Acetals aluminum trifluoromethanesulfonate

As an alternative to lithium enolates. silyl enolates or ketene acetals may be used in a complementary route to pentanedioates. The reaction requires Lewis acid catalysis, for example aluminum trifluoromethanesulfonate (modest diastereoselectivity with unsaturated esters)72 74 antimony(V) chloride/tin(II) trifluoromethanesulfonate (predominant formation of anti-adducts with the more reactive a,/5-unsaturated thioesters)75 montmorillonite clay (modest to good yields but poor diastereoselectivity with unsaturated esters)76 or high pressure77. 

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. ... 

Ketalization. Aluminum trifluoromethanesulfonate efficiently catalyzes the formation of acetals from various aromatic and ahphatic aldehydes and ketones in low catalyst loadings (1 mol%) and in short reaction times in neat conditions (eq 2). The title compound appears to be a mild catalyst for this reaction. Acid-sensitive sUyl ether of sahcylaldehyde was stable in these conditions. Notably, the catalyst could be recycled up to four times without loss of activity. An efficient method for thioacetaUzation of carbonyl compounds has also been described. ... 

Aluminum trifluoromethanesulfonate has proved to act as a mild catalyst for the Michael addition of 0-silylated ketene acetals with a./S-unsaturated esters (eq 14). A few glutarates were obtained in good yields using this method. ... 

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