Quaternary Ammonium‐Supported Scavenger Reagents for Acids and Electrophiles

Abstract

The present article describes how we devised new quaternary ammonium‐supported quench reagents (TAMA‐Cl and BAX‐sulfate) for scavenging acids and excess electrophiles from crude reaction mixtures. TAMA‐Cl is liquid at room temperature, but is very glutinous and has to be used in aqueous solution. It removes unchanged electrophiles very efficiently. An aqueous preparation of TAMA‐Cl may be easily added in automated syntheses, and high‐throughput phase‐separation techniques should allow purification of scavenger‐containing reaction mixtures. However, workup with TAMA‐Cl is more complex than simple filtration. Recognizing this major advantage of solid‐phase syntheses, we designed BAX‐sulfate, a highly crystalline scavenger reagent that allows reaction workup to be simplified to a single filtration and evaporation of solvent. BAX‐sulfate reacts with electrophiles, quenches acids and precipitates quantitatively when diethyl ether is added. It even precipitates from methanol solutions. With BAX‐sulfate the workup stage uses simple filtration to make crude separations. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)