The chemistry of trityl isoselenocyanate revisited: A preparative and structural investigation

The reaction of trityl chloride with KSeCN gives trityl isoselenocyanate which was structurally characterised by X-ray diffraction. Trityl isoselenocyanate reacts with hydrazine to give trityl selenosemicarbazide and with primary amines to give selenourea derivatives. However, with secondary amines mixtures of selenoureas and substitution products are formed. Trityl selenosemicarbazide undergoes a condensation reaction with salicylaldehyde to give the corresponding trityl selenosemicarbazone. In the case of 2-pyridinecarboxaldehyde, the analogous selenosemicarbazone cannot be isolated, instead a small quantity of the diselenide was isolated from the reaction mixture. The compounds prepared here were fully characterised spectroscopically and several also by X-ray diffraction.     

Synthesis of water‐dispersible,fluorinated particles with grafting sulfonate chains by the core crosslinking of block copolymer micelles

Fluorinated polymer particles with grafting sulfonate chains, which showed high dispersion stability in aqueous media, were synthesized by the crosslinking of block copolymer micelles. A crosslinkable block copolymer, poly[(2,3,4,5,6‐pentafluorostyrene)‐co‐4‐(1‐methylsilacyclobutyl)styrene]‐b‐poly(neopentyl 4‐styrenesulfonate), composed of a statistical copolymer segment of 2,3,4,5,6‐pentafluorostyrene with 4‐(1‐methylsilacyclobutyl)styrene and a neopentyl 4‐styrenesulfonate segment, was prepared by the nitroxy‐mediated living radical polymerization of a 2,3,4,5,6‐pentafluorostyrene/4‐(1‐methylsilacyclobutyl)styrene mixture and neopentyl 4‐styrenesulfonate. The block copolymer formed micelles with a poly[(2,3,4,5,6‐pentafluorostyrene)‐co‐4‐(1‐methylsilacyclobutyl)styrene] core in acetonitrile, which were crosslinked via the ring‐opening reaction of silacyclobutyl groups in the core by a treatment with a platinum catalyst. The deprotection of sulfonate groups in the micelle corona by exposure to trimethylsilyl iodide and a treatment with aqueous HCl, followed by neutralization with aqueous NaOH, provided a polymer particle with polymer chains of sodium 4‐styrenesulfonate grafted on its surface. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 1316–1323, 2007     

O-(1-Phenyl-1H-tetrazol-5-yl) Glycosides: Alternative synthesis and transformation into glycosyl fluorides

A number of new glycosyl donors, O-(1-phenyl-1H-tetrazol-5-yl) glycosides, are prepared from the corresponding hemiacetals, commercially available 5-chloro-1-phenyl-1H-tetrazole ( 2 ), and tetrabutylammonium fluoride (Bu₄NF) in either THF or DMF. The mild reaction conditions are compatible with a variety of protecting groups. The glycosyl donors are treated with hydrogen fluoride-pyridine complex (HF·py) to rapidly provide glycosyl fluorides in good-to-excellent yields, apparently by a (single or double) S_N2 mechanism as studied by both ¹H- and ¹⁹F-NMR spectroscopy. Under acidic conditions, glycosyl fluorides equilibrate partially or completely, equilibration requiring a large excess of HF · py.     

A Facile Synthesis of N γ-Glycosyl Asparagine Conjugates and Short N-Linked Glycopeptides

Both free and protected glycosyl azides were efficiently coupled to the side chain of aspartate by the Staudinger reaction for the synthesis of N ^γ-glycosyl asparagine conjugates and short N-linked glycopeptides that can be employed to construct complex N-linked glycopeptides. In the process, a facile two-step protocol was developed for free glycosyl azide synthesis, which includes reported direct transformation of free oligosaccharides into glycosyl amines through reaction with ammonium bicarbonate and then stereospecific diazo transfer reaction to convert glycosyl amines to glycosyl azides.     

