Nickel-Catalyzed Directed C6-Selective C–H Alkylation of 2-Pyridones with Dienes and Activated Alkenes

Overcoming the Challenges toward Selective C(6)-H Functionalization of 2-Pyridone with Maleimide through Mn(I)-Catalyst: Easy Access to All-Carbon Quaternary Center

An earth-abundant and inexpensive Mn(I)-catalyzed alkylation of 2-pyridone with maleimide has been reported for the first time, in contrast to previously reported Diels-Alder products. Notably, an unexpected rearrangement has been discovered in the presence of acetic acid, which also provides a unique class of compounds bearing three different N-heterocycles with an all-carbon quaternary center. Furthermore, single crystal X-ray and HRMS revealed a five-membered manganacycle intermediate. This methodology tolerates a wide variety of functional groups delivering the alkylated products in moderate to excellent yields.

RhIII -Catalyzed C6-Selective Oxidative C-H/C-H Crosscoupling of 2-Pyridones with Thiophenes

A rhodium(III)-catalyzed C6-selective dehydrogenative cross-coupling of 2-pyridones with thiophenes was developed for the synthesis of 6-thiophenyl pyridin-2(1H)-one derivatives. In this reaction, the excellent site selectivity was controlled by the 2-pyridyl directing group on the nitrogen of the pyridone ring. Control experiments indicated that the N-pyridyl was essential for the transformation. To the best of our knowledge, this procedure is the first successful example of the direct C6 heteroarylation of 2-pyridones with electron-rich thiophene derivatives. 4-Pyridone was also used as substrate to generate the corresponding C2 heteroarylated product. Moreover, this pyridyl directing group was readily removable to generate the biheteroaryl structures with a free N-H group.

Cobalt(III)-Catalyzed Regioselective C6 Olefination of 2-Pyridones Using Alkynes: Olefination/Directing Group Migration and Olefination

Co(III)-catalyzed highly regio- and stereoselective direct C6 olefination of 2-pyridones with alkynes has been developed with the assistance of chelation. Upon variation of the reaction conditions, 2-pyridones react well with diaryl alkynes via a C6 olefination/directing group migration pathway to give the tetrasubstituted 6-vinyl-2-pyridones, but the C6-H olefination with terminal alkynes works effectively to afford only the C6-olefinated 2-pyridones. A judicious choice of a solvent and an additive is crucial for catalysis. The protocols feature 100% atom economy, excellent site selectivity, high stereoselectivity, an ample substrate scope, and good compatibility of functional groups. Synthetic applications are demonstrated, and experimental studies and density functional theory calculations are conducted to gain mechanistic insight into the two transformations.

Rhodium(III)-Catalyzed C-H Bond Functionalization of 2-Pyridones with Alkynes: Switchable Alkenylation, Alkenylation/Directing Group Migration and Rollover Annulation

Cp*Rh(III)-catalyzed chelation-assisted direct C-H bond functionalization of 1-(2-pyridyl)-2-pyridones with internal alkynes that can be controlled to give three different products in good yields has been realized. Depending on the reaction conditions, solvents and additives, the reaction pathway can be switched between alkenylation, alkenylation/directing group migration and rollover annulation. These reaction manifolds allow divergent access to a variety of valuable C6-alkenylated 1-(2-pyridyl)-2-pyridones, (Z)-6-(1,2-diaryl-2-(pyridin-2-yl)vinyl)pyridin-2(1H)-ones and 10H-pyrido[1,2-a][1,8]naphthyridin-10-ones from the same starting materials. These protocols exhibit excellent regio- and stereoselectivity, broad substrate scope, and good tolerance of functional groups. A combination of experimental and computational approaches have been employed to uncover the key mechanistic features of these reactions.

Transition metal-catalyzed coupling of heterocyclic alkenes via C–H functionalization: recent trends and applications

Heterocyclic alkenes and their derivatives are an important class of reactive feedstock and valuable synthons. This review highlights the transition-metal-catalyzed coupling of heterocyclic alkenes via a C–H functionalization strategy.

Ru(ii)-catalyzed C6-selective C–H acylmethylation of pyridones using sulfoxonium ylides as carbene precursors

In this study, we describe a method using sulfoxonium ylides as carbene precursors to achieve C6-selective acylmethylation of pyridones catalyzed by a ruthenium(ii) complex. This approach featured mild reaction conditions, moderate to excellent yields, high step economy, and had excellent functional group tolerance with good site selectivity. Besides, gram-scale preparation, synthetic utility, and mechanistic studies were conducted. It offers a direct and efficient way to synthesize pyridone derivatives.

