A facile asymmetric synthesis of (S)-14-methyl-1-octadecene, the sex pheromone of the peach leafminer moth

Article abstract of DOI:10.3390/molecules18055201

An asymmetric synthesis of 14-methyl-1-octadecene, the sex pheromone of the peach leafminer moth has been achieved. The target molecule was synthesized in six linear steps and in 30.3% overall yield from commercially available hexanoyl chloride, (S)-4-benzyloxazolidin-2-one and 1,9-nonanediol. The hexanoyl chloride was connected with (S)-4-benzyloxazolidin-2-one, and with the induction of the chiral oxazolidinone auxiliary, after chiral methylation, LAH reduction and then tosylation gave the chiral key intermediate 5 in high stereoselectivity. 1,9-Nonanediol, was selectively brominated, THP protected and subjected to Li₂CuCl₄-mediated C-C coupling to afford a C₁₂ intermediate. The target molecule, (S)-14-methyl-1-octadecene, was obtained after the two parts were subjected to a second Li ₂CuCl₄-mediated C-C coupling. Our synthetic approach represents the first time a substrate-control asymmetric synthesis of (S)-14-methyl-1-octadecene has been reported.

Full text of DOI:10.3390/molecules18055201

Molecules 2013, 18, 5201-5208; doi:10.3390/molecules18055201
OPEN ACCESS
molecules
ISSN 1420-3049
www.mdpi.com/journal/molecules
Article
A Facile Asymmetric Synthesis of (S)-14-Methyl-1-Octadecene,
the Sex Pheromone of the Peach Leafminer Moth
Tao Zhang 1,†, Wei-Li Ma 1,†, Tian-Rui Li 1, Jia Wu 1, Jun-Run Wang 1 and Zhen-Ting Du 1,2,
*
1
College of Sciences, Northwest A&F University Yangling 712100, Shaanxi, China;
E-Mails: fuzitong@163.com (T.Z.); maweili@nwsuaf.edu.cn (W.-L.M.);
litianrui001@gmail.com (T.-R.L.); jiabaobao1991@gmail.com (J.W.); wangjr07@163.com (J.-R.W.)
Key Laboratory of Synthetic Chemistry of Natural Substances, Shanghai Institute of Organic
Chemistry, Chinese Academy of Sciences, Shanghai 20032, China
2
†
These authors contributed equally to this work.
* Author to whom correspondence should be addressed; E-Mail: duzt@nwsuaf.edu.cn;
Tel./Fax: +86-29-8709-2226.
Received: 28 March 2013; in revised form: 27 April 2013 / Accepted: 28 April 2013 /
Published: 7 May 2013
Abstract: An asymmetric synthesis of 14-methyl-1-octadecene, the sex pheromone of the
peach leafminer moth has been achieved. The target molecule was synthesized in six linear
steps and in 30.3% overall yield from commercially available hexanoyl chloride,
(S)-4-benzyloxazolidin-2-one and 1,9-nonanediol. The hexanoyl chloride was connected
with (S)-4-benzyloxazolidin-2-one, and with the induction of the chiral oxazolidinone
auxiliary, after chiral methylation, LAH reduction and then tosylation gave the chiral key
intermediate 5 in high stereoselectivity. 1,9-Nonanediol, was selectively brominated, THP
protected and subjected to Li2CuCl4-mediated C-C coupling to afford a C12 intermediate.
The target molecule, (S)-14-methyl-1-octadecene, was obtained after the two parts were
subjected to a second Li2CuCl4-mediated C-C coupling. Our synthetic approach represents
the first time a substrate-control asymmetric synthesis of (S)-14-methyl-1-octadecene has
been reported.
Keywords: 14-methyl-1-octadecene; asymmetric synthesis; peach leafminer moth;
(S)-4-benzyloxazolidin-2-one

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1. Introduction
Nowadays, there is a sharp conflict between intense agricultural production and environmental
issues. We all are facing a big challenge caused by the detrimental effects resulting from traditional
agricultural production [1], therefore, there is an urgent need to develop more green production modes,
such as the use of environmentally benign, low-dosage sex pheromones to control pests [2,3]. This mode
plays an important role in so-called Integrated Pest Management (IPM). The peach leafminer moth,
Lyonetia clerkella, is one of the most destructive pests in peach orchards in East Asia. It causes
defoliation when the leaves are infested by only a few larvae of this insect and Chinese orchardists use
traditional highly toxic pesticides to control it. We envisaged that an ideal way to control it could be by
using its sex pheromone to disrupt its mating process and to trap it at a suitable time.
