Practical Synthesis and Field Application of the Synthetic Sex Pheromone of Rice Stem Borer, Chilo suppressalis (Lepidoptera: Pyralidae)

Article abstract of DOI:10.1155/2020/5632534

Rice stem borer, Chilo suppressalis, is a common and major serious pest of rice, maize, and wheat crops across Asia, Europe, and Oceania countries. Its sex pheromone consists of three analogously compounds, i.e., (Z)-hexadec-11-enal (1), (Z)-octadec-13-enal (2), and (Z)-hexadec-9-enal (3), as long-chain aliphatic internal cis-alkenyl aldehydes. In order to perform an economic and widespread pest control management of rice stem borer, a versatile and efficient synthetic strategy is required. A versatile and efficient synthesis using a common synthetic route for cis-alkenals with high overall yields is described. Commercially available inexpensive aliphatic diols were chosen as starting materials. Two key steps were employed to synthesize the long-chain aliphatic internal cis-alkenes in excellent yields, including the alkylation of terminal alkynes without the utilization of a highly polar aprotic cosolvent and the versatile cis-selective semihydrogenation for the reduction of internal alkynes with excellent stereoselectivity. The results of field tests showed that the synthetic sex pheromone blend was highly effective for the capture of rice stem borer.

Full text of DOI:10.1155/2020/5632534

Hindawi
Journal of Chemistry
Volume 2020, Article ID 5632534, 9 pages
https://doi.org/10.1155/2020/5632534
Research Article
Practical Synthesis and Field Application of the Synthetic Sex
Pheromone of Rice Stem Borer, Chilo suppressalis (Lepidoptera:
Pyralidae)
1
,
2
,
3
2
1
2
2
Bin Liu ,
Kun-Jie Syu, Yuan-Xin Zhang, Sachin Gupta , Yu-Jhe Shen,
2
2
1
Wei-Jynn Chien, Jui-Chang Tseng , and Da Wei Lou
1
Department of Analytical Chemistry, Jilin Institute of Chemical Technology, 45 Chengde Street, Jilin 132022, China
Department of Applied Chemistry, Chaoyang University of Technology, 168, Jifeng E. Rd., Wufeng District,
Taichung 41349, Taiwan
2
3
College of Chemistry, Jilin University, 2699 Qianjin Street, Changchun 130012, China
Correspondence should be addressed to Jui-Chang Tseng; jctseng@cyut.edu.tw and Da Wei Lou; dwlou@hotmail.com
Received 6 September 2019; Revised 23 January 2020; Accepted 31 January 2020; Published 21 February 2020
Academic Editor: Claudia Crestini
Copyright © 2020 Bin Liu et al. ꢀis is an open access article distributed under the Creative Commons Attribution License, which
permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Rice stem borer, Chilo suppressalis, is a common and major serious pest of rice, maize, and wheat crops across Asia, Europe, and
Oceania countries. Its sex pheromone consists of three analogously compounds, i.e., (Z)-hexadec-11-enal (1), (Z)-octadec-13-enal
(2), and (Z)-hexadec-9-enal (3), as long-chain aliphatic internal cis-alkenyl aldehydes. In order to perform an economic and
widespread pest control management of rice stem borer, a versatile and efficient synthetic strategy is required. A versatile and
efficient synthesis using a common synthetic route for cis-alkenals with high overall yields is described. Commercially available
inexpensive aliphatic diols were chosen as starting materials. Two key steps were employed to synthesize the long-chain aliphatic
internal cis-alkenes in excellent yields, including the alkylation of terminal alkynes without the utilization of a highly polar aprotic
cosolvent and the versatile cis-selective semihydrogenation for the reduction of internal alkynes with excellent stereoselectivity.
ꢀe results of field tests showed that the synthetic sex pheromone blend was highly effective for the capture of rice stem borer.
of the target drops to form dead hearts and white heads
during the vegetative and reproductive stages [5, 6].
1
. Introduction
Rice, maize, and wheat are three of the most important food
crops in the world and are the primary staple foods for most
of world population [1]. According to Food and Agricultural
Organization of the United Nations, rice, maize, and wheat
are three of the top four world’s most produced crops, with
Asia and Americas constituting the largest consuming and
producing regions and India and China being the top two
largest countries for rice cultivation in the world [2, 3].
However, the infestation by agricultural pests, especially by
rice stem borer, is a major concern for farmers of rice, maize,
and wheat crops worldwide [4]. ꢀe rice stem borer, Chilo
suppressalis, is a common and major serious pest of rice,
maize, and wheat crops that causes extensive crop damage
and yield loss and is widely distributed in Asia, Europe, and
Oceania countries. It attacks the stems, leaves, and panicles
Introduction of improved rice varieties in the 1960s
embraced chemical insecticides and pesticides as a prom-
inent technology of agricultural revolution [7]. ꢀereafter,
four different methods have been employed to control the
pest population since 1970, i.e., agricultural control, bio-
logical control, chemical control, and breeding and growing
of resistant varieties [8, 9]. Regarding the efficiency and
effectiveness of the pest control method, chemical control is
still the main strategy for insect pest control. However, the
sporadically abuse of chemical pesticides has resulted in
serious environmental pollution, increased pesticide resis-
tance, and severe threat to human health due to pesticide
residue [10, 11]. In order to achieve a green and sustained
agricultural environment and to reduce the utilization fre-
quency and dosage of chemical pesticides, as well as to

2
Journal of Chemistry
ensure environmental and crop safety while controlling the
pest population, the application of biological pheromone-
based pest control methods serves as powerful alternative
pest management strategies with safer and environmentally
friendly concerns, thereby grabbing attention of organic
chemists, entomologists, and ecologists [12]. Moreover, the
development of convenient and highly effective formulation
of pheromone-based pest control products is currently a
very important task for integrated pest management and
biological pesticides. Pheromone-based pest control
methods exhibit several fascinating advantages; for example,
insect sex pheromones are species-specific and effective in
very small dosages, do not develop chemical resistance, and
are nontoxic and applicable without spreading. However,
regarding to their drawbacks, pheromone-based pest
managements should be applied to large areas in order to
achieve the acceptable economic and effective level of pest
controls.
