A new synthetic method for the preparation of protonated-NHCs and related compounds

Protonated versions of N-heterocyclic carbenes (NHC,H⁺) are classically prepared by closing the ring through the introduction of the CH⁺ fragment. Here we report a totally different synthetic approach, which can be viewed as the addition of a 1,3-diazaallyl anion to a compound featuring two leaving groups (hereafter named “di-electrophile”). Using 1,3- and 1,4-dibromides, six- and seven-membered NHC,H⁺s have been prepared in good yields. Similarly, with 1,3,2-dioxathiolane-2,2-dioxide as a di-electrophile, imidazolidinium salts were obtained. To illustrate its broad scope of application, this synthetic route has been expanded to the preparation of protonated cyclic amino alkyl carbenes (CAACs) and amino thio carbenes, using 1-aza-allyl and 1,3-azathio-allyl anions, respectively.     

A novel synthetic method for preparation of some folates

An improved method was developed for preparation of 5,6,7,8-tetrahydrofolic acid (THF) and calcium-5-methyltetrahydrofolate (5-MTHF-Ca) by reduction of folic acid using KBH₄ catalyzed by Pb(NO₃)₂. The yields of THF and 5-MTHF-Ca were 56.5 and 42.7 %, respectively. A convenient method for measurement of THF and 5-MTHF-Ca using liquid chromatography–mass spectrometry (LC–MS) was also established, enabling analysis of those folates within 10 min without application of gradient elution.     

Vine-twining polymerization: a new preparation method for well-defined supramolecules composed of amylose and synthetic polymers

In this article we describe a new method of polymerization called "vine-twining polymerization" for preparation of well-defined supramolecules, which are amylose-polymer inclusion complexes. The method was achieved by enzymatic polymerization of alpha-D-glucose-1-phosphate catalyzed by phosphorylase in the presence of various synthetic polymers such as polyethers, polyesters, poly(ester-ether), and amphiphilic block copolymer. Powder X-ray diffraction (XRD) and 1H-NMR measurements determined the structures of the products to be inclusion complexes. The XRD patterns were completely different from those of amylose and guest polymers. The 1H-NMR spectra of the products indicated that the structures were composed of amylose and guest polymers. The formation process of the inclusion complexes during the enzymatic polymerization was also evaluated. In addition, we revealed that the bulkiness of the end groups and the hydrophobicity of the guest polymers strongly affected the formation of the inclusion complexes. By means of this method of polymerization, a graft polymer having inclusion complexes as side chains was prepared. Furthermore, as an evolution of the "vine-twining polymerization," we attempted a system of parallel polymerization to form an inclusion complex of amylose with a strongly hydrophobic guest polymer.     

A new method for preparation of dihydrodinaphthopyranopyrans

The syntheses of 7a,15a-dlhydro-15a-methylnaphtho[2,l-b] naphtho [1',2':5,6] pyrano[3,2-e]pyran (II) and 7a,15a-dihydro-7a-methyl-15a-isopropyi naphtho [2,1-b] naphtho [1' ,2' : 5,6] pyrano [3,2-e] pyran (III) from 2-naphthol and corresponding dimethylol ketones in one step were described. Amberlyst-15® was used as catalyst.     

From isocyanides to trichloropyruvamides: application to a new preparation of oxamide derivatives

Isocyanides react readily with trichloroacetic acid anhydride forming stable hydrates of trichloropyruvamides. These compounds are valuable intermediates for obtaining oxamides by reaction with TMSCl/NEt₃ followed by addition of an amine.     

A new synthetic procedure for the preparation of pyridinium tetrafluoroborate and hexafluorosilicate

Pyridinium tetrafluoroborate (C₅H₅NHBF₄) and pyridinium hexafluorosilicate [(C₅H₅NH)₂SiF₆] have been prepared in good yields and high purity by the reaction of pyridinium poly(hydrogen fluoride) with oxides and acids of boron and silicon respectively. The salts have been characterised by melting points, IR, ¹H and ¹⁹F NMR spectroscopy and chemical analysis.     

A new synthetic method for 7α-methoxycephalosporins

A new synthetic route for 7α-methoxy-7β-acylaminocephalosporins is described.     

