Structural Variation Provided by Sulfur,Sulfinyl, and Sulfonyl Groups in Cyclic Silanes and Phosphoranes

A series of new monocyclic diorganosilanes were prepared by condensation reactions of the appropriate diorganodichlorosilane with sulfur containing diols.^1-3 The eight-membered rings containing bridging sulfinyl groups² are positioned in anti chair-like conformations which precluded any additional coordination at silicon. This contrasts with silanes having sulfur¹ or sulfonyl³ groups in place of sulfinyl in the ring system where Si–S or Si–O coordination was evident. In these molecules, X-ray studies showed^1,3 that the rings has syn boat-like conformations.     

酸催化甘油与苯甲醛缩合制备六员环缩醛

比较了对甲苯磺酸（PTSA）、磷钨酸（PWA）、KHSO₄和FeCl₃催化对甘油与苯甲醛的缩合反应收率,及对产物中六元环缩醛5-羟基-2-苯基-1,3-二氧六环(1)与五元环缩醛4-羟甲基-2-苯基-1,3-二氧五环(2)比例的影响。 当以环己烷为带水剂及苯甲醛与甘油的摩尔比为2∶3的情况下,KHSO4为催化剂的缩合产物（1+2）收率较高,为96.8%;PTSA催化的缩合产物中,化合物1的比例最高(m(1)∶m(2)=48.6∶51.4)。 室温下PTSA、PWA、KHSO₄和FeCl₃均可催化化合物2向化合物1的转化。 在-20 ℃下,只有PTSA能催化化合物2向化合物1的转化。 在-20 ℃,PTSA催化化合物[STHZ]2转化成化合物1a,并以晶体形式从苯（40%）-石油醚（60%）中析出。 母液循环转化3次后,化合物1a的累计收率可达91.1%。     

Polycondensation and disproportionation of an oligosiloxanol in the presence of a superbase

Kinetics of reactions of model oligosiloxanols, 1,1,3,3,3-pentamethyldisiloxane-1-ol (MDH) and 1,1,3,3,5,5,5-heptamethyltrisiloxane-1-ol (MD₂H), which occur in the presence of phosphazenium superbase, hexapyrrolidine-diphosphazenium hydroxide, in an acid-base inert solvent, toluene, was studied using sampling and gas chromatographic analysis method. In addition, kinetics of reactions of MDH and MD₂H with trimethylsilanol (MH) was studied. In the MDH and MD₂H systems the oligosiloxanol condensation competes with the oligosiloxanol disproportionation, the latter being the dominating process. The disproportionation products, i.e. MD_n+1H and MD_n−1H, n=1, 2, … undergo analogous consecutive disproportionation and condensation reactions. The kinetic law was derived and rate parameters determined from initial rates and by computer simulation to the best agreement with experimental data. Both competing reactions, the disproportionation and the condensation, conform to the same general kinetic law being first internal order in substrate and first order in catalyst. Activation parameters of these reactions were determined. The results were interpreted in terms of a bimolecular mechanism in which nucleophilic attack of the silanolate anion directed to silicon of the silanol group causes the cleavage of one of its geminal bonds to oxygen, either the one to hydroxyl leading to condensation or the one to siloxane which leads to disproportionation. The latter is faster as the silanolate is a better leaving group compared with OH⁻. Moreover, in the pentacoordinate silicon transition state (or intermediate) the siloxane substituent preferentially enters the apical position, thus driving the OH substituent into the unreactive equatorial position.     

Structure of aldose condensation products with 2-hydroxyand 2-sulfanylbenzohydrazides

The structure of the condensation products of 2-hydroxy- and 2-sulfanylbenzohydrazides with a series of aldoses (L-arabinose, D-ribose, L-ramnose, D-galactose, D-glucose, D-mannose) was studied by ¹H and ¹³C NMR spectroscopy. The condensation products of monosaccharides with 2-hydroxybenzohydrazide in DMSO-d ₆ solution exist as equilibrium mixtures of linear hydrazone and cyclic pyranose and furanose forms, the cyclic tautomers being represented by two stereoisomers (α- and β-anomers). The aldose condensation products with 2-sulfanylbenzohydrazide in the crystalline state have cyclic 1,3,4-benzothiadiazepine structure, while in DMSO-d ₆ solution they undergo complete or partial isomerization into cyclic pyranose tautomer.     

