Rate Study of Samarium Diiodide Reduction of Alkyl Halides and 2-Heptanone

Rate constants directly measured from GC-analyzed method for SmI₂ reduction of alkyl halides were obtained. The rates increase in the orders of primary, secondary, tertiary RX and RCl < RBr < RI as expected. 2-Heptanone was chosen as the partner of alkyl halide in the samarium Barbier reaction. In the absence of HMPA, the reaction orders of alkyl halide and ketone were determined as first and zero order, respectively.     

Rate constant estimation for C1 to C4 alkyl and alkoxyl radical decomposition

Rate coefficients for alkyl and alkoxy radical decomposition are important in combustion, biological, and atmospheric processes. In this paper, rate constant expressions for C₁? C₄ alkyl and alkoxy radicals decomposition via β‐scission are recommended based on the reverse, exothermic reaction, the addition of a hydrogen atom or an alkyl radical to an olefin or carbonyl species with the decomposition reaction calculated using microscopic reversibility. The rate expressions have been estimated based on a wide‐range study of available experimental data. Rate coefficients for hydrogen atom and alkyl radical addition to an olefin show a strong temperature curvature. In addition, it is found that there is a correlation between the activation energy for addition and (i) the type of atom undergoing addition and (ii) whether this radical adds to the internal or terminal carbon atom of the olefin. Rate coefficients for alkoxy radical decomposition show a strong correlation to the ionization potential of the alkyl radical leaving group and on the enthalpy of reaction. It is shown that the activation energy for alkyl radical addition to a carbonyl species can be estimated as a function of the alkyl radical ionization potential and enthalpy of reaction. © 2006 Wiley Periodicals, Inc. Int J Chem Kinet 38: 250–275, 2006     

A green and highly efficient alkylation of thiols in water

An environmentally benign and efficient process for the preparation of thioethers was developed by simple and practical reactions of alkyl halides and thiols in water in the presence of K₂CO₃ or Et₃N in very high yields. The reaction of aryl, alkyl, aliphatic and hindered thiols with various alkyl halides gave the corresponding products with significant advantages such as high conversions, short reaction time, mild reaction conditions, and low cost, simple workup with good to quantitative yields.     

One-pot catalytic C-C double bond cleavage of α,β-enones aided by alkyl group-immobilized silica spheres

Catalytic C-C double bond cleavage of α,β-enones with a 1-alkene and H₂O was carried out in the presence of a (Ph₃P)₃RhCl catalyst, 2-amino-3-picoline, cyclohexylamine, benzoic acid, and alkyl group-immobilized silica spheres. Upon completion of the reaction, the corresponding ketones were obtained without needing a further hydrolysis step. In this reaction, alkyl group-immobilized silica spheres act as a water reservoir for hydrolysis of an intermediate ketimine and as a phase divider between the organic solution and H₂O.     

Indium-catalyzed coupling reaction between silyl enolates and alkyl chlorides or alkyl ethers

The coupling reactions of alkyl chlorides with silyl enolates catalyzed by InBr₃, and the coupling reactions of alkyl ethers with silyl enolates catalyzed by the combined Lewis acid of InBr₃/Me₃SiBr are described. In both reaction systems, various types of silyl enolates were used to give corresponding α-alkylated esters, ketones, carboxylic acids, amides, thioesters, and aldehydes.     

Trinuclear Gold-Catalyzed 1,2-Difunctionalization of Alkenes

Activated alkyl halides have been extensively explored to generate alkyl radicals with Ru- and Ir- photocatalysts for 1,2-difunctionalization of alkenes, but unactivated alkyl bromides remain challenging substrates due to their strong reduction potential. Here we report a three-component 1,2-difunctionalization reaction of alkenes, unactivated alkyl bromides and nucleophiles (e.g., amines and indoles) using a trinuclear gold catalyst [Au₃(tppm)₂](OTf)₃. It can achieve the 1,2-aminoalkylation and 1,2-alkylarylation readily. This protocol has a broad reaction scope and excellent functional group compatibility (>100 examples with up to 96 % yield). It also affords a robust formal [2+2+1] cyclization strategy for the concise construction of pyrrolidine skeletons under mild reaction conditions. Mechanistic studies support an inner-sphere single electron transfer pathway for the successful cleavage of inert C−Br bonds.     

Acceleration of CuI-catalyzed coupling reaction of alkyl halides with aryl Grignard reagents using lithium chloride

In the presence of LiCl, CuI-catalyzed coupling reaction of R(alkyl)-X with Ar(aryl)MgBr at rt was completed within 2 h. Effective leaving groups X in R-X were Br, I, OTs, but not Cl. Grignard reagents ArMgBr with both standard and bulky Ar such as 2-MeC₆H₄, 2-MeOC₆H₄, and 2,6-(Me)₂C₆H₃ afforded the desired products in good yields. Ester and cyano groups in R-X were tolerated. Coupling reaction with R(alkyl)-MgBr proceeded as well.     

