Reaction of (+)-3-Carene and (+)-2-Carene with t-butyl Hypochlorite or N-Chlorsuccinimide in the Presence of Free Radical Catalysts

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1 Polish J. Chem., 74, (2000) Reaction of (+)-3-Carene and (+)-2-Carene with t-butyl Hypochlorite or N-Chlorsuccinimide in the Presence of Free Radical Catalysts by A. Uzarewicz *, J. Œcianowski and J. B¹kowska-Janiszewska Faculty of Chemistry, Nicolaus Copernicus University, Toruñ, Poland (Received October 4th, 999; revised manuscript February 0th, 2000) Allylic chlorination of (+)-3-carene () gave ( )-trans-4-chloro-3(0)-carene (2), (+)- 0-chloro-carene (4) and 3,4-dichlorocarane (5). Chlorination was done by two methods: with t-butyl hypochlorite or N-chlorsuccinimide in the presence of catalytic amount of, -azobisisobutyronitrile or benzoyl peroxide, UV irradiation and silica gel. Chlorination of (+)-2-carene (7) using these methods gave p-cymene (8), -isopropylene-4- methylbenzene (9) and dipentene (0). Key words: allylic chlorination, carene chlorides, t-butyl hypochlorite, N-chlorsuccinimide Allylic chlorination of terpenoid hydrocarbons is interesting with regard to the synthetic and theoretical importance of this type of compounds. In our previous paper, we have demonstrated that optically active allylic chlorides derived from -pinene can be good substrates for the synthesis of optically active oxygen and nitrogen derivatives of the pinane group []. Searching for a convenient method of the synthesis of (+)-3- and (+)-2-carene chlorides we found contradicting data about the synthesis of (+)-3-carene chlorides; there is no method for the allylic chlorination of (+)-2-carene reported. So far, a few papers about free radical allylic chlorination of 3-carene using chlorine, sodium hypochlorite, t-butyl chlorite, t-butyl hypochlorite, hypochloric acid and N-chlorsuccinimide were published [2 6]. As a major chlorination products trans-4-chloro-3(0)-carene (2), 4-chloro-2-carene (3) were obtained * Author for correspondence.

2 778 A. Uzarewicz, J. Œcianowski and J. B¹kowska-Janiszewska Tischtschenko and Chowanskaja [2] claim that the reaction of gaseous chlorine with (+)-3-carene in the presence of NaHCO 3 suspension afforded: 4-chloro-3(0)- carene (2) and 4-chloro-2-carene (3) along with traces of 0-chloro-3-carene (4). These authors assume that 4-chloro-3(0)-carene (2) tends to rearrange to 0-chloro- -3-carene (4) in temperature above 70 C due to the instability from the presence of the exocyclic double bond. We have proved that under Tischtschenko conditions chloride 2 is not rearranged. Isaeva [3] states that the chlorination of (+)-3-carene produces: 4-chloro-3(0)-carene (2) and dichlorides. Manukov [4] chlorinating (+)-3-carene with chlorine, sodium hypochlorite, t-butyl chlorite or t-butyl hypochlorite in various solvents between 50 C to 45 C obtained 4-chloro-3(0)-carene (2), 4-chloro- -2-carene (3) and dichlorides. In all reactions the amount of chloride 2 was higher then chloride 3. For authors, this is contradictory to classical opinion about the easiness of the formation of the trisubstituted double bound versus disubstituted. The preponderance of monochloride 2 is explained by the high strains in the structure of monochloride 3. Hegde [5] chlorinating (+)-3-carene with hypochlorite acid in methylene chloride solution got also two monochlorides 2 and 3 in ratio 3:. Ratner [6] carried out chlorination of (+)-3-carene with N-chlorsuccinimide