A Study on Some Copper (II) Complexes of Polyaza Cryptands and Planar Macrocycles—Synthesis,Characterization and Superoxide Dismutase Activity

Two kinds of macrocyclic copper(II) complexes were synthesized. One of them is composed of copper(II) cryptates of ligands L¹‐L⁴ which are condensation products of 5‐R‐2‐methoxy‐1,3‐phenyldialdehyde (R=OCH₃, L¹) with tris(2‐aminoethyl) amine and 5‐R‐2‐methothoxy‐1, 3‐phenyldialdehyde (R= CH₃, L³) with tris(2‐aminopropyl)amine as well as their reduced products of L¹ and L³ (L² and L⁴). The other is composed of two‐dimensional macrocyclic copper(II) complexes of ligands L⁵‐L⁸ of condensation products of diethylene triamine with 4‐R‐l‐methoxy‐2,6‐phenyldialdehyde (R= Cl, Br. CH₃, OCH₃). The relationship between their structures and superoxide dismutase (SOD) activity was investigated. The results can provide some clues to the synthesis of SOD mimics.     

A new synthesis of α,β-unsaturated ketones. Allylic alkylation of 1-isocyano-1-tosylalkenes

Ketone (1) are homologated to enones 2 by alkylating (introduction of R³) the condensation products 4 (derived from 1 and tosylmethyl isocyanide), followed by acid catalyzed hydrolysis.     

Synthesis,experimental, and DFT studies on FT-IR, 1H,and 13C NMR spectra of azo-linked dihydropyridines

An efficient one-pot synthesis of dihydropyridines by solid state three-component condensation reactions of aldehydes, dimedone, and ammonium acetate in the presence of HY-Zeolite has been achieved. The conversion took short time to form the products in excellent yields. HY-Zeolite can be recovered and reused. Density Functional Theory (DFT) calculations at the B3LYP level is used to optimize the geometry and calculate FT-IR, ¹H, and ¹³C NMR spectra of the compounds. We found that the calculated values are in accordance with the experimental data.     

Condensation reactions of indole with acetophenones affording mixtures of 3,3-(1-phenylethane-1,1-diyl)bis(1H-indoles) and 1,2,3,4-tetrahydro-3-(1H-indol-3-yl)-1-methyl-1,3-diphenylcyclopent[b]indoles

Condensation of indole 1a with eight acetophenones 8a–h in ethanolic HCl afforded the corresponding mixtures of condensation products: 3,3-(1-phenylethane-1,1-diyl)bis(1H-indoles) 11a–h (2:1 condensation of indole:acetophenone, –H₂O) and diastereomers of substituted 1,2,3,4-tetrahydro-3-(1H-indol-3-yl)-1-methyl-1,3-diphenylcyclopent[b]indoles 12a–h and 13a–h (2:2 condensation of indole:acetophenone, –2H₂O). Each mixture was analyzed by ¹H NMR. The use of substituted electron-withdrawing acetophenones favored formation of 2:1 condensation products, whereas the use of substituted electron-donating acetophenones favored formation of 2:2 condensation products. Increased reaction temperature gave higher 2:2 condensation yields, but temperatures above 40?°C were unfavorable, giving complex, tarry mixtures.     

Comparison of the stable products formed by fast atom bombardment and γ-irradiation of glycerol

The major end-products formed by fast atom bombardment (FAB) and γ-irradiation of glycerol have been identified using capillary gas chromatography/mass spectrometry. The product distributions differ dramatically. Products resulting from the recombination of either carbon-centered or oxygen-centered radicals are evident for both sources of irradiation. However, the major FAB-generated products are formed by the recombination of carbon-centered [G – H]^· radicals with other carbon-centered radicals while the major γ-radiolysis products result from the recombination of oxygen-centered [G–H]^· radicals with lower-weight carbon-centered species. γ-Radiolysis of an N₂O-saturated aqueous solution of glycerol, experimental conditions that strongly favor the formation of carbon-centered [G – H]^· radicals at the expense of the oxygen-centered species, yielded some products that were identical to those produced by FAB of neat glycerol. Finally, the free radicals produced by γ-radiolysis of glycerol were investigated by electron spin resonance spectroscopy and spin trapping with 5,5-dimethyl-1-pyrrolne-TV-oxide. The presence of only the carbon-centered free radical was established by this technique. The implications of these results are discussed.     

