Direct C5-Arylation Reaction between Imidazoles and Aryl Chlorides

ARTICLE pubs.acs.org/Organometallics

Direct C5-Arylation Reaction between Imidazoles and Aryl Chlorides Catalyzed by Palladium Complexes with Phosphines and N-Heterocyclic Carbenes P. Vijaya Kumar, Wu-Shien Lin, Jiun-Shian Shen, Debkumar Nandi, and Hon Man Lee* Department of Chemistry, National Changhua University of Education, Changhua 50058, Taiwan, Republic of China

bS Supporting Information ABSTRACT: Palladium(II) acetate complexes bearing phosphines and carbene ligands, Pd(L)(PR3)(OAc)2 (1a, R = Ph; 1b, R = Cy; L = 1,3dibenzylimidazol-2-ylidene), were prepared by salt metathesis reactions of their chloro complexes with AgOAc in good yields. The electron-rich 1b was efficient in catalyzing C-5 direct arylation of imidazoles with aryl halides. Most significantly, the catalytic system allows a range of aryl chlorides as substrates. Microwave irradiation effectively promotes the reactions, with good yields obtainable in only 2 h. In combination with the classical method of C
C bond formation reactions, novel imidazole derivatives featuring biaryl and styryl subunits were successfully obtained from 1,4-dichlorobenzene and 1-bromo-4-chlorobenzene.

’ INTRODUCTION Arylated imidazoles constitute an important class of compounds because of their diverse applications in pharmaceuticals, drug candidates, and functional materials.1 The construction of these heteroaromatic building blocks commonly involves palladium-catalyzed cross-coupling reactions.2 Since the initial work by Ohta and co-workers,3 transition-metal-catalyzed direct arylation reactions have been rapidly developing for the syntheses of a wide range of heteroaromatic compounds.4
15 Such methodology to construct biaryls without the need of a preliminary organometallic reagent is highly desirable, because of the reduced waste and fewer reaction steps. However, it is also quite challenging, since a kinetically significant aryl C
H bond activation step is involved. By far, Pd(OAc)2 associated with monodentate phosphines or arsene ligands is the most common catalyst system to prepare arylated imidazoles via direct arylations. Ligands such as PPh3,16
20 AsPh3,21 PCy3,22,23 P(2-furyl)3,24,25 P(n-Bu)Ad2,26,27 and X-phos28 have been commonly employed. Preformed precatalysts are also known but are relatively rare.3,29
32 It is quite common, however, in these catalyst systems that high palladium loadings of 5
10 mol % are required. An exception is the report by Doucet and co-workers on a range of C5-arylated imidazole derivatives obtained under ligandless conditions at low Pd(OAc)2 loading (0.01
0.5 mol %).33 However, either aryl iodides or aryl bromides were needed as substrates. More readily available aryl chlorides have been used only rarely because of the high strength of the C
Cl bond.26,27 In this regard, Daugulis et al. reported relevant arylation reactions which allow access to a wide variety of electron-rich heterocycles from aryl chlorides.26 r 2011 American Chemical Society

Lately, Sames et al. also reported regioselective sequential arylation of imidazole derivatives with aryl chlorides.27 Nevertheless, high palladium loadings (5 mol %) and sophisticated phosphine ligands (usually expensive and unstable) are still required. In view of all these previous reports, we have been searching for a new effective catalytic system, allowing relatively lower palladium loading (5 mol %) and use of reactive aryl halides (bromides and iodides) as coupling partners were commonly found in the literature. In contrast, we have successfully developed effective direct C5-arylation reactions of imidazoles with aryl chlorides using a moderate loading (2.5 mol %) of the preformed electron-rich 1b as precatalyst. We confirmed that the installation of a robust carbene and a labile phosphine ligand on 5166

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Organometallics Scheme 4. Proposed Catalytic Cycle of the Direct C-5 Arylation Reaction of Imdazoles Catalyzed by 1b

