A method for asymmetric synthesis of the sex pheromone of Phenacoccus solenopsis Tinsley

Abstract

The present invention belongs to the technical field of biopesticides, and discloses a new method for asymmetric synthesis of the sex pheromone of Phenacoccus solenopsis Tinsley. This method utilizes the asymmetric Kumada coupling reaction of vinyl Grignard reagent and benzyl bromopropionate catalyzed by bisoxazoline / Co(II) to prepare cinnamic acid benzyl ester 4, and then through Pd / C-catalyzed hydrogenation to prepare (S)-2-methylbutyric acid (5); furthermore, using (R)-4-phenyloxazolidin-2-one (7) as a chiral auxiliary to react with in-situ generated 3-methyl-2-butenoic anhydride to prepare oxazolidinone amide 8, then reacting with 3-methyl-1-bromo-2-butene (9) to prepare isopentenyl oxazolidinone amide 10, then using LiAlH4 reduction to obtain (R)-lavandulol, and finally reacting with (S)-2-methylbutyric acid to prepare the sex pheromone of Phenacoccus solenopsis Tinsley, namely (S)-2-methylbutyric acid (R)-lavandulyl ester (1). The present invention constructs the chiral methyl group of the carboxylic acid part by cobalt-catalyzed asymmetric Kumada coupling reaction, and constructs the chiral isopentenyl group of the alcohol part by Evans chiral induction method, with advantages such as mild reaction conditions and simple synthesis route.

Description

Technical Field

[0001] The present invention relates to the technical field of biopesticides, and particularly relates to a new method for asymmetric synthesis of the sex pheromone of Maconellicoccus hirsutus. Background Art

[0002] Maconellicoccus hirsutus is a polyphagous pest that mainly damages various plants such as mulberry, hibiscus, grape, citrus, soybean, and corn. By sucking the sap of young tissues such as the leaves, stems, and fruits of host plants, it secretes honeydew to induce "sooty mold", resulting in leaf wilting and fruit drop (Wu Fuzhong; Li Huiping; Fu Haibin. Acta Entomologica Sinica 2020, 42, 760. Liu Danzhu; Zhang Meng; Gao Yu; Cui Juan; Shi Shusen. Soybean Science 2016, 35, 649.). Zhang et al. identified the active components of its sex pheromone as (S)-2-methylbutyric acid (R)-nerolidyl ester and (S)-2-methylbutyric acid (R)-lavandulyl ester (1), and field experimental studies have shown that this sex pheromone has the biological activity of attracting male insects (Zhang, A.; Amalin, D.; Shirali, S.; Serrano Miguel, S.; Franqui Rosa, A.; Oliver James, E.; Klun Jerome, A.; Aldrich Jeffrey, R.; Meyerdirk Dale, E.; Lapointe Stephen, L. Proc Natl Acad Sci US A 2004, 101, 9601. Zhang, A.; Amalin, D. Environmental Entomology 2005, 34, 264.). Using insect sex pheromones for pest control has advantages such as low dosage, safety to the environment and natural enemies, and difficulty in generating resistance (Xia, Y.-H.; Ding, B.-J.; Dong, S.-L.; Wang, H.-L.; Hofvander, P.; Loefstedt, C. BMC Biology 2022, 20, 80.). Therefore, it is of great significance to study the asymmetric synthesis of the sex pheromone 1 of Maconellicoccus hirsutus (Formula 1). Currently, the reported synthesis methods mainly include the chiral auxiliary method, the chiral source method, and the asymmetric catalysis method.

[0003]

[0004] (1) In 2005, Zhang et al. used (4S,5R)-1,5-dimethyl-4-phenylimidazolidin-2-one as a chiral auxiliary, obtained (R)-lavandulol through acylation, asymmetric alkylation and LAH reduction, and then prepared (R)-lavandulyl (S)-2-methylbutyrate by esterification with (S)-2-methylbutyric acid (Zhang, A.; Nie, J. Journal of Agricultural and Food Chemistry 2005, 53, 2451.).

[0005] (2) In 2013, Fernandes et al. used (R)-isopropylidene glyceraldehyde as a chiral source, obtained (R)-lavandulol through 7 steps of reactions including Wittig coupling, DIBAL-H reduction, deprotection, NaIO4 oxidation and NaBH4 reduction, and then prepared (R)-lavandulyl (S)-2-methylbutyrate by esterification with (S)-2-methylbutyric acid (Fernandes, R. A.; Chowdhury, A. K. European Journal of Organic Chemistry 2013, 2013, 5165.)

