Highly regioselective hydroselenation and double-bond isomerization of terminal alkynes with benzeneselenol catalyzed by bis(triphenylphosphine)palladium(II) dichloride

Journal of Organometallic Chemistry 696 (2011) 450e455

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Highly regioselective hydroselenation and double-bond isomerization of terminal alkynes with benzeneselenol catalyzed by bis(triphenylphosphine)palladium(II) dichloride Toshiya Ozaki, Mao Kotani, Hiroki Kusano, Akihiro Nomoto*, Akiya Ogawa* Department of Applied Chemistry, Graduate School of Engineering, Osaka Prefecture University, 1-1 Gakuen-cho, Nakaku, Sakai, Osaka 599-8531, Japan

a r t i c l e i n f o

a b s t r a c t

Article history: Received 29 July 2010 Received in revised form 30 September 2010 Accepted 1 October 2010

Bis(triphenylphosphine)palladium(II) dichloride (PdCl2(PPh3)2) catalyzes regioselective addition of benzeneselenol to terminal alkynes and the subsequent double-bond isomerization to afford the corresponding internal alkenyl selenides in good yields. Ó 2010 Elsevier Ltd. All rights reserved.

Keywords: Palladium Selenol Markovnikov addition Double-bond isomerization Vinyl selenide

1. Introduction Transition-metal-catalyzed addition reactions of heteroatom compounds bearing a heteroatom-hydrogen linkage to carbone carbon unsaturated bonds are very useful in terms of highly regio- and stereoselective synthesis of heteroatom compounds as well as excellent atom economy [1]. Indeed, transition-metal-catalyzed hydroboration, hydrosilylation, hydrostannation, hydrophosphination, and hydrothiolation are widely employed for organic synthesis. In contrast, examples of transition-metal-catalyzed addition of group 15 and 16 heteroatom compounds bearing a heavy element-hydrogen linkage to unsaturated compounds are still rare. In particular, selenols and tellurols have been believed to be catalyst poisons, and this contributes to undevelopment of the transition-metal-catalyzed reactions of organic selenium and tellurium compounds [2,3]. In 1992, we found that palladium(II) diacetate (Pd(OAc)2) catalyzes the Markovnikov-type addition of selenols to terminal alkynes in benzene (Eq. (1)) [4], but the product selectivity was not so high compared with that of the corresponding Pd(OAc)2-catalyzed hydrothiolation of terminal alkynes with thiols [5].

Further detailed investigation on this hydroselenation led to the finding that the presence of pyridine or its derivatives improved the regioselectivity of the hydroselenation: Markovnikov-type adduct (2a) was obtained predominantly [6]. Ananikov and Beletskaya et al. reported mechanistic insight into the palladium- and platinum-catalyzed hydroselenation of alkynes in detail [7], and also found highly efficient nickel-based heterogeneous catalytic system for selective hydroselenation of terminal and internal alkynes [8]. Ishii et al. reported in detail the stoichiometric reaction of selenols with low-valent palladium and platinum complexes [9]. In the presence of Pd(OAc)2, benzeneselenol was also found to add to allenes preferentially via the internal addition along with small amounts of the regioisomers (Eq. (2)) [10]. In this paper, we wish to report that switching the catalyst from Pd(OAc)2 to PdCl2(PPh3)2 in the reaction of terminal alkynes (1) with benzeneselenol leads to sequential addition/isomerization reaction, affording internal vinyl selenides (4) selectively (Eq. (3)).

2. Results and discussion * Corresponding authors. Tel./fax: þ81 72 254 9290. E-mail address: [email protected] (A. Ogawa). 0022-328X/$ e see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.jorganchem.2010.10.005

When the reaction of 1-octyne (1a, 1 mmol) with equimolar amounts of benzeneselenol in the presence of bis-

T. Ozaki et al. / Journal of Organometallic Chemistry 696 (2011) 450e455

R

+ PhSeH

Pd(OAc)2 (2 mol%)

451

SePh R

SePh +

THF, 16 h

R

R=nBu

63%

16% [44/56]

R=cyclohexyl

69%

20% [50/50]

