Laurean Ilies

β-Arylation of Carboxamides via Iron-Catalyzed C(sp3)–H Bond Activation

A 2,2-disubstituted propionamide bearing an 8-aminoquinolinyl group as the amide moiety can be arylated at the β-methyl position with an organozinc reagent in the presence of an organic oxidant, a catalytic amount of an iron salt, and a biphosphine ligand at 50 °C. Various features of selectivity and reactivity suggest the formation of an organometallic intermediate via rate-determining C-H bond cleavage rather than a free-radical-type reaction pathway.

Cobalt-Catalyzed ortho-Alkylation of Secondary Benzamide with Alkyl Chloride through Directed C−H Bond Activation

Coupling of an alkyl chloride with a secondary benzamide derivative at the ortho-position can be achieved in good to excellent yield in the presence of a cobalt catalyst and cyclohexylmagnesium chloride in diethyl ether at room temperature. Cyclohexylmagnesium chloride formally acts to remove hydrogen atoms from the amide nitrogen and from the ortho-position and to generate the active cobalt species.

Synthesis of anthranilic acid derivatives through iron-catalyzed ortho amination of aromatic carboxamides with N-chloroamines.

Arenes possessing an 8-quinolinylamide group as a directing group are ortho aminated with N-chloroamines and N-benzoyloxyamines in the presence of an iron/diphosphine catalyst and an organometallic base to produce anthranilic acid derivatives in high yield. The reaction proceeds via iron-catalyzed C-H activation, followed by the reaction of the resulting iron intermediate with N-chloroamine. The choice of the directing group and diphosphine ligand is crucial for obtaining the anthranilic acid derivative with high yield and product selectivity.

Iron-Catalyzed Ortho-Allylation of Aromatic Carboxamides with Allyl Ethers

Arenes possessing an N-(quinolin-8-yl)amide directing group are ortho-allylated with allyl phenyl ether in the presence of an iron/diphosphine catalyst and an organometallic base at 50-70 °C. The reaction proceeds via fast iron-catalyzed C-H activation, followed by reaction of the resulting iron intermediate with the allyl ether in γ-selective fashion.

Iron-Catalyzed C–H Bond Activation

Catalytic C-H bond activation, which was an elusive subject of chemical research until the 1990s, has now become a standard synthetic method for the formation of new C-C and C-heteroatom bonds. The synthetic potential of C-H activation was first described for ruthenium catalysis and is now widely exploited by the use of various precious metals. Driven by the increasing interest in chemical utilization of ubiquitous metals that are abundant and nontoxic, iron catalysis has become a rapidly growing area of research, and iron-catalyzed C-H activation has been most actively explored in recent years. In this review, we summarize the development of stoichiometric C-H activation, which has a long history, and catalytic C-H functionalization, which emerged about 10 years ago. We focus in this review on reactions that take place via reactive organoiron intermediates, and we excluded those that use iron as a Lewis acid or radical initiator. The contents of this review are categorized by the type of C-H bond cleaved and the type of bond formed thereafter, and it covers the reactions of simple substrates and substrates possessing a directing group that anchors the catalyst to the substrate, providing an overview of iron-mediated and iron-catalyzed C-H activation reported in the literature by October 2016.

Cobalt-catalyzed chemoselective insertion of alkene into the ortho C-H bond of benzamide.

Insertion of 1-alkene, 2-alkene, and styrene into the ortho C-H bond of benzamide in the presence of an inexpensive cobalt catalyst, DMPU as a crucial ligand, and cyclohexylmagnesium chloride proceeds smoothly at 25 °C to selectively give the ortho-alkylated product. Notable features of this reaction include the structural variety of the alkene and the amide substrate and the tolerance of functional groups such as halide, olefin, ester, and amide groups.

Iron-Catalyzed C−C Bond Formation at α-Position of Aliphatic Amines via C−H Bond Activation through 1,5-Hydrogen Transfer

C-C bond formation reactions that take place through organoiron species sometimes exhibit radical-like character. The reaction of N-(2-iodophenylmethyl)dialkylamine with a Grignard or diorganozinc reagent in the presence of a catalytic amount of Fe(acac)(3) gives the product resulting from arylation, alkenylation, or alkylation of the sp(3) C-H bond next to the amine group in good to excellent yield. Mechanistic studies including labeling experiments indicate that the reaction involves radical translocation triggered by the formation of a radical-like species by removal of the iodide group.

Cobalt-Catalyzed Coupling of Alkyl Grignard Reagent with Benzamide and 2-Phenylpyridine Derivatives through Directed C–H Bond Activation under Air

Aromatic carboxamides and 2-phenylpyridine derivatives can be ortho-alkylated with Grignard reagents in the presence of a cobalt catalyst and DMPU as a ligand. The reaction proceeds smoothly at room temperature, using air as the sole oxidant. The dialkylated product is selectively obtained when N-methylcarboxamide is employed as a substrate, whereas N-phenyl- or N-isopropylcarboxamide preferentially gives the monoalkylated product.

Iron-catalyzed stereospecific activation of olefinic C-H bonds with grignard reagent for synthesis of substituted olefins

The reaction of an aryl Grignard reagent with a cyclic or acyclic olefin possessing a directing group such as pyridine or imine results in the stereospecific substitution of the olefinic C-H bond syn to the directing group. The reaction takes place smoothly and without isomerization of the product olefin in the presence of a mild oxidant (1,2-dichloro-2-methylpropane) and an aromatic cosolvent. Several lines of evidence suggest that the reaction proceeds via iron-catalyzed olefinic C-H bond activation rather than an oxidative Mizoroki-Heck-type reaction.

Iron-catalyzed directed alkylation of aromatic and olefinic carboxamides with primary and secondary alkyl tosylates, mesylates, and halides.

Alkenes, arenes, and heteroarenes possessing an 8-quinolylamide group as the directing group are alkylated with primary and secondary alkyl tosylates, mesylate, and halides in the presence of Fe(acac)3/diphosphine as a catalyst and ArZnBr as a base. The reaction proceeds stereospecifically for alkene substrates and takes place without loss of regiochemical integrity of the starting secondary tosylate, but with loss of the stereochemistry of the chiral center.