Diphenylboryl Trifluoromethanesulfonate

Ph2B-OSO2CF3

[100696-94-4]  · C13H10BF3O3S  · Diphenylboryl Trifluoromethanesulfonate  · (MW 314.11)

(Lewis acid utilized for the preparation of homoallyl alcohols and ethers;1,2 catalyst for asymmetric esterification of cyclic meso3 and racemic dicarboxylic acid anhydrides;4 catalyst for Friedel-Crafts acylation of acid anhydrides and acid chlorides5)

Alternate Name: diphenylboryl triflate.

Solubility: sol common inert organic solvents such as CH2Cl2 and toluene.

Preparative Method: generated in situ from equimolar amounts of Silver(I) Trifluoromethanesulfonate and diphenylchloroborane. The reactants are mixed in toluene at 0 °C and stirred for 1 h. The reagent is then used immediately.

Handling, Storage, and Precautions: solutions are moisture and air sensitive and therefore they should be used under a dry inert atmosphere.

Allylation.

Ph2BOTf is a mild and effective catalyst for the addition of allylsilanes to acetals to afford the corresponding homoallyl ethers. These reactions proceed at -78 °C in good yield, and with modest diastereoselectivity when a substituted allylsilane is utilized (eq 1). The allylation reaction of acetals is not catalyzed by either Ph2BCl or AgOTf, nor is it catalyzed by Bu2BOTf. Thus it has been postulated that stabilization of the boryl triflate by the two phenyl groups yields a boron atom with significant cationic character and it is this property that allows Ph2BOTf to serve as the activator of the reaction.1

Ph2BOTf has been utilized for the one-pot asymmetric allylation of aldehydes utilizing enantiomerically pure 1-phenylethyl trimethylsilyl ether as a coreactant and source of asymmetric induction (eq 2). The highest diastereomeric product ratios are typically observed with reactions run at -78 °C in toluene. The protecting group on the resulting homoallylic ethers can be easily removed via catalytic hydrogenation or by treatment with Iodotrimethylsilane.2

Asymmetric Esterification.

Ph2BOTf is a very efficient catalyst for the asymmetric esterification of cyclic meso and racemic dicarboxylic anhydrides. Various enantiomerically pure derivatives of mandelic acid have been utilized in reactions with anhydrides of cyclic meso-dicarboxylic acids with good to excellent degrees of asymmetric induction. The best results are achieved when the reaction is run with 2 equiv of the diphenylborate of a single enantiomer of 2-methoxy-1-phenylethanol as the nucleophilic species. When (R)-2-methoxy-1-phenylethanol is used, the (1S, 2R) diastereomer predominates, as shown for meso-1,2-cyclohexanedicarboxylic anhydride in eq 3.3 This method has been extended to the ring opening of racemic cyclic dicarboxylic anhydrides as well. In these cases the best results are achieved when >2 equiv of the anhydride per equivalent of nucleophile are used. Yields for the reported examples average approximately 75%, a typical example being shown in eq 4.4

Friedel-Crafts Acylation.

Ph2BOTf has been reported to be an effective catalyst for the acylation of aromatic compounds with acid chlorides or acid anhydrides under mild conditions (eq 5).5


1. Mukaiyama, T.; Nagaoka, H.; Murakami, M.; Ohshima, M. CL 1985, 977.
2. Mukaiyama, T.; Ohshima, M.; Miyoshi, N. CL 1987, 1121.
3. Ohshima, M.; Mukaiyama, T. CL 1987, 377.
4. Ohshima, M.; Miyoshi, N.; Mukaiyama, T. CL 1987, 1233.
5. Mukaiyama, T.; Nagaoka, H.; Ohshima, M.; Murakami, M. CL 1986, 165.

David S. Garvey

Abbott Laboratories, Abbott Park, IL, USA



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