Csp3-H Bond Research Articles

Palladium-catalyzed aerobic (1+2) annulation of Csp3-H bonds with olefin for the synthesis of 3-azabicyclo[3.1.0]hex-2-ene.

A novel palladium-catalyzed aerobic (1+2) annulation was developed for the synthesis of 3-azabicyclo[3.1.0]hex-2-ene. The palladation of Csp3-H bonds took place twice at the same position in the whole reaction process. Preliminary mechanistic studies by in situ IR revealed that the second C-H palladation and reductive elimination might be slow steps.

Hybrid of Polyoxometalate-Based Ionic Salt and N-Doped Carbon toward Reductant-Free Aerobic Hydroxylation of Benzene to Phenol

A novel carbon-based hybrid is composed of N-doped ordered mesoporous carbon (NC) and polyoxometalate (POM) based ionic salt (IL-POM), constructing the first efficient non-noble metal heterogeneous catalyst for reductant-free hydroxylation of benzene to phenol with molecular oxygen. Enhanced activity and reusability were achieved and were even better than the previous noble metal involved system. The newly task-specifically designed dicationic ionic liquid tethered with the nitrile group contributed to the high efficiency and heterogeneous property. Systematic structure–activity analysis revealed that the superior activity for this difficult reaction came from the simultaneous activation of benzene by NC and O2 by V species of IL-POM. This work suggests a new green reaction pathway toward heterogeneous aerobic hydroxylation of the Csp2-H bond in π-conjugated aromatic molecules.

Regioselective competition between the formation of seven-membered and five-membered cyclometalated platinacycles preceded by Csp2[sbnd]Csp3 reductive elimination

A mixture of seven-membered and five-membered platinacycle complexes are eventually formed after a series of substitution, oxidative addition, and reductive elimination reactions between the platinum dimer, cis-[Pt2Me4(μ-SMe2)2] and the naphthyl-derived CˆN chelate ligands, (8-XC10H6CH = N-R), X = I, Br; R = phenyl and 4-Cl-benzyl. From the tethered ligand, either an sp2 CH bond can be activated forming a five-membered ring or an sp3 CH bond can be activated forming a seven-membered ring. All compounds have the imine included in the platinacycle. The ratio of complexes as a function of ring size varies depending on ligand architecture of the chelate ligand and the nature of other ligands in the coordination sphere. The cyclometalated platinum complexes have been characterized by NMR spectroscopy. One complex with a seven-membered ring was characterized crystallographically. Reductive elimination reactions of isolated and/or identified cyclometalated, six-membered platinum(IV) compounds [PtMe2Br{C10H6CH = NCH2(4-ClC6H4)}L] and [PtMe2Br{C10H6CH = N(C6H5)}L] (L = SMe2) to form Csp3Csp2 bonds, followed by competition between Csp2H and Csp3H bond activation are also reported.

Acylation of Csp2-H bond with acyl sources derived from alkynes: Rh-Cu bimetallic catalyzed C[triple bond, length as m-dash]C bond cleavage.

A Rh-Cu bimetallic catalyzed o-acylation of acyloxacetamide with alkynes has been described. This transformation provides a novel, concise way to synthesize ortho-acylphenols using functionalized alkynes as acylating reagents. Mechanistic studies revealed a Rh-Cu relay process, in which O2 plays a critical role for the formation of carbonyl compounds.

ChemInform Abstract: I2‐ or NBS‐Catalyzed Highly Efficient α‐Hydroxylation of Ketones with Dimethyl Sulfoxide.

An efficient method for the direct preparation of high synthetic valuable α-hydroxycarbonyls is described. The simple and readily available I2 or NBS was used as catalyst. DMSO acts as the oxidant, oxygen source, and solvent. A diverse range of tertiary Csp3-H bonds as well as more challenging secondary Csp3-H bonds could be hydroxylated in this transformation. The reaction is mild, less toxic and easy to perform.

Synthesis and Reactivity of Cobalt Pincer Complexes Formed by Carbon-Hydrogen Bond Activation

By treating diphosphinito [PCP]-pincer ligand, (Ph2P(ortho-C6H4))2CH2 (1) with CoMe(PMe3)4 or CoMe3(PMe3)3 the same Csp3-H bond activation product [PCP]Co(I)(PMe3) (2) was obtained at room temperature. Treatment of 2 with C6Cl6, EtBr or BuBr and CH3I gave rise to the single electron oxidation addition products [PCP]Co(II)X(PMe3) (X = Cl (3); Br (4) and I (5)). The molecular structures of 2 – 6 were confirmed by X-ray diffraction analysis.