16
11
1
O
1
(Z11-16:Ald)
18
13
1
O
2
(Z13-18:Ald)
9
16
1
O
3 (Z9-16:Ald)
Figure 1: Sex pheromone components of rice stem borer, Chilo
suppressalis.
[
25, 26], while 2 and 3 were also synthesized via the ozo-
nolysis of 1,5-cyclooctadiene [27].
Since we are in need of large quantity of the sex pher-
omone of rice stem borer and the corresponding long-term
effective pheromone lure for its application and develop-
ment to the effective pest control of rice stem borer, we have
designed an efficient retrosynthetic plan to afford the desired
long-chain aliphatic internal cis-alkenyl aldehydes 1, 2, and
ꢀe sex pheromone of rice stem borer, Chilo suppressalis,
was first independently identified as a mixture of two aldehyde
components (Z)-hexadec-11-enal (1, abbreviated as Z11-16:
Ald) and (Z)-octadec-13-enal (2, abbreviated as Z13-18:Ald)
by Nesbitt et al. [13] and Ohta et al. [14] in 1975 and 1976,
respectively. It was later found that the attractiveness of the
blend of 1 and 2 was less efficient as compared to the at-
tractiveness by virgin females. Subsequently in 1983, Tatsuki
and coworkers reported the identification of (Z)-hexadec-9-
enal (3, abbreviated as Z9-16:Ald), as the third aldehyde
component of the sex pheromone of rice stem borer [15]. ꢀe
mixture of all three aldehyde components 1, 2, and 3, as shown
in Figure 1, in an approximate ratio of 48 : 6 : 5 [16], or an
alternative very similar ratio of 41 : 5 : 4 [17] was found to be
the most effective in attracting male counterparts of Chilo
suppressalis. However, the chemical compositions of the sex
pheromone of rice stem borer are all chemically unstable
aldehyde compounds, and aldehydes are known to be unstable
upon the exposure of air under sunlight for a long period of
time, which might lead to further oxidation into the corre-
sponding carboxylic acid derivatives. ꢀerefore, in order to
ensure the effectiveness of the pheromone lure of rice stem
borer, a proper formulation including the utilization of ap-
propriate antioxidants to protect this aldehyde blend from
decomposition should be performed.
3
, as shown in 1. Herewith, we report the practical synthesis
of the aldehydes 1, 2, and 3 using a simple six-step synthetic
strategy that is applicable to all three components, as shown
in 2. ꢀe readily available starting materials, i.e., decane-1,8-
diol (7a), dodecane-1,10-diol (7b), and octane-1,12-diol
(
7c), were chosen to make the overall synthesis practical and
inexpensive. In addition, we also report the field application
of the synthetic sex pheromone blend of rice stem borer for
the evaluation of effective duration and attractiveness of the
sex pheromone lure of rice stem borer.
2
. Results and Discussion
2.1.Synthesis. ꢀe chemical structures of the sex pheromone
components 1, 2, and 3 are analogously long-chain aliphatic
internal cis-alkenyl aldehydes, as shown in Figure 1, and can
be synthesized via a common and efficient synthetic plan, as
shown in 3. ꢀe aldehyde moieties of the cis-alkenyl alde-
hydes 1, 2, and 3 can be generated simply by the depro-
tection of the corresponding THP-protected alkenols 4,
followed by the oxidation of primary alcohol into the
aldehyde group. ꢀe key steps for the synthesis of THP-
protected alkenols 4 involve the alkylation of terminal
alkynes and cis-selective semihydrogenation to furnish
pure cis-fashioned internal alkenes. ꢀe counterparts for the
alkylation of terminal alkynes, i.e., 1-hexyne and 1-octyne,
were the THP-protected bromoalcohols 6, which can be
obtained from the corresponding symmetrical diols 7
(Schemes 1 and 2).
ꢀe synthesis of THP-protected bromoalcohols 6 was
started with the monobromination of the symmetrical diols
7. Treatment of diols 7 with 48% HBr in refluxing toluene
afforded the mono-brominated alcohols 8. ꢀe isolated
yields of alcohols 8a, 8b, and 8c were 90%, 85%, and 91%,
respectively. ꢀe hydroxyl groups of the mono-brominated
alcohols 8 were protected with DHP in the presence of
catalytic amount of PTSA to yield the THP-protected
ꢀ
e costs for the chemical substances of insect sex
pheromones are usually very expensive or some chemical
substances are not commercially available, especially those
with complicated chemical structures or specific stereo-
chemistry. In order to control the population of rice stem
borer ecofriendly and to reduce the cost for the manufacture
of pheromone-based biocontrol products, the development
of the practical synthesis of all three aldehyde components of
its sex pheromone is quite essential. Mestres and coworkers
had previously reported the synthesis of the dioxolane de-
rivatives of aldehydes 1, 2, and 3, which can serve as the
corresponding precursors of the final sex pheromone
components [18]. Aldehyde 1 and/or 2 has previously been
synthesized by several groups, mainly using Wittig reaction
for the formation of cis-fashioned alkene double bond
[19–24]. In addition, 3 was synthesized by few other groups

Journal of Chemistry
3
O
1. Deprotection
. Oxidation
OTHP
cis-Selective
m
n
m
n
2
Semihydrogenation
1
2
3
(n = 8, m = 2)
(n = 10, m = 2)
(n = 6, m = 4)
4a (n = 8, m = 2)
4b (n = 10, m = 2)
4c (n = 6, m = 4)
Alkylation of
terminal alkyne
Br
OTHP
m
OTHP
+
m
n
n
5
5
5
a (n = 8, m = 2)
b (n = 10, m = 2)
c (n = 6, m = 4)
1-Hexyne (m = 2)
1-Octyne (m = 4)
6a (n = 8)
6b (n = 10)
6c (n = 6)
Scheme 1: Retrosynthetic analysis for internal cis-alkenyl aldehydes 1, 2, and 3.
