Complex Purification Strategies

Covalent scavenger and resin capture strategies use a covalent bond for the phase switch, whereas solid-phase extraction is based on noncovalent interactions between the product, the impurities, and the two phases. A combination of both methodologies has been introduced as a "complementary molecular reactivity and recognition" (CMR/R) purification approach [42]. The CMR/R approach allows for the rapid purification of products by incuba tion with various resins simultaneously, avoiding serial and more time-consuming purification procedures. By quenching all the undesired byproducts of the reaction mixture simultaneously, the desired product was obtained in solution after a simple filtration. This strategy has been illustrated with amine acylations, the Moffat oxidation, and the reaction of organometallics with carbonyl compounds. In case of amine acylation, commercially available aminomethyl polystyrene resin was utilized to react with excess of electrophile and Am-berlyst A-21 or polyvinylpyridine was used to sequester HCl.The parallel Moffat oxidations of secondary alcohols to ketones were worked up by adding simultaneously sulfonic acid-substituted resin and tertiary amine-substituted resin. Simple filtration afforded the ketone products. The reaction of organo-metallics with carbonyl compounds and their CMR/R-work-up is illustrated in Scheme 22.

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