Scheme 3. Alkyl-aryl cross-coupling using potassiumand ammonium silicates.[Si] = bis(catecholato)silicate. COD = 1,5-cyclooctadiene. phen = 1,10-phenanthroline.Scheme 4. Alkyl-aryl cross-coupling using 1,4-dihydropyridines. ppy = 2-phenylpyridine. DMI = 1,3-dimethyl-2-imidazolidinone. bpy = 2,2'-bipyridine dMeObpy = 4-4'-dimethoxy-2-2'-bipyridine. Angewandte ChemieMinireviews 6157

DNA-encoded library (DEL) technology is a powerful tool commonly used by the pharmaceutical industry for the identification of compounds with affinity to biomolecular targets. Success in this endeavor lies in sampling diverse chemical libraries. However, current DELs tend to be deficient in C(sp) 3 carbon counts. We report unique solutions to the challenge of both increasing the chemical diversity of these libraries and their C(sp) 3 carbon counts by merging Ni/photoredox dual catalytic C(sp 2 )-C(sp 3 ) cross-coupling as well as photoredox catalyzed radical/polar crossover alkylation protocols with DELs. The successful integration of multiple classes of radical sources enables the rapid incorporation of a diverse set of alkyl fragments.

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A benchtop stable, bifunctional reagent for the redox-neutral cyclopropanation of olefins has been developed. Triethylammonium bis(catecholato)iodomethylsilicate can be readily prepared on multigram scale. Using this reagent in combination with an organic photocatalyst and visible light, cyclopropanation of an array of olefins, including trifluoromethyl- and pinacolatoboryl-substituted alkenes, can be accomplished in a matter of hours. The reaction is highly tolerant of traditionally reactive functional groups (carboxylic acids, basic heterocycles, alkyl halides, etc.) and permits the chemoselective cyclopropanation of polyolefinated compounds. Mechanistic interrogation revealed that the reaction proceeds via a rapid anionic 3- exo- tet ring closure, a pathway consistent with experimental and computational data.

Photoredox catalysis, using an organic photocatalyst and silanol reagent, enables the metal-free generation of aryl radicals to synthesize diverse gem-difluoroalkenes.