HETEROCYCLES

Paper | Regular issue | Vol. 87, No. 10, 2013, pp. 2015-2021
Received, 22nd July, 2013, Accepted, 26th August, 2013, Published online, 29th August, 2013.
DOI: 10.3987/COM-13-12786

■ Palladium-Catalyzed Mizoroki-Heck Type Reaction with Aryliodine Diacetates Using Hydrazone Ligand

Takashi Mino,* Kohei Watanabe, Taichi Abe, Taketo Kogure, and Masami Sakamoto

Department of Applied Chemistry and Biotechnology, Graduate School and Faculty of Engineering, Chiba University, 1-33 Yayoi-cho, Inage-ku, Chiba 263-8522, Japan

Abstract

We developed a palladium-catalyzed Mizoroki-Heck type reaction of olefins with such hypervalent iodine reagents as iodobenzene diacetate in good to high yields using 2 mol% of a heterocyclic hydrazone (1b)-Pd(OAc)2 system in NMP under air at 90 °C.

INTRODUCTION
The arylation of olefins, also known as the Mizoroki-Heck reaction, is one of the most widely used palladium-catalyzed methodologies in organic synthesis. The efficiency of several catalysts for the reaction of aryl halides with acrylates or styrene derivatives has been studied.1 Recently, palladium-catalyzed Mizoroki-Heck type reactions of olefins with aryliodine diacetates as hypervalent iodine reagents instead of aryl halides were reported.2 For example, Mao and co-workers reported a palladium-catalyzed Mizoroki-Heck type reaction with aryliodine diacetates with 4 mol% of Pd(OAc)2.3 But PEG-400 had to be used as a solvent because such commonly used organic solvents as DMF and THF were not effective under these conditions. Magedov and co-workers also reported a reaction with aryliodine diacetates.4 In this case, binary catalysts such as Pd(OAc)2 (3-5 mol%)-Ag2CO3 (50 mol%) systems with TEMPO (50 mol%) as an additive in MeCN are needed to efficiently obtain the products. On the other hand, we recently demonstrated hydrazone as an effective ligand for such palladium-catalyzed C-C bond formation as the Suzuki-Miyaura reaction,5 the Mizoroki-Heck reaction,6 the Sonogashira cross-coupling reaction,7 the Hiyama cross-coupling reaction,7a and the allyl cross-coupling reaction of allylic acetate8 and ether9 with boronic acid. We also reported a palladium-catalyzed Mizoroki-Heck type reaction with aryl trimethoxysilanes.10 We now report the use of hydrazone ligands (1a-e) and (2) (Figure 1) for a palladium-catalyzed Mizoroki-Heck type reaction of olefins with iodobenzene diacetates instead of aryl halides.

RESULTS AND DISCUSSION
Initially, we examined the reaction of iodobenzene diacetate and n-butyl acrylate as model substrates with 2 mol% of Pd catalyst for 4 h under an air atmosphere at 90 °C (Table 1). Using 2 mol% of PdCl2(MeCN)2 and hydrazone (1a) as a ligand, we observed that the reaction in the presence of Cs2CO3 as a base in NMP as a solvent gave corresponding product (3a) in a 62% yield (Table 1, Entry 1). We tested other hydrazones (1b-e) and (2) (Entries 2-6) and found that heterocyclic hydrazone (1b) was an effective ligand for this reaction (Entry 2). Several palladium sources were also tested (Entries 2, and 7–12). Palladium acetate was the most effective palladium source in this reaction (Entry 7). Next, the effects of various bases and solvents were investigated (Entries 7, and 13-22). Using Cs2CO3 in NMP led to a 96% yield for this reaction (Entry 7). Although the Mizoroki-Heck type reaction proceeded in MeCN under Magedov’s conditions,4 MeCN was not an effective solvent in the hydrazone (1b)-Pd(OAc)2 system (Entry 22).

