Synthesis of 1H-benzo[g]indazole derivatives: propargyl–allenyl isomerization and 6π-electrocyclization involving two aromatic π-bonds

Tetrahedron 70 (2014) 6831e6840

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Synthesis of 1H-benzo[g]indazole derivatives: propargyleallenyl isomerization and 6p-electrocyclization involving two aromatic p-bonds Jin Woo Lim, Ko Hoon Kim, Se Hee Kim, Jae Nyoung Kim * Department of Chemistry and Institute of Basic Science, Chonnam National University, Gwangju 500-757, Republic of Korea

a r t i c l e i n f o

a b s t r a c t

Article history: Received 3 July 2014 Received in revised form 11 July 2014 Accepted 12 July 2014 Available online 22 July 2014

An efficient synthesis of 1H-benzo[g]indazoles starting from MoritaeBayliseHillman (MBH) adducts is disclosed. The synthesis was carried out from MBH bromide via a sequential copper-catalyzed alkynylation, one-pot synthesis of pyrazole, propargyleallenyl isomerization, and a 6p-electrocyclization involving two aromatic p-bonds and an allenyl p-bond. Ó 2014 Elsevier Ltd. All rights reserved.

Keywords: 1H-Benzo[g]indazole MoritaeBayliseHillman adducts Propargyleallenyl isomerization 6p-Electrocyclization

1. Introduction

2. Results and discussion

The indazole nucleus is pharmaceutically important and constitutes the key subunit in many drug substances with a broad range of pharmacological activities.1 Thus numerous synthetic methods of indazole derivatives are known.1 However, there have been reported a few reports on the synthesis of tricyclic angular 1H-benzo[g]indazoles.2 Fujii and co-workers have reported a transition metal-catalyzed process involving a twofold Sonogashira coupling between 1,2-dihaloarene and acetylene derivatives and a gold-catalyzed three-component annulation and cyclization cascade.2a Chang and co-workers reported a synthesis of 1H-benzo[g] indazole from ortho-allylbenzaldehydes via a sequential aldol reaction, pyrazoline synthesis with arylhydrazine, dehydrogenative aromatization to pyrazole, and the final oxidative cleavage annulation protocol.2b Akbar and Srinivasan used ortho-alkynylarene chalcone derivative as a starting material, and the synthesis of 1Hbenzo[g]indazole has been performed via iodine-catalyzed tandem oxidative cyclocondensation and electrophilic hydroarylation process.2c Most of the syntheses of 1H-benzo[g]indazoles required a multi-step process. In this context, we decided to develop an efficient synthetic process of 1H-benzo[g]indazoles from readily available MoritaeBayliseHillman (MBH) bromides.3

Recently, we reported the synthesis of naphthalenes via coppercatalyzed tandem alkynylation, propargyleallenyl isomerization, and 6p-electrocyclization from MBH bromide of methyl acrylate, as shown in Scheme 1.4 One aromatic p-bond and two alkenyl pbonds were involved in the final 6p-electrocyclization step of Ia.4a In this regard, we presumed that 1H-benzo[g]indazole derivative 6a could be synthesized starting from the MBH bromide 1a derived from methyl vinyl ketone,3 as shown in Scheme 1. The benzo[g] indazole 6a could be synthesized from pyrazole 5a via a sequential propargyleallenyl isomerization5 and 6p-electrocyclization of Ib involving two aromatic p-bonds (benzene and pyrazole) and an allenyl p-bond. Although numerous allene-mediated 6p-electrocyclizations have been reported,6 the reactions involving two aromatic double bonds are rather limited.6c,i,7 In order to prepare pyrazole 5a, compound 3a was prepared from MBH bromide 1a by CuI-assisted introduction of phenylacetylene (CuI, Cs2CO3, CH3CN, rt) in good yield (81%).8 The pyrazoline 4a was prepared in moderate yield (66%) from a,b-enone 3a and phenylhydrazine hydrochloride in 1,2-dichlorobenzene (ODCB, 130
C, 2 h) under N2 balloon atmosphere along with a low yield of 5a (<5%). The oxidation of 4a to 5a was examined with 2,3dichloro-5,6-dicyano-p-benzoquinone (DDQ) in toluene. However, many intractable side products were formed instead of 5a including the side product caused by the reaction of triple bond of 4a and DDQ.9 The use of p-chloranil showed a similar result. Thus, we

* Corresponding author. Tel.: þ82 62 530 3381; fax: þ82 62 530 3389; e-mail address: [email protected] (J.N. Kim). http://dx.doi.org/10.1016/j.tet.2014.07.048 0040-4020/Ó 2014 Elsevier Ltd. All rights reserved.

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Scheme 1. Synthesis of 1H-benzo[g]indazole 6a: (a) phenylacetylene (2a, 1.5 equiv), CuI (20 mol %), Cs2CO3 (1.5 equiv), CH3CN, rt, 15 h; (b) PhNHNH2HCl (1.2 equiv), ODCB, 130
C, 2 h, N2 balloon; (c) DDQ (1.5 equiv), toluene, reflux, 10 h; (d) PhNHNH2HCl (1.2 equiv), ODCB, 130
C, 5 h, O2 balloon; (e) DBU (0.3 equiv), ODCB, 130
C, 15 h.

examined the reaction of 3a and phenylhydrazine hydrochloride under an aerobic oxidation condition.10,11 To our delight, when we carried out the reaction under O2 balloon atmosphere (ODCB, 130
C) 5a was obtained directly in good yield (65%).10h,11b,c With the pyrazole 5a in our hand, a sequential propargyleallenyl isomerization and 6p-electrocyclization was examined in the presence of 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) as a base catalyst (ODCB, 130
C, 15 h). We were pleased to obtain benzo[g]indazole 6a in good yield (67%) via the corresponding allene intermediate Ib. The reaction of 5a in refluxing xylene was slightly less effective than the use of ODCB. Encouraged by the successful results, we prepared some representative a,b-enones 3bej from MBH bromides 1aeg and acetylene derivatives 2aed, as shown in Scheme 2, in the presence of CuI (20 mol %) and Cs2CO3 (1.5 equiv) in CH3CN in moderate to good yields (65e81%). Phenylacetylene (2a), 1-ethynyl-4-methoxybenzene (2b), benzyl propargyl ether (2c), and propargyl acetate (2d) were examined as representative acetylenes.

Scheme 2. Preparation of starting materials 3aej.

The syntheses of the corresponding pyrazoles 5bej were carried out under the similar conditions in Scheme 1, and the results are summarized in Table 1. Various 1,3,4,5-tetrasubstituted pyrazoles 5bed and 5hej were prepared in ODCB (130
C, 5 h) under O2 balloon atmosphere in moderate yields (51e68%) in a one-pot reaction (entries 2e4 and 8e10). But, EtOH was used as a solvent for the preparation of 5e and 5f (entries 5 and 6). The yields of 5e and 5f were low in ODCB due to the formation of some side products. The yield of 5g (entry 7) was quite low when we used

