Manganese/bipyridine-catalyzed non-directed C(sp³)–H bromination using NBS and TMSN₃

• Kumar Sneh,
• Takeru Torigoe and
• Yoichiro Kuninobu

Beilstein J. Org. Chem. 2021, 17, 885–890, doi:10.3762/bjoc.17.74

• ]. The regioselectivity is controlled by the formation of a six-membered cyclic intermediate. Directing-group-assisted C(sp3)−H halogenation reactions are efficient for promoting regioselective C(sp3)−H halogenations (Scheme 1c) [24][25][26][27][28]. In these reactions, the C(sp3)–H bond at the β

Recent developments in enantioselective photocatalysis

• Callum Prentice,
• James Morrisson,
• Andrew D. Smith and
• Eli Zysman-Colman

Beilstein J. Org. Chem. 2020, 16, 2363–2441, doi:10.3762/bjoc.16.197

• amount of background reaction and the more rigid xanthone structure acting as a superior stereo-directing group. Further variation to a thioxanthone unit 185, which has a lower triplet energy (ET = 2.7 eV), was used to investigate a similar [2 + 2] photocycloaddition, giving comparable yields and

Photosensitized direct C–H fluorination and trifluoromethylation in organic synthesis

• Shahboz Yakubov and
• Joshua P. Barham

Beilstein J. Org. Chem. 2020, 16, 2151–2192, doi:10.3762/bjoc.16.183

• process and could not be ruled out (Scheme 20). 3.3 Directing-group-guided C(sp3)–H fluorination 3.3.1 Ketones as directing groups: Related to the curious near-exclusive C2 selectivity of 1-phenylbutan-1-one as reported by Tan and co-workers [198], Lectka and co-workers reported highly selective

• benzil (T1 = 53.7 kcal⋅mol−1, Scheme 23). Control reactions revealed that Selectfluor® as the fluorinating agent gave the highest product yield, and light was essential for the reaction. To demonstrate the importance of the ketone directing group, ethylbenzene was employed under the same reaction

• . The authors demonstrated that the transition state for Selectfluor® undergoing HAT at this position (see TS1) was more kinetically accessible, despite the bond dissociate free energies (BDFEs) suggesting C3 functionalization (Scheme 27). 3.4 Directing-group-guided benzylic C–H fluorination In another

When metal-catalyzed C–H functionalization meets visible-light photocatalysis

• Lucas Guillemard and
• Joanna Wencel-Delord

Beilstein J. Org. Chem. 2020, 16, 1754–1804, doi:10.3762/bjoc.16.147

• metal catalyst X2M into an aromatic C–H bond of a substrate (generally facilitated by the presence of a directing group (DG)), delivers a metal–aryl complex. Coordination and subsequent insertion of an alkene into the M–aryl bond then provides the desired coupling product after β-hydride elimination

Photocatalytic deaminative benzylation and alkylation of tetrahydroisoquinolines with N-alkylpyrydinium salts

• David Schönbauer,
• Carlo Sambiagio,
• Timothy Noël and
• Michael Schnürch

Beilstein J. Org. Chem. 2020, 16, 809–817, doi:10.3762/bjoc.16.74

• address a single C–H bond selectively without compromising the others. To circumvent this problem, directing groups can be installed, which guide a metal catalyst to a specific C–H bond [4][5]. In case the directing group is not needed in the final product, this strategy accounts for additional reaction

• steps for the installation and removal of the directing group. However, there is also a good number of substrates containing C–H bonds that are inherently more reactive than others in the same molecule, and in such cases a selective C–H functionalization can be achieved in the absence of any directing

• group [2][6][7]. For example, in tetrahydroisoquinolines (THIQs) the benzylic C1-position is significantly more reactive compared to the others and its selective functionalization has been reported [8]. The THIQ moiety is of special interest due to its presence in several different natural products [9

Recent advances in Cu-catalyzed C(sp³)–Si and C(sp³)–B bond formation

• Balaram S. Takale,
• Ruchita R. Thakore,
• Elham Etemadi-Davan and
• Bruce H. Lipshutz

