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Org. Synth. 2005, 81, 63
DOI: 10.15227/orgsyn.081.0063
HECK REACTIONS OF ARYL CHLORIDES CATALYZED BY PALLADIUM/TRI-tert-BUTYLPHOSPHINE: (E)-2-METHYL-3-PHENYLACRYLIC ACID BUTYL ESTER AND (E)-4-(2-PHENYLETHENYL)BENZONITRILE
[2-Propenoic acid, 2-methyl-3-phenyl-, butyl ester and Benzonitrile, 4-[(1E)-2-phenylethenyl]]
Submitted by Adam F. Littke and Gregory C. Fu1.
Checked by Michael H. Ober and Scott E. Denmark.
1. Procedure
A. (E)-2-Methyl-3-phenylacrylic acid butyl ester (1). An oven-dried, 250-mL, three-necked, round-bottomed flask equipped with a reflux condenser (fitted with an argon inlet adapter), rubber septum, glass stopper, and a teflon-coated magnetic stir bar is cooled to room temperature under a flow of argon. The flask is charged with bis(tri-tert-butylphosphine)palladium (Pd(P(t-Bu)3)2) (0.482 g, 0.943 mmol, 3.0 mol% Pd) (Notes 1, 2) and again purged with argon. Toluene (32 mL) (Notes 9, 10) is added, and the mixture is stirred at room temperature, resulting in a homogeneous brown-orange solution. Chlorobenzene (3.20 mL, 31.5 mmol) (Note 11), N-methyldicyclohexylamine (Cy2NMe) (7.50 mL, 35.0 mmol) (Note 12), and butyl methacrylate (5.50 mL, 34.6 mmol) (Note 12) are then added successively via syringe. The resulting mixture is allowed to stir at room temperature for 5 min, resulting in a homogeneous light-orange solution. The rubber septum is then replaced with a glass stopper, and the flask is heated in a 100°C oil bath under a positive pressure of argon for 22 hr (Note 13). Upon heating, the solution becomes bright canary-yellow in color, and within 10-15 min the formation of a white precipitate (the amine hydrochloride salt) is observed. Upon completion of the reaction, shiny deposits of palladium metal form on the sides of the flask, and a large quantity of white precipitate is present. The reaction mixture is allowed to cool to room temperature and then diluted with 100 mL of diethyl ether. The resulting solution is washed with 100 mL of H2O, and the aqueous layer is extracted with three 50-mL portions of diethyl ether. The combined organic phases are washed with 100 mL of brine and then concentrated by rotary evaporation. Any residual solvent is removed at 0.5 mm. The crude product, a dark-brown oil, is then purified by flash column chromatography (Note 14) to afford 6.67 - 6.72 g (95%) of 1 as a pale red-orange liquid. This liquid appears to be pure by 1H and 13C NMR spectroscopy; however, if desired, the discoloration can be removed by filtering the product through a small column of silica gel (3 cm diameter × 10 cm height), which furnishes 6.49-6.62 g (95-96%) of 1 as a clear, colorless liquid (Notes 15 and 16).
B. (E)-4-(2-Phenylethenyl)benzonitrile (2). An oven-dried, 250-mL, three-necked, round-bottomed flask equipped with an argon inlet adapter, rubber septum, glass stopper, and a teflon-coated magnetic stir bar is cooled to room temperature under a flow of argon. The flask is charged successively with bis(tri-tert-butylphosphine)palladium [(Pd(P(t-Bu)3)2] (0.238 g, 0.466 mmol, 1.5 mol% Pd) (Notes 1, 2), tris(dibenzylideneacetone)dipalladium(0) (Pd2(dba)3) (0.213 g, 0.233 mmol, 1.5 mol% Pd) (Note 3), and 4-chlorobenzonitrile (4.25 g, 30.9 mmol) (Note 17). The flask is purged with argon, and 62 mL of toluene is added (Notes 9, 10, 18). The resulting mixture is stirred at room temperature, resulting in a dark, red-purple solution. N-Methyldicyclohexylamine (7.5 mL, 35.0 mmol) (Note 12) and styrene (3.8 mL, 33.2 mmol) (Note 19) are then added via syringe. The reaction mixture is allowed to stir at room temperature under a positive pressure of argon for 72 hr (Note 13). Within the first 1-2 hr, the color changes from deep red-purple to dark brown, and a precipitate (the amine hydrochloride salt) begins to form. Upon completion of the reaction, 100 mL of ethyl acetate is added, and the resulting solution is washed with 100 mL of water. The aqueous layer is separated and extracted with three 50-mL portions of diethyl ether, and the combined organic phases are concentrated by rotary evaporation. Any residual solvent is removed at 0.5 mm. The crude product, a yellow solid, is purified via flash column chromatography (Note 20) to afford 5.30-5.34 g (83-84%) of 2 as white crystalline spheres (Notes 21, 22, 23).
2. Notes
