Synthesis of enantiomerically pure volatile compounds derived from (R)-3-hydroxynonanal

Article abstract of DOI:10.1016/S0957-4166(00)00019-7

Practical preparations of enantiomerically pure R-configured 3-hydroxynonanal dimethyl acetal, 3-acetoxynonanal dimethyl acetal, methyl 3-acetoxynonanoate, δ-undecalactone, 1,3-nonanediol and its esters, 1,4-decanediol and its esters and 2-hexyltetrahydro

Full text of DOI:10.1016/S0957-4166(00)00019-7

TETRAHEDRON:
ASYMMETRY
Pergamon
Tetrahedron: Asymmetry 11 (2000) 943–950
Synthesis of enantiomerically pure volatile compounds derived
from (R)-3-hydroxynonanal
Jozef Kula,∗ Thuat Bui Quang and Magdalena Sikora
Institute of General Food Chemistry, Lodz University of Technology, Lodz, Poland
Received 1 December 1999; accepted 10 January 2000
Abstract
Practical preparations of enantiomerically pure R-configured 3-hydroxynonanal dimethyl acetal, 3-acet-
oxynonanal dimethyl acetal, methyl 3-acetoxynonanoate, δ-undecalactone, 1,3-nonanediol and its esters, 1,4-
decanediol and its esters and 2-hexyltetrahydrofuran based on the ozonolysis product of commercial castor oil are
described. © 2000 Elsevier Science Ltd. All rights reserved.
1. Introduction
One of the methods for the preparation of chiral substances is based on the transformation of natural
substances. (R)-Configured 3-hydroxynonanal can be prepared by the oxidative cleavage of (R,Z)-(+)-12-
hydroxyoctadec-9-enoic acid (ricinoleic acid).1 As an α,β-hydroxyaldehyde, it is unstable and attempts
to purify (R)-3-hydroxynonanal were unsuccessful because of its tendency to undergo dehydration during
distillation or chromatography. This property complicates the published physical and spectral data of
the compound. 3-Hydroxynonanal was isolated from barley and wort,2 but there was no mention of its
optical activity. Since optically active 3-hydroxynonanal can be synthesized from enantiomerically pure
ricinoleic acid, the main component of inexpensive castor oil, it represents a tempting material for the
syntheses of optically active compounds.1,3 A few years ago we became interested in the synthesis of
olfactorily active compounds from castor oil and reported the synthesis of (R)-γ-decalactone.3 We now
describe the preparation of (R)-3-hydroxynonanal and other homochiral compounds which can serve as
building blocks for the synthesis of some natural products.
∗
Corresponding author. E-mail: jkula@snack.p.lodz.pl
0957-4166/00/$ - see front matter © 2000 Elsevier Science Ltd. All rights reserved.
PII: S0957-4166(00)00019-7
tetasy 3242