Br
OTHP
4
8% HBr
PhMe, refux, 16h
DHP, cat. PTSA·H O
HO
OH
Br
OH
2
n
n
n
CH2Cl2, RT, 16h
6
6
6
a (n = 8)
b (n = 10)
c (n = 6)
7
7
7
a (n = 8)
b (n = 10)
c (n = 6)
8a (n = 8)
8b (n = 10)
8c (n = 6)
1
2
. n-BuLi, THF, 0°C, 1h
. Alkyl bromides 6 (6a, 6b or 6c)
m
OTHP
Pd(OAc) , KOH
2
m
n
DMF, 145°C, 16h
NaI, refux, 16h
1
1
-Hexyne (m = 2)
-Octyne (m = 4)
5a (n = 8, m = 2)
5b (n = 10, m = 2)
c (n = 6, m = 4)
5
O
cat. PTSA·H O
OH
PCC
CH Cl
OTHP
2
m
n
m
n
m
n
MeOH
RT, 16h
2
2
1
2
3
(n = 8, m = 2)
(n = 10, m = 2)
(n = 6, m = 4)
RT, 4h
4
4
4
a (n = 8, m = 2)
b (n = 10, m = 2)
c (n = 6, m = 4)
9a (n = 8, m = 2)
9b (n = 10, m = 2)
9c (n = 6, m = 4)
Scheme 2: Efficient synthesis of sex pheromone components 1, 2, and 3.
bromoacetals 6. ꢀe isolated yields of THP-protected bro-
moacetals 6a, 6b, and 6c were 92%, 90%, and 88%, re-
spectively. It is noteworthy that THP-protected
bromoacetals 6 were stable in further steps and were easy to
undergo deprotection in acidic conditions.
cosolvents is usually required in stoichiometric or excess
quantities. As a result, the cost for the synthesis of sex pher-
omone substances and for the pest control management is
significantly increased and unaffordable. In addition, the iodide
anion plays an important bifunctional role, since iodide can
serve as a good nucleophile to replace the bromo substituent of
bromoacetals 6 and thus also serve as a good leaving group for
the further alkylation reactions.
ꢀe second crucial step involves the pure cis-selective
semihydrogenation of the internal alkynes 5. Since Wittig
olefination has been a prominent organic reaction for the
construction of internal cis-double bond [30, 31], the
practical utilization of Wittig olefination usually suffer with
some difficulties; e.g., the stereoselectivity of Wittig reaction
to obtain the pure long-chain cis-alkene isomer is practically
not easy to control, the phosphonium salt precursor is
gummy and usually leads to the remaining of undesired
solvent residue and the low yield of product isolation, and
equivalent phosphine oxide byproducts produced often
limits the practical application of this method. ꢀerefore,
catalytic transfer semihydrogenation of internal alkynes 5a,
5b, and 5c was performed to obtain cis-selective internal
ꢀereafter, in the further stage of the synthesis, crucial
modifications consist of two key steps were required to generate
stereoselectively the long-chain aliphatic internal cis-alkenes 4.
In the first crucial step, by employing the method reported by
Buck and Chong [28] or our modified procedure [29], terminal
alkynes, i.e., 1-hexyne and 1-octyne, were treated with n-BuLi at
°
0
C in anhydrous THF, which resulted in the formation of the
corresponding acetylide intermediates. After anhydrous solid
NaI was added to the acetylide intermediates, the solution of the
correlated THP-protected bromoacetals 6 in THF was injected
followed by refluxing overnight to afford the corresponding
internal alkynes 5. ꢀe isolated yields of internal alkynes 5a, 5b,
and 5c were 88%, 80%, and 85%, respectively. It is well known
that S 2 nucleophilic substitution can be significantly facilitated
N
upon the utilization of highly polar aprotic cosolvents, e.g.,
hexamethylphosphoramide (HMPA) or N,N′-dimethylpropy-
lene urea (DMPU); however, the amount of these polar aprotic

4
Journal of Chemistry
Table 1: Comparison of the attractiveness of different sex pheromone lures for capturing male rice stem borer in Changhua in 2015.
