Organic Syntheses, Coll. Vol. 6, p.531 (1988); Vol. 50, p.62 (1970).
A 300-ml., three-necked, round-bottomed flask
is fitted with a sealed mechanical stirrer
, a thermometer
, and a reflux condenser
to which is attached a T-tube connected to a source of pure nitrogen
. The remaining joint of the T-tube is connected to a bubbling device so that the rate of nitrogen
flow can be observed throughout the course of the reaction. The flask is flushed with nitrogen
and charged with 30 ml. of anhydrous dimethyl sulfoxide (Note 1)
and 2.4 g. of about 50% sodium hydride in oil (ca. 0.05 mole) (Note 2)
. Stirring is begun and the contents of the flask are heated to 75° for 30 minutes (Note 3)
under a slight pressure of nitrogen
. The flask is cooled in a water bath
to 30°, before a solution of 4.45 g. (0.0250 mole) of diphenylacetylene in 20 ml. of anhydrous dimethyl sulfoxide
is added dropwise with stirring to the dark-gray solution. During the addition, the temperature of the reaction mixture gradually rises until it approaches 40°. After the addition is completed, the reaction mixture is heated to 65° and held at this temperature for 2.5 hours. The resulting red-brown reaction mixture is cooled to room temperature and poured into 500 ml. of an ice and water mixture with stirring. After the ice has melted, the mixture is extracted with five 150 ml. portions of diethyl ether
. The ether
extracts are combined, washed with three 100-ml. portions of water, then dried over sodium sulfate
. The ether
is removed by distillation at reduced pressure, and the product (about 6.0 g.) is chromatographed on 180 g. of alumina (Note 5)
. Elution with 1:7 (v/v) benzene:n-hexane
gives ten 50-ml. fractions, of which the first two contain nearly all the mineral oil from the sodium hydride
reagent. Fractions 3 through 8 are combined, and the ether
is removed by distillation, yielding 1.2–1.4 g.
) of slightly impure 2,3-diphenyl-1,3-butadiene (Note 6)
. Recrystallization from methanol
gives 0.55–0.70 g.
) of pure 2,3-diphenyl-1,3-butadiene
, m.p. 47–48° (Note 7)
The 1H NMR spectrum (60 MHz., CCl4) shows a complex multiplet centered at δ 7.2 attributable to the aromatic protons, and two doublets centered at δ 5.4 and 5.2, respectively, attributable to the olefinic protons.
Sodium hydride in oil (about 50%), available from Metal Hydrides Inc., Beverly, Massachusetts
, was used.
The formation of dimsyl(methylsulfinyl) anion is essentially complete at this time.
Aluminum Oxide Woelm neutral, activity grade 1, available from M. Woelm, Eschwege, Germany
, was used. The column dimensions were 2.9 cm. × 29 cm., and the alumina
was packed with n-hexane
is unstable. The pure product should be stored in the dark in a refrigerator. The submitters have found it to be stable for at least one year under these conditions.
This method provides a simple, one-step synthesis of 2,3-diphenyl-1,3-butadiene
from the readily available diphenylacetylene
and illustrates an unusual, relatively uninvestigated reaction. The scope of the reaction is unknown, but it appears that the procedure could be applied to disubstituted acetylenes having aryl substituents unaffected by the strong basic conditions of the reaction.
Copyright © 1921-, Organic Syntheses, Inc. All Rights Reserved