Ru(3)(CO)(12)-catalyzed coupling reaction of sp(3) C-H bonds adjacent to a nitrogen atom in alkylamines with alkenes

Copper-catalyzed coupling of tertiary aliphatic amines with terminal alkynes to propargylamines via C-H activation

We have developed a convenient and efficient method for coupling of tertiary aliphatic amines with terminal alkynes to propargylamines via C-H activation. The protocol uses CuBr as the catalyst, NBS as the free radical initiator, CH(3)CN as the solvent, and the alkynylation was selectively performed on the methyl of tertiary aliphatic amines at 80 degrees C. This is an economical and practical method for the synthesis of propargylamines.

Palladium-catalyzed sp(3) CH activation of simple alkyl groups: direct preparation of indoline derivatives from N-alkyl-2-bromoanilines

The sp3 C-H activation of a simple alkyl group catalyzed by palladium(0) provides a novel and convenient strategy for the synthesis of various indolines from simple precursors, such as N-alkyl-2-bromoanilines. This study demonstrates that assisting moieties in the substrate such as a pyridine or quaternary carbon are not always necessary for sp3 C-H activation.

Chemoselective C(sp3)H Bond Activation for the Preparation of Condensed N-Heterocycles

Condensed N-heterocycles were prepared by using C-H activation reactions catalyzed by Pd(OAc)2 (5 mol %) and (p-tolyl)3P (10 mol %). The key step of these ring closures is chemoselective intramolecular C-H activation of the methyl group at position 2 of the pyrrole ring. Functionalized 9H-pyrrolo[1,2-a]indoles and pyrrolo[1,2-f]phenanthridine derivatives were prepared in good yields. The preparation of some complex N-heterocycles by using successive reactions is also described.

Direct sp3 C-H bond activation adjacent to nitrogen in heterocycles

Activation of sp(3) C-H bonds adjacent to nitrogen in heterocycles is an attractive transformation that is emerging as a practical method in organic synthesis. This tutorial review aims to summarize the key examples of direct functionalization of nitrogen-containing heterocycles via metal-mediated and metal-catalyzed processes, which is meant to serve as a foundation for future investigations into this rapidly developing area of research. The review covers functionalization of N-heterocycles via alpha-lithiation with alkyllithium/diamine complexes, alpha-amino radical formation, metal-catalyzed direct C-H activation, C-H oxidations and oxidative couplings, and metal-catalyzed carbene insertions.

Microwave-Assisted Heterogeneous Cross-Coupling Reactions Catalyzed by Nickel-in-Charcoal (Ni/C)

A study involving the relatively rare combination of heterogeneous catalysis conducted under microwave conditions is presented. Carbon-carbon bond formation, including Negishi and Suzuki couplings, can be quickly effected with aryl chloride partners by using a base metal (nickel) adsorbed in the pores of activated charcoal. Aminations were also studied, along with cross-couplings of vinyl alanes with benzylic chlorides as a means to stereodefined allylated aromatics. Reaction times for all these processes are typically reduced from several hours to minutes in a microwave reactor.

Palladium-Catalyzed Oxidation of Boc-Protected N-Methylamines with IOAc as the Oxidant: A Boc-Directed sp3 C−H Bond Activation

[Structure: see text] Pd-catalyzed selective oxidation of Boc-protected N-methylamines with IOAc as the oxidant is described. Evidence for the involvement of a Boc-directed C-H activation process is provided.

Cu-catalyzed cross-dehydrogenative coupling: a versatile strategy for C-C bond formations via the oxidative activation of sp(3) C-H bonds

Cu-catalyzed cross-dehydrogenative coupling (CDC) methodologies were developed based on the oxidative activation of sp(3) C-H bonds adjacent to a nitrogen atom. Various sp, sp(2), and sp(3) C-H bonds of pronucleophiles were used in the Cu-catalyzed CDC reactions. Based on these results, the mechanisms of the CDC reactions also are discussed.

Scope and mechanistic study of the ruthenium-catalyzed ortho-C-H bond activation and cyclization reactions of arylamines with terminal alkynes

The cationic ruthenium hydride complex [(PCy(3))(2)(CO)(CH(3)CN)(2)RuH](+)BF(4)(-) was found to be a highly effective catalyst for the C-H bond activation reaction of arylamines and terminal alkynes. The regioselective catalytic synthesis of substituted quinoline and quinoxaline derivatives was achieved from the ortho-C-H bond activation reaction of arylamines and terminal alkynes by using the catalyst Ru(3)(CO)(12)/HBF(4).OEt(2). The normal isotope effect (k(CH)/k(CD) = 2.5) was observed for the reaction of C(6)H(5)NH(2) and C(6)D(5)NH(2) with propyne. A highly negative Hammett value (rho = -4.4) was obtained from the correlation of the relative rates from a series of meta-substituted anilines, m-XC(6)H(4)NH(2), with sigma(p) in the presence of Ru(3)(CO)(12)/HBF(4).OEt(2) (3 mol % Ru, 1:3 molar ratio). The deuterium labeling studies from the reactions of both indoline and acyclic arylamines with DCCPh showed that the alkyne C-H bond activation step is reversible. The crossover experiment from the reaction of 1-(2-amino-1-phenyl)pyrrole with DCCPh and HCCC(6)H(4)-p-OMe led to preferential deuterium incorporation to the phenyl-substituted quinoline product. A mechanism involving rate-determining ortho-C-H bond activation and intramolecular C-N bond formation steps via an unsaturated cationic ruthenium acetylide complex has been proposed.