[0006] (3) In 2017, Bhosale and Waghmode used the asymmetric α-amination reaction of nitrobenzene and 3-benzyloxypropanal catalyzed by D-proline to construct a chiral center, then protected the diol with cyclohexanone, oxidized with DMSO to obtain the key intermediate cyclohexanone acetal glyceraldehyde, and then synthesized (R)-lavandulol through a total of 17 steps of reactions including Wittig coupling, Claisen rearrangement, NaBH4 reduction, protection of primary hydroxyl, ozonolysis, Grignard reagent addition, etc., and finally prepared (R)-lavandulyl (S)-2-methylbutyrate by esterification with (S)-2-methylbutyric acid (Bhosale, V. A.; Waghmode, S. B. ChemistrySelect 2017, 2, 1262.).

[0007] Although the synthesis of the sex pheromone 1 of Phenacoccus solenopsis has been reported in the literature, there are various problems such as cumbersome synthetic routes and harsh reaction conditions. Therefore, it is necessary to develop a new, simple, efficient method for synthesizing the sex pheromone 1 of Phenacoccus solenopsis. SUMMARY OF THE INVENTION

[0008] The present invention aims to provide a new method for synthesizing the sex pheromone 1 of Phenacoccus solenopsis Tinsley. The present invention utilizes the asymmetric Kumada coupling reaction of vinyl Grignard reagent and benzyl bromopropionate catalyzed by bisoxazoline / Co(II) to prepare cinnamic acid benzyl ester 4, and then through Pd / C-catalyzed hydrogenation, (S)-2-methylbutyric acid (5) is obtained; then using (R)-4-phenyloxazolidin-2-one (7) as a chiral auxiliary, reacting with in-situ generated 3-methyl-2-butenoic anhydride to prepare oxazolidinone amide 8, then undergoing an asymmetric alkylation reaction with 3-methyl-1-bromo-2-butene (9) to prepare isopentenyl oxazolidinone amide 10, then reducing with LiAlH4 to obtain (R)-lavandulol, and finally undergoing an esterification reaction with (S)-2-methylbutyric acid to prepare (S)-2-methylbutyric acid (R)-lavandulyl ester (1). The present invention constructs the chiral methyl group of the carboxylic acid part by cobalt-catalyzed asymmetric Kumada coupling reaction and constructs the chiral isopentenyl group of the alcohol part by Evans chiral induction method, with advantages such as mild reaction conditions and a simple synthetic route. The synthetic route for synthesizing the sex pheromone 1 of Phenacoccus solenopsis Tinsley in the present invention is shown in Formula 2.

[0009]

[0010] The method for synthesizing the sex pheromone 1 of Phenacoccus solenopsis Tinsley in the present invention comprises the following steps.

[0011] (1) Synthesis of (S)-benzyl 2-methyl-3-butenoate (4)

[0012] Under argon protection and at room temperature, in a mixture of CoCl2 and LiI, a mixed solution of THF and ligand (S,S)-L was added. Stir at room temperature for 2 h, then cool to -20 °C. Add racemic benzyl 2-bromopropionate (3), and then add a suspension of vinylmagnesium bromide (2). Stir at -20 °C for 48 h, and then stop the reaction. Then, the reaction was quenched, separated, extracted, washed, dried and concentrated in sequence, and finally purified by silica gel column chromatography to obtain (S)-benzyl 2-methyl-3-butenoate (4).

[0013] (2) Synthesis of (S)-2-methylbutyric acid (5)

[0014] Under a hydrogen atmosphere and at room temperature, add MeOH and alkenyl ester 4 to palladium carbon, react at room temperature for 6 h, and then stop the reaction. Filter, concentrate and purify by silica gel column chromatography in sequence to obtain (S)-2-methylbutyric acid (5).

[0015] (3) (R)-4-phenyl-3-(3-methyl-2-butenoyl) oxazolidinone (8) synthesis

[0016] At 0 °C, in a mixed solution of THF and 3-methyl-2-butenoic acid (6), triethylamine and pivaloyl chloride were added dropwise, and the mixture was stirred for reaction for 30 min, then the reaction was stopped. The crude product of 3-methyl-2-butenoic anhydride was obtained by concentration.

