Donatella Bartoli

The reaction of diphenyl diselenide with peroxydisulphate ions in methanol a convenient procedure to effect the methoxyselenenylation of alkenes

Abstract Methoxyselenenylation of several alkenes was effected, in one step, by oxidation of diphenyl diselenide with ammonium peroxydisulphate in methanol.

The reactions of some halogenated pyridines with methoxide and methanethiolate ions in dimethylformamide

Abstract The reactions of 2,6- and 2,5-dibromopyridines and of 2,3- and 3,5-dichloropyridines with sodium isopropanethiolate and methanethiolate afforded the products of mono- or of bis-substitution depending on the experimental conditions. The same pyridines reacted with sodium methoxide to give good yields of the mono-substituted products; bis-substitution occurred easily only in the case of the 2,6-dibromo- and of the 3,5-dichloropyridine. The syntheses of some methoxy thiomethoxypyridine, starting from the halogeno methoxypyridines or from the halogeno thiomethoxypyhdines are also described. The bis-(alkylthio)pyridines can be fragmented by sodium in HMPA to give the bis(mercapto)pyridines.

Methoxychlorination and dimethoxylation of alkenes the reactions of substituted styrenes with phenylselenenyl chloride in methanol

Abstract The addition of PhSeCl to α- and β-substituted styrenes in methanol is regio- and stereospecific and affords the products of methoxyselenenylation. These compounds further react with PhSeCl to give the deselenenylation products. In the case of α-substituted styrenes, 1-methoxy, 2-chloroalkanes are produced, whereas with β-substituted styrenes the major reaction products are the 1,2-dimethoxyalkanes and the 2,2-dimethoxyalkanes in which phenyl migration has occurred. It is shown that these reactions proceed through the intermediate formation of the alkyi phenylselenium dichlorides, PhCR(OMe)CHR1SeCl2Ph, which evolve with different mechanisms depending on the structure of the starting alkenes.

Phenylseleno-lactonization of olefinic nitriles promoted byperoxydisulphate ion oxidation of diphenyl diselenide

Abstract The oxidation of diphenyl diselenide with ammonium peroxydisulphate is a very simple and efficient method to produce phenylselenium cations in the absence of nucleophilic counter ions. The reaction carried out in the presence of an olefin, in acetonitrile or propionitrile containing trifluoromethanesulphonic acid and water afforded the amidoselenenylation products in good yield. The intramolecular version of this reaction, using appropriate unsaturated nitriles as the starting products and dioxane as solvent, took a different course and afforded phenylselenolactones in good yield. This new selenium induced ring closure reaction proceeded through the initial formation of the hydroxyselenenylation products in which the hydrolysis of the cyano group is suggested to be intramolecularly assisted by the hydroxy group.

Competition between vinylic substitution and conjugate addition in the reactions of vinyl selenoxides and vinyl selenones with nucleophiles in DMF

Abstract Vinyl selenoxides and vinyl selenones present a different reactivity towards thiolate or alkoxide anions in DMF. In the case of selenoxides the addition of the nucleophiles regioselectively occurs at the α-carbon leading to the formation of the vinylic substitution products with complete retention of configuration. These reactions occur under very mild conditions indicating that the seleninyl group markedly enhances nucleophilic vinylic substitution rates. The results obtained with vinyl selenones are consistent with competitive nucleophilic attack at the α- and at the β-carbon. The former yields irreversibly the vinylic substitution products, whereas attack at the β-carbon leads to the reversible formation of selenonyl stabilized carbanions. The fate of these intermediates depends upon the nucleophilic reagent employed. With thiolate anions the vinyl selenones are rapidly subtracted from the equilibrium and the carbanion does not give any other product. With methoxide anions, on the contrary, the vinylic substitution is a slow process and the carbanion can give rise to conjugate addition products also. Malonate anions react only at the β-carbon of vinyl selenones and the resulting carbanions suffer proton transfer and intramolecular displacement of the selenonyl group to afford cyclopropane derivatives.

Iodine (III) mediated acetoxy-lactonization of unsaturated nitriles

Abstract 4-Pentenenitriles reacted with PhI(OAc)2 in acetic acid in the presence of 48% HBF4 at 70 ° C to afford the dihydro-5-acetoxymethyl-2(3H)-furanones in good yields. Similarly 3-butenenitriles gave the dihydro-4- acetoxy-2(3H)-furanones although in lower yields. Parallel experiments showed that under the same conditions 4-pentenoic and 3-pentenoic acids reacted much more easily and gave the same acetoxy- lactonization process at room temperature.

Selenium catalyzed conversion of vinyl halides into α-alkoxy acetals

Abstract The reaction of vinyl halides with phenylselenenyl chloride in alcohols affords α-alkoxy acetals and diphenyl diselenide which can be oxidized to PhSe cations by nitrate or persulfate anions. The reaction can be carried out with catalytic amounts of PhSeCl or PhSeSePh. The reaction proceeds through the formation of the methoxyselenenylation product which then suffers solvolysis. Under controlled conditions, the 1-phenyl-1-methoxy-2-bromo-2-phenylselenenyl ethane was isolated from the reaction of β-bromostyrene and PhSeCl in methanol. Several deselenenylation reactions of this α-halogenoselenide are reported.

Formation and reactivity of the addition products of alkoxides and thiolate anions to vinyl selenones

Abstract Vinyl selenones react with sodium methanethiolate in methanol to give the product of conjugate addition and subsequent displacement of the selenonyl group. On the contrary, the same reaction carried out with alkoxide anions affords the conjugate addition products in excellent yields. These β-alkoxy alkyl phenyl selenones are stable compounds which can react in several ways with loss of the selenonyl group. Their reactions with MeONa or MeSNa have been investigated both in MeOH and in DMF. The products observed derive from substitution and elimination processes as well as from retro Michael reactions followed by nucleophilic substitution of the vinyl selenone thus generated. These results indicate that the ArSeO 2 is a strong electron attracting group with peculiar properties. Beside making acidic the α-hydrogen atoms it activates the carbon-carbon double bond towards the addition of anionic reagents and it acts as a good leaving group in nucleophilic substitution, both aliphatic and vinylic, and in elimination reactions. The appropriate choice of the reagent and of the solvent allows to direct the reaction towards the desired products. Useful synthetic applications of these reactions are presented.

Asymmetric oxidation of prochiral selenides to optically active selenoxides

Abstract Oxidation of 1,1-diphenyl-1-methoxy-2-phenylselenylethane and of 1,1-diphenyl-1-methoxy-2-(o-methoxy)phenylselenylethane with the Sharpless reagent afforded the corresponding selenoxides with moderate optical yields.

Synthesis of bis(alkylthio)bipyridils by nickel mediated homo coupling of halogenopyridyl alkyl sulphides

Abstract The homo coupling of some halogenopyridyl t-butyl sulphides with Ni(O) complex, formed in situ from nickel(II) chloride, triphenylphosphine and zinc dust in DMF, afforded bis(t-butylthio)bipyridyls in moderate to good yield. These compounds were dealkylated by electron transfer with sodium in HMPA; the resulting thiolate anions were directly treated with methyl iodide and the bis(methylthio)bipyridyls were obtained. The dealkylation with a solution of sodium in HMPA afforded the mono anions which, after treatment with methyl iodide, gave the t-butylthio(methylthio)bipridyls.