Toward selective reactions with C-H bonds: a rationale for the regio- and stereochemistry of dichlorocarbene insertions into cyclic hydrocarbons

DFT calculations have been performed to study the course of dichlorocarbene insertion reactions into alkanes and to better understand the regio- and stereoselectivities observed. At the B3LYP/6-31G(d) level of theory, the selectivity of dichlorocarbene insertions into a number of hydrocarbons agrees well with the obtained experimental results. The reactivity of a specific C-H bond is determined by the capacity of the remaining alkyl fragment to effectively delocalize the partial positive charge buildup during the reaction. This activity can readily be estimated by calculation of the hydride transfer potential (HTP). A comparison with the structure and the stability of the corresponding cation is useful to emphasize the origins of the selectivity. Dichlorocarbene is also predicted to react efficiently with acidic C-H bonds through a nucleophilic-electrophilic mechanism. In principle, an attack of a carbene on an appropriately substituted three-membered ring may lead to fragmentation of the molecule.     

Lewis acid-promoted imine synthesis by the insertion of isocyanides into C-H bonds of electron-rich aromatic compounds

The Lewis acid-promoted insertion of isocyanides into aromatic C-H bonds is reported. An imine functionality containing an array of N-substituents can be introduced directly into electron-rich aromatics in good yields.     

Rearrangement of biaryl monoaminocarbenes via concerted asynchronous insertion into aromatic C-H bonds

The biphenyl and binaphthyl diisopropylaminocarbenes were found to be only transient species that spontaneously and quantitatively rearrange into the corresponding aminofluorenes. DFT calculations confirm that these insertion reactions of aminocarbenes into proximal aromatic C-H bonds require only a moderate energy barrier and support a concerted, strongly asynchronous, mechanism dominated by C arom-->C carbene proton transfer.     

Novel insertion reactions into cyclic tin-oxygen compounds

A series of novel insertion reactions of cyclic carbonyl compounds into cyclic tinoxygen compounds is described. Cyclic carboxycarbonate (1) and isatoic anhydride (4) react with cyclic stannoxane (2) to give the acyclic diester (3) and diamide (5) respectively. Cyclic anhydrides derived from aspartic and glutamic acids (6, 7, 10 and 11) react with 2 to give the macrocyclic tetralactones (8) and (9), and dilactones (12) and (13) respectively. These reactions may be of general synthetic value because of their high specificity. They lead either to singly acylated, acyclic products (3 and 5), or to regiospecific macrocyclic products (8, 9, 12 and 13) in preference to oligomers. The high specificity of these reactions is attributed to: (i) the dual function of the tin element, which may act either as activating group or as protecting group, and (ii) the occurrence of non-covalent transannular interactions between tin and oxygen in the cyclic stannoxane 2.     

Catalytic insertion of diazo compounds into N-H bonds: the copper alternative

The complexes TpxCu (Tpx = homoscorpionate) catalyse the insertion of diazo compounds into nitrogen-hydrogen bonds of amines and amides, under very mild conditions, with quantitative yields being obtained with equimolar ratios of reactants.     

Rhenium-catalyzed insertion of terminal acetylenes into a C-H bond of active methylene compounds

[reaction: see text] A rhenium complex, [ReBr(CO)(3)(thf)](2), catalyzed the intermolecular reactions of 1,3-dicarbonyl compounds with terminal acetylenes and gave the corresponding alkenyl derivatives in excellent yields. These reactions could apply to an intramolecular version and gave the corresponding cyclic compounds quantitatively.     

Ru催化的C-H键的活化反应

概述了Ru催化的碳氢键的活化反应，包括C-H/烯烃，C-H/炔径和C-H/CO/烯烃 偶联反应，加氢酰化反应，硅化反应。     

Cyclohexane and benzene amination by catalytic nitrene insertion into C-H bonds with the copper-homoscorpionate catalyst TpBr3CuNCMe

The complex TpBr3Cu(NCMe) catalyzes, at room temperature, the insertion of a nitrene group from PhINTs into the carbon-hydrogen bond of cyclohexane and benzene, as well as into the primary C-H bonds of the methyl groups of toluene and mesitylene, in moderate to high yield.     