Pest captured (heads)
First day of date range
end date 02/07)
Interval days Cumulative days Cumulative rainfall
Total pest count
(heads)
Plastic capillary
lure (TG-A)
Paste lure
(TG-B)
(
(days)
(days)
(mm)
2
3
0
1
2
0
1
1
2
3/04–
0/04–
7/05–
4/05–
8/05–
4/06–
1/06–
8/06–
5/06–
7
7
7
0.0
24.5
61.0
398.5
52.5
30.0
8.0
21.5
2.5
598.5
82
65
188
81
147
380
265
232
170
247
171
113
168
1,893
14
21
35
42
49
56
63
70
70
192
†
7
184
†
14
7
117
38
115
†
132
†
7
55
192
†
†
7
36
135
96
7
17
8
729
7
160
Total
70
1164
†
Bird captured inside the wing sticky trap.
alkenes 4a, 4b, and 4c, respectively, thereby eliminating the
use of Wittig reaction [32–37, 38].
capillary lures (TG-A) was 729 heads, whereas that of the long-
term releasing paste lures (TG-B) was 1164 heads. No insect
pest was captured by the blank control trap. ꢀe results sug-
gested that the synthetic sex pheromone blend was effective with
no repellent chemical contained. After the application in paddy
field for two months, the attractiveness of long-term releasing
paste lure was still of satisfactory to attract the male rice stem
borer effectively without the decrease of attractiveness. How-
ever, during the last few weeks of field test, the attractiveness of
plastic capillary lure appeared to undergo a descending trend. In
addition, since the sex pheromone blend in the plastic capillary
lure was not encapsulated, the plastic capillary lure was indeed
to exhibit slightly better attractiveness in the first few weeks as
compared with the long-term releasing paste lure. It is note-
worthy that there were several “bird-captured situations”
happened during the field test period, as shown in Table 1. ꢀe
reasonable explanation for this situation might be that the
captured insect pest was treated as bird feed by those bird
victims.
ꢀ
e semihydrogenation using molecular hydrogen in the
presence of the Lindlar catalyst for the cis-selective reduction
of internal alkynes into cis-alkenes is an important tradi-
tional organic transformation [38], and the reduction is
often results in overreduced byproducts. ꢀerefore, the cis-
selective semihydrogenation of alkynes 5 was performed
using 2 mol% of Pd(OAc) in the presence of 1.5 equiv of
2
°
KOH in DMF at 145 C in a thick-walled sealed tube, which
is considered to be a more versatile and safe hydrogenation
process with excellent stereoselectivity [32]. It was found
that the freshly distilled DMF gave better yields, compared
with the undistilled DMF, and the cis-alkenes 4a, 4b, and 4c
were obtained in 81%, 76%, and 87% yields, respectively.
ꢀ
e resulting alkenes 4 were then subjected to the
deprotection conditions in the presence of catalytic amount
of PTSA in MeOH to afford the corresponding enols 9. ꢀe
isolated yields of enols 9a, 9b, and 9c were 92%, 80%, and
8
6%, respectively. ꢀese alcohols were then subjected to
PCC oxidation in presence of Celite in CH Cl as the solvent,
2
2
2
.2.2. Field Test in Jilin in 2018. In order to test the at-
and the desired aldehyde components 1, 2, and 3 were
tractiveness activity of the synthetic sex pheromone blend,
synthesized at Chaoyang University of Technology in Tai-
wan, that can be utilized as the attractant for the male rice
stem borer distributed in Jilin, the treatment group A, Trap
obtained in 89%, 84%, and 93% crude yields, respectively.
ꢀ
e purpose for the utilization of Celite was to prevent the
formation of inorganic lumps and to serve as an inorganic
carrier for the PCC reagent. ꢀe final sex pheromone
components 1, 2, and 3 were further purified using
Kugelrohr distillation to afford colorless oils in approxi-
mately 60%–80% recovery yields.
1
–10, was conducted first from 27th June to 11th July. ꢀe
total amount of male rice stem borer captured by these traps
baited with the synthetic sex pheromone blend reached 407
heads in 15 days, and the results showed that the synthetic
pheromone blend exhibited biological activity to attract the
male rice stem borer.
2
2
.2. Field Tests
ꢀ
e captured insect pest count of rice stem borer for the
.2.1. Field Test in Taiwan in 2015. Since the damage and the
field test in Jilin is shown in Table 2. ꢀe total number of the
male rice stem borer captured by sex pheromone traps 1–10
and 11–20 from 11th July to 20th September reached 2566
and 2774 heads, respectively. ꢀe duration with large
amount of trapped male rice stem borers were almost co-
incided with the mass occurrence period of rice stem borer
in Jilin. It is noteworthy that synthetic sex pheromone blend
not only can be used for mass trapping of rice stem borer,
but also can serve as an excellent tool for the forecasting of
the population of rice stem borer.
crop loss caused by rice stem borer was more severe during
the first rice harvest period in Taiwan, the attractiveness
activity of the synthetic sex pheromone blend was first
evaluated in the paddy field in Changhua County during the
period of 23rd April to 2nd July in 2015. ꢀe insect pest
count of rice stem borer for this field test in Taiwan is shown
in Table 1.
During the date range between 23rd April and 2nd July, the
total amount of male rice stem borer captured by the plastic

Journal of Chemistry
5
Table 2: ꢀe pest count of male rice stem borer captured using the paste lure of the synthetic sex pheromone blend in Jilin in 2018.
