Temporary Silicon Tether Strategy for Palladium-Catalyzed C-H Activation Reactions

A palladium-catalyzed intramolecular ortho C–H arylation of phenols has been developed. This methodology features the employment of a removable silicon tether strategy, allowing both TBDPS and a newly developed Br-TBDPS protecting groups to serve as efficient aryl group donors for arylation of phenols. Along this line, this removable silicon tether strategy was further applied to the intramolecular arylation of bisaryloxysilanes for the preparation of unsymmetrical ortho-biphenols, ortho-binaphthols, and mixed ortho-phenol-naphthols. We have also developed a silanol-directed, palladium-catalyzed C–H alkenylation of phenols. Thus, employment of silanol as a traceless directing group is very convenient as it can easily be installed and removed under mild conditions. This alkenylation method is general, as it tolerates a variety of differently substituted phenols and diverse electron-deficient alkenes. The synthetic usefulness of this novel transformation was demonstrated in the efficient synthesis of benzofuranone derivative. Furthermore, the application of this method to the olefination of estrone showcased the viability of this method for the late-stage modification of bioactive molecules for drug discovery. Mechanistic studies supported an electrophilic pathway for the C–H activation step. We have also shown that silanol can direct palladium-catalyzed C–H oxygenation of phenols en route to catechols. This protocol is highly site selective and general, as it allows for efficient oxygenation of phenols regardless of their electronic properties. Mechanistic studies indicated that this C–H oxygenation reaction undergoes ortho C–H acetoxylation first, the product of which is then converted into the cyclic silyl-protected catechol via a transesterification/cyclization sequence mediated by the in situ generated acetic acid

Synthesis of Unsymmetrical <i>o</i>-Biphenols and <i>o</i>-Binaphthols via Silicon-Tethered Pd-Catalyzed C−H Arylation

A mild, practical, and efficient method for the synthesis of unsymmetrical o-biphenols (including o-phenol-naphthols and o-binaphthols) has been developed. Unsymmetrical bis-aryloxy silanes, which were readily prepared in a semi-one-pot fashion, underwent the Pd-catalyzed intramolecular arylation followed by a routine TBAF desilylation step to furnish valuable unsymmetrical biphenols without necessity of isolation of seven-membered intermediates. The excellent functional group tolerance allows for synthesis of a variety of functionalized o-biphenols and o-binaphthols from easily available staring materials

TBDPS and Br-TBDPS Protecting Groups as Efficient Aryl Group Donors in Pd-Catalyzed Arylation of Phenols and Anilines

TBDPS and Br-TBDPS Protecting Groups as Efficient Aryl Group Donors in Pd-Catalyzed Arylation of Phenols and Aniline

Silanol: A Traceless Directing Group for Pd-Catalyzed <i>o</i>-Alkenylation of Phenols

A silanol-directed, Pd(II)-catalyzed C–H alkenylation of phenols is reported. This work features silanol, as a novel traceless directing group, and a directed o-C–H alkenylation of phenols. This new method allows for efficient synthesis of diverse alkenylated phenols, including an estrone derivative

Cleavage of C−S Bonds with the Formation of a Tetranuclear Cu(I) Cluster

The treatment of a ligand, 2,6-bis((4-(pyridin-2-yl)pyrimidin-2-ylthio)methyl)-4-chlorophenol (ClPPT2), with cuprous chloride under a weak base condition led to the formation of a neutral CuI4-centered cluster [Cu4(PPT2)4], whose X-ray diffraction analysis indicated that C−S bonds of the ligand were cleaved in the course of the reaction. To explain the C−S bond cleavage, a reasonable mechanism has been proposed. In support of it, four additional ligands, 2,6-bis((4-(pyridin-2-yl)pyrimidin-2-ylthio)methyl)-4-methylphenol (MePPT2), 2,6-bis((4-(pyridin-3-yl)pyrimidin-2-ylthio)methyl)-4-methylphenol (MePPT3), 2,6-bis((4-(pyridin-3-yl)pyrimidin-2-ylthio)methyl)-4-chlorophenol (ClPPT3), and 5-((4-(pyridin-3-yl)pyrimidin-2-ylthio)methyl)-2-hydroxybenzaldehyde (HBPPT2) were further tested to undertake the analogous reaction, and the cleaved products in these experiments were detected by electrospray ionization mass spectrometry techniques to clarify the process