Beilstein J. Org. Chem. 2020, 16, 691–737, doi:10.3762/bjoc.16.67

• from the directing group. This was attributed to the importance of both the negative charge at the carbon and the forming C–Cu bond being developed in the transition state, which is stabilized by the positive charge on the carbon bearing the directing group. Later, in 2017, the same group investigated

Copper-catalyzed remote C–H arylation of polycyclic aromatic hydrocarbons (PAHs)

• Anping Luo,
• Min Zhang,
• Zhangyi Fu,
• Jingbo Lan,
• Di Wu and
• Jingsong You

Beilstein J. Org. Chem. 2020, 16, 530–536, doi:10.3762/bjoc.16.49

• naphthalene rings were obtained in good yields (Scheme 3, 4p and 4q). A keto carbonyl group was also proved to be a suitable directing group, affording the corresponding arylation products in moderate yields (Scheme 3, 4r and 4s). Considering that Cu(0), Cu(I) and Cu(II) all could catalyze this C−H arylation

Room-temperature Pd/Ag direct arylation enabled by a radical pathway

• Amy L. Mayhugh and
• Christine K. Luscombe

Beilstein J. Org. Chem. 2020, 16, 384–390, doi:10.3762/bjoc.16.36

• directly influences the quality and electronic performance of the material [7][9]. More specific to this work, the direct arylation method should be catalytic, directing-group free and at room temperature; a handful of such methods have been reported [10][11][12][13][14]. One such method, an indole

• . There are limited examples across the aryl C–H functionalization literature indicating a transition metal-catalyzed radical process, limited largely to cobalt catalysis [31][32]. While there are several reports of palladium-catalyzed systems for room-temperature direct arylation (i.e., no directing

• group, transition-metal catalyzed), a radical mechanism has not been previously discussed. Some of these reports indicate a marked difference in selectivity between elevated and ambient temperatures, which we found may be due to a change in mechanism (Supporting Information File 1, Table S1, Figure S1

Synthesis of 3-alkenylindoles through regioselective C–H alkenylation of indoles by a ruthenium nanocatalyst

• Abhijit Paul,
• Debnath Chatterjee,
• Srirupa Banerjee and
• Somnath Yadav

Beilstein J. Org. Chem. 2020, 16, 140–148, doi:10.3762/bjoc.16.16

• explored, with some favourable results [35][36][37][38][39][40]. Other very important aspects of Ru catalysts are mechanistic aspects, which has also favoured their exploration for directing group-assisted C–H activation reactions [40]. With respect to non-directed Ru nanoparticle-catalysed reactions

Combining the Ugi-azide multicomponent reaction and rhodium(III)-catalyzed annulation for the synthesis of tetrazole-isoquinolone/pyridone hybrids

• Gerardo M. Ojeda,
• Prabhat Ranjan,
• Pavel Fedoseev,
• Lisandra Amable,
• Upendra K. Sharma,
• Daniel G. Rivera and
• Erik V. Van der Eycken

Beilstein J. Org. Chem. 2019, 15, 2447–2457, doi:10.3762/bjoc.15.237

• rhodium catalyst to promote C(sp2)–H activation in the presence of a suitable directing group. The Ugi-azide reaction provides broad molecular diversity and enables the introduction of the tetrazole moiety, which may further assist the catalytic reaction by coordinating the metal center. The scope of the

• regioselectivity, can be overcome when a suitable directing group assists the reaction [46][47]. Traditional directing groups for C–H activation include amide, hydroxamide, carboxylate, pyridyl, quinolyl, carbonyl, ether, hydroxy, oxazolinyl and cyano [47]. For example, Ackermann et al. reported a Ru(II)-catalyzed

• synthesis of isoquinolones using an N-methoxyamide as directing group for the ortho-position and alkynyl bromide to achieve the regioselective cyclization (Scheme 1B) [31]. In parallel, our group has developed Ru(II) and Rh(III)-catalyzed inter- and intramolecular annulations of aromatic rings with alkynes

