J. Rambaud

Isoxazolidines by cycloadditions of N,α-diphenyl nitrone in the benzo[b]thiophene S-oxide and SS-dioxide series

1,3-Dipolar cycloadditions of N,α-diphenyl nitrone have been investigated in the 2- or 3-substituted (methyl, phenyl, chloro, bromo, piperidino, acetyl) benzo[b]thiophene S-oxide and SS-dioxide series. The S-oxide and SS-dioxide derivatives show the same ability to form adducts. The 2,3-dihydrobenzo[b]-thieno[2,3-d]isoxazolidines are generally formed only as a single regioisomer, except in the case of 2-methyl dipolarophiles where both regioisomers are formed. The regioselectivity is discussed in terms of frontier orbital interactions on the basis of CNDO/S calculations and photoelectronic spectral ionization potentials. The nitrone, which has an elbow shape, could lead to the formation of diastereoisomers but in fact only the trans-isoxazolidines are formed. There is less stereoselectivity in the S-oxide series since we obtained only one adduct with the 3-methyl dipolarophiles but both syn- and anti-epimers with the 3-phenyl derivatives. The bromo derivatives do not lead to any adduct. X-Ray structures are presented for the two adducts corresponding to the addition of the nitrone to benzo[b]thiophene SS-dioxide and to the 2-methyl derivative.

Structure of polymorph II of (1R,3S)-1,2,2-trimethyl-3-(4-methylthiobenzoyl)-cyclopentanecarboxylic acid

C17H22O3S, M(r) = 306.407, orthorhombic, P2(1)2(1)2, a = 13.327 (5), b = 19.277 (8), c = 6.361 (2) angstrom, V = 1634 (1) angstrom3, Z = 4, D(x) = 1.245 Mg m-3, lambda(Cu Kalpha) = 1.54178 angstrom, mu = 1.77 mm-1, F(000) = 656, T = 293 K, R = 0.043 for 2574 observed reflections. Two crystalline forms of the title compound have been obtained but only one (form II) has given suitable crystals for X-ray structure analysis. The five-membered ring has an envelope conformation with C(2) 0.60 (1) angstrom out of the plane defined by the other four atoms. The absolute configuration has been established and appears to be identical to that of camphoric acid used in the synthesis. Molecules form dimers around the twofold axis by means of hydrogen bonds between their carboxylic groups.

Structure of 2,6-dicyclohexylnaphthalene

C22H28, M(r) = 292.4, monoclinic, C2/c, a = 25.691 (4), b = 5.663 (1), c = 13.279 (2) angstrom, beta = 113.83 (1)-degrees, V = 1767.3 (4) angstrom 3, Z = 4, D(x) = 1.06 Mg m-3, lambda(Mo K-alpha) = 0.71069 angstrom, mu = 0.63 mm-1, F(000) = 640, T = 293 K, R = 0.048 for 1137 observed reflections. The 2,6-dicyclohexylnaphthalene contains a crystallographic symmetry centre. The presence of two bulky substituents involves only slight deviation from flatness for the naphthalene ring. The cyclohexyl substituents adopt a chair conformation.

Polymorph(ii) of Methyl 3-(4-ethoxy-alpha-hydroxyiminobenzyl)-1,2,2-trimethylcyclopentanecarboxylate

The title compound, C19H27NO4, is an intermediate product in the synthesis of oxazepinic and piperidinic compounds. Two crystalline forms of the title compound have been obtained but only one [form (II)] gave suitable crystals for X-ray structure analysis. The five-membered ring has an envelope conformation with C(2) 0.60 (5) angstrom out of the plane defined by the other four atoms. It has been established that the oxime group has a syn conformation and the two enantiomers form a dimer around the centre of symmetry by means of hydrogen bonds between their oxime groups.

Structure of Potassium Hydrogen Diethylmalonate Monohydrate

[K(C7H11O4)].H2O, M(r) = 216.27, tetragonal, P4(3), a = 9.251 (3), c = 13.123 (4) angstrom, V = 1123 (1) angstrom 3, Z = 4, D(x) = 1.29 Mg m-3, lambda(Mo K-alpha) = 0.71069 angstrom, mu = 0.45 mm-1, F(000) = 456, T = 293 K, R = 0.041 for 1121 observed reflections. The asymmetric unit contains one formula unit of potassium hydrogen diethylmalonate linked by a hydrogen bond to the water molecule. Each molecule is intramolecularly hydrogen bonded and the carboxylic and carboxylate groups lying in the same plane of symmetry are equivalent.