Org. Synth. 1971, 51, 17
DOI: 10.15227/orgsyn.051.0017
ALDEHYDES FROM ALLYLIC ALCOHOLS AND PHENYLPALLADIUM ACETATE: 2-METHYL-3-PHENYLPROPIONALDEHYDE
[Benzenepropanal, α-methyl-]
Checked by Robert A. Clement and Richard E. Benson.
1. Procedure
A slurry comprised of 33.6 g. (0.0998 mole) of commercial phenylmercury(II) acetate, 200 ml. of acetonitrile, and 14.4 g. (16.8 ml., 0.200 mole) of methallyl alcohol (Note 1) is prepared in a 500-ml., three-necked flask fitted with a mechanical stirrer, a condenser, and a thermometer. The slurry is stirred and cooled in an ice bath, and 22.4 g. (0.0998 mole) of powdered palladium(II) acetate (Note 2) is added over 1 minute. Stirring is continued with cooling for 1 hour, then at room temperature for 3 more hours (Note 3). The temperature of the reaction mixture reaches a maximum of 27° after removal of the ice bath.
The black reaction mixture is diluted with about 100 ml. of diethyl ether and poured onto 200 g. of ether-wet alumina (Woelm, Activity Grade 1) in a 45 × 2.5 cm. glass chromatographic column. The product is washed through the alumina with about 1 l. of ether. The brown eluate is concentrated by distilling the ether through a 45-cm. Vigreux column on a steam bath at atmospheric pressure. When the ether has been distilled, a slight vacuum is applied, removing most of the acetonitrile. After the volume reaches about 50 ml., the mixture is filtered into a 100-ml. distillation flask, removing some precipitated palladium metal. The flask is rinsed with 10-ml. of ether, and the rinse is combined with the product. The flask is equipped with a 10 cm. Vigreux column for distillation at reduced pressure. After removal of the solvent, 8.1–8.5 g. (55–58%) of 2-methyl-3-phenylpropionaldehyde is collected, b.p. 75–85° (3 mm.) (Note 4), n25D 1.5113 (Note 5).
2. Notes
1.
Methallyl alcohol was obtained from Eastman Organic Chemicals.
2.
Palladium(II) acetate was purchased from Engelhard Industries.
3.
The yield improves slightly with stirring overnight; the checkers obtained the aldehyde in
69% yield in this manner.
4.
The bulk of the product has b.p.
77–80° (3 mm.).
5.
The product is 90–95% pure by GC and NMR analyses. The checkers estimated the purity to be at least 95% by these criteria. The
1H NMR spectrum (CDCl
3) shows peaks at δ 0.95 (d,
J = 6.5 Hz., 3H), ~2.7 (complex m, 3H), 7.20 (s, 5H) and 9.65 (d,
J = 1.5 Hz., 1H).
3. Discussion
The formation of 3-aryl-substituted aldehydes and 3-aryl-substituted ketones by the reaction of "arylpalladium salts" with allylic alcohols is general.
2 Illustrations of the preparation of two aldehydes and two ketones are given in Table I.
TABLE I
3-ARYLCARBONYL COMPOUNDS FROM ALLYLIC ALCOHOLS AND “PHENYLPALLADIUM ACETATE”2
|
|
Allylic Alcohol
|
Product
|
Yield, %
|
Boiling Point, °C.
|
|
|
CH2=CHCH2OH
|
C6H5CH2CH2CHO
|
35
|
220–225°a
|
|
trans-CH3CH=CHCH2OH
|
C6H5CH(CH3)CH2CHO
|
36
|
67–75° (1 mm.)
|
|
trans-CH3CH=CHCH(OH)CH3
|
C6H5CH(CH3)CH2COCH3
|
51
|
70–75° (3 mm.)
|
|
(CH3)2C=CHCH(OH)CH3
|
C6H5C(CH3)2CH2COCH3
|
29
|
83–87° (2 mm.)
|
|
a Purification by careful distillation is necessary in this example to remove cinnamaldehyde which is also formed in the reaction (b.p. 252°).
|
The presence of nitro, carboalkoxy, carboxyl, chloro, formyl, alkyl, and acyl groups does not interfere with the reaction. A single alkoxy group also does not interfere, but if two or more are present the yields are markedly decreased. The reaction is inhibited by the presence of unhindered, basic nitrogen substituents, by the phenolic group, and probably by the thiol group.
A variation of this procedure involves the use of a catalytic amount of
palladium(II) chloride with
copper(II) chloride as a reoxidant.
2 This method, however, generally gives lower yields and less pure products. Another related preparation uses
palladium(II) acetate with two equivalents of
triphenylphosphine, catalyzing the reaction of
iodo-3 or bromo-4 benzene with
methallyl alcohol in the presence of weak bases. Phenyldiazonium salts also may be used to react with
methallyl alcohol and a
palladium(0) catalyst to form the propionaldehyde.
Other preparations of
2-methyl-3-phenylpropionaldehyde include the pyrolysis of a mixture of the
calcium salts of 2-methyl-3-phenylpropionic acid and
formic acid,
5 the pyrolysis of the glycidic ester obtained from
2-phenyl-2-propanone and
ethyl chloroacetate,
6 the hydroformylation of
allylbenzene,
7 the benzylation of
2-ethylthiazoline followed by reduction with
aluminum amalgam and cleavage with
mercury(II) chloride,
8 and the reaction of
phenylmagnesium bromide with
2-vinyl-5,6-dihydro-1,3-oxazine followed by methylation and hydrolysis.
9This preparation is referenced from:
Appendix
Chemical Abstracts Nomenclature (Collective Index Number);
(Registry Number)
alumina
calcium salts of 2-methyl-3-phenylpropionic acid
ether,
diethyl ether (60-29-7)
acetonitrile (75-05-8)
formic acid (64-18-6)
aluminum (7429-90-5)
palladium,
palladium(0) (7440-05-3)
Ethyl chloroacetate (105-39-5)
mercury(II) chloride (7487-94-7)
copper(II) chloride (7758-89-6)
Phenylmagnesium bromide (100-58-3)
phenylmercury(II) acetate
cinnamaldehyde
palladium(II) chloride (7647-10-1)
methallyl alcohol (513-42-8)
allylbenzene (300-57-2)
triphenylphosphine (603-35-0)
palladium(II) acetate (3375-31-3)
PHENYLPALLADIUM ACETATE
2-Methyl-3-phenylpropionaldehyde,
Benzenepropanal, α-methyl- (5445-77-2)
2-phenyl-2-propanone
2-ethylthiazoline
2-vinyl-5,6-dihydro-1,3-oxazine
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