X. Hu et al. / Tetrahedron: Asymmetry xxx (2014) xxx–xxx
3
which the tertiary hydroxyl groups were free. Sequential methyla-
tion of the tertiary hydroxyl groups could conventionally be
performed by using excess NaH and MeI in THF, and the methyla-
tion could nearly quantitatively provide spiroborate salt, sodium
graphite monochromator. A total of 8584 unique reflections were
collected using Mok (k = 0.71073 Å) radiation by fine-focus sealed
tube at 273(2) K, of which 6130 reflections had I > 2 (I) and were
a
r
used in the structure solution and refinements. The corrections for
Lp factors and empirical absorption were applied to the intensity
data. All calculations were performed on Enraf-Nonius Molen/
VAX Software using the program SHELXL-97. The structure was
(
2R,3R,7R,8R)-2,3,7,8-tetrakis(methoxydiphenylmethyl)-1,4,6,9-tet
raoxa-5-boraspiro[4.4]nonan-5-uide 4, which was hydrolyzed by
HF in methanol to give (2R,3R)-1 in excellent yield.
2
solved by direct methods and refined on F using a full-matrix
least-squares technique. The non-hydrogen atoms were also re-
fined by a full-matrix least-squares technique, anisotropically,
and hydrogen atoms were included but not refined. Cell dimen-
sions were obtained by the least-squares refinement of well cen-
tered 289 reflections in the range of 2.21 < h < 25.50°.
Convergence with unweighted and weighted agreement factors
3
. Conclusion
In conclusion, a high-yielding approach to chiral diol (2R,3R)-1
based on a highly selective 2,3-spiroboration of (2R,3R)-2 has been
discovered. Compound (2R,3R)-1 could undergo quantitatively a
selective 2,3-spiroboration reaction with B(OH)
3
in the presence
2
2
was achieved at R = 0.0502 and R
w
= 0.1043 ðw ¼ 1=½ns ðFo Þ
of bases or with NaBH in refluxing THF to give the corresponding
4
2
2 2
þð0:0450PÞ þ 1:2659Pꢁ where P = (Fo + 2Fc )/3, S = 0.00065(16)
spiroborate salt 3 or 5. The tertiary hydroxyl groups of the spirob-
orate salt were methylated by using excess NaH and MeI, and then
hydrolyzed by HF in methanol to give (2R,3R)-1 in excellent yield.
This preparation avoids traditional oxidation and reduction steps,
and does not utilize the toxic and expensive DDQ and LiAlH
is a simplified and high-yielding synthesis.
ꢃ
2
3
ꢀ1=4
and Fc ¼ kFc½1 þ 0:001 ꢂFc n l = sinð2 n qÞꢁ
Þ. The maximum
and minimum peaks on the final difference Fourier map corre-
ꢀ
3
spond to 0.415 and ꢀ0.458 e Å
.
Crystal data for potassium salt 1: empirical formula, C56 H48 B
4
, and
3
K O8; formula weight, 898.85; calculated density, 1.296 g/cm ;
3
volume (V), 4605.4(12) Å ; crystal system, Orthorhombic; space
group, P2(1)2(1)2(1); Z = 4; unit cell dimensions, a = 13.088(2),
4
4
. Experimental
.1. General
b = 16.158(2), c = 21.778(3),
a = 90° b = 90°, c = 90°; absorption
ꢀ
coefficient
(l
), 0.173 mm 1; index ranges ꢀ15 6 h 6 15,
ꢀ14 6 k 6 19, ꢀ26 6 l 6 23; F(000), 1888; GOF, 0.997.
Diethyl (2R,3R)-tartrate was prepared from (2R,3R)-tartaric acid
and ethanol. (2R,3R)-2 was synthesized from diethyl (2R,3R)-tar-
trate and PhMgBr in THF using a conventional Grignard reaction
procedure. B(OH) and NaBH were purchased and used directly.
3 4
Commercially available starting materials were used without fur-
ther purification if not specified.
4
.4. Preparation of sodium (2R,3R,7R,8R)-2,3,7,8-2,3,7,8-tetrakis
(
methoxydiphenylmethyl)-1,4,6,9-tetraoxa-5-boraspiro[4.4]
nonan-5-uide 4
Under an argon stream, a dried two-neck round-bottomed
flask fitted with a magnetic stirrer bar was charged with 13.2 g
IR spectra were recorded on a Nicolet 170 SX FT-IR spectropho-
ꢀ1
tometer, in KBr, in cm . NMR spectra were recorded at 300 MHz
(
1
14.7 mmol) of potassium salt 1 from the previous step and
60 mL of dried THF. The flask was then placed in ice bath, after
1
13
for H, and 75 MHz for C on a Varian Mercury VS 300 (ppm, rel-
ative to TMS). Optical rotations were measured on a Perkin-Elmer
which 1.9 g of NaH (95%, 73.5 mmol) were added and then the
solution was stirred for 1 h at room temperature, followed by
adding 4.6 ml of MeI (73.5 mmol), and stirred for 5 h at room
temperature. A white precipitate appeared, which was filtered
and stirred with 120 mL water for 1 h. The undissolved white so-
lid (13.2 g) in water was filtered, dried, and used directly in the
next step without further purification. Yield: 96%, mp: 140–
3
41 Mc polarimeter. Mp: VEB Wagetechnik Rapio PHMK 05;
uncorrected.
