1-Ethoxyoxalyl-2-chloroacetylene as a new dienophile in Diels-Alder reactions

Full text of DOI:10.1134/S0012500808060062

ISSN 0012-5008, Doklady Chemistry, 2008, Vol. 420, Part 2, pp. 147–149. © Pleiades Publishing, Ltd., 2008.
Original Russian Text © A.B. Koldobskii, E.V. Solodova, I.A. Godovikov, V.N. Kalinin, 2008, published in Doklady Akademii Nauk, 2008, Vol. 420, No. 6, pp. 768–770.
CHEMISTRY
1-Ethoxyoxalyl-2-chloroacetylene as a New Dienophile
in Diels–Alder Reactions
A. B. Koldobskii, E. V. Solodova, I. A. Godovikov, and V. N. Kalinin
Presented by Academician Yu.N. Bubnov January 25, 2008
Received February 11, 2008
DOI: 10.1134/S0012500808060062
Acetylene dienophiles and enophiles containing two ond substituent to provide strong activation in cycload-
activating substituents one of which is a halogen are of
great interest not only for theory but also as substrates
in the synthesis of biologically active compounds [1, 2].
Previously, we obtained halogenated trifluoroacetyl-
acetylenes and studied their reactions with different
dienes [3], alkenes [4], and vinyl ethers [5]. Acetylenes
activated by the alkoxyoxalyl group are a very promis-
ing class of compounds in terms of synthesis because of
unique possibilities of their functionalization; however,
these compounds have been studied only over the past
fifteen years and their properties are inadequately
understood [6–9].
dition reactions followed by the substitution of the
halogen by different nucleophiles. However, such acet-
ylenes have not hitherto been obtained and their syn-
thetic possibilities have remained unclear.
In an attempt to solve this problem, we found that
the addition of lithium chloroacetylenide to various
oxalic acid derivatives and the catalyzed acylation of
bis(trimethylsilyl)acetylene were unsuccessful. Readily
available [10] bis(trimethylstannyl)acetylene was found
to undergo acylation with ethoxyoxalyl chloride at
20°C in the absence of a solvent and catalyst to give
1-ethoxyoxalyl-2-trimethylstannylacetylene 1, a stable
Within this class of compounds, special attention is
attracted by alkynes containing a halogen atom as a sec- compound distillable in vacuum:
O
O
20°C
Me3Sn–C≡C–SnMe3 +
Me3Sn–C≡C–COCOOEt + Me3SnCl,
1 (82%)
Cl
OEt
where the product yield is given parenthetically.
the target compound from trimethyltin chloride by dis-
tillation results in considerable loss; however, the latter
compound can be readily removed by washing of the
reaction mixture with water:
The chlorination of compound 1 proceeds rapidly
even at low temperature to give 1-ethoxyoxalyl-2-chlo-
roacetylene 2 in high yield. The attempted separation of
–20°C
Me3Sn–C≡C–COCOOEt + Cl2
Cl–C≡C–COCOOEt + Me3SnCl.
2 (90%)
1
Further studies showed that acetylene 2 is a reactive cycloadducts 3. The reaction proceeds rapidly even at
dienophile and readily undergoes the Diels–Alder reac- 20°ë and is complete in 1 h in the case of cyclopenta-
tion with different dienes to produce corresponding
diene, whereas it takes 48 h for the addition of less reac-
tive 2,3-dimethylbutadiene to be complete. Cycload-
duct 3‡ can easily be isolated from the reaction mix-
ture by vacuum distillation, whereas other
cycloadducts are isolable preferably by chromatog-
raphy. Furan, a heterocyclic diene, also reacts under
mild conditions with acetylene 2; however, we char-
Nesmeyanov Institute of Organoelement Compounds,
Russian Academy of Sciences, ul. Vavilova 28, Moscow,
119991 Russia
147

148
KOLDOBSKII et al.
acterized substituted oxanorbornadiene 3d and solution. The compound undergoes fast resinifica-
1
determined its yield only by H NMR in a dioxane tion in a pure state even at 0°ë.
Scheme 1.
H3C
H3C
COCOOEt
COCOOEt
H2C
H2C
CH3
CH3
Cl
Cl
3a (90%)
3e (53%)
0–20°C,
1 h
20°C, 48 h
Cl–C≡C–COCOOEt
2
20°C, 40 h
O
20°C, 4 h
O
20°C, 30 h
COCOOEt
Cl
COCOOEt
Cl
3b (80%)
3d (56%)
COCOOEt
Cl
3c (78%)
Initially, we failed to carry out the addition reaction of lyzed by stannic chloride and is complete in 1 h at 20°ë.
acetylene 2 with anthracene: the reaction did not proceed Such a strong acceleration of the reaction seems to be
at ambient temperature, whereas the decomposition of the explained by an increase in the electrophilicity of the
dienophile was observed on heating to 90–100°ë. We −ë≡ë– bond as the tin atom in the Lewis acid is chelated
found, however, that the reaction is very efficiently cata- by the 1,2-dicarbonyl system of the dienophile:
Cl
COCOOEt
20°C, 1 h
SnCl4
Cl–C≡C–COCOOEt +
2
3f (79%)
It is noteworthy that all cycloadducts 3a–3f contain certain modifications that allowed us to increase the
a reactive chlorine atom and ethoxyoxalyl group in a
fixed cisoid conformation, which opens wide possibili-
ties for the synthesis of different heterocycles contain-
ing carbocyclic fragments and ester group.
yield and facilitate the isolation of the product.
Acetylene was passed through a solution of n-butyl-
lithium (800 mL, 0.8 mol, c = 1 mol/L) in hexane with
cooling to –35°C and vigorous stirring until absorption
of the gas ceased, and the mixture was heated under
reflux with stirring for 1 h.A solution of 160 g (0.8 mol)
of trimethyltin chloride in 200 mL of hexane was added
in one portion to the resultant suspension of lithium
acetylenide at –35°C, the mixture was heated under
reflux for 1 h, and the reaction mixture was kept for 12
h at 20°C. The precipitate of lithium chloride was fil-
tered off, the filtrate was concentrated in vacuum, and
the residue was distilled with the use of an air-cooled
EXPERIMENTAL
All experiments with trimethylstannylacetylenes
were carried out under an argon atmosphere with the
use of anhydrous solvents. Ethoxyoxalyl chloride was
distilled immediately prior to use. The structure of the
compounds obtained was confirmed by elemental anal-
ysis data, 1H and 13C NMR, and IR spectroscopy.
Bis(trimethylstannyl)acetylene. The compound
was obtained by the well-known procedure [10] with condenser to give 101.5 g (71%) of bis(trimethylstan-
DOKLADY CHEMISTRY Vol. 420 Part 2 2008