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2. Results and discussion
Commercial castor oil (containing ca. 85% of ricinoleic acid) underwent ozonolysis to produce (R)-3-
hydroxynonanal 1 in 80% yield (Scheme 1).
Scheme 1. Dimerization of (R)-3-hydroxynonanal 1
In our hands, hydroxyaldehyde 1, when purified by distillation (102–121°C/0.8 torr), dehydrated in
part, and the rest crystallized spontaneously to give a mixture of two diastereoisomeric dimers 2. A
similar result was observed for racemic 3-hydroxynonanal.4 The mixture, after two recrystallizations
from hexane:ethyl acetate (3:1), had mp 57–58°C and specific rotation [α]D22=+28.7 (c 0.02, chloroform)
which changed only negligibly after two additional recrystallizations from the same solvent. TLC showed
one spot under all conditions tried. However, the 13C NMR spectrum (DEPT) showed a characteristic
pattern of eight oxygen-bonded carbon atoms (Table 1).
Table 1
13C NMR chemical shifts of oxygen-bonded carbon atoms in 2
This suggests that 2 exhibits stable chair conformations in a 1:1 ratio and the original configuration
of C4 and C8 is retained. All new stereogenic centers, except for C2 in 2b, are R and result from the
stereochemistry of original substrate. Treatment of dimer 2 with an excess of methanol in the presence of
a catalytic amount of ammonium chloride resulted in the formation of (R)-3-hydroxynonanal dimethyl
acetal 3, but the yield of the isolated product was moderate (55%).
As the hydroxyaldehyde 1 is unstable even at neutral pH, we developed a method for its purification
without destructive distillation. Castor oil, after ozonolysis in methanol and reduction of intermediate
methoxy hydroperoxides with dimethylsulfide, was cooled to 0°C and treated with a catalytic amount
of hydrochloric acid. The glycerides present in the mixture were treated with potassium hydroxide to
deliver a water soluble salt, and the hydroxyacetal 3 was isolated by extraction from the alkaline solution
in excellent yield. The enantiomeric excess was found to be 100%, as compared with chiral GC analysis
of a racemic product prepared according to Rychnovsky et al.5 Homochiral (R)-hydroxyacetal 3 is stable
at room temperature (at least for 5 weeks) and can be considered as a useful starting material for the
preparation of stereochemically related natural products (Scheme 2).
Optically active δ-undecalactone, an important sensory substance found in coconut,6 was prepared
by quantitative acetylation of hydroxyacetal 3 to acetoxyacetal 4 followed by a selective hydrolysis of
the acetal group7 to give 3-acetoxynonanal 5. A subsequent Wittig reaction8 gave E-configured diester 6

J. Kula et al. / Tetrahedron: Asymmetry 11 (2000) 943–950
945
Scheme 2. Synthesis of (R)-δ-undecalactone 8 and methyl (R)-3-acetoxynonanoate 9
(the crude product contained 5% of Z-isomer; GC–MS) which, after reduction and cyclization, provided
(R)-δ-undecalactone 8 in a total yield ca. 25%.
The intermediate acetoxyaldehyde 5 was only 82% pure due to the presence of 10% of acetal 4 and a
few percent of some unsaturated compounds. The aldehyde 5 could not be purified by vacuum distillation
and was employed in the next reaction as a crude material. Reduction of the unsaturated ester 6 with
magnesium in methanol9 delivered the saturated diester 7 and a considerable amount of lactone 8 and
other impurities difficult to remove by flash chromatography. Therefore, in the last step, the crude diester
7 was lactonized in refluxing dilute hydrochloric acid. The resulting δ-undecalactone 8 was 91% pure
(GC) but its ee was 100% in comparison with chiral GC analysis of the racemic lactone. The specific
rotation of the impure sample, [α]D20=+33.3 (c 0.2, chloroform), was much lower than the literature
data10 (+46.1, 98.3% ee).
We also oxidized acetoxyacetal 4 by ozone11 to prepare, in excellent yield, methyl (R)-3-
acetoxynonanoate 9, the parent hydroxyacid of which is a microcomponent of human blood plasma.12
The enantiomeric excess of the diester is presumably close to 100% in comparison with the specific
rotation of a chromatographically pure (>98%) sample in the literature (see Experimental). The oxidation
of the hydroxyacetal 3 under the same conditions resulted in the formation of a complex mixture.
Electrochemical reduction of methyl ricinoleate ozonolysis products13 or NaBH4 reduction of (R)-3-
hydroxynonanal 11 produced homochiral (R)-1,3-nonanediol 10 which was transformed into a series of
new optically pure compounds (Scheme 3).
Thus, acetylation of the diol 10 with an excess of acetic anhydride delivered pure diacetate 11 in 87%
yield. The lipase-catalyzed transesterification14 of the diol with 1 equiv. of vinyl acetate appeared to be
highly regioselective and gave a product containing 12, 13 and 10 in the ratio 98:1:1 (GC), respectively.
Our approach to obtain the secondary monoacetate 13 included acetylation of the substrate methyl
ricinoleate followed by ozonolysis of the (R)-12-acetoxyoctadec-9-enoic acid methyl ester15 in methanol
and reduction of the intermediate peroxides with NaBH4 in methanol.3 However, to our surprise, the
crude product was dominated by the primary monoester 12 (ratio 12 to 13 was 2.5:1). We concluded,
therefore, that under the reduction conditions an intramolecular transesterification took place and the
product reflected thermodynamic control. This was confirmed by a 4-hour stirring of monoacetate 12 in