(triphenylphosphine)palladium(II) dichloride (2 mol%) in benzene was conducted under the atmosphere of nitrogen at 80  C for 16 h, Markovnikov-type addition of the selenol to 1-octyne and the subsequent double-bond isomerization took place to give 2-(phenylseleno)-2-octene (4a) in 71% yield as a stereoisomeric mixture (E/Z ¼ 62/38) (Table 1, Entry 1). Although small amounts of the Markovnikov adduct (2a, 4%) and the (PhSe)2 adduct (1,2-bis (phenylseleno)-1-octene (6a), 3%) were formed as byproducts in this reaction, the desired product 4a could be separated easily from these byproducts upon treatment with preparative TLC on silica gel. Heating at 70  C in this sequential addition/isomerization reaction resulted in the decrease of the product selectivity: 4a (30% [E/Z ¼ 66/34]), 2a (7%), the anti-Markovnikov adduct 5a (10%), and the (PhSe)2 adduct 6a (4%). Switching the catalyst from PdCl2(PPh3)2 to RhCl(PPh3)3 led to the formation of 4a (55% [E/ Z ¼ 64/36]) and 2a (7%) [11]. Under the reaction conditions of Entry 1, the sequential addition/isomerization reaction of several alkynes was examined, and the results are summarized in Table 1 (Entries 2e6). In the case of 5-methyl-1-hexyne (1b), 37% of 4b was obtained along with 3% of the Markovnikov adduct 2b and 2% of the (PhSe)2 adduct 6b. Heating at 100  C in toluene improved the yield of 2b

(2)

(65%) (Entry 2). Chloro and cyano groups are tolerant to the sequential addition/isomerization reaction (Entries 3 and 4). Benzylacetylene (1e) also underwent the sequential addition/ isomerization reaction to give the corresponding styrene derivative (4e) in good yield (Entry 5). The presence of hydroxyl group led to somewhat lower yield of the desired product (4f (34%), along with the Markovnikov adduct 2f (3%) and the anti-Markovnikov adduct 5f (5%)) (Entry 6). In the case of heteroatom substitution on the propargyl position, however, the desired sequential reaction was difficult to proceed. For example, the attempted reaction of propargyl bromide and propargyl alcohol gave rise to a complex mixture. In the case of propargyl tetrahydropyranyl ether (1g), the (PhSe)2 adduct 6g was obtained as the major product along with phenyl tetrahydropyranyl selenide (7) (Eq. (4)). Probably, the coordination of the functional group at the propargyl position to the catalyst may contribute to the different reactivity. To get insight into the reaction pathway for this sequential hydroselenation/double bond isomerization reaction, we first examined the palladium-catalyzed reaction of the isolated 2a as the substrate, which afforded gradually the corresponding vinyl selenide (4a), as shown in Eq. (5). In addition, the time-dependency of the reaction of 1a with PhSeH was investigated, and the results are shown in Table 2. Vinyl selenide 2a was formed initially, and the double bond isomerization occurred affording 4a. Both experiments (Eq. (5) and Table 2) indicate that the E/Z ratio of 4a is almost the same [12]. Although the precise mechanism was wait for further detailed experiments, a possible pathway for this sequential addition/ isomerization reaction is shown in Scheme 1. The reaction of

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T. Ozaki et al. / Journal of Organometallic Chemistry 696 (2011) 450e455

PdCl2(PPh3)2 with benzeneselenol generates PdCl(SePh)(PPh3)2 8, which adds to alkyne 1 to form vinylpalladium intermediate 9. Protonation of 9 with benzeneselenol affords the Markovnikov adduct 2. Then, the reaction of 2 with 8 leads to the cationic intermediate 10, which provides allylic palladium species 11 by the proton elimination. Protonation of 11 affords the desired adduct 4 with the regeneration of the catalyst 8.

Table 1 PdCl2(PPh3)2-catalyzed sequential addition/isomerization reaction of alkynes with selenola.

. Entry

Alkyne

Product

Yield/%[E/Z]b

1

71%[62/38]

2

65%[63/37]c

3

73%[100/0]

4

66%[98/2]

5

70%[85/15]

(continued on next page)

T. Ozaki et al. / Journal of Organometallic Chemistry 696 (2011) 450e455

453

Table 1 (continued) Entry

Alkyne

Yield/%[E/Z]b

Product

6

a b c

34%[63/37]

Reaction conditions: Alkyne (1.0 mmol), PhSeH (1.0 mmol), PdCl2(PPh3)2 (0.02 mmol), C6H6 (0.5 mL), 80  C, 16 h. NMR yield. Toluene (0.5 mL), 100  C.

Table 2 The time dependency of the reaction of 1a with PhSeH.

