Pyridine, as solvent

Recently Hofmann has found that when the azide hydrochlorides of the lysergic and fsolysergic acids, or of their dihydro-derivatives, are boiled in dilute hydrochloric acid, a Curtius reaction occiys and the carboxyl is replaced by an amino-group. In this way he has prepared the following amines. They melt with decornposition and the specific rotations are for pyridine as solvent — ... 

Recently Tanabe and co-workers have found that several alcohols were smoothly and efficiently tosylated using tosyl chloride/triethylamine and a catalytic amount of trimethylamine hydrochloride as reagents.6 Compared with the traditional method using pyridine as solvent, this procedure has the merit of much higher reaction rates, and it avoids the side reaction in which the desired tosylate is converted into the corresponding chloride. 

Using method a, oligodeoxyribonucleotides were synthesized from di- to deca-deoxyribonucleotides by means of mesitylenesulfonylimidazole and mesitylenesulfonyl-1,2,4-triazole. With triisoproylbenzenesulfonylimidazole die condensation took place more slowly.11121 Compared widi the corresponding arylsulfonyl chlorides, imidazolides induced intemucleotide condensation much more slowly, but caused no darkening of the reaction mixture, did not affect acid-sensitive bonds in trityl protected nucleotides, and did not sulfonate the 3 -hydroxy groups.11111 The reaction conditions were room temperature, 5—6 days, and pyridine as solvent.11111... 

The presence of substituents and the use of pyridine as solvent changes the ratio of ligands. In the case of donor or weak acceptor substituents the formation of complexes with Cu(I) takes place, stable crystalline compounds being obtained only in the presence of pyridine. In all the cases copper forms complexes with one phosphorus ligand but the number of pyridine molecules varies from 1 to 3 [Eq. (155)]. 

Activated esters of A-alkoxycarbonylamino acids are prepared by two approaches, activation of the acid followed by reaction with the hydroxy compound, and trans-esterification. Most of the products are stable enough to be purified by washing a solution of the ester in an organic solvent with aqueous solutions. A few that are not crystalline are purified by passage through a column of silica. The commonly used method for their preparation is addition of dicyclohexylcarbodiimide to a cold mixture of the reactants in dimethylformamide or ethyl acetate. The first Boc-amino acid nitrophenyl esters were obtained using pyridine as solvent. Pyridine generates the nitrophenoxide ion that is more reactive. For one type of ester, 2-hydroxypyridino... 

Optically active iV-tosyl-N-methyl-p-toluenesulfinamide 80 was prepared (119) in low chemical yield by the reaction of optically active methyl p-tolyl sulfoximide 81 with 2 equiv of tosyl chloride in pyridine as solvent. The process of demethylation takes place with retention of configuration at sulfur. 

Mesoionic 4-amino-l,2,3,5-thiatriazoles constitute the only class of mesoionic 1,2,3,5-thiatriazoles known. They are prepared by the reaction of l-amino-l-methyl-3-phenylguanidine with approximately 2 equivalents of thionyl chloride with pyridine as solvent (88ACS(B)63>. They are obtained as the yellow 1 1 pyridine complexes (17). The dark-violet mesoionic 1,2,3,5-thiatriazole (18) was liberated on treatment with aqueous potassium carbonate (Scheme 3). The structure is established on the basis of elemental analysis and spectroscopic data. In particular, the IR spectrum is devoid of NH absorptions. Compound (18) exhibits a long-wavelength absorption at 463 nm in methanol. When mixed with an equivalent amount of pyridinium chloride, complex (17) is formed and the absorption shifts to 350 mn. The mesoionic thiatriazoles are sensitive towards mineral acids and aqueous base and although reaction takes place with 1,3-dipolarophiles such as dimethyl acetylene-dicarboxylate, a mixture of products were obtained which were not identified. 

An initial survey smdied the cycloaddition between 341 (R = Me) and mal-eimide in the presence of copper(II) acetate and 1 M equiv of EtsN with pyridine as solvent, leading to the formation of the expected adduct 342 at room temperature after a few hours. The reaction delivered a single product arising from an endo transition state in 60% yield. The reaction protocol was further extended to include... 

Electroreduction of the cobalt(II) salt in a mixture of either dimethylform-amide-pyridine or acetonitrile-pyridine as solvent, often in the presence of bipyridine, produces a catalytically active cobalt(I) complex which is believed to be cobalt(I) bromide with attached bipyridine ligands (or pyridine moieties in the absence of bipyridine). As quickly as it is electrogenerated, the active catalyst reduces an aryl halide, after which the resulting aryl radical can undergo coupling with an acrylate ester [141], a different aryl halide (to form a biaryl compound) [142], an activated olefin [143], an allylic carbonate [144], an allylic acetate [144, 145], or a... 

In the 1,3-diethyl derivative of the benzimidazolephosphamethin-cyanine series 8d, one finds the four ethyl groups to be equivalent (pyridine as solvent). 

