Org. Synth. 2002, 78, 135
DOI: 10.15227/orgsyn.078.0135
SYNTHESIS OF PENTA-1,2-DIEN-4-ONE (ACETYLALLENE)
[3,4-Pentadien-2-one]
Submitted by Thierry Constantieux and Gérard Buono
1
.
Checked by Dawn M. Bennett and Rick L. Danheiser.
1. Procedure
A 1-L, three-necked flask, equipped with a mechanical
stirrer, reflux condenser fitted with an argon
inlet adapter, and pressure-equalizing dropping funnel
is charged with
151 g (0.58 mol)
of triphenylphosphine
(Note 1)
and
350 mL of dichloromethane
(Note 2). The mixture is cooled with an ice-salt bath
to −5°C, and maintained under an argon atmosphere.
A solution of
92 g (0.58 mol)
of bromine
(Note 3) in
60 mL of dichloromethane
is added dropwise over 1 hr while the reaction mixture is vigorous stirred. Instantaneous
decoloration of bromine and formation of a precipitate of
dibromotriphenylphosphorane(Ph3PBr2)
is observed. After the addition, the reaction mixture is stirred for an additional
30 min while being cooled in the ice bath.
A solution of
57.2 g (0.570 mol)
of acetylacetone
(Note 4) in
60 mL of dichloromethane
is then added dropwise over 1 hr. An exothermic reaction occurs. At the end of the
addition, the solution is allowed to warm very slowly to room temperature (Note 5) and stirred at that temperature for 17 hr (Note 6).
The resulting clear yellow-orange solution is transferred to a 1-L,
one-necked, round-bottomed flask and concentrated at ca. 20 mm with a
rotary evaporator. Anhydrous diethyl
ether (230 mL) is added to precipitate
triphenylphosphine oxide hydrobromide
;
the solid is separated by suction filtration and washed with two
100-mL
portions of anhydrous ether. The filtrate is concentrated under reduced
pressure and the resulting orange liquid is taken up in
350
mL of anhydrous diethyl ether
. This solution
is filtered to separate any remaining salt and transferred to a 500-mL,
three-necked flask equipped with a magnetic stir bar,
reflux condenser fitted with an argon inlet adapter, a rubber
septum, and a pressure-equalizing dropping funnel.
A solution of
56.7 g (0.56 mol)
of triethylamine
(Note 7) in
60 mL of anhydrous diethyl ether
is added dropwise to the reaction mixture over 1 hr, and the resulting mixture is
stirred at room temperature for 12 hr.
The
triethylamine hydrobromide
precipitate is filtered and washed with two
60-mL
portions of diethyl ether
. The filtrate is washed
with three
30-mL portions of 5%
hydrochloric acid
to remove unreacted triethylamine,
and then washed with 25 mL of cold water (Note 8), dried over
anhydrous magnesium sulfate
,
and filtered.
Diethyl ether is removed by distillation (Note 9)
and the residual product is distilled under reduced pressure (Note 10)
to afford 30.5 g (65%) of
acetylallene
(Note 11) as a colorless liquid.
2. Notes
1.
Triphenylphosphine
was purchased by the submitters from Fluka Chemical Corp. or
Aldrich Chemical Company, Inc.
, and used without further
purification.
2.
Dichloromethane
was purchased from SDS Co. or Mallinckrodt Inc.
and distilled from
calcium hydride
.
The distilled solvent was passed through a plug of silica gel immediately before use.
3.
Bromine obtained
from Janssen Chimica or Aldrich Chemical Company, Inc.
,
was used as received.
4.
Acetylacetone (obtained
from Labosi Co. or Aldrich Chemical Company, Inc.)
was distilled prior to use.
5.
If the internal temperature is allowed to rise too quickly, rapid
decomposition of
2-bromo-4-oxo-pent-2-ene
occurs.
6.
The reaction was monitored by
31P NMR spectroscopic
analysis. The two organophosphorus compounds in the reaction mixture show the following
spectral properties (40.54
MHz, CDCl
3, external reference: H
3PO
4, 85% aqueous
solution, δ ppm): PPh
3Br
2, δ = 50.2
and (PPh
3OH
+, Br
−), δ = 47.4
.
Complete formation of (PPh
3OH
+, Br
−) was observed
after about 12 hr.
7.
Triethylamine from
Fluka Chemical Corp. or Aldrich Chemical Company, Inc.
,
was distilled from
potassium hydroxide
prior to use.
8.
It is essential to use a minimum of water for these washes because
of the high solubility of
acetylallene
.
9.
To minimize polymerization of
acetylallene
,
ca.
100 mg of hydroquinone
is added to the ether solution prior to concentration.
10.
Caution: The highly volatile product must be
trapped in a flask cooled in liquid nitrogen.
Acetylallene
distills at
48-50°C (60 mm) and
is obtained with a purity of
96.5%
as determined by gas chromatographic analysis using a
25-m SE30 capillary
column at 80°C (Vector gas : He, 1 bar; retention time: 4.09 min).
11.
The checkers obtained
acetylallene
in
59-65% yield, while the
submitters report isolating the product in
75%
yield.