[0017] At 0 °C, in a mixed solution of THF and (R)-4-phenyl oxazolidinone (7), n-butyllithium was added, and the mixture was stirred for 10 min. A THF solution of the crude product of 3-methyl-2-butenoic anhydride was added, and the mixture was stirred for reaction at room temperature for 12 h, then the reaction was stopped. Then, the reaction was quenched, liquid separation, extraction, washing, drying and concentration were carried out in sequence, and finally, it was purified by silica gel column chromatography to obtain (R)-4-phenyl-3-(3-methyl-2-butenoyl) oxazolidinone (8).

[0018] (4) Synthesis of (R)-4-phenyl-3-((R)-2-isopropenyl-5-methyl-6-hexenoyl) oxazolidinone (10)

[0019] Under argon protection and at -78 °C, in a mixed solution of oxazolidinone amide 8 and THF, a solution of NaHMDS was added dropwise first, and the mixture was stirred for 1 h; then 3-methyl-1-bromo-2-butene (9) was added dropwise, and the mixture was stirred for reaction for 4 h, then the reaction was stopped. Then, the reaction was quenched, liquid separation, extraction, drying and concentration were carried out in sequence, and finally, it was purified by silica gel column chromatography to obtain (R)-4-phenyl-3-((R)-2-isopropenyl-5-methyl-6-hexenoyl) oxazolidinone (10).

[0020] (5) Synthesis of (R)-lavandulol (11)

[0021] Under argon protection and at 0 °C, in a mixture of lithium aluminum hydride and Et2O, a THF solution of oxazolidinone amide 10 was added dropwise, and the mixture was stirred for reaction at room temperature for 1.5 h, then the reaction was stopped. Then, neutralization, liquid separation, extraction, washing, drying and concentration were carried out in sequence, and finally, it was purified by silica gel column chromatography to obtain (R)-lavandulol (11).

[0022] (6) Synthesis of Phenacoccus solenopsis sex pheromone 1

[0023] Under argon protection and at 0 °C, 2,4,6-trichlorobenzoyl chloride was added to a mixed solution of chiral acid 5, Et3N and toluene, and the mixture was stirred at room temperature for 1.5 h. A toluene solution of 4-dimethylaminopyridine and chiral alcohol 11 were added, and the mixture was stirred for reaction at room temperature for 2.5 h, then the reaction was stopped. Then, the reaction was quenched, liquid separation, extraction, drying and concentration were carried out in sequence, and finally, it was purified by silica gel column chromatography to obtain Phenacoccus solenopsis sex pheromone 1. Specific embodiments

[0024] Example 1

[0025] Synthesis of benzyl (S)-2-methyl-3-butenoate (4)

[0026] Anhydrous CoCl2 (0.013 g, 0.10 mmol) and anhydrous LiI (0.027 g, 0.20 mmol) were placed in a 50 mL Schlenk tube and heated under vacuum at 80 °C for 2 h using a heating mantle. After cooling to room temperature under an argon atmosphere, a mixed solution of anhydrous THF (2 mL) and ligand (S,S)-L (0.057 g, 0.12 mmol) was added. The resulting mixture was stirred at room temperature for 2 h and then cooled to -20 °C. Racemic benzyl 2-bromopropionate (3) (0.061 g, 0.25 mmol) was added via syringe, and then a suspension of vinylmagnesium bromide (2) (1.25 mmol, 1.0 M solution in tetrahydrofuran, 1.25 mmol) diluted with THF (5 mL) was added dropwise via a syringe pump over 2.5 h. The reaction mixture was stirred at -20 °C for 48 h, and the reaction was stopped. The reaction was quenched by adding saturated aqueous NH4Cl solution (3 mL), and the aqueous layer and organic layer were separated. The aqueous phase was extracted with Et2O (3 × 15 mL), and the organic layer and the ether extract were combined. Then it was washed with saturated aqueous NaCl solution (10 mL) and dried over anhydrous Na2SO4. It was concentrated using a rotary evaporator to remove the solvent, and a crude product was obtained. Finally, it was purified by silica gel column chromatography (petroleum ether / ethyl acetate 50:1) to obtain a pale yellow liquid, benzyl (S)-2-methyl-3-butenoate (4) (0.027 g, yield 57%, 90% ee). 1 1H NMR (500 MHz, CDCl3) δ 7.37–7.32 (m, 5H), 5.94 (ddd, J = 17.4, 10.2, 7.4 Hz, 1H), 5.13 (s, 2H), 5.12–5.10 (m, 2H), 3.24 –3.18 (m, 1H), 1.30 (d, J = 7.0 Hz, 3H); 13 13C NMR (126 MHz, CDCl3) δ 174.31, 137.00, 136.05, 128.56, 128.17, 128.02, 116.09, 66.36, 43.69, 16.70.

