Triisopropylbenzene sulfonate

Although considerable improvements have been made for endo-selective cycloadditions of azomethine imines, methods for exo and enantioselective cycloaddition of azomethine imines were relatively scarce. By employing novel, multifunctional primary amine catalysts 145 derived from cinchona alkaloids in the presence of triisopropylbenzene sulfonic acid (TIPBA) 146 as cocatalyst, Chen and coworkers developed the first organocatalytic, highly exo-selective, and enantioselective 1,3-DC reaction of cyclic enones 142 and azomethine imines 143 in 2007 [53]. The additional and synergistic hydrogen-bonding interaction of catalyst and 1,3-dipole is essential for enantiocontrol, and excellent stereoselectivities were achieved for a broad scope of substrates (dr > 99 1, up to 95% ee) (Scheme 2.37). 

In ref. [127] an investigation was made on the rate of phosphortriester formation and the percentage of sulfonated products in the cases of mesitylenesulfonyl-3-nitro-1,2,4-triazole (V), 2,4,6-triisopropylbenzenesulfonyltetrazole, and 2,4,6-triisopropylbenzene-sulfonyl-3-nitro-1,2,4-triazole (VI) as condensing agents. 

We find that j3-cyclodextrin reacts smoothly with 1-butyldimethyl-silylchloride to afford the heptasilyl derivative in which all of the primary hydroxyls are blocked. This then can be sulfonated on the secondary face for ease of separation, our preferred reagent is triisopropylbenzene sulfonyl chloride. The resulting monotrypsilated cyclodextrin is, from NMR evidence, sulfonated on hydroxyl-2. This is not easily displaced, but on treatment with base it is converted to the 2,3-epoxide, and this is relatively reactive towards nucleophiles. 

Triisopropylbenzene 12, by reaction with chlorosulfonic acid at 20 °C, cyclized to the sulfonic acid ester 13 (Equation 4)."... 

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