Photoredox with nickel catalysis
Something a little more generally applicable is the combination of photoredox chemistry with nickel catalysis. Focus in this article 1 is the coupling alpha-amino carboxyl sp3 carbons with aryl halides see scheme. Yields are generally excellent with examples of heterocyclic halides and of alpha O and aryl amino acids acting as substrates. With mild conditions this looks a versatile route to benzylic amines.
1. Z. Zuo et al Science 2014, 345, 437, http://www.sciencemag.org/content/345/6195/437.abstract
Over the past 40 years, transition metal catalysis has enabled bond formation between aryl and olefinic (sp2) carbons in a selective and predictable manner with high functional group tolerance. Couplings involving alkyl (sp3) carbons have proven more challenging.
Here, we demonstrate that the synergistic combination of photoredox catalysis and nickel catalysis provides an alternative cross-coupling paradigm, in which simple and readily available organic molecules can be systematically used as coupling partners.
By using this photoredox-metal catalysis approach, we have achieved a direct decarboxylative sp3–sp2 cross-coupling of amino acids, as well as α-O– or phenyl-substituted carboxylic acids, with aryl halides. Moreover, this mode of catalysis can be applied to direct cross-coupling of Formula–H in dimethylaniline with aryl halides via C–H functionalization.