Fluoroalkene chemistry: Part 1. Highly-toxic fluorobutenes and their mode of toxicity: reactions of perfluoroisobutene and polyfluorinated cyclobutenes with thiols

The reactions of four highly-toxic fluorobutenes - perfluoroisobutene (PFIB), 1-hydropentafluorocyclobutene (1-H), hexafluorocyclobutene (HFCB) and 3-chloropentafluorocyclobutene (3-Cl)—with propanethiol, 2,6-dimethoxybenzenethiol and N-acetylcysteine isopropyl ester were studied. PFIB and HFCB reacted with two molar equivalents of the aliphatic thiols, but with only one molar equivalent of the aromatic thiol (presumably due to steric hindrance) and resembled phosgene in their reactivity. The fluorocyclobutenes 1-H and 3-Cl reacted with one and up to three molar equivalents of the aliphatic thiols, respectively, but with only one molar equivalent of the aromatic thiol. The products of allyl and vinyl substitution were isolated and characterised as fully as possible. The inhalation toxicities of the fluorocyclobutenes to rodents correlated with the number of easily-displaceable fluorine substituents, supporting the contention that toxicity is due to reaction with biological thiols in the lung.     

1,2‐Bis(trifluoromethyl)ethene‐1,2‐dicarbonitrile and Vinyl Ethers: Cyclic Ketene Imines on the Pathway to 1 : 2 Cycloadducts

(E)‐ and (Z)‐1,2‐bis(trifluoromethyl)ethene‐1,2‐dicarbonitrile (BTE; (=E)‐ and (Z)‐1,2‐bis(trifluoromethyl)but‐2‐enedinitrile) were reacted with an excess of methyl vinyl ether, used as solvent, and furnished 1 : 2 adducts 6 (54%) and cyclobutanes 3 as 1 : 1 adducts (41%). The four diastereoisomeric bis‐adducts 6 (different ratios from (E)‐ and (Z)‐BTE) are derivatives of 1‐azabicyclo[4.2.0]oct‐5‐ene; X‐ray analyses and ¹⁹F‐NMR spectra revealed their structures. Since the cyclobutanes 3 are resistant to vinyl ether, the pathways leading to mono‐ and bis‐adducts must compete on the level of the intermediate l,4‐zwitterions 1 and 2 . The latter either cyclize to the cyclobutanes 3 or to six‐membered cyclic ketene imines 8 which accept a second molecule of vinyl ether to yield the bis‐adducts 6 . The occurrence of the highly strained ketene imines 8 gains credibility by comparison to stable seven‐membered cyclic ketene imines recently reported.     

Nickel-catalyzed acylstannylation and alkynylstannylation of 1,2-dienes

Carbostannylation of 1,2-dienes using acyl- and alkynylstannanes was achieved by means of nickel catalysis. In particular, acylstannylation of 1,2-dienes could be carried out with bis(1,5-cyclooctadiene)nickel [Ni(cod)₂] and acylstannanes to give selectively α-acylmethyl(vinyl)stannanes. The reaction was also applicable to acylstannanes prepared in situ by protonolysis of α-alkoxyalkenylstannanes or by reactions of α-silyloxyvinylstannanes with aldehyde acetals. For alkynylstannylation, a combination of Ni(cod)₂ and 1,3-bis(diphenylphosphino)propane (dppp) was found to be effective to afford α-alkynylmethyl(vinyl)stannanes, whereas the Ni(cod)₂-1,3-bis(dimethylphosphino)propane (dmpp) catalyst switched the regioselectivity to give (Z)-α-alkynylmethyl(alkenyl)stannanes. The acylstannylation products were successfully converted into various conjugated or unconjugated enones by a combination of cross-coupling and NaH-catalyzed isomerization. The alkynylstannylation products were transformed by cross- or homo-coupling reactions to various enynes or 2,3-bis(alkynylmethyl)-1,3-dienes, versatile precursors for variously substituted polycyclic compounds.     

Quantum chemical studies of mechanisms of organic reactions: VI. Reaction of ethane-1,2-dithiol with vinylidene chloride

A theoretical mechanism has been proposed for the reaction of vinylidene chloride with ethane-1,2-dithiol in the system hydrazine hydrate–potassium hydroxide on the basis of DFT quantum chemical calculations at the B3LYP/6-311++G(d,p) level of theory. The reaction includes two consecutive stages: dehydrochlorination of vinylidene chloride to chloroacetylene and nucleophilic addition of one thiol group of ethane-1,2-dithiol to the β-carbon atom of chloroacetylene, followed by closure of 2,3-dihydro-1,4-dithiine ring via nucleophilic substitution of chlorine by sulfur atom of the second thiol group.     

