Dokument

Summary:
This work describes the development of applications of chiral-at-metal iridium(III)- and rhodium(III) Lewis acid catalysts. Based on the reversible coordination to their metal center and enolization upon coordination, chiral Lewis acids are capable to facilitate various α-functionalizations of 2-acyl imidazoles. In the first part, the visible-light driven enantioselective α-alkylation with α-cyanoalkyl bromides is presented. By merging photoredox catalysis with chiral Lewis acid catalysis, the α-cyanoalkylated 2-acyl imidazoles could be obtained with excellent enantiocontrol. This is the first example that such chiral metal enolate complexes react with branched carbon-centered radicals. In the second part, the results of the development of the asymmetric α-benzoyloxylation are presented. While the chiral rhodium Lewis acid complex demonstrated excellent catalytic activity to facilitate the reaction, the enantioselectivity remains to be improved. In the third part, results of the direct coupling of electron-rich arenes with the α-position of 2-acyl imidazoles are presented. The Lewis acid catalysts were found to promote the α-bromination of 2-acyl imidazoles with 2-bromo-1,3-dicarbonyl compounds and a subsequent Friedel-Crafts alkylation with electronrich arenes yielding the coupling products. Because it appears that the latter step proceeds predominantly through a planar cationic intermediate, which results in low enantioselectivity, the investigations are focused on the racemic variants and arene scope under the optimized reaction conditions is presented.

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