Recent advances in transition-metal-catalyzed incorporation of fluorine-containing groups

• Xiaowei Li,
• Xiaolin Shi,
• Xiangqian Li and
• Dayong Shi

Beilstein J. Org. Chem. 2019, 15, 2213–2270, doi:10.3762/bjoc.15.218

• , Xu’s group [49] presented the palladium-catalyzed direct fluorination of unactivated C(sp3)–H bonds at the β-position of carboxylic acids with NFSI (Scheme 12). To achieve this transformation, an 8-aminoquinoline-derived auxiliary was developed as an effective directing group for the activation of the

• substrates was reported by Yu and co-workers (Scheme 13) [50]. Enantioenriched benzyl fluorides were obtained by aid of a chiral α-amino amide transient directing group (TDG). Notably, the condensation of this bulky amino amide with the aldehyde led to control of the stereochemistry of the C–H insertion step

• functionalization reactions. Aryl C–H fluorination with various directing groups: With Pd(OTf)2(MeCN)4 and N-methyl-2-pyrrolidinone (NMP) used as the catalyst system, in 2011 the Yu group [57] described the ortho-fluorination of benzoic acid substrates with a directing group, an electron-deficient removable acidic

Attempted synthesis of a meta-metalated calix[4]arene

• Christopher D. Jurisch and
• Gareth E. Arnott

Beilstein J. Org. Chem. 2019, 15, 1996–2002, doi:10.3762/bjoc.15.195

• whose chiral nature is a result of selective substitution on the calix[4]arene by various functional groups [9]. In particular, we have focused on the less-studied meta-substituted derivatives [10] whose inherent chirality is more commonly introduced by a suitable directing group [11][12][13][14][15

• this using a pyridyl sulfoxide directing group and palladium as the metal, but in this case the palladium caused a double C–H activation and formed an impressive bridge to the adjacent calix[4]arene aromatic ring [14]. The question for us was whether this bridge formation was a general principle or

• ) and rhodium(III) complexes underwent spontaneous, chemoselective cyclometalation via C–H bond activation of the N-bound phenyl group (see Figure 2) [19]. Incorporation of a mesoionic carbene directing group onto the upper rim of a calix[4]arene therefore offered potential for a new route to calix[4

Recent advances on the transition-metal-catalyzed synthesis of imidazopyridines: an updated coverage

• Gagandeep Kour Reen,
• Ashok Kumar and
• Pratibha Sharma

Beilstein J. Org. Chem. 2019, 15, 1612–1704, doi:10.3762/bjoc.15.165

A novel and efficient synthesis of phenanthrene derivatives via palladium/norbornadiene-catalyzed domino one-pot reaction

• Yue Zhong,
• Wen-Yu Wu,
• Shao-Peng Yu,
• Tian-Yuan Fan,
• Hai-Tao Yu,
• Nian-Guang Li,
• Zhi-Hao Shi,
• Yu-Ping Tang and
• Jin-Ao Duan

Beilstein J. Org. Chem. 2019, 15, 291–298, doi:10.3762/bjoc.15.26

• scope and relatively low reaction efficiency. Very recently, Fuk Yee Kwong and co-workers (Scheme 1d) developed a straightforward one pot π-extension method using norbornadiene instead of norbornene as directing group to afford the phenanthrenes [11]. However, ortho-haloaryl carboxylic acids employed in

Cobalt- and rhodium-catalyzed carboxylation using carbon dioxide as the C1 source

• Tetsuaki Fujihara and
• Yasushi Tsuji

Beilstein J. Org. Chem. 2018, 14, 2435–2460, doi:10.3762/bjoc.14.221

• AlMe2(OMe), and methyl–Rh(I) A is regenerated. Later, Iwasawa et al. achieved the Rh-catalyzed direct carboxylation of arenes without any directing group (Scheme 30) [60][61]. The reactions proceeded using a catalytic amount of Rh complex bearing dcype (dcype = 1,2-bis(dicyclohexylphosphino)ethane) as

