Hydroboration-oxidation of ricinoleic acid ester derivatives

Article abstract of DOI:10.1134/S1070428012120020

The chiral center in ricinoleic acid methyl ester (ee ～100%) strongly affects the regioselectivity of its hydroboration-oxidation, so that the resulting 1,3-diol dominates by 74% over the 1,4-isomer. Furthermore, new asymmetric centers are formed preferen

Full text of DOI:10.1134/S1070428012120020

ISSN 1070-4280, Russian Journal of Organic Chemistry, 2012, Vol. 48, No. 12, pp. 1509–1511. © Pleiades Publishing, Ltd., 2012.
Original Russian Text © G.Yu. Ishmuratov, V.A. Vydrina, M.P. Yakovleva, G.V. Nasibullina, I.S. Nazarov, R.R. Muslukhov, A.G. Tolstikov, 2012,
published in Zhurnal Organicheskoi Khimii, 2012, Vol. 48, No. 12, pp. 1538–1540.
Hydroboration–Oxidation of Ricinoleic Acid Ester Derivatives
G. Yu. Ishmuratov, V. A. Vydrina, M. P. Yakovleva, G. V. Nasibullina, I. S. Nazarov,
R. R. Muslukhov, and A. G. Tolstikov
Institute of Organic Chemistry, Ufa Research Center, Russian Academy of Sciences,
pr. Oktyabrya 71, Ufa, 450054 Bashkortostan, Russia
e-mail: insect@anrb.ru
Received May 26, 2012
Abstract—The chiral center in ricinoleic acid methyl ester (ee ~100%) strongly affects the regioselectivity of
its hydroboration–oxidation, so that the resulting 1,3-diol dominates by 74% over the 1,4-isomer. Furthermore,
new asymmetric centers are formed preferentially with (S)-configuration, up to 87% for 1,3-diols and up to
1
00% for 1,4-diols.
DOI: 10.1134/S1070428012120020
We previously showed [1] that the chiral center in
unsaturated alcohols I and II (which may be regarded
as ricinoleic acid derivatives) insignificantly affects
the regioselectivity of their hydroboration–oxidation.
Among isomeric 1,3- and 1,4-diols III, IV and V, VI
thus obtained, the former prevail by 6 and 10%,
respectively (Scheme 1). On the other hand, the new
asymmetric center is formed preferentially with
tivity of triglyceride VII toward the complex BH3·
THF may be rationalized by steric factors. Under more
severe conditions (heating under reflux), triglyceride
VII was converted in 85% yield into a mixture of
regioisomeric 1,3- and 1,4-diols IV and VI at a ratio of
1
57 :43 (according to the HPLC and H NMR data),
which are products of the reduction of the ester group
and oxidation of the double bond (see table;
Scheme 2).
(S)-configuration, which was proved by subsequent
cyclization of 1,3-diols III and IV (de 32 and 50%,
respectively) into the corresponding stereoisomeric
Hydroboration of ricinoleic acid methyl ester
(
VIII) with excess BH ·THF at room temperature,
3
1
2
,3-dioxanes, and of 1,4-diols V and VI (de 40 and
2%, respectively) into 2,5-dialkyltetrahydrofurans.
followed by oxidation with hydrogen peroxide in
alkaline solution, afforded a 87:13 mixture of triols IV
and VI (see table). The same reaction carried out at
elevated temperature was characterized by slightly
lower regioselectivity, and the ratio of compounds IV
and VI was 72:28 (Scheme 3).
In continuation of our studies on the effect of the
chiral center in (12R)-ricinoleic acid on the regio- and
stereoselectivity of hydroboration–oxidation of the
double bond, in the present work we examined the
behavior of its esters, castor oil (containing ~90% of
ricinoleic acid glyceride VII) and methyl ester VIII.
Comparison of the NMR spectra of triols IV and VI
with those of compounds III–VI obtained by hydro-
boration–oxidation of unsaturated alcohols I and II [2]
showed that in all cases the major stereoisomer had
(S)-configuration of the new chiral center. The data on
the regio- and stereoselectivity of hydroboration–
In the reaction of castor oil (VII) even with
a double excess of BH ·THF (THF, 20°C) the double
3
bond remained intact, whereas hydride reduction of the
carboxy group gave unsaturated diol II. The low reac-
Scheme 1.
OH
OH
OH
OH
(1) BH ·THF, THF, 20°C
3
(
2) H O , NaOH
2
2
(
CH ) R
(CH ) R
2 7
2
7
(R)
+
Me(CH2)5
Me(CH2)5
Me(CH2)5
(
CH ) R
OH
2
7
I, II
III, IV
V, VI
2
I, III, V, R = Me; II, IV, VI, R = HOCH .
1
509