1. Pd(P(t-Bu)3)2 was prepared according to the following procedure. In a nitrogen-filled Vacuum Atmospheres glovebox, a 100-mL, one-neck, round-bottomed flask equipped with a teflon-coated magnetic stir bar is charged with tris(dibenzylideneacetone)dipalladium(0) (Pd2(dba)3) (2.98 g, 3.25 mmol) (Note 3). A solution of tri-tert-butylphosphine (P(t-Bu)3) (2.88 g, 14.2 mmol) (Note 4) in 43 mL of N,N-dimethylformamide (DMF) (Note 5) is then added to the reaction flask via a glass pipette, and the resulting dark green-brown solution is stirred at room temperature for 23 hr. The reaction mixture is then filtered through a 30-mL medium-porosity glass frit to collect the unpurified product, Pd(P(t-Bu)3)2, as a gray solid. The reaction flask is rinsed with three 6-mL portions of DMF and 5 mL of methanol (Note 6), which are passed through the glass frit (the final rinses should be colorless). The reaction product is then dissolved in 100 mL of toluene (Note 7), and the resulting solution is filtered through a 3-cm diameter 0.45 µm Gelman acrodisc (to remove some insoluble black material) into a 250-mL Schlenk tube, affording a homogeneous orange-yellow solution. The Schlenk tube is removed from the glovebox, and the toluene solution is concentrated under high vacuum (0.5mm) to a volume of approximately 25 mL, at which point a white crystalline solid begins to precipitate. The Schlenk tube is taken into the glovebox, and the toluene solution and crystalline solid are transferred to a 250-mL Erlenmeyer flask via a glass pipette. MeOH (100 mL) is then added slowly via pipette over 10 min, resulting in the precipitation of additional white crystalline solid. The solution is allowed to stand for one hour, and then the mother liquor is separated from the solid via pipette. The solid is washed with two 10-mL portions of MeOH, transferred to a tared 20-mL glass vial, and dried under high vacuum, affording 2.41 g (72%) of Pd(P(t-Bu)3)2 as a white, crystalline solid (Note 8). The Pd(P(t-Bu)3)2 can be stored indefinitely under nitrogen in a Vacuum Atmospheres glovebox. Although Pd[P(t-Bu)3]2 has been reported to be "stable in air in the solid state,"2 if a glovebox is not available, it is recommended that Pd[P(t-Bu)3]2 be stored in a tightly capped vial in a desiccator, preferably under argon or nitrogen.
2. Alternatively, Pd[P(t-Bu)3]2 may be purchased from Strem Chemicals.
3. Pd2(dba)3 was purchased from the Aldrich Chemical Company and used as received.
4. P(t-Bu)3 (99%) was purchased from Strem Chemicals and used as received.
5. DMF (anhydrous, DriSolv) was purchased from EM Science and degassed under high vacuum for 10-15 min prior to use.
6. Methanol (certified A.C.S., purchased from Fisher Scientific) was distilled from Mg(OMe)2 and was degassed by three freeze-pump-thaw cycles prior to use.
7. Toluene (J. T. Baker; CYCLE-TRAINER solvent delivery kegs) was vigorously purged with argon for 2 hr and then passed through two packed columns of neutral alumina and copper(II) oxide under argon pressure.3
8. P{1H} NMR (C6D6, 202 MHz): δ 85.3; 1H NMR pdf(C6D6, 500 MHz): δ 1.51 (t, J = 5.4 Hz). The NMR sample must be prepared under inert atmosphere to avoid aerobic oxidation of the catalyst as evidenced by free P(t-Bu)3 at δ 1.27 ppm in the 1H NMR spectrum. Even with these precautions, ca. 1% of P(t-Bu)3 is observed.
9. Toluene (anhydrous, 99.8%, Sure/SealTM bottle) was purchased from the Aldrich Chemical Company and used as received.
10. 1,4-Dioxane is an equally suitable solvent for these Heck couplings (and is the solvent used in the published procedures); however, due to the lower cost and the lower toxicity of toluene, it was chosen as the solvent for these reactions.
11. Chlorobenzene (anhydrous, 99.8%, Sure/SealTM bottle) was purchased from the Aldrich Chemical Company and used as received.
12. N-Methyldicyclohexylamine (97%) and butyl methacrylate (99%) were purchased from the Aldrich Chemical Company and gently sparged with argon for 5-10 min prior to use.
13. The progress of the reaction was monitored by GC.
14. Flash column chromatography was performed using silica gel (6 cm diameter × 35 cm height), eluting with 19/1 hexane/diethyl ether.
15. Compound 1 has the following properties: bp 111°C (1 mm) 1H NMR pdf(CDCl3, 500 MHz) δ: 0.98 (t, J = 7.5, 3H), 1.45 (sext, J = 1.0, 2H), 1.71 (qn, J = 1.0, 2H), 2.12 (d, J = 1.5, 3H), 4.22 (t, J = 6.6, 2H), 7.33 (m, 1H), 7.39 (m, 4H), 7.68 (apparent d, J = 1.5, 1H); 13C NMR (CDCl3 126 MHz): δ 13.7, 14.0, 19.3, 30.7, 64.8, 128.2, 128.4, 128.7, 129.6, 136.0, 138.8, 168.8; IR (neat, cm−1): 3059, 3026, 2960, 2933, 2873, 1709, 1635, 1492, 1448, 1388, 1356, 1254, 1201, 1115, 1074, 1003, 931, 766, 704; Anal. Calcd for C14H18O2: C, 77.03; H, 8.31. Found: C, 77.02; H, 8.30.
16. The checkers found that the product could be further purified by distillation (110°C/1 mm).
17. 4-Chlorobenzonitrile (99%) was purchased from Aldrich Chemical Company and used as received.
18. To allow more efficient stirring, it was beneficial to run this reaction at half of the concentration (2 mL solvent per mmol of aryl chloride) of the original published procedure (1 mL solvent per mmol of aryl chloride).