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Crystals suitable for X-ray crystallography were obtained by vapor diffusion of ether into a THF solution of the compound. Synthesis of Pd(L)(PCy3)(OAc)2 (1b). The compound was prepared following a procedure similar to that for 1a. A mixtue of 2b (2.00 g, 2.840 mmol) and silver acetate (1.42 g, 8.250 mmol) was used. A yellowish compound was obtained. Yield: 1.53 g, 72%. Mp: 151
155 C dec. Anal. Calcd for C39H55N2O4PPd: C, 62.19; H, 7.36; N, 3.72. Found: C, 61.88; H, 7.48; N, 3.57. 1H NMR (300 MHz, CDCl3): δ 1.06
1.83 (m, 33H, Cy H), 1.86 (s, 3H, CH3), 1.94 (s, 3H, CH3), 5.52 (d, 2JHH = 15.0 Hz, 2H, PhCHAHBN), 6.17 (d, 2JHH = 15.0 Hz, 2H, PhCHAHBN), 6.61 (s, 2H, imi H), 7.24
7.35 (m, 10H, Ph H). 13C{1H} NMR (75 MHz, CDCl3): δ 22.6 (CH3), 24.3 (Cy C), 26.7 (d, 3JPC = 10.9 Hz, Cy C), 28.4 (Cy C), 34.1 (d, 1JPC = 23.5 Hz, Cy C), 54.3 (CH2), 120.3 (imi C), 127.5 (Ph C), 127.8 (Ph C), 128.0 (Ph C), 133.7 (Ph C), 160.0 (NCN), 176.6 (CO). 31P{1H} NMR (121 MHz, CDCl3): δ 40.3. Crystals suitable for X-ray crystallography were obtained by vapor diffusion of hexane into a THF solution of the compound.

General Procedure for Palladium-Catalyzed Direct Arylation. Typically, a mixture of aryl halide (2.5 mmol), imidazole

palladium acetate affords an effective precatalyst. Under microwave heating, good yields of arylated products can be obtained in 2 h. The same catalyst system was also versatile in catalyzing Suzuki and Heck coupling reactions. On combination of these classical methods of C
C bond formation reactions, we demonstrated that a variety of novel imidazole derivatives containing biaryl and styryl motifs were easily accessible from dihalobenzenes.

’ EXPERIMENTAL SECTION General Information. All manipulations were performed under a dry nitrogen atmosphere using standard Schlenk techniques. Solvents were dried with standard procedures. Starting chemicals were purchased from commercial sources and used as received. Compounds 2a,b were prepared according to the literature procedure.37 Microwave irradiation experiments were conducted in a Milestone Start S microwave system. Reaction times refer to hold times at the temperature indicated in Tables 3
5. The temperature was measured with an IR sensor on the outside of the reaction vessel. 1H, 13C{1H}, and 31P{1H} NMR spectra were recorded at 300.13, 75.48, and 121.49 MHz, respectively, on a Bruker AV-300 spectrometer. Elemental analyses were performed on a Thermo Flash 2000 CHN-O elemental analyzer. High-resolution mass spectroscopy (HRMS) was measured on a Finnigan/Thermo Quest MAT mass spectrometer at the National Chung Hsing University (Taiwan). Synthesis of Pd(L)(PPh3)(OAc)2 (1a). A mixture of 2a (2.00 g, 2.907 mmol) and silver acetate (1.46 g, 8.722 mmol) in acetonitrile (20 mL) was stirred at room temperature for 12 h. The mixture was then filtered through a short column of Celite. After removal of the solvent under vacuum, the residue was washed with diethyl ether to afford a yellowish solid. Yield: 1.78 g, 83%. Mp: 153
157 C dec. Anal. Calcd for C39H37N2O4PPd: C, 63.72; H, 5.07; N, 3.81. Found: C, 63.64; H, 5.11; N, 3.82. 1H NMR (300 MHz, CDCl3): δ 1.43 (s, 3H, CH3), 1.89 (s, 2H, CH3), δ 4.53 (d, 2JHH = 14.1 Hz, 2H, PhCHAHBN), 5.92 (d, 2JHH = 14.1 Hz, 2H, PhCHAHBN), 6.31 (s, 2H, imi H), 6.97
7.47 (m, 25H, Ph H). 13 C{1H} NMR (75 MHz, CDCl3): δ 23.3 (CH3), 54.1 (CH2), 120.8 (imi C), 128.2 (d, 3JPC = 4.9 Hz, Ph C), 128.4 (Ph C), 128.5 (d, 2JPC = 5.5 Hz, Ph C), 128.9 (Ph C), 129.2 (Ph C), 130.9 (d, 4JPC = 2.3 Hz, Ph C), 133.8 (Ph C), 134.0 (d, 1JPC = 3.5 Hz, Ph C), 157.4 (NCN), 176.5 (d, 3JPC = 31.2 Hz, CO). 31P{1H} NMR (121 MHz, CDCl3): δ 24.4.