A challenging redox neutral Cp*Co(III)-catalysed alkylation of acetanilides with 3-buten-2-one: synthesis and key insights into the mechanism through DFT calculations

• Andrew Kenny,
• Alba Pisarello,
• Arron Bird,
• Paula G. Chirila,
• Alex Hamilton and
• Christopher J. Whiteoak

Beilstein J. Org. Chem. 2018, 14, 2366–2374, doi:10.3762/bjoc.14.212

• exploited as a common directing group [13] and countless pharmaceutical and agrochemical compounds contain these moieties. If the amide is reversed in the benzamide, the resulting compounds are acetanilides, which have been utilised far less as substrates in C–H functionalisation protocols [13], although a

Catalyst-free synthesis of 4-acyl-NH-1,2,3-triazoles by water-mediated cycloaddition reactions of enaminones and tosyl azide

• Lu Yang,
• Yuwei Wu,
• Yiming Yang,
• Chengping Wen and
• Jie-Ping Wan

Beilstein J. Org. Chem. 2018, 14, 2348–2353, doi:10.3762/bjoc.14.210

• is a heterocyclic moiety showing exceptionally broad and important applications as privileged structure in the discovery of biologically functional scaffolds, organic materials preparation, as directing group in transition-metal-catalyzed transformations and as key building block in the synthesis of

Hydroarylations by cobalt-catalyzed C–H activation

• Rajagopal Santhoshkumar and
• Chien-Hong Cheng

Beilstein J. Org. Chem. 2018, 14, 2266–2288, doi:10.3762/bjoc.14.202

• synthesis owing to the necessity of green chemistry for the modern universe [1][2][3]. In this context, catalytic C–H functionalization has been acknowledged as an atom- and step-economical process [4][5][6]. A wide range of transition metal-catalyzed non-directed or directing group assisted C–H activation

• activation. In 1941, Kharasch and Fields applied a cobalt salt as the catalyst for the homocoupling of Grignard reagents [28]. After 15 years, Murahashi discovered a cobalt-catalyzed chelation-assisted ortho C–H carbonylation of azobenzene and imines as the preliminary example of directing group assisted C–H

• pyridine as an additive (Scheme 6) [46]. Similarly, benzothiazoles also efficiently underwent hydroheteroarylation by using suitable ligands [47]. The reaction was successfully extended to indoles and benzimidazoles 7 bearing a removable 2-pyrimidyl (2-pym) directing group with alkynes at ambient

Cobalt-catalyzed peri-selective alkoxylation of 1-naphthylamine derivatives

• Jiao-Na Han,
• Cong Du,
• Xinju Zhu,
• Zheng-Long Wang,
• Yue Zhu,
• Zhao-Yang Chu,
• Jun-Long Niu and
• Mao-Ping Song

Beilstein J. Org. Chem. 2018, 14, 2090–2097, doi:10.3762/bjoc.14.183

• system. Moreover, a series of biologically relevant fluorine-aryl ethers were easily obtained under mild reaction conditions after the removal of the directing group. Keywords: alkoxylation; C–H activation; cobalt catalysis; 1-naphthylamines; secondary alcohols; Introduction Aryl ethers are common

• re-oxidization. The current alkoxylation methodology also exhibited potential applications. When treated with NaOH at 80 °C, the picolinic acid directing group could be easily removed, and the corresponding 4 was obtained in 88% yield (Scheme 5). Conclusion In summary, a cobalt-catalyzed C8

• , trifluoroethanol, and 3-fluoropropanol etc.) shows that this strategy is highly valuable for the syntheses of biologically relevant fluorine-aryl ethers after the removal of the directing group. The above studies of the mechanism indicate that this reaction undergoes a SET process and cobalt salt is the actual

Recent applications of chiral calixarenes in asymmetric catalysis

• Mustafa Durmaz,
• Erkan Halay and
• Selahattin Bozkurt

Beilstein J. Org. Chem. 2018, 14, 1389–1412, doi:10.3762/bjoc.14.117

• anion with the two hydroxy groups of the calixarene ligand to selectively direct the nucleophile towards one carbon atom of the π-allyl intermediate in the presence of potassium cations. In 2009 and 2010, Arnott et al. utilized a chiral isopropyloxazoline as an ortho-lithiation directing group in order

