Electrophile scavengers

Table 4 Use of a electrophilic scavenger resin to improve yields in the heteroatom Diels-Alder reaction (Equation 34)...

Fig. 1. General approaches to the removal of excess reagents using nucleophilic and electrophilic scavenger resins.

Fig. 8. Oligo(ethyleneimine) (20), morpholinodiethanolamine (21), amine/aminoalcohol (22), guanidine (23), and 4-phenolsubstituted (24)-based custom made electrophilic scavenging resins.

Recently, a novel commercially available acetoacetoxyethyl metacry-late resin (37) is finding wide applications as a selective electrophilic scavenger resin. This resin has the ability to differentiate primary amines from a mixture where secondary amines are present.64,65 An illustrative example is depicted in the synthesis of dibenzylamine (38, Fig. 16) from benzaldehyde and benzylamine. Unreacted benzylamine is selectively removed from the reaction mixture upon treatment with the ketoacetate resin (37). 

Besides spectroscopic methods, quenching processes have been utilized to differentiate between various types of radical ion pairs, too. These chemical methods make use of the different reactivities of CIP and SSIP which are caused by the unequal solvation and distance of the charged species in the ion pairs. Depending on the ambivalent character of radical ions, these intermediates may be scavenged either by electron transfer quenchers (Q) or by nucleophilic and electrophilic scavengers (Scheme 7 and Eqs. (5—7)). 

Supported/Tagged Reactive Functionalities for the Sequestration of Nucleophiles (Nucleophile/Electrophilic Scavengers)... 

Electrophilic scavengers contain a reactive electrophilic functional group and, hence, can react with a compatible nucleophile, allowing for its sequestration and subsequent removal. Electrophilic scavengers are also referred to as nucleophile scavengers. Several electrophilic/nucleophile scavengers have been developed to date and are summarized in Table 8.1. 

Scheme 8.19 Utilization offluorous electrophilic scavengers for amine sequestration in library synthesis.

Scheme 8.21 The Lindsley fluorous electrophilic scavenger suite in library synthesis.

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