phenylhydrazine hydrochloride, due to the formation of benzocycloheptene derivative by the competitive acid-catalyzed intramolecular FriedeleCrafts alkenylation reaction (vide infra, Scheme 8). Thus, the synthesis of 5g was carried out in 2-propanol with phenylhydrazine (reflux, 40 h) under O2 balloon atmosphere. The reactions of 3a and 4-methoxyphenylhydrazine hydrochloride or 4chlorophenylhydrazine hydrochloride provided 5i and 5j, respectively, in moderate yields (entries 9 and 10). With these pyrazoles 5bej in our hand, various benzo[g]indazole derivatives 6bej were synthesized in good yields (68e83%) via a sequential DBU-mediated propargyleallenyl isomerization and the following 6p-electrocyclization. The results are summarized in Table 2. The reaction of 5b afforded 6b in a similar yield (68%) to that of 6a; however, somewhat longer reaction time (36 h) was required for the completion (entry 2). It is interesting to note that 3H-naphtho[1,2-g]indazole derivative 6c (entry 3) was formed regioselectively. The other regioisomeric 1H-naphtho[2,3-g]indazole was not formed in any trace amount.4a,6i The reaction of 1naphthyl derivative 5d gave 6d in good yield (83%, entry 4). The syntheses of 6c and 6d were completed in short time (5 h) as compared to 6a and 6b. The small resonance energy of one of the benzene rings of naphthalene facilitates the 6p-electrocyclization. In addition, 1H-furo[3,2-g]indazole 6e (entry 5) and 1H-thieno[3,2g]indazole 6f (entry 6) could be synthesized in good yields (74e81%). As in the cases of 6c and 6d, compounds 6e and 6f were produced in short time (5 h) because of the small resonance energy of furan or thiophene ring. Pyrazoles 5gej also produced 6gej in good yields (71e74%) for 15e25 h (entries 7e10). 1,3,5,6-Tetrasubstituted indazole derivative 6k could be prepared from 3i, prepared from 1g and phenylacetylene (Scheme 2), in good yield via the corresponding pyrazole 5k, as shown in Scheme 3. The conversion of 5k to 6k proceeded in short time (1 h). As compared to the entries in Table 2, 6p-electrocyclization of the corresponding allene intermediate II involved only one aromatic pbond (pyrazole), and the electrocyclization proceeded readily.4b Accordingly, the reaction of 5k was examined under mild condition in toluene (90
C), and 6k was obtained in a similar yield (81%) for 2 h. The synthesis of 5-vinyl-substituted benzo[g]indazole 6l has been examined with 3j bearing a propargyl acetate moiety, as shown in Scheme 4. The corresponding pyrazole 5l was prepared in moderate yield (57%); however, the reaction of 5l under the standard condition afforded 6l in low yield (15%) along with an enyne derivative 7 as a major product (37%). Although the yield of 7 could

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Table 1 Synthesis of pyrazoles 5aeja Entry

Pyrazole 5 (%)

Entry

1

6

2

7

3

8

4

9

5

10

a b c d e

Pyrazole 5 (%)

Conditions: 3 (1.0 mmol), arylhydrazine hydrochloride (1.2 equiv), ODCB, 130
C, O2 balloon, 5 h. EtOH, reflux, 24 h. Ar is 4-methoxyphenyl. 2-Propanol, reflux, 40 h. Ar is 4-chlorophenyl.

be increased to 77% by carrying out the reaction in DMF, every trial for the increase of 6l failed (see, Supplementary data). The reaction mechanism for the formation of 6l would be a sequential propargyleallenyl isomerization of 5l to III, a subsequent 6p-

electrocyclization of III to IV, and the final aromatization-driven 1,4-elimination of AcOH of IV to produce 6l.4b Enyne 7 could be formed from 5l via 1,4-elimination of AcOH to form [3]-cumulene V and a subsequent 1,3-H shift.4b

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Table 2 Synthesis of benzo[g]indazole 6aeja Entry

6 (Time/yield)b

Entry

1

6

2

7

3

8

4

9

6 (Time/yield)b

However, the reaction of 9a under the typical reaction conditions did not produce 11a. Instead, an allene derivative 10a was isolated in good yield (71%). The co-planarity of the three C]C double bonds of an allene intermediate 10a might be hindered due to the steric hindrance between the two phenyl groups. To our delight, however, the allene 10a could be converted to 11a in moderate yield (57%) when we raised the reaction temperature to reflux. Compound 11a could also be prepared directly from pyrazole 9a in refluxing ODCB for 60 h in reasonable yield (47%). Accordingly, the synthesis of 4-methylbenzo[g]indazole 11b was examined, as shown in Scheme 6. The reaction of 4-phenyl-3butyn-2-ol and dibenzoylmethane gave 8b in moderate yield (55%). Pyrazole 9b was prepared similarly in good yield (72%), and the synthesis of 11b was carried out in good yield (65%) in ODCB at refluxing temperature for 32 h. As compared to the reaction of 9a, the reaction of 9b at 130
C did not produce the corresponding allene intermediate. The propargylic hydrogen of 9b is less acidic than that of 9a, and this difference made the propargyleallenyl isomerization of 9b difficult at 130
C. The synthesis of 3-phenyl-4-unsubstituted benzo[g]indazole derivative 15a was accomplished in other route, as shown in Scheme 7. The reaction of enone 12 and phenylhydrazine in AcOH under O2 balloon atmosphere afforded the pyrazole 13 in moderate yield (62%). The bromination at the methyl group with N-bromosuccinimide (NBS) and a following introduction of phenylacetylene gave 14a in good two-step overall yield (61%). The reaction of 14a in ODCB in the presence of DBU afforded 15a in good yield (82%). By using the same protocol, 15b was synthesized in good yield (84%) from 14b; however, K2CO3 has to be used as a base instead of DBU as in our previous paper.4a The yield of 15b decreased dramatically (21%) when DBU was used as a base due to the formation of many side products. In contrast to the base-catalyzed propargyleallenyl isomerization and 6p-electrocyclization process of 5a, an acid-catalyzed intramolecular FriedeleCrafts alkenylation13 afforded 1,2diazabenzo[e]azulene derivative 16 in good yield (63%) via the corresponding vinyl cation intermediate VI, as shown in Scheme 8. 3. Conclusion In conclusion, we disclosed an efficient synthesis of 1H-benzo[g] indazole derivatives from MoritaeBayliseHillman bromides via a sequential copper-catalyzed alkynylation, one-pot synthesis of pyrazoles from a,b-enones, propargyleallenyl isomerization, and a thermal 6p-electrocyclization process involving two aromatic pbonds and an allenyl p-bond. 4. Experimental section

5

a b c d

10

Conditions: 5 (0.5 mmol), DBU (0.3 equiv), ODCB, 130
C, 5e36 h. Time in hours and % isolated yield. Ar is 4-methoxyphenyl. Ar is 4-chlorophenyl.

Introduction of a substituent at the 4-position of benzo[g] indazole was difficult by the above protocol using MBH bromides. Thus, in order to prepare 4-phenyl-substituted benzo[g]indazole 11a, we prepared b-diketone 8a according to the reported method,12 as shown in Scheme 5. The reaction of 8a and phenylhydrazine hydrochloride afforded pyrazole 9a in good yield (76%).

4.1. General procedure All reactions were carried out in oven-dried glassware under an atmosphere of dry nitrogen unless otherwise noted. Thin layer chromatography (TLC) was performed with pre-coated silica gel plates (Kieselgel 60F-254, Merck). Visualization on TLC was achieved by the use of UV light (254 nm) or treatment with p-anisaldehyde stain followed by heating. The separations were carried out by flash column chromatography over silica gel 60 (230e400 mesh ASTM). Organic extracts were dried over anhydrous MgSO4 and the solvents were removed on a rotary evaporator under water aspirator pressure. All reagents were purchased from commercial sources and used without further treatment. Melting points were measured with a Thomas-Hoover melting point apparatus and are uncorrected. 1H NMR (300 MHz) spectra were measured on a Varian Unity Plus 300. The signal positions are reported in parts per million (ppm) relative to TMS (d scale) used as

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spectrometer and are reported in cm1. Mass spectra were obtained from the Korea Basic Science Institute (Gwangju branch) using ESIþ method. Elemental analyses (C, H, and N) were performed with a Fisons EA-1108 Elemental Analyzer machine at Korea Research Institute of Chemical Technology, Daejeon, Korea.

4.2. Typical procedure for the synthesis of 3a A solution of MBH bromide 1a (383 mg, 1.5 mmol), phenylacetylene 2a (245 mg, 2.25 mmol), CuI (61 mg, 0.30 mmol), and Cs2CO3 (784 mg, 2.25 mmol) in CH3CN (5 mL) was stirred at room temperature for 15 h. After the aqueous extractive workup and

Scheme 3. Synthesis of indazole 6k.

Scheme 4. Trials for the synthesis of 5-vinylbenzo[g]indazole 6l.

Scheme 5. Synthesis of 4-phenylbenzo[g]indazole 11a.

an internal standard. Splitting patterns are indicated as s, singlet; d, doublet; t, triplet; q, quartet; m, multiplet. Chemical shifts of the 13C NMR (75 MHz) spectra were measured relative to CDCl3 (77.23 ppm). IR spectra were recorded on a Jasco FT-IR 410

column chromatographic purification process (hexanes/Et2O, 8:1) compound 3a was obtained as colorless oil, 337 mg (81%). Other compounds were synthesized similarly, and the spectroscopic data of 3aej are as follows.