R

R

PdCl2(PPh3)2 (2 mol%)

+ PhSeH

benzene (0.5 mL), 80 oC n (R = C5H11)

1a

R PhSe

+

+ PhSe

2a

(E)-4a

R PhSe (Z)-4a

. Time

2a

(E)-4a

(Z)-4a

4h

25%

8%

3%

[E/Z] [72/28]

8h

13%

27%

13%

[68/32]

12h

12%

33%

15%

[69/31]

16h

9%

38%

16%

[70/30]

Scheme 1. A possible pathway for the sequential addition/isomerization reaction.

3. Conclusion

4. Experimental

We have developed the novel sequential addition/isomerization reaction of benzeneselenol to terminal alkynes by switcing simply the catalyst from palladium diacetate to bis(triphenylphosphine)palladium(II) dichloride. This catalytic reaction provides a useful tool to the internal vinyl selenides, and open up a new field of the transition-metal-catalyzed reactions of organoselenium compounds.

4.1. General procedures All experiments were performed under the atmosphere of nitrogen unless otherwise noted. Solvents were dried by standard methods. Other reactants and reagents were purchased from commercial source and used without further purification. 1H NMR spectra were recorded on a JEOL JNM-ECX400 spectrometer

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T. Ozaki et al. / Journal of Organometallic Chemistry 696 (2011) 450e455

(400 MHz) using CDCl3 as the solvent with tetramethylsilane (TMS) as the internal standard. 13C NMR spectra were obtained on a JEOL JNM-ECX400 spectrometer (100 MHz) using CDCl3 as the solvent. Chemical shifts in 13C NMR were measured relative to CDCl3 by using d 77.0 ppm. High resolution mass spectra were obtained on a JEOL JMS-700 instrument supported by Kyoto-Advanced Nanotechnology Network.

4.2. Preparation of 2-phenylseleno-2-octene (4a) Into a two-necked flask equipped with a reflux condenser and a magnetic stirring bar were placed PdCl2(PPh3)2 (14.0 mg, 0.02 mmol), benzene (0.5 mL), alkyne (1.0 mmol), and benzeneselenol (106 mL, 1.0 mmol) under N2 atmosphere. The mixture was heated at 80  C with stirring for 16 h. After the reaction was complete, the resulting mixture was evaporated, and the products were purified by preparative TLC on silica gel with a mixed solvent of hexane/ethyl acetate as an eluent. The purification of the product 4a was performed by preparative TLC (PTLC) on silica gel and/or a recycling preparative HPLC (Japan Analytical Industry Co. Ltd., Model LC-908) equipped with JAIGEL-1H and -2H columns (GPC, using CHCl3 as an eluent). 