Access to C(sp3)-C(sp2) and C(sp2)-C(sp2) bond formation via sequential intermolecular carbopalladation of multiple carbon-carbon bonds

A synthetic strategy of 4-benzyl-substituted 1,3-butadiene derivatives through Pd-catalyzed three-component coupling reaction of benzyl chlorides, alkynes, and monosubstituted alkenes is described. This tandem coupling reaction forms a C(sp(3))-C(sp(2)) bond and a C(sp(2))-C(sp(2)) bond sequentially in a single-step operation.     

Pd(II)-catalyzed cross-coupling of sp3 C-H Bonds with sp2 and sp3 boronic acids using air as the oxidant

O-Methyl hydroxamic acids, readily available from carboxylic acids, are found to be extremely reactive for beta-C-H activation by Pd(OAc)2. This reactivity is exploited to develop the first example of cross-coupling sp3 C-H bonds with sp3 boronic acids. Air was shown to be a suitable stoichiometric oxidant for the catalytic oxidative coupling reaction. A biologically active natural product is readily converted to its novel analogues through this coupling reaction.     

Palladium-catalyzed Suzuki-Miyaura reaction involving a secondary sp3 carbon: studies of stereochemistry and scope of the reaction

Palladium-catalyzed C--C bond formation involving secondary sp3-hybridized carbon is described. These reactions occur with secondary 1-bromoethyl arylsulfoxides and different arylboronic acids, to produce the corresponding arylated sulfoxides in moderate to high yields and with complete stereospecificity. Despite the presence of beta hydrogens in the substrate, the competitive beta-hydride elimination is not a significant side reaction when coordinating solvents are used. The reported cross-coupling involves secondary C(sp3)--C(sp2) bond formation: this is the first time that a mechanistic study has been carried out with such substrates. The reaction proceeds with inversion of configuration at the stereogenic C(sp3) carbon. The high stereospecificity of the coupling and the mildness of the reaction conditions allow for the preservation of the optical purities of reagents and products and the preparation of useful chiral targets.     

Ruthenium catalyzed decarbonylative arylation at sp3 carbon centers in pyrrolidine and piperidine heterocycles

This paper describes the development of a new catalytic transformation, the ruthenium-catalyzed decarbonylative arylation of cyclic 2-amino esters, which replaces the ester group with an aryl ring at the sp3 carbon center. For example, proline ester amidine 1 is converted to 2-arylpyrrolidine 3 in the presence of arylboronic acids or esters as arene donors and Ru(3)(CO)(12) as the catalyst. This process provides a rapid access to a variety of 2-arylpyrrolidines and piperidines from commercially available proline, hydroxyproline, and pipecolinate esters. The examination of the substrate scope also showed that many arene boronic acids and boronate esters serve as coupling partners. The high chemoselectivity of this process was demonstrated and ascribed to the significant rate difference between the decarbonylative arylation and the C-H arylation. The decarbonylative arylation complements the C-H arylation, since the latter process lacks control over the extent of functionalization, affording a mixture of mono- and bis-arylpyrrolidines. When applied in tandem, these two processes provide 2,5-diarylpyrrolidines in two steps from the corresponding proline esters. It was also demonstrated that the required amidine or iminocarbamate directing group fulfills two major functions: first, it is essential for the ester activation step, which occurs via the coordination-assisted metal insertion into the acyl C-O bond; second, it facilitates the decarbonylation, via the stabilization of a metallacycle intermediate, assuring the formation of the 2-arylated products instead of the corresponding ketones observed before by others.     

Metal-free oxidative C-C bond formation of active methylenic sp C-H bonds with benzylic sp C-H and allylic sp C-H bonds mediated by DDQ

An efficient and simple method for the oxidative coupling of benzylic and allylic sp³ C-H bonds with active methylenic sp³ C-H bonds under metal-free conditions was developed by employing 2,3-dichloro-5,6-dicyanobenzoquinone (DDQ) as an oxidant. The reaction was shown to proceed smoothly for various 1,3-dicarbonyl compounds with a range of benzylic and allylic substrates in good to excellent yields.     

CuBr-catalyzed direct indolation of tetrahydroisoquinolines via cross-dehydrogenative coupling between sp3 C-H and sp2 C-H bonds

A novel and efficient C-C bond formation method was developed via the cross-dehydrogenative coupling (CDC) reaction of indoles and tetrahydroisoquinolines catalyzed by copper bromide in the presence of an oxidizing reagent, tert-BuOOH. The CDC reaction provides a simple and efficient catalytic method to construct indolyl tetrahydroisoquinolines via a combination of sp3 C-H bond and sp2 C-H bond followed by C-C bond formation.     