Scheme 6. Synthesis of 4-methylbenzo[g]indazole 11b.

Scheme 7. Synthesis of 3-phenyl-4-unsubstituted benzo[g]indazole 15.

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J¼2.1 Hz, 2H), 4.18 (t, J¼2.1 Hz, 2H), 4.58 (s, 2H), 7.25e7.38 (m, 5H), 7.38e7.49 (m, 3H), 7.56e7.62 (m, 3H); 13C NMR (CDCl3, 75 MHz) d 16.86, 25.87, 57.65, 71.25, 76.22, 84.40, 127.73, 128.07, 128.35, 128.69, 129.28, 129.69, 134.81, 136.70, 137.54, 141.12, 198.24; ESIMS m/z 305 [MþH]þ. Anal. Calcd for C21H20O2: C, 82.86; H, 6.62. Found: C, 82.74; H, 6.59. Scheme 8. Intramolecular FriedeleCrafts alkenylation of 5a.

4.2.1. Compound 3a. Yield 81%; colorless oil; IR (film) 1667, 1490, 1216 cm1; 1H NMR (CDCl3, 300 MHz) d 2.53 (s, 3H), 3.59 (s, 2H), 7.23e7.29 (m, 3H), 7.35e7.50 (m, 5H), 7.60e7.66 (m, 3H); 13C NMR (CDCl3, 75 MHz) d 17.46, 25.99, 80.76, 87.34, 123.60, 127.75, 128.11, 128.71, 129.27, 129.80, 131.69, 134.95, 136.80, 141.12, 198.34; ESIMS m/z 261 [MþH]þ. 4.2.2. Compound 3b. Yield 74%; white solid, mp 66e68
C; IR (KBr) 1671, 1490, 1210 cm1; 1H NMR (CDCl3, 300 MHz) d 1.21 (t, J¼7.2 Hz, 3H), 2.90 (q, J¼7.2 Hz, 2H), 3.60 (s, 2H), 7.23e7.29 (m, 3H), 7.35e7.49 (m, 5H), 7.59e7.65 (m, 3H); 13C NMR (CDCl3, 75 MHz) d 8.62, 17.71, 30.99, 80.75, 87.46, 123.63, 127.72, 128.11, 128.66, 129.09, 129.74, 131.68, 135.07, 136.29, 139.59, 201.03; ESIMS m/z 275 [MþH]þ. 4.2.3. Compound 3c. Yield 75%; colorless oil; IR (film) 1666, 1489, 1260 cm1; 1H NMR (CDCl3, 300 MHz) d 2.58 (s, 3H), 3.68 (s, 2H), 7.25e7.31 (m, 3H), 7.39e7.45 (m, 2H), 7.51e7.58 (m, 2H), 7.69e7.75 (m, 1H), 7.80 (s, 1H), 7.85e7.95 (m, 3H), 8.20 (s, 1H); 13C NMR (CDCl3, 75 MHz) d 17.59, 26.01, 80.93, 87.48, 123.62, 126.63, 126.82, 127.18, 127.69, 127.77, 128.15, 128.33, 128.59, 129.99, 131.68, 132.44, 133.10, 133.36, 136.93, 141.28, 198.28; ESIMS m/z 311 [MþH]þ. 4.2.4. Compound 3d. Yield 71%; pale yellow oil; IR (film) 1671, 1507, 1204 cm1; 1H NMR (CDCl3, 300 MHz) d 2.66 (s, 3H), 3.53 (s, 2H), 7.24e7.40 (m, 5H), 7.53e7.63 (m, 3H), 7.79 (d, J¼7.2 Hz, 1H), 7.89e7.98 (m, 3H), 8.20 (s, 1H); 13C NMR (CDCl3, 75 MHz) d 18.13, 26.33, 80.79, 87.60, 123.61, 124.23, 125.43, 126.31, 126.67, 126.98, 127.70, 128.09, 128.72, 129.46, 131.27, 131.63, 132.14, 133.42, 138.75, 139.03, 198.20; ESIMS m/z 311 [MþH]þ. 4.2.5. Compound 3e. Yield 65%; white solid, mp 84e86
C; IR (KBr) 1664, 1624, 1265, 1211 cm1; 1H NMR (CDCl3, 300 MHz) d 2.48 (s, 3H), 3.79 (s, 2H), 6.59 (dd, J¼3.3 and 1.5 Hz, 1H), 6.99 (d, J¼3.3 Hz, 1H), 7.20e7.27 (m, 3H), 7.31e7.36 (m, 2H), 7.39 (s, 1H), 7.64 (d, J¼1.5 Hz, 1H); 13C NMR (CDCl3, 75 MHz) d 17.08, 25.61, 79.92, 85.65, 112.72, 116.86, 123.66, 127.62, 127.79, 128.06, 131.65, 132.65, 145.18, 150.56, 197.48; ESIMS m/z 251 [MþH]þ. Anal. Calcd for C17H14O2: C, 81.58; H, 5.64. Found: C, 81.33; H, 5.79. 4.2.6. Compound 3f. Yield 68%; white solid, mp 92e94
C; IR (KBr) 1666, 1621, 1273 cm1; 1H NMR (CDCl3, 300 MHz) d 2.49 (s, 3H), 2.58 (s, 3H), 3.76 (s, 2H), 6.85 (d, J¼3.3 Hz, 1H), 7.20e7.29 (m, 3H), 7.32 (d, J¼3.3 Hz, 1H), 7.33e7.40 (m, 2H), 7.66 (s, 1H); 13C NMR (CDCl3, 75 MHz) d 15.72, 17.11, 25.64, 79.99, 86.49, 123.77, 126.46, 127.60, 128.03, 131.70, 131.91, 133.46, 134.16, 135.84, 146.63, 197.49; ESIMS m/z 281 [MþH]þ. 4.2.7. Compound 3g. Yield 67%; white solid, mp 87e88
C; IR (KBr) 1668, 1509, 1289, 1247 cm1; 1H NMR (CDCl3, 300 MHz) d 2.53 (s, 3H), 3.58 (s, 2H), 3.79 (s, 3H), 6.80 (d, J¼9.0 Hz, 2H), 7.32 (d, J¼9.0 Hz, 2H), 7.36e7.50 (m, 3H), 7.60e7.67 (m, 3H); 13C NMR (CDCl3, 75 MHz) d 17.44, 25.99, 55.21, 80.53, 85.70, 113.71, 115.74, 128.66, 129.20, 129.81, 133.03, 134.98, 136.94, 140.93, 159.16, 198.39; ESIMS m/z 291 [MþH]þ. 4.2.8. Compound 3h. Yield 75%; colorless oil; IR (film) 1666, 1217, 1070 cm1; 1H NMR (CDCl3, 300 MHz) d 2.51 (s, 3H), 3.44 (t,

