Palladium(II)-catalyzed directed trifluoromethylthiolation of unactivated C(sp³)-H bonds

Transition-metal-catalyzed C-H bond activation as a sustainable strategy for the synthesis of fluorinated molecules: an overview

The last decade has witnessed the emergence of innovative synthetic tools for the synthesis of fluorinated molecules. Among these approaches, the transition-metal-catalyzed functionalization of various scaffolds with a panel of fluorinated groups (XRF, X = S, Se, O) offered straightforward access to high value-added compounds. This review will highlight the main advances made in the field with the transition-metal-catalyzed functionalization of C(sp2) and C(sp3) centers with SCF3, SeCF3, or OCH2CF3 groups among others, by C-H bond activation. The scope and limitations of these transformations are discussed in this review.

Directed Palladium Catalyzed C-H (Ethoxycarbonyl)difluoromethylthiolation Reactions

The unprecedented Pd-catalyzed (ethoxycarbonyl)difluoromethylthiolation reaction of various unsaturated derivatives was studied. In the presence of the (ethoxycarbonyl)difluoromethylsulfenamide reagent I and under mild reaction conditions (60 °C), both 2-(hetero)aryl and 2-(α-aryl-vinyl)pyridine derivatives were smoothly functionalized with this methodology (37 examples, up to 87 % yield). Moreover, the synthetic interest of this fluorinated moiety was further showcased by its conversion into various original fluorinated residues. Finally, a plausible mechanism for this transformation was suggested.

Diastereoselective palladium-catalyzed functionalization of prochiral C(sp3)-H bonds of aliphatic and alicyclic compounds

We highlight the reported developments of the palladium-catalyzed C-H activation and functionalization of the inactive/unreactive prochiral C(sp³)-H bonds of aliphatic and alicyclic compounds. There exist numerous classical methods for generating contiguous stereogenic centers in a compound with a high degree of stereocontrol. Along similar lines, the Pd(II)-catalyzed, directing group-aided functionalization of inactive prochiral/diastereotopic C(sp³)-H bonds have been exploited to accomplish the stereoselective construction of stereo-arrays in organic compounds. We present a concise discussion on how specific strategies consisting of Pd(II)-catalyzed, directing group-aided C(sp³)-H functionalization have been utilized to generate two or more stereogenic centers in aliphatic and alicyclic compounds.

Transition metal catalysed direct sulfanylation of unreactive C-H bonds: an overview of the last two decades

Transition metal catalysed direct sulfanylations of unreactive C-H bonds have become a unique and straightforward synthetic strategy in late-stage C-S bond formation of relevant complex molecules. Such transformations have represented...

Transition-Metal-Catalyzed, Coordination-Assisted Functionalization of Nonactivated C(sp3)-H Bonds

Transition-metal-catalyzed, coordination-assisted C(sp³)-H functionalization has revolutionized synthetic planning over the past few decades as the use of these directing groups has allowed for increased access to many strategic positions in organic molecules. Nonetheless, several challenges remain preeminent, such as the requirement for high temperatures, the difficulty in removing or converting directing groups, and, although many metals provide some reactivity, the difficulty in employing metals outside of palladium. This review aims to give a comprehensive overview of coordination-assisted, transition-metal-catalyzed, direct functionalization of nonactivated C(sp³)-H bonds by covering the literature since 2004 in order to demonstrate the current state-of-the-art methods as well as the current limitations. For clarity, this review has been divided into nine sections by the transition metal catalyst with subdivisions by the type of bond formation. Synthetic applications and reaction mechanism are discussed where appropriate.

Cp*Rh(III)-Catalyzed Regioselective C(sp3)-H Electrophilic Trifluoromethylthiolation of 8-Methylquinolines

Rh(III)-catalyzed regioselective trifluoromethylthiolation of the unactivated C(sp³)-H bond of 8-methylquinolines with bench-stable electrophilic trifluoromethylthiolating reagent via C(sp³)-H activation is explored. Various substituted 8-methylquinolines provided the products in good yields with high regioselectivity. Current reaction conditions are also applicable for the late-stage functionalization of natural molecule santonin and caffeine-substituted 8-methylquinoline.

Radical-Promoted Distal C-H Functionalization of C(sp3 ) Centers with Fluorinated Moieties

Due to their unique properties, fluorinated scaffolds are pivotal compounds in pharmaceuticals, agrochemicals, and materials science. Over the last years, the development of versatile strategies for the selective synthesis of fluorinated molecules by direct C-H bond functionalization has attracted a lot of attention. In particular, the design of novel transformations based on a radical process was a bottleneck for distal C-H functionalization reactions, offering synthetic solutions for the selective introduction of fluorinated groups. This Minireview highlights the major contributions in this blossoming field. The development of new methodologies for the remote functionalization of aliphatic derivatives with various fluorinated groups based on a 1,5-hydrogen atom transfer process and a β-fragmentation reaction will be showcased and discussed.

Pd-Catalyzed Directed Thiocyanation Reaction by C-H Bond Activation

The Pd-catalyzed directed thiocyanation reaction of arenes and heteroarenes by C-H bond activation was achieved. In the presence of an electrophilic SCN source, this original methodology offered an efficient tool to access a panel of functionalized thiocyanated compounds (21 examples, up to 78 % yield). Post-functionalization reactions further demonstrated the synthetic utility of the approach by converting the SCN-containing molecules into value-added scaffolds.

