A convenient method for the synthesis of fluorinated α-cyanoacetates via phase-transfer catalysis

A simple and convenient method for the synthesis of fluorinated α-cyanoacetate derivatives has been developed by using electrophilic fluorination of allyl and benzyl substituted α-cyanoacetates with N-fluorobenzensulfonimide (NFSI) as electrophilic fluorinating agent via phase transfer catalysis. The reaction is transition metal free and carried out in aqueous and mild reaction conditions in the presence of readily available tetra-N-butylammonium iodide (TBAI) as phase-transfer catalyst.     

Radiation-induced oxidation of solid poly(ethylene oxide). I. Experimental results

γ-Initiated oxidations of solid poly(ethylene oxide) (PEO) have been carried out at ambient temperatures and the dependence of the rate of oxygen consumption on rate of initiation, O₂ pressure, and crystallinity has been determined. At 25°C, the radiation yield G for O₂ absorbed is 117–281, depending on dose rate, and decreases moderately with increasing crystallinity. The principal oxidation products are formate and hemiformal groups, hydroperoxides, and some volatile compounds, mainly formaldehyde and carbon dioxide. The rates of O₂ consumption and formation of products and chain scission are little affected by a change of the temperature in the range ?23 to +55°C except for hydroperoxide, the formation of which requires an activation energy of 4 kcal/mole. Experiments with 2,6-di-tert-butyl-p-cresol show that essentially all of the initiating PO₂· radicals escape cage termination; G value for formation of the initiating peroxy radicals was estimated from the inhibition period to be 5.0 ± 0.3.     

Effect of formaldehyde on the cationic polymerization of styrene

Polymerization of styrene has been carried out in the presence of formaldehyde at 30°C in benzene solution by using boron trifluoride etherate as a catalyst. The rate of polymerization in the initial stage was accelerated with addition of formaldehyde, while the steady-state rate of polymerization was retarded in the presence of formaldehyde. The acceleration for the rate of polymerization was found only in a short time from the beginning. The steady-state rate of polymerization followed the equation: where [C]₀ and [F]₀ are initial concentrations of catalyst and formaldehyde, [M] is the monomer concentration, and k₁, k₂, and k₃ are constants. It has been assumed that the chain-transfer reaction does not involve formaldehyde itself but rather the reaction products of formaldehyde, such as polystyrene having ethoxy or hydroxymethyl ends. The apparent chain-transfer constant for the added formaldehyde has been determined to be 1.63.     

亲电氟化反应的新进展

介绍了自八十年代以来亲电氟化反应的最新进展, 其中包括众多的N-F类电氟化试剂的制备, 它们和各种底物的反应以及此类亲电氟化反应可能的机理。     

Selectfluor: Mechanistic Insight and Applications

The replacement of hydrogen atoms with fluorine substituents in organic substrates is of great interest in synthetic chemistry because of the strong electronegativity of fluorine and relatively small steric footprint of fluorine atoms. Many sources of nucleophilic fluorine are available for the derivatization of organic molecules under acidic, basic, and neutral conditions. However, electrophilic fluorination has historically required molecular fluorine, whose notorious toxicity and explosive tendencies limit its application in research. The necessity for an electrophilic fluorination reagent that is safe, stable, highly reactive, and amenable to industrial production as an alternative to very hazardous molecular fluorine was the inspiration for the discovery of selectfluor. This reagent is not only one of the most reactive electrophilic fluorinating reagents available, but it is also safe, nontoxic, and easy to handle. In this Review we document the many applications of selectfluor and discuss possible mechanistic pathways for its reaction.     

Endo- and exocyclic N-alkylation of 1- and 5-aminotetrazoles with t-BuOH-HClO4: synthesis of mono-, di-, and tri-tert-butyl substituted aminotetrazolium salts

A new method for the synthesis of 1,3,5-trisubstituted aminotetrazolium salts based on alkylation of 1- and 5-aminotetrazoles with the t-BuOH-HClO₄ system is presented. Depending on the structure of the tetrazole substrate and reaction conditions, alkylation proceeds at the endocyclic nitrogen atoms as well as at the 1- and 5-amino groups giving mono-, di-, and tri-tert-butyl substituted tetrazolium salts. An X-ray diffraction investigation of 3-tert-butyl-1,5-bis(tert-butylamino)tetrazolium perchlorate and 5-amino-1,3-di-tert-butyltetrazolium chloride was carried out.     

