Synthesis of 2,2-dimethylchromans by the hydrogenation of 2,2-dimethyl-2H-chromenes

Summary 2,2-Dimethylchromans19–36 have been synthesized by the hydrogenation of 2,2-dimethyl-2H-chromenes1–18 in acetic acid solution in the presence of 10% Pd-C catalyst.Dedicated to Prof. Dr. W. Fleischhacker on the occasion of his 60th birthday     

Preparation of PVA-GA-CS/PVA-Fe-SA bipolar membrane and its application in electro-generation of 2,2-dimethyl-3-hydroxypropionic acid

PVA-GA-CS/PVA-Fe-SA bipolar membrane was prepared by a paste method. PVA-sodium alginate (SA) and PVA-chitosan (CS) were cross-linked by FeCl₃ and glutaraldehyde (GA), respectively. The charge densities of PVA-CS and PVA-SA solutions were determined by the colloid titration. The swelling level of bipolar membrane was in the range of 25–85%, meanwhile the permeability and the ion-exchange capacity as well as co-ion transport properties was investigated. FTIR was applied to analyze the functional groups of the bipolar membrane. Furthermore, SEM photographs of the BPM cross-section illustrated a structure that consists of an anion layer (PVA-GA-CS) and a cation layer (PVA-Fe-SA). TG analysis of PVA-GA-CS/PVA-Fe-SA bipolar membranes exhibited a good thermal stability. PVA-GA-CS/PVA-Fe-SA bipolar membranes were used as the separator in the electrolysis cell for electro-generation of 2,2-dimethyl-3-hydroxypropionic acid. The average current efficiency was 52.2%, and the highest current efficiency reached 68.9%.     

Efficient One-Pot Synthesis of 2,2-Dimethyl-2H-chromenes via Pd(II)-Catalyzed Coupling and SiO2-Promoted Condensation of o-Halophenols with 2-Methyl-3-buten-2-ol

An efficient synthesis of 2,2-dimethyl-2H-chromenes was accomplished by Pd(II)-catalyzed coupling and SiO₂-promoted condensation of o-halophenols with 2-methyl-3-buten-2-ol (1,1-dimethylallyl alcohol) in one pot. The method is very general and can be useful for the synthesis of some natural 2,2-dimethyl-2H-chromenes.     

Synthesis and conformational studies on some Nitro- and aminophthalideisoquinoline derivatives

Summary Nitro- and Aminophthalideisoquinolines were synthesized with a new efficient method. The molecular conformation of these derivatives was studied by¹H NMR methods. On the basis of these studies tritoqualine was to be found theerythro racemate.

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Synthese und Konformationsuntersuchungen von Nitro- und Aminophthalidisochinolin

Zusammenfassung Nitro- und Aminophthalidisochinoline wurden nach einem neuen effizienten Verfahren hergestellt. Konformationsuntersuchungen dieser Verbindungen wurden mit Hilfe von¹H-NMR-Methoden vorgenommen.

     

Steroids,LIII: New routes to aminosteroids

Summary Steroid ketoximes were reduced with sodium tetrahydroborate in the presence of nickel chloride or molybdenum trioxide. These processes yielded 17- and 20-aminosteroids (1c–5c) in higher yields than common reduction methods.

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Steroide, 53. Mitt.: Neue Wege zu Aminosteroiden

Zusammenfassung Oxime von Ketosteroiden wurden mit NaBH₄ in Gegenwart von NiCl₂ und MoO₃ reduziert. Dieses Verfahren lieferte 17- und 20-Aminosteroide(1c–5c) in größeren Ausbeuten als übliche Methoden.

     

ReCl(CO)5-catalyzed cyclocondensation of phenols with 2-methyl-3-butyn-2-ol to afford 2,2-dimethyl-2H-chromenes

A direct one-pot route for the synthesis of 2,2-dimethyl-2H-chromenes by Re(CO)₅Cl-catalyzed cyclocondensation of phenols with 2-methyl-3-butyn-2-ol has been developed. The easy availability of starting materials, mild reaction conditions, high atom-efficiency, and the use of a recoverable catalyst are advantages of this procedure.     

Asymmetric reduction of 2,2-dimethyl-6-(2-oxoalkyl/oxoaryl)-1,3-dioxin-4-ones and application to the synthesis of (+)-yashabushitriol

The asymmetric transfer hydrogenation of a series of 2,2-dimethyl-6-(2-oxoalkyl)-1,3-dioxin-4-ones and 2,2-dimethyl-6-(2-oxoaryl)-1,3-dioxin-4-ones was achieved in high enantiomeric excess using a Ru(II) catalyst. The aryl substrates were most compatible with the methodology and this process facilitated a total synthesis of enantiomerically pure (+)-yashabushitriol.     