(3.7 mmol), KOAc (5.0 mmol), and Pd precatalyst (0.087 mmol) was dissolved in DMA (5 mL) under a nitrogen atmosphere. The reaction mixture was stirred at 140 C in a preheated oil bath for 18 h or under microwave irradiation for 2 h. After the mixture was cooled, ethyl acetate (10 mL) was added. The solution was poured into water (50 mL) and extracted with ethyl acetate (3  25 mL). The combined extracts were washed with brine, dried over anhydrous MgSO4, and evaporated to dryness under vacuum to give the crude product, which was purified by column chromatography. Compounds 4, 6, 8, 9, 11, and 13,33 6B,47 5, 5B, and 15,16 and 1048 were identified by comparison of NMR data with those in the literature. Crystals of 3 and 8 suitable for X-ray crystallography were obtained by vapor diffusion of ether into a THF solution of the compound.

General Procedure for the Palladium-Catalyzed Suzuki Coupling Reaction. In a typical reaction, a mixture of aryl halides (1.0 mmol), phenylboronic acid (1.5 mmol), Cs2CO3 (2.0 mmol), and palladium(II) precatalyst (2.5 mol %) in 1,4-dioxane (2.5 mL) was stirred under nitrogen at 80 C for 2 h. After the mixture was cooled, ethyl acetate (25 mL) was added. The solution was filtered through a short column of Celite. The solvent was completely removed under vacuum to give a crude product, which was purified by column chromatography. Compounds 18a49 and 18b50 were identified by comparison of NMR data with those in the literature.

General Procedure for the Palladium-Catalyzed Heck Coupling Reaction. A 50 mL round-bottom flask was charged with aryl halide (1.0 mmol), alkene (1.2 mmol), anhydrous sodium acetate (1.2 mmol), palladium precatalyst (2.5 mol %), and NMP (5 mL) under nitrogen. The flask was heated with stirring in a preheated oil bath at 140 C for 18 h. After the mixture was cooled, ethyl acetate (25 mL) was added. The solution was poured into water (50 mL) and extracted with ethyl acetate (3  25 mL). The combined extracts were washed with brine, dried over anhydrous MgSO4, and evaporated to dryness under vacuum to give a crude product, which was purified by column chromatography. Compounds 21a,b were identified by comparison of NMR data with those in the literature.51 5-(4-Acetylphenyl)-1-methylimidazole (3). Light-yellow solid. Mp: 119
121 C. 1H NMR (300 MHz, CDCl3): δ 2.61 (s, 3H, CH3), 3.71 (s, 3H, NCH3), 7.19 (s, 1H, H4), 7.61 (s, 1H, H2), 7.48 (d, 3 J = 7.8 Hz, 2H, Ar H), 8.00 (d, 3J = 7.8 Hz, 2H, Ar H). 13C{1H} NMR (75 MHz, CDCl3): δ 26.5 (CH3), 32.9 (NCH3), 128.0, 128.8, 132.5, 134.2, 136.1, 140.0 (NCN), 197.3 (CdO). HRMS (EI; m/z): calcd for C12H12N2O 200.0945, found 200.0949. Crystals suitable for X-ray crystallography were obtained by vapor diffusion of ether into a dichloromethane solution of the compound. 5167

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Organometallics 1-[4-[2-(4-Acetylphenyl)-3-methylimidazol-4-yl]phenyl]ethanone (3B). 1H NMR (300 MHz, CDCl3): δ 2.54 (s, 6H, CH3),

