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Abstract

Many reactions involving aryl radicals result in several side products due to the high reactivity of aryl radicals. Although some remote C–H functionalization reactions involving aryl radicals by intramolecular hydrogen atom transfer (HAT) have been reported recently, the C–H functionalization through intermolecular HAT enabled by aryl radicals remains a great challenge.
Herein, we have developed the first facile alkane/heterocycle dehydrogenation reaction involving an intermolecular HAT enabled by aryl radicals. In this reaction, we have used a yet underexplored diimine as a novel redox noninnocent ligand to facilitate the aryl iodide to a highly reactive aryl radical in the presence of a Ru catalyst. This protocol is not only applicable to intermolecular HAT reactions (Scheme Ⅰ a) but also to intramolecular HAT reactions (Scheme Ⅰ b).
The synthetic applications of this protocol have been demonstrated on gram-scales. In these gram-scale reactions, two borylation products (from linear alkanes) were isolated from one-pot tandem reactions (Scheme ⅠI a), and an epoxide product was isolated in two separate steps (Scheme ⅠI b). Furthermore, a radical mechanism proceeding through an intermolecular HAT cascade has been supported by mechanistic and organometallic studies.
Following the above research, we have taken advantage of the same catalytic system to realize a rare example of selective cross-dehydrogenative coupling (CDC) reactions of innate Csp³−H (benzylic site, etc.) with hydroxyketonic Csp³−H bonds. Using this valuable redox neutral strategy, a wide range of functionalized substrates have given the desired products in moderate to good isolated yields (Scheme ⅠII). Subsequent mechanistic studies have also been performed, which support a radical mechanism proceeding through an intermolecular HAT.