Rogério A. Freitag

Ultrasound promoted synthesis of thioesters from 2-mercaptobenzoxa(thia)zoles

An ultrasound-enhanced method has been developed for the synthesis of a variety of thioesters from benzoyl chlorides and 2-mercaptobenzoxa(thia)zoles. Applying this methodology, 14 compounds were synthesized in excellent yields.

Molecular Structure of Heterocycles: NMR Spectroscopy, Semiempirical MO Calculations and X-Ray Diffraction of 3,3a,4,5,6,7-Hexahydro-3-trichloromethyl[2,1]benzoisoxazole

Abstract 1H and 13C NMR data, AMI calculations and X-ray diffraction in 3,3a,4,5,6,7-hexahydro-3-trichloromethyl[2,1]benzo isoxazole (1), obtained from the cyclization of trichloroacetyl cyclohexanone with hydroxylamine, are reported. 1H and 13C NMR data shown that only one pair of the diastereoisomers was obtained and the AMI calculations indicated that 1a (3S3aS/3R3aR) is 2.63 kc:al.mol−1 more stable than 1b (3S3aR/3R3aS). The X-Ray diffraction data confirmed that only the structure 1a was obtained. Crystals of 1 (C8H10Cl3NO2, Mr = 258.52) were obtained from acetone/n-hexane solution. The compound crystallizes in the monoclinic space group P21/c with the cell dimensions a = 10.153(2), b = 8.271(2) and c = 14.225(3) A, β = 103.8(3)°, V = 1160.0(4) A3, Z= 4, Dcalcd. = 1.480 Mg/m3, λ(MoKα) = 0.71073 A, = 0.764 mm-1, F(000) = 528, T= 293(2) K, R = 7.31 % and Rw = 17.91 % for an F 2 refinement on unique data with 2082 reflections and 1994 independent (Rint = 6.70%) were collected.

13C NMR Chemical Shifts of Heterocycles: Empirical Substituent Effects in 5-Halomethylisoxazoles

Abstract Evaluation by empirically derived equations for the Substituent effect (α, β, γ, δ) on the 13C NMR chemical shifts for C-3, C-4. C-5 and halomethyl-substituent carbon (C-6) in isoxazoles 1-5 [where C-3 substituent (R1) = H, alkyl or phenyl, C-4 Substituent (R2) = H, alkyl, and C-5 substituent (R3) = di-or trihalomethyl, methyl and H], taking as reference the compound la, is reported. From the calculated values for the α, β, γ, δ effects for each substituent it was possible to estimate the chemical shift of each carbon of the compounds 1–5. The 13 C chemical shifts of the C-3, C-4, C-5, C-6 of these compounds, can be estimated with good precision: 94% of the calculated chemical shifts are found to be within ±1.0ppm, and 100% are found to be within ±1.5ppm.

MOLECULAR STRUCTURE OF HETEROCYCLES: 17O NMR CHEMICAL SHIFTS: TORSION ANGLE RELATIONSHIPS IN 3-ALKYL SUBSTITUTED 4,5-DIHYDROISOXAZOLES AND ISOXAZOLES†

A quantitative relationship between the 17O substituent chemical shifts (SCS) of γ-alkyl substituents and the torsion angles calculated by the AM1 method is reported. A series of 3-alkyl substituted 5-trichloromethyl-5-hydroxy-4,5-dihydroisoxazoles and 5-trichloromethyl isoxazoles [where 3-alkyl substituents are Me, Et, n-Pr, iso-Bu, BrCH2, iso-Pr, Br2CH and tert-Bu] as model compounds were used. †For Parts 1–6, see References 14-15a, 15b-16, [19a], [19b].