New Mechanisms of Alkane Activation by Superelectrophiles. MNDO/PM3 Study of Activation of Methane and Propane by Cationic Bromine-Centered Electrophiles

Fragments of the potential energy surface for the systems C₃H₈ + Br₂·AlBr₃, CH₄ + CBr₃ ⁺, and CH₄ + CBr₃ ⁺ AlBr₄ ^- were simulated by the MNDO/PM3 method with a view to study the mechanisms of reactions of alkanes with new-generation superelectrophiles. Two new mechanisms were revealed for the reaction of alkanes with superelectrophiles. In the three examined systems, weakly bonded adducts are formed, which may be regarded as electrophile solvates with alkane molecules. Various ways of transformations of such solvates were examined. Radically new mechanisms were proposed for the bromination of methane with superelectrophiles CBr₃ ⁺ and CBr₃ ⁺ AlBr₄ ^-. The potential barrier to bromination is reduced to 17-25 kcal/mol due to nucleophilic assistance by lone electron pairs on the bromine atoms. By contrast, the reaction of propane with the Br₂·AlBr₃ complex is described in terms of the classical Olah scheme.     

Reactions of Nucleophiles with Nitroarenes: Multifacial and Versatile Electrophiles

In this overview, it is shown that there are many initial reactions between nitroarenes and nucleophiles: addition to the electron‐deficient ring at positions occupied by halogen and hydrogen atoms, addition to the nitro group, single‐electron transfer (SET), and other types of initial reactions. The resulting intermediates react further in a variety of ways to form products of nucleophilic substitution of a halogen atom (S_NAr), a hydrogen atom (S_NArH), and others. Many variants of these processes are briefly discussed, particularly in relation of rates of the initial reactions and further transformations.     

Enantioconvergent Substitution Reactions of Racemic Electrophiles by Organocatalysis

Over the past decades, the development of enantioselective catalysis using organocatalysts has evolved into an active research field and a number of enantioselective transformations have been established. However, despite their being a highly desirable process for the synthesis of organic molecules in an enantioenriched form, the enantioconvergent substitution reactions of racemic electrophiles using organocatalysts still present several challenges. Although intrinsic difficulties in the catalytic stereocontrol abound due to the initial chiral information of racemic electrophiles, in recent years, mechanistically diverse enantioconvergent processes have been intensively investigated in organocatalysis. This Minireview focuses on recent achievements in the development of enantioconvergent substitution reactions of racemic electrophiles using organocatalysts. The contents are classified on the basis of the mechanistic types of enantioconvergent processes.     

The Palladium-Catalyzed Cross-Coupling Reactions of Organotin Reagents with Organic Electrophiles [New Synthetic Methods (58)]

The cross-coupling of organotin reagents with a variety of organic electrophiles, catalyzed by palladium, provides a novel method for generating a carbon-carbon bond. Because this mild, versatile reaction is tolerant of a wide variety of functional groups on either coupling partner, is stereospecific and regioselective, and gives high yields of product, it is ideal for use in the synthesis of elaborate organic molecules. When the coupling reaction is carried out in the presence of carbon monoxide, instead of a direct coupling, carbon monoxide insertion takes place, stitching the two coupling partners together and generating a ketone.     

Preparation of Solid,Substituted Allylic Zinc Reagents and Their Reactions with Electrophiles

The treatment of various allylic chlorides or bromides with zinc dust in the presence of lithium chloride and magnesium pivalate (Mg(OCOtBu)₂) in THF affords allylic zinc reagents which, after evaporation of the solvent, produce solid zinc reagents that display excellent thermal stability. These allylic reagents undergo Pd‐catalyzed cross‐coupling reactions with PEPPSI‐IPent, as well as highly regioselective and diastereoselective additions to aryl ketones and aldehydes. Acylation with various acid chlorides regioselectively produces the corresponding homoallylic ketones, with the new C? C bond always being formed on the most hindered carbon of the allylic system.     

Reactions of Difunctional Electrophiles with Functionalized Aryllithium Compounds: Remarkable Chemoselectivity by Flash Chemistry

Flash chemistry using flow microreactors enables highly chemoselective reactions of difunctional electrophiles with functionalized aryllithium compounds by virtue of extremely fast micromixing. The approach serves as a powerful method for protecting‐group‐free synthesis using organolithium compounds and opens a new possibility in the synthesis of polyfunctional organic molecules.     