5:1 and 2:1 cocrystals of 2,3,4,5,6‐pentafluorophenol with phenazine

2,3,4,5,6‐Pentafluorophenol (pFp), unlike phenol, forms cocrystals with the weak heteroaromatic base phenazine (phz). Two types of cocrystals were prepared, (I) with a high content of pFp, 2,3,4,5,6‐pentafluorophenol–phenazine (5/1), 5C₆HF₅O·C₁₂H₈N₂, and (II) with a 2:1 pFp–phz molar ratio, 2,3,4,5,6‐pentafluorophenol–phenazine (2/1), 2C₆HF₅O·C₁₂H₈N₂. In both forms, homostacks are formed by the heterocyclic base and phenol molecules and no aryl–perfluoroaryl stacking interactions occur. The arrangement of the molecules in the crystal of (I) is determined by strong O—H...N and O—H...O hydrogen bonds, weak O—H...F, C—H...F and C—H...O interactions, π–π stacking interactions between the phz molecules and C—F...π_F interactions within the pFp stacks. Among the specific interactions in (II) are a strong O—H...N hydrogen bond, weak C—H...F interactions and π–π stacking interactions between the phz molecules. In (I) and (II), the heterocyclic molecules are located around inversion centres and one of the symmetry‐independent pFp molecules in (I) is disordered about an inversion centre. Remarkably, similar structural fragments consisting of six pFp stacks can be identified in cocrystal (I) and in the known orthorhombic polymorph of pFp with Z′ = 3 [Gdaniec (2007). CrystEngComm, 9 , 286–288].     

Specific solvent effects on the intramolecular electron transfer reaction in a neutral ferrocene donor polychlorotriphenylmethyl acceptor radical with extended conjugation

The synthesis and the optical, magnetic and electrochemical properties of the ferrocenylbutynene substituted polychlorotriphenylmethyl radical 1 are reported. Radical 1 is prepared in a three step synthetic route starting with a Wittig reaction to yield (E,Z)-{4-[4-(bis(2,3,4,5,6-pentachlorophenyl)methyl)-2,3,5,6-tetra-chlorophenyl]but-3-en-1-ynyl}-ferrocene (1H) which is subsequently deprotonated to yield the corresponding anion K⁺(18-crown-6) [1]^? and finally oxidized to (E)-4-[4-(ferrocenyl)but-3-yn-1-enyl]-2,3,5,6-tetrachlorophenyl-bis(2,3,4,5,6-pentachlorophenyl) methyl radical (1). Radical 1 exhibits a charge-transfer band transition in the near infrared region which is associated with an intramolecular electron transfer from the ferrocene unit (donor) to the radical unit (acceptor) of this dyad molecule; its solvatochromism is studied in detail. The X-ray crystal structure of [K⁺(18-crown-6)](E)-[4-[4-(ferrocenyl)but-3-yn-1-enyl]-2,3,5,6-tetrachlorophenyl-bis(2,3,4,5,6-pentachlorophenyl) methide] [1]^? has been determined. This organic salt forms an interesting one-dimensional coordination polymer by the coordination of the K⁺ cation with chlorine atoms of the organic carbanion.     

The preparation and reactions of a π-bound organic isoselenocyanate complex of platinum: Formation of an η2-diselenocarbonimidato complex

Reaction of Pt(Ph₃P)₂C₂H₄ with p-tolyl isoselenocyanate yields the first known example of a π-bound organic isoselenocyanate ligand in the complex Pt(η²-SeCNC₇H₇)(Ph₃P)₂. Reaction of this complex with methyl iodide results in alkylation at the selenium atom rather than at nitrogen, with resultant loss of selenium to yield PtI₂(CNC₇H₇)(Ph₃P) as the final product. If the reaction of Pt(Ph₃P)₂C₂H₄ with p-tolyl isoselenocyanate is carried out in CH₂Cl₂ solution, selenium abstraction occurs and the complex Pt(η²-Se₂CNC₇H₇)-(CNC₇H₇)(Ph₃P) is formed which contains both an isonitrile ligand and the as yet unreported diselenocarbonimidato ligand. Alkylation of this ligand failed to yield a diselenocarbamate complex.     

Polymerization of N-(2,3,4,5,6-pentafluorophenyl)-maleimide

A novel fluorine-containing polymer, poly[N-(2,3,4,5,6-pentafluorophenyl)maleimide], was prepared by the anionic polymerization of N-(2,3,4,5,6-pentafluorophenyl)maleimide (PFPMI). Anionic polymerization with alkali metal tert-butoxides gave poly(PFPMI) in 14–32% yield. Phenyllithium and sec-butyllithium also afforded poly(PFPMI). No polymer was obtained with a radical initiator such as 2,2′-azoisobutyronitrile. The polymerization took place only via the vinylene group of PFPMI and no appreciable side-reaction occurred. The obtained poly(PFPMI) shows unimodal molecular weight distribution and begins to decompose at 325°C.     