3.68 (s, 3H, NCH3), 7.24 (s, 1H, H4), 7.39
7.59 (m, 2H, Ar H), 7.65
7.84 (m, 2H, Ar H), 7.89
8.12 (m, 4H, Ar H). 13C{1H} NMR (75 MHz, CDCl3): δ 26.5 (CH3), 26.5 (CH3), 34.2 (NCH3), 128.1, 128.4, 128.6, 128.7, 129.0, 134.1, 134.5, 135.1, 136.0, 136.7, 149.0, 197.2 (CdO), 197.3 (CdO). HRMS (EI; m/z): calcd for C20H18N2O2 318.1368, found 318.1363. 4-(1-Methylimidazol-2-yl)benzonitrile (4A). 1H NMR (300 MHz, CDCl3): δ 3.77 (s, 3H, CH3), 7.00 (s, 1H, imi H), 7.13 (s, 1H, imi H), 7.64
7.97 (m, 4H, Ar H). 13C{1H} NMR (75 MHz, CDCl3): δ 34.8 (CH3), 76.6, 77.1, 77.5, 111.9, 118.5, 123.7, 128.8, 129.2, 132.3, 134.7, 145.6. HRMS (EI; m/z): calcd for C11H9N3 183.0796, found 183.0788. 5-(4-Formylphenyl)-1-methylimidazole (7). Yellow solid. Mp: 165
167 C. 1H NMR (300 MHz, CDCl3): δ 3.82 (s, 3H, CH3), 7.57 (s, 1H, H4), 7.80 (d, 3J = 8.0 Hz, 2H, Ar H), 8.01 (d, 3J = 8.0 Hz, 2H, Ar H), 8.35 (s, 1H, H2), 10.06 (s, 1H, CHO). 13C{1H} NMR (75 MHz, CDCl3): δ 34.0 (NCH3), 125.9, 128.8, 130.4, 132.7, 134.4, 135.8, 140.2 (NCN), 193.0 (CHO). HRMS (EI; m/z): calcd for C11H10N2 186.0793, found 186.0789. 5-(3-Methoxyphenyl)-1,2-dimethylimidazole (12). Lightbrown solid. Mp: 60
62 C. 1H NMR (300 MHz, CDCl3, 25 C, TMS): δ 2.52 (s, 3H, CCH3), 3.56 (s, 3H, NCH3), 3.82 (s, 3H, OCH3), 6.87
6.95 (m, 3H, Ar H), 7.02 (s, 1H, H4), 7.35 (t, 3J = 7.6 Hz, 2H, Ar H). 13C{1H} NMR (75 MHz, CDCl3): δ 13.0 (CCH3), 31.5 (NCH3), 55.2 (OCH3), 113.6, 114.5, 121.0, 123.5, 129.7, 130.6, 133.7, 145.6 (NCN), 159.7 (COCH3). HRMS (EI; m/z): calcd for C13H14N2O 214.1106, found 214.1111. 3-(4-Chlorophenyl)imidazolyl[1,2-a]pyridine (16). Offwhite solid. Mp: 117
119 C. 1H NMR (300 MHz, CDCl3): δ 6.81 (td, 3J = 6.9 Hz, 4J = 1.0 Hz, 1H, py H), 7.20 (ddd, 3J = 9.1 Hz, 3J = 6.7 Hz, 4 J = 1.2 Hz, 1H, py H), 7.48 (s, 4H, Ar H), 7.62
7.70 (m, 2H, imi H, py H), 8.26 (dt, 3J = 7.0 Hz, 4J = 1.2 Hz, 1H, py H). 13C{1H} NMR (75 MHz, CDCl3): δ 112.7, 118.3, 123.1, 124.3, 124.5, 127.7, 129.1, 129.4, 132.7, 133.9, 146.2 (NCN). HRMS (EI; m/z): calcd for C13H9ClN2 228.0454, found 228.0448.

3-[4-(2,3-Dimethylimidazol-4-yl)phenyl]imidazolyl[1,2-a]pyridine (17). Off-white solid. Mp: 184
186 C. 1H NMR (300 MHz,

CDCl3): δ 2.47 (s, 3H, CCH3), 3.58 (s, 3H, NCH3), 6.83 (t, 3J = 6.7 Hz, 1H, py H), 7.02 (s, 1H, imi H), 7.16
7.29 (m, 1H, py H), 7.49 (d, 3J = 7.6 Hz, 2H, Ar H), 7.56
7.77 (m, 4H, Ar H, py H, imi H), 8.37 (d, 3J = 7.0 Hz, 1H, py H). 13C{1H} NMR (75 MHz, CDCl3/DMSO-d6): δ 13.7 (CCH3), 31.6 (NCH3), 112.9, 118.0, 123.6, 124.6, 125.1, 125.7, 128.0, 128.3, 129.0, 130.0, 132.6, 132.9, 146.1 (NCN), 146.3 (NCN). HRMS (EI; m/z): calcd for C18H16N4 288.1375, found 288.1383.