Nucleophilic addition to 3,4-cis-diacetyl-1,2,3,4-tetramethyl-1-cyclobutene: remarkably fast intramolecular hemiketalization

Reduction of 3,4-cis-diacetyl-1,2,3,4-tetramethyl-1-cyclobutene 1 with NaBH₄ yielding 2-hydroxyoxolanes 2a and 2b with complete diastereoselectivity at the anomeric carbon atom suggests that a highly stereoselective intramolecular hemiketalization process leading to the formation of the 2-hydroxyoxolane unit is much faster than the attack of the second molecule of the nucleophile on the second carbonyl group. Further reduction of 2a at 0 °C gives selectively the meso-diol 3a. Reaction of 1 with MeLi or MeMgBr also involves the participation of the adjacent carbonyl, thereby yielding hydroxyoxolane 5a selectively. A mechanistic rationale is proposed on the basis of the relative energies of all isomeric hemiketals, 2a-d and 5a and b, (calculated by the PM3 method) and the relative stabilities of the conformers of 1 (calculated by the MM2 method).     

N-(2-Thenyl)derivatives of aminoalkyltriethoxysilanes,-silatranes and 2,2-dimethyl-1,3-dioxa-6-aza-silacyclooctane

The reactions of aminoalkylethoxysilanes and 2,2-dimethyl-1,3-dioxa-6-aza-2-silacyclooctane with 2-(chlormethyl)thiophene and its 5-chloroderivative lead to the correspondingN-(2-thenyl) derivatives. TheN-methyl-N-(2-thenyl)aminomethyltriethoxysilane and 5-chlorothyenyl derivative formed are converted by triethanolamine into silatranes.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 384–386, February, 1995.     

A simple reduction of methyl aromatic esters to alcohols using sodium borohydride-methanol system

Several aromatic esters were reduced to the corresponding alcohol by using sodium borohydride-methanol system. The reduction was completed within 2.0-4.0 h after refluxing in THF. The alcohol products were isolated after aqueous workup in good yields (88-97%).     

One-Pot Facile Synthesis of Noble Metal Nanoparticles Supported on rGO with Enhanced Catalytic Performance for 4-Nitrophenol Reduction

In this study, reduced graphene oxide (rGO)-supported noble metal (gold, silver, and platinum) nanoparticle catalysts were prepared via the one-pot facile co-reduction technique. Various measurement techniques were used to investigate the structures and properties of the catalysts. The relative intensity ratios of I_D/I_G in rGO/Au, rGO/Ag, rGO/Pt, and GO were 1.106, 1.078, 1.047, and 0.863, respectively. The results showed the formation of rGO and that noble metal nanoparticles were decorated on rGO. Furthermore, the catalytic activities of the designed nanocomposites were investigated via 4-nitrophenol. The catalysts were used in 4-nitrophenol reduction. The catalytic performance of the catalysts was evaluated using the apparent rate constant k values. The k value of rGO/Au was 0.618 min⁻¹, which was higher than those of rGO/Ag (0.55 min⁻¹) and rGO/Pt (0.038 min⁻¹). The result proved that the rGO/Au catalyst exhibited a higher catalytic performance than the rGO/Ag catalyst and the rGO/Pt catalyst. The results provide a facile method for the synthesis of rGO-supported nanomaterials in catalysis.     

Preparation of ginkgolide and F-seco-ginkgolide lactols: the unique reactivity of α-hydroxy lactones toward NaBH4

It has been found that NaBH₄ smoothly reduces the α-hydroxy-lactone moieties in ginkgolide and F-seco-ginkgolides to lactols. The reaction is rapid and stops at the lactol stage; the coordination of NaBH₄ to the conformationally rigid cage structure is involved in both the initiation and termination stages. This facile reduction of ginkgolide lactones yields a variety of new ginkgolide lactols.     

An Alternative Stereoselective Synthesis of Protected Trans-5-Alkyl-4-Hydroxy-2-Pyrrolidinones

A flexible approach to protected trans-5-alkyl-4-hydroxy-2-pyrrolidinones was described. The key step involved the α-amidoalkylation of benzene-sulfone derived from (S)-malic acid, with organozinc reagents generated in situ from Grignard reagents and anhydrous ZnCl₂-OEt₂.     