4a: a mixture of E and Z isomers; white oil; (E)-4a: 1H NMR (CDCl3): d 0.90 (t, J ¼ 6.9 Hz, 3H), 1.29e1.45 (m, 6H), 2.00 (s, 3H), 2.24e2.29 (m, 2H), 5.79 (dt, J ¼ 1.4, 7.1 Hz, 1H), 7.25e7.27 (m, 3H), 7.44e7.45 (m, 2H). 13C NMR (CDCl3): d 14.1 (CH3), 20.0 (CH2), 22.5 (CH2), 28.9 (CH2), 29.5 (CH2), 31.4 (CH3), 125.3 (C), 126.8 (CH), 129.0 (CH), 132.5 (CH), 133.0 (C), 137.9 (CH). (Z)-4a: 1H NMR (CDCl3): d 0.90 (t, J ¼ 6.9 Hz, 3H), 1.29e1.45 (m, 6H), 2.00 (s, 3H), 2.08e2.14 (m, 2H), 5.97 (dt, J ¼ 1.4, 7.3 Hz, 1H), 7.25e7.27 (m, 3H), 7.44e7.45 (m, 2H). 13C NMR (CDCl3): d 14.1 (CH3), 20.0 (CH2), 22.5 (CH2), 26.4 (CH2), 28.9 (CH2), 29.2 (CH3), 126.3 (C), 127.8 (CH), 130.0 (CH), 133.5 (CH), 134.0 (C), 138.9 (CH). HRMS (FAB) Calcd for [M þ Hþ] C14H21Se: 269.0808, Found 269.0809. 4.2.1. 5-Methyl-2-phenylseleno-2-hexene (4b) A mixture of E and Z isomers; white oil; (E)-4b: 1H NMR (CDCl3): d 0.91 (d, J ¼ 6.8 Hz, 6H), 1.57 (s, 3H), 1.64e1.72 (m, 1H), 2.25e2.29 (m, 2H), 5.80 (t, J ¼ 7.1 Hz, 1H), 7.17e7.28 (m, 3H), 7.43e7.54 (m, 2H). 13 C NMR (CDCl3): d 20.1 (CH), 22.3 (CH3), 28.6 (CH2), 38.6 (CH3), 126.8 (CH), 128.9 (C), 129.0 (CH), 132.6 (CH), 134.9 (C), 136.6 (CH). (Z)-4b: 1H NMR (CDCl3): d 0.91 (d, J ¼ 6.8 Hz, 6H), 1.57 (s, 3H), 1.64e1.72 (m, 1H), 2.13e2.19 (m, 2H), 5.97 (t, J ¼ 7.5 Hz, 1H), 7.17e7.28 (m, 3H), 7.43e7.54 (m, 2H). 13C NMR (CDCl3): d 20.1 (CH), 22.3 (CH3), 27.9 (CH2), 37.9 (CH3), 126.8 (CH), 128.9 (C), 129.0 (CH), 131.4 (CH), 134.9 (C), 136.4 (CH). HRMS (FAB) Calcd for [M þ Hþ] C13H19Se: 255.0652, Found 255.0646. 4.2.2. (E)-5-chloro-2-phenylseleno-2-pentene (4c) Colorless oil; (E)-4c: 1H NMR (CDCl3): d 2.01 (s, 3H), 2.55e2.60 (m, 2H), 3.53 (t, J ¼ 6.9 Hz, 2H), 5.85 (dt, J ¼ 1.4, 7.1 Hz, 1H), 7.25e7.28 (m, 4H), 7.45e7.46 (m, 1H). 13C NMR (CDCl3): d 21.0 (CH3), 33.6 (CH2), 44.5 (CH2), 128.3 (C), 130.0 (CH), 130.1 (CH), 131.6 (CH), 133.6 (C), 134.4 (CH). HRMS (FAB) Calcd for [M þ Hþ] C11H14ClSe: 260.9949, Found 260.9952. 4.2.3. 5-Phenylseleno-4-hexenenitrile (4d) A mixture of E and Z isomers; white oil; (E)-4d: 1H NMR (CDCl3): d 1.82 (t, J ¼ 7.6 Hz, 2H), 2.03 (s, 3H), 2.60e2.65 (m, 2H), 5.79 (t, J ¼ 6.6 Hz, 1H), 7.25e7.35 (m, 4H), 7.47e7.53 (m, 1H). 13C NMR (CDCl3): d 19.9 (CH3), 29.8 (CH2), 36.7 (CH2), 119.4 (CN), 127.6 (C), 129.4 (CH), 130.4 (CH), 132.1 (CH), 133.6 (C), 135.2 (CH). (Z)-4d: 1H NMR (CDCl3): d 1.82 (t, J ¼ 7.6 Hz, 2H), 2.03 (s, 3H), 2.47e2.53 (m, 2H), 5.93 (t, J ¼ 7.3 Hz, 1H), 7.25e7.35 (m, 4H), 7.47e7.53 (m, 1H). 13C NMR (CDCl3): d 19.9 (CH3), 29.5 (CH2), 36.4 (CH2), 119.4 (CN), 127.5