The sex pheromone of peach leafminer was first identified as (S)-14-methyl-1-octadecene (1, Figure 1)
by Sugie et al. [4] and syntheses of 1 in racemic form have been achieved by two teams [5,6].
Recently, Ando disclosed an informal synthesis of (±)-1 through a hard-to-get intermediate [7]. The
asymmetric syntheses of 1 were also reported by Mori [8] and Kharisov [9], who both used expensive
chiral starting materials. However, the existing synthetic pathways have some drawbacks such as
requiring too many chemical operations or lack of cost-effectiveness, so the development of a more
economical synthesis of 1 in consideration of applying this kind of chemical in the pesticide industry is
highly desirable.
Figure 1. Peach leafminer moth and the chemical structure of its sex pheromone.
Our research group is interested in finding new agrochemicals and lowering the cost of existing lead
compounds or pesticides [3,10]. We are interested in an efficient and convenient synthesis
of sex pheromones through more economical approaches. Herein, we wish to report a synthesis of
(S)-14-methyl-1-octadecene (1) from inexpensive starting materials by a substrate-induction strategy.
2. Results and Discussion
The retrosynthesis of 1 is shown in Scheme 1. First, the molecule was disconnected into a chiral C7
synthon A1 and a C12 moiety. Then the C12 moiety in turn could be disconnected into two parts to be
joined through a Li2CuCl4 mediated C-C coupling protocol, a C9 subunit A2 and an allyl bromide
which is highly active in SN2 reactions and helpful to apply the strategy.
As shown in Scheme 2, our synthesis commenced with (S)-4-benzyloxazolidin-2-one, which is
cheap and can be recycled in industry. After deprotonation, it reacted with hexanoyl chloride to give 2
in 70% yield. Compound 2 was deprotonated at −78 °C in the presence of a strong base such as LDA,
then it was stereoselectively methylated to afford 3 [11–13]. Because of the steric effect of chiral
benzyl group in the oxazolidine ring, the methyl groups was directed to the -face in d.r. = 1:50 and

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78% yield. Then the chiral oxazolidine auxiliary was smoothly removed by LAH reduction at −10 °C.
However, in attempting to purify compound 4 in the laboratory, this was found to be very laborious
and less effective, so the crude 4 was directly treated with TsCl in pyridine, thus the key intermediate 5
was obtained in 55% yield in two steps. 9-Bromononan-1-ol was prepared in large quantities from
nonane-1,9-diol through selective bromination of the α,ω-diol by a known method reported by
Kang et al. [14]. The hydroxyl group of 7 was protected as its tetrahydropyranyl ether in 92% yield by
3,4-dihydro-2H-pyran under acidic conditions. Compound 8 can be converted into a Grignard reagent,
and then this was coupled with allyl bromide under Li2CuCl4 catalysis to form 9 in 66% yield [15,16].
Afterwards, the THP group was removed in methanol in the presence of 4-methyl-benzenesulfonic
acid [17,18]. Compound 11 was produced in 90% yield after 10 was subjected to a Corey-Fuji protocol.
Scheme 1. Retrosynthesis of 1.
Scheme 2. Synthesis of (S)-1.
Reagents and conditions: a) BuLi, −78 °C then hexanoyl chloride, 70%; b) LDA, −78 °C, MeI, 78%,
d.r. = 1:50; c) LAH, −10 °C; d) TsCl, Pyr., −10 °C, 15h, 55% for two steps; e) 40% HBr, toluene, I2, Dean-Stark
trap, 80 °C, 89%; f) TsOH (cat.), DHP, CH2Cl2 0 °C - r. t. 92%; g) Mg then Li2CuC14, allylic bromide, 0 °C
to reflux, 66%; h) CH3OH/H2O, PPTS (cat.), reflux 3h, 96%; i) PPh3, CBr4, CH2Cl2, 90%; j) Mg then
Li2CuC14, 65%.