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Scheme 3. Transformation of (R)-3-hydroxynonanal 1 to (R)-1,3-nonanediol 10 and (R)-1,4-decanediol 15 and their derivatives
a water:methanol solution (1:9) with a little NaBH4, at room temperature, to produce a 2.6:1 mixture of
the corresponding acetates 12 and 13. The compound 13 could not be isolated in a pure state by flash
chromatography (silica gel; hexane/ethyl acetate, hexane/ether) and its structure was deduced from the
1H and 13C NMR spectra of the mixture.
Enantiomerically pure (R)-γ-decalactone 14 synthesized from (R)-1,3-nonanediol 103 was reduced
to (R)-1,4-decanediol 15. Its lipase-catalyzed transesterification with 1 equiv. of vinyl acetate gave
quantitatively an interesting sensory monoacetate 16. Diol 15 was also converted, in the usual way, to R-
configured diacetate 17 and THF derivative 18. To estimate the enantiomeric excess of compounds 15–18
by chiral GC, the corresponding racemates were prepared from the racemic lactone 14. No racemization
was observed during such transformations.
3. Experimental
3.1. General
Commercial-grade castor oil, [α]D20=+5.6 (neat), from Ricinus communis was used. The courses of all
reactions, composition products and their purities were checked by means of thin-layer chromatography
(TLC) and capillary gas chromatography (GC). The compounds which were not isolated by vacuum
distillation were purified by flash chromatography (silica gel: hexane, ethyl acetate, ether). GC was