5-[4-(2-Methoxyphenyl)phenyl]-1,2-dimethylimidazole (19a). Off-white solid. Mp: 127
129 C. 1H NMR (300 MHz, CDCl3): δ 2.47 (s, 3H, CCH3), 3.57 (s, 3H, NCH3), 3.83 (s, 3H, OCH3), 6.92
7.11 (m, 3H, imi H, Ph H), 7.27
7.43 (m, 4H, Ph H), 7.59 (d, 3J = 7.9 Hz, 2H, Ph H). 13 C{1H} NMR (75 MHz, CDCl3): δ 13.3 (CCH3), 31.5 (NCH3), 55.5 (OCH3), 111.2, 120.9, 124.8, 128.2, 128.5, 128.9, 129.7, 129.8, 130.7, 138.1 (NCN), 156.4 (CO). HRMS (EI; m/z): calcd for C18H18N2O 278.1419, found 278.1427.

5-[4-(4-Methoxyphenyl)phenyl]-1,2-dimethylimidazole (19b). Off-white solid. Mp: 204
206 C. 1H NMR (300 MHz, DMSO-

d6): δ 2.36 (s, 3H, CCH3), 3.56 (s, 3H, NCH3), 3.80 (s, 3H, OCH3), 6.90 (s, 1H, imi H), 7.04 (d, 3J = 8.5 Hz, 2H, Ph H), 7.48 (d, 3J = 8.2 Hz, 2H, Ph H), 7.69 (d, 3J = 8.2 Hz, 2H, Ph H), 7.65 (d, 3J = 8.8 Hz, 2H, Ph H). 13C{1H} NMR (75 MHz, DMSO-d6): δ 13.9 (CCH3), 31.8 (NCH3), 55.7 (OCH3), 115.0, 126.0, 127.0, 128.2, 128.9, 129.3, 132.4, 133.1, 139.1, 146.4 (NCN), 159.5 (CO). HRMS (EI; m/z): calcd for C18H18N2O 278.1419, found 278.1413.

3-(20 -Methoxybiphenyl-4-yl)imidazolyl[1,2-a]pyridine (20a).

Brown solid. Mp: 107
109 C. 1H NMR (300 MHz, CDCl3): δ 3.84

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(s, 3H, OCH3), 6.80 (t, 3J = 6.7 Hz, 1H, py H), 6.94
7.12 (m, 2H, Ar H), 7.20 (dd, 3J = 15.9, 8.9 Hz, 1H, py H), 7.28
7.46 (m, 2H, Ar H), 7.51
7.85 (m, 6H, Ar H, py H, imi H), 8.41 (d, 3J = 7.0 Hz, 1H, py H). 13C{1H} NMR (75 MHz, CDCl3): δ 55.4 (OCH3), 111.1, 112.4, 118.1, 120.8, 123.4, 124.1, 125.6, 127.4, 127.6, 128.9, 129.6, 130.2, 130.6, 132.5, 138.3, 146.0 (NCN), 156.3 (COCH3). HRMS (EI; m/z): calcd for C20H16ON2 300.1263, found 300.1266.

3-(40 -Methoxybiphenyl-4-yl)imidazolyl[1,2-a]pyridine (20b).

Brown solid. Mp: 186
188 C. 1H NMR (300 MHz, CDCl3): δ 3.85 (s, 3H, CH3), 6.82 (t, 3J = 6.8 Hz, 1H, py H), 7.00 (d, 3J = 8.5 Hz, 2H, Ar H), 7.09
7.34 (m, 1H, py H), 7.55
7.84 (m, 8H, Ar H, imi H, py H), 8.38 (d, 3J = 7.0 Hz, 1H, py H). 13C{1H} NMR (75 MHz, CDCl3): δ 55.3 (OCH3), 112.6, 114.3, 118.2, 123.4, 124.2, 127.4, 128.0, 128.3, 132.5, 132.8, 140.6, 146.1 (NCN), 159.4 (COCH3). HRMS (EI; m/z): calcd for C20H16ON2 300.1263, found 300.1257. 1,2-Dimethyl-5-[4-[(E)-styryl]phenyl]imidazole (21a). Offwhite solid. Mp: 123
125 C. 1H NMR (300 MHz, CDCl3): δ 2.47 (s, 3H, CCH3), 3.55 (s, 3H, NCH3), 7.01 (br s, 1H, imi H), 7.12 (s, 2H, overlapping Ph H and dCH), 7.25
7.43 (m, 5H, Ph H), 7.56 (d, 3J = 8.2 Hz, 2H, Ph H), 7.52 (d, 3J = 8.2 Hz, 2H, Ph H). 13C{1H} NMR (75 MHz, CDCl3): δ 13.3 (CCH3), 31.5 (NCH3), 126.6, 126.8, 127.7, 127.8, 128.7, 128.8, 128.9, 129.4, 136.9, 137.0. HRMS (EI; m/z): calcd for C19H18N2 274.1470, found 274.1472.