Pest captured (heads)
Trap 1–10 Trap 10–20
First day of date range (end date 20/09) Interval days (days) Cumulative days (days)
Total pest count (heads)
1
2
1
1
1/07–
6/07–
1/08–
9/08–
15
15
8
12
21
71
15
30
38
50
71
71
97
372
1112
896
89
125
507
1089
957
96
222
879
2201
1853
185
3
1/08–
Total
2566
2774
5340
3
. Conclusion
including octane-1,8-diol (4), decane-1,10-diol (5), dodec-
ane-1,12-diol (6), 1-hexyne, 1-octyne, hydrobromic acid,
sodium iodide, potassium hydroxide, 3,4-dihydropyran
In summary, we have developed a versatile and common
synthetic strategy for the synthesis of three analogously long-
chain aliphatic internal cis-alkenyl aldehydes 1, 2, and 3, as
the sex pheromone components of rice stem borer, Chilo
suppressalis. ꢀe modified synthesis of three cis-alkenyl al-
dehydes was accomplished in six steps, involving mono-
bromination of diols, THP-protection, alkylation of terminal
alkyne, cis-semihydrogenation, THP-deprotection, and
oxidation, with the overall yield of 48%, 31%, and 47% for
the sex pheromone components 1, 2, and 3, respectively. ꢀe
synthesis started with the monobromination of diols 7,
followed by the THP-protection of the remaining hydroxyl
group to yield the corresponding THP-protected bromoa-
cetals 6. Two key steps were required to generate the long-chain
aliphatic internal cis-alkenes 4 in excellent cis-stereoselectivity,
including the alkylation of the terminal alkyne under greener
conditions without the utilization of highly polar aprotic
cosolvents, and the versatile pure cis-selective semi-
hydrogenation process with excellent stereoselectivity for
the reduction of long-chain aliphatic internal alkynes 5.
Using this synthetic strategy, the sex pheromone compo-
nents 1, 2, and 3 can be obtained more practically in large
quantities and can be subjected to the practical pest control
of rice stem borer. ꢀe field tests performed in Changhua,
Taiwan, suggested that the synthetic sex pheromone blend
was effective. Since the sex pheromone blend in the long-
term releasing paste lure was encapsulated, the attractiveness
was competitive in the first few weeks as compared with the
plastic capillary lure. ꢀe attractiveness of long-term re-
leasing paste lure can last for at least two months to attract
the male rice stem borer effectively without the decrease of
attractiveness, whereas that of the plastic capillary lure
appeared to undergo a descending trend after one month of
field application. ꢀe field test results obtained in Jilin
showed the coincided match with the mass occurrence
period of rice stem borer in northern east of China. ꢀe
synthetic sex pheromone blend of rice stem borer not only
can be used for mass trapping but also can serve as an
excellent tool for the monitoring of the pest distribution.
(DHP), p-toluenesulfonic acid monohydrate (PTSA·H O),
2
and pyridinium chlorochromate (PCC) were purchased
from Alfa Aesar. Palladium acetate and Lindlar catalyst were
purchased from Strem Chemicals. n-BuLi was purchased as
a 2.5 M solution in n-hexane from Sigma-Aldrich or
Chemetall. Organic solvents including toluene, dichloro-
methane, and methanol were purchased from DUKSAN
Chemicals and used without prior drying procedure. Tet-
rahydrofuran and N,N-dimethylformamide were purchased
from Avantor and were dried by distillation using sodium-
benzophenone ketyl and calcium hydride, respectively.
ꢀ
e proton and carbon-13 nuclear magnetic resonance
NMR) spectra were recorded on a Varian Gemini 200 MHz
NMR spectrometer at ambient temperature. Chemical shift
(
(
δ) and coupling constant (J) were expressed in unit of ppm
and Hz, respectively. Samples for NMR measurements were
dissolved in CDCl , and the CHCl residue in the corre-
3
3
sponding deuterated solvent was used as the internal
standard. ꢀe chemical shift of CHCl was calibrated at δ
3
1
13
7
.26 ppm in H NMR spectra and δ 77.0 ppm in C NMR
spectra.
ꢀ
in-layer chromatography (TLC) was performed on
Merck 25 TLC aluminum sheets (silica gel 60 F ). ꢀe
2
54
developed TLC sheets were visualized under UV light
(
254 nm) or by using appropriate TLC stains, e.g., ethanolic
phosphomolybdic acid solution or potassium permanganate
solution. Column chromatography was performed on Merck
silica gel 60 (70–230 mesh), and Merck silica gel 60 (230–400
mesh) was used for flash column chromatography.
4
.1.2. General Synthesis Procedure for Bromoalcohols 8a, 8b,
and 8c. To a stirred solution of diol 7 (300 mmol, 1.0 equiv)
in toluene (600 mL) was added slowly 48% HBr (360 mmol,
°
1
.2 equiv) at RT. ꢀe reaction mixture was refluxed at 120 C
°
for 16 h. After cooling to 0 C for 30 min, the organic layer
was separated and washed with saturated NaHCO solution.
3
ꢀ
e resulting aqueous layer was extracted with hexane
(
120 mL × 3). ꢀe combined organic layer was washed with
brine (300 mL), dried over anhydrous MgSO , filtered, and
4
4
. Experimental Section
concentrated in vacuo to obtain the corresponding bro-
moalcohol 8 as a light yellow oil. ꢀe crude bromoalcohol 8
was employed in the next step without further purification.