19. Styrene (99+%) was purchased from Aldrich Chemical Company and gently sparged with argon for 5-10 min prior to use.
20. Flash column chromatography was performed using silica gel (10 cm diameter × 27 cm height), eluting with 4/1 toluene/hexane. A small amount of aryl chloride that remained unreacted after 72 hr was recovered mixed with a small quantity (<5%) of the desired product.
21. Compound 2 has the following properties: mp (corr.) 115-117°C (lit.4 mp 115 °C); 1H NMR pdf(CDCl3, 500 MHz): δ 7.09 (d, J = 16.5, 1H), 7.22 (d, J = 16.5, 1H), 7.33 (d, J = 7.1, 1H), 7.40 (t, J = 7.1, 2H), 7.54 (d, J = 7.5, 2H), 7.59 (d, J = 8.3, 2H), 7.64 (d, J = 8.4, 2H); 13C NMR (CDCl3, 126 MHz): δ 110.8, 119.3, 126.9, 127.0, 127.1, 128.9, 129.1, 132.6, 132.7, 136.5, 142.1; IR (neat, cm−1): 3029, 2964, 2225, 1648, 1604, 1531, 1450, 1278, 1226, 1174, 1095, 966, 821, 769; Anal. Calcd for C15H11N: C, 87.78; H, 5.40; N, 6.82. Found: C, 87.43; H, 5.26; N, 6.86.
22. The checkers found that the product could be further purified by sublimation (127°C/0.5 mm).
23. The submitters obtained the product in 89% yield.
Handling and Disposal of Hazardous Chemicals
The procedures in this article are intended for use only by persons with prior training in experimental organic chemistry. All hazardous materials should be handled using the standard procedures for work with chemicals described in references such as "Prudent Practices in the Laboratory" (The National Academies Press, Washington, D.C., 2011 www.nap.edu). All chemical waste should be disposed of in accordance with local regulations. For general guidelines for the management of chemical waste, see Chapter 8 of Prudent Practices.
These procedures must be conducted at one's own risk. Organic Syntheses, Inc., its Editors, and its Board of Directors do not warrant or guarantee the safety of individuals using these procedures and hereby disclaim any liability for any injuries or damages claimed to have resulted from or related in any way to the procedures herein.
3. Discussion
Since its discovery in the early 1970's, the palladium-catalyzed arylation of olefins (Heck reaction; eq 1 and Figure 1)5,6 has been applied to a diverse array of fields, ranging from natural products synthesis7,8 to materials science9 to bioorganic chemistry.10 This powerful carbon-carbon bond-forming process has been practiced on an industrial scale for the production of compounds such as naproxen11 and octyl methoxycinnamate.12 The Heck reaction is typically performed in the presence of a palladium/tertiary phosphine catalyst and a stoichiometric amount of an inorganic or organic base. High functional-group tolerance and the ready availability and low cost of simple olefins contribute to the exceptional utility of the Heck arylation.
FIGURE 1
OUTLINE OF THE CATALYTIC CYCLE FOR THE HECK COUPLING REACTION
FIGURE 1OUTLINE OF THE CATALYTIC CYCLE FOR THE HECK COUPLING REACTION
Until recently, one important unsolved problem for the Heck reaction was the poor reactivity of aryl chlorides, which are arguably the most attractive class of aryl halides, due to their lower price and greater availability as compared with the corresponding bromides and iodides.13,14 For the few catalyst systems that have displayed activity for Heck couplings of aryl chlorides (e.g., those of Milstein (bulky, electron-rich chelating bisphosphines),15 Herrmann (palladacycles, N-heterocyclic carbenes),16 Reetz (tetraphenylphosphonium salts),17 and Beller (phosphites),18,19,20 the scope of the reactions has been quite narrow and the reaction temperatures have been rather high (≥120 °C). This need for elevated temperatures can be problematic for a variety of reasons, including decomposition of thermally unstable substrates and decreased regio- and stereoselectivities.
Pd/P(t-Bu)3, in the presence of Cy2NMe, is an unusually mild and versatile catalyst for Heck reactions of aryl chlorides (Tables 1 and 2) (as well as for room-temperature reactions of aryl bromides).21,22,23 Example A, the coupling of chlorobenzene with butyl methacrylate, illustrates the application of this method to the stereoselective synthesis of a trisubstituted olefin; α-methylcinnamic acid derivatives are an important family of compounds that possess biological activity (e.g., hypolipidemic24 and antibiotic25) and serve as intermediates in the synthesis of pharmaceuticals (e.g., Sulindac, a non-steroidal anti-inflammatory drug26). Example B, the coupling of 4-chlorobenzonitrile with styrene, demonstrates that Pd/P(t-Bu)3 can catalyze the Heck reaction of activated aryl chlorides at room temperature.
TABLE 1.
HECK COUPLINGS OF ARYL CHLORIDES AT ELEVATED TEMPERATURE