(C), 129.4 (CH), 130.4 (CH), 132.1 (CH), 133.6 (C), 135.0 (CH). HRMS (FAB) Calcd for [M þ Hþ] C12H14NSe: 252.0291, Found 252.0285. 4.2.4. 1-Phenyl-2-phenylseleno-1-propene (4e) A mixture of E and Z isomers; white oil; (E)-4e: 1H NMR (CDCl3): d 3.6 (s, 3H), 7.08 (s, 1H), 7.23e7.51 (m, 10H). 13C NMR (CDCl3): d 45.0 (CH3), 126.7 (CH), 127.5 (C), 127.6 (CH), 128.4 (CH), 129.1 (CH), 129.3 (CH), 129.4 (C), 129.8 (C), 132.5 (CH), 133.4 (CH). (Z)-4e: 1H NMR (CDCl3): d 3.6 (s, 3H), 7.10 (s, 1H), 7.23e7.51 (m, 10H), 13C NMR (CDCl3): d 29.7 (CH3), 126.7 (CH), 127.5 (C), 127.6 (CH), 128.4 (CH), 128.6 (CH), 129.3 (CH), 129.4 (C), 129.8 (C), 131.0 (CH), 133.4 (CH). HRMS (FAB) Calcd for [M þ Hþ] C15H15Se: 275.0339, Found 275.0330. 4.2.5. 5-Phenylseleno-4-hexen-1-ol (4f) Colorless oil; (E)-4f: 1H NMR (CDCl3): d 2.00 (s, 3H), 2.28e2.37 (m, 2H), 3.54 (t, J ¼ 6.0 Hz, 2H), 5.77 (dt, J ¼ 1.4, 6.8 Hz, 1H), 7.22e7.31 (m, 5H). 13C NMR (CDCl3): d 25.8 (CH3), 29.7 (CH2), 32.1 (CH2), 62.3 (CH2), 127.0 (C), 128.4 (CH), 129.2 (CH), 129.3 (CH), 131.7 (C), 133.0 (CH). (Z)-4f: 1H NMR (CDCl3): d 2.00 (s, 3H), 2.16e2.23 (m, 2H), 3.54 (t, J ¼ 6.0 Hz, 2H), 5.92 (dt, J ¼ 1.4, 7.3 Hz, 1H), 7.22e7.31 (m, 5H). 13C NMR (CDCl3): d 25.7 (CH3), 29.7 (CH2), 31.9 (CH2), 62.2 (CH2), 127.0 (C), 128.4 (CH), 129.2 (CH), 129.3 (CH), 131.7 (C), 133.0 (CH). HRMS (FAB) Calcd for [M þ Hþ] C11H15OSe: 243.0288, Found 243.0293. 4.2.6. 1,2-Bis(phenylseleno)-3-{(tetrahydro-2H-pyran-2-yl)oxy}-1propene (6g) White oil; 1H NMR (CDCl3): d 1.46e1.76 (m, 6H), 3.39e3.42 (m, 1H), 3.73e3.79 (m, 1H), 4.17 (dd, J ¼ 13.5, 78.0 Hz, 2H), 4.54 (t, J ¼ 3.2 Hz, 1H), 7.14e7.28 (m, 5H), 7.40 (1H), 7.43e7.54 (m, 2H). 13C NMR (CDCl3): d 19.1 (CH2), 25.2 (CH2), 30.2 (CH2), 61.8 (CH2), 71.2 (CH), 97.4 (CH2), 127.1 (CH), 127.5 (C), 129.1 (CH), 132.2 (CH), 132.7 (CH), 133.9 (CH). HRMS (FAB) Calcd for [M þ Hþ] C20H22O2Se2: 453.9950, Found 453.9954. Acknowledgements This work was supported by a Grant-in-Aid for Scientific Research (B, 19350095) from the Ministry of Education, Culture, Sports, Science and Technology, Japan, and also supported by Kyoto-Advanced Nanotechnology Network. References [1] (a) F. Alonso, I.P. Beletskaya, M. Yus, Chem. Rev. 104 (2004) 3079e3159; (b) H. Yamamoto, K. Oshima (Eds.), Main Group Metals in Organic Synthesis, Wiley-VCH, Weinheim, 2004; (c) L.-B. Han, M. Tanaka, Chem. Commun. (1999) 395e402; (d) A. Ogawa, Palladium-catalyzed syn-addition reactions of X-Pd bonds (X ¼ group 15, 16, and 17 elements). in: E. Negishi (Ed.), Handbook of Organopalladium Chemistry for Organic Synthesis, vol. 2. Wiley, New York, 2002, pp. 2841e2849. [2] (a) A. Ogawa, J. Organomet. Chem. 611 (2000) 463e474; (b) I.P. Beletskaya, C. Moberg, Chem. Rev. 106 (2006) 2320e2354; (c) I.P. Beletskaya, V.P. Ananikov, Pure Appl. Chem. 79 (2007) 1041e1056; (d) G. Perin, E.J. Lenardao, R.G. Jacob, R.B. Panatieri, Chem. Rev. 109 (2009) 1277e1301; (e) S. Fujiwara, M. Toyofuku, H. Kuniyasu, N. Kambe, Pure Appl. Chem. 82 (2010) 565e575. [3] (a) H. Okamura, M. Miura, K. Kosugi, H. Takei, Tetrahedron Lett. 21 (1980) 87e90; (b) S.-I. Murahashi, T. Yano, J. Am. Chem. Soc. 102 (1980) 2456e2458; (c) H.J. Cristau, B. Chabaud, R. Labaudiniere, H. Christol, Organometallics 4 (1985) 657e661; (d) H.J. Cristau, B. Chabaud, R. Labaudiniere, H. Christol, J. Org. Chem. 51 (1986) 875e878; (e) K. Ohe, H. Takahashi, S. Uemura, N. Sugita, J. Org. Chem. 52 (1987) 4859e4863; (f) K. Ohe, H. Takahashi, S. Uemura, N. Sugita, J. Organomet. Chem. 326 (1987) 35e47;

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