Recent Advances in Trifluoromethylation Reactions with Electrophilic Trifluoromethylating Reagents

Electrophilic trifluoromethylation reactions have been the latest approach to achieve the fluoroalkylation of compounds with newly‐discovered reagents, such as the Togni’s (1‐trifluoromethyl‐1,2‐benziodoxol‐3‐(1 H)‐one), Umemoto’s (S‐(trifluoromethyl)dibenzothiophenium tetrafluoroborate), Yagupolskii’s (S‐(trifluoromethyldiarylsulfonium salts), Shreeve’s (S‐(trifluoromethyl)dibenzothiophenium triflate), and Shibata’s (trifluoromethylsulfoximine salts) reagents. All these reagents produce an electrophilic trifluoromethylating (CF₃⁺) species that undergoes reaction with nucleophiles. In addition, these latter reactive species (i.e. CF₃⁺) can undergo electron‐transfer (ET) processes affording CF₃ ^? radicals that expand the scope to substrates other than conventional nucleophiles that can undergo reaction. In this Review, we shall discuss the trifluoromethylation reactions of diverse families of organic substrates of biological interest as a means to comparing the reagents scope and best reaction conditions. Some, though not all, of these reactions require the assistance of metal or organometallic catalysts. Some require additives and catalysts to promote the fluoroalkylation reaction, but invariably all are initiated and carried out by electrophilic trifluoromethylating species.     

Synthesis of mono-, di-, tri-, and tetraethyl-o-carboranes by electrophilic alkylation ofo-carborane with ethyl bromide in the presence of AICl3 and their transformations

Optimal conditions for the preparation of 9-ethyl-, 9,12-diethyl, 8,9,12-triethyl-, and 8,9,10,12-tetraethyl-o-carboranes under the action of EtBr on o-carborane in the presence of AICl₃ were determined. The behavior of these o-carborane derivatives towards electrophilic and nucleophilic reagents was studied. The presence of four ethyl groups in positions 8, 9, 10, and 12 of the carborane polyhedron increases the electron density on the boron atoms in positions 4, 5, 7, and II to the point where they are able to enter into reactions of electrophilic substitution, and in positions 3 and 6 to the point that they become resistant to the action of nucleophilic reagents. Reactions of 1,2-dilithium-8,9,10,12-tetraethyl-o-carborane with various electrophilic reagents were studied.Translated fromIzvestiya Akademii Nauk, Seriya Khimicheskaya, No. 11, pp 2755–2763, November, 1996.     

Another Unprecedented Wieland Mechanism Confirmed: Hydrogen Formation from Hydrogen Peroxide,Formaldehyde, and Sodium Hydroxide

In 1923, Wieland and Wingler reported that in the molecular hydrogen producing reaction of hydrogen peroxide with formaldehyde in basic solution, free hydrogen atoms (H^.) are not involved. They postulated that bis(hydroxymethyl)peroxide, HOCH₂OOCH₂OH, is the intermediate, which decomposes to yield H₂ and formate, proposing a mechanism that would nowadays be considered as a “concerted process”. Since then, several other (conflicting) “mechanisms” have been suggested. Our NMR and Raman spectroscopic and kinetic studies, particularly the determination of the deuterium kinetic isotope effect (DKIE), now confirm that in this base‐dependent reaction, both H atoms of H₂ derive from the CH₂ hydrogen atoms of formaldehyde, and not from the OH groups of HOCH₂OOCH₂OH or from water. Quantum‐chemical CBS‐QB3 and W1BD computations show that H₂ release proceeds through a concerted process, which is strongly accelerated by double deprotonation of HOCH₂OOCH₂OH, thereby ruling out a free radical pathway.     