Bromoalcohols 8a, 8b, and 8c were synthesized indepen-
dently according to the general procedure with 90%, 85%,
4.1. Synthesis
4
.1.1. General Techniques and Materials. All substrates and
reagents were purchased as reagent grade from commercial
suppliers and used as received. Substrates and reagents
1
and 91% yields, respectively. H NMR (200 MHz, CDCl
3
,

6
Journal of Chemistry
ppm) for 8a: δ 3.63 (t, J � 6.5 Hz, 2H), 3.40 (t, J � 6.8 Hz, 2H),
4.1.5. General Synthesis Procedure [29, 32] for cis-Alkenes 4a,
4b, and 4c. To a mixture of internal alkyne 5 (100 mmol, 1.0
equiv), ground KOH powder (150 mmol, 1.5 equiv), and
1.90–1.75 (m, 2H), 1.55–1.40 (m, 3H), 1.40–1.20 (m, 12H);
1
3
C NMR (100 MHz, CDCl , ppm) for 8a: δ 62.54, 33.76,
3
3
2.66, 32.53, 29.33, 29.24, 29.21, 28.58, 27.99, 25.59.
catalytic amount of Pd(OAc) (2 mmol, 2 mol%) in a thick-
2
walled Pyrex seal tube was added degassed DMF (70 mL).
ꢀ
e tube was sealed, and the mixture was stirred vigorously
4
.1.3. General Synthesis Procedure for THP-Protected Bro-
°
at 145 C for 16 h. After the reaction mixture was cooled to
RT, the seal tube was opened carefully inside a hood with
good ventilation. ꢀe resulting reaction suspension was
filtered through a Celite bed (3 cm), and the cake was washed
repeatedly with n-hexane (300 mL). ꢀe combined filtrate
was washed with water (150 mL × 5) in order to remove
DMF. ꢀe combined aqueous layer was extracted with n-
hexane (200 mL × 3). ꢀe combined organic layer was
moacetals 6a, 6b, and 6c. To a stirred solution of bro-
moalcohol 8 (200 mmol, 1.0 equiv) and PTSA·H O (2 mmol,
2
1
1
.0 mol%) in CH Cl (250 mL) was added DHP (240 mmol,
2 2
°
.2 equiv) dropwise at 0 C. After the addition of DHP was
°
complete, the reaction mixture was stirred at 0 C for 30 min
and then stirred at RTfor 16 hr. Saturated NaHCO solution
3
(
100 mL) was added to the reaction mixture and stirred for
1
0 min to quench the reaction. ꢀe organic layer was sep-
washed with brine (300 mL), dried over anhydrous MgSO ,
4
arated, and the aqueous layer was extracted with n-hexane
filtered, and concentrated in vacuo to afford cis-alkene 4 as a
dark brown oil. ꢀe crude cis-alkene product was purified by
column chromatography over silica gel with 10% n-hexane/
ethyl acetate as a eluent to give pure cis-alkene 4 as a yellow
oil. Alkenes 4a, 4b, and 4c were synthesized independently
according to the general procedure with 81%, 76%, and 87%
(
50 mL × 3). ꢀe combined organic layer was washed with
brine (250 mL), dried over anhydrous MgSO , filtered, and
4
concentrated in vacuo to obtain the corresponding THP-
protected bromoacetal 6 as a light yellow oil. ꢀe crude
bromoacetal 6 was purified by Kugelrohr distillation. Bro-
moacetals 6a, 6b, and 6c were synthesized independently
1
yields, respectively. H NMR (200 MHz, CDCl ppm) for 4a:
3,
according to the general procedure with 92%, 90%, and 88%
1
δ 5.40–5.30 (m, 2H), 4.59–4.52 (m, 1H), 3.92–3.62 (m, 2H),
yields, respectively. H NMR (200 MHz, CDCl , ppm) for 6a:
3
3
.52–3.30 (m, 2H), 2.05–1.90 (m, 4H), 1.80–1.42 (m, 2H),
δ 4.60–4.52 (m, 1H), 3.92–3.60 (m, 2H), 3.55–3.30 (m, 4H),
13
13
1.40–1.16 (m, 24H), 0.94–0.80 (m, 3H). C NMR (100 MHz,
1
.90–1.70 (m, 4H), 1.65–1.20 (m, 18H). C NMR (100 MHz,
CDCl , ppm) for 4a: δ 129.80, 129.75, 98.38, 67.60, 62.21,
3
CDCl , ppm) for 6a: δ 98.62, 67.44, 62.10, 33.77, 32.66, 30.61,
3
3
2
1.90, 30.72, 29.70, 29.64, 29.60, 29.54, 29.52, 29.48, 29.23,
2
9.57, 29.29, 29.26, 29.21, 28.58, 27.99, 26.06, 25.36, 19.53.
7.12, 26.84, 26.18, 25.46, 22.75, 19.62, 13.93.
4
.1.4. General Synthesis Procedure [28] for Internal Alkynes
4
.1.6. General Synthesis Procedure for Alkenols 9a, 9b, and 9c.
5
a, 5b, and 5c. ꢀe appropriate terminal alkyne substrate 1-
A mixture of alkene 4 (160 mmol, 1.0 equiv) and PTSA·H O
2
hexyne was used for the preparation of internal alkynes 5a
and 5b, whereas the synthesis of internal alkyne 5c required
the utilization of 1-octyne as the terminal alkyne source.