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With compound 11 in hand, it was converted into the corresponding Grignard reagent and coupled
with 5 in the presence of Li2CuCl4 to afford (S)-1 in 65% yield. Thus, the asymmetric total synthesis of
(S)-1 in an overall yield of 30.3% was achieved in six linear steps. Compared with other asymmetric
synthesis of the target, our synthesis is apparently more cost-effective, even if the chiral oxazolidinone
auxiliary were not recycled.
3. Experimental
General
The 1H-NMR and 13C-NMR data were recorded in CDCl3 solution with Bruker NMR spectrometers
(DRX 500, AM 300) if not noted otherwise. The chemical shifts are measured relative to TMS  = 0)
or chloroform ( = 7.26) and the coupling J is expressed in Hertz. Mass spectra were recorded on a
Thermo Scientific TSQ Quantum Access MAX mass spectrometer (ESI, positive or negative). Standard
flash chromatography was employed to purify the crude reaction mixture using 200–300 mesh silica
gel (Tsingdao Ocean Company, Tsingdao, China) under a positive nitrogen pressure. Tetrahydrofuran
(THF) and diethyl ether were freshly distilled from lithium aluminium hydride under an argon atmosphere.
Dichloromethane, hexane and toluene were freshly distilled from calcium hydride under argon.
(S)-4-Benzyl-3-hexanoyloxazolidin-2-one (2). At −78 °C, to a solution of (S)-4-benzyloxazolidin-2-one
(5.32 g, 0.03 mol) in anhydrous THF (50 mL) was added BuLi (0.036 mol), then freshly distilled
hexanoyl chloride (4.63 g, 0.033 mol) in THF (25 mL) was added after half an hour. The mixture was
gradually warmed to 25 °C and maintained for 12 h. After completion, the reaction was quenched by
addition of saturated aqueous NH4Cl, and the volatiles were evaporated. The residue was extracted
with ethyl acetate (100 mL × 3), and the combined organic layers were washed with dilute NaOH and
brine, and dried over anhydrous MgSO4. Then the extract was evaporated, and purified by column
chromatography (15–25% gradient, EtOAc-hexane) to give 2 as a yellowish oil (5.78 g, 70%).
[α]2D5 = +97.6° (c 0.36, MeOH); H-NMR (500 MHz, CDCl3): 0.90 (br s, 3H), 1.34 (br s, 4H), 1.67
1
(br s, 2H), 2.73–2.77 (m, 1H), 2.84–2.93 (m, 2H), 3.22 (d, J = 13.3, 1H), 4.10 (s, 2H), 4.62 (s, 1H),
13
7.17–7.28 (m,5H); C-NMR (125 MHz, CDCl3): 13.9, 22.4, 23.9, 31.3, 35.4, 37.8, 55.0, 66.1, 127.2,
128.8, 129.4, 135.5, 153.4, 173.2.
(S)-4-Benzyl-3-((S)-2-methylhexanoyl)oxazolidin-2-one (3). To a cooled (−78 °C) solution of LDA
(0.051 mol) was added a solution of compound 2 (11.7 g, 43 mmol) in THF (90 mL). After 2 h, dry
MeI (13.3 mL, 0.213 mol) was introduced through a dropping funnel at this temperature. The reaction
mixture was allowed to stir at −78 °C for 3 h before being warmed to 25 °C and maintained overnight.
The reaction was quenched with saturated aqueous NH4Cl (50 mL), and the aqueous layer was
extracted with three 50 mL portions of EtOAc. The combined organic extracts were dried (MgSO4),
concentrated in vacuo, and chromatographed (15–25% gradient, EtOAc-hexane) to provide of pure 3
(9.7 g, 78%): [α]2D5 = +104.4° (c 0.28, MeOH); 1H-NMR (500 MHz, CDCl3) 0.89 (t, J = 6.8, 3H), 1.22
(d, J = 6.9, 3H), 1.27–1.40 (m, 4H), 1.40–1.44 (m, 1H), 1.72–1.76 (m, 1H), 2.77 (dd, J = 13.3, 9.6,
1H), 3.26 (dd, J = 13.3, 2.9, 1H), 3.38–3.73 (m, 1H), 4.15–4.21 (m, 2H), 4.65–4.69 (m, 1H), 7.21–7.34

Molecules 2013, 18
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13
(m, 5H); C-NMR (125 MHz, CDCl3): 14.0, 17.4, 22.7, 29.5, 33.2, 37.7, 37.9, 55.4, 66.0, 127.3,
128.9, 129.5, 135.4, 153.1, 177.4. ESI-MS: m/z: 290 (M+H), 276.
