Ruthenium-Catalyzed Direct Hydroxymethylation of Aryl C–H Bonds

Ruthenium(II)-Catalyzed Grignard-Type Nucleophilic Addition of C(sp2)-H Bonds to Unactivated Aldehydes

The Grignard-type nucleophilic addition of C(sp²)-H bonds to aldehydes catalyzed by high-oxidation-state transition metal complexes is limited to activated aldehydes. Herein, we report the first example of Grignard-type nucleophilic addition of C(sp²)-H bonds to unactivated aldehydes catalyzed by high-oxidation-state ruthenium(II). The reaction has mild reaction conditions and good functional group tolerance. The corresponding alcohol products are obtained in good to excellent yields.

Dimeric Manganese-Catalyzed Direct Nucleophilic Addition of C(sp2)-H Bonds to Inert Aldehydes

An efficient direct nucleophilic addition reaction of C(sp²)-H bonds to aldehydes catalyzed by a dimeric manganese has been developed. This reaction has a broad range of substrates, and high yields were also obtained with inert aliphatic aldehydes as substrates. A dimeric Mn₂(CO)₈Br₂ was proven to be a more efficient catalyst precursor than the monomeric Mn(CO)₅Br.

Free Amine-Directed Ru(II)-Catalyzed Redox-Neutral [4 + 2] C-H Activation/Annulation of Benzylamines with Sulfoxonium Ylides

An external oxidant free Ru(II)-catalyzed C-H functionalization/annulation of primary benzylamines with sulfoxonium ylides has been developed for the synthesis of isoquinolines. The reaction utilizes free amine as a directing group, which is generally considered to be a poor directing group. This work presents the first example of Ru-catalyzed C-H functionalization of benzylamines under redox-neutral conditions. The detection of the amine-directed ruthenacyclic intermediate using high-resolution mass spectrometry corroborated the involvement of free amine as a directing group.

Cobalt-catalyzed direct α-hydroxymethylation of amides with methanol as a C1 source

Herein, we report a cobalt-catalyzed α-hydroxymethylation of amides with methanol under mild conditions. Using CoCl₂·6H₂O as an inexpensive and efficient catalyst, some important bioactive β-hydroxyamides were obtained in moderate to excellent yields. The developed method features a wide substrate scope and good functional group tolerance. In addition, anticholinergic tropicamide was easily synthesized in this way.

Cobalt-Catalyzed Vinylic C-H Addition to Formaldehyde: Synthesis of Butenolides from Acrylic Acids and HCHO

A carboxyl-assisted C-H functionalization of acrylic acids with formaldehyde to give butenolides is described. It is the first time that the addition of an inert vinylic C-H bond to formaldehyde has been achieved via cobalt-catalyzed C-H activation. The unique reactivity of the cobalt species was observed when compared with related Rh or Ir catalysts. γ-Hydroxymethylated butenolides were produced by the treatment of Na₂CO₃ after the catalytic reaction in one pot.

KIO4 -mediated Selective Hydroxymethylation/Methylenation of Imidazo-Heteroarenes: A Greener Approach

Herein, we report a KIO₄ -mediated, sustainable and chemoselective approach for the one-pot C(sp² )-H bond hydroxymethylation or methylenation of imidazo-heteroarenes with formaldehyde, generated in situ via the oxidative cleavage of ethylene glycol or glycerol (renewable reagents) through the Malaprade reaction. In the presence of ethylene glycol, a series of 3-hydroxymethyl-imidazo-heteroarenes was obtained in good to excellent yields. These compounds are important intermediates to access pharmaceutical drugs, e.g., Zolpidem. Furthermore, by using glycerol, bis(imidazo[1,2-a]pyridin-3-yl)methane derivatives were selectively obtained in good to excellent yields.

Removal and modification of directing groups used in metal-catalyzed C–H functionalization: the magical step of conversion into ‘conventional’ functional groups

This feature review is focused on recent approaches for removing versatile directing groups.

