Regioselective synthesis of substituted naphthalenes

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Jul 11, 2012 - (a) Yang, L.; Lei, C. H.; Wang, D. X.; Huang, Z. T.; Wang, M. X. Org. Lett. ... 2009, 74, 5738e5741; (k) Maeda, S.; Horikawa, N.; Obora, Y.; Ishii, ...

Tetrahedron 68 (2012) 7960e7965

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Regioselective synthesis of substituted naphthalenes and phenanthrenes by FeCl3-promoted annulation of aryl and naphthyl acetaldehydes with alkynes Xiuli Bu a, Longcheng Hong a, Ruiting Liu a, Jianquan Hong a, Zhengxing Zhang a, Xigeng Zhou a, b, * a b

Department of Chemistry, Shanghai Key Laboratory of Molecular Catalysis and Innovative Materials, Fudan University, Shanghai 200433, People’s Republic of China State Key Laboratory of Organometallic Chemistry, Shanghai 200032, People’s Republic of China

a r t i c l e i n f o

a b s t r a c t

Article history: Received 16 April 2012 Received in revised form 22 June 2012 Accepted 3 July 2012 Available online 11 July 2012

The FeCl3-promoted annulation reaction of aryl acetaldehydes with alkynes has been established, which provides a new and versatile straightforward procedure for the regioselective synthesis of mono-, di-, and polysubstituted naphthalenes under mild conditions. Interestingly, the present catalytic system not only differentiates between internal and terminal alkynes but also shows unprecedented complete Me3SiOH elimination selectivity for silyl alkyne substrates. Furthermore, the synthesis of a series of substituted phenanthrenes via reactions of nathphyl acetaldehydes with internal alkynes is also achieved for the first time in good yields with excellent regioselectivity. Ó 2012 Elsevier Ltd. All rights reserved.

Keywords: o-(1-Alkynyl)benzoates Disulfides Sulfoesterification Bicyclization Iron (III) chloride

1. Introduction The development of new naphthalene- and phenanthrenebased structures and new methods for their construction has been of longstanding importance in organic chemistry because of the frequent existence of such moieties in biologically active compounds as well as their role as valuable synthetic intermediates.1,2 Over the past several years, the metal-promoted benzannulation of aryl acetaldehydes with arylalkynes has emerged as an efficient and regioselective method for the construction of substituted naphthalene derivatives.3 These transformations effect tandem coupling and cyclization in 1-step with water as the only waste material. Therefore, in principle, it is an efficient and simple strategy and can be considered as a ‘greener’ approach than the traditional procedures. Although several efficient Lewis acid catalysts, such as TiCl4,3b GaCl3,3a and AuCl3/AgSbF6,3c have been developed in this area, a more diverse selection of catalytic systems is still highly desirable. In particular the development of the catalysts that are complementary to the previously reported catalytic systems, with some behaving similarly, but others displaying behavior unprecedented in selectivity, is essential. In addition, the question of whether or not the corresponding phenanthrenes could also be achieved via similar reactions is still an open issue.

* Corresponding author. Tel./fax: þ86 21 65643769; e-mail address: [email protected] fudan.edu.cn (X. Zhou). 0040-4020/$ e see front matter Ó 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.tet.2012.07.007

The development of alternative catalytic methods for the activation of chemical bonds using iron salts in place of noble metal species is currently attracting considerable attention from both academic and industrial researchers due to their low price, commercial accessibility, environmentally friendly character, and exceptional reactivity.4 Iron (III) chloride has been utilized in a wide variety of organic reactions, such as reduction of nitroarenes to anilines,5 activation of C]O,6 C]N,7 C^C,8 CeH(X),9 and CeO10 bonds, and cross-coupling reactions.4a,11 In seeking to further broaden the scope of metal-catalyzed benzannulations of aryl acetaldehydes with arylalkynes, we were intrigued by the possibility that an iron-based species might offer a valuable alternative to other Lewis acid catalysts in terms of enhanced chemoselectivity. Herein we describe a new and selective FeCl3-promoted synthesis of substituted naphthalenes from aryl acetaldehydes and internal alkynes under mild and convenient reaction condition, including an unprecedented extension to substituted phenanthrenes. 2. Results and discussion In our initial experiments phenylacetaldehyde (1a) and diphenylacetylene (2a) were chosen as model substrates for exploring the optimum reaction conditions. As shown in Table 1, the most promising results were obtained in the presence of FeCl3. To optimize conditions with FeCl3 as a Lewis acid, we examined the effect of other reaction parameters. Different solvents were examined first (Table 1, entries 1e7). In general, use of coordinated solvents

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Table 2 Synthesis of substituted naphthalene derivatives via reaction of aldehydes with internal alkynesa

Table 1 Optimization of the reaction conditionsa

Entry

Additive (equiv)

Solvent

Time (h)

