Mild and efficient synthesis of propargylamines by copper-catalyzed Mannich reaction

Terminal alkynes undergo mild and efficient aminomethylation with aqueous formaldehyde and secondary amines under CuI catalysis. In most cases high to nearly quantitative yields of tertiary propargylamines are obtained in DMSO solution at room temperature. Aromatic, aliphatic and silylated acetylenes as well as alkynols can be used. Primary amines are less reactive and satisfactory yields of secondary propargylamines are obtained only with phenylacetylene.     

A new convenient synthesis of propargylic fluorohydrins and 2,5-disubstituted furans from fluoropropargyl chloride

Fluoropropargyl chloride reacted with carbonyl compounds to give propargylic fluorohydrins under mild conditions and in good yields; however, at higher temperatures and longer reaction times, 2,5-disubstituted furans are obtained, also in good yields. Fluorohydrins can be readily oxidized to alpha-fluoroketones and alpha-fluorocarboxylic acids with Jones' reagent.     

Magnesium Chloride–Catalyzed Thiolysis of Epoxides: Synthesis of β-hydroxy Sulfides

A mild and convenient ring opening of epoxides with thiophenol and its derivatives takes place at room temperature in the presence of magnesium chloride as catalyst to afford the corresponding β-hydroxy sulfides along with minor amounts of 2-chlorocycloalkanols in good yields. When the crude reaction mixtures are treated with aqueous sodium hydroxide solution, pure 2-arlythiocycloalkanols are obtained in good yields.     

Bridged tetraquaternary salts from N,N'-polyfluoroalkyl-4,4'-bipyridine

4,4'-Bipyridine (1) with excess of polyfluoroalkyl bromide or iodides 2a-d at 100-110 degrees C without solvent gave the monoquaternary salts 3a-d in >90% yields. However, 1 with 2.5 equiv of 2a-c in DMF at 110 degrees C resulted in the diquaternary salts 5a-c in >85% yields. In DMF, 5a-c were obtained in comparable yields when a molar excess of 2a-c reacted with 3a-c. 1,4-Dibromobutane with 3a,b in DMF at 100 degrees C led to the tetraquaternary salts 7a,b in approximately 85% yields. In water or acetone/water as a solvent, salts 3a-d and 5a-c were metathesized with LiN(SO(2)CF(3))(2) and KSO(3)CF(3) to produce monoquaternary ionic liquids 4a-h in >88% yields and diquaternary ionic liquids 6a-f in >86% yields, respectively. Tetraquaternary ionic liquids 8a,b were obtained when LiN(SO(2)CF(3))(2) was reacted with salts 7a,b. These compounds were stable to 340 degrees C as determined by DSC. They are the first N-mono-, N,N'-di-, and N,N,N',N'-tetra-4,4'-polyfluoroalkylbipyridinium quaternary salts and ionic liquids.     

Fluorescence Quantum Yields of Tryptophan and Tyrosine

Abstract

Fluorescence quantum yields (Q) for tyrosine, tryptophan, and phenylalanine in water at 23° determined by the comparative method using a quinine standard were found to be 0.14, 0.13, and 0.024, respectively. Similar values were obtained with phenol as the standard. The numbers are much lower than those literature values which have been widely used to calculate protein fluorescence quantum yields. Possible reasons for the discrepancies are discussed. The quantum yields of isomeric tyrosines and fluorophenylalanines are also reported.     

Palladium-catalyzed synthesis of 2-(aminomethyl)indoles from ethyl 3-(o-trifluoroacetamidophenyl)-1-propargyl carbonate

[reaction: see text] The palladium-catalyzed reaction of ethyl 3-(o-trifluoroacetamidophenyl)-1-propargyl carbonate with piperazines in the presence of Pd(PPh(3))(4) in THF at 80 degrees C affords 2-(piperazin-1-ylmethyl)indoles in excellent yields. Good to excellent yields are also obtained with other secondary amines.     

THE PREPARATION OF TRIALKYL PHOSPHITES DIRECTLY FROM THE ELEMENT

Abstract

The reaction between finely divided white phosphorus and several alkoxide ions in the presence of tetrachloromethane and excess of alcohol has been investigated under a variety of conditions. High yields of trialkylphosphite are obtained when two equivalents of alkoxide are used. With one equivalent of alkoxide, dialkylphosphonate is formed in comparable yield. Maximum yields of triester are obtained within 1–3 h at room temperature. Prolonged treatment results in the conversion of trialkylphosphite to phosphate by reaction with tetrachloromethane. Phenolate ions are unreactive under the same experimental conditions. The mechanism of the reaction is discussed.     