In this study, we describe a method using sulfoxonium ylides as carbene precursors to achieve C6-selective acylmethylation of pyridones catalyzed by a ruthenium(ii) complex.

Rhodium(i)-catalyzed C6-selective C-H alkenylation and polyenylation of 2-pyridones with alkenyl and conjugated polyenyl carboxylic acids

A versatile Rh(i)-catalyzed C6-selective decarbonylative C-H alkenylation of 2-pyridones with readily available, and inexpensive alkenyl carboxylic acids has been developed. This directed dehydrogenative cross-coupling reaction affords 6-alkenylated 2-pyridones that would otherwise be difficult to access using conventional C-H functionalization protocols. The reaction occurs with high efficiency and is tolerant of a broad range of functional groups. A wide scope of alkenyl carboxylic acids, including challenging conjugated polyene carboxylic acids, are amenable to this transformation and no addition of external oxidant is required. Mechanistic studies revealed that (1) Boc2O acts as the activator for the in situ transformation of the carboxylic acids into anhydrides before oxidative addition by the Rh catalyst, (2) a decarbonylation step is involved in the catalytic cycle, and (3) the C-H bond cleavage is likely the turnover-limiting step.

Metal-free regioselective direct thiolation of 2-pyridones

A highly regioselective metal-free direct C-H thiolation of 2-pyridones with disulfides or thiols has been developed. A combination of persulfate and a commercially available halide source such as LiCl, NCS or I₂ enables the successful direct incorporation of a sulfide moiety into the 5-position of pyridone under mild conditions, providing a useful and convenient approach for the preparation of a diverse array of 5-thio-substituted pyridones in moderate to excellent yields.

Recent advances and prospects in nickel-catalyzed C–H activation

Nickel-catalyzed C–H activation has become a predominant and ubiquitous research area in organic chemistry.

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.

Rhodium-catalyzed C-H functionalization of heteroarenes using indoleBX hypervalent iodine reagents

The C–H indolation of heteroarenes was realized using the benziodoxolone hypervalent iodine reagents indoleBXs. Functionalization of the C–H bond in bipyridinones and quinoline N-oxides catalyzed by a rhodium complex allowed to incorporate indole rings into aza-heteroaromatic compounds. These new transformations displayed complete regioselectivity for the C-6 position of bipyridinones and the C-8 position of quinoline N-oxides and tolerated a broad range of functionalities, such as halogens, ethers, or trifluoromethyl groups.

Ruthenium-catalyzed site-selective C-H arylation of 2-pyridones and 1-isoquinolinones

An efficient Ru(ii)-catalyzed site-selective C-H arylation of 2-pyridones and 1-isoquinolinones was achieved with boronic acids by using pyridine as a directing group. The developed protocol is general and provides rapid access to an array of C6-arylated 2-pyridones and C3-arylated 1-isoquinolinones in excellent yields. These designed arylated 2-pyridones and 1-isoquinolinones can serve as key structural motifs for accessing functionalized pyridines and isoquinolines.

A lesson for site-selective C-H functionalization on 2-pyridones: radical, organometallic, directing group and steric controls

A 2-pyridone ring is a frequently occurring subunit in natural products, biologically active compounds, and pharmaceutical targets. Thus, the selective synthesis of substituted 2-pyridone derivatives through decoration and/or formation of pyridone rings has been one of the important longstanding subjects in organic synthetic chemistry. This minireview focuses on recent advances in site-selective C-H functionalization on 2-pyridone. The reported procedures are categorized according to the site selectivity that is achieved, and the substrate scope, limitations, mechanism, and controlling factors are briefly summarized.

Ru(ii)-Catalyzed C6-selective C–H amidation of 2-pyridones

An efficient Ru-catalyzed C6 site-selective amidation of 2-pyridones has been accomplished with dioxazolone under mild conditions.

Cobalt(iii)-catalyzed site-selective C–H amidation of pyridones and isoquinolones

In this study, Cp*Co(iii)-catalyzed site-selective amidation of pyridones and isoquinolones using oxazolones as the amidation reagent is reported.