Yield (%)b

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

FeCl3 (1.0) FeCl3 (1.0) FeCl3 (1.0) FeCl3 (1.0) FeCl3 (1.0) FeCl3 (1.0) FeCl3 (1.0) FeCl3 (0.5) FeCl3 (0.1) FeCl3 (1.2) Fe(acac)3 (1.0) FeCl2 (1.0) FeCl3$6H2O InCl3 (1.0) BiCl3 (1.0) YCl3 (1.0) Y(OTf)3 (1.0) TsOH$H2O (0.2) FeCl3 (0.4)/YCl3 (0.2) FeCl3 (0.5)/4  A MS

DCM CH3NO2 Toluene THF CH3CN DME DCE DCE DCE DCE DCE DCE DCE DCE DCE DCE DCE DCE DCE DCE

7 28 28 28 4 3 2 24 14 2 2 13 12 2 2 2 2 2 16 14

24 26 15 NR NR NR 61 12 Trace 73 NR NR NR 12 NR NR NR NR 61c 25c

a Reaction conditions: Phenylacetaldehyde (0.34 mmol), diphenylacetylene (0.28 mmol), solvent (3 mL), rt (18e26  C). b Isolated yield. c Carried out at 50  C.

(e.g., THF, DME) tends to shut down the reacting system, and non-coordinated solvents (DCM, toluene) were also ineffective, although small amounts of 3aa were occasionally observed. 3aa was obtained in 61% yield when 1,2-dichloroethane (1,2-DCE) was used as solvent. We found that the stoichiometric ratio of FeCl3 and substrates had a large impact on the yield of the desired product. When FeCl3 was reduced to 10 mol %, only trace amount of 3aa could be detected along with recovery of the starting material alkyne (Table 1, entry 9). Best yield was obtained when 1.2 equiv of FeCl3 was applied (Table 1, entry 10). To further improve the yields in this transformation, the effect of metal source was systematically examined. It was discovered that use of FeCl2, Fe(acac)3 or FeCl3$6H2O in place of FeCl3 fails to provide the desired product (Table 1, entries 11e13). It indicates that the coordination of Fe3þ to H2O, which is formed during the reaction might prevent the annulation to occur. Moreover, treatment of a mixture of 1a and 2a with InCl3 in DCE gave 3aa only in low yield (Table 1, entry 14). Other metals tested showed no activity for the annulation (Table 1, entries 15e17). In addition, only starting materials were recovered when FeCl3 was replaced by a Bronsted acid, such as TsOH$H2O (Table 1, entry 18). Noticeably, FeCl3 can be decreased to a catalytic A amount in the presence of 0.2 equiv of YCl3 (entry 19), while 4  molecular sieves as a dehydrating reagent gave only a limited improvement possibly due to its moderate hydrophilicity, that is, not enough to compete overwhelmingly against anhydrous FeCl3 under the involved conditions (entries 20 vs 8). Taking into account the price of anhydrous YCl3, however, the reactions were carried out with FeCl3 alone thereafter. As shown in Table 2, the reaction conditions described above are effective for the transformation of a number of different substrate combinations, several functional groups are tolerated. The introduction of either the electron-donating or weak electronwithdrawing (e.g., chloro) group at the para-position of the nucleophilic benzene ring had only a slight influence on the reactivity compared with those without a substituent on the aromatic ring

Entry

1

2

R2

R3

3

Yield (%)b

1 2 3 4 5 6 7 8 9 10 11 12 13

1a 1a 1a 1a 1b 1b 1b 1b 1b 1c 1c 1c 1c

2a 2b 2c 2d 2a 2b 2c 2d 2e 2a 2b 2c 2d

Ph p-CH3OC6H4 p-CH3C6H4 Ph Ph p-CH3OC6H4 p-CH3C6H4 Ph Ph Ph p-CH3OC6H4 p-CH3C6H4 Ph

Ph Ph p-CH3C6H4 CH2CH3 Ph Ph p-CH3C6H4 CH2CH3 CH3 Ph Ph p-CH3C6H4 CH2CH3

3aa 3ab 3ac 3ad 3ba 3bb 3bc 3bd 3be 3ca 3cb 3cc 3cd

73(63c) 76 69 73 79 79 61 81 86 76 81 73 76

a Reaction conditions: Aldehyde (1.2 equiv), alkyne (1.0 equiv), FeCl3 (1.2 equiv), 1,2-DCE (3 mL), rt (18e26  C), 2 h. b Isolated yield. c Carried out in 8 mmol scale.