On the dichotomy of the SN2/ET reaction pathways: an apparent SN2 reactivity in the reaction of naphthalene dianion with alkyl fluorides

Dilithium naphthalene (Li₂C₁₀H₈) displays a S_N2 reactivity profile in its reaction with alkyl fluorides (n-, s- and t-octyl fluoride). S_N2 seems to be the dominant mechanism operating with primary alkyl fluorides, which presumably turns into competition with ET as we move to secondary and tertiary alkyl fluorides. Significantly, lithium naphthalene (LiC₁₀H₈) seems to have also an important nucleophilic component when reacting with alkyl fluorides, in contrast to the previously proposed general ET process valid for all alkyl halides. These results explain the observed distribution of products and are reinforced by a complete analysis of the products originated by the reaction with 6-halohexenyl radical probes, whose main alkylation products are described here for the first time.     

Tandem three-component reaction of aldehyde, alkyl acrylate, and amide using ethyl diphenylphosphine as organocatalyst

It is the first time that a chemoselective EtPPh₂-catalyzed three-component reaction of aromatic aldehyde, alkyl acrylate, and phthalimide or methyl toluenesulfonamide has been achieved. A variety of highly functional adducts can be generated efficiently in one step within 1-72 h in 38-93% yields. The reaction mechanism is proposed to undergo Morita-Baylis-Hillman reactions of aryl-substituted aldehydes and alkyl acrylates followed by Michael additions of amides. Our studies indicated that, in combination of EtPPh₂, alkyl acrylate also catalyzed this process.     

C4-C14-alkyl nitrates as organic trace compounds in air

The long chain alkyl nitrates (C _n >5) form a complex spectrum of natural and anthropogenic organic trace compounds in air. HRGC/ECD and HRGC/MSD using 56 amu as the signal reveal a standard pattern of isomeric n-alkyl nitrates in semi-rural air. This is regulated by the input of the corresponding alkanes, their rate constants for the reaction with OH, the rate constant of the alkylperoxy radicals for the reaction to alkyl nitrates, the atmospheric concentrations of NO/NO₂ and by the rate constants of the alkyl nitrates for the reaction with OH radicals as the major removal reaction. The complex pattern of signals given by the ECD in the retention index range between 700 and 2000 has been observed before but this is the first time that it has been assigned to a defined group of chemical compounds.The environmental impact of the occurrence of the different groups of alkyl nitrates has yet to be evaluated. Their general property as organic stabilizers for NO/NO₂ and therefore as precursors of NO ₃ ^- ions in rain and their biological potentials are also known. The long chain alkyl nitrates act as lipophilic carriers for nitric acid.     

Solvent-free synthesis of penta-substituted pyrroles: one-pot reaction of amine, alkyl acetoacetate, and fumaryl chloride

A novel, convenient, and efficient approach to the synthesis of penta-substituted pyrroles has been reported based on the multicomponent reaction. Solvent-free condition for the formation of enaminones from primary amines and alkyl acetoacetates and it's reaction with fumaryl chloride lead to the formation of pyrroles that have halide, CH₂CO₂H, ester functional groups, and two alkyl substitutions.     

Dehydrocoupling of boranes with amines using a scandium catalyst

The scandocene alkyl complex (C₅Me₅)₂ScCH₂SiMe₃ was found to be an efficient catalyst for the dehydrocoupling of the non-cyclic boranes, dicyclohexylborane and thexylborane, with amines under mild conditions. The reactions afforded the corresponding aminoboranes in high yields with good functional group tolerance. The stoichiometric reaction of scandium alkyl with amine led to the isolation of a scandium amide complex, which was shown to be an active species during the catalysis. Although a borane-coordinated scandium hydride was also obtained from the stoichiometric experiment, it was not involved in the catalytic cycle. In addition, kinetic studies provided insight into this intermolecular dehydrogenation reaction.     

Reactions between a superoxide anion and alkyl bromides in dimethyl sulfoxide

The activation parameters of the reactions between a superoxide anion (O₂^·−) and alkyl bromides are measured. An ab initio study of the transition states for various mechanisms of this reaction is performed. The mechanism of radical separation in a polar solvent becomes competitive upon an increase in the number of alkyl groups in an alkyl bromide molecule and depends on their arrangement relative to a reaction center.     

Reactivity of mixed organozinc and mixed organocopper reagents: 6. Nickel-catalyzed coupling of methylarylzincs with primary alkyl halides; an atom-economic aryl-alkyl coupling

A nickel-catalyzed process for the cross-coupling of mixed arylzincs and primary alkyl halides has been developed. The reaction of a methylarylzinc with a primary alkyl halide in THF in the presence of NiCl₂/PPh₃ takes place with selective aryl transfer at room temperature in moderate yields. This protocol provides an atom-economic alternative to aryl-primary alkyl coupling using diarylzincs.     

