NOHCs - 3-Alkoxyimidazolylidenes (NOHCs): A new class of highly nucleophilic carbenes. Preparation, structural and reactivity studies, and new applications in asymmetric catalysis

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This project describes the synthesis of a novel class of N-heterocyclic carbenes, namely 3- alkoxyimidazolylidenes (NOHCs) that are expected to be even more nucleophilic than the highly versatile and ubiquitously employed N-heterocyclic carbenes (NHCs). NOHCs will be prepared from their corresponding alkoxyimidazolium salts, which are accessible in a large variety in just two steps from imines and oximes as readily available starting materials. The proposed route will deliver NOHCs and NHCs with the same substitution patterns, thereby allowing swift comparison. First, the intrinsic properties of NOHCs will be studied including pKa determinations of their precursor salts, spectroscopy, dimerization, and computational assessments of their intrinsic reactivity in comparison with NHCs. Ideally, we will also be able to crystallize the 'Arduengo-NOHC' to directly determine structural analogies and differences. In a second step, these novel NOHCs, including a large series of chiral derivatives based on cinchona derivatives and chiral amines, will be applied to catalytic test reactions to outline their performance vs. NHCs, followed by their application to new and challenging catalytic, enantioselective transformations including trifluoromethylations, thia-Diels-Alder, and Kinugasa reactions. The two participating groups have complementary expertise with the Mloston group having ample experience in the synthesis of heteroatom-containing compounds, in particular, imidazole-N-oxides, and the Schreiner group being well versed in carbene chemistry and in enantioselective organocatalysis.