869
SYNTHESIS OF 3-(1-ADAMANTYL)-4-METHOXYPHENYLBORIC ACID
heating with flame and charged with 8 g of magnesium
turnings (0.33 mol), 200 ml of THF, and 8 g (0.19 M,
1.2 equiv.) of freshly powdered anhydrous lithium
chloride. All operations were carried out under a slow
stream of dry argon. While stirring vigorously the
reaction mixture was heated to 40ºС and 11 g (5 ml,
0.06 mol) of 1,2-dibromoethane was added dropwise
to initiate the reaction. After the end of boiling and gas
evolution, a solution of 50 g (0.16 mol) of 2-(1-ada-
mantyl)-4-bromoanisole in 400 ml of anhydrous THF
was added to the hot reaction mixture maintaining the
mixture at slight boiling. When the reagent was added
completely, the mixture was gently boiled for 30 min.
Then stirring was stopped and the solution of Grignard
reagent was decanted into a flask preliminarily flushed
with argon. The flask was then maintained in a
refrigerator at 0ºС for 2 h.
itself and its cyclic trimer (boroxine) in a random ratio.
Therefore spectral identification of the product was
carried out after synthesis of cyclic pinacol ester of the
acid. The ester was synthesized without additioanal
acid catalysis by heating a mixture of 3-(1-adamantyl)-
4-methoxyphenylboric acid and 2,3-dimethyl-2,3-
butane-diol (pinacol) in equimolar amounts in toluene
and distilling off the formed water.
3-(1-Adamantyl)-4-methoxyphenylboric
acid
pinacol ester. One-liter round-bottom flask, equipped
with a Dean-Stark trap was charged with 100 g
(0.35 mol) of 3-(1-adamantyl)-4-methoxyphenylboric
acid, 45.5 g (0.39 mol) of 2,3-dimethyl-2,3-butanediol
(pinacol), and 500 ml of toluene. The reaction mixture
was refluxed for 2 h until the expected volume of
water (~13 ml) was collected. On completing the
reaction the solvent was distilled off under a reduced
pressure at heating with a water bath at 60°С. The
residue was dissolved in 200 ml of ethyl acetate and
maintained at 0°С for 16 h. The precipitate formed was
filtered off, washed with the smallest volume of cold
ethyl acetate, and dried at 80°С. Yield 108 g (84%) of
pinacol 3-(1-adamantyl)-4-methoxyphenylboronate, mp
162–164°С.
A one-liter dry three-neck round-bottom flask was
purged with argon and charged with 33 g (36 ml,
0.35 mol) of trimethylborate and 100 ml of anhydrous
THF. The reaction mixture was cooled in ice bath (0 to
+5°С) and at vigorous stirring a solution of Grignard
reagent was added during 10 min. The flask was
stoppered and the solution was allowed to stand in a
refrigerator (0ºС) for 16 h.
1H NMR spectrum (DMSO-d6), δ, ppm: 1.30 s
(12H), 1.76 s (6Н), 2.07 s (3Н), 2.09 s (6H), 3.85 s
(3Н), 6.83 d (1H, J = 8 Hz), 7.49 s (1Н), 7.50 d (1H,
J = 8 Hz).
The GLC analysis was performed on a Varian 3700
chromatograph with a flame-ionization detector. The
1H NMR spectra were recorded on a Bruker AMX-500
spectrometer from solutions in DMSO-d6 using TMS
as internal reference.
The reaction mixture was then decomposed by
adding 50 ml of hydrochloric acid and 50 ml of water
at stirring without additional cooling. Organic layer
was separated; water layer was extracted with 2×
100 ml of diethyl ether. Combined organic layers were
dried over sodium sulfate. The solvent was distilled off
under a reduced pressure at 50°С. The residue was
treated with 200 ml of ethyl acetate and left overnight
in a refrigerator (0ºС). The resulting precipitate was
filtered off with suction, washed with cold ethyl
acetate, and dried at 100°С. 3-(1-Adamantyl)-4-meth-
oxyphenylboric acid yield was 32 g (72%), mp ~300°С.
REFERENCES
1. Krasovskiy, A. and Knochel, P., Synthesis, 2006, no. 5,
p. 890.
1H NMR spectrum of 3-(1-adamantyl)-4-methoxy-
2. Seaman, W. and Jonson, J.R., J. Am. Chem. Soc., 1931,
phenylboric acid corresponds to a mixture of the acid
vol. 53, no. 2, p. 711.
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 80 No. 4 2010