4.2.9. Compound 3i. Yield 70%; white solid, mp 78e80
C; IR (KBr) 1666, 1620, 1357, 1206 cm1; 1H NMR (CDCl3, 300 MHz) d 2.47 (s, 3H), 3.67 (s, 2H), 7.01 (d, J¼15.0 Hz, 1H), 7.20e7.49 (m, 10H), 7.52e7.59 (m, 2H); 13C NMR (CDCl3, 75 MHz) d 15.85, 25.55, 80.58, 87.49, 123.57, 124.05, 127.39, 127.66, 128.08, 128.86, 129.28, 131.57, 135.35, 136.13, 140.99, 141.35, 197.44; ESIMS m/z 287 [MþH]þ. 4.2.10. Compound 3j. Yield 77%; colorless oil; IR (film) 1747, 1667, 1219 cm1; 1H NMR (CDCl3, 300 MHz) d 2.08 (s, 3H), 2.49 (s, 3H), 3.40 (t, J¼2.1 Hz, 2H), 4.65 (t, J¼2.1 Hz, 2H), 7.31e7.50 (m, 3H), 7.49e7.57 (m, 2H), 7.60 (s, 1H); 13C NMR (CDCl3, 75 MHz) d 16.81, 20.77, 25.85, 52.73, 74.25, 84.72, 128.69, 129.32, 129.65, 134.73, 136.32, 141.42, 170.28, 198.19; ESIMS m/z 257 [MþH]þ. 4.3. Typical procedure for the synthesis of 5a10h A mixture of 3a (260 mg, 1.0 mmol) and phenylhydrazine hydrochloride (174 mg, 1.2 mmol) in ortho-dichlorobenzene (2.0 mL) was heated to 130
C under O2 balloon atmosphere for 8 h. After the usual aqueous extractive workup the crude product was purified by column chromatographic purification process (hexanes/Et2O, 8:1) to afford 5a as pale yellow oil, 226 mg (65%). Other compounds were synthesized similarly, and the spectroscopic data of 5ael are as follows. 4.3.1. Compound 5a. Yield 65%; pale yellow oil; IR (film) 1597, 1501, 1361, 1341 cm1; 1H NMR (CDCl3, 300 MHz) d 2.49 (s, 3H), 3.55 (s, 2H), 7.18e7.30 (m, 10H), 7.31e7.42 (m, 5H); 13C NMR (CDCl3, 75 MHz) d 12.20, 14.58, 80.69, 87.62, 114.42, 123.61, 124.67, 126.67, 127.72, 128.15, 128.30, 128.53, 128.66, 129.88, 130.15, 131.54, 139.93, 140.54, 148.57; ESIMS m/z 349 [MþH]þ. Anal. Calcd for C25H20N2: C, 86.17; H, 5.79; N, 8.04. Found: C, 86.01; H, 5.96; N, 7.85. 4.3.2. Compound 5b. Yield 59%; pale yellow oil; IR (film) 1596, 1493, 1360 cm1; 1H NMR (CDCl3, 300 MHz) d 1.43 (t, J¼7.5 Hz, 3H), 2.89 (q, J¼7.5 Hz, 2H), 3.56 (s, 2H), 7.15e7.45 (m, 15H); 13C NMR (CDCl3, 75 MHz) d 13.66, 14.52, 20.31, 80.61, 88.10, 113.86, 123.68, 124.73, 126.62, 127.72, 128.17, 128.27, 128.52, 128.66, 129.94, 130.26, 131.52, 140.03, 140.60, 153.75; ESIMS m/z 363 [MþH]þ. Anal. Calcd for C26H22N2: C, 86.15; H, 6.12; N, 7.73. Found: C, 86.03; H, 6.01; N, 7.59. 4.3.3. Compound 5c. Yield 63%; pale yellow oil; IR (film) 1678, 1597, 1501, 1261 cm1; 1H NMR (CDCl3, 300 MHz) d 2.52 (s, 3H), 3.60 (s, 2H), 7.15e7.32 (m, 9H), 7.34e7.41 (m, 2H), 7.46e7.56 (m, 2H), 7.76 (d, J¼8.4 Hz, 1H), 7.79e7.85 (m, 2H), 7.90 (s, 1H); 13C NMR (CDCl3, 75 MHz) d 12.27, 14.72, 80.79, 87.74, 114.83, 123.64, 124.60, 126.48, 126.69, 126.72, 127.29, 127.71, 127.74, 128.17, 128.19, 128.26, 128.75, 129.24, 131.55, 132.81, 133.10, 140.03, 140.51, 148.68, one carbon is overlapped; ESIMS m/z 399 [MþH]þ. Anal. Calcd for C29H22N2: C, 87.41; H, 5.56; N, 7.03. Found: C, 87.63; H, 5.81; N, 6.96. 4.3.4. Compound 5d. Yield 68%; pale yellow solid, mp 67e69
C; IR (KBr) 1597, 1502, 1366 cm1; 1H NMR (CDCl3, 300 MHz) d 2.83 (s, 3H), 3.38 (s, 2H), 7.05e7.18 (m, 5H), 7.21e7.30 (m, 5H), 7.34e7.50 (m, 4H), 7.70 (d, J¼7.1 Hz, 1H), 7.84e7.91 (m, 2H); 13C NMR (CDCl3, 75 MHz) d 12.37, 14.63, 80.55, 87.25, 116.06, 123.48, 123.64, 125.26, 125.54, 126.21, 126.40, 126.79, 127.62, 127.96, 128.09, 128.33, 128.56, 129.25, 129.39, 131.46, 132.16, 133.52, 138.95, 140.02, 148.50; ESIMS

J.W. Lim et al. / Tetrahedron 70 (2014) 6831e6840

6837

m/z 399 [MþH]þ. Anal. Calcd for C29H22N2: C, 87.41; H, 5.56; N, 7.03. Found: C, 87.23; H, 5.68; N, 6.88.

m/z 375 [MþH]þ. Anal. Calcd for C27H22N2: C, 86.60; H, 5.92; N, 7.48. Found: C, 86.57; H, 5.75; N, 7.59.

4.3.5. Compound 5e. Yield 52%; pale yellow oil; IR (film) 1598, 1504, 1276, 1261 cm1; 1H NMR (CDCl3, 300 MHz) d 2.40 (s, 3H), 3.64 (s, 2H), 6.28 (dd, J¼3.3 and 0.9 Hz, 1H), 6.36 (dd, J¼3.3 and 1.8 Hz, 1H), 7.17e7.35 (m, 10H), 7.37 (dd, J¼1.8 and 0.9 Hz, 1H); 13C NMR (CDCl3, 75 MHz) d 11.98, 14.59, 80.69, 87.07, 111.18, 111.39, 115.36, 123.53, 124.66, 127.61, 127.78, 128.18, 128.88, 131.56, 131.73, 139.92, 143.22, 143.25, 148.41; ESIMS m/z 339 [MþH]þ. Anal. Calcd for C23H18N2O: C, 81.63; H, 5.36; N, 8.28. Found: C, 81.78; H, 5.61; N, 8.03.

4.3.12. Compound 5l. Yield 57%; pale yellow oil; IR (film) 1713, 1627, 1491, 1261 cm1; 1H NMR (CDCl3, 300 MHz) d 2.02 (s, 3H), 2.35 (s, 3H), 3.29 (t, J¼2.1 Hz, 2H), 4.59 (t, J¼2.1 Hz, 2H), 7.08e7.21 (m, 7H), 7.23e7.30 (m, 3H); 13C NMR (CDCl3, 75 MHz) d 12.11, 13.94, 20.77, 52.67, 74.23, 84.96, 113.84, 124.63, 126.69, 128.34, 128.54, 128.66, 129.82, 130.04, 139.90, 140.57, 148.43, 170.29; ESIMS m/z 345 [MþH]þ. Anal. Calcd for C22H20N2O2: C, 76.72; H, 5.85; N, 8.13. Found: C, 76.96; H, 5.58; N, 7.92. 4.4. Typical procedure for the synthesis of 6a