1
510
ISHMURATOV et al.
Scheme 2.
OH
(
(
1) BH ·THF, THF, 20°C
3
2) H O , NaOH
2
2
Me(CH2)5
(
CH ) CH OH
2 7 2
II
RO
OR
OR
OH
OH
OH
(
(
1) BH ·THF, THF, Δ
3
VII
2) H O , NaOH
2
2
(
CH ) CH OH
(CH ) CH OH
2 7 2
2
7
2
+
Me(CH2)5
Me(CH2)5
OH
IV
VI
OH
VII, R =
.
Me(CH2)5
(
CH ) C(O)–
2 7
Scheme 3.
OH
(
(
1) BH ·THF, THF, 20°C or Δ
3
2) H O , NaOH
2
2
Me(CH2)5
IV
+
VI
(
CH ) COOMe
2 7
VIII
oxidation of ricinoleic acid derivatives VII and VIII
are given in table.
The ratios of diastereoisomers were determined from
the NMR spectra recorded with a 10-s pulse delay.
HPLC analyses were performed on a Du Pont liquid
chromatograph (USA) equipped with a refractive index
detector and a 300 ×3.9-mm stainless steel column
packed with μ-Porasil Waters (5 μm); eluent hexane–
propan-2-ol (92 :8), room temperature. Silica gel
Thus ricinoleic acid methyl ester demonstrated the
highest regio- and stereoselectivity in hydroboration–
oxidation: the resulting 1,3-diol dominated over its
1
,4-isomer by 74%, and the new asymmetric center
had preferentially (S)-configuration (up to 87% for
(
Sorbfil, Russia) was used for thin-layer chromatog-
1
,3-diol and up to 100% for 1,4-diol).
EXPERIMENTAL
raphy. Column chromatography was performed on
Macherey-Nagel silica gel (70–230 μm, Germany).
The elemental compositions of all the isolated com-
pounds were consistent with the calculated values.
The IR spectra were recorded from films on
1
13
a Specord M-82 instrument. The H and C NMR
spectra were measured on a Bruker AMX-300 spec-
trometer at 300.13 and 75.47 MHz, respectively, using
tetramethylsilane as internal reference. Signals in the
NMR spectra were assigned using COSY H–H and
COSY C–H two-dimensional correlation techniques.
(9Z,12R)-Octadec-9-ene-1,12-diol (II). A solution
of 2.4 ml (15.0 mmol) of BF ·Et O in 8 ml of anhy-
3
2
drous tetrahydrofuran was added dropwise to a suspen-
sion of 2.0 g (2.1 mmol) of triglyceride VII and 0.55 g
(14.4 mmol) of NaBH in 45 ml of anhydrous THF
4
(argon, 20°C). The mixture was kept for 24 h at room
Composition of the hydroboration–oxidation products of ricinoleic acid derivatives VII and VIII
Compound IV
fraction in the reaction isomer ratio
Compound VI
Initial
compound no.
Temperature, °C
fraction in the
(10S,12R)/(10R,12R) reaction mixture, %
isomer ratio
(9S,12R)/(9R,12R)
mixture, %
VII
Δ
20
Δ
57
87
72
1.8:1.0
5.0:1.0
1.3:1.0
43
13
28
1.0:1.0
1.0:0.0
5.0:1.0
VIII
VIII
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 48 No. 12 2012

