Studies in the tetraarylborates: Part II. The preparation and reagent properties of sodium tetrakis(p-fluorophenyl)borate,a selective reagent for cesium

Sodium tetrakis(p-fluorophenyl)borate has been synthesized and found to be a very selective gravimetric reagent for the determination of cesium. It formed precipitates with cesium, silver, thallium(I) and rubidium but not with potassium and ammonium ions. The cesium tetrakis(p-fluorophenyl)borate separated as a white crystalline compound, which was easily filterable. It achieved constant weight rapidly at 110° and showed no signs of decomposition after 18 h of drying.     

Studies in the tetraarylborates : The preparation and reagent properties of sodium tetrakis(p-chlorophenyl)borate

Sodium tetrakis(p-chlorophenyl)borate was synthesized. It formed precipitates with K⁺, Rb⁺, Cs⁺, quarternary ammonium and protonated basic nitrogen compounds. The potassium salt was more soluble than potassium tetraphenylborate but flocculated more readily and filtered more easily. The salts formed with nitrogen compounds offer possibilities as derivatives suitable for qualitative analysis.     

Studies in the tetraarylborates : Part VII. The preparation and reagent properties of some new nitrogen heterocyclic tetraarylboraees — especially sodium tetrakis(l-imidazolyl) borate,a novel gravimetric reagent for hydrogen ion

Three new tetraarylborates containing nitrogen heterocycles have been synthesized. Sodium tetrakis(1-imidazolyl)borate and sodium tetrakis(1-benzimidazolyl)borate were prepared in very high yield by syntheses which were easy to perform in situ. Interesting analytical properties which are very different from the carbocyclic tetraarylborates were noted in both compounds. Precipitate formation oftetrakis(1-imidazolyl)borate with hydrogen and divalent cations was observed. The feasibility of determination of the hydrogen cation by tetrakis(1-imidazolyl)borate was demonstrated.     

The synthesis and reagent properties of magnesium tetrakis(4-tert.butylphenyl)borate

Magnesium tetrakis(4-tert.butylphenyl)borate, Mg(BAr(4))(2), has been synthesized and screened for its properties as an analytical reagent. Although rather more selective than tetraphenylborate, the compound surprisingly precipitates sodium and proves a good gravimetric reagent for its determination. Quaternary ammonium and trialkylamine ions are precipitated only slowly (in contrast to the rapid precipitation with tetraphenylborate). The new compound exhibits better resistance to proton-initiated decomposition and to free radical attack than the other known tetra-arylborates. The presence of the parent peak, NaBAr(+)(4), in the mass spectrum of the sodium salt is further proof of the remarkable stability. The other tetra-arylborates do not produce parent peaks in the mass spectra of their precipitates.     

The synthesis and reagent properties of tetrakis-(3,5-dichlorophenyl)borate

Cesium tetrakis(3,5-dichlorophenyl)borate shows similar precipitation and gravimetric properties as tetrakis(m-chlorophenyl)- and tetrakis(p-chlorophenyl)borates. Its overall stability is worse than those of the chloro-substituted borates but it is more stable toward acid attack.     

The Vilsmeier reagent: a useful and versatile reagent for the synthesis of 2-azetidinones

(Chloromethylene)dimethylammonium chloride (Vilsmeier reagent), prepared easily from N,N-dimethylformamide and oxalyl chloride or thionyl chloride, works as a versatile acid activator reagent for the direct [2+2] ketene-imine cycloaddition of substituted acetic acid and imines in one-pot synthesis under mild conditions. Monocyclic, spirocyclic and 3-electron-withdrawing group β-lactams were synthesized by this method and optimization of conditions were performed.     

Studies directed toward the synthesis of the massileunicellins. Part 2

The fully substituted hydroisobenzofuran core of the massileunicellins containing eight contiguous stereocenters was prepared in 12 steps from (S)-(+)-carvone. Noteworthy elements of the synthesis include a one-step oxidative rearrangement/epoxidation, a novel stereoselective directed reduction of a keto diol, and a directed hydrogenation of a congested tetrasubstituted alkene.     

Studies on the synthesis of heterocyclic compounds. Part I. The pschorr reaction in the pyrazole series

Preparation and structural evidence of N-methyl-(1,3-R,R'-pyrazol-5-yl)-o-nitrobenzamides (VIIIa, b) are discussed. Diazotisation of related o-aminobenzamides XIa,b followed by the Pschorr reaction afforded a very complex mixture from which pyrazolo[3,4-c]isoquinolin-5-ones XIIa.b in 7–10% yields together with N-methyl-(1,3-R,R'-pyrazol-5-yl)-o-hydroxybenzamides (XIIIa) in 15–20% yields were isolated.     