Under optimized reaction conditions (Table 1, Entry 7), we explored the scope and limitation of both aryliodine diacetates and olefins (Table 2). The reaction of iodobenzene diacetate with n-butyl acrylate for 2 h also gave product (3a) with high yield instead of 4 h (Table 2, Entry 1 vs. Table 1, Entry 7). When the reaction was carried out without using ligand (1b), the yield of 3a was decreased (Entry 1 vs. Entry 2). Using iodobenzene diacetate with tert-butyl acrylate and ethyl acrylate for 4 h led to good yields of corresponding products (3b) and (3c) (Entries 3 and 4). The reaction of methyl acrylate also gave corresponding product (3d) in 81% for 18 h (Entry 5). Moreover, methyl vinyl ketone and styrene led to good yields of products (3e) and (3f) (Entries 6 and 7). We also found that the reaction of iodomesitylene diacetate and m-(diacetoxyiodo)anisole with various acrylates gave corresponding products (3g-l) with moderate to good yields (Entries 8-13). Although true mechanism was not revealed, we thought the aryliodine was generated in situ from aryliodine diacetate and then the related Mizoroki-Heck type reaction occurred.3,4

In summary, we found that a palladium-catalyzed Mizoroki-Heck type reaction of olefins with aryliodine diacetates in NMP gave corresponding products in good to high yields using 2 mol% of heterocyclic hydrazone (1b)-Pd(OAc)2 system under air at 90 °C for 2-24 h.

EXPERIMENTAL
General
Melting points were measured on a Asone micromelting point apparatus and are uncorrected. 1H and 13C NMR spectra were recorded on a Bruker DPX-300 spectrometer. Chemical shifts are reported in δ ppm referenced to an internal SiMe4 standard. Infrared (IR) spectra were obtained using a JASCO FT/IR 230 spectrophotometer. Mass spectra were recorded on a GCMS-QP5050. HRMS was recorded on a Thermo Fisher Scientific Exactive using ESI.