[0027] Example 2

[0028] Synthesis of (S)-2-methylbutyric acid (5)

[0029] Under argon protection, palladium carbon (0.019 g, 10% Pd, with 55% H2O) was added to a 50 mL Schlenk flask. The vacuum-argon filling process was repeated three times, and the gas in the system was replaced with hydrogen using a hydrogen balloon. MeOH (10 mL) was added at room temperature, and vinyl ester 4 (0.019 g, 1.00 mmol) was added using a microsyringe. The reaction was carried out at room temperature for 6 h and then stopped. The palladium carbon was removed by filtration, and the solvent was removed by rotary evaporation to obtain the crude product. Finally, it was purified by silica gel column chromatography (petroleum ether / ethyl acetate 10:1) to obtain the colorless liquid (S)-2-methylbutyric acid (5) (0.058 g, yield 57%). 1 H NMR (500 MHz, CDCl3) δ 10.07 (br s, 1H), 2.40 (p, J = 7.0 Hz, 1H), 1.71 (dq, J = 14.7, 7.3 Hz, 1H), 1.50 (dq, J = 14.2, 7.2 Hz, 1H), 1.18 (d, J = 7.1 Hz, 3H), 0.95 (t, J = 7.5 Hz, 3H); 13 C NMR (126 MHz, CDCl3) δ 183.35, 41.02, 26.67, 16.49, 11.66.

[0030] Example 3

[0031] (R)-4-phenyl-3-(3-methyl-2-butenoyl) Synthesis of oxazolidinone (8)

[0032] At 0 °C, THF (30 mL) and 3-methyl-2-butenoic acid (6) (2.03 g, 20.23 mmol) were successively added to a 200 mL Schlenk flask. Triethylamine (4.84 g, 47.80 mmol) was slowly added dropwise and mixed evenly. Then pivaloyl chloride (2.88 g, 23.91 mmol) was slowly added dropwise. The reaction was stirred at 0 °C for 30 min and then stopped. The reaction solvent was removed by rotary evaporation to obtain the crude product of 3-methyl-2-butenoic anhydride as a light yellow solid.

[0033] At room temperature, THF (90 mL) and (R)-4-phenyl Oxazolidinone (7) (3.00 g, 18.39 mmol) was mixed evenly. The mixture was cooled to 0 °C in an ice-water bath, and n-butyllithium (8.43 mL, 2.4 M solution in tetrahydrofuran, 20.23 mmol) was slowly added dropwise. The reaction was continued at 0 °C for 10 min. Then the crude product of 3-methyl-2-butenoic anhydride was dissolved in THF (30 mL) and slowly added to the above system. The reaction solution was slowly warmed to room temperature and stirred for an additional 12 h to stop the reaction. At 0 °C, saturated aqueous NH4Cl solution (10 mL) was added to quench the reaction, and the aqueous layer and organic layer were separated. The aqueous layer was extracted with ethyl acetate (3 × 30 mL), and the organic layer and the ethyl acetate extract were combined. Then it was washed with saturated aqueous NaCl solution (50 mL) and dried over anhydrous Na2SO4, concentrated using a rotary evaporator to remove the solvent, and a crude product was obtained. Finally, it was purified by silica gel column chromatography (petroleum ether / ethyl acetate 5:1) to obtain a white solid (R)-4-phenyl-3-(3-methyl-2-butenoyl) Oxazolidinone (8) (3.43 g, yield 76%). 1 H NMR (500 MHz, CDCl3) δ 7.37 (dd, J = 8.4, 6.5 Hz, 2H), 7.33–7.30 (m, 3H), 6.96 (t, J = 1.8 Hz, 1H), 5.47 (dd, J = 8.8, 4.1 Hz, 1H), 4.65 (td, J = 8.9, 1.6 Hz, 1H), 4.20 (ddd, J = 8.7, 4.4, 1.9 Hz, 1H), 2.09 (d, J = 1.5 Hz, 3H), 1.97 (d, J = 1.5 Hz, 3H); 13 C NMR (126 MHz, CDCl3) δ 164.48, 159.91, 159.89, 153.80, 139.51, 129.20, 128.55, 125.87, 115.76, 77.17, 69.78, 57.68, 28.15, 21.43.