Fluoroalkene chemistry: Part 3. Reactions of arylthiols with perfluoroisobutene, perfluoropropene and chlorotrifluoroethene

Reactions of perfluoroisobutene (PFIB), perfluoropropene (PFP) and chlorotrifluoroethene (CTFE) with benzenethiol and 2-methoxybenzenethiol in acetonitrile, with potassium carbonate as base, were compared. PFIB reacted with benzenethiol to give ketene thioacetal (CF₃)₂CC(SAr)₂ and with 2-methoxybenzenethiol to give mono- and bis-vinyl species (CF₃)₂CCFSAr and (CF₃)₂CC(SAr)₂. PFP reacted with both thiols to give the addition product CF₃CFHCF₂SAr and vinyl isomers CF₃CFCFSAr (6:1 E/Z ratio). CTFE reacted with several methoxy-substituted arylthiols to give addition products of structure CFClHCF₂SAr. The arylthiols used throughout the study imitate biological thiols. Inhalation toxicities of the fluoroalkenes decrease in the order PFIB > PFP > CTFE and correlate with their reactivities towards the model thiols, supporting the current view that their toxicity relates to their ability to react with biological thiols.     

Synthesis of CO2-based functional poly(carbonate-co-lactide)

TPPAlCl-PPN⁺Cl⁻ binary catalyst (where TPPAlCl is 5,10,15,20-tetraphenylporphyrin aluminum chloride, PPN⁺Cl⁻ is bis[triphenylphosphine] iminium chloride, the molar ratio of TPPAlCl to PPN⁺Cl⁻ is 1 to 0.5) can initiate the effective one-pot/one-step ternary copolymerization of CO₂, lactide and 4-vinyl-1-cyclohexene-1,2-epoxide, and the quaternary copolymerization of CO₂, propylene oxide, lactide, 4-vinyl-1-cyclohexene-1,2-epoxide, to form multiblock poly(carbonate-co-lactide) products with pendant vinyl group. The ternary copolymerization product composes of polylactide (PLA) block and poy(vinylcyclohexylene carbonate) (PVCHC) block, and the quaternary copolymerization product composes of poy(propylene carbonate) (PPC) block, PLA block and PVCHC block, which are verified by ¹H NMR, ¹³C NMR, ¹H-¹H cosy, hetero-nuclear multiple bond correlation, DTG, and Gel permeation chromatography analysis. The functionality and glass-transition temperature of the products can be easily adjusted by the copolymerization variables, such as the molar ratio of comonomers, copolymerization temperature, pressure of CO₂, the concentration of the catalyst.     

Selective synthesis of bis[1,2]dithiolo[1,4]thiazines from 4-isopropylamino-5-chloro-1,2-dithiole-3-ones

Reaction of 4-isopropylamino-5-chloro-1,2-dithiole-3-ones 3 and S₂Cl₂ in acetonitrile gave selectively 3-oxo-bis[1,2]dithiolo[1,4]thiazine-5-thiones 1 by the addition of triethylamine and bis[1,2]dithiolo[1,4]thiazine-3,5-diones 5 under the action of formic acid. 3,5-Diones 5 were also obtained by intramolecular cyclization of N,N-bis(5-chloro-3-oxo[1,2]dithiol-4-yl)amines 6 with S₂Cl₂ in the presence of Et₃N.     

Oxidative sulfamidation of vinyl silanes: A route to diverse silylated N-Heterocycles

The reaction of trimethyl(vinyl)silane 1 and dimethyl(divinyl)silane 2 with various sulfonamides in the oxidative system (tert-BuOCl + NaI) has been studied and shown to be an efficient approach for the synthesis of silylated N-heterocycles. Triflamide demonstrated the reactivity principally different from that of arenesulfonamides. With silane 1, it afforded the products of iodochlorination and bis(triflamidation) (major), whereas arenesulfonamides gave N-arenesulfonylaziridines in up to 91% yield. Silane 2 with arenesulfonamides yielded the products of mono and bis(iodochlorination), mono and bis(aziridination), and 3,5-diiodo-4,4-dimethyl-1-(arylsulfonyl)-1,4-azasilinanes. By contrast, triflamide, apart from the products of halogenation and iodotriflamidation, unexpectedly gave 3-(trifluoromethylsulfonyl)-5-(triflamido)oxazolidine as the main product. The structure of most heterocyclic products is proved by X-ray analysis. The effect of the silyl group in the substrate and of the substituent in the reagent on the course of oxidative sulfamidation is discussed by comparing with all-carbon analogues.     

