Development of Polymer-Supported π-Acid Catalyst

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(1) A combination of 2-(4-vinylbenzyl)-propane-1, 3-diol (1) and tetracyanoethylene (TCNE) led to formation of a dicyanoketene acetal (DCKA) (2) bearing the styrene moiety in the molecule, which was polymerized with ethyleneglycol dimethacrylate (EGDMA) to produce a polymer-supported DCKA (poly-DCKA)(3) as a powder insoluble in the common solvents.(2) In a amount of 0.2 equiv. to the substrates, poly-DCKA (3) was found to catalyze effectively the Mukaiyama-type aldol condensation reactions of dimethyl acetals of aromatic, saturated, and α, β-unsaturated aldehydes and ketones with silyl-type carbon nucleophiles such as TMS-CN and Ar-C (=CH_2) O-TMS at 60 ℃ in MeCN.(3) Poly-DCKA (3) was found to catalyze effectively the Mannich reaction of imines with enolsilyl ethers of ketones aud esters at 60 ℃ in MeCN.The catalyst (3) promoted exclusively the three component Mannich reaction in the presence of an aldehyde, an amine, and a silyl-type carbon nucleophile.(4) Poly-DCKA (3) was found to catalyze deprotection reactions of acetal-type protecting groups of alcohols, aldehydes, and ketones and chemoselective deprotection of silyl ethers of alcohols. Particularly in the deacetalization recations under aqueous conditions (MeCN/water mixed solvent and water only) a remarkable positive polymer effect of poly-DCKA (3) was observed in the examination of acitivity of catalysts, (3), dicyanoketene ethylene acetal, and monomeric DCKA (2).(5) The polymeric catalysts (3) was recovered easily from the mixtures in the reactions mentioned above ((2), (3), (4)) and could be reused several times without any loss of activities.