Mapping the Relationship between Glycosyl Acceptor Reactivity and Glycosylation Stereoselectivity

The reactivity of both coupling partners—the glycosyl donor and acceptor—is decisive for the outcome of a glycosylation reaction, in terms of both yield and stereoselectivity. Where the reactivity of glycosyl donors is well understood and can be controlled through manipulation of the functional/protecting‐group pattern, the reactivity of glycosyl acceptor alcohols is poorly understood. We here present an operationally simple system to gauge glycosyl acceptor reactivity, which employs two conformationally locked donors with stereoselectivity that critically depends on the reactivity of the nucleophile. A wide array of acceptors was screened and their structure–reactivity/stereoselectivity relationships established. By systematically varying the protecting groups, the reactivity of glycosyl acceptors can be adjusted to attain stereoselective cis‐glucosylations.     

Synthesis of 5‐(6‐Pyridazinone‐3‐yl)‐2‐Glycosylamino‐1,3,4‐Oxadiazoles

N‐Glycosyl‐2‐(1,4,5,6‐tetrahydropyridazin‐6‐one‐3‐carbonyl)‐hydrazinecarbothioamides 3a‐3g and N‐glycosyl‐2‐(1,6‐dihydropyridazin‐6‐one‐3‐carbonyl)‐hydrazinecarbothioamides 5a‐5g were prepared by the reaction of glycosyl isothiocyanates with the compounds 1,4,5,6‐tetrahydro‐3‐hydrozinecarbonyl‐6‐pyridazinone ( 1 ) and 1,6‐dihydro‐3‐hydrozinecarbonyl‐6‐pyridazinone ( 2 ). The terminal heterocyclic compounds 1,3,4‐oxadiazole derivatives were obtained from cyclization of compounds ( 3a‐3g ) and ( 5a‐5g ) by mercuric acetate. Their structures were confirmed by IR, ¹H NMR, MS and elemental analyses.     

Synthesis of sugar-derived isoselenocyanates, selenoureas, and selenazoles

Aryl, alkyl, and sugar-derived isoselenocyanates were prepared by a one-pot procedure starting from the corresponding formamides, using triphosgene as a dehydrating agent, triethylamine, and black selenium powder. The preparation of sugar selenoureas by coupling of O-protected sugar-derived isoselenocyanates with different amines, and by coupling of unprotected glycopyranosyl amines with phenyl isoselenocyanate was also accomplished. The synthesis of a glucopyranos-2-yl-selenazole starting from O-protected 2-amino-2-deoxy-d-glucose by coupling with benzoyl isoselenocyanate, Se-alkylation with phenacyl bromide, and acid-catalyzed dehydration is also reported. Unprotected N-(β-d-glucopyranosyl)-N′-phenylselenourea was transformed into a 1,2-trans-fused bicyclic isourea upon treatment with aqueous hydrogen peroxide; the same isourea was prepared by a one-pot three-step procedure from β-d-glycopyranosylamine by thiophosgenation, coupling with aniline, and HgO-mediated desulfurization.     

Über Chalkogenolate. 136 [1]. Alkylester der Cyanoameisensäure und der Cyanomonothioameisensäure

On Chalcogenolates. 136. Alkyl Esters of Cyanoformic Acid and of Cyanomonothioformic Acid By use of the phase transfer catalyst 18-crown-6 the esters CH₃O—CO—CN, C₂H₅O—CO—CN, C₂H₅S—CO—CN, and ⁿC₃H₇S—CO—CN have been prepared by reaction of the corresponding chloro compound with potassium cyanide. The prepared compounds have been characterized by means of electron absorption, infrared, nuclear magnetic resonance (¹H and ¹³C), and mass spectra.     