(Table 2, entries 1, 5, and 10). The annulation reactions of electronrich (entries 2, 3, 6, 7, 11, 12) and electron-neutral (entries 1, 5, 10) aryl acetylenes proceeded smoothly, and alkylated acetylenes 2d and 2e also afforded the naphthalene products in good yields (entry 4, 8, 9, 13). However, alkyne bearing the strong electronwithdrawing substituents, such as dimethyl acetylenedicarboxylate, was inefficient substrate. Significantly, for the asymmetrically internal acetylenes bearing different substituents at 1- and 2-positions, only one isomer was obtained, indicating that these transformations allow for synthesis of a variety of di- and poly-substituted naphthalenes in good yields with excellent regioselectivity (entries 2, 4, 6, 8, 9, 11, and 13). The observed effects of internal alkyne structures on regioselectivity are clearly in agreement with the involvement of vinyl cations in this process and suggest that the regioselectivity depends on the electronic effect. The selectivity would favor the vinyl cation intermediate, that is, most stabilized to effect electrophilic attack. In striking contrast to the observation that the terminal alkynes are generally more reactive than the internal alkynes in other metal-catalyzed benzannulation of aryl acetaldehydes and arylalkynes, only trace amount of the desired product could be detected even with a prolonged heating at 60  C when the terminal alkyne PhC^CH was subjected to the present annulation reaction conditions. After several experiments, we were pleased to find that replacement of terminal alkynes with silylated internal alkynes could provide the desired mono- and di-substituted naphthalenes in 56e78% isolated yields, companying with the elimination of Me3SiOH (Table 3). The present reaction provides the first probe of the chemoselectivity of annulation of aryl acetaldehydes and silyl alkynes. It was found that the reactivity of silyl alkynes is controlled by the electronic property of the substituents. Silyl acetylene with electron-deficient aryl, such as p-chlorophenyl silyl acetylene, reacted smoothly with various aryl-substituted acetaldehydes, affording the corresponding substituted naphthalenes in satisfactory yields with complete regioselectivity (Table 3, entries 2, 4, and 6). At the same time, electron-rich aryl, like p-methoxylphenyl, seems to negatively affect the yields, but the regioselectivity remained essentially constant (Table 3, entries 3 and 7). We then went to the extent of attempting the reaction of 1a and 2g with a catalytic amount (20 mol %) of FeCl3. To our delight, the reaction

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Table 3 Synthesis of substituted naphthalene derivatives via reaction of aldehydes with silylated alkynesa

Table 4 Synthesis of substituted phenanthrene derivatives via reaction of aldehydes with substituted alkynesa CHO

R

+ R

1d Entry

1

2 (R4)

3

Yield (%)b

1 2 3 4 5 6 7 8

1a 1a 1a 1b 1c 1c 1c 1a

2f (p-CH3C6H4) 2g (p-ClC6H4) 2h (p-CH3OC6H4) 2g (p-ClC6H4) 2f (p-CH3C6H4) 2g (p-ClC6H4) 2h (p-CH3OC6H4) 2g (p-ClC6H4)

3af 3ag 3ah 3bg 3cf 3cg 3ch 3ag

66 78 56 71 70 78 61 58c

a Reaction conditions: Aldehyde (1.2 equiv), alkyne (1.0 equiv), FeCl3 (1.2 equiv), 1,2-DCE (3 mL), rt (18e26  C), 2 h. b Isolated yield. c FeCl3 (0.2 equiv).

worked with catalytic amount of FeCl3 as well, giving 3ag in 58% yield (Table 3, entry 8). This finding further hints that the key to the success of the iron-based catalytic cycle relies on the possibility of preventing the Fe3þ ion from coordinating to the resulting water through either the judicious avoidance of water formation or the use of strong dehydrating reagents. Phenanthrene ring is extensively presented in natural products, pharmaceuticals, materials, and many other important organic molecules.2 A number of methods for construction of phenanthrene ring have been developed.12 Although quite efficient, these reactions usually require the initial synthesis of complex starting materials or the use of high cost of catalysts; an additional step that sometimes involves expensive or toxic reagents and requires chemical separations. Having demonstrated the feasibility of FeCl3promoted benzannulation reaction of aryl acetaldehydes with internal alkynes, we sought to determine whether annulation reaction of naphthyl acetaldehydes and internal alkynes could also be achieved. Thus, naphthyl acetaldehyde 1d was prepared and treated with several different internal alkynes in the presence of FeCl3 under the reaction conditions similar to those described above (Table 4). As observed in the related transformations of substrates bearing aryl nucleophiles, the corresponding substituted phenanthrenes were also been synthesized in moderate to good yields with excellent regioselectivity (Table 4, entries 1e4). In addition, the reaction works well for a variety of silylated alkynes to give the desilylation products 1-arylphenanthrenes with complete regioselectivity in moderate yields (Table 4, entries 5e7). The structures of 3df (Fig. 1), 3dg (Fig. 2) and 3dh (Fig. 3) were further confirmed by X-ray diffraction analysis. Based on the above results, a plausible mechanism for the formation of 3 is proposed in Scheme 1. Initially, the coordination of the carbonyl oxygen to FeCl3 followed by electrophilic attack on the aryl acetylene leads to the formation of a new CeC bond at the b carbon of the aryl acetylene as the resulting vinyl carbocation is stabilized by the aryl group. Then, the intramolecular FriedeleCrafts reaction of intermediate II effects closure of the dihydronaphthalene ring, which undergo subsequently the tandem H-transfer/H2O elimination in order to aromatize the rings to form the product. In case of silylated alkynes, 1,5-hydrogen shift should be involved along with the preferential elimination of Me3SiOH or Me3SiOSiMe3. This difference between the elimination products of silylated alkynes and other alkynes might be attributed to the stronger oxophilic character and larger steric hindrance of trimethylsilyl compared with the hydrogen atom. The observed influence of the resulting water on the loading

'

R

FeCl3

R'

rt

2a-h

3da-dh 3

Yield (%)b

Entry

2

1

2a

75

2

2b

58

3

2c

69

4

2d

81

5

2f

63

6

2g

62

7

2h

55

a Reaction conditions: Aldehyde (1.2 equiv), alkyne (1.0 equiv), FeCl3 (1.0 equiv), 1,2-DCE (3 mL), rt, 2 h. b Isolated yield.

