Mariella Fiorenza

Fluoride ion induced reactions of organosilanes with electrophiles

Abstract Benzyl- 4-picolyl- and phenylallyl(trimethyl)silanes react with electrophiles in the presence of KF/18-crown-6 or silica-TBAF under mild conditions.

Fluoride ion induced reactions of organocilanes with saturated lactones and αβ-enones

Abstract Benzyl-, heteroaryl-, and allylsilanes, under the catalytic action of CsF or silica/TBAF, react in mild conditions with electrophiles such as σ-valero and e-caprolactone, and with cyclohexen-2-one.

Bis (trimethylsilyl) thioketone

Abstract Tris (trimethylsilyl) methylsulphenylbromide undergoes facile Me 3 SiBr elimination to give bis (trimethylsilyl) thioketone.

Fluoride ion induced reactions of organosilanes: the preparation of mono and dicarbonyl compounds from β-ketosilanes

Abstract β-ketosilanes react with a variety of carbon electrophiles in the presence of CsF to give mono- and dicarbonyl derivatives in reasonably good yields.

Ring opening reactions of thiiranes with group IV B organometallics: a new regioselective route to β-amino and β-cyanide thiols.

Abstract Regioselective opening of the thiirane ring occurs spontaneously with Group IV B organometallics such as Me 3 SnNR 2 and under the catalytic action of AlCl 3 with Me 3 SiCN, affording difunctional thiols.

Base-catalysed solvolysis of acylsilanes

Abstract Kinetic studies have been made of the hydrolysis of XC 6 H 4 COSiR 3 compounds (R = Me, Et, Ph) in a mixture of THF (3 vol.) and aqueous sodium hydroxide (1 vol.). The rates of cleavage of p -NO 2 C 6 H 4 CH 2 SiMe 3 , C 6 H 5 COSiMe 2 C 6 H 5 and C 6 H 5 COSiMe 2 C 6 H 4 Cl- p compounds under the same conditions have also been measured. Electron-attracting substituents on either side of the bond being broken lead to an increase in the rate. For the XC 6 H 4 COSiR 3 compounds, the effects of the substituents X correlate excellently with their Hammett σ constants (ϱ = 3.5 and 2.5 for R = Me and Ph, respectively). The data are consistent with a mechanism in which the attack of the hydroxide ion occurs at the carbonyl C atom.

Primary aminomethylation of organometallic compounds via N,N-bis(trimethylsilyl)methylthiomethylamine

Abstract The reaction of various organometallic compounds with N,N -bis(trimethylsilyl) methylthiomethylamine provides an easy way for the introduction of a primary aminomethyl unit into a variety of organic substrates.

Methanolysis of the benzylideneaniline derivatives ArC(MMe3)NAr' (M = Si or Sn)

Rates of cleavage of compounds (I) and (II) of the type p-XC6H4C(MMe3)NC6H4Y-p, X = H, Y = OMe, Me, or Cl, or Y = H, X = H, OMe, Me, or Cl, in MeOH (to give the benzylideneanilines XC6H4CHNC6H4Y) have been measured spectrophotometrically at 25 °C. The cleavages occur readily in methanol alone, but are catalysed by NaOMe and, at least for the tin compounds, by MeCO2H. In the neutral cleavage the tin compound (IIa) is ca. 49 times as reactive as the corresponding silicon compound (Ia). The rate isotope effect (r.i.e.), the ratio of the rate constant in MeOH to that in MeOD, is ca. 1.3 for (II), and the product isotope effect (p.i.e.), given by the product ratio RH : RD on cleavage in 1 : 1 MeOH–MeOD is 1.1, while for the silicon compounds the r.i.e. is ca. 1.8. Electron release by X or Y increases the ease of reaction. The results are interpreted in terms of a cyclic mechanism in which transfer of a proton from an MeOH molecule to the nitrogen of the CN bond is synchronous with formation of the M–OMe bond, and probably also with the breaking of the C–M bond, the proton transfer to the imine being considerably advanced in the transition state. In the base cleavage the tin compound (IIa) gives normal values for the r.i.e., p.i.e., and r.i.e. : p.i.e. ratio (ca. 0.96, 1.65, and 0.58, respectively), consistent with an electrophilically-assisted mechanism in which a proton is transferred from the solvent to the carbon atom of the imino-group as the C–Sn bond breaks. For the silicon compounds, the r.i.e. values, of ca. 1, are wholly abnormal, as is the fact that the silicon compound (Ia) is more reactive, by a factor of 2, than its tin analogue (IIa), and it is suggested that there is electrophilic assistance even for the silicon compounds, but involving proton transfer to nitrogen. For both tin and silicon compounds electron withdrawal in Y facilitates the base cleavage. Cleavage of (II) is catalysed 70 times as effectively by MeCO2H as by MeONa, and in the media used oxonium ion does not compete with MeCO2H as the catalyst.

The Effect of Long Irradiation on the Fluorescence Emission of Anthracene Crystals at Room Temperature

Abstract Microphotographs showing the effect of increasing irradiation time of anthracene single crystals are reported and the surface effect correlated to the fluorescence emission changing.

Transmission of substituent effects through furan and thiophen rings. Rates of reaction of substituted 2-benzoyl-furans and -thiophens with sodium borohydride

Rates of reduction by sodium borohydride in propan-2-ol have been measured for the 2-furyl and 2-thienyl ketones 2-(XC6H4CO)C4H2YE (E = O or S) for a range of X groups with Y = H, and of Y groups with X = H. The results permit direct comparisons to be made of transmission of substituent effects through the various aromatic rings to the same reaction centre, and it is concluded that the substituent effects are transmitted to virtually identical extents through the two heterocyclic rings, but markedly less effectively through the benzene ring. Charge distributions have been calculated by an ab initio method for furan, thiophen, and benzene and for the carbanions, 2-furylCH2–, 2-thienylCH2–, and PhCH2–. The change in the π-electron density at the 5-position on introduction of the 2-CH2– groups is smaller for furan than for thiophen, and the change in the latter case is slightly smaller than that induced at the 4-position on introduction of the 1-CH2– group for benzene, suggesting that transmission of conjugative effects between p-positions in the benzene ring is greater than that between the 5- and 2-positions in the heterocyclic compounds. The corresponding changes in total electron density, however, are effectively the same for all three rings. The electron density on the CH2– group is virtually identical in all three carbanions, suggesting that, contrary to the usual assumption, the π-systems of furan and thiophen rings do not interact more readily than those of benzene with a substituent capable of conjugation. Some of the data have been used to derive σ5,2 and σ4,2 constants for thiophen and furan systems.