Microwave Mediated Extensive Rate Enhancement of the Baylis-Hillman Reaction

Kundu, Mrinal K.; Mukherjee, Semanti; Balu, Narayanan; Padmakumar, R.; Bhat, Sujata V.

doi:10.1055/s-1994-22883

Cited by 105 publications

(35 citation statements)

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“…7 However, recent conditions employing DABCO in aqueous conditions 6 or protic solvent (MeOH) under the influence of microwave 13 or novel base 14 resulted in moderate to high yields of adducts, but only with select aldehydes. Since N-methylmorpholine is commercially used as a solvent apart from other uses, 11 reaction of acrylamide with aldehydes (2, 5, 7, 9-13) in N-methylmorpholine as solvent catalyzed by standard base (DABCO) at room temperature is conceived as an attractive proposition.…”

Section: Methodsmentioning

confidence: 99%

Novel aprotic polar solvents for facile Baylis-Hillman reaction

Krishna¹,

Manjuvani²,

Sekhar³

2004

Arkivoc

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Section: Methodsmentioning

confidence: 99%

Novel aprotic polar solvents for facile Baylis-Hillman reaction

Krishna¹,

Manjuvani²,

Sekhar³

2004

Arkivoc

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“…7 ) A similar, weakly Lewis acidic role of ionic liquids has been suggested for Diels ± Alder reaction in ionic liquids (see [13]). 8 ) Under these conditions, the Baylis ± Hillman adduct was produced in 63% yield after 14 h (see Exper.…”

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confidence: 93%

“…To overcome this problem, a number of additives have been reported to speed up the reaction, including Lewis acids [2], tertiary phosphines [3], quaternary ammonium salts [4], H-bond donors [5], and combinations thereof. In addition, high concentrations (often without solvent) and pressure [6], and ultrasound [7] and microwave irradiations [8] have been tried.…”

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confidence: 99%

“…In particular, the conditions of Entry 2, Table 3, allow a use of organic liquid (up to 100 ml [bmim] [PF 6 ] per mmol substrate, which is a relatively large amount for the Baylis ± Hillman process), while still producing the highest reaction rate reported at this concentration 8 ). This may prove useful for Baylis ± Hillman reactions with solid reactants wherein even such a small amount of organic liquid will help maintain the reaction mixture homogeneous.…”

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confidence: 99%

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

Kim

Song

2003

Helvetica Chimica Acta

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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.

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“…As the reactants and packing absorbed microwave energy, heat was transferred to the reaction mixture essentially by a combination of direct microwave and normal conduction heating. Giguere's approach was later adopted for transformations of long chain fatty acid esters [32][33][34] , racemisation 35 , intramolecular Diels-Alder reactions 36,37 , decarboxylation 38 , reactions of ethers 39 , Ferrier rearrangement 40 , Baylis-Hillman reaction 41 and for isoflavone synthesis 42 .…”

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confidence: 99%

Scale‐Up of Microwave‐Assisted Organic Synthesis

Roberts

Strauss

2005

Microwave Assisted Organic Synthesis

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In 1986 it was first reported that organic reactions could be conducted by heating in sealed containers in domestic microwave ovens 1,2 . Rate enhancements of up to three orders of magnitude were disclosed 3 . However, temperature and pressure measurement were technically difficult to achieve and in some instances the vessels deformed or exploded 1-3 .From these publications, workers interested in exploring the microwave technique perceived it to be simultaneously beneficial through increased rates, yet hazardous in the presence of flammable organic solvents. Subsequently, a vast body of work was carried out with domestic microwave ovens, but under solvent-free conditions and without recourse to sample mixing or temperature measurement. This continued across a broadening front on the laboratory scale. These and other developments in microwave chemistry have been reviewed extensively in journals, book chapters 4-20 and in a recent monograph 21 .Although relatively inexpensive in terms of purchase price, domestic microwave ovens are not designed to contain chemical explosions or toxic fumes and are incompatible with corrosive and inflammable compounds 13 . Flux densities within the microwave cavity can vary considerably, resulting in 'hot' and 'cold' spots. Mode stirrers and circulation of the vessel within the cavity are sometimes incorporated to assist in overcoming the non-uniformity of the energy distribution, but such measures are usually inadequate. Domestic ovens operate on duty cycles and intervals between zero and full power can be many seconds. This is not always ideal for heating common foods and beverages, let alone for performing delicate chemical manipulations. Intermittent bursts of power afford poor temperature control in chemical reactions. When these matters are considered in conjunction with the initial lack of dedicated pressure vessels for microwave-assisted organic chemistry, it is not surprising that explosions occurred 1-3 and that reactions are not necessarily reproducible in domestic microwave systems 6 .During the decade after 1986, disadvantages of domestic microwave ovens for organic chemistry became apparent to many researchers. Because of the unavailability of specifically designed commercial equipment, however, workers with volatile organic solvents, still found it necessary to adapt domestic units for reflux conditions or for operations under pressure. For reactions at reflux 22-30 , domestic microwave ovens were modified by fitting with a shielded opening to prevent microwave leakage and through which the reaction vessel within the microwave cavity could be connected to an external condenser 22,23,30 . Commercial systems adopting this approach have since appeared. When microwave-transparent coolants (chilled hydrocarbons, ice or solid carbon dioxide) are used, along with the reaction vessel, the condenser can also be located within the microwave cavity, thereby avoiding potential problems with microwave leakage 26,29,31 . 237Microwave Assisted Organic Synthesis Edited by Jason P. T...

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Microwave Mediated Extensive Rate Enhancement of the Baylis-Hillman Reaction

Cited by 105 publications

References 0 publications

Novel aprotic polar solvents for facile Baylis-Hillman reaction

Novel aprotic polar solvents for facile Baylis-Hillman reaction

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

Scale‐Up of Microwave‐Assisted Organic Synthesis

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