in the presence of benzoyl peroxide to obtain as a major product 4-chloro-3(0)-carene (2) and dichlorides. He assumed that chlorine in very low concentration forming from N- chlorsuccinimide is an active chlorinating agent. The high energetic chlorine atom attacked the more accessible group at C-0 to form less stable free radical. This radical rearranges to a more stable at C-4, from which 4-chloro-3(0)-carene (2) was produced. In continuation of our investigation of free radical chlorination of terpenoid hydrocarbons [7 8] we examined the reaction of allylic chlorination of (+)-3-carene and (+)-2-carene under the typical free radical conditions. t-butyl hypochlorite or N- chlorsuccinimide in the presence of catalytic amount, -azobisisobutyronitrile or benzoyl peroxide, UV-irradiation and silica gel were used for chlorination. Based on investigations of Walling [9 0] and stability of free radicals, it was expected to obtain: 2-chloro-3-carene, 5-chloro-3-carene and small amounts of 0-chloro-3-carene from (+)-3-carene. (+)-2-Carene could give two monochlorides 4-chloro-2-carene and less probable 0-chloro-2-carene or products formed due to the carene free radicals rearrangement. The opening of the cyclopropane ring should also be considered with the formation of the chlorinated derivatives of meta- and para-mentadiene. In addition, the electrondonating character of cyclopropane ring could have influence for the direction of the reaction. RESULTS AND DISCUSSION Allylic chlorination of (+)-3-carene () was carried out in methylene chloride or without a solvent using as a chlorinating agent N-chlorsuccinimide (NCS) or t-butyl hypochlorite (t-buo) in the presence of catalytic amounts of, -azobisisobutyronitrile (AIBN) or benzoyl peroxide [(C 6 H 5 CO) 2 O 2 ], ultraviolet irradiation

3 Reaction of (+)-3-carene and (+)-2-carene (UV) and silica gel. In all reactions three products were obtained, which were separated by fractional distillation. The structures of ( )-trans-4-chloro-3(0)-carene (2), (+)-0-chloro-3-carene (4) and 3,4-dichlorocarane (5) were established for these products on the grounds of H, 3 C NMR and IR spectra (Scheme ). Scheme NCS or t-buo cat The results of allylic chlorination of (+)-3-carene are presented in Table. Table. Chlorinating Time The ratio of the chlorides Catalyst agent (h) t-buo AIBN t-buo (C 6 H 5 CO) 2 O t-buo UV t-buo silica gel NCS silica gel NCS AIBN NCS UV ( )-trans-4-chloro-3(0)-carene (2) was the major product in free radical chlorination of (+)-3-carene with t-buo or NCS. 4-Chloro-2-carene (3) was not detected in the reactions products. The formation of ( )-trans-4-chloro-3(0)-carene (2) and 0-chloro-3-carene (4) under reaction conditions can confirm that probably in first step of the reaction free radical 6 is formed (Scheme 2). Scheme 2 tbuoorncs - cat

4 780 A. Uzarewicz, J. Œcianowski and J. B¹kowska-Janiszewska The structure of monochloride 4 was confirmed by chemical methods. Chloride 4 was oxidized by Gollnick method [] to 3-caren-0-al, which 2,4-dinitrophenylhydrazone derivative did not give the temperature depression after mixing with original compound. Chlorination of (+)-3-carene under a typical free radical conditions using t-buo or NCS enhances the yield of monochlorinated products even twice in comparison to [4,6]. Chlorination of (+)-2-carene (7) was also achieved using the same chlorinating agents and catalysts as in reactions of (+)-3-carene (). Products were isolated by distillation. Three