TABLE 2.
HECK COUPLINGS OF ACTIVATED ARYL CHLORIDES AT ROOM TEMPERATURE


From a practical point of view, it is worth noting that Heck reactions catalyzed by Pd/P(t-Bu)3 do not typically require rigorously purified reagents or solvents. In addition, the palladium and phosphine sources, Pd[P(t-Bu)3]2 and Pd2(dba)3, are commercially available and can be handled in air.
Thus, in terms of scope, mildness, and convenience, Pd/P(t-Bu)3 provides an attractive method for achieving Heck couplings of aryl chlorides.

References and Notes
  1. Department of Chemistry, Massachusetts Institute of Technology, Cambridge, MA 02139.
  2. (a) Otsuka, S.; Yoshida, T.; Matsumoto, M.; Nakatsu, K. J. Am. Chem. Soc. 1976, 98, 5850-5858. (b) Yoshida, T.; Otsuka, S. J. Am. Chem. Soc. 1977, 99, 2134-2140. (c) Yoshida, T.; Otsuka, S. Inorg. Synth. 1990, 28, 113-119.
  3. (a) Pangborn, A. B.; Giardello, M. A.; Grubbs, R. H.; Rosen, R. K.; Timmers, F. J. Organometallics 1996, 15, 1518-1520. (b) Alaimo, P. J.; Peters, D. W.; Arnold, J.; Bergman, R. J. J. Chem. Ed. 2001, 78, 64-64.
  4. Gusten, H.; Salzwedel, M. Tetrahedron 1967, 23, 173-185.
  5. (a) Mizoroki, T.; Mori, K.; Ozaki, A. Bull. Chem. Soc. Jpn. 1971, 44, 581. (b) Heck, R. F.; Nolley, J. P., Jr. J. Org. Chem. 1972, 37, 2320-2322.
  6. For reviews of the Heck reaction, see: (a) Bräse, S.; de Meijere, A. In Metal-Catalyzed Cross-Coupling Reactions; Diederich, F., Stang, P. J., Eds.; Wiley: New York, 1998; Chapter 3. (b) Beletskaya, I. P.; Cheprakov, A. V. Chem. Rev. 2000, 100, 3009-3066. (c) Heck, R. F. In Comprehensive Organic Synthesis; Trost, B. M., Ed.; Pergamon: New York, 1991; Vol. 4, Chapter 4.3. (d) Heck R. F. Org. React. 1982, 27, 345-390. (e) Crisp, G. T. Chem. Soc. Rev. 1998, 27, 427-436. (f) de Meijere, A.; Meyer, F. E. Angew. Chem., Int. Ed. Engl. 1994, 33, 2379-2411. (g) Jeffery, T. In Advances in Metal-Organic Chemistry; Liebeskind, L. S., Ed.; JAI: London, 1996; Vol. 5, pp. 153-260. (h) Cabri, W.; Candiani, I. Acc. Chem. Res. 1995, 28, 2-7.
  7. For example, see: (a) Taxol: Danishefsky, S. J.; Masters, J. J.; Young, W. B.; Link, J. T.; Snyder, L. B.; Magee, T. V.; Jung, D. K.; Isaacs, R. C. A.; Bornmann, W. G.; Alaimo, C. A.; Coburn, C. A.; Di Grandi, M. J. J. Am. Chem. Soc. 1996, 118, 2843-2859. (b) Scopadulcic acid: Overman, L. E.; Ricca, D. J.; Tran, V. D. J. Am. Chem. Soc. 1993, 115, 2042-2044.
  8. For overviews of applications of the Heck reaction in natural products synthesis, see: (a) Link, J. T.; Overman, L. E. In Metal-Catalyzed Cross-Coupling Reactions; Diederich, F., Stang, P. J., Eds.; Wiley-VCH: New York, 1998; Chapter 6. (b) Bräse, S.; de Meijere, A. In Metal-Catalyzed Cross-Coupling Reactions; Diederich, F., Stang, P. J., Eds.; Wiley: New York, 1998; Chapter 3.6. (c) Nicolaou, K. C.; Sorensen, E. J. Classics in Total Synthesis; VCH: New York, 1996; Chapter 31. These authors refer to the Heck reaction as "one of the true "power tools" of contemporary organic synthesis" (p. 566).
  9. For example, see: (a) Step-Growth Polymers for High-Performance Materials; Hedrick, J. L., Labadie, J. W., Eds.; ACS Symp. Ser. 624; American Chemical Society: Washington, DC, 1996; Chapters 1, 2, and 4. (b) DeVries, R. A.; Vosejpka, P. C.; Ash, M. L. Catalysis of Organic Reactions; Herkes, F. E., Ed.; Marcel Dekker: New York, 1998; Chapter 37. (c) Tietze, L. F.; Kettschau, G.; Heuschert, U.; Nordmann, G. Chem. Eur. J. 2001, 7, 368-373.