J. Kula et al. / Tetrahedron: Asymmetry 11 (2000) 943–950
947
performed on a Carlo Erba Vega 6000 gas chromatograph equipped with a column Rtx-1 (30 m):
temperature program 60–250°C (4°C/min), nitrogen as carrier gas (0.8 ml/min). Chiral GC analysis was
performed using a Chiraldex G-TA capillary column. A CP-Chirasil-Dex column (30 m) was employed
for lactone 8 analysis. In the case of dimer 2 and aldehyde 5, TLC and NMR were used to estimate
1
the purity. H NMR (250 MHz) and 13C NMR (62.90 MHz) were recorded by a Bruker apparatus for
CDCl3 solutions with TMS as the internal standard. Optical rotations were measured using an Autopol
IV polarimeter.
3.2. (R)-3-Hydroxynonanal dimer 2
A solution of commercial castor oil (30 g containing ca. 0.08 mol of ricinoleic acid) in methanol (120
ml) was ozonized and the intermediate hydroperoxides were reduced with dimethyl sulfide under the
conditions described elsewhere.16 The crude hydroxyaldehyde 1 was isolated by extraction with ether
(4×50 ml) to give 10.3 g (81%). Distillation of this material (bp 102–121°C/0.8 torr) delivered a product
which crystallized as a white solid. Its twice recrystallization gave crystals which were found to be (R)-3-
hydroxynonanal dimers 2a and 2b: mp 57–58°C; IR (microscope): 3423.66, 3270.80, 1138.44, 1085.13
cm−1; 1H NMR (δ): 5.44 (m, 1H), 4.97–4.84 (m, 1H), 3.99–3.10 (5m, 4H), 1.84–1.60 (m, 4H), 1.51–1.28
(m, 20H), 0.88 (t, J=6.5 Hz, 6H); 13C NMR (δ): 98.90, 95.41, 93.63, 91.17, 75.83, 71.99, 69.01, 68.85,
41.23, 39.16, 37.64, 36.25, 36.14, 35.94, 32.21, 32.14, 32.12, 29.70, 29.58, 29.55, 25.76, 25.37, 25.23,
22.99, 22.98, 14.46. Anal. calcd for C18H36O4: C, 68.31; H, 11.47. Found: C, 68.18; H, 11.49.
3.3. (R)-3-Hydroxynonanal dimethyl acetal 3
A solution of commercial castor oil (30 g containing ca. 0.08 mol of ricinoleic acid) in methanol (120
ml) was ozonized under the conditions described elsewhere,16 and the ozonide products were reduced
with dimethylsulfide (18 g, 0.29 mol, −5 to 0°C) for 3 h and left overnight at room temperature. After
being cooled to −5°C, 35% HCl (1.8 ml) in methanol (30 ml) was added at 0°C for 2 h during an intensive
stirring. The mixture was stirred for another 1 h and left overnight. Then KOH (15 g, 0.7 mol) in water
(25 ml) and methanol (25 ml) were added at 0–5°C for 1.5 h. Excess of Me2S and a little methanol
(entirely 40 ml) was evaporated and the residue was refluxed (71°C) for 3 h. Methanol was vacuum
distilled off, water (50 ml) was added and the hydroxyacetal 2 was extracted with ether (4×50 ml). The
ether solution was washed neutral with water and dried over anh. MgSO4. After solvent evaporation, the
crude product was fractionally distilled to give pure (>98%, GC) acetal 3 (14.1 g, 86%): bp 90–92°C/0.7
torr; [α]D21=−13.7 (c 0.9, MeOH); IR (film): 3450 cm−1; 1H NMR (δ): 4.58 (t, J=5.6 Hz, 1H), 3.76 (m,
1H), 3.38 (s, 3H), 3.35 (s, 3H), 1.8–1.7 (m, 2H), 1.48–1.28 (10H), 0.88 (t, J=7 Hz, 3H); 13C NMR (δ):
103.13, 67.67, 52.88, 52.31, 39.15, 37.24, 31.42, 29.02, 25.10, 22.20, 13.60. Anal. calcd for C11H24O3:
C, 57.82; H, 10.59. Found: C, 57.61; H, 10.60.
3.4. (R)-3-Acetoxynonanal dimethyl acetal 4
Hydroxyacetal 3 was quantitatively acetylated with acetic anhydride in pyridine and dichloromethane
according to conventional procedures to give acetal 4: purity >98% (GC); [α]D20=−10.4 (c 0.12, CHCl3);
IR (film): 1745 cm−1; 1H NMR (δ): 4.99 (quin, J=6 Hz, 1H), 4.43 (t, J=5.6 Hz, 1H), 3.32 (s, 3H), 3.31
(s, 3H), 2.04 (s, 3H), 1.8 (br m, 2H), 1.54 (br m, 2H), 1.27 (m, 8H), 0.88 (t, J=6.5 Hz, 3H); 13C NMR
(δ): 170.27, 101.70, 70.77, 52.93, 52.08, 37.14, 34.31, 31.47, 28.86, 24.85, 22.32, 20.88, 13.79. Anal.
calcd for C13H26O4: C, 63.38; H, 10.64. Found: C, 63.22; H, 10.66.

