Zisong Qi

Rhodium(III)-Catalyzed Azidation and Nitration of Arenes by CH Activation†

CHOH (Table 1, entries 6–8). Gratifyingly, 2awasisolated in high yield when the reaction was conducted inacetone, even under mild conditions (508C; Table 1, entry 9).However,loweringofthereactiontemperatureorthecatalystloading led to a sluggish reaction (Table 1, entries 10 and 11).Impressively, this coupling system proceeded equally wellwithout the extrusion of air or moisture with bench-topacetone, which highlights the operational simplicity of themethod (Table 1, entry 13). The reaction also proceededsmoothly when PhI(OTs)OH (Koser reagent, 1.5 equiv) wasused in place of PIDA as an oxidant in the presence of AcOH(3 equiv; Table 1, entry 12), which appears to be an activeoxidant in the transformation, because it is readily generatedfrom the reaction of PIDA and TsOH.

Rhodium(III)-catalyzed C-C and C-O coupling of quinoline N-oxides with alkynes: combination of C-H activation with O-atom transfer.

[Cp*Rh(III)]-catalyzed C-H activation of arenes assisted by an oxidizing N-O or N-N directing group has allowed the construction of a number of hetercycles. In contrast, a polar N-O bond is well-known to undergo O-atom transfer (OAT) to alkynes. Despite the liability of N-O bonds in both C-H activation and OAT, these two important areas evolved separately. In this report, [Cp*Rh(III)] catalysts integrate both areas in an efficient redox-neutral coupling of quinoline N-oxides with alkynes to afford α-(8-quinolyl)acetophenones. In this process the N-O bond acts as both a directing group for C-H activation and as an O-atom donor.

Rhodium(III)‐Catalyzed Coupling of Arenes with 7‐Oxa/Azabenzonorbornadienes by CH Activation

Rhodium(III)-Catalyzed Coupling of Arenes with 7-Oxa/ Azabenzonorbornadienes by C H Activation Under chelation assistance, rhodium(III) complexes can catalyze the redox-neutral coupling of arenes with 7-oxabenzonorbornadienes and the oxidative coupling of arenes with 7-azabenzonorbornadienes (see scheme; Cp* = C5Me5). A sevenmembered rhodacycle containing a Rh C(alkyl) bond has been established as the key intermediate. Angewandte Chemie

Iridium- and Rhodium-Catalyzed C–H Activation and Formyl Alkynylation of Benzaldehydes under Chelation-Assistance

Mild and efficient synthesis of ynones via Ir(III)- and Rh(III)-catalyzed, chelation-assisted formyl C-H alkynylation of benzaldehydes has been achieved using hypervalent iodine-alkyne reagents. Rhodium and iridium catalysis exhibited complementary substrate scope.

Rh(III) -catalyzed hydroacylation reactions between N-sulfonyl 2-aminobenzaldehydes and olefins.

Metal-catalyzed hydroacylation of olefins represents an important atom-economic synthetic process in Cuf8ffH activation. For the first time highly efficient Rh(III) Cp*-catalyzed hydroacylation was realized in the coupling of N-sulfonyl 2-aminobenzaldehydes with both conjugated and aliphatic olefins, leading to the synthesis of various aryl ketones. Occasionally, oxidative coupling occurred when a silver(I) oxidant was used.

The Mechanism of NO Bond Cleavage in Rhodium‐Catalyzed CH Bond Functionalization of Quinoline N‐oxides with Alkynes: A Computational Study

Metal-catalyzed C-H activation not only offers important strategies to construct new bonds, it also allows the merge of important research areas. When quinoline N-oxide is used as an arene source in C-H activation studies, the N-O bond can act as a directing group as well as an O-atom donor. The newly reported density functional theory method, M11L, has been used to elucidate the mechanistic details of the coupling between quinoline N-O bond and alkynes, which results in C-H activation and O-atom transfer. The computational results indicated that the most favorable pathway involves an electrophilic deprotonation, an insertion of an acetylene group into a Rh-C bond, a reductive elimination to form an oxazinoquinolinium-coordinated Rh(I) intermediate, an oxidative addition to break the N-O bond, and a protonation reaction to regenerate the active catalyst. The regioselectivity of the reaction has also been studied by using prop-1-yn-1-ylbenzene as a model unsymmetrical substrate. Theoretical calculations suggested that 1-phenyl-2-quinolinylpropanone would be the major product because of better conjugation between the phenyl group and enolate moiety in the corresponding transition state of the regioselectivity-determining step. These calculated data are consistent with the experimental observations.

Ruthenium(II)‐Catalyzed C−H Activation of Imidamides and Divergent Couplings with Diazo Compounds: Substrate‐Controlled Synthesis of Indoles and 3H‐Indoles

Indoles are an important structural motif that is commonly found in biologically active molecules. In this work, conditions for divergent couplings between imidamides and acceptor-acceptor diazo compounds were developed that afforded NH indoles and 3H-indoles under ruthenium catalysis. The coupling of α-diazoketoesters afforded NH indoles by cleavage of the C(N2 )-C(acyl) bond whereas α-diazomalonates gave 3H-indoles by C-N bond cleavage. This reaction constitutes the first intermolecular coupling of diazo substrates with arenes by ruthenium-catalyzed C-H activation.

Rhodium-Catalyzed CS and CN Functionalization of Arenes: Combination of CH Activation and Hypervalent Iodine Chemistry

Rhodium-catalyzed sulfonylation, thioetherification, thiocyanation, and other heterofunctionalizations of arenes bearing a heterocyclic directing group have been realized. The reaction proceeds by initial Rh(III) -catalyzed C-H hyperiodination of arene at room temperature followed by uncatalyzed nucleophilic functionalization. A diaryliodonium salt is isolated as an intermediate, which represents umpolung of the arene substrate, in contrast to previous studies that suggested umpolung of the coupling partner.

Nitrone Directing Groups in Rhodium(III)‐Catalyzed C−H Activation of Arenes: 1,3‐Dipoles versus Traceless Directing Groups

Functionalizable directing groups (DGs) are highly desirable in C-H activation chemistry. The nitrone DGs are explored in rhodium(III)-catalyzed C-H activation of arenes and couplings with cyclopropenones. N-tert-butyl nitrones bearing a small ortho substituent coupled to afford 1-naphthols, where the nitrone acts as a traceless DG. In contrast, coupling of N-tert-butyl nitrones bearing a bulky ortho group follows a C-H acylation/[3+2] dipolar addition pathway to give bicyclics. The coupling of N-arylnitrones follows the same acylation/[3+2] addition process but delivers different bicyclics.

Rh(III)-catalyzed coupling of nitrones with alkynes for the synthesis of indolines

Abstract Rh-catalyzed redox-neutral coupling between N-aryl nitrones and alkynes has been achieved under relatively mild conditions. The reaction proceeded via C–H activation at the N-aryl ring with subsequent O-atom transfer, affording trisubstituted indolines in good chemoselectivity and moderate to good diasteroselectivity.