Caution: Acetylallene is an allergen and
is highly lachrymatory. The product exhibits the following spectral properties:
IR (film) cm
−1: 3025,
1940, 1660, 850
;
1H NMR (500 MHz, CDCl
3) δ:
2.26 (s, 3 H), 5.25 (d, 2 H, J = 6.4), 5.77 (t, 1
H, J = 6.4)
;
13C
NMR (125 MHz, CDCl
3) δ: 27.0, 79.9, 97.7,
198.6, 217.7
.
Handling and Disposal of Hazardous Chemicals
The procedures in this article are intended for use only by persons with prior training in experimental organic chemistry. All hazardous materials should be handled using the standard procedures for work with chemicals described in references such as "Prudent Practices in the Laboratory" (The National Academies Press, Washington, D.C., 2011 www.nap.edu). All chemical waste should be disposed of in accordance with local regulations. For general guidelines for the management of chemical waste, see Chapter 8 of Prudent Practices.
These procedures must be conducted at one's own risk. Organic Syntheses, Inc., its Editors, and its Board of Directors do not warrant or guarantee the safety of individuals using these procedures and hereby disclaim any liability for any injuries or damages claimed to have resulted from or related in any way to the procedures herein.
3. Discussion
Acetylallene
(
1)
behaves as an excellent dienophile in Diels-Alder reactions and induces peculiar orienting
effects, allowing reactions with high regio- and stereo-selectivities.
2 Retro
Diels-Alder reactions of modified adducts of
furan and
1
afford a general method of synthesis of α-functionalized allenes.
3
Hydrochlorination of
acetylallene in the presence of
N,N'-dimethylhydrazine dihydrochloride
leads stereoselectively to the corresponding
β-chloroenone
that is a valuable intermediate in organic synthesis.
4
Recently, it was disclosed that the hydrohalogenation reaction of 3,4-pentadien-2-one with metal halides in acetic acid at room temperature selectively afforded 4-halo-4-penten-2-ones in high yields17.
5
Transition metal-catalyzed dimerization of
acetylallene leads
to the expected dimeric product in mixture with
2-methylfuran
.
6 The latter compound may be also obtained
by thermal intramolecular cyclization of
1.
7
1,3-Dipolar cycloaddition of diazoalkanes to
acetylallene
leads to five-membered heterocycles containing two nitrogen atoms,
8 e.g.,
pyrazole
and pyrazoline derivatives. Addition of trivalent phosphorus reagents to
1
allows entry to the exomethylene 1,2-oxaphospholene ring system.
9
Triphenylphosphonio groups may also be used as umpolung agents to change the regioselectivity
of the addition of nucleophilic compounds on
acetylallene. In
this case, α,β-unsaturated ketones are obtained with heteroatomic substituents
in the γ-position.
10
Acetylallene
is a valuable
starting material in α,β-unsaturated γ-lactones synthesis: the tandem
nucleophilic addition-aldol reaction of
1, iodide ion and aldehydes gives 3-iodohomoallylic
alcohols in good yields, which can be further transformed to α,β-unsaturated
γ-lactones by palladium-catalyzed cyclocarboxylation.
11
Various complex and low yield procedures for the preparation of
acetylallene
have been described: oxidation of homopropargylic alcohol with
chromium
trioxide in sulfuric acid
,
12 mild
acid hydrolysis of conjugated ethoxyenyne,
13
reaction of
propargyltrimethylsilane
with acyl halide,
14
flash vacuum thermolysis of
β-keto trimethylsilyl enol ether
15 and cycloelimination of
β-silylethyl
sulfoxide.
16
The method reported here is a modification of a previously published procedure
by Buono.
17 The yields have been increased by control of the reaction
temperature during the first step, i.e., zero to room temperature instead of heating,
and by direct dehydrobromination of the non-purified bromo intermediate. By monitoring
the reaction by
31P NMR spectroscopy, the submitters have determined precisely
the end time of the first step, and that the
triphenylphosphine oxide
generated in the medium is immediately protonated by the
hydrogen bromide.
One of the major advantages of this procedure lies in the commercial availability
of the starting materials. Moreover, only two steps, without purification of the intermediates,
are required. Thus, the submitters have developed a new, efficient and cheap procedure
for the preparation of
acetylallene
in large scale (0.5 mol up to 1 mol).
Appendix
Chemical Abstracts Nomenclature (Collective Index Number);
(Registry Number)
Penta-1,2-dien-4-one:
Acetylallene:
3,4-Pentadien-2-one (8,9); (2200-53-5)
Triphenylphosphine:
Phosphine, triphenyl-
(8,9); (603-35-0)
Bromine (8,9); (7726-95-6)
Dibromotriphenylphosphorane:
Phosphorane,
dibromotriphenyl- (8,9); (1034-39-5)
Acetylacetone: Aldrich:
2,4-Pentanedione
(8,9); (123-54-6)
Triphenylphosphine oxide hydrobromide:
Phosphine
oxide, triphenyl-, compd. with
hydrobromic acid (1:1)
(9); (13273-31-9)
Triethylamine (8);
Ethanamine, N,N-diethyl-
(9); (121-44-8)
Triethylamine hydrobromide (8);
Ethanamine,
N,N-diethyl-, hydrobromide (9); (636-70-4)
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