Stereospecific cyclodehydration of 1,4-sulfanylalcohols to thiolanes: mechanistic insights

A series of thiolanes were prepared by cyclodehydration of sulfanylalcohols in the presence of catalytic amounts of p-toluenesulfonic acid or by using K10 clay. The sulfur heterocycles were synthesised in good to excellent yields using either a conventional Dean-Stark method or microwave irradiation under solvent-free conditions. The reaction could be performed regio- and stereoselectively and its mechanism was investigated by means of enantio- and diastereomerically enriched substrates. In contrast to previous studies, our results are consistent with an intramolecular S_N2-type mechanism as a general pathway.     

Rearrangement thermique des adduits du tetracyanoethylene de 2H-pyrannes

The addition of tetracyanotehylene to 2H-pyrans 1 results in a mixture of two isomeric adducts 6. The thermal decomposition of the compounds 6 gives rise to both a small percentage of the retro Diels-Alder, and a new mode of evolution leading to a mixture of furans (E+Z) 7. A detailed interpretation of the ¹³C spectra of the compounds 7 was established by comparison with the ¹³C spectra of 2,5-diphenylfuran and trans-stilbene. The structure 7 is confirmed by chemical degradation.     

HPLC determination of morphine with amperometric detection at low potentials under basic pH conditions

Summary A simple, sensitive, accurate and reliable method for morphine determination in biological samples has been developed. It uses reverse-phase HPLC on a polymeric column with an eluent (0.05 mol/L dibasic sodium phosphate: acetonitrile, 8515) at pH 9.5, allowing both the suppression of ionization of morphine amine and the promotion of oxidation of the phenolic group. Amperometric detection at mild oxidizing potential (350 mV) proves very selective, and, therefore, only a simple and rapid one-step liquid-liquid sample preparation is required. Under these conditions clean chromatograms are obtained even with complex biological matrices such as cadaveric blood, urine and hair.Minimum detectable amount of morphine is about 200 pg injected. A calibration line with a correlation coefficient of 0.99996 has been produced over the range 7.5–250 ng/mL. Precision results comparable to other HPLC methods.A preliminary report was presented at the 25th T.I.A.F.T. Meeting 1988, Groningen (NL), June 27–30 1988.     

A facile synthesis of α-chloroboronic esters via the base induced reaction of α,α-dichloromethyl methyl ether with hindered borinic esters

Treatment of hindered borinic esters, R₂ BOR′; with an equimolar quantity of α,α-dichloromethyl methyl ether and lithium triethylcarboxide yields the α-chloroboronic esters, R₂ CHClB(OCH₃)OR′, in excellent yields. In cases where the steric requirements of R are not sufficient, the steric requirements of R′ can be increased to achieve the synthesis.     

Carbon-13 spin–lattice relaxation in some polyfluoroaromatic compounds

Carbon-13 chemical shifts, spin-lattice relaxation times and nuclear Overhauser enhancement factors are reported for five polyfluoroaromatic compounds at 28°C. In all cases the relaxation of the fluorine bearing carbon is predominantly dipolar. Effective correlation times are smaller than those of the analogous benzene derivatives by a factor of 3–4, in qualitative agreement with predictions from the Stokes–Einstein diffusion theory. The T₁ values for the para-carbon of monosubstituted fluorobenzenes is clearly shorter than the T₁ values for the ortho- and meta-carbons. This phenomenon was traced to anisotropic tumbling, and D∥ and D⊥ diffusion coefficients were computed using Woessner's equations for molecules assumed to behave like symmetric rotors about their C₂ in-plane principal symmetry axis. Equal tumbling ratios, D∥/D⊥, were found in this way for toluene and perfluorotoluene.     

Determination of ethyl formate in magnesium chloride used as Ziegler-Natta catalyst support by Fourier transform infrared attenuated total reflectance spectrometry

FT-IR Spectroscopy with total attenuated reflectance (ATR) was used for the quantitative determination of ethyl formate coordinated in inorganic matrices such as magnesium chloride. The spectra were recorded directly on solutions obtained by dissolving the inorganic Ziegler-Natta supports in water. The method proposed is sensitive and rapid and appears to be very reliable when compared with other methods, such as solvent extraction followed by gaschromatographic or thermogravimetric analysis.