(S)-2-Methylhexyl 4-methylbenzenesulfonate (5). To a cooled (0 °C) suspension of LiAlH4 (606 mg,
16 mmol) in anhydrous THF (20 mL) was added a solution of the imide 3 (1.4 g, 5 mmol) in THF
(30 mL) over a 15 min period. After an additional 30 min of stirring, the cold (0 °C) reaction was
slowly quenched with water (0.6 mL), then 10% aqueous NaOH (1.2 mL) and water (1.8 mL) to
precipitate the aluminum salts, which were then filtered. The filtrate was dried (MgSO4), and the
solution was concentrated in vacuo. Because of the volatility of the product, the crude product was
used directly for the next step. To the cooled (−10 °C) solution of the above alcohol 4 in pyridine
(20 mL) was added 4-methylbenzene-1-sulfonyl chloride (1.0 g, 5.1 mmol). After the solution was stirred
an additional 30 min at −10 °C, the reaction mixture was slowly warmed to 20 °C for an additional
30 min period. The reaction was then quenched with brine (30 mL), and the aqueous layer was
extracted with three 30 mL portions of CH2Cl2. The combined organic extracts were washed with
brine, diluted HCl and saturated aqueous CuSO4 and dried over MgSO4, concentrated in vacuo, and
chromatographed (10% EtOAc-hexane) to provide pure 5 (0.75 g, 55% for two steps) [α]2D5 = −2.6°
1
(c 1.67, CH2Cl2); H-NMR (500 MHz, CDCl3) 0.85 (t, J = 7.0, 3H), 0.87 (d, J = 6.7, 3H), 1.09–1.13
(m, 2H), 1.20–1.25 (m, 4H), 1.73–1.79 (m, 1H), 2.45 (s, 3H), 3.80 (dd, J = 6.5, 6.4, 1H), 3.88 (dd,
J = 5.6, 5.7, 1H), 7.34 (d, J = 8.1, 2H), 7.787(d, J = 8.1, 2H). ESI-MS: m/z: 270 (M+H), 173, 155, 91.
9-Bromononan-1-ol (7). A mixture of nonane-1,9-diol 6 (24 g, 0.15 mol), a catalytic amount of iodine
(0.5 g, 2 mmol) and 40% HBr (33 mL) in toluene (240 mL) was heated to reflux and the water formed
was separated continuously for 30 h. Then the mixture was washed successively with water, aqueous
NaOH, HCl, water and brine. The organic phase was concentrated in vacuo, and chromatographed (10%
1
EtOAc-hexane) to give 30 g of pure 7 as a colorless oil in 89% yield. H-NMR (500 MHz, CDCl3)
1.31–1.36 (m, 8H), 1.41–1.43 (m, 2H), 1.49 (br s, 1H), 1.53–1.59 (m, 2H), 1.82–1.88 (m, 2H), 3.41
(t, J = 6.85, 2H), 3.63(t, J = 6.62, 2H). ESI-MS: m/z: 223 (M+H), 207.
2-((9-Bromononyl)oxy)tetrahydro-2H-pyran (8). To a solution of 9-bromononan-1-ol (7, 25 g,
0.112 mol) in anhydrous CH2Cl2 (150 mL) was added 4-methylbenzenesulfonic acid (0.3 g) and
freshly distilled 3, 4-dihydro-2H-pyran (11.24 mL, 0.123 mol) in CH2Cl2 (10 mL), at 0 °C. After
addition, the mixture was allowed to stir for 5 h at room temperature and monitored by TLC. Then the
solution was diluted by addition of another portion of CH2Cl2 (150 mL) and then the reaction mixture
was washed with saturated aqueous NaHCO3 and brine, dried over anhydrous MgSO4 and then
concentrated in vacuo and chromatographed to afford 31.6 g (92% yield) of pure 8 as a colorless oil.