Fig. 1. ORTEP plot of the X-ray crystal structure of 3df.

amount of the catalyst and ligand effects provide further evidence to support our mechanistic hypothesis and suggest that the bonding strength of iron ion to aldehyde plays a key role in determining the reaction, thereby the compatitive coordination of H2O to Fe3þ hindering the progress of the catalytic cycle.

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3. Conclusions In conclusion, we have developed a simple, highly regioselective, and versatile protocol to synthesize substituted naphthalene and phenanthrene derivatives via FeCl3 promoted annulation of aryl and naphthyl acetaldehydes with a variety of internal alkynes. The experiments described herein suggest that the coordination of the iron ion to aldehyde plays a key role in determining the reaction, and is strongly influenced by both the structure of the Fe catalyst and the competitive coordination of the newly formed water. Significantly, the present catalytic system not only differentiates between internal and terminal alkynes but also shows unprecedented complete Me3SiOH elimination selectivity for silyl alkyne substrates. 4. Experimental section 4.1. General methods Fig. 2. ORTEP plot of the X-ray crystal structure of 3dg.

The solvents were dried using the standard technique. The reaction was carried out under an argon atmosphere. 1H NMR spectra and 13C NMR specta were recorded at a Bruker 400 MHz using CDCl3 as solvent. High resolution mass spectra (HRMS) were recorded on Bruker micrOTOF II using ESI ionization sources. Melting points were performed on WRS-2 Melting Point Apparatus. Infrared spectra were recorded on a FTIR spectrometer. The naphthalenes 3aa,9a 3ad,4b 3af,9b 3ag,9c 3ah,9d 3bg,9e 3cf,9e 1b,9f 1c,9f 1d,9g were identified by comparing their spectral data with those reported in the literature. 4.2. General procedure for the synthesis of aldehydes

Fig. 3. ORTEP plot of the X-ray crystal structure of 3dh.

To a suspension of LiAlH4 in dry THF was added the corresponding acid dissolved in dry THF dropwisely at room temperature. Then the mixture was stirred for 2 h and quenched with saturated NH4Cl. The mixture was extracted with chloroform and dried over anhydrous Na2SO4. Then the solvent was evaporated and the product was used without further purification. The crude alcohol was dissolved in dry DCM and DMP (DesseMartin Periodinane) was added. The resulting mixture was stirred at room temperature for 2 h and quenched with Na2S2O3/NaHCO3 (v/v¼1/1). The aqueous phase was extracted with DCM and dried over anhydrous Na2SO4. The solvent was evaporated to afford the corresponding aldehydes. 4.3. General procedure for the synthesis of naphthalene and phenanthrene derivatives To a mixture of alkyne and aldehyde in 1,2-DCE was added anhydrous FeCl3. The solution was stirred at room temperature until the alkyne disappeared detected by TLC. Then the solvent was evaporated and the residue was subjected to chromatography directly eluting with petro ether to afford the corresponding product. 4.3.1. 1-(4-Methoxyphenyl)-2-phenylnaphthalene (3ab). Pale yellow crystal; mp 104.5e105.9 oC; IR (KBr) n(cm1): 3055, 2947, 2927, 1607, 1509, 1489, 1458, 1437, 1380, 867, 837, 759, 698 cm1; 1H NMR (CDCl3, 400 MHz) d 7.94 (d, J¼8 Hz, 2H), 7.76 (d, J¼8 Hz, 1H), 7.61 (d, J¼8.4 Hz, 1H), 7.53e7.49 (m, 1H), 7.46e7.42 (m, 1H), 7.25e7.13 (m, 7H), 6.90e6.86 (m, 2H), 3.83 (s, 3H); 13C NMR (CDCl3, 100 MHz) d 158.48, 142.33, 138.64, 137.43, 133.16, 132.98, 132.60, 131.32, 130.27, 128.46, 128.01, 127.78, 127.54, 127.00, 126.28, 126.22, 125.77, 113.44, 55.28; HRMS (ESI) calcd for C23H19O (MþH) 311.1436, found 311.1421.

Scheme 1. Possible mechanism for the formation of 3.

