Marco Tingoli

Alkynyl phenyl selenides as convenient precursors for the synthesis of stereodefined trisubstituted alkenes

Abstract The addition of p-toluensulfonic acid to alkynyl phenyl selenides is regio- and stereospecific and affords (Z)-α-(phenylseleno)vinyl p-toluensulfonates in good yield. α-(Phenylseleno)vinyl halides are obtained from the reactions of these compounds with magnesium halides. The reactions of (Z)-α-(phenylseleno)vinyl p-toluensulfonates with cyanocuprates afford the corresponding trisubstituted alkenes in which the tosyl group has been selectively substituted by an aryl or an alkyl group with retention of configuration. Finally, the cross coupling reaction of these vinyl selenides with methylmagnesium bromide, in the presence of a nickel catalyst, occurs with retention of configuration and affords the selenium free trisubstituted alkenes.

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.

A convenient synthesis of aromatic thiols from unactivated aryl halides

Abstract Aromatic thiols are obtained in good yields from unactivated aryl halides and excess MeSNa in HMPA.

New synthesis of vinyl selenides nucleophilic substitutions of unactivated vinyl halides by selenide anions

Abstract Alkyl and aryl selenide anions react with unactivated vinyl halides, in dipolar aprotic solvents, to give alkyl or aryl vinyl selenides in good yields. These reactions are stereospecific and occur with retention of configuration.

IODOSOBENZENE DIACETATE AND DIPHENYL DISELENIDE : AN ELECTROPHILIC SELENENYLATING AGENT OF DOUBLE BONDS

Abstract Phenylseleno-acetoxylation, hydroxylation, etherification and lactonization products are obtained in good yields from the reaction of alkenes with diphenyl diselenide and iodosobenzene diacetate, in acetonitrile. present address: Dipartimento di Scienza degli Alimenti, Universita di Napoli “Federico II” Via Universita, 100 - 80055-Portici, Napoli-Italy. e-mail tingoli@unina.it.

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.

Selective mono-arylation and -alkylation of chlorophenyl alkyl sulfides by nickel catalysed cross-coupling with grignard reagents

Abstract Chlorophenyl alkyl sulfides are mono-arylated and -alkylated selectively with Grignard reagents, in the presence of Ni(PPh 3 ) 2 Cl 2 , to give aryl- and alkyl-phenyl alkyl sulfides.

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.