1H-NMR (500 MHz, CDCl3): 1.36 (br s, 8H), 1.36–1.42 (m, 2H), 1.50–1.60 (m, 6H), 1.69–1.71 (m,
1H), 1.80–1.88 (m, 3H), 3.36–3.42 (m, 3H), 3.48–3.51 (m, 1H), 3.36–3.75 (m, 1H), 3.85–3.89 (m, 1H),
13
4.57 (t, J = 3.4, 1H); C-NMR (125 MHz, CDCl3) 19.7, 25.5, 26.2, 28.2, 28.7, 29.4, 29.4, 30.8, 32.8,
34.0, 62.3, 67.6, 98.8. EI-MS: m/z: 305 (M-H).
2-(Dodec-11-en-1-yloxy)tetrahydro-2H-pyran (9). Under a nitrogen atmosphere at 20 °C, Mg turnings
(56 mmol, 1.37 g), a catalytic amount of iodine and anhydrous THF (25 mL) were placed in a dry 500 mL
three-necked round-bottomed flask equipped with a condenser and a dropping funnel. A solution of

Molecules 2013, 18
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compound 8 (13 g, 42 mmol) in THF (150 mL) was added dropwise to the above mixture (approx.
20 min). Then the mixture was allowed to reflux for another 5 h. Another dry 500 mL three-necked
round-bottomed flask was charged with allyl bromide (84 mmol), NMP (4 mL) and Li2CuCl4 (0.3 M in
THF, 4 mL). The above Grignard reagent was transferred to this flask through a double-ended needle
with stirring. After transfer, the reaction mixture was warmed to 85 °C for 12 h. After cooling, the
reaction mixture was quenched by dropwise addition of saturated aqueous NH4Cl solution. The THF
was recovered on a rotavapor and the residue was extracted with ethyl acetate (100 mL × 3). The
combined organic extracts were dried (MgSO4), concentrated in vacuo, and chromatographed (15–25%
1
gradient, EtOAc-hexane) to provide 7.5 g (66%) of pure 9 as a colorless oil. H-NMR (500 MHz,
CDCl3) 1.27–1.30 (m, 10 H), 1.40–1.57 (m, 4H), 1.58–1.94 (m, 8H), 1.95–2.13 (m, 2H), 3.37–3.38 (m,
2H), 3.68–3.73 (m, 2H), 4.57 (t, J = 6.8, 1H), 4.91–4.96 (m, 1H), 5.01–5.23 (m, 1H), 5.74–5.99 (m,
1H), 13C-NMR (125 MHz, CDCl3) some signals were overlapped. 139.2, 114.1, 98.8, 67.6, 62.2, 31.8,
30.8, 29.8, 29.6, 29.5, 29.3, 26.2, 25.5. EI-MS: m/z: 267 (M-H), 191.
Dodec-11-en-1-ol (10). To a solution of compound 9 (7.0 g, 26 mmol) in MeOH (100 mL) was added
a catalytic amount of PPTS with stirring. Then the reaction mixture was heated to 50 °C overnight and
monitored by TLC. After completion, the methanol was removed on a rotavapor, And the residue was
purified by column chromagraphy (15–25% gradient, EtOAc-hexane) to give dodec-11-en-1-ol (4.3 g,
1
96% yield) as a colorless oil. H-NMR (500 MHz, CDCl3) 1.27–1.30 (m, 14H) 1.52–1.59 (m, 2H),
2.01–2.06 (m, 2H), 2.10 (br s, 1H), 3.62 (t, J = 6.6, 2H), 4.92 (dd, J = 12.1, 1.6, 1H), 4.98 (dd,
13
J = 17.1, 1.6, 1H), 5.75–5.83 (m, 1H); C-NMR (125 MHz, CDCl3) 139.2, 114.2, 62.90, 33.8, 32.7,
31.9, 29.7, 29.5, 29.4, 29.3, 29.1, 28.9. EI-MS: m/z: 184.