Sequential injection analyzer for glycerol monitoring in yeast cultivation medium

A smart and versatile flow system for the at-line monitoring of glycerol based on sequential injection analysis is proposed. Formaldehyde, generated by oxidation of glycerol with sodium periodate, is transformed into 2,4-diacetyl-1,4-dihydrolutidine applying the Hantzsch condensation reaction with acetylacetone and ammonium. Dual-wavelength detection was carried out to minimize the contribution of the schlieren effect using a single blue LED. In-line sample dilution is accomplished applying the concept of zone-penetration and a new concept of sample splitting. Under optimized physical and chemical variables, regression curves over two dynamic working ranges of 0.1-4 and 1-40 g l⁻¹ were attained. The injection throughputs were 14 and 12 h⁻¹, respectively. Applying on-line data evaluation and conditional inquiries, the smart and independent selection of the adequate analytical procedure for the required working range was accomplished. The system was successfully applied to the at-line monitoring of glycerol in a continuous, cell-free medium flow from a yeast cultivation process during batch and fed-batch phase with glycerol as the only carbon source.     

Utilization of deuterium labelling and 13C NMR spectroscopy in the investigation of the condensation of 1-Methyl-5-nitroimidazole-2-aldehyde and 2-Amino-4-methylpyrimidine

The product obtained condensing l-methyl-5-nitroimidazole-2-aldehyde with 2-amino-4-trideuteriomethyl-pyrimidine and showing total deuterium incorporation at one of the olefinic carbons and partial deuterium incorporation para to the amino group, served to assign ¹³C and ¹H resonances in the condensation products 3. The nature of the species undergoing condensation has been inferred from labelling experiments and from ¹H and ¹³C nmr spectra of precursors and products in dimethylsulfoxide and trifluoroacetic acid.     

Nitrogen bridgehead compounds. Part 76 Synthesis and stereochemistry of ethyl 9-benzylidene-6,7,8,9-tetrahydro-2-oxo-2H- and 4-oxo-4H-pyrido[1,2-a]pyrimidine-3-carboxylates and their homologues

Ethyl 4-oxo-6,7,8,9-tetrahydro-4H-pyrido[1,2-a]pyrimidine-3-carboxylates 1–4 , their piperidine ring homologues 5–6 and their 2-oxo isomers 7–9 were reacted with benzaldehyde. At low temperature, kinetically stable addition products were formed. Thermodynamically stable condensation products were obtained at higher temperature, which were also formed when the addition products were refluxed in benzene. The 9-benzyl derivatives were prepared by the hydrogenation of the condensation products over Pd/C. The stereochemical features of the new compounds were determined via ¹H and ¹³C nmr chemical shift and coupling constant analysis and NOE measurements.     

Enzymatic Synthesis of Fructosyl Glycerol

ABSTRACT

The enzymatic synthesis of ß2-2' and ß2-1'-D- fructopyranosyl glycerol was carried out with levansucrase from Bacillus circulans or B.subtilis, using sucrose as fructosyl donor and glycerol. The specificity and efficiency of the enzyme was modified by controlling both the water and the total substrate concentrations. The products were purified by HPLC and analyzed by ¹H, ¹³C NMR and GC-MS.     

Synthesis,experimental and DFT studies on crystal structure,FT-IR, 1H,and 13C NMR spectra,and evaluation of aromaticity of three derivatives of xanthens

Several derivatives of xanthenes are prepared by the condensation of aldehydes and dimedone in H₂O in the presence of a catalytic amount of trichlorotriazine. The crystalline products were characterized by FTIR, ¹H, and ¹³C NMR spectra. Density Functional Theory (DFT) calculations on the B3LYP level were used to optimize the geometry and calculate the crystal structure, FTIR, ¹H NMR and ¹³C NMR spectra of the selected synthesized compounds. We found that the values of FTIR, ¹H, and ¹³C NMR spectra obtained by the B3LYP method are in accordance with experimental data. The calculated NICS indicate that the six-membered rings in xanthenes are essentially homoaromatic.     

A Novel Thermal Knoevenacel Condensation via A Thermal Michael Reaction

In connection with the total synthesis of natural products by retro-mass spectral approach,^1–3 the thermal reaction between 6,7-dimethoxy-3-isochromanone 1 and benzalmalononitrile 3 was studied. The Knoevenagel condensation product⁴ was obtained over and above the expected Diels-Alder adduct. The scope, limitation and mechanism of the aforesaid unusual thermal Knoevenagel condensation through a thermal Michael reaction is described.     