Cleavage of C−S Bonds with the Formation of a Tetranuclear Cu(I) Cluster

The treatment of a ligand, 2,6-bis((4-(pyridin-2-yl)pyrimidin-2-ylthio)methyl)-4-chlorophenol (ClPPT2), with cuprous chloride under a weak base condition led to the formation of a neutral CuI4-centered cluster [Cu4(PPT2)4], whose X-ray diffraction analysis indicated that C−S bonds of the ligand were cleaved in the course of the reaction. To explain the C−S bond cleavage, a reasonable mechanism has been proposed. In support of it, four additional ligands, 2,6-bis((4-(pyridin-2-yl)pyrimidin-2-ylthio)methyl)-4-methylphenol (MePPT2), 2,6-bis((4-(pyridin-3-yl)pyrimidin-2-ylthio)methyl)-4-methylphenol (MePPT3), 2,6-bis((4-(pyridin-3-yl)pyrimidin-2-ylthio)methyl)-4-chlorophenol (ClPPT3), and 5-((4-(pyridin-3-yl)pyrimidin-2-ylthio)methyl)-2-hydroxybenzaldehyde (HBPPT2) were further tested to undertake the analogous reaction, and the cleaved products in these experiments were detected by electrospray ionization mass spectrometry techniques to clarify the process

Cleavage of C−S Bonds with the Formation of a Tetranuclear Cu(I) Cluster

The treatment of a ligand, 2,6-bis((4-(pyridin-2-yl)pyrimidin-2-ylthio)methyl)-4-chlorophenol (ClPPT2), with cuprous chloride under a weak base condition led to the formation of a neutral CuI4-centered cluster [Cu4(PPT2)4], whose X-ray diffraction analysis indicated that C−S bonds of the ligand were cleaved in the course of the reaction. To explain the C−S bond cleavage, a reasonable mechanism has been proposed. In support of it, four additional ligands, 2,6-bis((4-(pyridin-2-yl)pyrimidin-2-ylthio)methyl)-4-methylphenol (MePPT2), 2,6-bis((4-(pyridin-3-yl)pyrimidin-2-ylthio)methyl)-4-methylphenol (MePPT3), 2,6-bis((4-(pyridin-3-yl)pyrimidin-2-ylthio)methyl)-4-chlorophenol (ClPPT3), and 5-((4-(pyridin-3-yl)pyrimidin-2-ylthio)methyl)-2-hydroxybenzaldehyde (HBPPT2) were further tested to undertake the analogous reaction, and the cleaved products in these experiments were detected by electrospray ionization mass spectrometry techniques to clarify the process

Cleavage of C−S Bonds with the Formation of a Tetranuclear Cu(I) Cluster

The treatment of a ligand, 2,6-bis((4-(pyridin-2-yl)pyrimidin-2-ylthio)methyl)-4-chlorophenol (ClPPT2), with cuprous chloride under a weak base condition led to the formation of a neutral CuI4-centered cluster [Cu4(PPT2)4], whose X-ray diffraction analysis indicated that C−S bonds of the ligand were cleaved in the course of the reaction. To explain the C−S bond cleavage, a reasonable mechanism has been proposed. In support of it, four additional ligands, 2,6-bis((4-(pyridin-2-yl)pyrimidin-2-ylthio)methyl)-4-methylphenol (MePPT2), 2,6-bis((4-(pyridin-3-yl)pyrimidin-2-ylthio)methyl)-4-methylphenol (MePPT3), 2,6-bis((4-(pyridin-3-yl)pyrimidin-2-ylthio)methyl)-4-chlorophenol (ClPPT3), and 5-((4-(pyridin-3-yl)pyrimidin-2-ylthio)methyl)-2-hydroxybenzaldehyde (HBPPT2) were further tested to undertake the analogous reaction, and the cleaved products in these experiments were detected by electrospray ionization mass spectrometry techniques to clarify the process

Synthesis of Catechols from Phenols via Pd-Catalyzed Silanol-Directed C–H Oxygenation

A silanol-directed, Pd-catalyzed C–H oxygenation of phenols into catechols is presented. This method is highly site selective and general, as it allows for oxygenation of not only electron-neutral but also electron-poor phenols. This method operates via a silanol-directed acetoxylation, followed by a subsequent acid-catalyzed cyclization reaction into a cyclic silicon-protected catechol. A routine desilylation of the silacyle with TBAF uncovers the catechol product

A Mild Liquid Reduction Route toward Uniform Blue-Emitting EuCl₂ Nanoprisms and Nanorods

In this work, for the first time, uniform blue-emitting EuCl2 nanoprisms and nanorods were synthesized from Eu(CCl3COO)3·2H2O [or Eu(CH3COO)3·H2O] by a novel mild liquid reduction route, using acetamidine hydrochloride (or picolinamidine hydrochloride) as the reductant in oleylamine. The synthetic reaction even can take place under an atmosphere in the absence of inert gas at around 300 °C. The EuCl2 nanoprism dispersion in n-hexane showed an intense blue emission when excited by UV light