Room Temperature Hydroalkylation of Electron-Deficient Olefins: sp3 C−H Functionalization via a Lewis Acid-Catalyzed Intramolecular Redox Event

A practical method for the intramolecular hydroalkylation of electron-deficient olefins has been developed. The direct transformation of benzylic, tertiary, and sterically hindered secondary sp3 C-H bonds into C-C bonds under the action of a catalytic amount of a variety of Lewis acids is described. The mechanism of these transformations is proposed to involve a tandem hydride transfer/cyclization sequence.

Regiospecific Functionalization of Methyl C−H Bonds of Alkyl Groups in Reagents with Heteroatom Functionality

We report the regiospecific, rhodium-catalyzed borylation of saturated terminal C-H bonds in molecules with existing functionality. Moderate to good yields were obtained with the organic substrate in excess and as limiting reagent. The borylations of trialkylamines, protected alcohols, protected ketones, and fluoroalkanes occurred regiospecifically at the methyl group that is least sterically hindered. Reactions were also conducted that probed electronic effects on the alkyl borylation. These reactions showed that the borylation occurred preferentially at the methyl group that is most electron-deficient. Methods to conduct tandem borylation of C-H bonds and conversion of the resulting boronate esters to alcohols, alkylarenes, and alkyltrifluoroborates were also developed.

Aromatic vs Aliphatic C−H Cleavage of Alkyl-Substituted Pyridines by (PNPiPr)Re Compounds

Both (PNP)Re(H)(4) and (PNP)ReH(cyclooctyne) (PNP(i)(Pr) = ((i)Pr(2)PCH(2)SiMe(2))(2)N) react with alkylpyridines NC(5)H(4)R to give first (PNP)ReH(2)(eta(2)-pyridyl) and cyclooctene and then, when not sterically blocked, (PNP)Re(eta(2)-pyridyl)(2) and cyclooctane. The latter are shown by NMR, X-ray diffraction, and DFT calculations to have several energetically competitive isomeric structures and pyridyl N donation in preference to PNP amide pi-donation. DFT studies support NMR solution evidence that the most stable bis pyridyl structure is one that is doubly eta(2)- with the pyridyl N donating to the metal center. When both ortho positions carry methyl substituents, cyclooctane and the carbyne complex (PNP)ReH(tbd1;C-pyridyl) are produced. Excess 2-vinyl pyridine reacts with (PNP)Re(H)(4) preferentially at the vinyl group, to give 2-ethyl pyridine and the sigma-vinyl complex (PNP)ReH[eta(2)-CH=CH(2-py)]. The DFT and X-ray structures show, by various comparisons, the ability of the PNP amide nitrogen to pi-donate to an otherwise unsaturated d(4) Re(III) center, showing short Re-N distances consistent with the presence of pi-donation.

Stereoretentive C-H bond activation in the aqueous phase catalytic hydrogenation of amino acids to amino alcohols

[reaction: see text] At 100 degrees C and 1000 psi of hydrogen, aqueous l-alanine undergoes facile hydrogenation to l-alaninol over a 5% Ru/C catalyst. In the presence of added acid to protonate the carboxylate moiety, the reaction is faster and more selective than analogous reductions of simple alkanoic acids. Stereochemistry at the alpha-carbon is retained despite complete exchange of hydrogen at this site, as shown by deuterium incorporation. Similar stereoretentive C-H bond activation at C2 is seen in l-alaninol itself, and when acid is omitted, in l-alanine. These processes reveal a class of mild, highly stereoretentive C-H bond activations occurring in water over a heterogeneous catalyst.

Ru3(CO)12-catalyzed C-H/CO/olefin coupling of N-pyridylindolines. Direct carbonylation at a C-H bond delta to the pyridine nitrogen

The reaction of N-pyridylindolines with CO and ethylene in the presence of Ru3(CO)12 results in direct carbonylation at a C-H bond delta to the pyridine sp2 nitrogen, which represents a new type of C-H/CO/olefin coupling. The presence of a pyridine ring as a directing group on the substrates is essential for the reaction to proceed. The choice of N,N-dimethylacetamide (DMA) as the solvent is crucial for the reaction to proceed efficiently.