Brønsted acid promoted imino-ene reactions

A series of all-carbon olefins react with glyoxylate derived imines in the presence of a phosphonic acid through an ene reaction. The isolation of the α-aminoester products is a clear indication that Brønsted acids efficiently promote the imino-ene reaction with hydrocarbon nucleophiles to deliver functionalized α-aminoesters in good yield. The reaction scope and preliminary mechanistic investigations are discussed.     

Adamantane-like aluminum amide-phosphate from alumazene

A dealkylsilylation reaction between alumazene [2,6-(i-Pr)(2)C(6)H(3)NAlMe](3) (1) and tris(trimethylsilyl) ester of phosphoric acid (2) in a 1:3 molar ratio provides the heteroadamantane molecule (MeAl)[2,6-(i-Pr)(2)C(6)H(3)N](3)[Al[OP(OSiMe(3))(3)]](2)(O(3)POSiMe(3)) (3). Compound 3 was characterized by analytical and spectroscopic methods, and its molecular structure was established by a single-crystal X-ray diffraction experiment. Moreover, trialkyl and triaryl phosphates and dialkyl phosphonates react with 1 at elevated temperature to afford an intractable mixture of products. The reaction of phosphonic acids with 1 proceeds under decomposition to yield 2,6-diisopropylaniline and aluminophosphonates.     

Synthesis of alkyl-H-phosphinic acid alkyl esters from red phosphorus and alkyl bromides

Alkyl-H-phosphinic acid alkyl esters are synthesized in 65–71% yield via chemoselective reaction of alkyl bromides with available alkyl-H-phosphinic acids (60–65 °C, Et3N). The latter are prepared, in turn, by direct phosphorylation of alkyl bromides with red phosphorus under phase-transfer conditions.     

磺化笼型介孔碳催化的1,1-二乙酸酯的选择性合成

以磺化的笼型介孔碳为催化剂温和、高效、高选择性地合成了缩羰基二乙酸酯. 在室温和无溶剂条件下,用磺化的笼型介孔碳作催化剂使醛类化合物与乙酸酐之间在5~12 min内反应生成1,1-二乙酸酯,产率高达89%~98%. 在相同条件下酮类化合物不会发生此反应. 反应后催化剂经过简单的处理即可回收利用,回收利用7次活性无明显降低.     

Über eine Reaktion von o-Hydroxybenzylalkoholen mit Estern von Säuren des Phosphors mit der Koordinationszahl 3

Abstract

o-Hydroxybenzyl alcohol reacts with trimethyl phosphite under smooth conditions to o-hydroxyphenylmethane phosphonic acid dimethyl ester. This unusual reaction is of widest applicability. Derivatives of o-hydroxybenzyl alcohol independent of type, number or position of substituents in the ring, react with alkyl esters of phosphorous, phosphonous or phosphinous acids in an analogous process, forming the corresponding o-hydroxyphenylmethane phosphonic or phosphinic esters or phosphine oxides.     

Synthesis of non-peptidyl alpha,alpha-difluoromethylenephosphonic acids on a soluble polymer support

The polymer-supported syntheses of a series of biaryl derivatives bearing the alpha,alpha-difluoromethylenephosphonic acid group is reported. Non-cross-linked polystyrene (NCPS) was used as the support which enabled the reactions to be carried out under homogeneous conditions and reactions to be followed using conventional (19)F NMR. Synthesis of the biaryl phosphonic acids was initiated by attaching mono-ethyl esters of alpha, alpha-difluorophosphonic acids 11 and 12 to 3% alkylhydroxy-modified NCPS via a phosphate ester linkage. Suzuki reaction conditions were developed which allowed for the formation of a series of polymer-bound biaryl phosphonates at ambient temperature. Removal of phosphonic acids from the support and cleavage of the ethyl protecting group was achieved in a single step using TMSI or TMSBr. Yields of the phosphonic acids ranged from 43 to 89% and, in most cases, were obtained in a purity (96-99%), after cleavage from the support, that was sufficient for biological screening.     

