2.4.6- trimethylbenzoic acid TMBA

In 2012, Melchiorre et al. reported a novel stereoselective access to chiral frans-fused tetracyclic indole-based products having four stereogenic centres on the basis of a multicatalytic tandem Diels-Alder-benzoin reaction involving JV-Boc protected 3-(2-methyl-indol-3-yl)acrylaldehyde derivative and fra s-l,2-dibenzoylethylene derivative as substrates." As shown in Scheme 2.32, the process was successively induced by chiral diphenylproli-nol trimethylsilyl ether in the presence of bullgr 2,4,6-trimethylbenzoic acid (TMBA) as co-catalyst for the Diels-Alder reaction (trienamine catalysis), and an AT-heterocyclic carbene for the following cross-benzoin condensation... 

General Procedure for One-Pot Diels-Alder/Benzoin Condensation A vial equipped with a Teflon-coated stir bar and a plastic screw cap was charged with (f )-2-(diphenyl((trimethylsilyl)oxy)methyl)pyrrolidine (0.02 mmol, 6.5 mg, 20 mol%). Then, 2,4,6-trimethylbenzoic acid (TMBA, 0.02 mmol, 3.2 mg, 20mol%) and toluene (0.2 mL) were added in one portion, and the resulting solution was stirred at ambient temperature for 10 min to allow the catalyst salt formation. The reaction was started by the sequential addition of the aldehyde (0.12 mmol, 1.2 equiv) and dibenzoylethylene (0.1 mmol). The vial was sealed and kept in a water bath (ther-mostated at 40 °C). After 48 h, the vial was removed from the water bath and cooled to room temperature. Then, 0.3 mL of toluene, sodium acetate (0.2 mmol, 16.4 mg. 

TMPhen = 7,8-tetramethyl-l,10-pheiianthioline TMBA = 2,4,6-trimethylbenzoic acid... 

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See also in sourсe #XX -- [ ]

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