12-Bromododec-1-ene (11). A dry 250 mL three-necked round-bottomed flask was charged with PPh3
(14.7 g, 56 mmol), dichloromethane (80 mL) and CBr4 (22.2 g, 67 mmol) and the mixture was allowed
to stir for 20 min. To the above solution was added compound 10 portionwise at −10 °C. After
completion, the volatiles were removed on a rotavapor, and the residue was purified by column
1
chromagraphy directly to give 12-bromododec-1-ene (11, 90% yield) as a colorless oil. H-NMR
(500 MHz, CDCl3) 1.30–1.35 (m, 14H) 1.35–1.45 (m, 2H), 1.83–1.90 (m, 1H), 2.02–2.08 (m, 1H),
3.62 (t, J = 6.8, 2H), 4.93–4.96 (m, 1H), 5.00 (ddd, J = 21.4, 4.6, 1.6, 1H), 5.75–5.83 (m, 1H);
13C-NMR (125 MHz, CDCl3) 139.2, 114.1, 33.9, 33.8, 32.7, 31.9, 29.7, 29.5, 29.4, 29.3, 29.1, 28.9.
EI-MS: m/z: 247 (M-H), 245, 191, 189.
(S)-14-Methyloctadec-1-ene (1). Under nitrogen atmosphere at 20 °C, Mg turnings (0.2 g, 8.4 mmol),
a catalytic amount of iodine, and anhydrous THF (5 mL) were placed in a dry 250 mL three-necked
round-bottomed flask equipped with a condenser and a dropping funnel. A solution of compound 11
(1.6 g, 6.5 mmol) in THF (50 mL) was added dropwise to the above mixture (approx. 20 min). Then
the mixture was allowed to reflux for another 5 h. Another dry 500 mL three-necked round-bottomed
flask was charged with the chiral intermediate 5 (1.8 g, 6.5 mmol), NMP (2 mL) and Li2CuCl4 (0.3 M
in THF, 2 mL). The above Grignard reagent was transferred to this flask through a double-ended
needle with stirring. After transfer, the reaction mixture was warmed to 85 °C for 3 days. After
cooling, the reaction mixture was quenched by dropwise addition of saturated aqueous NH4Cl solution.

Molecules 2013, 18
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The THF was recovered on a rotavapor and the residue was extracted with ethyl acetate (100 mL × 3).
The combined organic extracts were dried (MgSO4), concentrated in vacuo, and chromatographed to
provide 0.8 g (65%) of pure 1 as a colorless oil. Colorless liquid, [α]2D5 = +1.17° (c 1.82, n-hexane).
1H-NMR (300 MHz, CDCl3): 6.05–5.83 (1H, m), 5.03–4.90 (2H, m), 2.08–2.00 (2H, m), 1.57–1.09
13
(27H, m), 0.93 (6H, m). C-NMR (75 MHz, CDCl3): 139.3, 114.1, 41.6, 35.2, 34.6, 33.8, 31.9, 29.7,
29.6, 29.5, 29.3, 29.17, 29.0, 22.7, 14.1. EI-MS: m/z: 266 (M+, 3%), 43 (100%).
4. Conclusions
In summary, we have completed an asymmetric total synthesis of (S)-14-methyl-1-octadecene, the
sex pheromone of the peach leafminer moth, by chiral oxazolidinone auxiliary induced methylation
and Li2CuCl4 catalytic cross coupling reactions. Compared with the reported syntheses, this process
has several advantages such as high yield, easy operation and cost-effectiveness. This may be helpful
to develop a new generation of affordable pesticides to control peach leafminer moths for Chinese
orchardists in the future.
Supplementary Materials
Supplementary materials can be accessed at: http://www.mdpi.com/1420-3049/18/5/5201/s1.
Acknowledgments
Financial support from the open funding of Key Laboratory of Synthetic Chemistry of Natural
Substances of SIOC as well as the National Natural Science Foundation of China (31270388) is greatly
appreciated. We are grateful to Special Fund for Forestry Scientific Research in Public Interest
(200904004) for partial support of this work.
Conflict of Interest
The authors declare no conflict of interest.
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Sample Availability: Samples of the compounds 1–10 are available from the authors.
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