Halogen bond donor (XBD) catalysts have been shown to be effective at catalyzing a variety of reactions, at times showing superior reactivity when compared to their hydrogen bond donor counterparts. Recent reports have shown that the Lewis acid character imparted onto electron deficient halogen atoms can enable unique reactivity in reactions where other organocatalysts have failed. One of the most successful and well-studied structural scaffolds for this class of monodentate catalysts utilizes an electron deficient imidazolium core. However, these cationic catalysts do not always demonstrate optimal solubility in organic solvents thus requiring long alkyl appendages to increase their utility. Therefore, there is a need to synthesize highly soluble monodentate imidazolium XBD catalysts with high activity and simplified methods of preparation. To this end, diarylimidizolium structures were designed bearing two tunable substituents to aid in developing optimal catalytic activity, in contrast to previous reports requiring long alkyl chains that only served to increase solubility. Our simple design has led to new and ongoing efforts to generate novel catalysts bearing two highly electron deficient substituents to optimize activity. The catalysts from this report can be synthesized from simple anilines and dicarbonyl compounds through a short three step sequence. The effectiveness of the catalysts was tested with a model Friedel-Crafts reaction. Initial tests performed on catalysts bearing mesityl and 2,6-diisopropylbenzene substituents showed predictably low reactivity, but also the desired high organic solubility. Furthermore, catalytic activity could be enhanced through exchange with weakly coordinating counterions. With positive initial studies resulting in readily soluble catalysts, new studies have begun to incorporate electron deficient aryl substituents, and these initial efforts will also be presented.

Diarylimidazolium halogen bond donor catalysts for Lewis acid catalyzed transformations

2019 Spring National Meeting

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