The activation of N-hydroxy compounds by μ-oxo-bis-[tris-(dimethylamino)-phosphonium] bis-tetrafluoroborate

A study is made of the effect of 1-hydroxybenzotriazole on μ-oxo-bis-[tris(dimethylamino)-phosphonium]-bis-tetrafluoroborate 1 during amide bond formation. The reagent 1 is used to activate phenylhydroxamic acid towards a Lossen-type rearrangement and bring about Beckmann rearrangement of ketoximes under mild conditions. Both syn- and anti-benzaldoxime give benzonitrile by elimination.     

2-(Aminomethyl)phthalimide. A new reagent for the synthesis of 2,4-benzodiazepines

2,4-Benzodiazepines can be prepared by condensation of an activated 2-benzoylbenzoic acid with 2-(aminomelhyl)phthalimide. A synthesis of this reagent is described.     

Nucleophilic difluoromethylation and trifluoromethylation using tetrakis(dimethylamino)ethylene (TDAE) reagent

In an effort to find new methodologies to introduce difluoromethylene and trifluoromethyl moieties into organic molecules of synthetic and biological interest, tetrakis(dimethylamino)ethylene (TDAE) was found to be an effective reductant of a series of good electron-acceptors such as bromodifluoromethyl heterocycles, chlorodifluoromethylated ketones as well as perfluoroalkyl iodides; the corresponding anions thus generated under very mild conditions, were successfully engaged in a number of intra- and intermolecular coupling reactions with a series of electrophiles (aldehydes, ketones, α-keto esters, N-tosyl aldimines, acyl chlorides, diol sulphates, disulfides, and diselenides). The corresponding adducts were usually obtained in moderate to good yields and the present method was found to be as good or even better as other most popular approaches. This paper gives an overview of our research efforts in this area as well as results from other groups.     

Silafunctional compounds in organic synthesis. 27. (Isopropoxydimethylsilyl)methyl grignard reagent: A new nucleophilic hydroxymethylating agent for aldehydes and ketones

Nucleophilic hydroxymethylation of aldehydes and ketones has been achieved by the reaction with the (isopropoxydimethylsilyl)methyl Grignard reagent and the subsequent oxidative cleavage of the carbon-silicon bond.     

S-(2-pyridinyl)-1,1,3,3-tetramethylthiouronium hexafluorophosphate. A new reagent for the synthesis of 2-pyridinethiol esters

[reaction: see text] A new thiouronium-based reagent for the synthesis of 2-pyridinethiol esters under non-nucleophilic conditions from the corresponding carboxylic acids was developed. The resulting procedure enables the preparation of previously unavailable alpha,beta-unsaturated 2-pyridinethiol esters as well as their aliphatic and aromatic counterparts.     

Chemically removable derivatization reagent for liquid chromatography I. 2-(N-Phthalimido)ethyl 2-(dimethylamino)ethanesulfonate

A sulfonate derivatization reagent, 2-(N-phthalimido)ethyl 2-(dimethylamino)ethanesulfonate, was synthesized and examined for use in liquid chromatography. The reagent contains two key moieties, a chromophore (phthalimido) necessary for detection and a dimethylamino function that is chemically removable after derivatization. The reagent was applied to the derivatization of 2,4,6-trichlorophenol as a model analyte. The results indicated that the reagent can be readily removed after derivatization by simple acid treatment.     

A new reagent for the mediation of amide bond formation in peptide synthesis.

The potential application of 1-oxo-1-chlorophospholane (5) as a novel reagent for the in situ activation of Nα -protected amino acids for use in peptide bond forming reactions has been examined. Wherever possible, 32.4Mhz ³¹P nuclear magnetic resonance (n.m.r.) spectroscopy was employed to follow both the formation of the intermediate phospholanic-carboxylic mixed anhydride and the subsequent aminolysis reaction.     

A new reagent for the cleavage of NPS-amino protecting groups in peptide synthesis.

The value of several reagents capable of removing quantitatively the α-amino protecting group of NPS-aminoacyl- or peptidyl-derivatives is assessed, by comparison with the reagents currently used, i.e. hydrogen chloride, RS^–-nucleophiles or alkyl thioamides, especially with regard to reaction specificity and end-product solubility. New reagents proposed, 3-nitro-4-mercapto-benzoic acid, and its methyl ester, appear to optimize the numerous, and often competing, requirements. These were probed, under conditions suitable for both conventional and solid-phase methods, on a series of model compounds, including diversely protected amino acids and short peptides, as well as for the actual synthesis of a triacontapeptide by the stepwise, solid-phase approach.     

