Rolf Stomberg

Studies on the conformation of α-arylcinnamic acids and their esters: Crystal structures of methyl (E)-2,3-bis(3,4-dimethoxyphenyl)propenoate and methyl (Z)-2,3-bis(3,4-dimethoxyphenyl)propenoate

The conformations of stereoisomers of α-arylcinnamic acids and their esters are discussed based on crystal structures of the E and Z forms of 2,3-bis(3,4-dimethoxyphenyl)propenoic acid and its methyl ester. In the E forms of the cinnamic acid and the cinnamic acid ester, the plane of the α-aryl substituent is approximately perpendicular to that of the rest of the molecule. In the Z forms the plane of the carboxyl or methoxycarbonyl group is approximately perpendicular to that of the ethylenic group, and both the aromatic group planes are significantly twisted out of the ethylenic group plane. Crystal structures of methyl (E)-2,3-bis(3,4-dimethoxyphenyl)propenoate (space group P21/n with a = 8.1697(5), b = 11.3882(9), c = 19.7766(9) Å, β = 90.058(4)°, V = 1840.0(2) Å3, and Z = 4), monoclinic methyl (Z)-2,3-bis(3,4-dimethoxyphenyl)propenoate (space group P21/n with a = 11.183(2), b = 5.640(2), c = 29.737(7) Å, β = 99.19(2)°, V = 1851.4(9) Å3, and Z = 4), and orthorhombic methyl (Z)-2,3-bis(3,4-dimethoxyphenyl)propenoate (space group P212121 with a = 8.849(4), b = 24.288(9), c = 8.734(3) Å, V = 1877(1) Å3, and Z = 4) are reported.

Investigation of an inclusion compound of trans-1,3-bis(3,4-dimethoxyphenyl)-2,3-epoxy-1-propanone with chloroform by NMR spectroscopy and X-ray crystallography

Abstracttrans-1,3-Bis(3,4-dimethoxyphenyl)-2,3-epoxy-1-propanone crystallizes in a monoclinic form (m.p. 155–156°C, from ethanol) and a trigonal form (m.p. 125–126°C, from chloroform/hexane or chloroform). NMR studies revealed that chloroform is present in the crystals of the trigonal form (epoxide/chloroform ratio ≈ 3:1). Solid-state NMR experiments showed that the trigonal form was gradually converted into the monoclinic form on storage in vacuo. On the basis of NMR and X-ray examinations it was concluded that the trigonal form is an inclusion compound of trans-1,3-bis(3,4-dimethoxyphenyl)-2,3-epoxy-1-propanone with chloroform. The crystal structure of the trigonal form with space group of R

(Z)-3-(3,4-Dimethoxyphenyl)-2-(2-methoxyphenoxy)-2-propenoic acid.

{\bar 3}

Investigation of 2-(3,4-dimethoxyphenyl)-5,6-dimethoxy-1H-indene by X-ray crystallography and NMR spectroscopy

, a = 36.0354(4), c = 8.2743(2) Å, and Z = 18, has been refined to R = 0.0506 by the employment of the SQUEEZE procedure implemented in PLATON-94.

2,3-Diaryl-3-hydroxypropionic acid intermediates in the synthesis of threo forms of 1,2 -diaryl -1,3 -propanediols

ABSTRACT The erythro8-O-4′ neolignan IIIb was synthesized and was found to have identical 1H and 13C NMR characteristics to a neolignan reported as a component of the roots of Nardostachys jatamansi. The NMR spectral characteristics of compound IIIb were also identical with those of a neolignan previously obtained from the roots of Piper capense, for which the unlikely 8-O-3′ structure IVa had been proposed. Two further erythro 8-O-4′ compounds IIIc and IIId were prepared, and their assigned 13C NMR signals were consistent with those of IIIb. At this time, there appears to be no evidence for the existence of 8-0-3′ neolignans as plant extracts.

A second polymorph of (+)‐pinoresinol–dioxane (1/1)

In the crystal structure of the title compound, C18H18O6, molecules are connected by strong O-H...O hydrogen bonds to form centrosymmetric dimers. The angle Caryl-Cvinyl-Cvinyl is considerably larger (130.2°) than could be expected (ca 120°). This is attributed to steric interactions. The structure of the title compound provides a basis for the assignment of the stereoisomers of 3-(3,4-dimethoxyphenyl)-2-(2-methoxyphenoxy)-2-propenal.

(Z)-2,3-Bis(3,4-dimethoxyphenyl)-2-propen-1-ol

The crystal structure of the title compound, C20H22O6, an intermediate in the synthesis of the flavone 2-(4-methoxy-phenyl)-5,7-dimethoxy-3,8-dimethyl-4H-1-benzopyran-4-one, has been determined. The molecules are held together by van der Waals forces. There is an intramolecular hydrogen bond between the hydroxy group and the neighbouring keto O atom. The molecules in the crystal structure are disordered, with significantly different orientations of the methyl group in the disordered 4-methoxyphenyl substituent.

(Z)-α-Chloromethyl-3,3',4,4'-tetramethoxystilbene

Abstract2-(3,4-Dimethoxyphenyl)-5,6-dimethoxy-1H-indene (obtained by acid treatment of 1,2-bis(3,4-dimethoxyphenyl)-1,3-propanediol) crystallizes in space groupP21/c witha=6.836(6),b=28.631(9),c=16.344(6) Å, β=95.73(5)°, andZ=8. There are two molecules in the asymmetric unit; the conformations of these molecules exhibit minor differences. In the crystals the double bond in the five-membered ring of the compound is disordered over two positions. The nature of the bonds in the five-membered ring could be ensured by1H-NMR and13C-NMR spectral examinations.