Carbohydrate-metallocene conjugates: selective formation of a zirconadioxacyclopentane-type dimer from the reaction of a bis(enolate)ZrCp2 reagent with a glucofuranoside derivative

The zirconocene enolate complex bis(2-propenolato)ZrCp2 (1) reacts with two molar equivalents of the 1,2,3,4-O-tetramethyl-alpha-D-glucopyranoside (2) with liberation of two equivalents of acetone to yield cleanly the bis(carbohydrate)zirconcene complex (3). Alternatively 1 and the "bifunctional" glucose derivative 3-O-benzyl-1,2-O-isopropylidene-glucofuranoside (4) react to the corresponding zirconadioxacyclopentane-type metallacyclic product that was isolated as the respective dimer (5) featuring a sequence of linearly anellated five-, four-, five-membered metallacycles. Both carbohydrate zirconocene complexes 3 and 5 were characterized by NMR experiments as well as by X-ray diffraction.     

Thermophysical Properties of the Ternary System 2-Methoxyethanol + Acetonitrile + 1,2-Dichloroethane, and the Binary Systems at 25°C

Excess molar volumes, change of refractive indexes, and deviation of dynamic viscosity of the 2-methoxyethanol + acetonitrile, 2-methoxyethanol + 1,2-dichloroethane, and acetonitrile + 1,2-dichloroethane binary systems and the excess molar volumes of 2-methoxyethanol + acetonitrile + 1,2-dichloroethane ternary system have been determined at 25°C and at atmospheric pressure, by measuring densities, refractive indexes, and viscosities over the entire range of composition. These derived data of binary and ternary mixtures were fitted to Redlich–Kister and Cibulka equations, respectively. An estimation of excess volumes is also evaluated using a modified Heller equation, which depends on the refractive indexes of the mixture. A comparison of the predictions by different methods with the experimental values of the physical properties has been made.     

Iodocyclization of 6-allylamino-4,5-dihydropyrazolo[3,4-d]pyrimidines

6-Allylamino-1-R-4,5-dihydro-1H-pyrazolo[3,4-d]pyrimidines treated with iodine in the presence of potassium carbonate are converted into 6-allylamino-1-R-1H-pyrazolo[3,4-d]pyrimidines that at further reaction with iodine undergo the cyclization into 6-iodomethyl-1-R-1,6,7,8-tetrahydroimidazo [1,2-a]pyrazolo[3,4-d]-pyrimidin-5-ium iodide of a linear structure. In the absence of potassium carbonate alongside the mentioned linear products 8-iodo-methyl-1-R-1,4,5,6,7,8-hexahydroimidazo[1,2-a]pyrazolo[4,3-e] pyrimidin-9-ium iodides of an angular structure have been obtained.     

A domino approach to pyrazino- indoles and pyrroles using vinyl selenones

Herein we disclose an efficient and flexible approach to biologically relevant 3,4-dihydropyrazino[1,2-a]indol-1(2H)ones and 3,4-dihydropyrrolo[1,2-a]pyrazin-1(2H)ones through a domino Michael/intramolecular nucleophilic substitution pathway using potassium hydroxide in dichloromethane. Variously substituted vinyl selenones and 1H-indole-2-carboxamides or 1H-pyrrole-2-carboxamides have been employed with success in chemo and regio-selective processes. The introduction of an amino acid portion on the amidic function is well tolerated without racemization.     

Zwitterionic spirocyclic λ5 Si-silicates with two cis-1,2-diphenylethene-1,2-diolato(2–) ligands: Synthesis and structural characterization

The zwitterionic ⁵ Si-silicates bis[cis-1,2-diphenylethene-1,2-diolato(2–)](morpholiniomethyl)silicate (2) and bis[cis-1,2-diphenylethene-1,2-diolato(2–)][(2,2,6,6-tetramethylpiperidinio)methyl]silicate (3) were synthesized by various methods, including remarkableSi–C cleavage reactions with benzoin. Treatment of trimethoxy(morpholinomethyl)silane (4), dimethoxy(morpholinomethyl)phenylsilane (5), or dimethoxy(methyl)(morpholinomethyl)silane (6) with two molar equivalents of benzoin in acetonitrile yielded 2. Compound 3 was synthesized by treatment of trimethoxy[(2,2,6,6-tetramethylpiperidino)methyl]silane (7) with two molar equivalents of benzoin in 1,4-dioxane/n-pentane and was isolated as the 1,4-dioxane solvate 3 ·3/2C₄H₈O₂. Compounds 2 and 3 ·3/2C₄H₈O₂ were structurally characterized by solution and solid-state NMR spectroscopy and by single-crystal X-ray diffraction. In addition, the dynamic behavior of 3 in solution was studied by VT ¹H NMR experiments.     

An efficient route to unsymmetrical bis(azolium) salts: CCC-NHC pincer ligand complex precursors

The coupling of N-heterocyclic azoles (imidazoles, benzimidazoles, triazoles) to bromobenzenes (1,2-; 1,3-; or 1,4) in a step-wise, sequential manner was accomplished by manipulation of reaction time and stoichiometry, which provided straight-forward access to unsymmetrical bis(azolium) salts in only three isolation steps from commercially-available starting materials. Eight mono(azole) substituted bromobenzenes, four mono(azolium)bromobenzene salts, twelve unsymmetrical bis(azole)benzenes, and fourteen unsymmetrical bis(azolium) salts, which are precursors for pincer ligand complexes, are reported.     

