Unusual hydroalumination-bromination reaction of 1,4-butynediol

Full text of DOI:10.1134/S1070363213010271

ISSN 1070-3632, Russian Journal of General Chemistry, 2013, Vol. 83, No. 1, pp. 138–139. © Pleiades Publishing, Ltd., 2013.
Original Russian Text © H.A. Gharibyan, 2013, published in Zhurnal Obshchei Khimii, 2013, Vol. 83, No. 1, pp. 146–147.
LETTERS
TO THE EDITOR
Unusual Hydroalumination-Bromination Reaction
of 1,4-Butynediol
H. A. Gharibyan
Scientific and Technological Center of Organic and Pharmaceutical Chemistry,
National Academy of Sciences of the Republic of Armenia, Institute of Organic Chemistry,
pr. Azatutyana 26, Yerevan, 0014 Armenia
e-mail: hgaribyan@mail.ru
Received January 26, 2012
DOI: 10.1134/S1070363213010271
The hydroalumination-halogenation of propargyl
alcohols with a lithium aluminum hydride–iodine or
lithium aluminum hydride–pyridinium dibromide
system followed by methylation of the obtained vinyl
halides with lithium dimethyl copper is used as a
convenient method for the synthesis of a variety of
natural terpenoid products [1]. For the hydroalumina-
tion-bromination 1.2–1.3-fold excess of brominating
agent is commonly used. Its residual amount is
neutralized with a sodium hydroxide solution [2]. Use
of the pyridinium dibromide complex was intended to
exclude the electrophilic addition to double bonds [3].
This complex is also known to add to the triple bonds [4].
pyridinium dibromide complex as a brominating agent.
However, instead of the expected 2-bromo-2-butene-
1,4-diol II a crystalline substance was isolated from
the reaction mixture. Its physicochemical and spectral
data differ sharply from that of diol II.
Thus, in the mass spectrum of this compound there
are no molecular peaks with m/z 166 and 168, which
would indicate the formation of diol II. The number of
the bromine atoms in the resulting compound was
proved by the mass spectral data. The presence of the
molecular peaks with m/z 248(5), 246(10) and 244(5),
as well as peaks with m/z 169(9) and 167(9) indicate
the presence of two bromine atoms in the molecule.
The IR spectra contain the absorption bands at 3400
and 3050 cm–1 belonging to the hydroxy and the
terminal epoxy groups, respectively.
In this work we studied the hydroalumination-
bromination of 1,4-butynediol I. For the carbon–
aluminum bond cleavage we used a threefold excess of
HO
Al−
Li+
HO
OH
H
H
I
Br
Py Br2
Br
OH
Py Br2
HO
HO
OH
Br
Br
II
III
NaOH
b
а
Br
Br
O
Br
O
OH
HO
Br
V
IV
138

UNUSUAL HYDROALUMINATION-BROMINATION REACTION
139
Apparently, the reaction proceeds through several
stages. In the first stage the triple bond in 1,4-
butynediol I is hydrogenated by lithium aluminum
hydride, and the resulting organometallic complex is
decomposed by pyridinium dibromide to form 2-
bromo-2-butene-1,4-diol II. Then, the second molecule
of pyridinium dibromide adds to the C=CBr bond to
give 2,2,3-tribromo-1,4-butanediol III. The latter, in
turn, loses the hydrogen bromide molecule at the
action of sodium hydroxide. This leads to the closure
of the epoxide ring to form 2,2-dibromo-2-(2-
oxyranyl)ethanol V. From two possible ways the path
b is realized. This is supported by the 1H NMR spectral
data. The diagnostic is a singlet at 4.33 ppm belonging
to the CH2 group located near the hydroxy group.
СН, J 12.0), 4.94 br. s (1Н, ОН). 13С NMR spectrum,
δ, ppm: 56.71 (СН), 64.12 (СН2), 65.41 (СН2), 122.45
(СВr2). Mass spectrum, m/z (Irel, %): 248 (5) [M]+, 246
(10) [M]+, 244 (5) [M]+, 169 (9) [M – Br]+, 167 (9)
[M – Br]+, 151(17), 149 (25), 121 (29), 119 (30), 87
(18), 85(23).
1
The Н and 13С NMR spectra were recorded on a
Varian Mercury-300VX spectrometer [300.077 MHz
(1H), 75.462 MHz (13C)] in DMSO-d6 relative to
internal TMS. The IR spectrum was registered on a
Specord 75IR spectrometer in a thin layer. The mass
spectrum obtained on a MX-1320 instrument at the
direct injection of the sample into the ion source at
ionizing voltage of 70 eV. The reaction progress was
monitored by the TLC on Silufol UV-254 plates
eluting with a hexane–diethyl ether mixture (2:1) and
detecting with iodine vapor and KMnO4 solution.
The hydroalumination-bromination of 1,4-butyne-
diol. To a suspension of 3.6 g (0.15 mol) of lithium
aluminum hydride in 70 ml of anhydrous ether was
added 2.7 g (0.03 mol) of 1,4-butynediol in 30 ml of
anhydrous THF at 0°C under argon. The reaction
mixture was refluxed (39–40°C) for 7 h, cooled to
from 0 to –5°С, mixed with 8.8 g (0.1 mol) of ethyl
acetate and stirred for 0.5 h. Then to the reaction
mixture was added a solution of pyridinium dibromide
prepared from 5 ml (0.1 mol) of bromine and 12 ml of
pyridine in 6 ml of THF. After 0.5 h to the reaction
mixture was added dropwise 3.6 ml of water, 3.6 ml of
15% sodium hydroxide solution, and 10.8 ml of water
at 0°C. The precipitate was filtered off and washed
with ether. The filtrate was extracted with ether,
washed with dilute hydrochloric acid, with saturated
sodium carbonate solution,with brine, and dried over
magnesium sulfate. After the solvent removal, the
residue was distilled (bp 138–140°C, 1 mm Hg). The
formed crystals were washed with hexane. 2,2-
Dibromo-2-(2-oxyranyl)ethanol V was obtained in a
yield of 58.4% (4.3 g), mp 128–129°C. IR spectrum, ν,
cm–1: 620, 890, 930, 1140, 1610, 3050, 3400. 1Н NMR
spectrum, δ, ppm (J, Hz): 3.84 d and 3.88 d (2Н, СН2
oxyrane ring, J 12.0), 4.33 s (2Н, СН2ОН), 4.39 t (1Н,
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RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 83 No. 1 2013