Atom-economical group-transfer reactions with hypervalent iodine compounds

• Andreas Boelke,
• Peter Finkbeiner and
• Boris J. Nachtsheim

Beilstein J. Org. Chem. 2018, 14, 1263–1280, doi:10.3762/bjoc.14.108

• reaction sequence proceeds under metal-free conditions, the selective transfer of the more electron-deficient aryl group of the unsymmetrical iodonium salts 1 is achieved. The N-arylated heterocycle NAr1 then serves as the directing group in the following ortho-C–H functionalisation with the iodoarene as

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

• Erwann Grenet,
• Ashis Das,
• Paola Caramenti and
• Jérôme Waser

Beilstein J. Org. Chem. 2018, 14, 1208–1214, doi:10.3762/bjoc.14.102

• procedures have been described for the modification of pyridinones to introduce other substituents, especially based on highly efficient C–H functionalization methods [10]. Very recently, several research groups have selectively functionalized the C-6 C–H bond by using a 2-pyridyl directing group on the

• unique reactivity of the benziodoxolone hypervalent iodine reagent. The scope and limitations of the reaction were then studied (Scheme 2). The diversification of the directing group was examined first. The unsubstituted pyridine group led to the formation of product 7a in 86% yield. The electron-rich 5

• not be used as directing group (5e), confirming what has already been reported by others authors [13]. Quinoline 7f was obtained in 79% yield. Concerning the pyridinone core, both an electron-donating methyl group and electron-withdrawing trifluoromethyl and fluoro groups (7g–i) were well tolerated in

Selective carboxylation of reactive benzylic C–H bonds by a hypervalent iodine(III)/inorganic bromide oxidation system

• Toshifumi Dohi,
• Shohei Ueda,
• Kosuke Iwasaki,
• Yusuke Tsunoda,
• Koji Morimoto and
• Yasuyuki Kita

Beilstein J. Org. Chem. 2018, 14, 1087–1094, doi:10.3762/bjoc.14.94

• benzyl esters from non-functionalized aromatic hydrocarbons, and thus has attracted continuous interest in the community of synthetic chemists. Significant advances for realizing such transformations have been made over the last decade, however, strategies that do not utilize a directing group to

Cobalt-catalyzed directed C–H alkenylation of pivalophenone N–H imine with alkenyl phosphates

• Wengang Xu and
• Naohiko Yoshikai

Beilstein J. Org. Chem. 2018, 14, 709–715, doi:10.3762/bjoc.14.60

• , directing group-assisted arene C–H activation reactions have been extensively studied over the last few decades to offer a broad array of atom and step-economical methods for the synthesis of functionalized aromatic compounds [1][2][3][4][5][6]. Among various C–H transformations, the introduction of alkenyl

• -directed arene C–H alkenylation reaction with alkenyl phosphates using a different cobalt–NHC catalyst (Scheme 1b) [28]. Meanwhile, we have also demonstrated that pivaloyl N–H imine serves as a powerful directing group for cobalt-catalyzed arene C–H functionalization reactions such as the hydroarylation of

• previously reported cobalt-catalyzed ortho C–H functionalization reactions [22][23][28][29], this regioselectivity may be ascribed to the role of the oxygen or fluorine atom as a secondary directing group to have an electrostatic interaction with the cobalt center during the C–H activation. For compound 3ja

Synthesis and stability of strongly acidic benzamide derivatives

• Frederik Diness,
• Niels J. Bjerrum and
• Mikael Begtrup

Beilstein J. Org. Chem. 2018, 14, 523–530, doi:10.3762/bjoc.14.38

• ][32][33]. Finally, two examples of syntheses via palladium-catalyzed carbonylation of trifluoromethanesulfonamide (1) have been reported [34][35]. The N-triflylbenzamides have only been explored as substrates in a few reactions. A recent report describes using N-triflylbenzamide as a directing group