4.3.6. Compound 5f. Yield 54%; pale yellow oil; IR (film) 1678, 1597, 1502, 1379 cm1; 1H NMR (CDCl3, 300 MHz) d 2.37 (d, J¼1.2 Hz, 3H), 2.39 (s, 3H), 3.54 (s, 2H), 6.61 (dq, J¼3.6 and 1.2 Hz, 1H), 6.73 (d, J¼3.6 Hz, 1H), 7.14e7.28 (m, 8H), 7.28e7.36 (m, 2H); 13C NMR (CDCl3, 75 MHz) d 12.17, 14.72, 15.26, 80.71, 87.42, 115.40, 123.63, 125.08, 125.50, 127.26, 127.51, 127.72, 128.15, 128.72, 129.29, 131.55, 134.77, 139.68, 142.58, 148.27; ESIMS m/z 369 [MþH]þ. Anal. Calcd for C24H20N2S: C, 78.23; H, 5.47; N, 7.60. Found: C, 78.46; H, 5.63; N, 7.43. 4.3.7. Compound 5g. Yield 55%; pale yellow oil; IR (film) 1604, 1508, 1247 cm1; 1H NMR (CDCl3, 300 MHz) d 2.51 (s, 3H), 3.54 (s, 2H), 3.80 (s, 3H), 6.82 (d, J¼8.7 Hz, 2H), 7.16e7.40 (m, 10H), 7.32 (d, J¼8.7 Hz, 2H); 13C NMR (CDCl3, 75 MHz) d 12.24, 14.59, 55.24, 80.43, 86.06, 113.80, 114.67, 115.80, 124.69, 126.65, 128.28, 128.53, 128.68, 129.91, 130.24, 132.91, 140.02, 140.49, 148.62, 159.16; ESIMS m/z 379 [MþH]þ. Anal. Calcd for C26H22N2O: C, 82.51; H, 5.86; N, 7.40. Found: C, 82.39; H, 5.93; N, 7.27. 4.3.8. Compound 5h. Yield 60%; pale yellow oil; IR (film) 1597, 1505, 1378 cm1; 1H NMR (CDCl3, 300 MHz) d 2.45 (s, 3H), 3.39 (t, J¼2.1 Hz, 2H), 4.18 (t, J¼2.1 Hz, 2H), 4.58 (s, 2H), 7.16e7.37 (m, 15H); 13 C NMR (CDCl3, 75 MHz) d 12.15, 13.95, 57.68, 71.45, 76.15, 84.68, 114.31, 124.65, 126.67, 127.78, 128.04, 128.32, 128.39, 128.54, 128.67, 129.81, 130.11, 137.53, 139.95, 140.48, 148.43; ESIMS m/z 393 [MþH]þ. Anal. Calcd for C27H24N2O: C, 82.62; H, 6.16; N, 7.14. Found: C, 82.49; H, 6.31; N, 7.17. 4.3.9. Compound 5i. Yield 51%; pale yellow oil; IR (film) 1597, 1494, 1367 cm1; 1H NMR (CDCl3, 300 MHz) d 2.48 (s, 3H), 3.55 (s, 2H), 3.77 (s, 3H), 6.78 (d, J¼9.0 Hz, 2H), 7.13 (d, J¼9.0 Hz, 2H), 7.22e7.31 (m, 5H), 7.31e7,41 (m, 5H); 13C NMR (CDCl3, 75 MHz) d 12.19, 14.65, 55.38, 80.64, 87.77, 113.86, 123.68, 125.50, 126.17, 127.71, 128.17, 128.20, 128.49, 129.91, 130.21, 131.56, 133.32, 140.57, 148.12, 158.25; ESIMS m/z 379 [MþH]þ. Anal. Calcd for C26H22N2O: C, 82.51; H, 5.86; N, 7.40. Found: C, 82.22; H, 5.89; N, 7.35. 4.3.10. Compound 5j. Yield 55%; pale yellow oil; IR (film) 1495, 1378, 1276 cm1; 1H NMR (CDCl3, 300 MHz) d 2.42 (s, 3H), 3.46 (s, 2H), 7.07 (d, J¼9.0 Hz, 2H), 7.15 (d, J¼9.0 Hz, 2H), 7.16e7.23 (m, 5H), 7.26e7.34 (m, 5H); 13C NMR (CDCl3, 75 MHz) d 12.14, 14.54, 80.85, 87.29, 109.72, 114.95, 123.51, 127.81, 128.19, 128.67, 128.76, 128.87, 129.72, 129.85, 131.55, 132.38, 138.25, 140.70, 148.88; ESIMS m/z 383 [MþH]þ, 385 [MþHþ2]þ. Anal. Calcd for C25H19ClN2: C, 78.42; H, 5.00; N, 7.32. Found: C, 78.25; H, 5.21; N, 7.42. 4.3.11. Compound 5k. Yield 55%; pale yellow oil; IR (film) 1597, 1498, 1452, 1360 cm1; 1H NMR (CDCl3, 300 MHz) d 2.44 (s, 3H), 3.73 (s, 2H), 6.88 (d, J¼16.2 Hz, 1H), 7.13 (d, J¼16.2 Hz, 1H), 7.14e7.64 (m, 15H); 13C NMR (CDCl3, 75 MHz) d 12.00, 15.24, 80.92, 87.39, 113.57, 116.12, 123.52, 124.98, 126.61, 127.43, 127.81, 128.20, 128.27, 128.74, 129.10, 131.57, 133.75, 136.69, 138.16, 139.85, 148.47; ESIMS

A stirred solution of 5a (174 mg, 0.5 mmol) and DBU (23 mg, 0.3 equiv) in ODCB (1.5 mL) was heated to 130
C for 15 h. After removal of ODCB under reduced pressure, the product was purified by column chromatographic purification process (hexanes/Et2O, 8:1) to afford 6a as a pale yellow solid, 117 mg (67%). Other compounds were synthesized similarly, and the spectroscopic data of 6ael and 7 are as follows. 4.4.1. Compound 6a. Yield 67%; pale yellow solid, mp 124e126
C; IR (KBr) 1597, 1497, 1454, 1391 cm1; 1H NMR (CDCl3, 300 MHz) d 2.65 (s, 3H), 4.49 (s, 2H), 7.16e7.31 (m, 7H), 7.39e7.46 (m, 1H), 7.51e7.62 (m, 5H), 7.68 (dd, J¼8.4 and 1.5 Hz, 1H), 8.02 (d, J¼7.8 Hz, 1H); 13C NMR (CDCl3, 75 MHz) d 11.81, 39.81, 119.71, 120.31, 121.44, 122.85, 125.27, 125.76, 126.08, 126.15, 127.14, 128.46, 128.56, 128.70, 129.50, 130.15, 132.13, 136.55, 140.73, 141.94, 143.68; ESIMS m/z 349 [MþH]þ. Anal. Calcd for C25H20N2: C, 86.17; H, 5.79; N, 8.04. Found: C, 86.23; H, 5.94; N, 7.87. 4.4.2. Compound 6b. Yield 68%; white solid, mp 146e148
C; IR (KBr) 1672, 1596, 1504, 1262 cm1; 1H NMR (CDCl3, 300 MHz) d 1.46 (t, J¼7.5 Hz, 3H), 3.07 (q, J¼7.5 Hz, 2H), 4.49 (s, 2H), 7.15e7.31 (m, 6H), 7.37e7.45 (m, 1H), 7.48e7.63 (m, 6H), 7.66 (d, J¼8.1 Hz, 1H), 8.01 (d, J¼8.4 Hz, 1H); 13C NMR (CDCl3, 75 MHz) d 13.85, 20.26, 39.85, 119.51, 119.76, 121.52, 122.81, 125.23, 125.75, 126.07, 126.08, 127.23, 128.44, 138.53, 128.67, 129.50, 130.01, 132.10, 136.66, 140.77, 142.02, 149.05; ESIMS m/z 363 [MþH]þ. Anal. Calcd for C26H22N2: C, 86.15; H, 6.12; N, 7.73. Found: C, 86.01; H, 6.28; N, 7.62. 4.4.3. Compound 6c. Yield 79%; pale yellow solid, mp 176e178
C; IR (KBr) 1597, 1499, 1432 cm1; 1H NMR (CDCl3, 300 MHz) d 2.67 (s, 3H), 4.87 (s, 2H), 7.25e7.30 (m, 1H), 7.32e7.44 (m, 5H), 7.46e7.63 (m, 7H), 7.69 (s, 1H), 7.71 (d, J¼9.0 Hz, 1H), 7.85 (dd, J¼7.8 and 1.5 Hz, 1H), 8.58 (d, J¼8.7 Hz, 1H); 13C NMR (CDCl3, 75 MHz) d 11.91, 43.79, 119.79, 121.44, 121.85, 123.57, 125.42, 126.01, 126.19, 126.34, 126.52, 128.07, 128.25, 128.43, 128.71, 128.80, 129.49, 130.26, 130.59, 130.75, 132.81, 136.91, 141.79, 142.15, 143.64; ESIMS m/z 399 [MþH]þ. Anal. Calcd for C29H22N2: C, 87.41; H, 5.56; N, 7.03. Found: C, 87.17; H, 5.72; N, 7.24. 4.4.4. Compound 6d. Yield 83%; white solid, mp 182e184
C; IR (KBr) 1599, 1495, 1431 cm1; 1H NMR (CDCl3, 300 MHz) d 2.74 (s, 3H), 4.60 (s, 2H), 6.94e7.01 (m, 1H), 7.12e7.32 (m, 10H), 7.32e7.39 (m, 1H), 7.72 (m, 1H), 7.77e7.84 (m, 2H), 7.96 (d, J¼8.7 Hz, 1H), 8.02 (d, J¼9.0 Hz, 1H); 13C NMR (CDCl3, 75 MHz) d 12.08, 39.97, 118.55, 120.31, 122.99, 123.43, 124.25, 124.40, 125.81, 126.14, 126.33, 127.00, 127.12, 127.53, 128.51, 128.57, 128.69, 128.88, 131.17, 131.22, 131.71, 137.14, 140.78, 142.31, 146.17; ESIMS m/z 399 [MþH]þ. Anal. Calcd for C29H22N2: C, 87.41; H, 5.56; N, 7.03. Found: C, 87.33; H, 5.68; N, 6.91. 4.4.5. Compound 6e. Yield 74%; colorless oil; IR (film) 1600, 1512, 1499, 1453 cm1; 1H NMR (CDCl3, 300 MHz) d 2.65 (s, 3H), 4.31 (s,

