FeCl₂‐Catalyzed Selective CC Bond Formation by Oxidative Activation of a Benzylic CH Bond

Abstract

Any old iron: Readily available and nontoxic FeCl2 effectively catalyzes CC bond formation by oxidative activation of benzylic CH bonds in the presence of tert‐butyl peroxide as a stoichiometric oxidant (see scheme). The mild reaction conditions, good yields, low catalyst cost, and easy operation are the major advantages of this cross‐dehydrogenation coupling reaction.

Iron Catalysis: Historic Overview and Current Trends

“…This chemistry is further explained by Masumi Itazaki and Hiroshi Nakazawa in [51]. Two notable examples of the reaction are shown in Scheme 3 [43,44]. Li pioneered the reaction catalyzed by iron in his work published in 2007 [43].…”

“…Two notable examples of the reaction are shown in Scheme 3 [43,44]. Li pioneered the reaction catalyzed by iron in his work published in 2007 [43]. The reaction typically proceeds under oxidative conditions, with tBuOOtBu, DDQ (2,3-dichloro-5,6-dicyano-1,4-benzoquinone), or K 2 S 2 O 8 commonly applied as oxidants.…”

Iron-Catalyzed Cross-Dehydrogenative-Coupling Reactions

“…In 2007, Li and coworkers reported the first example of selective CDC reaction of benzylic C-H bond catalyzed by iron salt FeCl 2 in the presence of t BuOO t Bu as the oxidant (Scheme 2) [8]. In this reaction, the catalytic activity of the iron salt was higher than those of Cu and Co salts.…”

“…The yield dramatically decreased by using an Iron-Catalyzed Cross-Dehydrogenative-Coupling Reactionsortho-substituted substrate (entry 7). Furthermore, substituted phenyls, naphthyl, seven-membered cyclic diphenyl methane derivatives, and isochroman were also adaptable to this reaction (entries 5,[8][9][10]. This catalytic system is also adaptable to the Mizoroki-Heck-type reaction of styrene with diphenylmethane, although the catalytic activity is low and substrate scope is limited (Scheme 18).…”

Copper‐Catalyzed Cross‐Dehydrogenative Coupling (CDC) of Alkynes and Benzylic CH Bonds

“…The benzylic C À H bond lacking an adjacent hetero-A C H T U N G T R E N N U N G atom is more difficult to activate; [14] however, Shi recently disclosed the use of DDQ for the arylation of diphenylmethane derivatives. [15] With this in mind, we began our study using the copper/indium system that we previously reported for the alkylation of benzylic ethers [16] but with DDQ as the oxidant in chlorobenzene (C 6 H 5 Cl).…”