Photoredox catalyzed C(sp3)C(sp) coupling of dihydropyridines and alkynylbenziodoxolones

A visible light mediated deformylative alkynylation of aldehydes is presented. Under photo irradiation, 1,4-dihydropyridine (DHP), derived from an aldehyde, generated a C(sp³)- radical which couples with an alkynylbenziodoxolone to generate an alkyl substituted alkyne coupling product. This strategy is mild and easy to operate, a wide range of functional groups were tolerated, and 16 examples of products with 35–86% yields were obtained.     

Aza-oxindole synthesis by oxidative coupling of C(sp2)-H and C(sp3)-H centers

A Cu(II) mediated oxidative C(sp(2))-H and C(sp(3))-H coupling protocol gives access to aza-oxindoles in good to excellent yield in the presence of NaOtBu as base and toluene as solvent.     

On some carbon clusters containing sp2- and sp3-hybridized atoms

A new class of thread-like carbon clusters consisting of dodecahedra and containing sp²- and sp³-hybridized atoms is described. Molecular and electronic structures of the simplest representative of this class (the C₁₀₂ cluster) and of the polyhedral C₉₀H₁₂ hydrocarbon molecule, whose carbon framework is identical to the toroidal fragment of the C₁₀₂ cluster, have been calculated by the MNDO and MNDO-PM3 methods.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya. No. 3, pp. 551–553, March, 1996.     

Palladium-catalyzed alkylation of sp2 and sp3 C-H bonds with methylboroxine and alkylboronic acids: two distinct C-H activation pathways

Palladium-catalyzed alkylations of sp2 and sp3 C-H bonds with either methylboroxine or alkylboronic acids were developed. Ag2O or AgCO3 is used as a crucial oxidant and promoter for the transmetalation step. Ether, ester, alcohol, and alkene functional groups are tolerated. A new C-H activation pathway differing from the cyclometalation process is elucidated using methylboroxine as the coupling partner.     

Raman and SERS investigation of isolated sp carbon chains

Carbon chains with sp hybridization and a known distribution of lengths have been studied by Raman and Surface Enhanced Raman Scattering (SERS). With the support of density functional theory simulations the observed Raman features have been assigned to active modes of individual chains. SERS spectra show remarkable differences, attributed to the interaction between sp chains and Ag nanoparticles used as a SERS active medium. The results obtained for this model system permit in principle to explain a large number of Raman data from molecular and solid sp/sp² carbon systems.     

Photophysics of diplatinum polyynediyl oligomers: chain length dependence of the triplet state in sp carbon chains

The series of polyynes with the structure trans, trans-[Ar-Pt(P 2)-(C[triple bond]C) n -Pt(P 2)-Ar], where P = tri( p-tolyl)phosphine, Ar = p-tolyl, and n = 3, 4, 5, 6 (6, 8, 10, 12 sp carbon atoms), has been subjected to a comprehensive photophysical investigation. At low temperature ( T < 140 K) in a 2-methyltetrahydrofuran (MTHF) glass, the complexes exhibit moderately efficient phosphorescence appearing as a series of narrow (fwhm < 200 cm (-1)) vibronic bands separated by ca. 2100 cm (-1). The emission is assigned to a (3)pi,pi* triplet state that is concentrated on the sp carbon chain, and the vibronic progression arises from coupling of the excitation to the -C[triple bond]C- stretch. The 0-0 energy of the phosphorescence decreases with increasing sp carbon chain length, spanning a range of over 6000 cm (-1) across the series. Transient absorption spectroscopy carried out at ambient temperature confirms that the (3)pi,pi* triplet is produced efficiently, and it displays a strongly allowed triplet-triplet absorption. In the MTHF solvent glass ( T < 140 K), the emission lifetimes increase with emission energy. Analysis of the triplet nonradiative decay rates reveals a quantitative energy gap law correlation. The nonradiative decay rates can be calculated by using parameters recovered from a single-mode Franck-Condon fit of the emission spectra.     

Equation de Karplus appliquée à des systèmes sp2–sp3

A method of best fitting for the calculation of vicinal coupling constants is presented for sp²-sp³ systems. Results for 68 vicinal coupling constants from 32 different products are presented. We obtain the best Karplus-type equation to date with a dispersion factor of 31,01%.     