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3.5. (R)-3-Acetoxynonanal 5
Acetal 4 was selectively hydrolyzed by CuCl2·2H2O in acetonitrile.7 Crude acetoxyaldehyde 5 was
obtained in 82% yield. Purity ca. 80% (based on TLC and 1H NMR). IR (film): 2750, 1745, 1730 cm−1
;
1H NMR (δ): 9.74 (t, J=1.5 Hz), 5.22 (m), 2.63 (m), 2.04 (s), 1.27 (m), 0.88 (t); 13C NMR (δ): 199.69,
170.51, 70.23, 38.65, 33.74, 31.45, 28.79, 24.85, 22.33, 20.82, 13.81.
3.6. Ethyl (R,E)-5-acetoxy-2-undecenoate 6
Diester 6 was obtained from crude aldehyde 5 (10 g) and triphenylcarbethoxymethylenephosphorane17
(10.8 g) in the presence of silica gel8 in 5.5 g yield (52%) (distilled product contained 2.3% of Z-isomer):
bp 108–110°C/0.2 torr; [α]D20=+30.1 (c 0.2, CHCl3); IR (film): 1745, 1730, 1660 cm−1; 1H NMR (δ):
6.81 (dt, J=15.0, 7.5 Hz, 1H), 5.79 (dt, J=15.0, 1.5 Hz, 1H), 4.88 (quin, J=6 Hz, 1H), 4.11 (q, J=5 Hz,
2H), 2.38 (m, 2H), 1.97 (s, 3H), 1.48 (m, 2H), 1.21 (m, 11H), 0.80 (t, J=6.5 Hz, 3H); 13C NMR (δ):
169.34, 164.95, 142.67, 123.08, 71.40, 59.17, 35.74, 32.70, 30.70, 28.06, 24.25, 21.56, 20.00, 13.23,
13.02; MS (70 eV, EI); m/z (%): (trans) 270 (M+, 0), 183 (31), 156 (30), 125 (39), 114 (100), 97 (64), 95
(50), 86 (48), 68 (62), 67 (52), 43 (39); MS (70 eV, EI); m/z (%): (cis) 270 (M+, 0), 183 (42), 156 (51),
125 (75), 114 (100), 97 (82), 86 (82), 68 (80), 43 (94), 41 (71). Anal. calcd for C15H26O4: C, 66.63; H,
9.69. Found: C, 66.30; H, 9.69.
3.7. (R)-δ-Undecalactone 8
1
Magnesium/methanol reduction9 of the unsaturated diester 6 (5.5 g) was monitored by GC and H
NMR. The obtained saturated diester 7 (5 g) was refluxed with 5% HCl (100 ml) for 3 h during an
intensive stirring. The crude product was extracted with ether (4×50 ml), washed with water and dried
over MgSO4. Lactone 8 was isolated by vacuum distillation to yield a 2.8 g (82%) sample, 91% pure: bp
80–81°C/0.5 torr. Its GC and MS data were identical with those of an authentic sample.
3.8. Methyl (R)-3-acetoxynonanoate 9
Acetal 4 (5 g) was oxygenated by ozone11 in ethyl acetate for 2 h to give diester 9 (3.1 g, 66%): bp
98–100°C/0.6 torr; [α]D21=+2.17 (c 0.1, CHCl3), lit.18 +1.3 (61% ee); IR (film): 1740 cm−1; 1H NMR
(δ): 5.21 (m, 1H), 3.68 (s, 3H), 2.56 (ddd, J=6.25, 3.75, 2.50 Hz, 2H), 2.04 (s, 3H), 1.58 (m, 2H), 1.27
(m, 8H), 0.88 (t, J=6.5 Hz, 3H); 13C NMR (δ): 170.56, 170.06, 70.19, 51.33, 38.66, 33.66, 31.32, 28.65,
24.72, 22.18, 20.64, 13.65. Anal. calcd for C12H22O4: C, 62.58; H, 9.63. Found: C, 62.54; H, 9.64.
3.9. (R)-Nonanediol-(1,3)-diacetate 11
Bp: 103–104°C/0.5 torr; [α]D23=−15.3 (c 0.1, CHCl3); IR (film): 1735 cm−1; 1H NMR (δ): 4.98 (m,
1H), 4.09 (t, J=6.5 Hz, 2H), 2.04 (s, 6H), 1.88 (m, 2H), 1.55 (m, 2H), 1.27 (m, 8H), 1.88 (t, J=7 Hz,
3H); 13C NMR (δ): 167.43, 167.26, 68.40, 58.34, 32.16, 31.08, 29.63, 27.09, 23.03, 20.43, 18.23, 18.01,
11.67. Anal. calcd for C13H24O4: C, 63.90; H, 9.90. Found: C, 63.91; H, 9.89.

