in Ionic Liquids and Heterogeneous Catalysis... 

The basic ionic liquid [BmimJOH has been introduced as a catalyst for the aza-Michael addition of aromatic amines and A-heterocycles to cyclic or acyclic ketones under solvent-free conditions.138... 

The catalytic application of L-proline in the asymmetric Michael addition of unmodified aldehydes or ketones with nitroalkenes in ionic liquids has been studied. The ... 

A task-specific ionic liquid, [bmIm]OH, has been introduced as a catalyst and as a reaction medium for Michael addition. The addition of open-chain 1,3-dicarbonyls to ,/Tunsaturatcd ketones gave the mono-addition products, whereas a,fi-unsaturated esters and nitriles afforded mainly bis-addition products.162... 

Ying A-G, Liu L, Wu G-F et al (2009) Aza-Michael addition of aliphatic or aromatic amines to [alpha], [beta]-unsaturated compounds catalyzed by a DBU-derived ionic liquid under solvent-free conditions. Tetrahedron Lett 50(14) 1653-1657... 

Finally, it should be noted that Lewis acids and bases can also be used in other non-conventional media, as described in Chapter 7, e.g. fluorous solvents, supercritical carbon dioxide and ionic liquids by designing the catalyst, e.g. for solubility in a fluorous solvent or an ionic liquid, to facilitate its recovery and reuse. For example, the use of the ionic liquid butylmethylimidazolium hydroxide, [bmim][OH], as both a catalyst and reaction medium for Michael additions (Fig. 2.45) has been recently reported [151]. 

Sulfonic acid functionalised ionic liquids may also be prepared via a zwitterionic intermediate from a Michael-type addition, as shown in Scheme 2.5.[84 85] In the first step 1-methylimidazole reacts with the sulfonic acid precusor 1,3-propane sultone to form a zwitterionic intermediate. Protonation with Bronsted acids affords ionic liquids with high purity that have proven to be highly efficient reaction media in, for example, esterification reactions.[86] Task-specific ionic liquids may also be prepared using semi-combinatorial methods.1871... 

Michael additions of various aldehydes and ketones to 2-(/3-nittovinyl)thiophene have been carried out in the ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate. Yields were in general better with aldehydes than with ketones. The best catalyst was L-proline <2004EJ01577>. 

Freemantle, Michael. Green Applications of Ionic Liquids. Chem. Eng. News, March 30, 1998, pp. 32-33. 

In terms of chiral ionic liquids, the discussion will focus on Michael addition reactions (Figure 6.8). This reaction has been performed using lactate as... 

Figure 6.8 Asymmetric Michael addition reactions using chiral ionic liquids (a) derived from lactate, (b) derived from proline.

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