4.3.2. 1,2-Dip-tolylnaphthalene (3ac). Pale yellow crystal; mp 112.5e113.8  C; IR (KBr) n(cm1): 3045, 3024, 2922, 2850, 1612,

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1514, 1494, 1458, 1371, 857, 811, 749, 724, 682, 590, 585, 554, 539, 508, 431 cm1; 1H NMR (CDCl3, 400 MHz) d 7.93 (d, J¼8.4 Hz, 2H), 7.72 (d, J¼8.4 Hz, 1H), 7.61 (d, J¼8.4 Hz, 1H), 7.52e7.49 (m, 1H), 7.44e7.40 (m, 1H), 7.18e7.10 (m, 6H), 7.04 (d, J¼8.4 Hz, 2H), 2.41 (s, 3H), 2.33 (s, 3H); 13C NMR (CDCl3, 100 MHz) d 139.34, 138.33, 137.63, 136.25, 136.20, 135.77, 133.06, 132.83, 131.39, 130.11, 128.71, 128.64, 128.51, 127.95, 127.50, 127.01, 126.19, 125.63, 21.42, 21.26; HRMS (ESI) calcd for C24H21 (MþH) 309.1643, found 309.1639. 4.3.3. 7-Chloro-1,2-diphenylnaphthalene (3ba). Yellow crystal; mp 149.9e151.8  C; IR (KBr) n(cm1): 3060, 3024, 1614, 1597, 1586, 1487, 1446, 1361, 1258, 1081, 1028, 967, 841, 765, 701 cm1; 1H NMR (CDCl3, 400 MHz) d 7.91 (d, J¼8.4 Hz, 1H), 7.86 (d, J¼8.8 Hz, 1H), 7.70 (s, 1H), 7.60 (d, J¼8.4 Hz, 1H), 7.47e7.44 (dd, J¼2.4 and 8.8 Hz, 1H), 7.36e7.31 (m, 3H), 7.25e7.15 (m, 7H); 13C NMR (CDCl3, 100 MHz) d 141.68, 139.53, 138.36, 137.10, 133.59, 132.36, 131.43, 131.13, 130.13, 129.61, 128.72, 128.15, 127.79, 127.52, 127.16, 126.72, 126.54, 125.77; HRMS (ESI) calcd for C22H15Cl (MþH) 314.0862, found 315.0917. 4.3.4. 7-Chloro-1-(4-methoxyphenyl)-2-phenylnaphthalene (3bb). Yellow solid; mp 118.6e119.2  C; IR (KBr) n(cm1): 3060, 3024, 2927, 1607, 1504, 1489, 1458, 1443, 1242, 1027, 878, 826, 754, 698 cm1; 1H NMR (CDCl3, 400 MHz) d 7.71 (s, 1H), 7.58 (d, J¼8.4 Hz, 1H), 7.45e7.43 (dd, J¼2.0 and 8.4 Hz, 1H), 7.24e7.15 (m, 5H), 7.09 (d, J¼8.8 Hz, 2H), 6.87 (d, J¼8.8 Hz, 2H), 3.84 (s, 3H); 13C NMR (CDCl3, 100 MHz) d 158.60, 141.84, 139.64, 136.76, 133.92, 132.44, 132.23, 131.15, 130.48, 130.09, 129.55, 128.70, 127.79, 127.27, 126.60, 126.40, 125.79, 113.60, 55.25; HRMS (ESI) calcd for C23H17ClONa (MþNa) 367.0866, found 367.0861. 4.3.5. 