Ru(ii)-Catalyzed C-H addition and oxidative cyclization of 2-aryl quinazolinones with activated aldehydes

The ruthenium(ii)-catalyzed cross-coupling reaction between 2-aryl quinazolinones and activated aldehydes is described. This method enables the site-selective hydroxyalkylation under redox-neutral conditions. Moreover, this protocol provides a facile access to various tetracyclic isoindoloquinazolinones by using Cu(OAc)₂ as an external oxidant via C-H addition and subsequent intramolecular cyclization. A wide substrate scope and a high level of chemoselectivity as well as broad functional group tolerance are observed.

Hunzeylanines A-E, Five Bisindole Alkaloids Tethered with a Methylene Group from the Roots of Hunteria zeylanica

Five novel bisindole alkaloids, hunzeylanines A-E (1-5), with an unprecedented skeleton were isolated from the roots of Hunteria zeylanica. Compounds 1-5 represent the first examples of akuammine-pleioarpamine-type bisindole alkaloids fused with a dihydropyran unit. Their structures including absolute configurations were established through comprehensive spectroscopic data analyses and computational calculation methods. The plausible biogenetic pathway of 1 was also proposed. Alkaloids 1 and 2 displayed moderate cytotoxicity toward three human cancer cell lines (MDA-MB-231, AV3, and Huh7).

Ru(II)-Catalyzed C-H Hydroxyalkylation and Mitsunobu Cyclization of N-Aryl Phthalazinones

Ruthenium(II)-catalyzed C(sp²)-H functionalization of N-aryl phthalazinones with a range of aldehydes and activated ketone is described. Initial formation of hydroxyalkylated phthalazinones and subsequent Mitsunobu cyclization provided facile access to biologically relevant indazolophthalazinones. The utility of this method is highlighted by synthetic transformations into a series of potentially bioactive scaffolds.

Ruthenium(II)-Catalyzed Regioselective Ortho C-H Allenylation of Electron-Rich Aniline and Phenol Derivatives

Ortho C-H allenylation of electron-rich benzene derivatives with propargylic alcohol derivatives has been a challenge, due to their great innate tendency toward a para C-H allenylation via an SN₂'-type substitution process. Here, we described a Ru(II)-catalyzed regioselective ortho C-H allenylation of electron-rich aniline and phenol derivatives, which allows the previously challenging synthesis of a broad range of ortho allenylated aniline and phenol derivatives. More significantly, highly optically active fully substituted allenes can also be prepared with high enantiomeric excess via a highly efficient chirality transfer. No para C-H allenylation product was observed in the current catalytic system, thus showing a complete reversibility of the regioselectivity.

Construction of All-Carbon Chiral Quaternary Centers through CuI -Catalyzed Enantioselective Reductive Hydroxymethylation of 1,1-Disubstituted Allenes with CO2

A catalytic enantioselective construction of all-carbon chiral quaternary centers through reductive hydroxymethylation of 1,1-disubstituted allenes with CO₂ has been developed. In the presence of a copper/Mandyphos catalyst, CO₂ is transformed into an alcohol oxidation level by an asymmetric reductive C-C bond formation with allenes by using hydrosilane (HSi(OMe)₂ Me) as a reductant. The resulting chiral homoallylic alcohols are versatile synthetic intermediates and can be conveniently converted into a variety of useful chiral chemicals.

Cobalt-catalyzed hydroxymethylarylation of terpenes with formaldehyde and arenes

A cobalt(iii)-catalyzed C–H activation strategy has been developed to facilitate hydroxymethylarylation of terpenes with formaldehyde and arenes with high chemo- and regio-selectivities.