5-[4-[(E)-2-(4-Methoxyphenyl)vinyl]phenyl]-1,2-dimethylimidazole (21b). Pale yellow solid. Mp: 218
220 C. 1H NMR (300

MHz, CDCl3): δ 2.46 (s, 3H, CCH3), 3.54 (s, 3H, NCH3), 3.82 (s, 3H, OCH3), 6.83
7.16 (m, 5H, imi H, dCH, Ph H), 7.31 (d, 3J = 8.2 Hz, 2H, Ph H), 7.45 (d, 3J = 8.5 Hz, 2H, Ph H), 7.53 (d, 3J = 8.2 Hz, 2H, Ph H). 13C{1H} NMR (75 MHz, CDCl3): δ 13.5 (CCH3), 31.5 (NCH3), 55.3 (OCH3), 114.1, 125.0, 125.7, 126.5, 127.8, 128.7, 128.8, 129.8, 137.2 (NCN), 159.4 (CO). HRMS (EI; m/z): calcd for C20H20N2O 304.1576, found 304.1570. 3-[4-[(E)-Styryl]imidazolyl[1,2-a]pyridine (23a). Pale yellow solid. Mp: 157
159 C. 1H NMR (300 MHz, CDCl3): δ 6.82 (t, 3J = 6.4 Hz, 1H, py H), 7.10
7.32 (m, 4H, dCH, py H, Ar H), 7.37 (t, 3J = 7.3 Hz, 2H, Ar H), 7.54 (m, 4H, imi H, py H, Ar H), 7.61
7.81 (m, 4H, Ar H), 8.37 (d, 3J = 7.0 Hz, 1H, py H). 13C{1H} NMR (75 MHz, CDCl3): δ 112.6, 118.3, 123.4, 124.3, 125.5, 126.6, 127.2, 127.7, 127.9, 128.0, 128.3, 128.7, 129.4, 132.6, 137.0, 137.1, 146.2 (NCN). HRMS (EI; m/z): calcd for C21H16N2 296.1313, found 296.1320.

3-[4-[2-(4-Methoxyphenyl)ethyl]phenyl]imidazolyl[1,2-a]pyridine (23b). Pale yellow solid. Mp: 187
189 C. 1H NMR (300

MHz, CDCl3): δ 3.83 (s, 3H, CH3), 6.81 (t, 3J = 6.7 Hz, 1H, py H), 6.91 (d, 3J = 8.8 Hz, 2H, Ph H), 6.96
7.23 (m, 3H, HCdCH, py H), 7.45
7.72 (m, 8H, py H, imi H, Ph H), 8.36 (d, 3J = 7.0 Hz, 1H, py H). 13 C{1H} NMR (75 MHz, CDCl3): δ 55.3 (OCH3), 112.6, 114.2, 118.2, 123.4, 124.2, 125.6, 126.9, 127.8, 128.0, 128.9, 129.8, 132.5, 137.5, 146.2 (NCN), 159.5 (CO). HRMS (EI; m/z): calcd for C22H18N2O 326.1419, found 326.1411. X-ray Diffraction Studies. Data for compounds 1a,b, 3, and 8 were collected at 150(2) K on a Bruker APEX II equipped with a CCD area detector and a graphite monochromator utilizing Mo Kα radiation (λ = 0.710 73 Å). The unit cell parameters were obtained by leastsquares refinement. Data collection and reduction were performed using the Bruker APEX2 and SAINT software.52 Absorption corrections were performed using the SADABS program.53 All the structures were solved by direct methods and refined by full-matrix least-squares methods against F2 with the SHELXTL software package.54 All non-H atoms were refined anisotropically. All H atoms were fixed at calculated positions and refined with the use of a riding model. Crystallographic data are given in Table S1 of the Supporting Information. CCDC files 783655 (1a), 783656 (1b 3 0.5C4H8O 3 H2O), 783654 (3), and 786904 (8) contain supplementary crystallographic data for this paper. These 5168

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Organometallics data can be obtained free of charge from The Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_request/cif.