Comparison of Phosphonic and Pyrophosphonic Acids as Collectors for the Cassiterite Flotation

Abstract

Styryl phosphonic acid (SPA) is a collector used in the industrial flotation of cassiterite, During its production from styrene and PCl₅ by-products are formed in different amounts. One of these is condensed SPA caused by uncomplete hydrolysis of the intermediary phosphonic acid chloride. Attempts were made to synthesize definite forms of condensed SPA in order to study their influence on the results of flotation. Conventional methods-partial hydrolysis of phosphonic acid chlorides or reaction of acid chlorides with the free acid-did not lead to the desired result. Diammonium salt of the pyro-SPA was obtained by the method of (1) using dehydration of phosphonic acid by heating with urea. A series of analogous aromatic pyro-phosphonic acids was synthesized. The hydrophobization effect on Sn0₂ surfaces was studied by microflotation tests in a modified Hallimond tube. Pyrophosphonic acids are more hydrophobic than the corresponding phosphonic acids. The results of the microflotation experiments were confirmed by batch flotation tests with a natural tin ore in a 2–1 cell. The Sn recovery was higher with the pyro compounds.     

About the choice of the protogenic group in polymer electrolyte membranes: Ab initio modelling of sulfonic acid, phosphonic acid, and imidazole functionalized alkanes

The possible use of sulfonic acid, phosphonic acid, or imidazole as the protogenic group in polymer electrolyte membranes for fuel cells operating at intermediate temperature (T>100 degrees C) and very low humidity conditions is examined by comparing specific molecular properties obtained with first principles based electronic structure calculations. Potential energy profiles determined at the B3LYP/6-311G** level for rotation of imidazole, phosphonic acid and sulfonic acid functional groups on saturated heptyl chains revealed that the torsional barriers are 3.9, 10.0, and 15.9 kJ mol-1, respectively; indicating that the imidazole is clearly the most labile when tethered to an alkyl chain. Minimum energy conformations (B3LYP/6-311G**) of methyl dimers of each of the acids indicated that the binding of the pairs of the acids is greatest in the phosphonic acids and lowest for the imidazoles. Comparison of the ZPE corrected total energies of the methyl acid dimers with corresponding pairs consisting of the conjugate acid and conjugate base revealed that the energy penalty in transferring the proton (from acid to acid) was greatest for imidazole (120.1 kJ mol-1) and least for the phosphonic acid (37.2 kJ mol-1). This result is in agreement with experimentally measured proton conductivities of acid-functionalized heptyl compounds under dry conditions and further underpins the observation that phosphonic acid possesses the best amphoteric character critical in achieving proton conductivity when no solvent (i.e. water) is present. Finally, BSSE corrected binding energies were computed for the methyl acids with a single water molecule and indicated that while the magnitude of the interaction of the sulfonic and phosphonic acids with water are similar (47.3 and 44.4 kJ mol-1, respectively), the binding is much weaker to the imidazole (28.8 kJ mol-1). This result suggests that the oxo-acids will probably retain water better under very low humidity conditions and that the dynamics of the hydrogen bonding of the first hydration water molecules will be more constrained with -SO3H and -PO3H2 than imidazole.     

Side reactions in controlling the quality, yield, and stability of high quality colloidal nanocrystals

Effects of side reactions during the formation of high quality colloidal nanocrystals were studied using ZnO as a model system. In this case, an irreversible side reaction, formation of esters, was identified to accompany formation of ZnO nanocrystals through the chemical reaction between zinc stearate and an excess amount of alcohols in hydrocarbon solvents at elevated temperatures. This irreversible side reaction made the resulting nanocrystals stable and with nearly unity yield regardless of their size, shape, and size/shape distribution. Ostwald ripening and intraparticle ripening were stopped due to the extremely low solubility/stability of the possible monomers because all free ligands in the solution were consumed by the side reaction. However, focusing on size distribution and 1D growth that are needed for the growth of high quality nanocrystals could still occur for high yield reactions. Upon the addition of a small amount of stearic acid or phosphonic acid, immediate partial dissolution of ZnO nanocrystals took place. Although the excess alcohol could not react with the resulting zinc phosphonic acid salt, it could force the newly formed zinc stearate gradually but completely back onto the existing nanocrystals. The results in this report indicate that side reactions are extremely important for the formation of high quality nanocrystals by affecting their quality, yield, and stability under growth conditions. Due to their lack of information in the literature and obvious practical advantages, studies of side reactions accompanying formation of nanocrystals are important for both fundamental science related to crystallization and industrial production of high quality nanocrystals.     