The reagents used to effect the dehydration of (V.iV -dicyclohexylurea to Af,7V -dicyclohexylcarbodiimide in 82% yield is p-toluenesulfonyl chloride in pyridine as solvent and base [17] (Eq. 12). Methylene chloride may also be... 

Oxyaminatkm.1 The ratio of amino alcohol to diol formed by reaction of alkenes with the reagent is considerably improved by the presence of tertiary alkyl bridgehead amines. Of these ligands, quinuclidine (I, 976 4, 417) is the most efficient. In this case DME is used in place of pyridine as solvent. 

While solvent effects are small for the ring redox ( 0.2 V), the effect of donor solvents which stabilize the higher oxidation state is marked for the metal redox, especially so for those of low-spin d6/d7 and d1jd%. There is a linear relationship between E° for the Feu/I couple and the Gutmann donicity number. The Com u and Cou/I couples shift positively as the pof substituted pyridine, as solvent, decreases and the ring oxidation precedes the CoIII/n couple in noncoordinating solvents such as CH2C12. 

The use of pyridine as solvent dramatically alters the spectral properties of the iron complex of octamethylcorrole. Such a spectrum is reported in Fig. 20 and pertinent data in Table 12. The three resonances (A-C) observed at low field have been attributed to the methyl substituents, the fourth resonance probably being located in the diamagnetic region obscured by the solvent resonances. 

The ester 14, used both as an insect repellent and as a solvent for perfumery, is easily made this way. The analysis reveals two available compounds benzyl alcohol 15 and benzoyl chloride 16. Combining the two with pyridine as solvent and catalyst gives the ester 14. 

Regioselective reactions in systems which contain multiple functional groups are an area ideally suited for biocatalysis. Linhardt and co-workers at the University of Iowa s Division of Medicinal and Natural Products Chemistry recently published the synthesis of a series of 1 -O-acyl sucrose derivatives [31], Using Chiro-CLEC -BL (the CLC of subtilisin) and vinyl esters of the acylating agent in pyridine as solvent, the authors prepared l -O-lauryl sucrose, l -O-myristyl sucrose, and l -O-stearyl sucrose in 80-90% yield (Fig. 9). Their method represents a green alternative to the tin chemistry previously used [32],... 

In pyridine as solvent, the unstable adduct 77, generated from decamethylsilicocene and carbon dioxide, easily formed a dimerization product after ring opening of one of the Si-O bonds (Equation 4). Insertion of decamethylsilicocene into the ring of the more stable dithiasiletane derivative 43 afforded a five-membered heterocycle (Equation 5) <19960M753>. 

The substitution path b) (Eq. (94) ), is favored by the following experimental conditions low current density, grapliite as anode material, alkaline medium, water or water-pyridine as solvent, and admixture of foreign ions e.g., bicarbonate, sulfate, perchlorate, dihydrogen phosphate, Pb2+, Mn2+, Cu2+, Fe2+, Co2+. The carbonium ion path b) can furthermore be expected for carboxylates RR CHOO with a-substituents R such as alkyl, phenyl 198 hydroxy, halogen 1 amino, or alkoxy. These substituents facilitate oxidation of the intermediate alkyl radical R to the carbonium ion R+. Product formation occurs via carbonium ions and not, as is also conceivable, via mixed coupling of R with Nu ... 

With the finding that silver phenylacetylide was soluble in pyridine, Agawa and coworkers attempted to react the acetylide with benzoyl chloride in pyridine as solvent. While the expected ynone was isolated in poor yield, the predominant product of reaction was from initial acylation of the pyridine nitrogen to produce the electrophilic pyridinium salt, followed by addition of the silver acetylide to the 2... 

The El reaction is not ideal for the dehydration of primary or secondary alcohols since vigorous heating is needed to force the reaction and this can result in rearrangement reactions. In alternative methods which are useful, reagents like phosphorus oxychloride (POCl3) dehydrate secondary and tertiary alcohols under mild basic conditions using pyridine as solvent (Following fig.). The phosphorus oxychloride serves to activate the alcohol,... 

In the S l Ar and the S l Ar mechanisms, the aryl halide becomes reactive towards nucleophiles by loss of an electron or a halide anion. Another means of activation is protonation, followed by excitation. This mechanistic pathway has been proposed for the photohydroxydehalogenation of 1-chloroanthraquinones in 97% sulphuric acid734, which leads to high yields (60-70%) of 1-hydroxyanthraquinones. The yields of the photochemical replacement of chlorine by pyridine in 1- and 2-chloroanthraquinone are much lower (3-6%)735. The reactions were performed with pyridine as solvent and the products were converted into aminoanthraquinones by treatment with alkali. Pyridine as nucleophilic... 

Pyridine is consumed during both of these reactions, since it ends up protonated. One whole equivalent of pyridine is therefore necessary and, in fact, the reactions are often carried out with pyridine as solvent... 

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