Intramolecular hetero-Diels-Alder reactions of imine and iminium dienophiles: quantum mechanical exploration of mechanisms and stereoselectivities

A series of intramolecular hetero-Diels-Alder reactions of iminium and imine dienophiles has been explored with density functional theory using the B3LYP functional and 6-31+G* basis set. Aqueous solvation energies were calculated with the CPCM method. DFT predicts that these reactions are concerted but involve highly asynchronous transition states. Stereochemical preferences of imine cycloaddition transition states arise from electron repulsion of the nitrogen lone pair with electron density from the butadiene moiety. Protonation of the nitrogen leads to a highly asynchronous transition state. The iminium dienophiles are predicted to have a 17 kcal/mol lower barrier than the corresponding imines, even in aqueous solution.     

S-alkylation of thiacalixarenes: how the regio- and stereoselectivities depend on the starting conformation

S-alkylation of all four thiacalix[4]arene conformations was accomplished using alkyl triflates. The corresponding sulfonium salts are formed in a highly regio- and stereoselective manner depending on the conformation used. Interestingly, only mono- or disubstituted sulfonium salts can be prepared. Although many regio- and stereoisomers are theoretically possible, only one dialkylated cone and 1,2-alternate derivatives were formed, while only a single isomer of monoalkylated partial cone and 1,3-alternate were isolated. The combination of experimental results with the quantum-chemical approach using the B3LYP/6-311G(d,p) method resulted in the elucidation of the rules governing the regio- and stereochemical outcomes of the alkylation reactions. All S-alkylated compounds represent a novel type of substitution pattern in calixarene chemistry showing the wide-ranging possibility of thiacalixarene skeleton modifications.     

Vinyldiazolactone as a vinylcarbene precursor: Highly selective C-H insertion and cyclopropanation reactions

Vinylcarbenes are versatile synthetic intermediates, capable of asymmetric cyclopropanation and insertion into unactivated C-H bonds. The vinyldiazolactone precursor to the metal vinylcarbene possesses superior stability in comparison to previously known vinyldiazoacetates and, for the first time, allows the use of Z-vinylcarbenes in asymmetric C-H insertion and cyclopropanation reactions. Dirhodium azetidinone ligated compounds are optimal catalysts. Cyclopropanation coupled with the Cope rearrangement provides access to trans-3,4-disubstituted hydroazulenes.     

N-tosyloxycarbamates as a source of metal nitrenes: rhodium-catalyzed C-H insertion and aziridination reactions

The rhodium-catalyzed decomposition of N-tosyloxycarbamates to generate metal nitrenes which undergo intramolecular C-H insertion or aziridination reaction is described. Aliphatic N-tosyloxycarbamates produce oxazolidinones with high yields and stereospecificity through insertion in benzylic, tertiary, and secondary C-H bonds. Intramolecular aziridination occurs with allylic N-tosyloxycarbamates to produce aziridines as single diastereomers. The reaction proceeds at room temperature using a rhodium catalyst and an excess of potassium carbonate and does not require the use of strong oxidant, such as hypervalent iodine reagents. A rhodium nitrene species is presumably involved, as both reactions are stereospecific.     

Intermolecular amidation of unactivated sp2 and sp2 C-H bonds via palladium-catalyzed cascade C-H activation/nitrene insertion

This communication describes the Pd(OAc)2-catalyzed intermolecular amidation reactions of unactivated sp2 and sp3 C-H bonds using primary amides and potassium persulfate. The substrates containing a pendent oxime or pyridine group were amidated with excellent chemo- and regioselectivities. It is noteworthy that reactive C-X bonds were well-tolerated and a variety of primary amides can be effective nucleophiles for the Pd-catalyzed C-H amidation reactions. For the reaction of unactivated sp3 C-H bonds, beta-amidation of 1 degrees sp3 C-H bonds versus 2 degrees C-H bonds is preferred. The catalytic reaction is initiated by chelation-assisted cyclopalladation involving C-H bond activation. Preliminary mechanistic study suggested that the persulfate oxidation of primary amides should generate reactive nitrene species, which then reacted with the cyclopalladated complex.