Synthesis, characterization and crystal structure determination of zinc (II) and mercury (II) complexes with 2,2′-dimethyl-4,4′-bithiazole

The 2,2′-dimethyl-4,4′-bithiazole ligand (1), (dm4bt), and its Zn and Hg complexes have been prepared. A conformational property calculation at the DFT level for the ligand shows the anti conformation is energetically more stable by about 22.83 kJ/mol and the rotational barrier is about 32.01 kJ/mol for the anti → syn conversion, a phenomena happening during complex formation. The complexes [Zn(dm4bt)Cl₂] (2) and [Hg(dm4bt)Cl₂] (3) have spectral properties typical for d¹⁰ metal diimine systems. The structures of the ligand and the two complexes have been determined by the single crystal diffraction method. The X-ray structure determinations show that both complexes are four coordinated by two chloride atoms and one bidentate dm4bt. In the Hg complex one of the two chlorides is set at a semi-bridging position.     

Synthesis, structure and electrochemical behaviour of 2,2-diferrocenylpropane-substituted dihydropyrazole derivatives

The reaction of α,β-unsaturated ketones of 2,2-diferrocenylpropane with hydrazine led to the formation of 2,2-diferrocenylpropane-substituted dihydropyrazole. The further reaction of dihydropyrazole with p-pyridinecarboxylic acid chloride or benzoyl chloride resulted in the isolation of two novel 2,2-diferrocenylpropane-substituted acyl dihydropyrazole derivatives. All of these compounds were analyzed by MS, IR and ¹H NMR spectra. The crystal structure of representative compound, 1-p-pyridine acyl-3-ferrocenyl-5-(2,2-diferrocenylpropane)-4,5-dihydropyrazole (5a) has been elucidated by X-ray diffraction. The electrochemical behaviours of all the compounds have been examined.     

Pt/Cu双金属纳米颗粒的制备及其催化制氢活性

采用化学共还原法合成了聚乙烯吡咯烷酮保护的Pt/Cu双金属纳米颗粒(BNPs),并采用紫外可见吸收光谱、透射电子显微镜、高分辨透射电子显微镜等对所合成的Pt/Cu BNPs进行了表征。研究了化学组成对Pt/Cu BNPs催化Na BH4水解制氢性能的影响。结果表明,所制备的Pt/Cu BNPs平均粒径为1.8~2.3nm,其催化活性远高于单金属Pt和Cu NPs的活性,其中Pt90Cu10BNP的催化活性最高,其在30℃的条件下,催化Na BH4制氢的活性可达6570mol-H2·mol-cat-1·h-1,约为相同粒径的Pt单金属NP的1.6倍。密度泛函理论的计算结果表明,Pt/Cu BNPs优异的催化性能可归因于电荷转移效应,Pt原子与Cu原子之间发生的电子转移使得Pt原子带负电而Cu原子带正电,荷电的Pt和Cu原子成为催化反应的活性中心。     

纳米复合固体超强酸SO42-/ZnFe2O4的制备与催化合成癸二酸二乙酯的研究

以硫酸盐为原料,添加NaOH和NaHCO₃以制备出碱式碳酸盐前驱体,合成出新型的纳米固体超强酸催化剂SO₄^2-/ZnFe₂O₄,经XRD、BET、IR等检测,粒径为35nm,比表面积很大(137m^2-1),粒度均匀。首次以该固体酸为催化剂,癸二酸和无水乙醇为原料合成癸二酸二乙酯,考察了影响反应的因素。结果表明,醇酸摩尔比为4.0∶1,催化剂用量为1.0g(癸二酸0.1mol),带水剂苯15mL,反应时间2.5h是最佳反应条件,酯化率可达91%,并推断出该催化剂的酸强度-16.02< H_o< -14.52.     

Synthesis of 2,2-difluoro-2H-chromenes through the tandem reaction of ethyl 3-bromo-3,3-difluoropropionate with salicylaldehyde derivatives

A series of 2,2-difluoro-2H-chromenes were synthesized from the tandem reactions of ethyl 3-bromo-3,3-difluoropropionate with salicylaldehyde derivatives in good yields under basic conditions. In acidic environment defluorination took place during the reaction. A plausible mechanism was proposed based on the experimental results.     

Anti-AIDS agents 83. Efficient microwave-assisted one-pot preparation of angular 2,2-dimethyl-2H-chromone containing compounds

A novel and efficient microwave-assisted one-pot reaction was developed to synthesize angular 2,2-dimethyl-2H-chromone-containing compounds, which is the first and key step in the synthesis of potent DCK and DCP anti-HIV agents. The newly developed microwave synthesis conditions dramatically shortened the reaction time from 2 days to 4 h with improved yields.