Lanthanides Mannich-type reaction

Recently, Kobayashi has disclosed significant advances regarding rare-earth and lanthanide triflates as catalysts for Mannich-type reactions [65-68] and there are several reviews available on catalytic Mannich-type reactions [69-73]. High catalytic activity, low toxicity, and low tolerance to moisture and air make lanthanide triflates valuable catalysts. However, the high cost of these catalysts restricts their use. Bismuth compounds are of interest as lower toxicity and cheaper alternatives to such catalysts. 

The effectiveness of lanthanide Lewis acid in Mannich-type reaction was further highlighted by three-component coupling reaction of aldehydes, amines, and enol silyl ethers [7]. With MS 4A or MgS04 as dehydrating agent, 5-10 mol% ofYb(OTf)3 worked well to afford corresponding -amino ketone and esters in good to excellent yield (Table 13.3). It should be noted that the present reaction conditions were... 

Achiral Lanthanide Lewis Acid Catalysis 639 Table 13.2 Mannich-type reaction of N-(a-aminoalkyl)benzotriazoles catalyzed by Yb(OTf)3... 

Considering the water tolerance of lanthanide Lewis acids, a logical extension of the above-mentioned three-component coupling reaction is the reaction in aqueous media. Kobayashi et al. reported Mannich-type reaction of aldehydes, aniline derivative, and methyl enol ethers with 10mol% of Yb(OTf)3 in THF/H2O solvent system (Table 13.4) [8]. Applicability of commercially available aqueous formaldehyde and chloroacetaldehyde solution is of particular importance from the synthetic point of view (entries 1-3). A wide variety of aldehydes were transformed... 

Mannich-type reactions are among the most useful methodologies for the synthesis of /3-aminoketones or esters, which are versatile synthetic intermediates. Lanthanides triflates... 

This methodology was further extended to allylstannanes (Grieco and Bahsas, 1987). Still in the context of Mannich-type reactions, it was shown that the rate of reaction of phenols and ketones with secondary amines in the presence of formaldehyde was greatly increased in aqueous media compared with alcoholic or hydrocarbon solvents (Tychopoulos and Tyman, 1986). More recently, Kobayashi and Ishitani (1995) reported the catalysis of the reaction of vinyl ethers with iminium salts by lanthanide triflates ... 

Kobayashi, S. Ishitani, H. (1995) A novel Mannich-type reaction in aqueous media. Lanthanide triflate-catalyzed condensation of aldehydes, amines and vinyl ethers for the synthesis of P-amino ketones,Chem. Soc., Chem. Commun., 1379. 

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