A new reagent for the spectrophotometric determination of magnesium (II): Khimduchlorophosphonazo-I

Summary The colour reaction of magnesium(II) with Khimduchlorophosphonazo-I (KCPA-I) has been studied spectrophotometrically with a view to develop a procedure for the determination of exchangeable magnesium in acidic soils.The optimum acidities are pH 8.78–9.90. The absorption maximum and molar absorptivity of the coloured complex are 580 nm and 1.85 · 10⁴ l · mol^–1 · cm^–1, respectively. The colour intensity is stable for 4 h and is found to obey Beer's law within the concentration range of 0–20 g per 25 ml. The method is simple and reliable (standard deviation 0.8–1.2%). It has been applied to the determination of exchangeable magnesium.

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Neues Reagens für die spektralphotometrische Bestimmung von Magnesium (II): Khimduchlorophosphonazo-I

Zusammenfassung Die Farbreaktion von Magnesium mit Khimduchlorophosphonazo-I wurde im Hinblick auf die Entwicklung eines entsprechenden Analysenverfahrens untersucht. Der optimale pH-Wert liegt im Bereich von 8,78–9,90. Das Absorptionsmaximum liegt bei 580 nm, der molare Extinktionskoeffizient beträgt 1,85 · 10⁴l · mol^–1 · cm^–1. Die Färbung bleibt 4 h lang stabil und befolgt das Beersche Gesetz von 0 bis 20 g/25 ml. Das Verfahren ist einfach und zuverlässig (Standardabweichung 0,8–1,2%) und wurde zur Bestimmung von austauschbarem Magnesium in sauren Böden angewendet.

     

A new polymer-supported reagent for the synthesis of beta-lactams in solution

A modified Mukaiyama reagent was prepared on a PS-DVB resin. This reagent was used for the preparation of beta-lactams, using the Staudinger reaction. The products were obtained by generating the ketene from a carboxylic acid under sonication with the resin followed by reaction with the imine. Excess of the imine was removed by reduction followed by acid scavenging.     

A new facile synthesis of chelate reagent via 2-aminomethylpyridine-Co(III) complex: 2,3,5,6-tetra(2-pyridyl)pyrazine

2-Aminomethylpyridine $\text{(1)}$ readily reacted with Co(II) ion to give a chelate complex which reacted with oxygen to form, presumably, a μ-peroxodicobalt(III) complex or a Co(III)-$\text{(1)}$ complex, and finally it was transformed to 2,3,5,6-tetra(2-pyridyl) pyrazine.     

A new synthesis of (PhPSe2)2 (Woollins reagent) and its use in the synthesis of novel P-Se heterocycles

A new and improved method for the preparation of (PhPSe2)2 (Woollins reagent (WR), 1) is reported. Reaction of dichlorophenylphosphine with Na2Se, (prepared from the reaction of elemental selenium and sodium in liquid ammonia) gives WR with excellent purity, high yield and on a larger scale than was previously possible. Four novel phosphorus-selenium heterocycles, including a spirocyclic heterocycle exhibiting a four-membered P2SeC ring, were obtained from the reaction of WR with two reactive substrates (diphenylcyclopropenone and methyl phenylpropiolate). Useful selenocarbonyl and thiocarbonyl compounds were obtained from the reaction of both WR and Lawesson's reagent with diphenylcyclopropenone. All new compounds were characterised spectroscopically and three demonstrative X-ray structures are reported.     

Fluorous (trimethylsilyl)ethanol: a new reagent for carboxylic acid tagging and protection in peptide synthesis

Starting with a fluorous analogue of 2-(trimethylsilyl)ethanol, we have designed an easy method for preparing a new fluorous tag ((F)TMSE) for the protection of carboxylic acids. Because mild conditions are employed in the tag cleavage (TBAF in the presence of 4 A molecular sieves, which prevent racemization), this tag can be advantageously used in the synthesis of peptides and modified peptides, as we have demonstrated with several examples, including the fluorous synthesis of short alpha- and beta-peptides as well as of modified fluorinated retropeptides.