4
.2. Preparation of potassium (2R,3R,7R,8R)-2,3,7,8-tetrakis
(
hydroxydiphenylmethyl)-1,4,6,9-tetraoxa-5-boraspiro[4.4]
nonan-5-uide 3
2
D
5
1
1
42 °C, ½
aꢁ
¼ þ16:7 (c 0.8, DMSO). H NMR (300 Hz, DMSO-d
6
):
).
To a round-bottomed flask fitted with a magnetic stirrer bar,
d 6.74–7.31 (m, 40H, Ar-H), 4.3 (s, 4H, CH), 2.4 (s, 12H, CH
3
1
1
2.8 g (30 mmol) of (2R,3R)-1,1,4,4-tetraphenylbutanetetraol and
00 mL of THF were added and stirred to give a transparent solu-
13
6
C NMR (75 MHz, DMSO-d ): d 146.2, 143.6, 128.3, 128.1,
+
1
27.3, 126.9, 126.7, 88.6, 84.5, 59.7. ES-MS (ES ): 961.
3
tion. To this solution 0.93 g (15 mmol) of B(OH) and approxi-
mately 10 ml of saturated KOH solution were added and refluxed
for 4 h. The solvent was then removed, and to the residue was
added water after which it was stirred for 0.5 h and filtered to give
a white solid, which was washed with ethanol to give 13.2 g of 3
4
.5. Preparation of (2R,3R)-1,4-dimethoxy-1,1,4,4-tetraphenyl
butane-2,3-diol 1
25
1
In a 250 mL plastic bottle fitted with a magnetic stirrer bar was
charged with 13.2 g (14.1 mmol) of sodium salt 4 from the previous
step and 165 mL of methanol and stirred. The resulting solution was
placed in an ice bath, and 2.9 mL (58.4 mmol) 40% HF was added
slowly. The mixture was stirred for 3 h and quenched with a satu-
with mp >300 °C, 98% yield. ½
a
ꢁ
¼ þ169:7 (c 0.13, MeOH),
H
D
NMR (300 MHz, DMSO-d ): d 7.06–6.95 (m, 32H, Ph-H), 6.76 (s,
6
13
8
H), 4.46 (s, 4H, OC-H), 4.18 (s, 4H, O-H). C NMR (75 MHz,
6
DMSO-d ): d 149.1, 145.1, 128.4, 127.9, 127.5, 126.7, 126.1, 81.1,
ꢀ1
7
8.8. IR (KBr): 3416, 1618, 1384 cm .
rated NaHCO
organicphasewasdriedoveranhydrousNa
and purification by flash column chromatography on silica gel,
1.9 g of the desired product (2R,3R)-1,4-dimethoxy-1,1,4,4-tetra-
phenylbutane-2,3-diol were obtained in 93% yield, mp: 78–80 °C,
3
solution. The solution was extracted by Et
2
O and the
2
SO . Afterconcentration
4
4
.3. X-ray crystal structure analysis of 3
1
A single crystal suitable for X-ray structural analysis was
obtained by slowly cooling a hot methanol solution of potassium
salt 3 to room temperature. A colorless crystal of dimensions
1
D
5
1
½
a
ꢁ
¼ þ59:6 (c 0.08, CHCl
3
), H NMR (300 MHz, CDCl
3
): d 7.25–
),
): d 142.8, 141.5, 129.0,
28.3, 128.1, 128.0, 127.5, 127.7, 85.4, 71.3, 53.7. ESI: 477 [M+23].
7
2
1
.44 (m, 20H, Ph-H), 4.71 (d, J = 3.3 Hz, 2H, CH), 3.16 (s, 6H, OCH
.74 (br, 2H, OH). C NMR (75 MHz, CDCl
3
0
.32 mm ꢂ 0.28 mm ꢂ 0.27 mm was mounted on a glass fiber.
1
3
X-ray diffraction intensity data collection and cell refinement were
performed on Bruker P4 four-circle diffractometer equipped with a
3
Hu, Xiaoyun