Synthesis of 2-hydroxy-6-{[(16R)-β-δ-mannopyransyloxy]heptadecyl}benzoic acid, a fungal metabolite with GABAA ion channel receptor inhibiting properties

An expeditious total synthesis of the physiologically active fungal metabolite 1 is described. The stereoselective formation of its β-δ-mannopyranosidic linkage is achieved in two steps upon reaction of the hexopyranos-2-ulosyl bromide 15 with the glycosyl acceptor 13, followed by reduction of the resulting β-δ-glycos-2-uloside 16. Alcohol 13 was efficiently prepared via a Suzuki reaction of the aryltriflate 11 with the 9-alkyl-9-BBN derivative 10.     

Tandem addition-cyclization of o-ethynylphenyllithiums and isoselenocyanates: a convenient preparation of functionalized benzo[c]selenophenes

The o-bromoethynylbenzenes were lithiated with tert-BuLi in Et₂O followed by treatment with isoselenocyanate, and then EtOH was added as a proton source, producing the desired (Z)-3-methylidenebenzo[c]selenophenes as the sole 5-exo-dig mode cyclization products in one-pot with yields ranging from 54-87%. The iodocyclization of the o-ethynylphenyllithium with isoselenocyanate stereoselectively gave the (E)-1′-iodo-3-methylidenebenzo[c]selenophene, which was converted into the more functionalized benzo[c]selenophenes via the Suzuki- and Sonogashira-coupling reactions.     

Two cadmium(II) fluorous coordination compounds tuned by different bipyridines

Fluorine is the most electronegative element and can be used as an excellent hydrogen‐bond acceptor. Fluorous coordination compounds exhibit several advantageous properties, such as enhanced high thermal and oxidative stability, low polarity, weak intermolecular interactions and a small surface tension compared to hydrocarbons. C—H…F—C interactions, although weak, play a significant role in regulating the arrangement of the organic molecules in the crystalline state and stabilizing the secondary structure. Two cadmium(II) fluorous coordination compounds formed from 2,2′‐bipyridine, 4,4′‐bipyridine and pentafluorobenzoate ligands, namely catena‐poly[[aqua(2,2′‐bipyridine‐κ²N ,N ′)(2,3,4,5,6‐pentafluorobenzoato‐κO )cadmium(II)]‐μ‐2,3,4,5,6‐pentafluorobenzoato‐κ²O :O ′], [Cd(C₇F₅O₂)₂(C₁₀H₈N₂)(H₂O)]_n , (1), and catena‐poly[[diaquabis(2,3,4,5,6‐pentafluorobenzoato‐κO )cadmium(II)]‐μ‐4,4′‐bipyridine‐κ²N :N ′], [Cd(C₇F₅O₂)₂(C₁₀H₈N₂)(H₂O)₂]_n , (2), have been synthesized solvothermally and structurally characterized. Compound (1) shows a one‐dimensional chain structure composed of Cd—O coordination bonds and is stabilized by π–π stacking and O—H…O hydrogen‐bond interactions. Compound (2) displays a one‐dimensional linear chain structure formed by Cd—N coordination interactions involving the 4,4′‐bipyridine ligand. Adjacent one‐dimensional chains are extended into two‐dimensional sheets by O—H…O hydrogen bonds between the coordinated water molecules and adjacent carboxylate groups. Moreover, the chains are further linked by C—H…F—C interactions to afford a three‐dimensional network. In both structures, hydrogen bonding involving the coordinated water molecules is a primary driving force in the formation of the supramolecular structures.     

Click novel glycosyl amino acid hydrophilic interaction chromatography stationary phase and its application in enrichment of glycopeptides

A novel glycosyl amino acid hydrophilic interaction chromatography (HILIC) stationary phase was prepared via click chemistry. The key intermediate N₃-glycosyl d-phenylglycine was prepared by a three steps procedure, including selective condensation of amino glucose with N-succinimidyl ester of Boc-d-phenylglycine, deprotection and transformation of amino group to azido group. The structure of all the intermediates and functionalized silica beads were confirmed by ¹H NMR, IR, elemental analysis and ¹³C CP-MAS. The chromatography test showed that this new type of separation material possessed good HILIC properties and glycopeptide enrichment characteristics. Nucleosides and bases could be separated in a simple eluent composition (only acetonitrile in combined with water), and with the same condition, these model compounds could not be separated on the commercial HILIC column (Atlantis). Click glycosyl amino acid thus prepared also showed longer retention and better separation ability in the separation of polar organic acids.     