Mass yields in 229Th(n,f)

Cumulative yields of 27 fission products have been determined in ²²⁹Th(n,f) by recoil catcher technique followed by gamma-ray spectrometry. Absolute fission yields were arrived at from the fission rate measured by track etch counting method. Mass yields were obtained from the cumulative yields using the charge distribution parameters reported in the literature. The values agree well with the reported values obtained both by physical and radiochemical methods. The resulting asymmetric mass distribution shows strong fluctuation in the yields in the light and heavy wings with a periodicity of five mass units.     

Asymmetric sulfoxidation of a β-carbonyl sulfide series by chloroperoxidase

The chloroperoxidase (CPO)-catalyzed oxidation of a series of β-carbonyl sulfides to sulfoxides has been studied at room temperature in aqueous citrate buffer. For dialkyl β-carbonyl sulfides, the products with methyl and ethyl substituents are obtained in ca. 100% yield. However when the alkyl group is n-propyl or i-propyl the yield drops dramatically (25%). An aryl sulfide derivative afforded product in very low yield (4%), but when the phenyl group bears a carbonyl, and the sulfur substituents are methyl or ethyl, the oxidation occurs with high yields (91–95%). Steric control of the sulfoxidation reaction is also confirmed with cyclohexanone derivatives, where a low product yield is observed even at high enzyme concentrations. Noteworthy are the yields obtained with cyclopentanone sulfide (65%) and an unexpected quantitative yield obtained with the γ-butyrolactone sulfide.     

BENZOPHENONE-SENSITIZED LIPID PEROXIDATION IN LINOLEATE MICELLES

Abstract— Benzophenone-photosensitized peroxidation in linoleic acid micelles (Type I reaction) has been investigated and quantum yields of both sensitizer photolysis and lipid peroxidation have been obtained. Benzophenone as well as its derivative, benzophenone-4'-heptyl-4-pentanoic acid (BHPA) have been utilized as sensitizers in this study. A quantum yield of 1.2 for hydroperoxide formation, compared with a benzophenone disappearance quantum yield of 0.41 (in the same linoleate micellar solution) was obtained; yields of 1.3 and 0.6 were found for comparable systems in which BHPA was the sensitizer. Although such data are consistent with the peroxidation mechanism of chain reaction, it is necessary to know the yields of initiating species to arrive at chain reaction lengths in these systems. Such yields have been determined by flash photolysis. The dependencies of sensitizer photolysis and hydroperoxide yields on linoleate concentration have also been determined in order to elucidate the effects of micelle formation or molecular organization on the peroxidative process. Additionally, for comparison in a saturated surfactant (lipid) system hydrogen abstraction was investigated by photolysis techniques in sodium dodecyl sulfate alone using these two sensitizers.     

Singlet and triplet products of the geminate recombination of a radical pair with a single magnetic nucleus (I = 1/2)

The double-channel recombination and separation of the photochemically created singlet radical pair is investigated, taking into account the spin conversion in a zero magnetic field and the arbitrary initial distance between the radicals. The quantum yields of the singlet and triplet products and the free radicals production are found analytically, assuming that the recombination of the diffusing radicals occurs at contact. All the yields are related to the singlet and triplet populations of the recombining radical pair, subjected to spin conversion and contact exchange interaction. The general analytical expressions for the quantum yields are specified for the particular limits of the weak and strong exchange. They are greatly simplified in the case of polar solvents, especially at the contact start. A close similarity is obtained with the results of a previously developed incoherent model of spin conversion, provided that the conversion rate is appropriately related to the hyperfine coupling constant.     

First prebiotic generation of a ribonucleotide from adenine, D-ribose and trimetaphosphate

Adenosine monophosphate isomers are obtained by self-assembling of adenine, D-ribose and trimetaphosphate in aqueous solution in good yields. This generation of a ribonucleotide from its three molecular components occurs in a one-pot reaction at room temperature for about 30-40 days and with high chemio-, regio-, and stereo-selectivity. Similar results are obtained with guanine. A mechanism is also proposed.     

Reaction of sulfonium ylides complexed with tricarbonylchromium

Oxiranes and olefins are obtained from the reactions of free and complexed phenylmethylsulfonium methylides with tricarbonylchromium with benzophenone, benzaldehyde and cyclohexanone. Good yields of olefins are obtained from the Cr(CO)₃ complexes with benzophenone, but yields of 0.1-0.5% are obtained with benzaldehyde and cyclohexanone.     

Palladium-catalyzed sequential one-pot reaction of aryl bromides with O-homoallylhydroxylamines: synthesis of N-aryl-beta-amino alcohols

The palladium-catalyzed sequential one-pot N-arylation-carbo-amination-C-arylation of O-homoallylhydroxylamines with two different aryl bromides provides rapid entry to differentially arylated N-aryl-3-arylmethylisoxazolidines in good yields with excellent diastereoselectivity. The obtained isoxazolidines can be reductively cleaved to cis-N-aryl-beta-amino alcohols in short times and in high yields at room temperature.     