Molecular iodine-catalyzed efficient and highly rapid synthesis of bis(indolyl)methanes under mild conditions

Highly rapid and efficient electrophilic substitution reactions of indoles with various aldehydes and ketones were carried out using I₂ in CH₃CN to afford the corresponding bis(indolyl)methanes in excellent yields.     

Synthesis of Tetraazide Derivatives of <Emphasis Type="Italic">p-tert</Emphasis>-Butylcalix[4]arene Using Copper-Catalyzed Nucleophilic Aromatic Substitution

Aromatic azido derivatives of p-tert-butylcalix[4]arene have been obtained for the first time using copper-catalyzed nucleophilic aromatic substitution of azide anion for bromide in 5,11,17,23-tetrabromo- 25,26,27,28-tetrabuthoxycalix[4]arene in a dioxane–water (3: 1) solvent mixture with N,N-dimethylethylenediamine as a stabilizing ligand for copper(I). When the reaction is carried out under with microwave heating, partial substitution products (mono-, distally di-, proximally di-, and trisubstituted) can be isolated in satisfactory yields.     

卤化吡啶具有区域选择性的锂化反应与2,6-二甲氧基-3-溴-4-二苯基膦基吡啶的合成

在卤化吡啶的锂化反应的区域选择性研究基础上,以2,6-二甲氧基吡啶为原料,经溴化反应、邻位锂化反应和亲电取代反应制备了2,6-二甲氧基-3-溴-4-二苯基膦基吡啶,最终收率可达57．9％。     

Se-(Fluoromethyl) Benzenesulfonoselenoates: Shelf-Stable,Easily Available Reagents for Monofluoromethylselenolation

A new class of electrophilic monofluoromethylselenolation reagents, Se-(fluoromethyl) benzenesulfonoselenoates, has been developed. They can be readily prepared from sodium benzenesulfinates, Se powder and ClCFH₂ in one step under mild reaction conditions. Se-(fluoromethyl) benzenesulfonoselenoates are efficient electrophilic monofluoromethylselenolation reagents for a wide range of nucleophiles including indole, 6-azaindole, pyrrole, thiophene, electron-rich arene, aryl boronic acid and alkyne. The monofluoromethylselenolation approach features mild and environmentally friendly reaction conditions, good tolerance of various functional groups, and broad substrate scope.     

A Catalytic SEAr Approach to Dibenzosiloles Functionalized at Both Benzene Cores

A general procedure for the catalytic preparation of dibenzosiloles functionalized at one or both benzene rings starting from readily available ortho‐silylated biphenyls is reported. This method provides rapid access to silole building blocks substituted with chlorine atoms at both phenylene groups, thereby allowing catalytic access to directly polymerizable dibenzosiloles. Moreover, it is shown that, despite the involvement of highly electrophilic intermediates, a considerable range of Lewis‐basic, for example, oxygen‐ and nitrogen‐containing, functional groups is tolerated. The mechanism of this intramolecular electrophilic aromatic substitution (S_EAr) proceeds through a sulfur‐stabilized silicon cation, generated catalytically from the hydrosilane precursor.     

Synthesis of spiro-o-carboranylenecyclophosphazenes

Conclusions The reaction of bis(hydroxymethyl)-o-carborane and hexachlorocyclophosphazene gave previously unreported mono-, di-, and trispirobis(oxymethyl)-o-carboranylenecyclotriphosphazenes.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 9, pp. 2128–2129, September, 1986.     

Ethylene Biosynthesis part 10. Synthesis and study of racemic, (1R, 2S)-, and (1S, 2R)-1-Amino-2-(hydroxymethyl)cyclopropanecarboxylic Acid

The preparation of optically active 1-amino-2-(hydroxymethyl)cyclopropanecarboxylic acid has been achieved by a route involving cycloalkylation of dimethyl malonate with epichlorohydrin and subsequent Hofmann rearrangement. The reaction of epichlorohydrin with nucleophiles may occur al either electrophilic site, epoxide or halide. Based on the absolute configuration of the starting materials and the lactones obtained, it has been shown that the initial step of the cycloalkylation occurs at the epoxide moiety. The 1-amino-2-(hydroxymethyl)-cyclopropanecarboxylic acid, an analogue of the precursor to the plant growth hormone ethylene, is to be used in affinity purification techniques and in generation of antibodies.     

