Investigation of Three Stilbene Derivatives by X-ray Crystallography and NMR Spectroscopy

Stomberg, Rolf; Li, S. M.; Lundquist, Knut; Albinsson, Bo

doi:10.1107/s0108270198008877

Cited by 10 publications

(6 citation statements)

References 2 publications

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“…All the C-C bond lengths in the benzene rings have typical values; the average C-C bond lengths of these two rings are 1.376 and 1.388 Å . The C10-O2 bond length is 1.350 (2) Å , consistent with literature values (Jottier et al, 1991;Stomberg et al, 1998).…”

supporting

confidence: 88%

(E)-5-[(3-Chlorophenyl)diazenyl]-2-hydroxy-3-methoxybenzaldehyde

et al. 2006

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supporting

confidence: 88%

(E)-5-[(3-Chlorophenyl)diazenyl]-2-hydroxy-3-methoxybenzaldehyde

et al. 2006

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“…However, the ~H NMR spectral data given in their paper for the acetylated product are not in accordance with the spectral data for (3a) or (3b) obtained in this study. It was noted in previous 1H NMR spectral studies of stilbenes of type (1) (Stomberg et al, 1998) that the signal from one of the methoxy groups in the Z forms is located at a comparatively high field (ca 6 3.5). The present study shows that this is also true for (2b) (6 3.62) and (3b) (6 3.54).…”

Section: Commentmentioning

confidence: 94%

“…The E stilbene, (2a), adopts a conformation that deviates only slightly from planarity [angle between the ring planes 8.90(9)°; torsion angles C2--Cl--C7---C8 and C7--C8--C11--C16 175.1 (2) and 175.4(2) °, respec-tively]. It is noteworthy that a related 2-hydroxystilbene, (E)-2-hydroxy-3,3',4'-trimethoxystilbene, also adopts a nearly planar conformation (Stomberg et al, 1998). In (2a) there are intramolecular hydrogen bonds between the hydroxy groups and the adjacent methoxj-O atoms [O1...02 2.598 (2) and 03.-.04 2.716(2)A], as well as intermolecular hydrogen bonds…”

Section: Commentmentioning

confidence: 99%

An investigation of 2,4'-dihydroxy-3,3'-dimethoxy-5'-methylstilbene using X-ray crystallography and NMR spectroscopy

Li¹,

Lundquist²,

Stomberg³

1999

Acta Crystallogr C

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“…The preparation of 9a (m. p. 101°C) is described elsewhere (Stomberg et al 1998; see also Li et al 1996b). 1 H NMR spectrum: δ 3.60 (3H, s, OCH 3 ), 3.85 (3H, s, OCH 3 ), 3.90 (3H, s, OCH 3 ), 5.77 (1H, s, OH), 6.60 (2H, s, vinyl H), 6.6-6.9 (6H, m, H-Ar).…”

Section: Cis-2-hydroxy-33′4′-trimethoxystilbene (9 A)mentioning

confidence: 99%

Acid Reactions of Lignin Models of β-5 Type

Li¹,

Lundquist²

1999

Holzforschung

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IntroductionDehydrodiconiferyl alcohol (1) is obtained in moderate yield on oxidation of coniferyl alcohol (Freudenberg and Hübner 1952). Catalytic hydrogenation of 1 gives the dihydro derivative 2. This latter compound has frequently been used as a model compound representative of β-5 structures of the phenylcoumaran type (3) in lignins. Refluxing of 2 with 0.2M HCl in dioxane-water (9 : 1) gives the phenylcoumarone 4 (Adler and Lundquist 1963) (Fig. 1). Compound 4 exhibits a strong absorbance in the UV region and a UV spectroscopic method for the estimation of phenylcoumaran structures (3) in spruce lignin was developed on the basis of this fact (Adler and Lundquist 1963). Later it was found that small amounts of a stilbene (5) also formed on the acidolytic treatment of 2 (Lundquist and Hedlund 1971) (Fig. 1). In more recent work it was found that stilbene formation from phenylcoumarans is the predominant reaction if HCl is replaced by H 2 SO 4 as the catalyst (Yasuda 1984; cf. also Yasuda 1988). This together with recent results from studies of the acid reactions of hydrobenzoins (Karlsson and Lundquist 1992) and lignin models of the β-1 type (Li et al. 1997 b) in the presence of different catalysts prompted a reinvestigation of acid reactions of lignin models representative of lignin structures of the phenylcoumaran type (3). Materials and MethodsReagent grade dioxane was freshly distilled over Na. Silica gel (Grace, Matrex LC 60 Å /35-70 µm) was used for flash chromatography. Compound 6a was prepared according to Li and Lundquist SummaryRefluxing of trans-2- (3,4-dimethoxyphenyl)-3-hydroxymethyl-7-methoxy-2,3-dihydrobenzo[b]furan with dioxane-water (9 : 1) in the presence of various acid catalysts led to the formation of 2-(3,4-dimethoxyphenyl)-7-methoxy-3-methylbenzo[b]furan, the trans and cis forms of 2-hydroxy-3,3′,4′-trimethoxystilbene and cis-2- (3,4-dimethoxyphenyl)-3-hydroxymethyl-7-methoxy-2,3-dihydrobenzo[b]furan. The proportions of the products were strongly dependent on the particular acid used as catalyst. HCl and to a greater extent HBr favored the formation of the 2-arylbenzofuran (phenylcoumarone) while the trans-stilbene derivative predominated in reaction products from the experiments with trifluoromethane sulfonic acid as the catalyst. Isomerization of the starting material occurred, regardless of the nature of the catalyst (small amounts of the cis-isomer formed). The number of phenylpropane units in spruce lignin attached to an adjacent unit by a β-5 linkage was estimated to be 6-9 % on the basis of 1 H NMR spectrometric measurements of the formation of phenylcoumarone structures on refluxing of milled wood lignin from spruce with 0.1M HBr in dioxane-water (9 : 1).

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Investigation of Three Stilbene Derivatives by X-ray Crystallography and NMR Spectroscopy

Cited by 10 publications

References 2 publications

(E)-5-[(3-Chlorophenyl)diazenyl]-2-hydroxy-3-methoxybenzaldehyde

(E)-5-[(3-Chlorophenyl)diazenyl]-2-hydroxy-3-methoxybenzaldehyde

An investigation of 2,4'-dihydroxy-3,3'-dimethoxy-5'-methylstilbene using X-ray crystallography and NMR spectroscopy

Acid Reactions of Lignin Models of β-5 Type

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