Cobalt(III)-catalyzed synthesis of indazoles and furans by C-H bond functionalization/addition/cyclization cascades

Cobalt-Catalyzed Cyclization of N-Methoxy Benzamides with Alkynes using an Internal Oxidant through C-H/N-O Bond Activation

The cyclization of substituted N-methoxy benzamides with alkynes in the presence of an easily affordable cobalt complex and NaOAc provides isoquinolone derivatives in good to excellent yields. The cyclization reaction is compatible with a range of functional group-substituted benzamides, as well as ester- and alcohol-substituted alkynes. The cobalt complex [Co(III) Cp*(OR)2 ] (R=Me or Ac) serves as an efficient catalyst for the cyclization reaction. Later, isoquinolone derivatives were converted into 1-chloro and 1-bromo substituted isoquinoline derivatives in excellent yields in the presence of POCl3 or PBr3 .

Cationic Cobalt(III) Catalyzed Indole Synthesis: The Regioselective Intermolecular Cyclization of N-Nitrosoanilines and Alkynes

The unique regioselectivity and reactivity of cobalt(III) in the direct cyclization of N-nitrosoanilines with alkynes for the expedient synthesis of N-substituted indoles is demonstrated. In the presence of a cobalt(III) catalyst, high regioselectivity was observed when using unsymmetrical meta-substituted N-nitrosoanilines. Moreover, internal alkynes bearing electron-deficient groups, which are almost unreactive in the [Cp*Rh(III)]-catalyzed system, display good reactivity in this transformation.

Cobalt-Catalyzed, Aminoquinoline-Directed Functionalization of Phosphinic Amide sp2 C-H Bonds

In this paper, we introduce arylphosphinic acid aminoquinoline amides as competent substrates for cobalt-catalyzed sp² C-H bond functionalization. Specifically, the feasibility of their coupling with alkynes, alkenes, and allyl pivalate has been demonstrated. Reactions are catalyzed by simple Co(NO₃)₂ hydrate in ethanol or mixed dioxane/tBuOH solvent in the presence of Mn(OAc)₃·2H₂O additive, sodium pivalate, or acetate base and use oxygen from the air as an oxidant. Directing group removal affords ortho-functionalized P,P-diarylphosphinic acids.

Transmetallation from CCC-NHC pincer Zr complexes in the synthesis of air-stable CCC-NHC pincer Co(iii) complexes and initial hydroboration trials

Development of CCC-NHC pincer Co complexes via transmetalation from Zr is reported. Formation of these air-stable Co(iii) complexes was achieved through use of a CoCl2 or Co(acac)3in situ or with a discrete CCC-NHC pincer Zr transmetallating agent. Preliminary activity in the hydroboration of styrene is reported. This facile methodology will further the development of CCC-NHC pincer first-row transition metal complexes.

Synthesis of isoquinolines via Rh-catalyzed C–H activation/C–N cyclization with diazodiesters or diazoketoesters as a C2 source

Synthesis of isoquinolines based on efficient C–C and C–N bond formation through Rh(iii)-catalyzed C–H functionalization and subsequent intramolecular cyclization is reported. Diazodiesters serving as a C₂ source in the newly formed heterocycles are first demonstrated.

Cobalt(iii)-catalyzed alkenylation of arenes and 6-arylpurines with terminal alkynes: efficient access to functional dyes

A method for cobalt(iii)-catalyzed alkenylation of arenes and 6-arylpurines has been developed. This reaction takes place under mild conditions with only equivalent terminal alkynes in high yields. A mitochondria-targeted imaging dye was simply prepared through this method.

Low-valent cobalt-catalyzed C–H allylation

A mild C–H allylation promoted by a cobalt salt combined with a Grignard reagent is described.

Cobalt(iii)-catalyzed C–H halogenation of 6-arylpurines: facile entry into arylated, sulfenylated and alkoxylated 6-arylpurines

Cp*Co(iii)-catalyzed C–H halogenation of 6-arylpurines has been reported under mild conditions and this protocol was further applied for the synthesis of arylated, sulfenylated and alkoxylated purine analogues.

The palladium and copper contrast: a twist to products of different chemotypes and altered mechanistic pathways

Unprecedented Pd–Ag/Cu–Ag nanocluster-catalyst switch leads to a phenazine/azoarene twist for non-radical mode C–H activation vs. radical mode N–N self-coupling of anilines.

