DABCO-promoted Baylis-Hillman reaction

It should be noted that catalytic amounts of feA-arylureas and bis-arylthioureas greatly accelerated the DABCO-promoted Baylis-Hillman reaction of aromatic aldehydes with methyl acrylate in the absence of solvent. These robust organocatalysts were better mole-per-mole promoters of the reaction than either methanol or water and they were recovered in higher yields.106... 

The DABCO-promoted Baylis-Hillman reaction was run continuously using the CYTOS College System (CPC Systems GmbH) with yields comparable to those of the batch reaction and with a significant reduction in reaction time (Scheme 4.10) [14]. Coupled with the stopped-flow technique, an almost complete conversion was achieved. 

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... 

Selenium-containing six-membered ring heterocycles have proved to be useful catalysts in a variety of transformations. The Baylis-Hillman reaction involves the reaction of alkenes containing electron-withdrawing groups such as a,/3-unsaturated carbonyl compounds with aldehydes leading to carbon-carbon bond formation (Equation 79). The reaction is promoted by tertiary amines such as l,4-diazabicyclo[2.2.2]octane (DABCO), or tertiary phosphines and Lewis acids. Unfortunately, the Baylis-Hillman reaction is severely limited because it proceeds only very slowly <1998CC197>. Much research has been carried out in attempts to increase the rate of this reaction. 

Chiral 2,3-disubstituted DABCOs promote asymmetric Baylis-Hillman reactions under high pressure. While the yields are acceptable, the enantioselectivity is dismal. 

In the catalytic asymmetric aza-Morita-Baylis-HiUman reaction using unactivated methyl acrylate, the combined use of a La(0- Pr)3/(5, 5 )-TMS-linked-BINOL complex with a catalytic amount of l,4-diazabicyclo[2.2.2]octane (DABCO) promoted the aza-Morita-Baylis-Hillman reaction of a broad range of A-diphenylphosphinoyl imines." ... 

In 2004, Krishna and coworkers [59] reported that optically active a-methylene-y- and S-lactones can be obtained via intramolecular asymmetric Morita-Baylis-Hillman reaction starting from enantiomerically pure starting materials (Scheme 4.28). Diastereoselective cyclizations of chiral acrylates 103 and 105 were realized using DABCO as nucleophilic promoter. P,y-Disubstituted-a-methylene-y-lactone 104 and bicyclic a-methylene-8-lactone 106 with hydroxyl substituent in the 3-position were readily accessed following such strategy. 

A phosphine sulfonamide derived from L-threonine promotes aza-Morita-Baylis-Hillman (aza-MBH) reactions of sulfinylimines in up to 96% yield and 97% ee. A review describes the synthesis of chiral amines under mild conditions via catalytic asymmetric aza-MBH reactions. Proline/DABCO (l,4-diazabicyclo[2.2.2]octane) co-catalysis of enantioselective aza-MBH reactions gives good to high yields and up to 99%... 

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