[0034] Example 4

[0035] (R)-4-phenyl-3-((R)-2-isopropenyl-5-methyl-6-hexenoyl) Synthesis of Oxazolidinone (10)

[0036] Under argon protection and at room temperature, in a 250 mL three-necked flask, add A solution of oxazolidinone amide 8 (2.40 g, 9.78 mmol) in THF (50 mL). The solution was cooled to -78 °C using a low-temperature bath, and NaHMDS (5.87 mL, 2.0 M THF solution, 11.74 mmol) was slowly added dropwise over 15 min. The resulting mixture was stirred at -78 °C for 1 h. Then, 3-methyl-1-bromo-2-butene (9) (5.83 g, 39.14 mmol) was slowly added dropwise, and the mixture was stirred at -78 °C for 4 h before the reaction was stopped. Saturated aqueous NH4Cl solution (10 mL) was added to quench the reaction, and the organic layer was separated from the aqueous layer. The aqueous layer was extracted with ethyl acetate (3 × 60 mL), and the organic layer and the ethyl acetate extract were combined. Then, it was washed with saturated aqueous NaCl solution (200 mL) and dried over anhydrous Na2SO4, concentrated using a rotary evaporator to remove the solvent, and a crude product was obtained. Finally, it was purified by silica gel column chromatography (petroleum ether / ethyl acetate 20:1) to obtain a white solid (R)-4-phenyl-3-((R)-2-isopropenyl-5-methyl-6-hexenoyl) oxazolidinone (10) (1.84 g, yield 60%). 1 H NMR (500 MHz, CDCl3) δ 7.34–7.29 (m, 3H), 7.28–7.23 (m, 2H), 5.37 (dd, J = 8.7, 3.6 Hz, 1H), 4.88–4.84 (m, 3H), 4.60 (t, J = 8.8 Hz, 1H), 4.45 (dd, J = 9.3, 5.6 Hz, 1H), 4.17 (dd, J = 8.9, 3.6 Hz, 1H), 2.42 (dt, J = 14.1, 8.4 Hz, 1H), 2.18–2.14 (m, 1H), 1.77 (t, J = 1.1 Hz, 3H), 1.52 (d, J = 1.6 Hz, 3H), 1.40 (d, J = 1.4 Hz, 3H); 13 C NMR (126 MHz, CDCl3) δ 173.03, 153.51, 143.07, 139.43, 133.91, 129.18, 128.61, 125.92, 121.16, 113.63, 69.68, 58.07, 50.32, 30.18, 25.80, 21.33, 17.69.

[0037] Example 5

[0038] Synthesis of (R)-lavandulol (11)

[0039] Under argon protection, lithium aluminum hydride (0.42 g, 11.17 mmol) and Et2O (30 mL) were added to a 100 mL three-necked flask, cooled to 0 °C in an ice bath, and slowly added dropwise A THF solution (10 mL) of oxazolidinone amide 10 (1.75 g, 5.58 mmol) was added dropwise over 30 min. The reaction mixture was slowly warmed to room temperature and stirred for 1.5 h, then the reaction was stopped. HCl aqueous solution (2.5 M) was added to neutralize the reaction mixture to pH 6, and the aqueous layer was separated from the organic layer. The aqueous layer was extracted with Et2O (3 × 30 mL), and the organic layer and the ether extract were combined. The combined organic layer was washed successively with saturated NaHCO3 aqueous solution (20 mL) and saturated NaCl aqueous solution (20 mL), dried over anhydrous Na2SO4, and then concentrated using a rotary evaporator to remove the solvent, giving a crude product. Finally, the crude product was purified by silica gel column chromatography (petroleum ether / ethyl acetate 5:1) to give a white solid (R)-lavandulol (11) (0.63 g, yield 73%, 83% ee). 1 H NMR (500 MHz, CDCl3) δ 5.10–5.06 (m, 1H), 4.93 (p, J = 1.6 Hz, 1H), 4.82–4.81 (m, 1H), 3.57 (dd, J = 10.7, 5.0 Hz, 1H), 3.50 (dd, J = 10.7, 8.2 Hz, 1H), 2.28 (qt, J = 7.7, 3.8 Hz, 1H), 2.14–2.01 (m, 2H), 1.70–1.69 (m, 6H), 1.61 (s, 3H); 13 C NMR (126 MHz, CDCl3) δ 145.54, 132.83, 122.15, 113.17, 63.75, 50.05, 28.48, 25.83, 19.60, 17.91.