New methods and reagents in organic synthesis. 8. Trimethylsilyldiazomethane. A new,stable, and safe reagent for the classical arndt-eistert synthesis

Stable and safe trimethylsilyldiazomethane(TMSCHN₂) can be used efficiently for the Arndt-Eistert synthesis in place of highly toxic and explosive diazomethane.     

Pyrrolopyridazine derivatives as blue organic luminophores: synthesis and properties. Part 2

Two environmentally friendly methods, one in liquid and other in solid phase, for preparation of highly fluorescent pyrrolopyridazine (PP) derivatives under microwave (MW) irradiation is presented. The first synthesis in solid phase of fluorescent PP derivatives using activated alkynes under MW and conventional heating is also reported. Under MW irradiation the yields are higher, the amount of used solvent in liquid phase is at least five-fold less while solid phase does not use solvents, so these reactions may be considered as environmentally friendly. Eight new blue fluorescent 2-aryl-pyrrolopyridazine derivatives were synthesised. A certain influence of the PP substituents concerning absorption and fluorescent properties was observed. Introduction of a π-conjugated system in the second position of PP moiety increase the fluorescent properties. In the absorption spectra were observed a gradual decrease of wavelengths simultaneously with an increasing of molar extinction coefficient, due to increased number of ester groups from pyrrolic ring.     

Pyrrolodiazine derivatives as blue organic luminophores: synthesis and properties. Part 3

A fast, efficient, general and environmentally friendly method for preparation of highly fluorescent derivatives containing the pyrrolodiazine moiety using microwave (MW) irradiation, in liquid phase, is reported. Under MW irradiation the yields are much higher, sometimes substantially (by almost double) and, the amount of solvent used is at least 5-fold less. The pyrrolopyridazine (PP) derivatives are very intense blue emitters and have high quantum yields (up to 90%) while pyrrolophthalazine (PHP) compounds are still intense blue emitters but the quantum yield is negligible. A certain influence of the substituents concerning fluorescence was found, those ones at the 7 position being crucial for fluorescence. The number of the substituents from the pyrrolo ring seems not to play an important role in regard with the fluorescence but, with an increasing number of substituents a certain hypsochromic shift in the absorption spectra was found.     

Studies in the analytical chemistry of sodium : 6:8-Dichlorobenzoylene urea as a reagent for sodium

6:8-Dichlorobcnzoylene urea has been. examined as a reagent for sodium. The reagent cannot be recommended for this purpose. Precipitation is incomplete and the reagent tends to hydrolyse so that it is impossible to differentiate sodium in the presence of potassium.     

Pteridines. Part XLII. Synthesis and properties of 8-substituted 2,4-dithiolumazines

Condensation reactions of the 5-amino-6-(subst. amino)-2,4-dithiouracils 12 and 13 with diacetyl or benzil led to the 6,7,8-trisubstituted 2,4-dithiolumazines 14 – 16 . Methylation of these compounds affected both thio functions forming various types of 2,4-bis(methylthio)lumazine derivatives depending on the nature of the substituents at C(7) and N(8). The 6,7,8-trimethyl-2,4-dithiolumazine ( 14 ) was converted into 7,8-dihydro-6,8-dimethyl–7-methylidene-2,4-bis(methylthio)pteridine ( 17 ), whereas the 8-methyl-6,7-diphenyl-(15) and the 8-(2-hydroxyethyl)-6,7-diphenyl-2,4-dithiolumazine ( 16 ) yielded the corresponding covalent inter- or intramolecular 7,8-adducts 18 – 21 . The unusual structures were proven by spectroscopic means and those of the alcohol adducts 20 and 21 , furthermore, confirmed by X-ray analysis.     

Application of directed metallation in synthesis. Part 3: Studies in the synthesis of (±)-semivioxanthin and its analogues

The synthesis of several analogues of (±)-semivioxanthin including five thiophene analogues, using directed metalation are reported. The strategy consisted of the synthesis of functionalized naphthalene or benzo[b]thiophene as building blocks followed by annelation of the pyrone.     

Studies on the reactivity of methyl γ-tosylcrotonoate as ambident reagent in organic synthesis

The treatment of methyl(E)-4-tosyl-2-butenoate (4) with two equiv. of sodium hydride and different mono and dihalides gives mainly γ,γ- and ,- or ,γ- and ,-dialkylated products (5–7) depending on the electrophile. The corresponding monoanion dimerizes with iodine to afford stereoselectively dimethyl cis-4,5-ditosyl-2,6-cyclohexadiene-1,2-dicarboxylate (11). The tosyl group in compounds 6 and 7 is reduced and in the case of γ,γ-dimethylated 5a substituted by sodium dimethyl malonate under Pd(PPh₃)₄ catalysis. Michael addition of different nucleophiles provides the corresponding β-substituted methyl γ-tosylbutanoates 16.