products were detected by GC and then separated by preparative gas chromatography. The structures of the products were established by H and 3 C NMR analyses. In all reactions p-cymene (8, 70 78% yield), -isopropyleno-4-methylbenzene (9) and dipentene (0) were obtained We think that the lack of chlorinated products is due to the conjugation of the double bond with cyclopropane ring. Free radical once formed undergoes rearrangement with opening of the three membered ring leads to aromatization of the product. EXPERIMENTAL The IR spectra were recorded on Carl Zeiss Jena UR-20 or FT-IR Spectrum H and 3 C NMR spectra were obtained using Tesla BS 487 C or Varian Gemini 200 spectrometers for solutions in CD 3 (internal TMS). Assignment of the signals (in H and 3 C spectra) was made by the appropriate COSY ( H- H and H- 3 C) experiments. GLC analyses were performed: chlorides on Chromatoprep chromatograph (SE-30 or SAIB on Celite 525), hydrocarbons on Perkin Elmer 990 chromatograph [Carbowax 20M(3m 3 mm) or SE-30 on Chromosorb G AW DMCS], or Hewlett-Packard 5890 chromatograph [Supelcowax-0 (30 m 0.32 mm)]. Melting points were determined on Mel-temp Laboratory Devices inc., USA, or B chi SMP-20 and are uncorrected. t-butyl hypochlorite was prepared according to Teeter and Bell [2], b.p C, n D 20 =.404, d 4 20 = (+)-3-Carene used for the reaction was chromatographically pure and had b.p C/760 mm Hg, n D 20 =.4723, [ ] D 20 = +8.4 (neat). (+)-2-Carene, N-chlorsuccinimide, silica gel (Kieselgel 60, mesh),, -azobisisobutyronitrile and benzoyl peroxide were obtained from Aldrich. Reaction of t-butyl hypochlorite with (+)-3-carene: Free radical chlorination of (+)-3-carene with t-butyl hypochlorite was carried out using four procedures: A) with UV-irradiation, B) catalyzed with, -azobisisobutyronitrile (AIBN), C) catalyzed with benzoyl peroxide, D) catalyzed with silica gel. Method A: To a freshly distilled and vigorously stirred (+)-3-carene (272.4 g, 2.0 mole ) freshly distilled t-butyl hypochlorite (72.0 g, 0.75 mole ) was added dropwise. The reaction was carried in quartz vessel with UV-irradiation (Hanau Q-350, 5 h, 20 C, Ar). t-butanol and unreacted (+)-3-carene were removed at 40 C/0 mm Hg. Vacuum distillation on a Perkin Elmer 25 Auto Annular Still column afforded:

5 Reaction of (+)-3-carene and (+)-2-carene trans-4-chloro-3(0)-carene (2) yield 33.3 g (26.0%), b.p C/0.5 mm Hg, n 20 D =.4992,[ ] 20 D = 74.0 (neat); IR (liquid film): 900, 80, 3075 cm (exocyclic double bond), 020 cm (cyclopropane ring in the carene system), 730 cm (C ); H NMR, : 0.84 (s, 3H, C-8),.0 (s, 3H, C-9), 4.53 (t, H, C-4), 4.79 (m, H, C-0), 4.89 (m, H, C-0); 3 C NMR, : 46.5 (C-3), 0.2 (C-0), 6.7 (C-4), 30.0 (C-2), 27.9 (C-9), 23.7 (C-5), 20.0 (C-), 7.7 (C-7), 5.2 (C-6) 4.0 (C-8); (+)-0-chloro-3-carene (4) yield 4.5 g (3.5%), b.p C/0.5 mm Hg, n 20 D =.5054, [ ] 20 D = +2 (neat), H NMR, : 0.76 (s, 3H, C-8),.05 (s, 3H, C-9), 3.98 (s, 2H, C-0), 5.68 (t, H, C-4); 3 C NMR, : 32.2 (C-3), 26.3 (C-4), 50.5 (C-0), 28.3 (C-9), 2. (C-2), 20.9 (C-5), 8.0 (C-), 7.2 (C-7), 6.8 (C-6) 3.3 (C-8). 