6-exo versus 7-endo iodolactonizations of 2-(alkynyl)phenylacetic acids

Exposure of 2-alkynylphenylacetic acids to excess iodine in acetonitrile containing anhydrous potassium carbonate delivers good yields, either of the corresponding isochroman-3-ones or benzo[d]oxepin-2(1H)-ones, depending upon the alkyne substituent: when this is alkyl, the former 6-exo products dominate, otherwise the 7-endo products are formed largely or, more often, exclusively.     

Synthesis of new polydentate pyrazolyl‐ethene ligands by interaction of 1H‐pyrazole and 1,1,2,2‐tetrabromoethane in a superbasic medium

Reaction of pyrazole and 1,1,2,2‐tetrabromoethane in a superbasic medium dimethylsulfoxide‐potassium hydroxide was investigated, and a number of pyrazolyl‐ and bromo‐substituted ethenes, which are the products of concurrent substitution and elimination reactions, were identified. Carrying out the reaction using different reagent mole ratios allowed to selectively isolate Z‐1,2‐bis(pyrazol‐1‐yl)ethene, 1,1,2‐tris(pyrazol‐1‐yl)ethane, and 1,1,2,2‐tetrakis(pyrazol‐1‐yl)ethane. Crystal structure of {Z‐1,2‐bis (pyrazol‐1‐yl)ethene}dichlorozinc was established using X‐ray diffraction method. J. Heterocyclic Chem., (2011).     

A one-pot four-component synthesis of N-arylidene-2-aryl-imidazo[1,2-a]azin-3-amines

N-Arylidene-2-aryl-imidazo[1,2-a]azin-3-amines were synthesized via a one-pot, four-component condensation reaction using a 2-aminoazine, toluene-4-sulfonylmethyl isocyanide (TsCH₂NC), and two equivalents of readily available aromatic aldehydes. The reaction was performed in diethyl ether as the solvent, with p-toluenesulfonic acid (p-TSA) as the catalyst at reflux temperature.     

A novel 2:1 cycloadduct of dimethyl acetylenedicarboxylate with 3,5-diphenyl-4-methoximino-4H-pyrazole 1,2-dioxide

Two equivalents of dimethyl acetylenedicarboxylate react with 3,5-diphenyl-4-methoximino-4H-pyrazole 1,2-dioxide in acetonitrile under reflux. The major product was shown by X-ray analysis to be a 5,8-epoxyisoxazolo[2,3-d]-[1,4]-diazepine derivative.     

Studies on electrophilic reaction of Br2 with 1,2-allenylic sulfones. A highly regio- and stereoselective synthesis of 1-phenylsulfonyl-2-bromo-1(E)-alken-3-ols and 1-phenylsulfonyl-2-bromo-1(E),3(E)-butadienes

The reaction of 1,2-allenyl sulfones with Br₂ afforded E-bromohydroxylation- or E-bromination-elimination products highly regio- and stereoselectively depending on the substitution pattern of the allene functionality. The five-membered intermediate cis-3h was isolated and characterized by X-ray diffraction study. The study on its reactivity of this intermediate revealed the origin of the regio- and stereoselectivity of this reaction.     

Photochemical generation of highly destabilized vinyl cations: the effects of alpha- and beta-trifluoromethyl versus alpha- and beta-methyl substituents

The photochemical reactions in methanol of the vinylic halides 1-4, halostyrenes with a methyl or a trifluoromethyl substituent at the alpha- or beta-position, have been investigated quantitatively. Next to E/Z isomerization, the reactions are formation of vinyl radicals, leading to reductive dehalogenation products, and formation of vinyl cations, leading to elimination, nucleophilic substitution, and rearrangement products. The vinyl cations are parts of tight ion pairs with halide as the counterion. The elimination products are the result of beta-proton loss from the primarily generated alpha-CH(3) and alpha-CF(3) vinyl cations, or from the alpha-CH(3) vinyl cation formed from the beta-CH(3) vinyl cation via a 1,2-phenyl shift. The beta-CF(3) vinyl cation reacts with methanol yielding nucleophilic substitution products, no migration of the phenyl ring producing the alpha-CF(3) vinyl cation occurs. The alpha-CF(3) vinyl cation, which is the most destabilized vinyl cation generated thus far, gives a 1,2-fluorine shift in competition with proton loss. The experimentally derived order of stabilization of the vinyl cations photogenerated in this study, alpha-CF(3) < beta-CF(3) < beta-CH(3) < alpha-CH(3), is corroborated by quantum chemical calculations, provided the effect of solvent is taken into account.