Isokinetic correlation analysis of the series of electrophilic substitution reactions of o -substituted phenylmercurials

Isokinetic relationships of the series of electrophilic substitution reactions ofo-substituted phenylmercurials are studied, and the results show, for the first time, that isokinetic correlation analysis can reveal the dominant factor in the system of the reactions. The analysis of S_E2 ofo-substituted phenylmercuric chlorides indicates that the steric effect ofo-substituents is the predominant factor when I₂ is used as electrophilic agent, however, the electronic effect ofo-substituents would become the predominant factor when HCl is used as the electrophilic agent. In S_E1 ofo-substituted phenylmercuric chlorides, the results of the analysis display that the predominant factor is the field effects ofo-substituents. The determination of predominant factors in those reactions would provide further scientific basis for those reaction mechanisms.     

焦脱镁叶绿酸-a甲酯20-meso-1-位的亲电取代反应

利用焦脱镁叶绿酸-a甲酯与亲电试剂发生的取代反应, 在焦脱镁叶绿酸-a甲酯的20-meso-位上分别引进硝基和卤原子, 得到了20-meso位取代的焦脱镁叶绿酸衍生物. 所合成的新叶绿素-a衍生物均经UV, IR, ¹H NMR及元素分析证明其结构. 另外, 对叶绿素-a卟吩环上的芳香性和相应的化学反应活性也进行了讨论, 提出了可能的亲电取代反应机理.     

Insight into Markovnikov Reactions of Alkenes in Terms of Ab Initio and Molecular Face Theory

Electrophilic additions of hydrogen halides to alkenes in the gas phase are investigated with a high‐level ab initio method, MP2/6‐311+G(3df,2p). Based on this, the interesting features of these reactions along the IRC routes are characterized by the molecular face (MF) theory. For an alkene at the initial state, if the representative electron density (ED) encoded on the molecular face (MF) of the Markovnikov (M) carbon atom (the carbon with more hydrogen atoms) is larger than that of the anti‐Markovnikov (AM) carbon atom (the carbon with fewer hydrogen atoms), the electrophilic addition reaction is predicted to proceed along the Markovnikov addition route; in the reverse situtation, the anti‐Markovnikov addition route would be slightly preferred. It is then demonstrated that for a series of alkenes, the difference between activation energies of Markovnikov and anti‐Markovnikov addition routes [ΔE^#_(M?AM)] has a good linear correlation with sign(K_ED)K²_ED, where K_ED is characteristic of the electron density (ED) at the π region in the initial state of the alkenes. Interestingly, there is a good linear correlation between our sign (K_ED)K²_ED and the absolute values of difference in the core ionization energy between M and AM carbon atoms obtained by others (L. J. Sæthre, T. D. Thomas, S. Svensson J. Chem. Soc. P2 1997 , 2, 749.) in terms of the experimental study. In addition, the spatial dynamic changing features of the MF faces and interesting pictures of the electron transfer are clearly shown during the course of the electrophilic addition reactions. These results indicate that not only regioselectivity, but also activation energy and reactivity correlate with the π charge distribution in the initial state of the alkenes for electrophilic addition reactions.     

Intramolecular electrophilic aromatic substitution of α-alkylcinnamaldehydes affording 1-alkoxy-2-alkylindenes

Treatment of α-alkylcinnamaldehydes with orthoesters, alcohols, or thiols in the presence of BF₃·OEt₂ induces an intramolecular electrophilic aromatic substitution reaction to afford 1-alkoxy-2-alkylindenes. The reaction mechanisms of the indene formation have been elucidated on the basis of the reaction behaviors of β-deuterated α-methylcinnamaldehyde and the NMR studies of the reaction mixture. The transformation process involves successive reactions, i.e., alkoxylation of the carbonyl carbon of α-alkylcinnamaldehydes to form acetals, elimination of alkoxide from the acetals to give alkoxycarbenium ion and γ-alkoxyallyl cation, and intramolecular electrophilic arylation to afford the indene ring structure.