3,4-dichlorocarane (5) yield 3. g (4.0%), b.p C/0.5 mm Hg, n 20 D =.5085,[ ] 20 D = 42 (neat), H NMR, : 0.99 (s, 3H, C-8),.0 (s, 3H, C-9),.66 (s, 3H, C-0), 3.95 (m, H, C-4); 3 C NMR, : 7.7 (C-3), 67.5 (C-4), 38. (C-2), 30.8 (C-5), 28.2 (C-0), 22.6 (C-9), 2.0 (C-), 9.8 (C-6), 8.0 (C-7) 5.6 (C-8). Anal. calc. for C 0 H 4 2 (205.): 58.6% C, 6.9% H, 34.6% ; found: 58.7% C, 6.7% H, 34.4%. Method B: Chlorination was carried out as in the method A with one exception: 0.5 g of AIBN was used as catalyst instead UV-irradiation. Work-up was identical as described in the method A. Yield g (25.5%); g (4.7%); g (5.7%). Method C: The reaction was carried out as in the method A with one exception: 0.5 g of benzoyl peroxide was used as a catalyst instead UV-irradiation. Further work-up was identical as described in method A. Yield g (26.5%); g (2.2%); g (5.8%). Method D: To a vigorously stirred at 0 C mixture of (+)-3-carene (25.0 g, 0.8 mole), silica gel (40.0 g) and methylene chloride (400 ml), t-butyl hypochlorite (23.8 g, 0.22 mole) was added dropwise. The reaction was carried out under argon atmosphere (24 h, 20 C). Silica gel was filtered, washed with methylene chloride (200 ml), methylene chloride was removed and further work-up was identical as described in the method A. Yield g (2.2%); g (2.6%); g (3.9%). Reaction of N-chlorsuccinimide with (+)-3-carene: Free radical chlorination of (+)-3-carene with N-chlorsuccinimide was carried out using three procedures: A) catalyzed with, -azobisisobutyronitrile (AIBN), B) catalyzed with silica gel, C) with UV-irradiation. Method A: To a freshly distilled and vigorously stirred (+)-3-carene (25.0 g, 0.8 mole) and AIBN (.0 g) in methylene chloride (200 ml) NCS (27.2 g, mole) was added slowly. The reaction was carried out under argon (44 h, 20 C). Methylene chloride and unreacted (+)-3-carene were removed in vacuo, n-hexane (200 ml) was added, the residue was filtered of and the filtrate was washed with water (50 ml), 0% solution of Na 2 CO 3 (2 50 ml) and water (50 ml). The organic layer was dried (MgSO 4 ), n-hexane was removed, and the products were isolated by distillation under 0.5 mm Hg pressure. Yield 2 8. g (26.4%); g (7.8%); g (3.9%). Method B: The reaction was carried out as in the method A with one exception: 40.0 g of silica gel was used as a catalyst instead AIBN. The reaction was carried out under argon (24 h, 20 C). Silica gel was filtered of, washed with methylene chloride (200 ml) and further work-up was identical as described in method A. Yield 2 7. g (23.%); g (8.%); 5.4 g (6.%). Method C: The reaction was carried out as in the method A with one exception: the reaction was carried in quartz vessel with UV-irradiation (Hanau Q-350, 24 h, 20 C, Ar) and AIBN was not added. Further work-up was identical as described in method A. Yield g (22.8%); g (7.2%); 5.3 g (5.7%). 3-Carene-0-al: Oxidation was carried out according to Gollnick s method []. To a vigorously stirred solution of (+)-0-chloro-3-carene (4) (23.5 g) in benzene (20 ml) was added dropwise a solution of K 2 Cr 2 O 7 (50.0 g) in water (00 ml) containing concentrated H 2 SO 4 (20 ml). The reaction was carried out at 60 C for 3 h. After cooling the organic layer was separated and the aqueous layer was extracted with diethyl ether. The etheral and benzene solution were dried over anhydrous MgSO 4. Solvents were removed and the residue was purified via semicarbazones. A substance (7.0 g) which was obtained had: b.p. 82 C/3 mm Hg, n 20 D =.5068, d 20 4 = , 20 D = 20.0 (c = 2.3, benzene) UV MeOH max = 226 and 295 nm ( = 8700, 30). IR: 3030, 685, 660, 805 (trisubstituted double bond), 2730, 270 (CHO) cm. H NMR, : 9.20 (s, H, C-0), 6.52 (m, H, C-4),.06 (s, 3H, C-9), 0.80 (m, 2H, C-, C-6), 0.70 (s, 3H, C-8); 3 C NMR, : 93.5 (C-0), 49.9 (C-4), 39.5 (C-3), 27.7 (C-9), 2.9 (C-5), 7.2 (C-), 7.2 (C-7), 6.6 (C-6), 6. (C-2), 3.0 (C-8).