General Procedure for Palladium-Catalyzed Mizoroki-Heck Type Reaction with Aryliodine Diacetates.
To a mixture of aryliodine diacetate (0.5 mmol), Cs2CO3 (1.4 mmol), Pd(OAc)2 (10 µmol), and 1b (10 µmol) in NMP (2 mL) was added olefin (3.0 mmol) at room temperature under an air atmosphere. The mixture was stirred at 90 °C. After 2-24 h, the mixture was diluted with EtOAc and water. The organic layer was washed with brine, dried over MgSO4, and concentrated under reduced pressure. The residue was purified by silica gel chromatography (hexane:EtOAc = 20-10:1 or CHCl3:EtOAc = 10:1).
(E)-n-Butyl cinnamate (3a):10 96% as a colorless oil; IR (neat, cm-1): 1713 (C=O); 1H NMR (CDCl3) δ: 0.97 (t, J = 7.3 Hz, 3H), 1.38-1.50 (m, 2H), 1.65-1.72 (m, 2H), 4.21 (t, J = 6.7 Hz, 2H), 6.45 (d, J = 16.0 Hz, 1H), 7.38-7.40 (m, 3H), 7.52-7.55 (m, 2H), 7.69 (d, J = 16.1 Hz, 1H); 13C NMR (CDCl3) δ: 13.7, 19.2, 30.7, 64.4, 118.2, 128.0, 128.9, 130.2, 134.4, 144.5, 167.1; EI-MS m/z (rel intensity) 204 (M+, 23).
(E)-t-Butyl cinnamate (3b):10 71% as a colorless oil; IR (neat, cm-1): 1708 (C=O); 1H NMR (CDCl3) δ: 1.54 (s, 9H), 6.37 (d, J = 16.0 Hz, 1H), 7.36-7.38 (m, 3H), 7.50-7.53 (m, 2H), 7.59 (d, J = 16.0 Hz, 1H); 13C NMR (CDCl3) δ: 28.2, 80.5, 120.1, 127.9, 128.8, 129.9, 134.6, 143.5, 166.3; EI-MS m/z (rel intensity) 204 (M+, 10).
(E)-Ethyl cinnamate (3c):10 88% as a colorless oil; IR (neat, cm-1): 1708 (C=O); 1H NMR (CDCl3) δ: 1.34 (t, J = 7.1 Hz, 3H), 4.27 (q, J = 7.1 Hz, 2H), 6.44 (d, J = 16.0 Hz, 1H), 7.38-7.40 (m, 3H), 7.52-7.55 (m, 2H), 7.69 (d, J = 16.0 Hz, 1H); 13C NMR (CDCl3) δ: 14.3, 60.5, 118.2, 128.0, 128.8, 130.2, 134.4, 144.5, 167.0; EI-MS m/z (rel intensity) 176 (M+, 40).
(E)-Methyl cinnamate (3d):10 81% as a white solid; mp 33-34 ºC; IR (KBr, cm-1): 1718 (C=O); 1H NMR (CDCl3) δ: 3.81 (s, 3H), 6.45 (d, J = 16.0 Hz, 1H), 7.37-7.40 (m, 3H), 7.51-7.55 (m, 2H), 7.70 (d, J = 16.0 Hz, 1H); 13C NMR (CDCl3) δ: 51.7, 117.7, 128.0, 128.9, 130.3, 134.3, 144.9, 167.4; EI-MS m/z (rel intensity) 162 (M+, 53).
(E)-4-Phenylbut-3-en-2-one (3e):10 58% as a yellow oil; IR (neat, cm-1): 1668 (C=O); 1H NMR (CDCl3) δ: 2.39 (s, 3H), 6.72 (d, J = 16.3 Hz, 1H), 7.39-7.41 (m, 3H), 7.49-7.57 (m, 3H); 13C NMR (CDCl3) δ: 27.5, 127.1, 128.2 128.9, 130.5, 134.4, 143.4, 198.4; EI-MS m/z (rel intensity) 146 (M+, 65).
trans-Stilben (3f):10 79% as a white solid; mp 124-125 ºC; 1H NMR (CDCl3) δ: 7.11 (s, 2H), 7.24-7.28 (m, 2H), 7.36 (t, J = 7.5 Hz, 4H), 7.52 (d, J = 7.3 Hz, 4H); 13C NMR (CDCl3) δ: 126.5, 127.6, 128.7, 137.3; EI-MS m/z (rel intensity) 180 (M+, 100).