Efficient amidation from carboxylic acids and azides via selenocarboxylates: application to the coupling of amino acids and peptides with azides

A facile one-pot procedure for the coupling of carboxylic acid and azide via selenocarboxylate and selenatriazoline has been developed and successfully applied to the coupling of amino acids and peptides with azides. Selenocarboxylates are readily prepared by the reaction of the activated carboxylic acids with LiAlHSeH under mild conditions. The selenocarboxylates formed in situ are used to react directly with azides to form the corresponding amides via a selenatriazoline intermediate. Excellent yields were obtained for electron-deficient azides, and moderate to good yields were obtained for electron-rich azides. The selenocarboxylate/azide amidation reaction is clean and chemoselective. It provides an attractive alternative method to the conventional acylation of amines when an amide bond needs to be formed without going through an amine intermediate.     

A new method for enol lactone synthesis by a Michael addition/cyclization sequence

Reactions of cyclic 1,3-dicarbonyl compounds with 1-(2-alkenoyl)-4-bromo-3,5-dimethylpyrazoles under the double catalytic activation conditions using both catalytic amounts of Lewis acid and amine catalysts provide a new direct synthetic route to enol lactones. Thus, 1,3-cyclohexanedione is allowed to react with 4-bromo-1-crotonoyl-3,5-dimethylpyrazole, in tetrahydrofuran at room temperature in the presence of both catalytic amounts (10 mol% each) of nickel(II) perchlorate hexahydrate and 2,2,6,6-tetramethylpiperidine, to give 4,7,7-trimethyl-3,4,5,6,7,8-hexahydrobenzopyran-2(H),5-dione in a good yield. This reaction does not proceed or is too slow under the reaction conditions other than the double catalytic activation conditions.     

A family of microporous materials formed by Sn(IV) phosphonate nanoparticles

Reaction of Sn(IV) with phosphonic acids results in the formation of tin phosphonates with a spherical morphology arising from the aggregation of nanosized individual particles. Under high magnification, the spheres are shown to be porous with surface areas of 200-515 m2/g, depending on the type of phosphonic acid and the synthesis conditions used. The pores are largely micro in nature but also somewhat dependent on the type of phosphonic acid utilized in the preparation. Both aliphatic and aromatic organic phosphonates form these spherical aggregates. Functional groups, such as amino and carboxyl, may be introduced as part of the phosphonic acid or subsequently by further reaction, leading to a large family of naturally formed nanoparticles with accompanying microporosity.     

Investigation of thermal decomposition of phosphonic acids

The paper compares building and decomposition pathways of two phosphonic acids, amino trimethylene phosphonic acid (ATMP) and 1-hydroxy ethylidene-1,1-diphosphonic acid (HEDP).The theoretical formation reactions were composed using elementary reactions and compared to reaction routes published in literature. As result, summary reaction pathways for both phosphonic acids are proposed which only vary in the number of reaction steps required. These reaction steps include carbonyl reactions, S_N2-reactions, and ionic reactions. The synthesis of ATMP proceeds in three reaction steps, whereas HEDP is formed in one reaction. The thermal decomposition of both phosphonic acids in solid state was examined by combination of thermogravimetry coupled with infrared spectroscopy as well as pyrolysis gas chromatography coupled with mass spectrometry. Decomposition mechanisms were deduced and compared to the theoretical findings resulting in the conclusion that the decomposition processes of ATMP and HEDP follows the formation mechanism.Thus, the suitability of theoretical considerations for the understanding of thermal decomposition processes is shown.     

Direct phosphorylation of fullerene C<Subscript>60</Subscript> with phosphine

Fullerene C₆₀ reacts with phosphine (PH3) under free radical initiation conditions (azobis(isobutyronitrile), xylene, 65°C, 6–11 h) to give in the presence of air oxygen functional oligofullerenes (yield up to 32%) containing functional groups of phosphinic and phosphonic acids.     

Some azole derivative phosphoric and thiophosphoric esters

Reaction of spiro[cyclohexane-1, 2-oxazolidine] (I) with phosphorochloridic and phosphorochloridothionic acids gave the corresponding ethers. It did not prove possible to prepare derivatives containing dispiro[cyclohexane-1, 2′-oxazolidine] radicals. Reaction of 2-thio-5, 5-dimethyloxazolid-4-one with diethylphosphorochloridate led to isolation of an alkylation product. 5, 5-Dimethylhydrantoin did not react with chlorides of phosphoric acid under the reaction conditions of these particular experiments.     