GaCl3-catalyzed allenyne cycloisomerizations to allenenes

Cycloisomerizations of allenynes to allenenes have been studied in the presence of catalytic amounts of [Au(PPh3)]SbF6 in dichloromethane or GaCl3 in toluene. Both catalytic systems are quite effective for terminal 1,6-allenynes. However, they showed different reactivities toward allenynes with di-substituents at the allenic terminal carbon. For the GaCl3-catalyzed reactions, allenenes were obtained in reasonable to high yields. However, for a Au(I)-catalyzed reaction, a triene was obtained in a poor yield. Thus, GaCl3 serves as an effective catalyst for the cycloisomerization of allenynes bearing a terminal alkyne to give cyclic allenenes in reasonable to high yields.     

Solvent-free Knoevenagel condensations and Michael additions in the solid state and in the melt with quantitative yield

Numerous Knoevenagel condensations of solid or liquid aromatic aldehydes are performed with four barbituric acids, Meldrum's acid, dimedone, cyanoacetamide, malodinitrile and methyl cyanoacetate in stoichiometric mixtures of the solids or of stoichiometric melts. The product yields are quantitative in 23 reported cases and the products do not require purifying workup. Therefore, these reactions are truly solvent-free, atom economic and sustainable and no wastes are produced. They are highly superior to less productive so-called ‘solvent-free’ techniques using solid supports and microwave irradiation that require solvents for removal of the support or reagents or side products. Similarly, the solution reactions generally requiring catalysts suffer from low yields and purifying workup. The new techniques provide numerous common electron-poor alkenes very easily. These are valuable building blocks for example in Michael additions. Also the latter can be quantitatively obtained in stoichiometric melts in the absence of any auxiliaries or microwave irradiation and this is demonstrated with stable and rearranging/cyclizing Michael adducts using dimedone. The quantitative yields are most easily obtained if the products are formed in the solid-state or if they crystallize directly from the melt at the reaction temperature.     

Synthesis of nitrogen-containing heterocycles. 5. A new route to 5-amino-[1,2,4]triazolo[1,5-a][1,3,5]triazine derivatives

Treatment of certain diaminomethylenehydrazones 1 of aromatic carbonyl compounds with ethyl N-cyanoimidate ( 2 ) in acetonitrile in the presence of a tertiary amine at room temperature gives the corresponding amino(N-cyanoiminomethyl)aminomethylenehydrazones 3 in high yields. The intermediate 3 can readily be cyclized to the corresponding 5-amino-2,3-dihydro[1,2,4]triazolo[1,5-a][1,3,5]triazines 4 in moderate to good yields by brief heating in acetonitrile. When the reaction of diaminomethylenehydrazones 1 with ethyl N-cyanoimidate ( 2 ) is performed at reflux temperature in the presence of a tertiary amine, 5-amino-2,3-dihydro[1,2,4]triazolo[1,5-a]1,3,5]triazines 4 can be directly obtained in moderate yields. The yields of triazolotriazine produced by the one-step synthesis are generally comparable or even higher than the overall yields from the two-step procedure.     

Selenium- and tellurium-based ionic liquids and their use in the synthesis of octahydroacridines

A general and easy method for the synthesis of several selenonium and telluronium salts is described. These compounds are acidic liquids at room temperature and were obtained in excellent yields. Phenyl butyl ethyl selenonium tetrafluoroborate was employed in the hetero-Diels-Alder cyclization of aryl imines derived from citronellal, affording octahydroacridines in good yields.     

Photochemistry of ketone polymers. XII. Studies of ring-substituted phenyl isopropenyl ketones and their styrene copolymers

The synthesis of a number of ring-substituted phenyl isopropenyl ketones and their polymerization with styrene is reported. The ultraviolet absorption spectra of the polymers are analogous to those of ring-substituted acetophenones and valerophenones. The quantum yields of the Norrish type II photoreaction were estimated in 1,2-dichloroethane solution at 364 nm by automatic viscometry. These quantum yields are comparable to those of substituted butyrophenones and valerophenones, in that relatively high quantum yields were obtained for the unsubstituted and p-chloro-substituted compounds with low yields for p-amino and p-hydroxy compounds. The p-nitro-substituted compound gives no type II reaction, presumably because the excitation becomes localized on the nitro groups which photolyzes by a mechanism which does not involve chain scission. The implications of these studies on possible applications to photoimaging are discussed.     

On the use of boronates in the Petasis reaction

Alcohols are solvents of choice to react boronates, aldehydes and either primary or secondary amines. Thus, while the reaction proceeds sluggishly, or not at all, in aprotic solvents, the desired aminoacids are in most cases obtained in high yields when conducted in methanol or hexafluoro-iso-propanol. In the case of secondary amines, microwave activation is shown to strongly accelerate the process without altering the yields.