Acceleration of the Baylis–Hillman Reaction in the Presence of Ionic Liquids

Abstract

The Baylis ± Hillman reaction is accelerated in the presence of ionic liquids. Of various 1-butyl-3-methylimidazolium (bmim)-based ionic liquids tested, [bmim] [PF 6 ] has been found to result in the highest rate increase. In the company of Lewis acid and H-bond-donor additives, the reaction rates further improve, albeit only modestly. A preparatively useful Baylis ± Hillman procedure prescribes the use of [bmim] [PF 6 ] with La(OTf) 3 and 2,2'2''-nitrilotris [ethanol], in which the net effect of the ionic liquid is to bring about a more than twofold rate increase over the otherwise same reaction in MeCN.Introduction. ± The Baylis ± Hillman reaction, a coupling of activated alkenes with aldehydes promoted by tertiary amines, is emerging as a useful CÀC bond-forming reaction (for reviews, see [1]). The adduct possesses rich functionalities, including an allylic alcohol and an activated alkene, that can be utilized in further transformations. A major drawback of the Baylis ± Hillman reaction is the low reaction rate; reaction times as long as several weeks are sometimes required. To overcome this problem, a number of additives have been reported to speed up the reaction, including Room-temperature ionic liquids are gaining much attention in organic chemistry as reaction solvents and catalysts (for reviews, see [9]). The advantages of using ionic liquids are diverse. Due to their low volatility, they are regarded as environmentally friendly −green solvents×. Product isolation or catalyst recycling can be very easy in ionic liquids [10]. In some cases, great rate accelerations or selectivity improvements are observed [11]. An example of the reactions wherein this last advantage of using ionic liquids has been realized is a Sc(OTf) 3 -catalyzed Diels ± Alder reaction [11c]. Noting that Sc(OTf) 3 was also one of the effective additives for accelerating the Baylis ± Hillman reaction [2b], we speculated that the Lewis acid-catalyzed Baylis ± Hillman reaction might be further accelerated in the presence of ionic liquids. This led us to investigate the effects of ionic liquids on the rate of Baylis ± Hillman reaction. In a recent publication, a rate-accelerating effect of ionic liquids in Baylis ± Hillman reactions has been reported [12]. Disclosed herein are our own findings.

Lanthanides and Actinides in Ionic Liquids

“…198 The Baylis-Hillman reaction, that is, the coupling of activated alkenes with aldehydes promoted by tertiary amines, proceeds faster in ionic liquids than in acetonitrile. 199 The authors tested the reaction of methyl acrylate, benzaldehyde, and 1,4-diazabicyclo[2,2,2]octane (DABCO) (1:1:1 molar ratio) in different ionic liquids of the type [C 4 mim]X . Lanthanum-(III) triflate was found to be a more efficient catalyst than scandium(III) triflate for this reaction.…”

Experimental and DFT studies of ethyl N′-3-(1H-imidazol-1-yl) propylcarbamoyl benzohydrazonate monohydrate

“…Recently, the interest in this heterocyclic system has widened as it is a precursor to a class of compounds called room temperature ionic liquids [12,13]. Ionic liquids, of which imidazolium salts are most widely used, have gained initial notice of synthetic chemists as environmentally friendly 'green' organic solvents, and continue to hold their attention as reaction catalysts or promoters [14][15][16]. Additionally, they have the ability to dissolve an enormous range of inorganic, organic, and polymeric materials at very high concentrations, are noncorrosive, and have low viscosities and no significant vapor pressures [17,18].…”

Efficient catalyst reuse by simple dissolution in non-conventional media

“…In contrast, ILs can be potential candidates for the substitution of common VOCs due to their almost non-volatility. 36 However, the high cost and toxicity concerns 32 have limited their use which, is probably only acceptable if the IL reuse is easily feasible or if the IL medium presents some advantage for the synthetic transformation. One of the first examples studied was the Morita-Baylis-Hillman reaction (MBH) as a potential candidate mainly because involved the formation of zwitterionic intermediates that could probably be stabilized in the IL environment.…”