Giacomo Garbarino

A mild and efficient SRN1 approach to diaryl sulfides from arenediazonium tetrafluoroborates

Abstract The reaction between arenediazonium tetrafluoroborates and sodium arenethlolates in Me2SO at 25°C represents an efficient access to diaryl sulfides. A number of evidences suggest the occurrence of a radical, radical-anion SRNl mechanism, the arenethlolate acting both as electron donor and as aryl-radical trapping nucleophile. Valuable improvements with respect to recent SRNl syntheses of diaryl sulfides from haloarenes are represented. Inter alia , by the compatibility of both electron-withdrawing and releasing substituents as well as by the insensitivity to steric hindrance In the diazonlum salt. When the arenedlazonlum ion bears another SRNl leaving group (such as Cl, Br, or I) disubstitution products are predomnantly formed.

A convenient srn1 synthesis of aromatic nitriles from diazonium salts via diazosulfides

Properly substituted diazosulfides XC6H4-N=N-SPh (1) (either isolated or generated in situ from arenediazonium tetrafluoroborates and sodium benzenethiolate) react with tetrabutylammonium cyanide, in Me2SO under photon or electron stimulation, leading to nitriles XC6H4CN (2). Satisfactory yields of 2, comparable with those of the Sandmeyer reaction, are obtained when X = 3- or 4-CF3 , 2-, 3-, or 4-CN, 4-F, 4-MeO, 3-MeCO, 4-NO2, 4-PhCO, and 4-PhSO2. For different reasons, the reaction practically fails as a useful nitrile synthesis when X = H, 4-MeO, 2-, or 3-NO2. The collected evidences agree well with the intervention of an SRN1 mechanism, to which diazosulfides 1, given their easy reduciblity followed by a prompt fragmentation of the C-N and N-S bonds, are convenient participating substrates. An important consequence of the mechanism involved is the behaviour of bromo and chloro derivatives (1: X = Br, Cl) which lead, through the contemporaneous introduction of two cyano functionalities, to more than satisfactory yields of the corresponding dicyanobenzenes.

The reaction between arenediazonium tetrafluoroborates and alkaline thiocarboxylates in DMSO: A convenient access to aryl thiolesters and other aromatic sulfur derivatives.

Abstract The reaction between potassium thioacetate or sodium thiobenzoate and arenediazonium tetrafluoroborates in DMSO leads to the corresponding aryl thiolesters 1 which can either be isolated or further reacted providing a convenient one-pot access to a number of other aromatic sulfur derivatives.

A simple preparation of symmetrical and unsymmetrical diarylsulfides from arenediazonium tetrafluoroborates

Abstract The reaction between arenediazonium tetrafluoroborates and arenethiolates in Me2SO represents a mild, efficient, and safe alternative to the Ziegler synthesis of diaryl sulfides.

SRN1 syntheses of bis(phenylthio)- and dicyano-naphthalenes via diazosulfides

Abstract The reactions of bromonaphthalenediazonium tetrafluoro-borates (6a,b and 11a,b) with sodium benzenethiolate in DMSO give, through the preliminary formation of the corresponding diazosulfides (7a,b and 12a,b), bis(phenylthio)naphthalenes (8a,b and 13a,b) deriving from substitution of both the diazo group and the bromine. Isolated diazosulfides (7a,b and 12a,b) likewise furnish satisfactory yields of dinitriles (9a,b and 14a,b) by reaction with excess tetrabutylammonium cyanide in DMSO under photostimulation by a sunlamp. The intervention of an SRN1 process accounting for the formation of the disubstitution products is postulated.

The reactivity of sulfur nucleophiles towards arenediazonium tetrafluoroborates in aprotic solvents: Synthesis of S-aryl thioacetates

Abstract Various S-aryl thioacetates are prepared in 40-60% yield by treatment of arenediazonium tetrafluoroborates with commercial potassium thioacetate in DMSO at room temperature.

Kimetic resolution of racemic sulphilimines by enantioselective reduction with arenethiols catalyzed by chiral amines

Abstract S -Methyl- S - p -tolyl- and S -ethyl- S - p -tolyl- N -tosylsulphilimine can be obtained in optically active form by enantioselective reduction of their racemic mixture with arenethiols catalyzed by chiral amines.

Kinetic study of substituent effects on the mechanism of β-elimination of arenethiol from trans-2,3-bis(arylthio)-4-nitro-2,3-dihydrothiophenes in toluene

The 2,3-dihydrothiophene derivatives (1b–f) readily undergo, in toluene, regiospecific tributylamine-promoted syn-elimination of arenethiol to give the 2-(arylthio)-4-nitrothiophenes (2b–f). For the rather complex kinetic behaviour displayed by each member of the series, a rationalisation is proposed based on a stability of the substrates conjugate base sufficient to allow formation of non-negligible concentrations of an intermediate ion pair along the reaction co-ordinate. The system allows direct conclusions to be drawn concerning the leaving-group expulsion step: an advanced extent of bond cleavage between carbon and the leaving group can be postulated in the transition state.

Biphenyl series—I : The synthesis of some 2′-, 3′- and 4′-substituted 3-nitro-4-bromobiphenyls

Abstract The synthesis of a range of 2′-, 3′- and 4′-substituted 3-nitro-4-bromobiphenyls and of their intermediates is described.

Biphenyl series—II: The kinetics of piperidino-debromination reactions of 3′-, 4′-substituted 3-nitro-4-bromobiphenyls

Abstract In order to obtain information on the electronic transmission of polar substituent effects in biarylic systems, a kinetic study of the piperidino-debromination reactions of some 3′-. 4′-substituted 3-nitro-4-bromobiphenyls (substituents = H, Hal, CH 3 CO, SO 2 CH 3 , NO 2 ) in methanol has been carried out. A good fit to the Hammett equation was found with ϱ = + 1·00. The experimental data obtained show that the polar effects of 3′-substituents and 4′-Hal in the reactions studied are similar to the ones exerted by the same substituents in the 5- and 4-positions respectively in the piperidino-debromination reaction of o -nitrobromobenzene. For the strongly electron withdrawing 4′-substituents (COCH 3 , SO 2 CH 3 , NO 2 ) we found it necessary to use values [σ p + 0·32 (σ − - σ p ] for the substituent constants. This result is consistent with a lower contribution of extraconjugative effects to the total polar effect for the 4′-substituents with respect to that reported for the para -substituents in nucleophilic substitution reactions on benzenic derivatives.