The Preparation and Reactions of Cationic Ruthenium(II) Complexes Containing 1,5-Cyclooctadiene and Acetonitrile

The polymer [(C₈H₁₂)RuCl₂]x, (C₈H₁₂  1,5-cyclooctadiene, x > 2), dissolves in refluxing acetonitrile to form [(C₈H₁₂)RuCl(CH₃CN)₃]⁺ and, on treatment with AgPF₆, [(C₈H₁₂)Ru(CH₃CN)₄]²⁺; some reactions of these cations are described.     

[3.3.2]- and [3.3.3]Propellanes in Reactions with Oxidizing Electrophiles

The structure of [3.3.2]- and [3.3.3]propellanes, their framework analogs, and their radical-cations was investigated by computational methods (BLYP and B3LYP) in the 6-31G* basis set. The reactivity of the propellanes toward model oxidizing electrophiles does not contradict the quantum-chemical calculations. In the case of the tetracyclic framework analog of [3.3.3]propellane the reaction takes place as C—H substitution, whereas in the case of [3.3.2]propellanes it takes place as C—C-oxidative addition.     

Diastereoselective Synthesis of Open‐Chain Secondary Alkyllithium Compounds and Trapping Reactions with Electrophiles

A practical stereoselective iodide–lithium exchange was used in the first general preparation of functionalized stereodefined acyclic secondary nonstabilized lithium reagents from the corresponding secondary alkyl iodides. These lithium reagents react with various electrophiles including carbon electrophiles with high retention of configuration. Kinetic data on the configurational stability of these acyclic alkyllithium reagents are given. This methodology offers a new entry to chiral synthons for the stereoselective synthesis of open‐chain molecules.     

贵金属及其掺杂团簇与甲烷反应研究进展

贵金属在甲烷活化与转化中呈现出优良的反应性。研究气态条件下贵金属物种与甲烷的反应,可以从分子水平上揭示凝聚相贵金属催化体系的活性位点与基元反应机理,为理性设计和改进催化剂提供理论基础。本文综述了贵金属原子、离子、团簇、氢化物、卤化物、氧化物、甲基配合物以及掺杂团簇活化、转化甲烷取得的新进展,并针对不同贵金属体系的甲烷活化机理展开讨论。     

Synthesis and Reactions of New Thiazoles and Pyrimidines Containing Sulfonate Moiety

Treatment of 2‐tosyloxybenzylidinethiosemicarbazone ( 2 ) with active halo compounds afforded thiazoles 3 – 5 . Moreover, reaction of compound 2 with acetic anhydride or dimethylformamide dimethylacetal gave N,N diacetyl 6 and dimethylamino derivatives 7 , respectively. Cyclization of thiazole derivatives 3 with some arylidenemalononitriles yielded thiazolo[2,3‐d]pyrans 8 – 12 . Multicomponent reaction of 2‐tosyloxybenzaldehyde ( 1 ) with urea, thiourea, or compound 2 and ethyl acetoacetate or acetylacetone afforded pyrimidines 13 – 14 . The structures of compounds were elucidated by elemental and spectral analyses.     

Cationic Micelle-catalyzed Ring-Opening Reactions of Aziridines with Thiols in Water

An efficient and practical method is described for the ring‐opening reactions of N‐tosylaziridines with various thiols in water under mild conditions. Various surfactants have been evaluated to optimize the reactions. Under optimal conditions, these reactions gave rise to the corresponding β‐amino sulfides in good to excellent yields.     

Reactions with Addition Compounds Containing Activated Formic Acid

Addition compounds of formic acid with tertiary organic bases in ratios higher than that required for salt formation (3:1 and 2:1 adducts) contain formic acid in a highly activated form. In particular, the 3:1 adducts of formic acid with trimethylamine and triethylamine are liquid reducing agents that are convenient to handle and are suitable for use in many selective reductions. These addition compounds have a surprisingly strong reducing action on sulfur dioxide, which is rapidly converted, even at low concentrations, into crystalline rhombic sulfur. Sulfones and polysulfones can be prepared in good yields by three-component reactions from activated formic acid, sulfur dioxide, and polarized vinyl compounds.