  10. For some recent examples, see: (a) Haberli, A.; Leumann, C. J. Org. Lett. 2001, 3, 489-492. (b) Burke, T. R., Jr.; Liu, D.-G.; Gao, Y. J. Org. Chem. 2000, 65, 6288-6292.
  11. Stinson, S. C. Chem. Eng. News January 18, 1999, p. 81.
  12. Octyl methoxycinnamate (OMC) is the most common UV-B sunscreen that is on the market: Eisenstadt, A. In Catalysis of Organic Reactions; Herkes, F. E., Ed.; Marcel Dekker: New York, 1998; Chapter 33.
  13. For discussions of coupling reactions of aryl chlorides, see: (a) Grushin, V. V.; Alper, H. In Activation of Unreactive Bonds and Organic Synthesis; Murai, S., Ed.; Springer-Verlag: Berlin, 1999; pp. 193-226. (b) Grushin, V. V.; Alper, H. Chem. Rev. 1994, 94, 1047-1062.
  14. The low reactivity of aryl chlorides is usually attributed to the strength of the C-Cl bond (bond dissociation energies for aryl-X: Cl = 96 kcal/mol; Br = 81 kcal/mol; I = 65 kcal/mol).
  15. (a) Ben-David, Y.; Portnoy, M.; Gozin, M.; Milstein, D. Organometallics 1992, 11, 1995-1996. (b) Portnoy, M.; Ben-David, Y.; Milstein, D. Organometallics 1993, 12, 4734-4735. (c) Portnoy, M.; Ben-David, Y.; Rousso, I.; Milstein, D. Organometallics 1994, 13, 3465-3479.
  16. (a) Herrmann, W. A.; Brossmer, C.; Ofele, K.; Reisinger, C.-P.; Priermeier, T.; Beller, M.; Fischer, H. Angew. Chem., Int. Ed. Engl. 1995, 34, 1844-1848. (b) Herrmann, W. A.; Brossmer, C.; Reisinger, C.-P.; Reirmeier, T. H.; Ofele, K.; Beller, M. Chem. Eur. J. 1997, 3, 1357-1364. (c) Herrmann, W. A.; Elison, M.; Fischer, J.; Köcher, C.; Artus, G. R. J. Angew. Chem., Int. Ed. Engl. 1995, 34, 2371-2374. (d) See also: Herrmann, W. A.; Brossmer, C.; Ofele, K.; Beller, M.; Fischer, H. J. Mol. Catal. A 1995, 103, 133-146.
  17. Reetz, M. T.; Lohmer, G.; Schwickardi, R. Angew. Chem. Int. Ed. 1998, 37, 481-483.
  18. Beller, M.; Zapf, A. Synlett 1998, 792-793.
  19. See also: Kaufmann, D. E.; Nouroozian, M.; Henze, H. Synlett 1996, 1091-1092.
  20. For very early work on Heck reactions of aryl chlorides, see: (a) Davison, J. B.; Simon, N. M.; Sojka, S. A. J. Mol. Cat. 1984, 22, 349-352. (b) Spencer, A. J. Organomet. Chem. 1984, 270, 115-120.
  21. Littke, A. F.; Fu, G. C. J. Am. Chem. Soc. 2001, 123, 6989-7000. See also: Littke, A. F.; Fu, G. C. J. Org. Chem. 1999, 64, 10-11.
  22. See also: Shaughnessy, K. H.; Kim, P.; Hartwig, J. F. J. Am. Chem. Soc. 1999, 121, 2123-2132.
  23. Generally, for Pd/P(t-Bu)3-catalyzed Heck couplings that proceed at elevated temperature, a 1:2 Pd:phosphine ratio is preferred. For reactions that occur at room temperature, a 1:1 Pd:phosphine ratio is usually desirable (2:1 mixture of Pd(P(t-Bu)3)2:Pd2(dba)3).
  24. For example, see: Watanabe, T.; Hayashi, K.; Yoshimatsu, S.; Sakai, K.; Takeyama, S.; Takashima, K. J. Med. Chem. 1980, 23, 50-59.
  25. For example, see: Buchanan, J. G.; Hill, D. G.; Wightman, R. H.; Boddy, I. K.; Hewitt, B. D. Tetrahedron 1995, 51, 6033-6050.
  26. Eisenstadt, A. In Catalysis of Organic Reactions; Herkes, F. E., Ed.; Marcel Dekker: New York, 1998; Chapter 33.