Über die Synthese von 4,9-Dihydro-9-(2-dimethylaminoäthyl)-4-methyl-thieno[3,4-b][1,5]benzodiazepin-10-on

The synthesis of the title compound6 c, starting with the condensation of o-phenylenediamine and methyl 4-oxotetrahydrothiophene-3-carboxylate (1) to 1.3.4.9-tetrahydrothieno[3.4-b] [1.5]benzodiazepin-10-one (2), is described. The structures of other products of this condensation, 1.3-dihydro-1-[3-(2.5-dihydrothienyl)]-benzimidazol-2-one (3) and 1.3-dihydro-1-[3-(2.3-dihydrothienyl)]-benzimidazol-2-one (4), are confirmed by their¹H-NMR-spectra and by the¹H-NMR-spectra of their desulfurization products.     

Concise and efficient synthesis of E-stereoisomers of exo-cyclic carbohydrate enones. Aldol condensation of dihydrolevoglucosenone with five-membered aromatic aldehydes Part 1

Stereoselective synthesis of exocyclic enones 10–17 via a base-catalyzed direct aldol condensation between dihydrolevoglucosenone 1 and heterocyclic aldehydes 2–9 is described. The reaction is performed under mild conditions and is applicable to variety of heterocyclic aldehydes. E-Steroisomers of exo-cyclic enones are the only products. They are very easy to isolate and were formed in good to excellent (72–88%) yield. ¹H NMR, ¹³C NMR analyses provide the structural assignment and absolute stereochemistry of the condensation products. Single-crystal X-ray diffraction of condensation product 12, additionally supports the structural assignment.     

NMR Study of the Hydrolysis and Oligomerization of Alkyltrichlorosilanes in Silanizing Solutions Used to Prepare Alkylsiloxane Self-Assembled Monolayers

²⁹Si NMR spectroscopy is not suited to following a number of fast occurring processes involving silicon centres due to long accumulation times resulting from low detector sensitivity factors and poor natural abundance. By observing subtle changes in signals due to the methylene protons adjacent to the silicon centre, the hydrolysis of alkyltrichlorosilanes in tetrahydrofuran and acetone-d₆ solutions, and subsequent polycondensation reactions, were studied using ¹H and ¹³C NMR spectroscopy, to gain an understanding of the processes that lead to formation of oligomers in silanizing solutions. The hydroxysilanes formed by hydrolysis of alkyltrichlorosilanes were characterized by ¹H and ¹³C NMR studies at low temperatures. Formation of oligomeric and polymeric species from these hydroxysilanes at higher temperatures was monitored by ¹H NMR studies. The data for oligomer formation were fitted to the kinetic model of an acid-catalyzed stepwise condensation. The implications of these results for the problem of oligomer formation competing with self-assembly processes in formation of alkylsiloxane monolayers are discussed.     

Synthesis of methylcyclotetra(hexa)siloxanes with different reactive groups at the same silicon atom

Representatives of methylcyclotetra(hexa)siloxanes with two different reactive groups at the same silicon atom (CH₂=CH and Cl, H and Cl, CH₂=CH and OH) were synthesized for the first time by condensation of trichlorovinylsilane with dihydroxydimethylsilane, and by stepwise condensation of trichloro-and trichlorovinylsilane with 1,3-dihydroxy-1,1,3,3-tetramethyldisiloxane in the presence of amines (aniline, pyridine, and triethylamine). The condensation with 1,3-dihydroxy-1,1,3,3-tetramethyldisiloxane with a large excess of trichlorosilane, unlike the condensation with trichlorovinylsilane, occured intramolecularly to give monochlorotetramethylcyclotrisiloxane in a high yield and intermolecularly to give 1,1,7,7-tetrachloro-3,3,5,5-tetramethyl-1,7-dihydrotetrasiloxane. The structures of the synthesized compounds were confirmed by ¹H and ²⁹Si NMR spectroscopy, IR spectroscopy, and mass spectrometry. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 932–936, June, 2006.     

Silicon tetraacetate as a sol-gel precursor

Variations in the starting materials, solvent, catalyst, and water to alkoxide ratio affect gel times and gel properties in sol-gel reactions. Silicon tetraacetate-derived sols gel surprisingly quickly. This paper discusses the acid catalyzed hydrolysis and condensation of silicon tetraacetate in an attempt to understand this rapid gelation. ²⁹Si and ¹H NMR spectra show that tetraethoxysilane is an intermediate, and ethyl acetate is produced via a secondary reaction. A correlation between gel times and H⁺ concentration is demonstrated.