7-Chloro-1,2-dip-tolylnaphthalene (3bc). Pale yellow crystal; mp 138.8e140.0 oC; IR (KBr) n(cm1): 3022, 2923, 2850, 1611, 1511, 1493, 1433, 1384, 1362, 1112, 1080, 881, 842, 818, 791, 587, 520 cm1; 1H NMR (CDCl3, 400 MHz) d 7.87 (d, J¼8.4 Hz, 1H), 7.83 (d, J¼8.8 Hz, 1H), 7.68 (s, 1H), 7.57 (d, J¼8.8 Hz, 1H), 7.44e7.41 (dd, J¼2.0 and 8.4 Hz, 1H), 7.15 (d, J¼8.0 Hz, 2H), 7.09e7.01 (m, 6H), 2.39 (s, 3H), 2.31 (s, 3H); 13C NMR (CDCl3, 100 MHz) d 139.41, 138.88, 137.00, 136.61, 136.05, 135.42, 133.87, 132.18, 131.25, 131.06, 130.01, 129.55, 128.93, 128.58, 127.30, 126.53, 125.83, 21.44, 21.25; HRMS (ESI) calcd for C24H20Cl (MþH) 343.1254, found 343.1230. 4.3.6. 7-Chloro-2-ethyl-1-phenylnaphthalene (3bd). White oil; IR (KBr) n(cm1): 3055, 2963, 2927, 2870, 1612, 1586, 1499, 1458, 1360, 1083, 965, 888, 837, 765, 724, 708 cm1; 1H NMR (CDCl3, 400 MHz) d 7.83e7.78 (m, 2H), 7.56e7.47 (m, 4H), 7.39e7.37 (m, 2H), 7.31e7.28 (m, 2H), 2.60e2.54 (q, J¼7.2 Hz, 2H), 1.71e1.13 (t, J¼7.2 Hz, 3H); 13C NMR (CDCl3, 100 MHz) d 140.74, 138.81, 137.06, 133.98, 131.82, 130.31, 130.24, 129.42, 128.57, 127.59, 127.54, 127.43, 125.86, 125.41, 27.19, 16.05; HRMS (ESI) calcd for C18H16Cl (MþH) 267.0941, found 267.0930. 4.3.7. 7-Chloro-2-methyl-1-phenylnaphthalene (3be). Colorless oil; IR (KBr) n(cm1): 3055, 3019, 2922, 2855, 1617, 1597, 1494, 1442, 1360, 1129, 1078, 831, 775, 734, 703, 616 cm1; 1H NMR (CDCl3, 400 MHz) d 7.79e7.75 (m, 2H), 7.55e7.42 (m, 5H), 7.38e7.35 (dd, J¼2.0 and 8.4 Hz, 1H), 7.28e7.26 (m, 2H), 2.25 (s, 3H); 13C NMR (CDCl3, 100 MHz) d 139.11, 137.67, 134.57, 133.81, 131.88, 130.31, 130.15, 129.48, 129.03, 128.73, 127.46, 127.15, 125.79, 125.13, 21.03; HRMS (ESI) calcd for C17H14Cl (MþH) 253.0784, found 253.0778. 4.3.8. 7-Methyl-1,2-diphenylnaphthalene (3ca). Yellow crystal; mp 121.8e122.7  C; IR (KBr) n(cm1): 3045, 3019, 2963, 2911, 2845, 1627, 1597, 1489, 1437, 1365, 842, 775, 759, 739, 698 cm1; 1H NMR (CDCl3, 400 MHz) d 7.93 (d, J¼8.8 Hz, 1H), 7.87 (d, J¼8 Hz, 1H), 7.56 (d, J¼8.4 Hz, 1H), 7.50 (s, 1H), 7.39e7.30 (m, 4H), 7.26e7.21 (m, 7H), 2.45 (s, 3H); 13C NMR (CDCl3, 100 MHz) d 142.31, 139.29, 138.57, 137.10, 136.07, 132.89, 131.61, 131.17, 130.24, 128.07, 127.91, 127.89,

