Highly regioselective functionalization of aliphatic carbon-hydrogen bonds with a perbromohomoscorpionate copper(I) catalyst

The complex Tp(Br3)Cu(NCMe) (1) is an excellent catalyst for the regioselective carbene transfer reaction to tertiary C-H bonds of hydrocarbons, at room temperature, using the readily available ethyl diazoacetate (EDA) as the carbene source.     

Palladium-catalyzed fluorination of carbon-hydrogen bonds

This communication describes the development of a new Pd-catalyzed method for the fluorination of carbon-hydrogen bonds. A key step of these transformations involves palladium-mediated carbon-fluorine coupling-a much sought after, but previously unprecedented, transformation. These reactions were successfully achieved under oxidative conditions using electrophilic N-fluoropyridinium reagents. Microwave irradiation in the presence of catalytic palladium acetate served as optimal conditions for the fluorination of C-H bonds in a variety of substituted 2-arylpyridine and 8-methylquinoline derivatives.     

Synthesis of sulfur-containing heterocycles through oxidative carbon-hydrogen bond functionalization

Vinyl sulfides react rapidly and efficiently with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) to form α,β-unsaturated thiocarbenium ions through oxidative carbon-hydrogen bond cleavage. These electrophiles couple with appended π-nucleophiles to yield sulfur-containing heterocycles through carbon-carbon bond formation. Several nucleophiles are compatible with the procedure, and the reactions generally proceed through readily predictable transition states.     

Anaerobic functionalization of remote unactivated carbon-hydrogen bond by polyoxometalates

The excited states of a representative heteropolytungstate. -PW₁₂O₄₀^3-, and a representative Isopotytungstate, W₁₀O₃₂^4-, accessible with near UV or blue light, oxidize alkanes and conventionally far more reactive organic molecules including alcohols, alkenes, N-alkylacetamides, and Ketones. at comparable rates. One or more of the latter three types of compounds are produced upon irradiation of acetonitrile solutions containing the polyoxotungstate and alkane substrate under anaerobic conditions. Comparison of alcohol versus alkane reactivities under absolute and competitive kinetic conditions indicates that alcohol- polyoxotungstate preassociation can be important in these processes. Reaction of cis- and trans-2-decalones in these systems indicates that functionalization of unactivated positions (primarily incorporation of the olefiaic unit) remote from the usually activating ketone group can be accomplished.     

Facile amine formation by intermolecular catalytic amidation of carbon-hydrogen bonds

A simple copper-based catalytic system has been developed for the carbon-hydrogen amidation reaction. The copper-homoscorpionate complex Tp(Br3)Cu(NCMe) catalyzes the transfer of the nitrene unit NTs (Ts = p-toluenesulfonyl) and its subsequent insertion into the sp(3) C-H bonds of alkyl aromatic and cyclic ethers or the sp(2) C-H bonds of benzene using PhI=NTs as the nitrene source, affording the corresponding trisubstitued NR(1)HTs amines in moderate to high yields. The use of the environmentally friendly chloramine-T has also proven effective, with the advantage that sodium chloride is formed as the only byproduct. A tandem, one-pot consecutive nitrene-carbene insertion system has been developed to yield amino acid derivatives.     

Selective fluorination on tertiary carbon-hydrogen single bonds in the aliphatic series

Fluorine acts as an electrophile and, as such, reacts with remote and unactivated tertiary hydrogens in aliphatic alcohols and acids, resulting in the corresponding fluorine derivatives.     

Robust fuzzy principal component analysis (FPCA). A comparative study concerning interaction of carbon-hydrogen bonds with molybdenum-oxo bonds

Principal component analysis (PCA) is a favorite tool in chemometrics for data compression and information extraction. PCA finds linear combinations of the original measurement variables that describe the significant variations in the data. However, it is well-known that PCA, as with any other multivariate statistical method, is sensitive to outliers, missing data, and poor linear correlation between variables due to poorly distributed variables. As a result data transformations have a large impact upon PCA. In this regard one of the most powerful approaches to improve PCA appears to be the fuzzification of the matrix data, thus diminishing the influence of outliers. In this paper we discuss a robust fuzzy PCA algorithm (FPCA). The new algorithm is illustrated on a data set concerning interaction of carbon-hydrogen bonds with transition metal-oxo bonds in molybdenum complexes. Considering, for example, a two component model, FPCA accounts for 97.20% of the total variance and PCA accounts only for 69.75%.     

Cyclam functionalization through isocyanate insertion in Zr-N bonds

The insertion of isocyanates in (Bn(2)Cyclam)ZrX(2) is regioselective; (Bn(2)Cyclam)Zr(OR)(2) produces urea-like moieties by the insertion of RN═C═O in the Zr-N(amido) bonds of the cyclam ring. Depending on the bulkiness of the isocyanate R groups, O- and N-bound ureates are formed. (Bn(2)Cyclam)Zr(NH(t)Bu)(2) reacts with MesN═C═O at the terminal Zr-N bonds.     

Activation of carbon-hydrogen bonds via 1,2-addition across M-X (X = OH or NH(2)) bonds of d(6) transition metals as a potential key step in hydrocarbon functionalization: a computational study

Recent reports of 1,2-addition of C-H bonds across Ru-X (X = amido, hydroxo) bonds of TpRu(PMe3)X fragments {Tp = hydridotris(pyrazolyl)borate} suggest opportunities for the development of new catalytic cycles for hydrocarbon functionalization. In order to enhance understanding of these transformations, computational examinations of the efficacy of model d6 transition metal complexes of the form [(Tab)M(PH3)2X]q (Tab = tris-azo-borate; X = OH, NH2; q = -1 to +2; M = TcI, Re(I), Ru(II), Co(III), Ir(III), Ni(IV), Pt(IV)) for the activation of benzene C-H bonds, as well as the potential for their incorporation into catalytic functionalization cycles, are presented. For the benzene C-H activation reaction steps, kite-shaped transition states were located and found to have relatively little metal-hydrogen interaction. The C-H activation process is best described as a metal-mediated proton transfer in which the metal center and ligand X function as an activating electrophile and intramolecular base, respectively. While the metal plays a primary role in controlling the kinetics and thermodynamics of the reaction coordinate for C-H activation/functionalization, the ligand X also influences the energetics. On the basis of three thermodynamic criteria characterizing salient energetic aspects of the proposed catalytic cycle and the detailed computational studies reported herein, late transition metal complexes (e.g., Pt, Co, etc.) in the d6 electron configuration {especially the TabCo(PH3)2(OH)+ complex and related Co(III) systems} are predicted to be the most promising for further catalyst investigation.     

Enzymatic clickable functionalization of peptides via computationally engineered peptide amidase

The computationally engineered peptide amidase exhibits great promising potential in the C-terminal modification of peptides using prop-2-yn-1-amine (PYA) or prop-2-en-1-amine (PEA) as the nucleophile. Subsequently, modified peptides could be further functionalized via click reaction without elaborate isolation of the intermediate.     

A highly selective catalytic method for the oxidative functionalization of C-H bonds

This communication describes a new and highly practical Pd(II)-catalyzed method for the regio- and chemoselective oxidative functionalization of arenes and alkanes. Carbon-hydrogen bonds of substrates that contain a variety of directing groups (e.g., pyridine, azobenzene, pyrazole, and imine derivatives) are selectively transformed into esters, ethers, and aryl-halides under mild conditions. The scope of this reaction in terms of substrate, directing group, and oxidant is described, and a preliminary catalytic cycle is proposed.