6 782 A. Uzarewicz, J. Œcianowski and J. B¹kowska-Janiszewska 2,4-Dinitrophenylhydrazone obtained in the usual way had m.p C (dioxane), not depressed when mixed with an authentic sample. Reaction of t-butyl hypochlorite with (+)-2-carene: Chlorination of (+)-2-carene (7) with t-butyl hypochlorite was carried out in two methods: A) catalyzed with, -azobisisobutyronitrile (AIBN), B) catalyzed with silica gel. Method A: To a freshly distilled and vigorously stirred (+)-2-carene (0.0 g, mole) and AIBN (0.5 g) in CH 2 2 (00 ml) freshly distilled t-butyl hypochlorite (8.8 g, 0.08 mole) was added dropwise. The reaction was carried out at 0 C under argon for 3 hrs and left over night at room temperature. The mixture was washed with water (30 ml), 0% solution of Na 2 CO 3 (3 30 ml) and water (30 ml). The organic layer was dried (MgSO 4 ), and the solvents were removed, and the product (8.9 g) was isolated by distillation under 0.5 mm Hg. GLC analysis showed that the product was a mixture of three compounds. p-cymene (8, 7.0%), -isopropyleno-4-methylbenzene (9, 25.2%), dipentene (0, 3.8%) by preparative GLC were obtained. p-cymene (8) n D 20 =.4906; H NMR: 7.5 (s, 4H, aromat), 2.90 (q, H, C-7), 2.35 (s, 3H, C-0),.27 (d, 6H, C-8, C-9, J = 7.0 Hz); 3 C NMR: 45.9 (C aromat), 35.2 (C aromat), 29. (2 CH aromat, C-2, C-6), 26.4 (2 CH aromat, C-3, C-5), 33.7 (C-7), 24. (2 CH 3, C-8, C-9), 20. (C-0). -Isopropyleno-4-methylbenzene (9) n D 20 =.5294; H NMR: 7.40 (d, 2H, aromat, J = 8.2 Hz), 7.5 (d, 2H aromat, J = 8.2 Hz), 5.36 (s, H, C-8), 5.05 (s, H, C-8), 2.36 (s, 3H, C-9), 2.4 (s, 3H, C-0); 3 C NMR: 43. (C aromat), 38.4 (C aromat), 28.9 (2 CH aromat), 25.3 (2 CH aromat),.5 (C-8), 2.7 (C-9), 20.9 (C- 0). Dipentene (0) n D 20 =.4755; H NMR: 5.38 (m, H, C-2), 4.69 (s, 2H, C-8),.7 (s, 3H, C-0),.63 (s, 3H, C-9); 3 C NMR: 50.2 (C-), 33.7 (C-7), 20.6 (C-2), 08.3 (C-8), 40.9 (C-4), 30.7 (C-5), 30.4 (C-3), 27.8 (C-6), 27.3 (C-9), 20.6 (C-0). Method B: To a vigorously stirred at 0 C mixture of (+)-2-carene (0.0 g, mole), silica gel (6.4 g) and metylene chloride (60 ml), t-butyl hypochlorite (8.8 g, 0.08 mole) was added dropwise. The reaction was carried out under argon atmosphere (24 h, 20 C). Silica gel was filtered of, washed with methylene chloride (200 ml) and further work-up was identical as described in method A. Yield 8.7 g 8 (70.4%); 9 (9.2%); 0 (0.4%). Reaction of N-chlorsuccinimide with (+)-2-carene: Chlorination of (+)-2-carene with N-chlorsuccinimide was carried out in three methods: a) catalyzed with, -azobisisobutyronitrile (AIBN), b) catalyzed with silica gel, c) with UV-irradiation. Method a: To a freshly distilled and vigorously stirred (+)-2-carene (0.0 g, mole) and AIBN (0.5 g) in methylene chloride (00 ml) NCS (0.8 g, 0.08 mole) was added slowly. The reaction was carried out under argon (20 C, 24 h). Methylene chloride (75 ml) and unreacted (+)-2-carene were removed in vacuo, n-hexane was added, the residue was filtered of and the filtrate was washed with water (30 ml), 0% solution of Na 2 CO 3 (2 30 ml) and water (30 ml). The organic layer was dried (MgSO 4 ), n-hexane was removed, and the products were isolated by distillation under 0.5 mm Hg pressure. GLC analysis showed that the product was a mixture of three compounds. Yield 9.0 g 8 (69.6%); 9 (6.5%); 0 (3.9%). Method b: The reaction was carried out as in the method a with one exception: 6.4 g of silica gel was used as a catalyst instead AIBN. Further work-up was identical as described in method a. GLC analysis showed that the product was a mixture of two compounds. Yield 8.5 g 8 (75.8%); 9 (24.2%). Method c: The reaction was carried out as in the method a with one exception: the reaction was carried in quartz vessel with UV-irradiation (Hanau Q-350, 5 h, 20 C, Ar) and AIBN was not added. Further work-up was identical as described in method a. GLC analysis showed that the product was a mixture of three compounds. Yield 8.6 g 8 (77.8%); 9 (8.3%); 0 (3.9%). Acknowledgments This work was supported by the Polish State Committee for Scientific Research (Grant NR 3T09A 05 6).

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