1-ETHOXYOXALYL-2-CHLOROACETYLENE AS A NEW DIENOPHILE
149
nyl)acetylene, bp 100°C (8 mmHg), mp 58–60°C general procedure from acetylene 2 and furan in 2 mL
(lit. [10]: mp 58–60°C).
of 1,4-dioxane. Reaction time 40 h, yield 56% (accord-
ing to 1H NMR). The compound is stable only in solu-
tion.
1-Ethoxyoxalyl-2-chloro-4,5-dimethylcyclohexa-
diene-1,4 3e. The compound was obtained by the gen-
eral procedure from acetylene 2 and 2,3-dimethylbuta-
diene. Reaction time 48 h, Rf = 0.25. Yield 0.40 g
(53%).
1-Ethoxyoxalyl-2-trimethylstannylacetylene 1. A
solution of 50 g (0.14 mol) of bis(trimethylstan-
nyl)acetylene in 77.56 g (63.5 mL, 0.57 mol) of ethoxy-
oxalyl chloride was kept at 20°C for 8 days. Excess
ethoxyoxalyl chloride and resulting trimethyltin chlo-
ride were distilled off in a vacuum of 10–15 mmHg (the
obtained distillate may be redistilled at atmospheric
pressure collecting a fraction with bp 128–134°C that
contains about 90% of ethoxyoxalyl chloride and can
be reused in the same reaction) until the distillation res-
idue temperature rose to 70°C. The residue was dis-
tilled to give 33.7 g (82%) of compound 1, bp 95°C
(0.5 mmHg). Distillation at higher pressure leads to the
partial decomposition of the compound and a sharp
decrease in the yield.
Ethyl
(12-chloro-9,10-dihydro-9,10-ethenoan-
thracen-11-yl)(oxo)acetate 3f. A solution of 0.36 mL
(0.8 g, 0.0031 mol) of tin tetrachloride in 5 mL of meth-
ylene chloride was added dropwise to a solution of
0.6 g (0.0034 mol) of anthracene and 0.4 mL (0.49 g,
0.0031 mol) of acetylene 2 in 25 mL of the same sol-
vent with stirring at 20°C. The mixture was stirred for
1 h at 20°C and treated with 60 mL of 5% aqueous
hydrochloric acid. The organic layer was separated, and
the aqueous layer was extracted with 20 mL of methyl-
ene chloride. The combined organic extracts were
washed with cold water (3 × 20 mL), dried with
Na2SO4, and concentrated in vacuum, and the residue
was chromatographed on a column (ethyl acetate–ben-
zene (1 : 20) mixture as eluent). Rf = 0.95, yield 0.83 g
(79%).
1-Ethoxyoxalyl-2-chloroacetylene 2. A solution of
6.1 g of chlorine in 18 mL of carbon tetrachloride was
added dropwise to a solution of 20.70 g (0.072 mol) of
acetylene 1 in 35 mL of methylene chloride at –35°C.
The mixture was stirred for 20 min at 20°C, and the
main amount of CCl4 was removed in vacuum at 20°C.
The residue was diluted with 150 mL of hexane and
washed with cold water (3 × 100 mL), the organic layer
was dried with anhydrous Na2SO4 and concentrated in
vacuum, and the residue was distilled to give 9.0 g
(78%) of compound 2, bp 53°C (1 mmHg).
REFERENCES
General procedure of the synthesis of com-
pounds 3a–3e. A solution of 0.49 g (0.4 mL, 0.0031 mol)
of 1-ethoxyoxalyl-2-chloroacetylene 2 and 0.0043 mol
of a diene in 5 mL of methylene chloride was kept at
20°C for different times (see Scheme 1) and the solvent
was removed in vacuum. Cycloadduct 3a was isolated
by vacuum distillation; other cycloadducts were iso-
lated by column chromatography (silica gel, eluent
used was an ethyl acetate–hexane (1 : 20) mixture).
2-Ethoxyoxalyl-3-chlorobicyclo[2.2.1]heptadi-
ene-2,5 3a. The compound was obtained by the general
procedure from acetylene 2 and cyclopentadiene. Reac-
tion time 1 h, yield 0.63 g (90%), bp 110°C (2 mmHg).
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DOKLADY CHEMISTRY Vol. 420 Part 2 2008