(
8 mmol, 5 mol%) in MeOH (300 mL) was stirred at RT for
1
6 h. After the evaporation of MeOH, the residue was treated
with 1 M HCl solution (300 mL) and extracted with n-
hexane (250 mL × 3). ꢀe combined organic layer was
Under N atmosphere, a solution of 2.5 M n-BuLi in
2
hexane (360 mmol, 1.2 equiv) was introduced dropwise to a
stirred solution of the terminal alkyne (1-hexyne or 1-octyne,
washed with brine (300 mL), dried over anhydrous MgSO ,
4
filtered, and concentrated in vacuo to afford alkenol 9 as a
pale yellow oil. ꢀe crude product was used directly for the
next reaction without further purification. Alkenols 9a, 9b,
and 9c were synthesized independently according to the
°
3
15 mmol, 1.05 equiv) in THF (150 mL) at –30 C. ꢀe re-
°
action mixture was warmed to 0 C and stirred for 1 h. To this
reaction mixture was added anhydrous solid NaI (45 mmol,
0
.15 equiv) and freshly distilled bromoacetal 6 (300 mmol,
.0 equiv) at RT. ꢀe resulting mixture was refluxed for 16 h.
general procedure with 92%, 80%, and 86% yields, respec-
1
1
tively. H NMR (200 MHz, CDCl , ppm) for 9a: δ 5.35 (t,
3
After cooling to RT, the reaction was quenched with sat-
J � 4.5 Hz, 2H), 3.64 (t, J � 6.5 Hz, 2H), 2.08–1.88 (m, 4H),
urated NaHCO solution (300 mL). ꢀe organic layer was
3
1
.68–1.40 (m, 4H), 1.40–1.16 (m, 16H), 0.92–0.80 (m, 3H);
separated, and the aqueous layer was extracted with n-
hexane (200 mL × 3). ꢀe combined organic layer was
13
C NMR (100 MHz, CDCl , ppm) for 9a: δ 29.89, 129.86,
3
6
2
3.01, 32.87, 31.66, 29.78, 29.60, 29.52, 29.44, 29.36, 29.22,
7.24, 26.96, 25.82, 22.71, 14.15.
washed with brine (300 mL), dried over anhydrous MgSO ,
4
filtered, and concentrated in vacuo to afford the corre-
sponding internal alkyne 5 as a light yellow oil. ꢀe crude
product was used directly for next reaction without further
purification. Alkynes 5a, 5b, and 5c were synthesized in-
4.1.7. General Synthesis Procedure for the Desired Alkenals 1,
2, and 3. To a mixture of PCC (104 mmol, 1.3 equiv) and
Celite (25 g) in CH Cl (400 mL) was added dropwise
dependently according to the general procedure with 88%,
2
2
1
8
0%, and 85% yields, respectively. H NMR (200 MHz,
alkenols 9 (80 mmol, 1.0 equiv). ꢀe reaction mixture was
stirred vigorously for 16 h at RT. ꢀe resulting reaction
suspension was filtered through a silica gel plug (10 cm), and
CDCl , ppm) for 5a: δ 4.60–4.52 (m, 1H), 3.92–3.62 (m, 2H),
3
3
0
5
2
1
.55–3.30 (m, 2H), 2.20–2.08 (m, 2H), 1.90–1.20 (m, 28H),
1
3
.90 (t, J � 7.1 Hz, 3H). C NMR (100 MHz, CDCl , ppm) for
the cake was washed repeatedly with Et O (300 mL). ꢀe
3
2
a: δ 98.68, 80.05, 80.01, 67.56, 62.15, 31.18, 30.68, 29.67,
9.62, 29.46, 29.40, 29.29, 29.08, 28.75, 26.16, 25.43, 21.83,
9.57, 18.66, 18.34, 13.54.
combined solution was concentrated in vacuo to afford the
crude product which was subjected to Kugelrohr distillation
to give pure alkenal as a colorless oil. ꢀe desired alkenals 1,

Journal of Chemistry
7
2
, and 3 were synthesized independently according to the
4.2.2. Pheromone Traps. ꢀe commercial available wing
sticky trap with sticky pad was employed for the capture of
rice stem borer and was purchased from Zhen-Yong En-
terprise Ltd., Taiwan. ꢀe wing sticky traps were fixed on a
bamboo stick and were placed close to the edge of the paddy
field with 30 m distance apart from each other. ꢀe elevation
of the pheromone trap was set 20 cm above the top leaves of
rice crops and was adjusted while necessary as the rice crop
grew. Once the pheromone lure was applied to the center of
the wing-type trap cover, no replacement of the cover and no
additional pheromone lure were applied, where the bottom
sticky pad was examined and pest count was recorded every
week. ꢀe bottom sticky pad should be replaced to a new one
when the pad is full of insect pests.
general procedure with 89%, 84%, and 93% yields, respec-
1
tively. 1: H NMR (200 MHz, CDCl , ppm): δ 9.76 (t,
J � 1.9 Hz, 1H), 5.35 (t, J � 4.8 Hz, 2H), 2.42 (dt, J � 1.8,
3
7
.6 Hz, 2H), 2.06–1.90 (m, 4H), 1.72–1.52 (m, 2H), 1.42–1.20
m, 16H), 0.96–0.82 (m, 3H); 1 C NMR (50 MHz, CDCl3,
ppm): δ 202.73, 129.76, 129.70, 43.98, 32.06, 29.83, 29.55,
9.49, 29.44, 29.35, 29.26, 27.28, 27.02, 22.46, 22.20, 14.13.
3
(
2
+
HRMS (ESI) calcd for C H O [M+H] : 238.2297; found:
16
30
1
2
38.2294. 2: H NMR (200 MHz, CDCl , ppm): δ 9.75 (t,
3
J � 1.9 Hz, 1H), 5.35 (t, J � 4.5 Hz, 2H), 2.42 (dt, J � 1.9,
7
.3 Hz, 2H), 2.08–1.90 (m, 4H), 1.72–1.52 (m, 2H), 1.42–1.20
m, 20H), 0.96–0.82 (m, 3H); 1 C NMR (50 MHz, CDCl ,
3
(
3
ppm): δ 202.75, 129.72(2), 43.98, 32.06, 29.86, 29.67(3),
9.52, 29.44, 29.39, 29.26, 27.30, 27.02, 22.46, 22.21, 14.12.
