H H

separated by SPE

Inorganic salts separated by LPE

Organic byproducts separated by SPE

Scheme 23

Another approach using chemically tagged reagents in combination with ion-exchange resin has recently been published [47] for high-throughput purification of Mitsunobu reactions. Masked carboxylic acid tags (t-butyl esters) were used for both Mitsunobu reagents so that, upon postreaction unmasking with trifluoroacetic acid, a base-functionalized ion-exchange resin 85 could be used to sequester the carboxy tagged reagents 81 and 83, the car-boxy-tagged byproducts 82 and 84, as well as excess nucleophile 79. An overview is given in Scheme 24.

RlX 80

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