Acetonyltriphenylphosphonium bromide

Finally, achiral phosphonium salts have been applied as Lewis acid catalysts in some other reactions. The examples will be listed here but not discussed in more detail. Phosphonium salts have been used as catalysts for the A,A-dimethylation of primary aromatic amines with methyl alkyl carbonates giving the products in good yields [123]. In addition acetonyltriphenylphosphonium bromide has been found to be a catalyst for the cyclotrimerization of aldehydes [124] and for the protection/ deprotection of alcohols with alkyl vinyl ethers [125, 126]. Since the pK of the salt is 6.6 [127-130], the authors proposed that, next to the activation of the phosphonium center, a Brpnsted acid catalyzed pathway is possible. 

Dihydropyran, acetonyltriphenylphosphonium bromide, CH2CI2, 5 min, 80-97% yield. The EE and THE ethers are also formed using this reagent. "... 

Acetonyltriphenylphosphonium bromide, MeOH, 7 min to 6 h, 70-95% yield. Phenolic TBDMS ethers are preserved during cleavage of aUcyl TBDMS ethers. ... 

Acetonyltriphenylphosphonium bromide (0.05 mmol) was added to a mixture of the alcohol, or phenol, or amine or thiol (1 mmol) and acetic anhydride (1.5-2.0 mmol) and the mixture was stirred at room temperature for ca. 0.5-3.5 h. After complete disappearance of the starting material, as monitored by TLC, the mixture was quenched with a saturated hydrogencarbonate solution (2mL). Finally, the reaction mixture was extracted with ethyl acetate (20mLx3). The combined organic extract was washed with water and dried over anhydrous sodium sulfate. After removal of the organic solvent in a rotary evaporator, the crude residue was passed through a silica gel column to isolate the desired pure acetate. 

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