HYDROBORATION–OXIDATION OF RICINOLEIC ACID ESTER DERIVATIVES
1511
temperature and treated with 2.0 ml of water; after
0 min, 4.8 ml of 3 N NaOH and 4.8 ml of 30% H O
stirred for 3 h, diluted with 200 ml of tert-butyl methyl
1
ether, washed with brine, dried over Na SO , and evap-
2
2
2
4
were added, and the mixture was stirred for 3 h. The
mixture was then diluted with 200 ml of tert-butyl
methyl ether, washed with brine, dried over Na SO ,
orated. The residue was subjected to flash chromatog-
raphy to isolate 1.56 g (85%) of a mixture of com-
pounds IV and VI at a ratio of 57:43.
2
4
and evaporated, and the residue was subjected to flash
(
10S,12R)- and (10R,12R)-Octadecane-1,10,12-
–
1
chromatography to isolate 1.52 g (86%) of diol II
triols (IV). IR spectrum, ν, cm : 3340 (OH), 1110
C–O), 1050. H NMR spectrum (CDCl ), δ, ppm:
.90 t (3H, CH , J = 7.0 Hz), 1.20–1.45 m (20H,
3
1
13
1
whose H and C NMR spectra were identical to those
reported in [2].
(
0
3
3
(
10RS,12R)- and (9RS,12R)-Octadecane-1,10,12-
and -1,9,12-triols IV and VI. a. A solution of 7.3 ml
45.7 mmol) of BF ·Et O in 24 ml of anhydrous THF
CH
2
), 1.45–1.65 m (8H, 2-H, 9-H, 11-H, 13-H),
3
2.25 br.s (3H, OH), 3.65 t (2H, 1-H, J = 6.5 Hz), 3.94
[4.05]* m (2H, 10-H, 12-H). C NMR spectrum
1
3
(
3
2
1
8
17
was added dropwise to a suspension of 2.0 g
6.4 mmol) of methyl ester VIII and 1.68 g
43.9 mmol) of NaBH in 137 ml of anhydrous THF
argon, 20°C), and the mixture was kept for 24 h at
room temperature. The mixture was treated with 6.0 ml
of water; after 10 min, 14.6 ml of 3 N NaOH and
4.6 ml of 30% H O were added, and the mixture was
stirred for 3 h, diluted with 200 ml of tert-butyl methyl
ether, washed with brine, dried over Na SO , and
(CDCl
3
), δ
C
, ppm: 14.16 q (C ), 22.66 t (C ), 25.62 t
8
3
14
7
15
(
(
(
(C ), 25.83 t (C , C ), 29.39 t (C ), 29.44 t (C ),
5
6
4
2
4
29.55 t (C , C ), 29.65 t (C ), 31.90 t (C ), 32.65 t
1
6
9
13
11
(C ), 37.57 t (C ), 37.61 t (C ), 42.40 t (C ), 63.13 t
1
10
12
(C ), 69.56 d [69.53 d] (C , C ).
(
9S,12R)- and (9R,12R)-Octadecane-1,9,12-triols
1
–1
2
2
(VI). IR spectrum, ν, cm : 3340 (OH), 1110 (C–O),
1
1
050. H NMR spectrum (CDCl ), δ, ppm: 0.90 t (3H,
3
3
2
4
CH , J = 7.2 Hz), 1.20–1.45 m (18H, CH ), 1.46 m
3
2
evaporated. The residue was subjected to flash chro-
matography to isolate 1.90 g (98%) of a mixture of
compounds IV and VI at a ratio of 87:13.
(
2H, 2-H), 1.45–1.70 m (8H, 8-H, 10-H, 11-H, 13-H),
2
3
.25 br.s (3H, OH), 3.42 [3.47] m (2H, 9-H, 12-H),
.64 t (2H, 1-H, J = 6.6 Hz). C NMR spectrum
3
13
1
8
17
b. A solution of 7.3 ml (45.7 mmol) of BF ·Et O in
(CDCl ), δ , ppm: 14.14 q (C ), 22.68 t (C ), 25.76 t
3
2
3 C
14
7
6
15
3
4
5
6
2
4 ml of anhydrous THF was added dropwise to a sus-
pension of 2.0 g (6.4 mmol) of methyl ester VIII and
.68 g (43.9 mmol) of NaBH in 137 ml of anhydrous
THF (argon, 20°C), and the mixture was heated for 5 h
under reflux. The mixture was cooled and treated as
described above in a to isolate 1.87 g (97%) of a mix-
ture of compounds IV and VI at a ratio of 72:28.
(C , C ), 29.42 t (C , C ), 29.62 t (C , C , C , C ),
2
16
10
11
3
1.90 t (C ), 32.84 t (C ), 33.35 t (C ), 34.08 t (C ),
1
3
8
1
1
4
37.62 [37.57] t (C ), 37.87 [37.82] t (C ), 63.07 t (C ),
9
12
7
2.38 d [72.02 d] (C , C ).
REFERENCES
1
2
. Muslukhov, R.R., Shayakhmetova, A.Kh., Yakovle-
va, M.P., Shitikova, O.V., Ishmuratov, G.Yu., and Tolsti-
kov, G.A., Russ. J. Org. Chem., 2008, vol. 44, p. 1130.
. Mikhailov, B.M. and Bubnov, Yu.N., Bororganicheskie
soedineniya v organicheskom sinteze (Organoboron Com-
pounds in Organic Synthesis), Moscow: Nauka, 1977.
c. A solution of 2.4 ml (15.0 mmol) of BF ·Et O in
3
2
8
ml of anhydrous THF was added dropwise to a sus-
pension of 2.0 g (2.1 mmol) of triglyceride VII and
.55 g (14.4 mmol) of NaBH in 45 ml of anhydrous
0
4
THF (argon, 20°C), and the mixture was heated for 5 h
under reflux. The mixture was then treated with 2.0 ml
of water and kept for 10 min, 4.8 ml of 3 N NaOH and
*
The data for minor triol isomers (10R,12R)-IV and ((9R,12R)-VI
4
.8 ml of 30% H O were added, and the mixture was
are given in brackets.
2
2
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 48 No. 12 2012