Oxidative dealkylation of 4a-alkylated 4a,5-dihydroflavins: Properties of 4a-alkylated flavin radicals

Covalent coenzyme substrate adducts (“σ-complexes”) are probable intermediates in flavin-dependent biological dehydrogenations. As chemical model reaction for the σ-complex decay, oxidative dealkylation of stable 4a-alkyl-4a,5-dihydroflavins was studied as a function of alkyl mobility and nature of the oxidizing agent. The alkyl groups studied were n-propyl, allyl and benzyl, the oxidizing agents ³O₂, ¹O₂^*, nitroxide radical, ferricyanide and light-excited flavin.For all three alkyl residues, the primary reaction is formation of the 4a-alkyl-4a-hydroflavin radical by le^?-abstraction. ³O₂ and ferricyanide are too weak to initiate this step. If, however, the radical 4a-RFl is once formed, at least five decay modes can be observed depending on the nature of R:(1) For saturated R the exclusive decay is back transfer of the electron initially abstracted. In this case, dealkylation can only be obtained with ¹O₂*, albeit with the relatively slow rate of < 10⁶ M^?1s^?1.(2) For unsaturated R further 1e^?-oxidation leads to quantitative formation of oxidized flavin, while the fate of the alkyl group is still uncertain: In any case, ROH and the corresponding aldehydes as well as the dimers R₂ can be excluded as products.(3) Further oxidation by ³O₂ again leads to a quantitative yield of oxidized flavin while the alkyl residues are converted to peroxy radicals. In an autocatalytic reaction they form the corresponding hydroperoxides with starting 4a-R-Fl_redH, leading to acrolein (R = allyl) or benzaldehyde (R = benzyl) as the major products.(4) In the absence of further oxidant, slow intramolecular alkyl migration is observed leading to the stable 5-alkyl-l,5-dihydroflavin isomer.(5) Competitively, alkyl migration occurs intermolecularly with the starting material as carbenium acceptor, resulting in formation of the stable 4a,5-dialkyl-4a,5-dihydroflavin and unsubstituted radical HFl, which disproportionates.     

Insertion de germylenes dans la liaison etain—carbone. Germylenes a substituants perhalogenes

The electrophilic germylenes GeCl₂ and EtGeCl react with allyl- and (trichloromethyl)-trialkylstannanes with insertion in the SnC bond. The germylstannanes obtained give an α-elimination reaction leading to R₃SnCl and divalent species of germanium with an allyl or trichloromethyl substituent. The alkyl(dichloromethyl)germylenes are also obtained by an α-elimination reaction from the alkyl(dichloromethyl)methoxyhydrogermanes.     

Site‐Selective Tertiary Alkyl–Fluorine Bond Formation from α‐Bromoamides Using a Copper/CsF Catalyst System

A copper‐catalyzed site‐selective fluorination of α‐bromoamides possessing multiple reaction sites, such as primary and secondary alkyl?Br bonds, using inexpensive CsF is reported. Tertiary alkyl?F bonds, which are very difficult to synthesize, can be formed by this fluorination reaction with the aid of an amide group. Control experiments revealed that in situ generated CuF₂ is a key fluorinating reagent that reacts with the tertiary alkyl radicals generated by the reaction between an α‐bromocarbonyl compound and a copper(I) salt.     

Reduced Species （HSO2^-, SO2^·-） Promoted One-Pot Efficient Synthesis of Phenyl Alkyl Selenides

Reduced species （HSO2^-, SO2^·-） promoted one-pot synthesis of phenyl alkyl selenides has been developed. This synthetic method was achieved by reactions of diphenyl diselenide with alkyl halides at room temperature. It is noteworthy that the reactions were operated under mild reaction conditions, required short time, and got good resuits. A single electron transfer reaction mechanism was proposed for the reaction.     

Iron‐Catalyzed Diboration and Carboboration of Alkynes

An iron‐catalyzed diboration reaction of alkynes with bis(pinacolato)diboron (B₂pin₂) and external borating agents (MeOB(OR)₂) affords diverse symmetrical or unsymmetrical cis‐1,2‐diborylalkenes. The simple protocol for the diboration reaction can be extended to the iron‐catalyzed carboboration of alkynes with primary and, unprecedentedly, secondary alkyl halides, affording various tetrasubstituted monoborylalkenes in a highly stereoselective manner. DFT calculations indicate that a boryliron intermediate adds across the triple bond of an alkyne to afford an alkenyliron intermediate, which can react with the external trapping agents, borates and alkyl halides. In situ trapping experiments support the intermediacy of the alkenyl iron species using radical probe stubstrates.     

Syntheses of polycarbonate and polyurethane precursors utilizing CO2 over highly efficient, solid as-synthesized MCM-41 catalyst

As-synthesized MCM-41 was used as a reusable, heterogeneous catalyst for the eco-friendly synthesis of cyclic carbonate precursors of polycarbonates via a cycloaddition reaction of CO₂ with epoxides. This catalyst is also efficient for the synthesis of alkyl and aryl carbamate precursors of polyurethanes via the reaction of amines, CO₂ and alkyl halides. Both these reactions were carried out under mild conditions and without using any solvent or co-catalyst. CO₂ is utilized as a raw material replacement for toxic phosgene in the conventional synthesis of these chemicals.