Copper-catalyzed diastereoselective aerobic intramolecular dehydrogenative coupling of hydrazones via sp3 C-H functionalization.

Transition metal-catalyzed cross dehydrogenative coupling is an important tool for functionalization of the α Csp3-H bond of amines. Among this reaction category, copper-catalyzed selective C-C bond formation under atmospheric O2 is of considerable research interest and significant progress has been achieved in recent years. In comparison, development of the intramolecular version of this transformation is still in its infancy. Furthermore, diastereoselective cyclization with this transformation has not been achieved. Here, we describe the highly diastereoselective intramolecular dehydrogenative cyclization of N,N-disubstituted hydrazones by a copper-catalyzed sp3 C-H bond functionalization process. The reaction protocol utilizes O2 as the oxidant and shows great functional group compatibility. Computational studies suggest that a 5-center/6-electron disrotatory cyclization mechanism is probably involved in the process for controlling the diastereoselectivity. This work represents the first example of a copper-catalyzed, direct intramolecular diastereoselective coupling reaction via an iminium ion intermediate. Additionally, it provides an environmentally friendly and atom efficient approach to access substituted pyrazolines, an important structural unit in many biologically active compounds.

Metal-free oxidation of aromatic carbon–hydrogen bonds through a reverse-rebound mechanism

Methods for carbon-hydrogen (C-H) bond oxidation have a fundamental role in synthetic organic chemistry, providing functionality that is required in the final target molecule or facilitating subsequent chemical transformations. Several approaches to oxidizing aliphatic C-H bonds have been described, drastically simplifying the synthesis of complex molecules. However, the selective oxidation of aromatic C-H bonds under mild conditions, especially in the context of substituted arenes with diverse functional groups, remains a challenge. The direct hydroxylation of arenes was initially achieved through the use of strong Brønsted or Lewis acids to mediate electrophilic aromatic substitution reactions with super-stoichiometric equivalents of oxidants, significantly limiting the scope of the reaction. Because the products of these reactions are more reactive than the starting materials, over-oxidation is frequently a competitive process. Transition-metal-catalysed C-H oxidation of arenes with or without directing groups has been developed, improving on the acid-mediated process; however, precious metals are required. Here we demonstrate that phthaloyl peroxide functions as a selective oxidant for the transformation of arenes to phenols under mild conditions. Although the reaction proceeds through a radical mechanism, aromatic C-H bonds are selectively oxidized in preference to activated Csp3-H bonds. Notably, a wide array of functional groups are compatible with this reaction, and this method is therefore well suited for late-stage transformations of advanced synthetic intermediates. Quantum mechanical calculations indicate that this transformation proceeds through a novel addition-abstraction mechanism, a kind of 'reverse-rebound' mechanism as distinct from the common oxygen-rebound mechanism observed for metal-oxo oxidants. These calculations also identify the origins of the experimentally observed aryl selectivity.

Magnetically Recoverable Iron Nanoparticle Catalyzed Cross-Dehydrogena­tive Coupling (CDC) between Two Csp³-H Bonds Using Molecular Oxygen

The oxidative C-C bond formations between Csp³-H bond adjacent to nitrogen and Csp³-H bond of nitroalkanes are catalyzed efficiently by magnetically recoverable iron nanoparticles using oxygen. The catalyst can be magnetically removed and recycled easily for nine times without decreasing activity.

有機合成化学の挑戦‐２１世紀に向けて 合成反応 Ｃ‐ＨおよびＣ‐Ｃ結合の合成化学的変換への挑戦

Breaking of inert chemical bonds by transition metals under homogeneous conditions has recently made rapid progress. In this review is described an overview of this field, especially the feature related to organic synthesis. The first part deals with breaking of carbon-hydrogen bonds. Ruthenium complexes catalyze the direct addition of ortho carbon-hydrogen bonds in aromatic ketones to olefins with high efficiencies and selectivities. A variety of analogous synthetic reactions involving breaking of Csp2-H bonds have been developed. The latter part features a recent aspect on the activation of C-C bonds through a process of oxidative addition to a soluble transition metal complex. Selective breaking of the C-C bonds α to the carbonyl group of cyclobutanones is achieved by a rhodium (I) complex.

Polarity, polarizability, and conformations of the benzylidene chlorides

1. The conformations of benzylidene chloride and its ring-substituted derivatives show a shielded Csp3-H bond and planar aromatic ring. 2. Introduction of an o substituent brings about a total, and introduction of a polar m substituent a partial, destabilization of the conformer, the chlorine atom approaching the substituent. 3. Interaction of the chlorine atom and the aromatic system leads to an alteration in the alteration in the polarizability ellipsoid in the benzylidene chlorides.