127.67, 127.53, 127.45, 126.74, 126.22, 125.80, 22.17; HRMS (ESI) calcd for C23H19 (MþH) 295.1487, found 295.1471. 4.3.9. 1-(4-Methoxyphenyl)-7-methyl-2-phenylnaphthalene (3cb). Yellow solid; mp 99.8e101.7  C; IR (KBr) n(cm1): 3045, 2999, 2922, 1608, 1511, 1493, 1454, 1289, 1244, 1177, 1030, 840, 824, 762, 752, 702 cm1; 1H NMR (CDCl3, 400 MHz) d 7.89 (d, J¼8.8 Hz, 1H), 7.85 (d, J¼8.4 Hz, 1H), 7.55e7.52 (dd, J¼2.8 and 8.8 Hz, 2H), 7.37e7.35 (dd, J¼2.0 and 8.4 Hz, 1H), 7.24e7.13 (m, 7H), 6.91e6.87 (m, 2H), 3.85 (s, 3H), 2.45 (s, 3H); 13C NMR (CDCl3, 100 MHz) d 158.35, 142.49, 138.72, 136.74, 135.96, 133.24, 132.62, 131.46, 131.21, 130.25, 128.00, 127.88, 127.71, 127.57,127.27, 126.12,125.85, 113.38, 55.25, 22.17; HRMS (ESI) calcd for C24H21O (MþH) 325.1592, found 325.1583. 4.3.10. 7-Methyl-1,2-dip-tolylnaphthalene (3cc). Pale yellow crystal; mp 115.4e116.6  C; IR (KBr) n(cm1): 3040, 3024, 2963, 2937, 2916, 2850, 1622, 1494, 1432, 1376, 842, 826, 790, 729 cm1; 1H NMR (CDCl3, 400 MHz) d 7.89 (d, J¼8.8 Hz, 1H), 7.84 (d, J¼8.4 Hz, 1H), 7.53 (d, J¼8.0 Hz, 1H), 7.50 (s, 1H), 7.35 (d, J¼8.4 Hz, 1H), 7.18e7.09 (m, 6H),7.03 (d, J¼8.0 Hz, 2H), 2.44 (s, 3H), 2.42 (s, 3H), 2.33 (s, 3H); 13C NMR (CDCl3, 100 MHz) d 139.50, 138.43, 136.97, 136.31, 136.11, 135.86, 135.64, 133.15, 131.41, 131.09, 130.10, 128.69, 128.45, 127.89, 127.83, 127.76, 127.24, 125.85, 22.15, 21.43, 21.24; HRMS (ESI) calcd for C25H23 (MþH) 323.1800, found 323.1786. 4.3.11. 2-Ethyl-7-methyl-1-phenylnaphthalene (3cd). Pale yellow oil; IR (KBr) n(cm1): 3045, 3014, 2963, 2922, 2870, 1622, 1597, 2509, 1489, 1437, 1371, 837, 770, 744, 698 cm1; 1H NMR (CDCl3, 400 MHz) d 7.83 (d, J¼8.0 Hz, 1H), 7.78 (d, J¼8.4 Hz, 1H), 7.56e7.46 (m, 3H), 7.43 (d, J¼8.4 Hz, 1H), 7.35e7.28 (m, 3H), 7.17 (s, 1H), 2.57 (q, J¼7.6 Hz, 2H), 2.40 (s, 3H), 1.16 (t, J¼7.6 Hz, 3H); 13C NMR (CDCl3, 100 MHz) d 139.81, 139.53, 137.03, 135.50, 133.30, 130.46, 130.24, 128.33, 127.70, 127.45, 127.18, 127.03, 126.38, 125.47, 27.16, 22.08, 16.18; HRMS (ESI) calcd for C19H19 (MþH) 247.1487, found 247.1490. 4.3.12. 1-(4-Chlorophenyl)-7-methylnaphthalene (3cg). Yellow solid; mp 120.5e122.3  C; IR (KBr) n(cm1): 3050, 2916, 2845, 1622, 1597, 1489, 1427, 1093, 1016, 816, 749 cm1; 1H NMR (CDCl3, 400 MHz) d 7.85 (d, J¼4.4 Hz, 1H), 7.83 (d, J¼5.2 Hz, 1H), 7.63 (s, 1H), 7.51e7.43 (m, 5H), 7.37 (dd, J¼1.2 and 7.2 Hz, 2H), 2.48 (s, 3H); 13C NMR (CDCl3, 100 MHz) d 139.49, 138.35, 136.12, 133.29, 131.47, 128.58, 128.33, 128.28, 127.86, 127.16, 124.63, 124.58, 22.12; HRMS (ESI) calcd for C17H14Cl (MþH) 253.0784, found 253.0757. 4.3.13. 1-(4-Methoxyphenyl)-7-methylnaphthalene (3ch). Yellow oil; IR(KBr) n(cm1): 3040, 2999, 2932, 2855, 2829, 1607, 1509, 1458, 1437, 1371, 1278, 1247, 1170, 1032, 821, 790, 759, 569, 518 cm1; 1H NMR (CDCl3, 400 MHz) d 7.82 (dd, J¼4.0 and 8.4 Hz, 2H), 7.71 (s, 1H), 7.48e7.44 (m, 3H), 7.40e7.34 (m, 2H), 7.07 (dd, J¼2.4 and 6.8 Hz, 2H), 3.92 (s, 3H), 2.47 (s, 3H); 13C NMR (CDCl3, 100 MHz) d 158.99, 139.35, 135.75, 133.48, 132.21, 132.10, 131.23, 128.25, 128.08, 127.23, 127.17, 125.05, 124.63, 113.83, 55.46, 22.11; HRMS (ESI) calcd for C18H17O (MþH) 249.1279, found 249.1287. 4.3.14. 1,2-Diphenylphenanthrene (3da). Yellow crystal; mp 143.8e144.7  C; IR (KBr) n(cm1): 3055, 3023, 2924, 1598, 1493, 1483, 1456, 1443, 1433, 1257, 1025, 828, 795, 759, 750, 701, 684, 584 cm1; 1H NMR (CDCl3, 400 MHz) d 8.82 (t, 2H), 7.92 (d, J¼8.0 Hz, 1H), 7.80e7.66 (m, 5H), 7.40e7.22 (m, 10H); 13C NMR (CDCl3, 100 MHz) d 141.97, 139.47, 139.41, 138.65, 131.70, 131.65, 130.97, 130.27, 130.20, 129.72, 128.64, 128.54, 127.96, 127.73, 127.14, 126.88, 126.83, 126.81, 126.37, 125.38, 123.00, 122.28; HRMS (ESI) calcd for C26H19 (MþH) 331.1487, found 331.1481. 4.3.15. 1-(4-Methoxyphenyl)-2-phenylphenanthrene (3db). Yellow solid; mp 177.6e178.9  C; IR (KBr) n(cm1): 3050, 3004, 2957, 2922,

