Cobalt-Catalyzed Arylative Cyclization of Acetylenic Esters and Ketones with Arylzinc Reagents through 1,4-Cobalt Migration

1,4-Migrations of organopalladium and organorhodium species have been utilized for the development of various cascade reactions involving remote C–H bond activation. Recently, we reported a cobalt-catalyzed migratory arylzincation reaction of an alkyne that features alkenyl-to-aryl 1,4-cobalt migration and cobalt-to-zinc transmetalation as key steps. We report herein that the cobalt/arylzinc combination can also promote a cascade arylative cyclization reaction of alkynes bearing pendant ester or ketone moieties to afford benzo-fused cyclic ketone or alcohol products, respectively. The reaction is considered to proceed through insertion of the alkyne into an arylcobalt species, 1,4-cobalt migration, and intramolecular organocobalt addition to the carbonyl group. The present cobalt/arylzinc system may not only serve as an alternative to previously reported rhodium/arylboron and iridium/arylboron systems but also complement their scopes in the arylative cyclization

Cobalt-Catalyzed Arylative Cyclization of Acetylenic Esters and Ketones with Arylzinc Reagents through 1,4-Cobalt Migration

1,4-Migrations of organopalladium and organorhodium species have been utilized for the development of various cascade reactions involving remote C–H bond activation. Recently, we reported a cobalt-catalyzed migratory arylzincation reaction of an alkyne that features alkenyl-to-aryl 1,4-cobalt migration and cobalt-to-zinc transmetalation as key steps. We report herein that the cobalt/arylzinc combination can also promote a cascade arylative cyclization reaction of alkynes bearing pendant ester or ketone moieties to afford benzo-fused cyclic ketone or alcohol products, respectively. The reaction is considered to proceed through insertion of the alkyne into an arylcobalt species, 1,4-cobalt migration, and intramolecular organocobalt addition to the carbonyl group. The present cobalt/arylzinc system may not only serve as an alternative to previously reported rhodium/arylboron and iridium/arylboron systems but also complement their scopes in the arylative cyclization

Phenanthrene Synthesis via Chromium-Catalyzed Annulation of 2‑Biaryl Grignard Reagents and Alkynes

A chromium/2,2′-bipyridine-catalyzed annulation reaction of 2-biarylmagnesium reagents with alkynes is reported. The reaction is applicable to a variety of aryl- and/or alkyl-substituted internal alkynes as well as 2-biaryl and related Grignard reagents, thus affording phenanthrene derivatives in moderate to good yields. The reaction proceeds at the expense of excess alkyne as a hydrogen acceptor and thus does not need an external oxidant. Deuterium-labeling experiments shed light on the reaction mechanism, which likely involves multiple intramolecular C–H activation processes on chromium

Cobalt-Catalyzed, N–H Imine-Directed Hydroarylation of Styrenes

A cobalt-catalyzed, N–H imine-directed hydroarylation reaction of styrenes is reported. A variety of diaryl and aryl alkyl N–H imines participated in the reaction to afford the corresponding branched adducts in good yield and regioselectivity. Interestingly, unsymmetrical diaryl imines with modest electronic biases reacted regioselectively at one of the aryl rings. Furthermore, the branched selectivity was reversed for substrates bearing a secondary directing group or a bulky pivaloyl N–H imine

Mechanisms of Nucleophilic Organocopper(I) Reactions

Mechanisms of Nucleophilic Organocopper(I) Reaction

Mechanisms of Nucleophilic Organocopper(I) Reactions

Mechanisms of Nucleophilic Organocopper(I) Reaction

Cobalt-Catalyzed Ortho Alkylation of Aromatic Imines with Primary and Secondary Alkyl Halides

We report here cobalt–N-heterocyclic carbene catalytic systems for the ortho alkylation of aromatic imines with alkyl chlorides and bromides, which allows the introduction of a variety of primary and secondary alkyl groups at room temperature. The stereochemical outcomes of the reaction of secondary alkyl halides suggest that the present reaction involves single-electron transfer from a cobalt species to the alkyl halide to generate the corresponding alkyl radical. A cycloalkylated product obtained by this method can be transformed into unique spirocycles through manipulation of the directing and cycloalkyl groups

Rhodium(III)-Catalyzed Directed <i>peri</i>-C–H Alkenylation of Anthracene Derivatives

Rhodium­(III)-catalyzed oxidative coupling reactions of anthracene-9-carboxylic acid derivatives with electron-deficient olefins are reported. A cationic rhodium­(III) catalyst, in combination with a copper­(II) oxidant, promotes selective monoalkenylation of anthracene-9-carboxamide, affording 1-alkenyl­anthracene-9-carbox­amide in moderate to good yields. A similar catalytic system also promotes the reaction of anthracene-9-carboxylic acid and an electron-deficient olefin, which affords a lactone derivative through C–H alkenylation followed by intramolecular conjugate addition

Modular Pyridine Synthesis from Oximes and Enals through Synergistic Copper/Iminium Catalysis

We describe here a [3+3]-type condensation reaction of <i>O</i>-acetyl ketoximes and α,β-unsaturated aldehydes that is synergistically catalyzed by a copper­(I) salt and a secondary ammonium salt (or amine). This redox-neutral reaction allows modular synthesis of a variety of substituted pyridines under mild conditions with tolerance of a broad range of functional groups. The reaction is driven by a merger of iminium catalysis and redox activity of the copper catalyst, which would initially reduce the oxime N–O bond to generate a nucleophilic copper­(II) enamide and later oxidize a dihydropyridine intermediate to the pyridine product

Phenanthridine Synthesis through Iron-Catalyzed Intramolecular <i>N</i>‑Arylation of <i>O</i>‑Acetyl Oxime

<i>O</i>-Acetyl oximes derived from 2′-arylacetophenones undergo N–O bond cleavage/intramolecular <i>N</i>-arylation in the presence of a catalytic amount of iron(III) acetylacetonate in acetic acid. In combination with the conventional cross-coupling or directed C–H arylation, the reaction offers a convenient route to substituted phenanthridines