2
+
HRMS (ESI) calcd for C H O [M+H] : 266.2610; found:
16
30
1
4.2.3. Field Test in Taiwan in 2015. In order to prove the
attractiveness of the synthetic sex pheromone components,
the field test was performed during the first rice harvest
period in Taiwan, starting from 23rd April to 2nd July in
2
66.2614. 3: H NMR (200 MHz, CDCl , ppm): δ 9.76 (t,
3
J � 1.8 Hz, 1H), 5.42–5.24 (m, 2H), 2.42 (dt, J � 1.6, 7.4 Hz,
2
1
H), 2.06–1.88 (m, 4H), 1.76–1.50 (m, 2H), 1.46–1.18 (m,
13
6H), 0.96–0.82 (m, 3H). C NMR (50 MHz, CDCl , ppm):
3
2
015. ꢀe rice cultivation area was located in Dacun
δ 202.76, 130.18, 129.83, 44.28, 32.18, 30.14(2), 30.06, 29.65,
Township, Changhua County, Taiwan. ꢀis field test area
was approximately 0.26 ha (96 m × 27 m). ꢀe north, the
east, and the south sides were surrounded by paddy fields,
and the west was close to an 8 meter wide road next to other
paddy fields. Two different treatment groups and one blank
control group were applied to the field test. ꢀe number of
the plastic capillary lure group (Treatment Group A, TG-A),
the paste lure group (Treatment Group B, TG-B), and blank
control group (CK) were set to be 3 : 3 :1, due to the limi-
tation of the rice cultivation area in Taiwan. ꢀe position of
all wing sticky traps was switch clockwise every two weeks.
2
9.54, 29.45, 29.40, 27.64, 23.08, 22.50, 14.55. HRMS (ESI)
+
calcd for C H O [M+H] : 238.2297; found: 238.2299.
1
6
30
4
4
.2. Field Tests
.2.1. Pheromone Lures. ꢀe sex pheromone blend of rice
stem borer was prepared by mixing the aldehyde com-
ponents 1, 2, and 3 in an exact ratio of 48 : 6 : 5 by weight
[16] and was used for the preparation of sex pheromone
lures, e.g., conventional plastic capillary lure and long-
term releasing paste lure. ꢀe quantities of the sex pher-
omone blend of rice stem borer contained in each plastic
capillary lure and long-term releasing paste lure were
controlled to be 0.85 mg.
4
.2.4. Field Test in Jilin in 2018. A collaborated field test was
carried out in a rice cultivation area from 11th July to 20th
September in 2018 in Jilin, the northeastern province in
China, where rice stem borer is the most significant insect
pest of rice crops. ꢀe field test area was approximately
ꢀ
e preparation procedure of the plastic capillary is
described below, whereas the long-term releasing formu-
lation was obtained by sending the pheromone blend to
Pheromone Center, Chaoyang University of Technology,
and was performed according to the well-known micro-
encapsulation process using modified interfacial polycon-
densation strategy [39, 40]. ꢀe long-term releasing lure
provided by Pheromone Center was packaged into a 4 g
weight ointment tube and appeared as a brown paste. For
each of the pheromone trap for rice stem borer, the required
amount of the pheromone paste lure was approximately 0.1 g
with an applied length of ca. 1.0 cm of the very paste, which
as described earlier has 0.85 mg of the sex pheromone blend
of rice stem borer.
3
.3 ha (300 m × 110 m), of which 1.8 ha was treated with sex
pheromone traps and 0.9 ha was left untreated. ꢀe north
and the west were surrounded by paddy fields, the south was
next to a soybean field, and the east was close to a road. ꢀe
number of the paste lure group and blank control group was
set to be 20 :10.
Data Availability
ꢀ
e data used to support the findings of this study are in-
cluded within the article.
ꢀ
e conventional plastic capillary lure using the syn-
Conflicts of Interest
thetic sex pheromone blend was also prepared by Phero-
mone Center, Chaoyang University of Technology,
according to the following procedure. ꢀe freshly prepared
sex pheromone blend of rice stem borer was diluted with
hexane to an appropriate concentration. To the center a of
ꢀ
e authors declare that they have no conflicts of interest.
Acknowledgments
6
cm long plastic capillary was injected 5 μL of the hexane
ꢀe authors thank the Pheromone Center of Chaoyang
University of Technology for technical assistance for the
preparation of long-term releasing paste lures and valuable
solution of the sex pheromone blend , and then both ends of
the corresponding plastic capillary were sealed.

8
Journal of Chemistry
instruction for field tests. ꢀe authors gratefully acknowl-
edge financial support of this work by the Project of Science
and Technology Development of Jilin Province
Pyralidae): the third component, Z-9-hexadecenal,” Applied
Entomology and Zoology, vol. 18, no. 3, pp. 443–446, 1983.
[
16] S. Tatsuki, “Status of application of sex pheromone of rice
stem borer moth, Chilo suppressalis in Japan,” International
Journal of Tropical Insect Science, vol. 11, no. 4-5, pp. 807–812,
(
20190303116SF). Financial support from the Key Labora-
tory of Fine Chemicals of Jilin Province is also
acknowledged.
1990.
[
17] J. W. Su, W. J. Xuan, C. F. Sheng, and F. Ge, “Suppression of
rice stem borer, Chilo suppressalis by mass trapping using
synthetic sex pheromone in paddy field,” Rice Science, vol. 11,
pp. 52–56, 2003.
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