Org. Synth. 1969, 49, 53
DOI: 10.15227/orgsyn.049.0053
trans-4,4'-DIMETHOXYSTILBENE
[trans-Stilbene, 4,4'-dimethoxy-]
Submitted by J. W. A. Findlay and A. B. Turner
1.
Checked by R. E. Ireland and G. Brown.
1. Procedure
A solution of 100 mg. (0.41 mmole) of 4,4'-dimethoxybibenzyl (Note 1) in 1.5 ml. of anhydrous dioxane (Note 2) was placed in a 10-ml. round-bottomed flask. To this was added 103 mg. (0.45 mmole) of 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ; (Note 3)) dissolved in 1.5 ml. of anhydrous dioxane. The flask was fitted with a reflux condenser and heated in an oil bath at 105° for 18 hours. The solution, which was initially deep green, became pale yellow as the hydroquinone crystallized out. The mixture was cooled, and the solid was filtered off. It was washed with 1 ml. of warm benzene followed by 6 ml. of warm chloroform (Note 4), and dried at 100° to give 95 mg. (91%) of pure 2,3-dichloro-5,6-dicyanohydroquinone (Note 5). The filtrate and washings were combined and evaporated under reduced pressure. The semisolid residue was dissolved in 5 ml. of ethyl acetate and passed through a short column of neutral alumina (2.0 g.; (Note 6)). The column was eluted with 100 ml. of ethyl acetate (Note 7). Evaporation of the solvent under reduced pressure left the crude product, which was recrystallized from 35 ml. of ethanol to give 82–84 mg. (83–85%) of trans-4,4'-dimethoxystilbene as colorless plates, m.p. 212–213.5°.
2. Notes
1.
The starting bibenzyl was prepared from
p-methoxybenzyl chloride by a modified Wurtz reaction.
2 The checkers found the procedure described by Buu-Hoï and Lavit
2 inadequate and used the
copper(I) chloride-catalyzed coupling of
p-methoxybenzylmagnesium chloride in its place.
2.
Dioxane was purified by the method of Vogel
3 and stored over molecular sieves.
3.
DDQ was obtained from Koch-Light Laboratories, Ltd. It can be recrystallized from
benzene if required.
4.
Washing with
chloroform is necessary to dissolve some of the
stilbene which crystallizes out with
hydroquinone. In many reactions, washing the
hydroquinone with hot
benzene is sufficient, as the dehydrogenation products crystallize to a limited extent from
dioxane.
5.
The amount of precipitated hydroquinone is a convenient measure of the extent of
hydrogen transfer.
DDQ is readily regenerated in good yield from the hydroquinone by oxidation with
nitric acid.
46.
Woelm neutral alumina, activity grade 1.
7.
The volume of
ethyl acetate required to elute the product can be reduced considerably for more soluble products.
3. Discussion
DDQ was first introduced for the dehydrogenation of hydroaromatic compounds, such as
tetralin and
bibenzyl, which yield
naphthalene and
stilbene, respectively.
5 A benzene ring or an olefinic bond provides sufficient activation, although it is sometimes difficult to force the reaction to completion. This highpotential quinone has since found wide application,
6 particularly in the steroid field, and its scope has been extended by the dehydrogenation of carbonyl compounds (ketones and lactones) and alcohols. DDQ is also useful for preparing stable cations and radicals. These reactions are commonly carried out in refluxing
benzene or
dioxane, and the procedure described here is a general one. An alternative workup procedure involves washing with alkali.
A number of compounds react rapidly with
DDQ at room temperature. They include allylic and benzylic alcohols, which can thus be selectively oxidized, and enols and phenols,
7 which undergo coupling reactions or dehydrogenation, depending on their structure. Rapid reaction with DDQ is also often observed in compounds containing activated tertiary hydrogen atoms.
8 The workup described here can be used in all these cases.
A number of side products can arise with this quinone. They include Diels-Alder adducts (DDQ is a powerful dienophile) and Michael adducts derived from the hydroquinone.
General methods for the preparation of
trans-stilbenes have been covered previously.
9 4,4'-Dimethoxystilbene has been prepared from
deoxyanisoin and
n-propylmagnesium iodide,
10 by treatment of
thiophenol with
2-bromo-1, 1-di-p-methoxyphenylethane,
11 and by the action of
nitrous acid on the corresponding amine.
12
Appendix
Chemical Abstracts Nomenclature (Collective Index Number);
(Registry Number)
Deoxyanisoin
DDQ
ethanol (64-17-5)
Benzene (71-43-2)
ethyl acetate (141-78-6)
hydrogen (1333-74-0)
chloroform (67-66-3)
hydroquinone (123-31-9)
nitric acid (7697-37-2)
nitrous acid (7782-77-6)
Naphthalene (91-20-3)
copper(I) chloride (7758-89-6)
Thiophenol (108-98-5)
Tetralin (119-64-2)
dioxane (123-91-1)
stilbene
bibenzyl (103-29-7)
2,3-dichloro-5,6-dicyano-1,4-benzoquinone
2,3-dichloro-5,6-dicyanohydroquinone
p-methoxybenzyl chloride (824-94-2)
p-methoxybenzylmagnesium chloride
n-propylmagnesium iodide
2-bromo-1, 1-di-p-methoxyphenylethane
trans-4,4'-Dimethoxystilbene,
trans-Stilbene, 4,4'-dimethoxy- (15638-14-9)
4,4'-dimethoxybibenzyl
4,4'-Dimethoxystilbene
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