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2H), 6.81 (d, J¼2.1 Hz, 1H), 7.17e7.38 (m, 7H), 7.48e7.55 (m, 2H), 7.60 (d, J¼2.1 Hz, 1H), 7.84e7.91 (m, 2H); 13C NMR (CDCl3, 75 MHz) d 12.12, 39.50, 106.73, 114.95, 122.86, 123.95, 125.84, 126.21, 126.27, 126.75, 127.38, 128.50, 128.70, 128.91, 139.34, 140.47, 140.51, 143.73, 144.97; ESIMS m/z 339 [MþH]þ. Anal. Calcd for C23H18N2O: C, 81.63; H, 5.36; N, 8.28. Found: C, 81.48; H, 5.41; N, 8.11. 4.4.6. Compound 6f. Yield 81%; pale yellow solid, mp 150e152
C; IR (KBr) 1597, 1508, 1452, 1331 cm1; 1H NMR (CDCl3, 300 MHz) d 2.41 (d, J¼0.9 Hz, 3H), 2.57 (s, 3H), 4.27 (s, 2H), 7.01 (q, J¼0.9 Hz, 1H), 7.09e7.26 (m, 5H), 7.29 (s, 1H), 7.36e7.43 (m, 1H), 7.43e7.51 (m, 2H), 7.53e7.60 (m, 2H); 13C NMR (CDCl3, 75 MHz) d 12.04, 15.88, 40.17, 117.06, 120.81, 120.86, 121.06, 125.98, 126.12, 128.10, 128.38, 128.48, 128.62, 129.14, 135.14, 139.38, 139.88, 140.57, 140.62, 144.32; ESIMS m/z 369 [MþH]þ. Anal. Calcd for C24H20N2S: C, 78.23; H, 5.47; N, 7.60. Found: C, 78.11; H, 5.33; N, 7.51. 4.4.7. Compound 6g. Yield 74%; pale yellow solid, mp 134e136
C; IR (KBr) 1598, 1508, 1247 cm1; 1H NMR (CDCl3, 300 MHz) d 2.66 (s, 3H), 3.78 (s, 3H), 4.43 (s, 2H), 6.84 (d, J¼8.7 Hz, 2H), 7.17 (d, J¼8.7 Hz, 2H), 7.21e7.32 (m, 2H), 7.39e7.48 (m, 1H), 7.52 (s, 1H), 7.50e7.63 (m, 4H), 7.69 (d, J¼8.1 Hz, 1H), 8.04 (d, J¼8.4 Hz, 1H); 13C NMR (CDCl3, 75 MHz) d 11.83, 38.91, 55.21, 113.86, 119.46, 120.31, 121.43, 122.83, 125.24, 125.73, 126.11, 127.13, 128.68, 129.49 (2C), 130.59, 132.11, 132.72, 136.50, 141.95, 143.66, 157.91; ESIMS m/z 379 [MþH]þ. Anal. Calcd for C26H22N2O: C, 82.51; H, 5.86; N, 7.40. Found: C, 82.27; H, 5.98; N, 7.32. 4.4.8. Compound 6h. Yield 72%; colorless oil; IR (film) 1598, 1505, 1453, 1432 cm1; 1H NMR (CDCl3, 300 MHz) d 2.67 (s, 3H), 3.47 (t, J¼7.2 Hz, 2H), 3.90 (t, J¼7.2 Hz, 2H), 4.60 (s, 2H), 7.22e7.39 (m, 6H), 7.49e7.62 (m, 7H), 7.70 (d, J¼8.4 Hz, 1H), 8.13 (d, J¼8.4 Hz, 1H); 13C NMR (CDCl3, 75 MHz) d 11.81, 33.93, 70.53, 73.09, 118.92, 120.31, 121.28, 122.95, 124.95, 125.06, 125.21, 126.11, 127.11, 127.59, 127.68, 128.37, 128.65, 129.48, 132.02, 136.41, 138.32, 141.93, 143.55; ESIMS m/z 393 [MþH]þ. Anal. Calcd for C27H24N2O: C, 82.62; H, 6.16; N, 7.14. Found: C, 82.44; H, 6.41; N, 7.13. 4.4.9. Compound 6i. Yield 71%; white solid, mp 126e128
C; IR (KBr) 1517, 1452, 1442, 1250 cm1; 1H NMR (CDCl3, 300 MHz) d 2.64 (s, 3H), 3.92 (s, 3H), 4.48 (s, 2H), 7.07 (d, J¼9.0 Hz, 2H), 7.16e7.31 (m, 6H), 7.38e7.45 (m, 1H), 7.48 (d, J¼9.0 Hz, 2H), 7.52 (s, 1H), 7.65 (d, J¼8.1 Hz, 1H), 8.01 (d, J¼8.1 Hz, 1H); 13C NMR (CDCl3, 75 MHz) d 11.80, 39.81, 55.60, 114.63, 119.73, 119.92, 121.53, 122.71, 125.29, 125.72, 126.06, 128.44, 128.54, 128.57, 129.87, 132.07, 134.87, 136.76, 140.77, 143.21, 159.80, one carbon is overlapped; ESIMS m/z 379 [MþH]þ. Anal. Calcd for C26H22N2O: C, 82.51; H, 5.86; N, 7.40. Found: C, 82.46; H, 5.67; N, 7.31.