Model reactions for preparing poly(imino-tetrafluoro-1,4-phenylene)

2,3,4,5,6-Pentafluoroformanilide was prepared giving, in addition, two new compounds 4,5,6,7-tetrafluoro-1-pentafluorophenyl-benzimidazole and 2,3,4,5-tetrafluoro-6-[(pentafluorophenyl)amino]formanilide. Sodium 2,3,4,5,6-pentafluoro-formanilide was reacted with hexafluorobenzene in a molar ratio of 1:4 to give oligomers of α-pentafluorophenyl-ω-fluoro-poly(imino-tetrafluoro-1,4-phenylene). Some of the oligomers were isolated. The results indicate that poly(imino-tetrafluoro-1,4-phenylene) could be formed. Model reaction on hexafluorobenzene with sodium acetanilide, molar ratio 1:2, gave a low yield of N,N′-diacetyl-diphenyl-tetrafluoro-1,4-phenylenediamine.     

Reaction of dilfuorocarbene and hexafluoropropene with polyfluorinated N-metal-diphenylamides

N-difluoromethyl and N-(perfluoropropenyl)-decafluorodiphenylamine together with N-(perfluoropropenyl)-2,3,4,5,6-pentafluorodiphenylamine have been prepared by reacting N-lithium or sodium diphenylamides with difluorocarbene or hexafluoropropene. The amines were hydrolyzed to the respective N,N-decafluorodiphenyl amides with sulphuric acid. The ¹⁹F NMR spectra of the N,N-decafluorodiphenylamides showed a set reasonances for each of the phenyl groups indicating hindered internal rotation around the N-C(O) bond.     

Reactions of fused dihydro-1,2,4-thiadiazoles with isoselenocyanates giving 6aλ4-thia-1,3,4,6-tetraazapentalene derivatives and 5,10-dihydro-1,2,4-thiaselenazolo[4,5-b][2,4]benzodiazepines

3-Methyl-6,7-dihydro-5H-1,2,4-thiadiazolo[4,5-a]pyrimidine (1) reacted with isoselenocyanates with elimination of acetonitrile and concomitant addition of two molecules of the isoselenocyanate to give 2,3-di-substituted-6,7-dihydro-5H-2aλ⁴-thia-2,3,4a,7a-tetraazacyclopent[cd]indene-1(2H),4(3H)-diselones (6a)–(6j). 3-Methyl-5,10-dihydrobenzo[e]-1,2,4-thiadiazolo[4,5-a][1,3]diazepine (3) likewise reacted with alkyl isoselenocyanates to give the 2,3-dialkyl-5-10-dihydro-2aλ⁴-thia-2,3,4a,10a-tetraazapentaleno[3,3a,4-gh]benzocycloheptene-1,4-diselones (9a)–(9h), but reaction of (3) with aryl isoselenocyanates took place with elimination of acetonitrile and incorporation of one molecule of the aryl isoselenocyanate in the product to give 3-arylimino-5,10-dihydro-1,2,4-thiaselenazolo[4,5-b][2,4]benzodiazepines (10a)–(10h). Structure (10) is a new heterocyclic system. The pyrimidine (1) and the diazepine (3) reacted with aryl isoselenocyanates at room temperature in solvents of low polarity to give zwitterion 1:1 addition compounds (7) and (12), respectively. NMR studies reveal that the thiaselenazoles (10) react in solution with aryl isoselenocyanates to give diaryl diselones (11) in a reversible process involving a Dimroth rearrangement. © 1996 John Wiley & Sons, Inc.     

α-Selective glycosidation of d-tagatofuranose with a 3,4-O-isopropylidene protection

An α-selective glycosidation reaction of d-tagatofuranose was successfully achieved using 3,4-O-isopropylidene-protected d-tagatofuranose as a glycosyl donor. A variety of glycosyl acceptors, including primary, secondary, and β-amino alcohols, and carbohydrates, can be used for this d-tagatofuranosidation reaction with complete α-selectivities and good yields (57–83%). The stereochemistries at the anomeric positions were determined by nuclear Overhauser effect spectroscopic correlations, as well as comparison of the chemical shifts in the ¹³C NMR spectra.