Polystyrene-Supported Al OTf

Friedel-Crafts Reactions. Aluminum trifluoromethanesulfonate has been used for the Friedel-Crafts alkylation reaction of toluene with isopropyl and tert-butyl chlorides (eq 1), and for the acylation of benzene and toluene with acetyl and benzoyl chlorides in low to moderate yields. Intramolecular Friedel-Crafts acylation of an aromatic compound with Meldrum s acid has also been reported using catalytic amounts of Al(OTf)3. Acylation of 2-methoxynaphthalene with acetic anhydride has been reported using Al(OTf)3 and lithium perchlorate as an additive to afford the corresponding 6-acetylated adduct in 83% yield. Effective acylation of arenes with carboxylic acids has also been disclosed using polystyrene-supported Al(OTf)3. ... 

An efficient tetrahydropyranyl and tetrahydrofuranyl protection of various alcohols and phenols has been reported using Al(OTf)3 as a catalyst. The reaction proceeded efficiently with only 1.5 equiv of dihydropyran or dihydrofuran and 1 mol % of Al(OTf)3 at room tenperature (eq 3). The deprotection was also possible in the presence of methanol and Al(OTf)3. Polystyrene-supported Al(OTf)3 was also disclosed for the formation of thio-acetals and acylals. ... 

Acylation of aldehydes has also been possible over polystyrene-supported Al(OTf)3 catalysts affording valuable acylals (Equation (8.54)) [137]. This catalyst exhibited comparable activity with AICI3 and Al(OT 3, but with added advantages involving the abhity to be recycled, nontoxicity, noncorrosiveness, and ease of and high chemoselectivity. 

Another example of polymer-supported A1 based Lewis acid is cross-linked polystyrene-supported aluminum triflate (79). Cross-linked polystyrene-supported AICI3 (72) was easily converted into (79) by treatment with triflic acid. This catalyst was applied to dithioacetalization of carbonyl compounds and transdithioacetal-ization of acetals (Scheme 19.19) [44]. From benzaldehyde the corresponding dithioacetal (84) was obtained in the presence of the polymeric catalyst (79) in 98% yield in 30 minutes. The same product was also obtained from the dimethyl acetal (85) in 94% yield. Chemoselectivity of the polymeric catalyst was also demonstrated in Scheme 19.19. Aldehydes reacted faster in the presence of ketone (34) to give the dithioacetals with (79). Aliphatic ketone (89) exclusively reacted with dithiol (81) in the presence of aromatic ketone (34). These chemoselectivities were higher than those obtained from the reactions using nonsupported Al(OTf)3. 

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