[0040] Example 6

[0041] Synthesis of Phenacoccus solenopsis Tinsley sex pheromone 1

[0042] Under argon protection and at 0 °C, chiral acid 5 (0.02 g, 0.19 mmol), Et3N (54 μL, 0.39 mmol) and toluene (5 mL) were successively added to a 50 mL Schlenk tube and stirred until dissolved. Stir at 0 °C for 30 min, then add 2,4,6-trichlorobenzoyl chloride (27 μL, 0.26 mmol) using a microsyringe. Warm the mixture to room temperature and stir at room temperature for 1.5 h. Cool the reaction system to 0 °C in an ice-water bath, add a toluene solution (0.5 mL) of 4-dimethylaminopyridine (0.022 g, 0.39 mmol), and then slowly add chiral alcohol 11 (0.020 g, 0.13 mmol) using a microsyringe. After addition, warm the reaction solution to room temperature and continue to stir the reaction at room temperature for 2.5 h to stop the reaction. Add saturated NH4Cl aqueous solution (2 mL) to quench the reaction, and separate the organic layer and the aqueous layer. The aqueous layer was extracted with ether (3 × 10 mL), and the organic layer and the ether extract were combined. Then it was washed with saturated NaCl aqueous solution (30 mL) and dried over anhydrous Na2SO4, concentrated using a rotary evaporator to remove the solvent, and a crude product was obtained. Finally, it was purified by silica gel column chromatography (petroleum ether / ethyl acetate 20:1) to obtain colorless liquid Phenacoccus solenopsis sex pheromone 1 (0.029 g, 94% yield). 1 1H NMR (500 MHz, CDCl3) δ 5.09–5.04 (m, 1H), 4.83–4.81 (m, 1H), 4.74–4.73 (m, 1H), 4.08–4.02 (m, 2H), 2.40–2.33 (m, 1H), 2.19–2.03 (m, 2H), 1.69 (d, J = 6.5 Hz, 6H), 1.67–1.64 (m, 1H), 1.62 (s, 3H), 1.49–1.41 (m, 1H), 1.13 (d, J = 7.0 Hz, 3H), 0.89 (td, J = 7.5, 1.5 Hz, 3H); 13 13C NMR (126 MHz, CDCl3) δ 176.84, 145.02, 133.01, 121.82, 112.55, 65.62, 46.37, 41.33, 28.75, 26.87, 25.89, 20.01, 17.95, 16.80, 11.78。

Claims

1. A method for the asymmetric synthesis of the sex pheromone of Phenacoccus solenopsis Tinsley by using cobalt-catalyzed asymmetric Kumada coupling reaction and Evans chiral induction method, characterized in that It includes the following steps: preparing cinnamic acid benzyl ester 4 by using the asymmetric Kumada coupling reaction of ethylene Grignard reagent and benzyl bromopropionate catalyzed by bisoxazoline / Co(II); then obtaining (S)-2-methylbutyric acid (5) through Pd / C-catalyzed hydrogenation; using (R)-4-phenyloxazolidin-2-one (7) as a chiral auxiliary to react with in-situ generated 3-methyl-2-butenoic anhydride to prepare oxazolidinone amide 8; then carrying out an asymmetric alkylation reaction with 3-methyl-1-bromo-2-butene (9) to prepare isopentenyl oxazolidinone amide 10; then reducing it with LiAlH4 to obtain (R)-lavandulol (11), and finally carrying out an esterification reaction with (S)-2-methylbutyric acid to prepare (S)-2-methylbutyric acid (R)-lavandulyl ester (1), namely the sex pheromone of Phenacoccus solenopsis Tinsley; the synthetic route of the sex pheromone of Phenacoccus solenopsis Tinsley (1) is as follows:

Images