’ ASSOCIATED CONTENT Supporting Information. Tables, figures, and CIF files giving additional characterization data and full crystallographic data for 1a,b, 3, and 8. This material is available free of charge via the Internet at http://pubs.acs.org.

bS

’ AUTHOR INFORMATION Corresponding Author

*Tel: +886 4 7232105 ext. 3523. Fax: +886 4 7211190. E-mail: [email protected].

’ ACKNOWLEDGMENT We are grateful to the National Science Council of Taiwan for financial support of this work. We also thank the National Center for High-performance Computing of Taiwan for computing time and financial support of the Conquest software. ’ REFERENCES (1) Bellina, F.; Cauteruccio, S.; Rossi, R. Tetrahedron 2007, 63, 4571. (2) Schn€urch, M.; Flasik, R.; Khan, A. F.; Spina, M.; Mihovilovic, M. D.; Stanetty, P. Eur. J. Org. Chem. 2006, 2006, 3283. (3) Aoyagi, Y.; Inoue, A.; Koizumi, I.; Hashimoto, R.; Tokunaga, K.; Gohma, K.; Komatsu, J.; Sekine, K.; Miyafuji, A.; Kunoh, J.; Honma, R.; Akita, Y.; Ohta, A. Heterocycles 1992, 33, 257. (4) Godula, K.; Sames, D. Science 2006, 312, 67. (5) Satoh, T.; Miura, M. Chem. Lett. 2007, 36, 200. (6) Seregin, I. V.; Gevorgyan, V. Chem. Soc. Rev. 2007, 36, 1173. (7) Alberico, D.; Scott, M. E.; Lautens, M. Chem. Rev. 2007, 107, 174. (8) Campeau, L. C.; Stuart, D. R.; Fagnou, K. Aldrichim. Acta 2007, 40, 35. (9) McGlacken, G. P.; Bateman, L. M. Chem. Soc. Rev. 2009, 38, 2447. (10) Ackermann, L.; Vicente, R.; Kapdi, A. R. Angew. Chem., Int. Ed. 2009, 48, 9792. (11) Bellina, F.; Rossi, R. Tetrahedron 2009, 65, 10269. (12) Roger, J.; Gottumukkala, A. L.; Doucet, H. ChemCatChem 2010, 2, 20. (13) Fairlamb, I. J. S. Chem. Soc. Rev. 2007, 36, 1036. (14) Campeau, L.-C.; Fagnou, K. Chem. Commun. 2006, 1253. (15) Bellina, F.; Cauteruccio, S.; Rossi, R. Curr. Org. Chem. 2008, 12, 774. (16) Pivsa-Art, S.; Satoh, T.; Kawamura, Y.; Miura, M.; Nomura, M. Bull. Chem. Soc. Jpn. 1998, 71, 467. (17) Kondo, Y.; Komine, T.; Sakamoto, T. Org. Lett. 2000, 2, 3111. (18) Li, W.; Nelson, D. P.; Jensen, M. S.; Hoerrner, R. S.; Javadi, G. J.; Cai, D.; Larsen, R. D. Org. Lett. 2003, 5, 4835. (19) Koubachi, J.; El Kazzouli, S.; Berteina-Raboin, S.; Mouaddib, A.; Guillaumet, G. Synlett 2006, 2006, 3237. (20) Koubachi, J.; El Kazzouli, S.; Berteina-Raboin, S.; Mouaddib, A.; Guillaumet, G. J. Org. Chem. 2007, 72, 7650. (21) Bellina, F.; Cauteruccio, S.; Mannina, L.; Rossi, R.; Viel, S. J. Org. Chem. 2005, 70, 3997. (22) Liegault, B. t.; Lapointe, D.; Caron, L.; Vlassova, A.; Fagnou, K. J. Org. Chem. 2009, 74, 1826. (23) Liegault, B. t.; Petrov, I.; Gorelsky, S. I.; Fagnou, K. J. Org. Chem. 2010, 75, 1047. (24) Bellina, F.; Cauteruccio, S.; Fiore, A. D.; Rossi, R. Eur. J. Org. Chem. 2008, 2008, 5436. (25) Bellina, F.; Cauteruccio, S.; Di Fiore, A.; Marchetti, C.; Rossi, R. Tetrahedron 2008, 64, 6060. (26) Chiong, H. A.; Daugulis, O. Org. Lett. 2007, 9, 1449.

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dx.doi.org/10.1021/om200490k |Organometallics 2011, 30, 5160–5169