Terpenes, consisting of isoprene monomer units, represent a family of naturally abundant compounds. The difunctionalization of terpenes is highly appealing yet remains challenging, since the multiple unbiased C Created by potrace 1.16, written by Peter Selinger 2001-2019 ]]> C bonds of terpenes lead to difficulty in controlling the regioselectivity. Herein, a cobalt(iii)-catalyzed C–H activation strategy has been developed to facilitate hydroxymethylarylation of terpenes with formaldehyde and arenes with high chemo- and regio-selectivities. These (chemo- and regio-) selectivities are governed by the coordination abilities of isoprene, directing groups and the steric effect. This terpene difunctionalization also features high atom and step economy through a C–H addition pathway.

Nickel-catalyzed regioselective C–H acylation of chelating arenes: a new catalytic system for C–C bond formation via a radical process and its mechanistic explorations

An unprecedented acylation at the ortho C–H bond of chelating arenes via the Ni(ii)-catalyzed cross dehydrogenative coupling strategy has been developed here.

A comprehensive overview of directing groups applied in metal-catalysed C-H functionalisation chemistry

The present review is devoted to summarizing the recent advances (2015-2017) in the field of metal-catalysed group-directed C-H functionalisation. In order to clearly showcase the molecular diversity that can now be accessed by means of directed C-H functionalisation, the whole is organized following the directing groups installed on a substrate. Its aim is to be a comprehensive reference work, where a specific directing group can be easily found, together with the transformations which have been carried out with it. Hence, the primary format of this review is schemes accompanied with a concise explanatory text, in which the directing groups are ordered in sections according to their chemical structure. The schemes feature typical substrates used, the products obtained as well as the required reaction conditions. Importantly, each example is commented on with respect to the most important positive features and drawbacks, on aspects such as selectivity, substrate scope, reaction conditions, directing group removal, and greenness. The targeted readership are both experts in the field of C-H functionalisation chemistry (to provide a comprehensive overview of the progress made in the last years) and, even more so, all organic chemists who want to introduce the C-H functionalisation way of thinking for a design of straightforward, efficient and step-economic synthetic routes towards molecules of interest to them. Accordingly, this review should be of particular interest also for scientists from industrial R&D sector. Hence, the overall goal of this review is to promote the application of C-H functionalisation reactions outside the research groups dedicated to method development and establishing it as a valuable reaction archetype in contemporary R&D, comparable to the role cross-coupling reactions play to date.

Ruthenium(II)-Catalyzed Positional Selective C-H Oxygenation of N-Aryl-2-pyrimidines

Efficient Ru-catalyzed regioselective C-H oxygenation of N-aryl-2-pyrimidines is described with aryl carboxylic acids in the presence of AgSbF₆ as an additive and Ag₂CO₃ as an oxidant. The reaction can be extended to alkyl, heteroaryl, and α,β-unsaturated carboxylic acids. The regioselectivity, broad substrate scope, and functional group tolerance are the significant practical advantages.

Total synthesis of the isoquinoline alkaloid decumbenine BviaRu(iii)-catalyzed C–H activation

Decumbenine B could be easily synthesized from commercially available materials by only five steps with an overall yield of 26.1%.

Rhodium(III)-Catalyzed Selective C-H Acetoxylation and Hydroxylation Reactions

An efficient Cp*Rh(III)-catalyzed, chelation-assisted C(sp²)-H acetoxylation and hydroxylation reaction has been developed for the first time. The reaction proceeds under mild conditions and allows for selective preparation of C-H acetoxylation and hydroxylation products, thus providing a good complement to previous C-H oxygenation reactions and expanding the field of Cp*Rh(III)-catalyzed C-H functionalizations.

Rhodium(iii)-catalyzed and MeOH-involved regioselective mono-alkenylation of N-arylureas with acrylates

A new and versatile Rh(iii)-catalyzed C–H activation/alkenylation/MeOH-involved ammonolysis/esterification cascade reaction has been disclosed.

The one-pot synthesis of quinolines via Co(iii)-catalyzed C–H activation/carbonylation/cyclization of anilines

A new and versatile Co(iii)-catalyzed C–H activation/carbonylation/cyclization cascade reaction has been disclosed.