[MþH]þ. Anal. Calcd for C27H22N2: C, 86.60; H, 5.92; N, 7.48. Found: C, 86.51; H, 5.99; N, 7.43. 4.4.12. Compound 6l. Yield 15%; colorless oil; IR (film) 1598, 1504, 1433 cm1; 1H NMR (CDCl3, 300 MHz) d 2.70 (s, 3H), 5.48 (dd, J¼10.8 and 1.8 Hz, 1H), 5.81 (dd, J¼17.1 and 1.8 Hz, 1H), 7.28e7.35 (m, 1H), 7.46 (dd, J¼17.1 and 10.8 Hz, 1H), 7.50e7.62 (m, 6H), 7.67 (d, J¼8.4 Hz, 1H), 7.79 (s, 1H), 8.17 (d, J¼8.1 Hz, 1H); 13C NMR (CDCl3, 75 MHz) d 11.83, 116.45, 116.48, 120.44, 120.76, 122.73, 125.24, 125.52, 126.21, 127.12, 128.78, 129.53, 130.70, 131.44, 135.42, 136.77, 141.78, 144.21; ESIMS m/z 285 [MþH]þ. Anal. Calcd for C20H16N2: C, 84.48; H, 5.67; N, 9.85. Found: C, 84.23; H, 5.51; N, 9.95. 4.4.13. Compound 7. Yield 77%; white solid, mp 89e91
C; IR (KBr) 2205, 1597, 1508, 1382 cm1; 1H NMR (CDCl3, 300 MHz) d 2.36 (s, 3H), 5.37 (dd, J¼11.1 and 2.1 Hz, 1H), 5.53 (dd, J¼17.4 and 2.1 Hz, 1H), 5.88 (dd, J¼17.4 and 11.1 Hz, 1H), 7.12e7.30 (m, 10H); 13C NMR (CDCl3, 75 MHz) d 12.55, 82.04, 91.96, 104.00, 117.41, 125.08, 125.65, 127.39, 128.27, 128.56, 128.88, 129.19, 129.30, 139.67, 144.22, 151.91; ESIMS m/z 285 [MþH]þ. Anal. Calcd for C20H16N2: C, 84.48; H, 5.67; N, 9.85. Found: C, 84.20; H, 5.72; N, 9.76. 4.5. Synthesis of 9a and 9b Compounds 8a and 8b were prepared according to the reported methods.12 The synthesis of 9a and 9b was carried out by following the typical procedure for the synthesis of 5a. 4.5.1. Compound 9a. Yield 76%; pale yellow solid, mp 74e76
C; IR (KBr) 1597, 1493, 1452 cm1; 1H NMR (CDCl3, 300 MHz) d 5.38 (s, 1H), 7.04e7.32 (m, 23H), 7.61e7.66 (m, 2H); 13C NMR (CDCl3, 75 MHz) d 30.89, 32.97, 84.10, 89.75, 118.57, 123.37, 124.77, 126.36, 126.90, 127.45, 127.82, 128.01, 128.06, 128.10, 128.30, 128.48, 128.91, 130.17, 130.40, 131.55, 133.20, 139.87, 140.47, 142.08, 151.46, one carbon is overlapped; ESIMS m/z 487 [MþH]þ. Anal. Calcd for C36H26N2: C, 88.86; H, 5.39; N, 5.76. Found: C, 88.97; H, 5.23; N, 5.61. 4.5.2. Compound 9b. Yield 72%; pale yellow solid, mp 56e58
C; IR (KBr) 1596, 1498, 1451, 1360 cm1; 1H NMR (CDCl3, 300 MHz) d 1.35 (d, J¼7.2 Hz, 3H), 4.10 (q, J¼7.2 Hz, 1H), 7.18e7.50 (m, 18H), 7.89e7.94 (m, 2H); 13C NMR (CDCl3, 75 MHz) d 21.64, 22.62, 81.40, 93.74, 119.95, 123.76, 124.91, 126.89, 127.66, 127.90, 128.14, 128.30, 128.44, 128.59, 128.61, 129.16, 130.65, 130.67, 131.49, 133.84, 139.93, 141.25, 151.12; ESIMS m/z 425 [MþH]þ. Anal. Calcd for C31H24N2: C, 87.70; H, 5.70; N, 6.60. Found: C, 87.89; H, 5.93; N, 6.72.

4.4.10. Compound 6j. Yield 73%; white solid, mp 170e172
C; IR (KBr) 1502, 1452, 1092 cm1; 1H NMR (CDCl3, 300 MHz) d 2.64 (s, 3H), 4.48 (s, 2H), 7.15e7.34 (m, 6H), 7.40e7.48 (m, 1H), 7.48e7.56 (m, 5H), 7.69 (d, J¼8.4 Hz, 1H), 8.03 (d, J¼8.1 Hz, 1H); 13C NMR (CDCl3, 75 MHz) d 11.81, 39.80, 119.65, 120.58, 121.26, 122.69, 125.43, 125.91, 126.13, 126.32, 128.30, 128.48, 128.54, 129.68, 130.50, 132.19, 134.36, 136.51, 140.48, 140.62, 144.21; ESIMS m/z 383 [MþH]þ, 385 [MþHþ2]þ. Anal. Calcd for C25H19ClN2: C, 78.42; H, 5.00; N, 7.32. Found: C, 78.21; H, 5.19; N, 7.09.

Compound 10a was synthesized under the typical reaction conditions for 6a using DBU (0.3 equiv) as a base in ODCB (130
C, 20 h). The synthesis of 11a and 11b was carried out in refluxing ODCB for 32e60 h, and the spectroscopic data of an allene derivative 10a and 1H-benzo[g]indazole derivatives 11a and 11b are as follows.

4.4.11. Compound 6k. Yield 78%; colorless oil; IR (film) 1598, 1513, 1496, 1439 cm1; 1H NMR (CDCl3, 300 MHz) d 2.56 (s, 3H), 3.96 (s, 2H), 6.84e6.89 (m, 2H), 7.02e7.23 (m, 6H), 7.23e7.30 (m, 3H), 7.35e7.42 (m, 2H), 7.46 (s, 1H), 7.50 (s, 1H), 7.59e7.65 (m, 2H); 13C NMR (CDCl3, 75 MHz) d 11.95, 39.43, 111.48, 121.48, 122.18, 124.36, 125.77, 126.04, 127.14, 128.00, 128.19, 128.76, 129.36, 129.39, 132.13, 138.27, 140.10, 141.38, 141.76, 142.67, 143.68; ESIMS m/z 375

4.6.1. Compound 10a. Yield 71%; pale yellow solid, mp 140e142
C; IR (KBr) 1596, 1498, 1449, 1363 cm1; 1H NMR (CDCl3, 300 MHz) d 6.30 (s, 1H), 6.74e6.80 (m, 2H), 6.92e7.41 (m, 21H), 7.75e7.84 (m, 2H); 13C NMR (CDCl3, 75 MHz) d 96.98, 104.02, 114.12, 124.97, 126.65, 127.04, 127.09, 127.14, 127.18, 127.44, 127.75, 128.28, 128.30, 128.39, 128.53, 128.58, 128.74, 129.95, 130.16, 133.01, 133.42, 136.32, 139.92, 142.60, 150.38, 208.74; ESIMS m/z 487 [MþH]þ. Anal. Calcd

4.6. Synthesis of 10a, 11a, and 11b

J.W. Lim et al. / Tetrahedron 70 (2014) 6831e6840

for C36H26N2: C, 88.86; H, 5.39; N, 5.76. Found: C, 88.61; H, 5.48; N, 5.65. 4.6.2. Compound 11a. Yield 57%; pale yellow solid, mp 106e108
C; IR (KBr) 1597, 1496, 1452 cm1; 1H NMR (CDCl3, 300 MHz) d 4.37 (s, 2H), 6.92e7.34 (m, 17H), 7.35e7.44 (m, 1H), 7.56e7.65 (m, 3H), 7.68e7.74 (m, 2H), 7.97 (d, J¼8.7 Hz, 1H); 13C NMR (CDCl3, 75 MHz) d 35.42, 118.98, 120.88, 122.67, 125.21, 125.56, 126.54, 126.63, 126.95, 127.02, 127.11, 127.40, 127.42, 127.48, 128.09, 128.27, 129.06, 129.36, 129.61, 130.04, 132.63, 133.56, 134.47, 136.70, 138.03, 141.89, 142.02, 148.40; ESIMS m/z 487 [MþH]þ. Anal. Calcd for C36H26N2: C, 88.86; H, 5.39; N, 5.76. Found: C, 88.53; H, 5.22; N, 5.61. 4.6.3. Compound 11b. Yield 65%; white solid, mp 84e86
C; IR (KBr) 1596, 1495, 1452 cm1; 1H NMR (CDCl3, 300 MHz) d 2.30 (s, 3H), 4.44 (s, 2H), 7.01e7.19 (m, 7H), 7.29e7.43 (m, 4H), 7.44e7.64 (m, 7H), 7.90 (d, J¼8.4 Hz, 1H); 13C NMR (CDCl3, 75 MHz) d 17.39, 34.10, 120.05, 120.08, 122.64, 124.46, 125.59, 125.85, 126.53, 127.41, 127.49, 127.93, 127.96, 128.12, 128.44, 128.77, 129.00, 129.57, 130.50, 133.07, 135.11, 136.49, 140.38, 142.01, 148.00; ESIMS m/z 425 [MþH]þ. Anal. Calcd for C31H24N2: C, 87.70; H, 5.70; N, 6.60. Found: C, 87.55; H, 5.81; N, 6.52.