Purge-and-membrane with ECD. A new screening method for chlorinated aliphatic hydrocarbons

Summary A new analytical technique; purge-and-membrane-electron capture detection (ECD), is described and applied to the screening of halogenated aliphatic hydrocarbons. A water sample is first purged by helium and the purged compounds are collected from the gas phase through a silicone membrane to the analytical system. Purge-and-membrane-ECD provides very fast, selective and sensitive screening method for halogenated aliphatic hydrocarbons. The method was compared with conventional direct membrane extraction. Results obtained show that the limits of detection (0.01–2 μg L⁻¹) were comparable with both methods. However, significant shorter response times were measured with purge-and-trap than with direct membrane extraction.     

Purge-and-membrane with ECD. A new screening method for chlorinated aliphatic hydrocarbons

Summary A new analytical technique; purge-and-membrane-electron capture detection (ECD), is described and applied to the screening of halogenated aliphatic hydrocarbons. A water sample is first purged by helium and the purged compounds are collected from the gas phase through a silicone membrane to the analytical system. Purge-and-membrane-ECD provides very fast, selective and sensitive screening method for halogenated aliphatic hydrocarbons. The method was compared with conventional direct membrane extraction. Results obtained show that the limits of detection (0.01–2 g L^–1) were comparable with both methods. However, significant shorter response times were measured with purge-and-trap than with direct membrane extraction.     

A new method for the preparation of polyfluoroalkanedithiocarboxylates

A new method for synthesis of alkyl and aryl polyfluoroalkyldithiocarboxylates by reaction of 1,1-dichloropolyfluoroalkylsulfenylchlorides with mercaptans in the presence of ZnCl₂ was developed. The sulfenylchlorides are easily obtained by chlorination of benzyl 1,1-dihydropolyfluoroalkylsulfides or benzyl dithioacetals of polyfluoroaldehydes.     

A new method for99mTc generator preparation

The authors report here a new approach for making^99mTc generators based on neutron irradiation of metallic molybdates and direct elution eliminating intermediate chemical processing steps. This approach tested using zirconium molybdate was found to yield^99mTc with good yield and purity. This seems to be the simplest way of making column type^99mTc generator even using low flux reactors and merits further detailed evaluation.     

A new synthetic method for alpha-alkoxycarbonyl iminium salt and its reaction with nucleophiles

An iminium salt was easily prepared using the oxidation of amino ketene silyl acetal with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone, and the subsequent nucleophilic addition to this iminium species proceeded efficiently to afford alpha-amino esters in good yields.     

Synthesis of vinca alkaloids and related compounds. Part 110: A new synthetic method for the preparation of pandoline-type alkaloid-like molecules

A practicable synthesis of a pandoline-type alkaloid-like molecule is reported through an efficient preparation of carbinolamine ether intermediates (9a and 9b). The key step of the synthesis consists of an intramolecular cycloaddition of the secodine-type intermediate (2), which was formed from the tryptamine derivative (3) and lactol (4). The mechanism of the cycloaddition reaction was investigated by quantum chemical calculations and it was found to follow a step-wise mechanism involving a zwitterionic intermediate (15). By employing this strategy, other members of the family of pandoline alkaloids or alkaloid-like molecules could be synthesized by reacting the tryptamine derivative with appropriately functionalized aldehydes.     

A new method for the preparation of modified oligonucleotides

[reaction-see text] N-Nitrothymidine can be transformed into a phosphoramidite building block suitable for oligonucleotide synthesis using the standard phosphite triester solid-phase approach. The N-nitrothymidine residues remain stable during the elongation cycles and react smoothly with primary amines, furnishing oligonucleotides containing N3-modified thymidines. A number of N3-substituted oligonucleotides have been prepared using this methodology, some of them incorporating aminoalkyl or hydroxyalkyl groups.     

A new general method for the preparation of N-sulfonyloxaziridines

[reaction: see text] A simple procedure to obtain N-alkylsulfonyl- and N-arylsulfonyloxaziridines from the corresponding N-sulfinylimines involving a one-pot, two-step oxidation process with m-CPBA (1 equiv) and m-CPBA/KOH (1.1 equiv) is reported. The method is applicable to N-sulfinylimines derived from aldehydes (aliphatic and aromatic) and ketones (dialkyl and aryl alkyl) and preserves C=C-conjugated double bonds. Almost quantitative yields, very mild conditions (usually less than 5 min at room temperature), and easy purification by filtration are the main features of this new procedure, which can be performed at a gram scale.     

A new method for the preparation of diphenylboryldipivaloyl phosphide

Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 11, pp. 2670–2671, November, 1990.