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949
3.10. Acetic acid (R)-3-hydroxynonyl ester 12
To a solution of 0.01 mol of diol 10 and 0.011 mol of vinyl acetate in 100 ml hexane and 20 ml CH2Cl2,
200 mg of Lipozyme IM was added and the mixture was stirred for 12 h. The enzyme was filtered and
the solvent was removed in vacuo. The residue was purified on a silica gel column to deliver monoacetate
1
12: [α]D23.5=−5.58 (c 0.1, CHCl3); IR (film): 3450, 1745 cm−1; H NMR (δ): 4.29 (m, 1H), 4.16 (m,
2H), 2.92 (m, 1H, OH), 2.05 (s, 3H), 1.77–11.69 (br m, 2H), 1.46 (m, 2H), 1.29 (m, 8H), 0.88 (t, J=6 Hz,
3H); 13C NMR (δ): 170.63, 67.48, 61.30, 36.99, 35.52, 31.24, 28.74, 24.97, 21.97, 20.02, 13.30. Anal.
calcd for C11H22O3: C, 65.31; H, 10.96. Found: C, 65.35; H, 10.95.
3.11. (R)-3-Acetoxynonanol 13
1H NMR (δ): 5.02 (m, CHOAc), 2.08 (s, CH3CO); 13C NMR (δ):170.63, 71.13, 57.67, 36.56, 33.82,
31.10, 28.50, 24.60, 21.91, 20.20, 13.30. Both sets of data have been deduced from the spectra of the
mixtures 12 and 13 (2.5:1, GC).
3.12. (R)-Decane-1,4-diol 15
Mp: 41°C (AcOEt:hexane, 4:1); [α]D25=−4.1 (c 0.1, CHCl3); IR (CHCl3): 3400 cm−1; 1H NMR (δ):
4.48 (br s, 2H, OH), 3.58 (m, 3H), 1.67–1.28 (14H), 0.88 (t, J=7 Hz, 3H). Its 13C NMR and MS data
matched those reported in the literature.19
3.13. Acetic acid (R)-4-hydroxydecyl ester 16
The preparation procedure was the same as described for monoacetate 12. [α]D25=−4.6 (c 0.07,
CHCl3); IR (film): 3460, 1745 cm−1; 1H NMR (δ): 4.02 (t, J=7.5 Hz, 2H), 3.55 (m, 1H), 1.98 (s, 3H),
1.70–1.22 (15 H), 0.82 (t, J=7 Hz, 3H); 13C NMR (δ): 170.67, 70.28, 64.14, 36.97, 32.93, 31.31, 28.84,
25.11, 24.36, 22.05, 20.18, 13.42. Anal. calcd for C12H24O3: C, 66.63; H, 11.18. Found: C, 66.58; H,
11.19.
3.14. (R)-Decane-(1,4)-diol-diacetate 17
Bp 110–112°C/0.4 torr; [α]D24=−1.3 (0.1, CHCl3); IR (film): 1745 cm−1; 1H NMR (δ): 4.89 (m, 1H),
4.06 (t, J=7 Hz, 2H), 2.05 (s, 3H), 2.03 (s, 3H), 1.67–1.51 (6H), 1.27 (m, 8H), 0.88 (t, J=7 Hz, 3H); 13
C
NMR (δ): 170.31, 170.16, 73.45, 64.10, 34.43, 32.00, 30.84, 29.41, 25.50, 24.89, 22.81, 20.94, 20.68,
14.17. Anal. calcd for C14H26O4: C, 65.08; H, 10.14. Found: C, 65.06; H, 10.15.
3.15. (R)-2-Hexyltetrahydrofuran 18
1
[α]D27=+1.7 (c 0.08, CHCl3); H NMR (δ): 3.90–3.66 (two m, 3H), 1.92–1.86 (m, 3H), 1.46–1.28
(11H), 0.88 (t, J=6 Hz, 3H); 13C NMR (δ): 78.60, 66.69, 35.15, 31.26, 30.77, 28.83, 25.74, 25.04, 21.98,
13.29. All the spectral data coincided with those of literature data.20

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J. Kula et al. / Tetrahedron: Asymmetry 11 (2000) 943–950
Acknowledgements
Support has been provided by the State Committee for Scientific Research (KBN, 3T09 B03012). The
authors thank Teresa Olejniczak (Agricultural University of Wroclaw) for the performance of the chiral
GC analysis of δ-undecalactone 8.
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