Acid and vitamin E: Trimethylsilyl super Lewis acids, such as [C6F5C(Tf)2]− Me3Si+ and Tf3CSiMe3, are extremely active and highly effective catalysts for the regioselective condensation of trimethylhydroquinone with isophthyol to afford (±)‐α‐tocopherol (vitamin E; see scheme, Tf=CF3SO2.
[Structure: see text] A new Brønsted acid-assisted chiral Brønsted (chiral BBA) acid catalyst (1) was developed by substituting a hydroxy group of optically active 1,1'-bi(2-naphthol) with a stronger Brønsted acidic group such as a bis(trifluoromethanesulfonyl)methyl group. The enantioselective Mannich-type reaction of ketene silyl acetals with aldimines catalyzed by (R)-1 in the presence of stoichiometric achiral proton sources gave (S)-beta-amino esters in high yield with moderate to good enantiomeric excesses.
Various arylbis(trifluoromethylsulfonyl)methanes (1) have been synthesized by reacting the corresponding benzylic halides with sodium trifluoromethanesulfinate and then with triflic anhydride. In addition, when the aryl group of 1 is a pentafluorophenyl group, the nucleophilic para-substitution of the aryl group with alkyllithiums and sodium alkoxides occurs. This reaction is useful for the design of new Brønsted acids.
Several advantages over inorganic solid acids such as zeolites and perfluororesinsulfonic acids such as Nafion are offered by the new reusable polystyrene‐bound catalyst 1: a broader range of applications, improved yields, improved selectivity, and milder reaction conditions. Tf = F3CSO2.
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