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2850, 1612, 1514, 1458, 1247, 1178, 1029, 821, 761, 750, 701 cm1; 1H NMR (CDCl3, 400 MHz) d 8.80 (d, J¼3.6 Hz, 1H), 8.78 (d, J¼3.2 Hz, 1H), 7.91 (dd, J¼1.6 and 8.0 Hz, 1H), 7.78e7.62 (m, 5H), 7.28e7.22 (m, 5H), 7.18e7.15 (m, 2H), 6.90 (dd, J¼2.0 and 7.2 Hz, 2H), 3.84 (s, 3H); 13C NMR (CDCl3, 100 MHz) d 158.44, 142.13, 139.65, 138.30, 132.65, 131.68, 131.53, 131.29, 130.28, 130.19, 129.74, 128.66, 128.51, 127.78, 127.03, 126.76, 126.27, 125.44, 122.99, 122.10, 113.40, 55.25; HRMS (ESI) calcd for C27H21O (MþH) 361.1592, found 361.1574. 4.3.16. 1,2-Dip-tolylphenanthrene (3dc). Yellow solid; mp 147.6e148.7  C; IR (KBr) n(cm1): 3046, 3016, 2918, 2854, 1513, 1490, 1455, 840, 812, 775, 746, 587 cm1; 1H NMR (CDCl3, 400 MHz) d 8.80 (d, J¼8.8 Hz, 2H), 7.90 (d, J¼7.6 Hz, 1H), 7.78e7.64 (m, 5H), 7.18e7.13 (m, 6H), 7.07 (d, J¼7.6 Hz, 2H), 2.43 (s, 3H), 2.35 (s, 3H); 13 C NMR (CDCl3, 100 MHz) d 139.39, 139.15, 138.57, 136.47, 136.29, 135.82, 131.66, 131.46, 131.20, 130.31, 130.06, 129.56, 128.83, 128.73, 128.52, 128.50, 126.93, 126.73, 126.68, 125.51, 122.98, 122.09, 21.42, 21.25; HRMS (ESI) calcd for C28H23 (MþH) 359.1800, found 359.1772. 4.3.17. 2-Ethyl-1-phenylphenanthrene (3dd). Off-white crystal; mp 84.4e85.6  C; IR (KBr) n(cm1): 3044, 2960, 2926, 2866, 1598, 1492, 1458, 1439, 1368, 821, 753, 726, 703 cm1; 1H NMR (CDCl3, 400 MHz) d 8.74 (t, J¼8.8 Hz, 2H), 7.87 (d, J¼8.0 Hz, 1H), 7.71e7.75 (m, 7H), 7.39e7.35 (m, 3H), 2.63 (q, J¼8.0 Hz, 2H), 1.20 (t, J¼8.0 Hz, 3H); 13C NMR (CDCl3, 100 MHz) d 140.54, 139.93, 138.91, 131.40, 131.20, 130.47, 130.37, 128.51, 128.49, 128.41, 127.37, 127.18, 126.68, 126.39, 125.34, 122.79, 122.31, 27.11, 16.01; HRMS (ESI) calcd for C22H19 (MþH) 283.1487, found 283.1474. 4.3.18. 1-p-Tolylphenanthrene (3df). White crystal; mp 83.5e84.3  C; IR (KBr) n(cm1): 3045, 3019, 2916, 1586, 1504, 1489, 1458, 1412, 1381, 867, 831, 801, 754, 724, cm1; 1H NMR (CDCl3, 400 MHz) d 8.77 (t, J¼8.4 Hz, 2H), 7.90 (t, J¼8.4 Hz, 2H), 7.73e7.57 (m, 5H), 7.45 (d, J¼8.0 Hz, 2H), 7.36 (d, J¼8.0 Hz, 2H), 2.51 (s, 3H); 13 C NMR (CDCl3, 100 MHz) d 141.09, 138.25, 137.04, 131.83, 130.78, 130.54, 130.22, 130.11, 129.12, 128.55, 128.03, 126.87, 126.77, 126.72, 126.09, 124.83, 123.08, 122.08, 21.39; HRMS (ESI) calcd for C21H16Na (MþNa) 291.1150, found 291.1126. 4.3.19. 1-(4-Chlorophenyl)phenanthrene (3dg). White solid; mp 95.7e98.7  C; IR (KBr) n(cm1): 3070, 3060, 3045, 3019, 2916, 1597, 1504, 1489, 1448, 1381, 1104, 1016, 1001, 872, 837, 801, 744, 713, 482 cm1; 1H NMR (CDCl3, 400 MHz) d 8.77 (d, J¼8.8 Hz, 2H), 7.90 (dd, J¼1.2 and 8.0 Hz, 1H), 7.78e7.62 (m, 5H), 7.54e7.44 (m, 5H); 13C NMR (CDCl3, 100 MHz) d 139.59, 133.47, 131.61, 130.83, 130.43, 129.85, 128.62, 127.94, 127.26, 126.94, 126.90, 126.08, 124.27, 123.06, 122.59; HRMS (ESI) calcd for C20H14Cl (MþH) 289.0784, found 289.0777. 4.3.20. 1-(4-Methoxyphenyl)phenanthrene (3dh). Yellow crystal; 1H NMR (CDCl3, 400 MHz) d 8.74 (q, J¼8.8 Hz, 2H), 7.87 (q, J¼8.8 Hz, 2H), 7.71e7.60 (m, 4H), 7.55 (d, J¼7.2 Hz, 1H), 7.45 (d, J¼8.8 Hz, 2H), 7.06 (d, J¼8.4 Hz, 2H), 3.91 (s, 3H); 13C NMR (CDCl3, 100 MHz) d 159.03, 140.74, 133.52, 131.80, 131.38, 130.78, 130.51, 130.18, 128.55, 128.07, 126.85, 126.77, 126.73, 126.09, 124.78, 123.07, 121.97, 113.83, 55.48; HRMS (ESI) calcd for C21H17O (MþH) 285.1279, found 285.1289. Acknowledgements We thank the NNSF of China, 973 program (2009CB825300), the Research Fund for the Doctoral Program of Higher Education of China, and Shanghai Leading Academic Discipline Project for financial support (B108).

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Supplementary data Supplementary data associated with this article can be found, in the online version, at http://dx.doi.org/10.1016/j.tet.2012.07.007.

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