Gioanna Gelli

Study of dimethyl-substituted benzene derivatives by 13C nuclear magnetic resonance spectroscopy and INDO MO calculations

A 13C n.m.r. investigation of some substituted dimethyl benzenes is reported. The spectral analysis were carried out by the iterative Laocoon III and a spin-simulation program furnished carbon–proton coupling constants that have been rationalized with the aid of the FPT–INDO MO calculations. The angular dependences of the calculated 3JC,CHO and 1JCHO coupling constants have been analysed and the preferred conformations are discussed.

Metalation reactions. XIV. Regiospecific preparation of polysubstituted benzenes via mono- or di-lithiation reactions of aromatic thioethers☆

Abstract The preparation of polyfunctionalized aromatic thioethers either by one-step dilithiation or by two successive one-flask monometalation reactions is described. By acting on 1 two equal or different electrophiles one on the thiomethyl group and one in the ortho -position with respect to it are introduced; by acting on 11 and on 35 the substitution involves the thiomethyl carbon atom and that in the ortho -position with respect to the alkoxy group. In the case of the homologous isopropylthio (23) the substitution involves the two aryl carbon atoms in the ortho -position to both functions. In the case of the p -disubstituted isomers (49, 59) analogous behaviour to ortho isomers in one-step metalation reaction is observed, while the two hydrogen atoms in the ortho -positions to the methoxy group are substituted when two successive monometalations are employed. The metalation of 40 results low selective. The behaviour of 79 and 93 is analogous to 1, while 72, 88 and 96 undergo only one-step monometalation reactions.

Metalation reactions: XIII. The reactions of electrophiles with the dilithiated species 1-(α-lithiomethyl)-2-[(α-lithiomethyl)thio]benzene☆

Abstract Direct dimetalation of 1-methyl-2-(methylthio)benzene ( 1 ) gives the dilithiated species ( 2 ) in good yield, which can be used to introduce substituents into the thiomethyl and methyl groups. Species 2 can react also with a variety of dichlorosilanes and dichlorostannanes, and with sulphur chloride, to yield derivatives of 1,3-benzothiasilin, 1,3-benzothiastannin and 1,3-benzodithiin respectively. Reaction of 2 with tetrachlorosilane yields a spirocyclic silicon compound, while reaction with benzoyl chloride yields a derivative of 1-benzothiopyran.

Metallation Reactions. XX. Regioselective Metallation of (Alkylthio)methoxybenzenes by Superbases versus Organolithium Compounds

Abstract (Alkylthio)methoxybenzenes have been metallated using two different metallating agents. The results show that sometimes superbases and butyllithium do not functionalize the same sites. Superbases monometallate the thiomethylic carbon of meta and para (methylthio)methoxybenzenes. The same substrates on the other hand are metallated by butyllithium in ortho to the methoxy group. One-step dimetallation performed with either superbases or butyllithium occurs at the thiomethylic carbon and at the aryl carbon ortho to the methoxy group. Two consecutive one-pot monometallations of the para isomer ( 1c ) with superbases occur at the thiomethylic carbon and at the annular carbon ortho to the methoxy group, in this order. A similar procedure with butyllithium metallates the two ortho positions to the methoxy group. Monometallation of (ethylthio) derivative ( 1d ) yields products substituted in ortho to the methoxy group using either superbases or butyllithium. Dimetallation of this compound always substitutes the hydrogen ortho to the methoxy group and a thiomethylenic hydrogen.

Metallation reactions: XVIII. Regioselective metallation of (alkylthio)benzenes by superbases

Abstract (Alkylthio)benzenes were monometallated at the alpha position by a stoichiometric mixture of butyllithium and potassium t-butoxide and bimetallated at both the alpha and the ortho positions by two equivalents of the same reagent.

Addition of 1,3-Benzoxathiole 3-Oxide Anion to Azomethines under Varying Reaction Conditions

The reaction of benzoxathiole 3-oxide with LDA in THF gave an anion which was reacted with azomethines under varying conditions of temperature and solvent. At −78 °C in THF, the two diastereomers resulting from a trans addition were mainly obtained, while at temperatures higher than −40 °C, or upon increasing the solvent polarity, only one trans and one cis diastereomer were obtained. (© Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002)

Metalation reactions. XVI. Polylithiation of 1,3,5- and 1,2,4-trimethoxybenzene

Abstract Polylithiation reactions of 1,3,5- and 1,2,4-trimethoxybenzenes have been investigated. Results showed that it is possible to substitute all arylic hydrogens through one-pot sequential bimetalation/monometalation, monometalation/bimetalation or three monometalations. This reaction is strongly affected by steric hindrance.

Metalation reactions. XII: One-pot synthesis of 1,3-benzothiasiloles, 1,3-benzothiastannoles and 1,3-benzodithioles

Preparation des composes du titre a partir du lithiomethyl lithio-2 phenyl sulfure (synthetise au prealable a partir du methyl phenyl sulfure)

Anion reaction of 1,3-benzoxathiole-3-oxide with several electrophilic compounds

Abstract The reaction of benzoxathiole-3-oxide with LDA in THF or THF/hexane or THF/HMPA gave a carbanion which was reacted with methyl iodide, aromatic aldehydes or carbon dioxide. The conformational stability (α-diastereoselectivity) of the carbanion and the asymmetric induction due to the prochiral electrophiles (β-diastereoselectivity) was studied. The temperature and the solvent effects on the α- and β-diastereoselectivity are discussed.

A kinetic study of the 1,3-cycloaddition of benzonitrile oxides to para-substituted β-aminocinnamonitriles

Stable arylnitrile oxides undergo 1,3-cycloaddition to β-aminocinnamonitriles at the CN or the CC bond, which gives rise to 3,5-disubstituted 1,2,4-oxadiazoles or 3,5-diaryl-4-cyanoisoxazoles, respectively, by parallel reactions in different solvents. Overall kinetics were measured at temperatures in the range 50–90 °C; product selectivities were determined by HPLC rate coefficients for the parallel reactions were, thus, obtained. Rates were enhanced by increasing the solvent polarity. Hammett plots for substitution on the nitrile oxide benzene ring were V-shaped; those for substitution on the enaminonitrile benzene ring had negative ρ-values.