Rhodium(III)-catalyzed C4-amidation of indole-oximes with dioxazolones via C-H activation

A novel method for the Rh(iii)-catalyzed oxime-directed C-H amidation of indoles with dioxazolones has been developed. This strategy provides an exclusive site selectivity and the directing group can be easily removed. This transformation features a wide substrate scope, good functional group tolerance and excellent yields, and may serve as a significant tool to construct structurally diverse indole derivatives for the screening of potential pharmaceuticals in the future.

Pd-Catalyzed Selective Chlorination of Acrylamides at Room Temperature

In this Letter, the transition-metal-catalyzed chlorination of alkenes is reported. In the presence of the commercially available and inexpensive N-chlorosuccinimide and without additive, the Pd-catalyzed chlorination of acrylamides by C-H bond activation was developed at room temperature under air. Under these mild reaction conditions, the versatility of the methodology was demonstrated as an array of acrylamides was functionalized to selectively provide the corresponding difficult-to-synthesize chlorinated olefins as a single Z stereoisomer. Mechanistic studies were conducted to get insights into the reaction mechanism, and post-functionalization reactions further demonstrated the synthetic utility of the approach toward the access to high value-added chlorinated compounds.

C-N and C-O Bond Formation in Copper-Catalyzed/Mediated sp3 C-H Activation: Mechanistic Studies from Experimental and Computational Aspects

Mechanistic studies on Cu-catalyzed/mediated sp³ C-H amidation and acetoxylation are investigated from experimental and computational aspects. The concerted metalation-deprotonation (CMD) mechanism rather than a radical-involved pathway is proved to occur in amidation and acetoxylation reactions, and this is the rare example of the CMD mechanism involved in the more challenging sp³ C-H activations. Theoretical calculations demonstrated that CMD is the rate-determining step either for methylic or benzylic positions in amidation and acetoxylation reactions, and intermolecular nucleophilic addition of acetate anions is more favorable than the ring opening of β-lactams and intramolecular acetoxylation. These mechanistic studies on the divergent and condition-dependent product formation are critical for developing Cu-promoted C-H functionalization via the CMD mechanism.

Catalytic Approaches for the Direct Heterofunctionalization of Aliphatic Carboxylic Acids and Their Equivalents with Group 16 Elements

In contrast to traditional multistep synthesis, modern organic synthesis extensively depends on the direct functionalization of unactivated C-H bonds for the construction of various C-C and C-heteroatom bonds in atom- and step-economic manner. Common aliphatic substrates, e. g. carboxylic acids and their synthetic equivalents, are regiospecifically functionalized based on either a directed approach, in which the polar directing group assists to functionalize a specific C-H bond positioned at β- and γ-carbon centers, or a non-directed approach typically leading to α-functionalization. While numerous reviews on catalytic C-H functionalization have appeared, a concise review on the direct C(sp³ )-H heterofunctionalization of carboxylic acid synthons with Group 16 elements has been awaited. The recent advances on the direct oxy-functionalization and chalcogenation of aliphatic carboxylic acid synthons enabled by transition metal, organo- and photocatalysts are described herein.

Revisiting the mechanism of the Fujiwara–Moritani reaction

A new perspective of the Fujiwara–Moritani reaction is presented, including its kinetic profile and catalyst deactivation studies.

Copper-Catalyzed, N-Directed Csp3-H Trifluoromethylthiolation (-SCF3) and Trifluoromethylselenation (-SeCF3)

A direct and versatile copper-catalyzed trifluoromethylthiolation and trifluoromethylselenation of primary, secondary, and tertiary aliphatic C-H bonds was developed. The reaction provides direct access to molecules containing these emerging moieties in the presence of a wide range of common functional groups and in complex molecular environments.

Novel Bifunctionalization of Activated Methylene: Base-Promoted Trifluoromethylthiolation of β-Diketones with Trifluoromethanesulfinyl Chloride

A novel bifunctionalization of activated methylene was achieved successfully through the base-promoted trifluoromethylthiolation of β-diketones or β-ketoesters with trifluoromethanesulfinyl chloride. A series of α-trifluoromethylthiolated α-chloro-β-diketones and α-chloro-β-ketoesters were obtained in moderate to good yields under mild conditions. When β-diketones containing a phenyl group with a hydroxyl or amino substituent at the ortho position were used as substrates, intramolecular trifluoromethylthiolation/cyclization reaction took place to give the corresponding cyclic products. Furthermore, the protocol could be extended to perfluoroalkylthiolation with the sodium perfluoroalkanesulfinate/POCl₃ system. On the basis of experimental results, plausible mechanisms are proposed.

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.

Complementary Strategies for Directed C(sp3 )-H Functionalization: A Comparison of Transition-Metal-Catalyzed Activation, Hydrogen Atom Transfer, and Carbene/Nitrene Transfer

The functionalization of C(sp3 )-H bonds streamlines chemical synthesis by allowing the use of simple molecules and providing novel synthetic disconnections. Intensive recent efforts in the development of new reactions based on C-H functionalization have led to its wider adoption across a range of research areas. This Review discusses the strengths and weaknesses of three main approaches: transition-metal-catalyzed C-H activation, 1,n-hydrogen atom transfer, and transition-metal-catalyzed carbene/nitrene transfer, for the directed functionalization of unactivated C(sp3 )-H bonds. For each strategy, the scope, the reactivity of different C-H bonds, the position of the reacting C-H bonds relative to the directing group, and stereochemical outcomes are illustrated with examples in the literature. The aim of this Review is to provide guidance for the use of C-H functionalization reactions and inspire future research in this area.