Cobalt(iii)-catalyzed annulation of esters and alkynes: a facile route to indenones

An efficient protocol for the synthesis of indenones has been developed via the annulation of benzoic esters and internal alkynes by exploiting the cobalt catalyst.

Cobalt-catalyzed synthesis of quinolines from the redox-neutral annulation of anilides and alkynes

A new method of cobalt-catalyzed annulation of anilides and internal alkynes for the efficient synthesis of quinoline scaffolds was developed.

Cobalt(iii)-catalyzed synthesis of pyrroles from enamides and alkynes

An efficient and regioselective cobalt-catalyzed synthesis of multi-substituted pyrroles is reported by the use of readily available enamides and alkynes.

An efficient synthesis of 1-arylindazole-3-carboxamides using nitrile imines, isocyanides and 2-hydroxymethylbenzoic acid, followed by a chemoselective Buchwald–Hartwig intramolecular cyclization

A convergent, efficient and regio-selective two-step synthesis of pharmaceutically relevant 1-arylindazole-3-carboxamides through an isocyanide-based reaction and a Buchwald–Hartwig cyclization.

Cp*Co(iii)-catalyzed, N–N bond-based redox-neutral synthesis of isoquinolines

We report herein a redox-neutral Cp*Co(iii)-catalyzed cyclization of acetophenone N-Boc hydrazones with alkynes for streamlined synthesis of isoquinolines, accomplished via formation of a C–C and a C–N bond along with N–N bond cleavage.

Cobalt(iii) catalyzed C-8 selective C–H and C–O coupling of quinoline N-oxide with internal alkynes via C–H activation and oxygen atom transfer

An efficient, scalable, atom-economical, regio-selective air stable Cp*Co(iii) catalyzed C–H and C–O coupling via a C–H activation/oxygen atom transfer reaction of quinoline N-oxide and an internal alkyne is reported.

Cp*Co(iii)-catalyzed vinylic C–H bond activation under mild conditions: expedient pyrrole synthesis via (3 + 2) annulation of enamides and alkynes

Cobalt(iii)-catalyzed (3 + 2) oxidative annulation of enamides and alkynes for the synthesis of pyrroles has been developed under mild conditions and simple tuning of reaction temperature lead to the formation of bothN-Ac andN-H pyrroles under an exactly identical catalytic system.

Cobalt(iii)-catalyzed efficient synthesis of indenones through carboannulation of benzoates and alkynes

Cobalt(iii)-catalyzed C–H activation of simple benzoate esters has been achieved, and redox-neutral annulative coupling with internal alkynes allowed efficient synthesis of indenones.

Regioselective Ir(iii)-catalyzed C–H alkynylation directed by 7-azaindoles

Herein we report a novel iridium(iii)-catalyzed ortho-mono-alkynylation of 7-azaindoles. The reactions proceeded highly efficiently and selectively under mild conditions over a broad range of substrates with excellent functional group tolerance.

Mechanistic insights into cobalt(ii/iii)-catalyzed C-H oxidation: a combined theoretical and experimental study

Cobalt-mediated C-H functionalization has been the subject of extensive interest in synthetic chemistry, but the mechanisms of many of these reactions (such as the cobalt-catalyzed C-H oxidation) are poorly understood. In this paper, possible mechanisms including single electron transfer (SET) and the concerted metalation-deprotonation (CMD) pathways of the CoII/CoIII-catalyzed alkoxylation of C(sp2)-H bonds have been investigated for the first time using the DFT method. CoII(OAc)2 has been employed as an efficient catalyst in our previous experimental study, but the calculated results unexpectedly indicated that the intermolecular SET pathway with CoIII as the actual catalyst might be the most favorable pathway. To support this theoretical prediction, we have explored a series of Cp*CoIII(CO)I2 catalyzed C(sp2)-H bond alkoxylations, extending the application of cobalt-catalyzed functionalization of C-H bonds. Furthermore, kinetic isotope effect (KIE) data, electron paramagnetic resonance (EPR) data, and TEMPO inhibition experiments also support the SET mechanism in both the Co-catalyzed alkoxylation reactions. Thus, this work should support an understanding of the possible mechanisms of the CoII/CoIII-catalyzed C(sp2)-H functionalization, and also provide an example of the rational design of novel catalytic reactions guided by theoretical calculations.