Appendix
Chemical Abstracts Nomenclature (Collective Index Number);
(Registry Number)

(E)-2-Methyl-3-phenylacrylic acid butyl ester:
2-Propenoic acid, 2-methyl-3-phenyl-, butyl ester, (2E)-; (21511-00-5).

Bis (tri-tert-butylphosphine)palladium:
Palladium, bis[tris(1,1,-dimethylethyl)phosphine]-; (53199-31-8).

N-Methyldicyclohexylamine:
Cyclohexanamine, N-cyclohexyl-N-methyl-; (7560-83-0)

Chlorobenzene:
Benzene, chloro-; (108-90-7)

Butyl methacrylate:
1-Propenoic acid, 2-methyl-, butyl ester; (97-88-1)

(E)-4-(2-Phenylethenyl)benzonitrile:
Benzonitrile, 4-[(1E)-2phenylethenyl]-; (13041-79-7)

Tris(dibenzylideneacetone)dipalladium:
Palladium,tris[μ-[(1,2-η:4,5-η)-(1E,4E)-1,5,-diphenyl-1,4-pentadien-3-one]]di-; (51364-51-3]

4-Chlorobenzonitrile:
Benzonitrile, 4-chloro-; (623-03-0)

Tri-tert-butylphosphiine:
Phosphine, tris(1,1-dimethylethyl)-; (13716-12-6)