Palladium-Catalyzed Ortho-Arylation of O-Phenylcarbamates with Simple Arenes and Sodium Persulfate

Abstract

By palladium catalysis, the C-H bond functionalization of O-phenylcarbamates with simple arenes has been achieved using sodium persulfate (Na(2)S(2)O(8)), an inexpensive, easy-to-handle, and environmentally friendly oxidant. This oxidative cross-coupling involves two aromatic C-H bonds undergoing concomitant oxidation to furnish a new biaryl C-C linkage. Excellent reaction efficiencies and regioselectivities were observed with a range of electron-rich, electron-neutral, and electron-deficient arenes; minimal homocoupling of either component was observed. When two reactive C-H bonds are present on the O-phenylcarbamate, selective diarylation can be achieved via quadruple C-H bond functionalization. This work represents a rare example of using O-carbamates as directing groups for catalytic C-H bond activation. Additionally, a palladacycle obtained from an O-phenylcarbamate was prepared and fully characterized. This trifluoroacetate-bridged bimetallic Pd complex exhibits clean conversion to the ortho-arylation product upon treatment with simple arenes. The addition of trifluoroacetic acid (TFA) was found to be critical for successful cyclopalladation of O-phenylcarbamates. We propose this oxidative arene cross-coupling occurs via two discrete C-H bond activations, namely cyclopalladation and electrophilic metalation, within a Pd(0/II) catalytic cycle.

Mechanistic Studies of Pd‐Catalyzed Regioselective Aryl CH Bond Functionalization with Strained Alkenes: Origin of Regioselectivity

“…In addition, the Pd1ÀPd2 bond 2.86 is in a range of typical Pd À Pd bond lengths for known palladium dimers, 2.7-3.0 . [14,21] Summary of mechanistic studies and proposed mechanism of benzocyclobutene formation: Our NMR studies to identify the palladium intermediates in the reactions of aryl halides with norbornene, together with kinetic studies for each reaction parameter, have shown that the reaction occurs through the Pd-1, Pd-3, Pd-4, and Pd-5 intermediates as shown in Schemes 4 and 8. To establish a correlation between the reactions using 2-pyrrole substituted phenyl iodide 4 a and phenyl iodide, 31 P NMR data of 4 a under modified biphasic conditions (25 8C for two days) were obtained for both catalytic and stoichiometric reactions (see Supporting Information for NMR data).…”

Ohne dirigierende Gruppen: übergangsmetallkatalysierte C‐H‐Aktivierung einfacher Arene

“…Für die oxidative Kreuzkupplung symmetrisch 1,2-disubstituierter Benzolderivate ermittelten Dong et al [48] Schema 11. Kontrolle der Regioselektivität in dehydrierenden Kupplungen.…”

“…Reaktionsbedingungen für die dehydrierende Kupplung von Arenen mit verschiedenen DG von Dong et al [48] . [49] Wurden monosubstituierte Arene in dieser Reaktion eingesetzt, konnten die Produkte interessanterweise als einzige Regioisomere erhalten werden.…”

O desafio da ativação das ligações C-H em síntese orgânica

“…33 Outros grupos de pesquisa, embora ainda trabalhem com a hipótese de substituição aromática eletrofílica, admitem também que o mecanismo CMD pode ocorrer. 34 Arockiam e colaboradores 16 sugeriram que a mesma maneira de clivar ligações C-H ocorre com complexos de rutênio (II). Ou seja, é possível que este mecanismo venha a ser estendido a outros metais.…”