Solvent-free conditions Morita-Baylis-Hillman

Methylimidazole 3-A-oxide (49) catalyses the Morita-Baylis-Hillman reaction at room temperature under solvent-free conditions addition to the enone reactant to give a zwitterionic enolate (50) is proposed, followed by reaction with aldehyde.177... 

A A /V /V -Tetramethylelhylcncdiaminc (TMEDA) as catalyst of the Morita-Baylis-Hillman reaction has been found to be more efficient than DABCO in aqueous media.146 1-Methylimidazole 3-/V-oxide promotes the Morita-Baylis-Hillman reaction of various activated aldehydes with ,/i-unsaturated ketones and esters CH2= CHCOR (R = Me, OMe) in solvent-free systems.147 In another study, the Morita-Baylis-Hillman reaction has been successfully performed under aqueous acidic conditions at pH 1, using a range of substrates and tertiary amines as catalysts.148... 

Significant rate enhancement of the Morita-Baylis-Hillman reaction through solid-state milling has been noted by Mack et al. (Scheme 2.44). [39], In such conditions, Baylis-HiUman products 130 were obtained in up to >98% yield in as little as 0.5 h by solvent-free reaction of p-nitrobenzaldehyde 129 and methyl acrylate 128. Various bases were tested and l,4-diazabicyclo[2.2.2]octane (DABCO) showed the best performance (Table 2.41). Other p-substimted aromatic aldehydes reacted with methyl acrylate much slower, within 9 5 h and lower yields (28-97%) were obtained. This represents one of the fastest methods of Bayhs-Hilhnan reactions under neat conditions. One of the main drawbacks of this reaction carried out in classical conditions is its slow rate, which has been shown typically to take days to weeks to produce adequate product yields. 

A remarkable rate acceleration of the Morita-Baylis-Hillman reaction of aldehyde ArCHO and activated alkene CH2=CH(EWG), catalysed by 1,4-diazabicyclo[2.2.2]octane (DABCO) (20mol%), has been reported for the solvent-free neat conditions. ... 

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