Photochemistry of bicyclo[2.2.2]oct-7-ene-2,5-diones and the corresponding 5-hydroxyimino and 5-methylene derivatives

Synthesis and photochemistry of several title compounds 1-3 containing multiple chromophoric systems are described. The Diels-Alder reactions of 2,6,6-trimethylcyclohexa-2,4-dienone (5) with acetylenes 6a-d provided the adducts 7a-d, which upon hydrolysis furnished the desired bicyclo[2.2.2]octenediones 1a-d. Oximes 2a-d were prepared from diones 1a-d by treatment with hydroxylamine hydrochloride in pyridine. 5-Methylenebicyclo[2.2.2]oct-7-en-2-ones 3a-d were obtained via chemoselective Wittig reaction of the corresponding diones 1a-d. Bicyclo[2.2.2]octenediones 1a-c underwent chemoselective oxa-di-pi-methane rearrangement under sensitized conditions and suffered formal ketene extrusion upon direct irradiation. Direct irradiation of 1d afforded 11d via formal ketene extrusion but under sensitization it remained unchanged. Oximes 2a-d suffered ketene extrusion upon direct irradiation and E/Z isomerization under sensitized conditions. On the other hand, 5-methylenebicyclo[2.2.2]oct-7-en-2-ones 3a-d generally underwent 1,3-acyl shift. The plausible courses of all these photochemical processes are discussed.     

Total synthesis of (S)-(-)-(E)-15,16-dihydrominquartynoic acid: a highly potent anticancer agent

The conjugated entriyne natural product, (S)-(E)-15,16-dihydrominquartynoic acid (1), is synthesized in five linear steps and 30% overall yield from the known aldehyde 11. The key step is a one-pot in situ desilylation/Cadiot-Chodkiewicz coupling reaction affording the entriyne unit. The bromoalkyne 6 with an omega-carboxylic acid group was found to undergo a copper-catalyzed cross-coupling reaction producing the desired diyne intermediate 10, while the corresponding omega-ester bromoalkyne 14 failed to couple with triethylsilylacetylene under a variety of conditions.     

Orthosilicate-mediated esterification of monosubstituted phosphinic acids

Monosubstituted phosphinic acids are esterified with orthosilicates in excellent yields. Phosphinylidene-containing acids react selectively under these conditions, while disubstituted phosphinic acids and phosphonic acids remain unchanged. One-pot procedures are also described for the preparation of phosphinate esters from an alcohol. This novel method provides a convenient and general alternative to more commonly employed conditions such as diazomethane or carbodiimide.     

Reaction of perfluoroalkyl grignard reagents with phosphorus trihalides: a new route to perfluoroalkyl-phosphonous and -phosphonic acids

The reaction of perfluoroalkyl Grignard reagents with phosphorus(III) halides was explored. In the process a new convenient, one-pot, high yield method for the synthesis of (perfluoroalkyl)phosphonic acids has been developed. Perfluoroalkyl Grignard reagents react with phosphorus trichloride or phosphorus tribromide to form (perfluoroalkyl)phosphonous dihalides. Hydrolysis gives the corresponding (perfluoroalkyl)phosphonous acids. Oxidation of the phosphonous acids with H(2)O(2) produces (perfluoroalkyl)phosphonic acids in 60-78% overall yields, based on the corresponding perfluoroalkyl iodide. The X-ray crystal structures of the toluidinium salts, [MeC(6)H(4)NH(3)](2)[C(2)F(5)PO(3)] and [MeC(6)H(4)NH(3)][C(8)F(17)P(O)(2)OH], are reported.     

Succinimide sulfonic acid (SuSA): an efficient and recyclable catalyst for the chemoselective <Emphasis Type="Italic">N</Emphasis>-Boc protection of amines

Abstract  

Succinimide sulfonic acid (SuSA) as a stable reagent is easily prepared by the reaction of succinimide with neat chlorosulfonic acid. This compound is able to catalyze the chemoselective conversion of amines to their corresponding N-Boc protected derivatives with (Boc)₂O. All reactions were performed under mild conditions, giving the desired products in good to high yields.