Copper-catalyzed decarboxylative C(sp2)-C(sp3) coupling reactions via radical mechanism

We have successfully developed an example of copper-catalyzed decarboxylative C(sp(2))-C(sp(3)) coupling reactions via C-H functionalization for the first time. It is noteworthy that our catalytic system is very stable, low-cost, palladium-free, ligand-free, and easily accessible.     

ortho‐Directing Chromium Arene Complexes as Efficient Mediators for Enantiospecific C(sp2)–C(sp3) Cross‐Coupling Reactions

A new strategy for the coupling of a broad scope of electronically diverse aromatics to boronic esters is reported. The coupling sequence, which relies on the directed ortho‐lithiation of chromium arene complexes followed by boronate formation and oxidation, occurs with complete ortho‐selectivity and enantiospecificity to give the coupling products in excellent yields and with high functional group tolerance. An intermediate chromium arene boronate complex was characterized by X‐ray, NMR, and IR experiments to elucidate the reaction mechanism.     

Cross-Electrophile C(sp2)−Si Coupling of Vinyl Chlorosilanes

The cross-electrophile coupling has become a powerful tool for C−C bond formation, but its potential for forging the C−Si bond remains unexplored. Here we report a cross-electrophile Csp²-Si coupling reaction of vinyl/aryl electrophiles with vinyl chlorosilanes. This new protocol offers an approach for facile and precise synthesis of organosilanes with high molecular diversity and complexity from readily available materials. The reaction proceeds under mild and non-basic conditions, demonstrating a high step economy, broad substrate scope, wide functionality tolerance, and easy scalability. The synthetic utility of the method is shown by its efficient accessing of silicon bioisosteres, the design of new BCB-monomers, and studies on the Hiyama cross-coupling of vinylsilane products.     

Iron-catalysed tandem cross-dehydrogenative coupling (CDC) of terminal allylic C(sp3) to C(sp2) of styrene and benzoannulation in the synthesis of polysubstituted naphthalenes

A novel iron-catalysed tandem cross-dehydrogenative coupling and benzoannulation process was developed for the synthesis of biologically and synthetically important polysubstituted naphthalene derivatives from simple 1,2-aryl-propenes and styrenes in moderate to good yields.     

Regioselective control of the nickel-mediated coupling of acetylene and carbon dioxide - A DFT study

The nickel-mediated coupling of asymmetric alkynes with carbon dioxide is known to be highly regioselective with respect to the formation of nickelacycle intermediates and α,β-unsaturated carboxylic acid products. Using density functional theory (DFT), we have investigated the effect that parameters such as acetylene-substituent, ancillary ligand and solvent have on the potential energy surface of the nickelacycle coupling reaction. 3-R-substituted nickelacycles are the thermodynamically preferred product in all cases surveyed, however, the transition structure characterised by the attack of CO₂ on the alkyne carbon distal from the R-group is generally lower in energy, making the 2-R-substituted nickelacycle the kinetically favoured product. Ligating the zerovalent nickel species with the diazabicyclo[5.4.0]undec-7-ene (DBU) ancillary ligand in preference to 2,2′-bipyridine (BIPY) leads to lower activation energies for the coupling reaction and products that are less susceptible to steric bulk in the 2-position of the nickelacycle. Solvation with dimethylformamide (DMF) has the advantage of lowering the activation barrier for the coupling reaction when compared to tetrahydrofuran (THF).     

Synthesis of hetero- and carbocycles by nucleophilic substitution at sp carbon

Vinylic halides having alcohol, sulfonamide, active methine, and thiol moieties as nucleophiles cyclize to hetero- and carbocycles by intramolecular nucleophilic substitution at the sp² carbon centers. The density functional theory calculations suggest that the cyclization proceeds through S_N2-type substitution (the in-plane vinylic nucleophilic substitution, S_NVσ), when vinyl halides are substituted with oxygen, nitrogen, and carbon nucleophiles. The substitution with sulfur nucleophiles, in contrast, proceeds through both routes of S_NVσ and out-of-plane vinylic nucleophilic substitution (S_NVπ).     

Unexpected copper-catalyzed aerobic oxidative cleavage of C(sp3)-C(sp3) bond of glycol ethers

An unexpected Cu-catalyzed oxidative cleavage of the C(sp(3))-C(sp(3)) bond in glycol ethers by using air or molecular oxygen as the terminal stoichiometric oxidant is demonstrated. As a result, the corresponding α-acyloxy ethers and formates of 1,2-ethanediol are formed by direct coupling of carboxylic acids and aldehydes with glycol ethers under the reaction conditions. This method represents the first example of Cu-catalyzed aerobic cleavage of saturated C-C bond in ethers.