(E)-n-Butyl 3-mesitylacrylate (3g).11 79% as a white solid; mp 30-31 ºC; IR (KBr, cm-1): 1709 (C=O); 1H NMR (CDCl3) δ: 0.97 (t, J = 7.4 Hz, 3H), 1.38-1.50 (m, 2H), 1.65-1.74 (m, 2H), 2.28 (s, 3H), 2.33 (s, 6H), 4.21 (t, J = 6.7 Hz, 2H), 6.06 (d, J = 16.4 Hz, 2H), 6.89 (s, 2H), 7.84 (d, J = 16.4 Hz, 1H); 13C NMR (CDCl3) δ: 13.8, 19.2, 21.0, 21.1, 30.7, 64.4, 123.1, 129.1, 130.1, 136.8, 138.3, 143.1, 167.1; EI-MS m/z (rel intensity) 246 (M+, 24).
(E)-t-Butyl 3-mesitylacrylate (3h): 39% as a white solid; mp 62-63 ºC; IR (KBr, cm-1): 1711 (C=O); 1H NMR (CDCl3) δ: 1.54 (s, 9H), 2.28 (s, 3H), 2.33 (s, 6H), 5.98 (d, J = 16.3 Hz, 1H), 6.88 (s, 2H), 7.75 (d, J = 16.3 Hz, 1H); 13C NMR (CDCl3) δ: 21.0, 21.1, 28.2, 80.4, 124.8, 129.1, 131.1, 136.8, 138.0, 138.1, 142.0; EI-MS m/z (rel intensity) 246 (M+, 28); HRMS (ESI-MS) m/z calcd for C16H22O2+Na 269.1512, found 269.1510.
(E)-Ethyl 3-mesitylacrylate (3i):12 58% as a white solid; mp 36-37 ºC; IR (KBr, cm-1): 1701 (C=O); 1H NMR (CDCl3) δ: 1.35 (t, J = 7.1 Hz, 3H), 2.28 (s, 3H), 2.33 (s, 6H), 4.27 (q, J = 7.1 Hz, 2H), 6.06 (d, J = 16.3 Hz, 1H), 6.90 (s, 2H), 7.84 (d, J = 16.3 Hz, 1H); 13C NMR (CDCl3) δ: 14.3, 21.0, 21.1, 60.5, 123.1, 129.1, 130.9, 136.8, 138.3, 143.1, 167.0; EI-MS m/z (rel intensity) 218 (M+, 40).
(E)-n-Butyl 3-(3-methoxyphenyl)acrylate (3j):13 93% as a colorless oil; IR (neat, cm-1): 1713 (C=O); 1H NMR (CDCl3) δ: 0.97 (t, J = 7.3 Hz, 3H), 1.38-1.50 (m, 2H), 1.65-1.74 (m, 2H), 3.84 (s, 3H), 4.21 (t, J = 6.7 Hz, 2H), 6.43 (d, J = 15.9 Hz, 1H), 6.93 (dd, J = 8.2 and 1.8 Hz, 1H), 7.05 (t, J = 2.0 Hz, 1H), 7.12 (d, J = 7.7 Hz, 1H), 7.30 (t, J = 7.9 Hz, 1H), 7.65 (d, J = 16.0 Hz, 1H); 13C NMR (CDCl3) δ: 13.7, 19.2, 30.7, 55.2, 64.4, 112.8, 116.1, 118.5, 120.7, 129.8, 135.8, 144.4, 159.8, 167.0; EI-MS m/z (rel intensity) 234 (M+, 40).
(E)-t-Butyl 3-(3-methoxyphenyl)acrylate (3k):14 59% as a yellow oil; IR (neat, cm-1): 1706 (C=O); 1H NMR (CDCl3) δ: 1.54 (s, 9H), 3.83 (s, 3H), 6.36 (d, J = 16.0 Hz, 1H), 6.91 (dd, J = 8.2 and 2.5 Hz, 1H), 7.03 (t, J = 1.9 Hz, 1H), 7.10 (d, J = 7.8 Hz, 1H), 7.29 (t, J = 7.7 Hz, 1H), 7.55 (d, J = 16.0 Hz, 1H); 13C NMR (CDCl3) δ: 28.2, 55.2, 80.5, 112.7, 115.8, 120.4, 120.7, 129.8, 136.0, 143.4, 159.8, 166.3; EI-MS m/z (rel intensity) 234 (M+, 28).
(E)-Ethyl 3-(3-methoxyphenyl)acrylate (3l):15 91% as a colorless oil; IR (neat, cm-1): 1712 (C=O); 1H NMR (CDCl3) δ: 1.34 (t, J = 7.1 Hz, 3H), 3.83 (s, 3H), 4.27 (q, J = 7.1 Hz, 2H), 6.43 (d, J = 16.0 Hz, 1H), 6.93 (dd, J = 8.2 and 1.9 Hz, 1H), 7.04 (t, J = 1.9 Hz, 1H), 7.12 (d, J = 7.6 Hz, 1H), 7.30 (t, J = 7.9 Hz, 1H) 7.65 (d, J = 16.0 Hz, 1H); 13C NMR (CDCl3) δ: 14.3, 55.3, 60.5, 112.8, 116.1, 118.5, 120.7, 129.8, 135.8, 144.5, 159.8, 166.9; EI-MS m/z (rel intensity) 206 (M+, 67).

ACKNOWLEDGEMENTS
This work was partially supported by Iodine Research Project in Chiba University and the Society of Iodine Science.

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