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2H), 7.15e7.34 (m, 6H), 7.38e7.73 (m, 10H), 7.93 (s, 1H), 7.97e8.08 (m, 3H); 13C NMR (CDCl3, 75 MHz) d 40.01, 118.75, 120.53, 121.50, 122.75, 125.50, 125.83, 126.09, 126.35, 127.43, 128.03, 128.13, 128.44, 128.46, 128.80, 129.09, 129.62, 131.23, 132.03, 133.21, 137.38, 140.68, 141.93, 146.16; ESIMS m/z 411 [MþH]þ. Anal. Calcd for C30H22N2: C, 87.77; H, 5.40; N, 6.82. Found: C, 87.71; H, 5.64; N, 6.69. 4.8.2. Compound 15b. Yield 84%; white solid, mp 108e110
C; IR (KBr) 1732, 1498, 1178, 1155 cm1; 1H NMR (CDCl3, 300 MHz) d 1.26 (t, J¼7.2 Hz, 3H), 4.14 (s, 2H), 4.20 (q, J¼7.2 Hz, 2H), 7.31e7.38 (m, 1H), 7.41e7.49 (m, 1H), 7.51e7.72 (m, 9H), 7.98 (s, 1H), 8.01e8.06 (m, 2H), 8.08 (d, J¼8.4 Hz, 1H); 13C NMR (CDCl3, 75 MHz) d 14.17, 40.01, 60.98, 118.62, 121.26, 121.31, 122.81, 125.05, 125.70, 125.75, 126.57, 127.40, 128.07, 128.18, 128.78, 129.11, 129.60, 131.88, 133.07, 137.56, 141.82, 146.30, 171.77; ESIMS m/z 407 [MþH]þ. Anal. Calcd for C27H22N2O2: C, 79.78; H, 5.46; N, 6.89. Found: C, 79.47; H, 5.53; N, 6.83. 4.9. Synthesis of 16 Compound 16 was synthesized from 5a by the intramolecular FriedeleCrafts reaction in the presence of H2SO4 in CH2Cl2 at room temperature according to the reported method.13

4.7. Typical procedure for the synthesis of 14a A mixture of 4-methyl-1,3,5-triphenyl-1H-pyrazole 13 (310 mg, 1.0 mmol), N-bromosuccinimide (196 mg, 1.1 mmol), and AIBN (16 mg, 0.1 mmol) in CCl4 (4.0 mL) was heated to reflux for 4 h. After the usual aqueous extractive workup, the crude 4bromomethylpyrazole derivative was dissolved in CH3CN (4.0 mL). To the solution phenylacetylene (153 mg, 1.5 mmol), Cs2CO3 (489 mg, 1.5 mmol) and CuI (38 mg, 0.2 mmol) were added, and the reaction mixture was stirred at 50
C for 12 h. After the aqueous extractive workup and column chromatographic purification process (hexanes/Et2O, 8:1) compound 14a was obtained as a pale yellow solid, 251 mg (61%). Compound 14b was synthesized similarly, and the spectroscopic data of 14a and 14b are as follows. 4.7.1. Compound 14a. Yield 61%; pale yellow solid, mp 58e60
C; IR (KBr) 1598, 1495, 1452 cm1; 1H NMR (CDCl3, 300 MHz) d 3.68 (s 2H), 7.22e7.47 (m, 16H), 7.48e7.57 (m, 2H), 8.01e8.06 (m, 2H); 13C NMR (CDCl3, 75 MHz) d 15.65, 81.38, 88.84, 114.27, 123.63, 124.85, 127.01, 127.78, 127.91, 128.17 (2C), 128.53, 128.59, 128.72, 130.01, 130.06, 131.58, 133.20, 139.99, 141.92, 151.20, one carbon is overlapped; ESIMS m/z 411 [MþH]þ. Anal. Calcd for C30H22N2: C, 87.77; H, 5.40; N, 6.82. Found: C, 87.62; H, 5.55; N, 6.65. 4.7.2. Compound 14b. Yield 56%; white solid, mp 72e74
C; IR (KBr) 1712, 1491, 1273 cm1; 1H NMR (CDCl3, 300 MHz) d 1.24 (t, J¼7.2 Hz, 3H), 3.48 (s, 2H), 4.16 (q, J¼7.2 Hz, 2H), 7.11e7.46 (m, 13H), 7.74e7.82 (m, 2H); 13C NMR (CDCl3, 75 MHz) d 14.01, 15.03, 61.90, 73.59, 87.10, 111.71, 124.82, 127.17, 128.11, 128.12, 128.65, 128.75, 128.77, 128.78, 129.56, 129.97, 132.74, 139.79, 142.32, 151.20, 153.71; ESIMS m/z 407 [MþH]þ. Anal. Calcd for C27H22N2O2: C, 79.78; H, 5.46; N, 6.89. Found: C, 79.98; H, 5.41; N, 6.77. 4.8. Synthesis of 15a and 15b 4-Unsubstituted 1H-benzo[g]indazole 15a was synthesized under the typical reaction conditions for 6a using DBU (0.3 equiv) as a base in ODCB (130
C, 15 h). The synthesis of 15b was carried out in the presence of K2CO3 (0.3 equiv) instead of DBU, and the spectroscopic data of 15a and 15b are as follows. 4.8.1. Compound 15a. Yield 82%; white solid, mp 112e114
C; IR (KBr) 1597, 1497, 1462 cm1; 1H NMR (CDCl3, 300 MHz) d 4.53 (s,

4.9.1. Compound 16. Yield 63%; pale yellow oil; IR (film) 1597, 1530, 1275, 1261 cm1; 1H NMR (CDCl3, 300 MHz) d 2.36 (s, 3H), 2.97 (br s, 2H), 6.42 (d, J¼7.2 Hz, 1H), 7.01e7.11 (m, 2H), 7.13e7.19 (m, 1H), 7.19e7.42 (m, 11H); 13C NMR (CDCl3, 75 MHz) d 11.49, 21.72, 124.47, 125.86, 126.31, 126.44, 126.89, 127.06, 128.14, 128.68, 128.91, 129.01, 129.32, 131.39, 131.40, 137.83, 138.09, 140.44, 141.54, 143.86, 144.91; ESIMS m/z 349 [MþH]þ. Anal. Calcd for C25H20N2: C, 86.17; H, 5.79; N, 8.04. Found: C, 86.30; H, 5.64; N, 7.93. Acknowledgements This research was supported by Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education, Science and Technology (2012R1A1B3000541). Spectroscopic data were obtained from the Korea Basic Science Institute, Gwangju branch. Supplementary data These data include copies of 1H and 13C NMR spectra. Supplementary data associated with this article can be found in the online version, at http://dx.doi.org/10.1016/j.tet.2014.07.048. References and notes 1. For the synthesis and biological activity of indazole derivatives, see: (a) Schmidt, A.; Beutler, A.; Snovydovych, B. Eur. J. Org. Chem. 2008, 4073e4095 and further references cited therein; (b) Li, X.; He, L.; Chen, H.; Wu, W.; Jiang, H. J. Org. Chem. 2013, 78, 3636e3646; (c) Zhang, T.; Bao, W. J. Org. Chem. 2013, 78, 1317e1322; (d) Clutterbuck, L. A.; Posada, C. G.; Visintin, C.; Riddall, D. R.; Lancaster, B.; Gane, P. J.; Garthwaite, J.; Selwood, D. L. J. Med. Chem. 2009, 52, 2694e2707; (e) Jin, T.; Yamamoto, Y. Angew. Chem., Int. Ed. 2007, 46, 3323e3325; (f) Cho, C. S.; Lim, D. K.; Heo, N. H.; Kim, T.-J.; Shim, S. C. Chem. Commun. 2004, 104e105; (g) Lee, K. Y.; Gowrisankar, S.; Kim, J. N. Tetrahedron Lett. 2005, 46, 5387e5391. 2. For the synthesis of benzo[g]indazole and 4,5-dihydrobenzo[g]indazole derivatives, see: (a) Suzuki, Y.; Oishi, S.; Takei, Y.; Yasue, M.; Misu, R.; Naoe, S.; Hou, Z.; Kure, T.; Nakanishi, I.; Ohno, H.; Hirasawa, A.; Tsujimoto, G.; Fujii, N. Org. Biomol. Chem. 2012, 10, 4907e4915; (b) Chang, M.-Y.; Tai, H.-Y.; Chen, Y.-L.; Hsu, R.-T. Tetrahedron 2012, 68, 7941e7948; (c) Akbar, S.; Srinivasan, K. Eur. J. Org. Chem. 2013, 1663e1666; (d) Povalyakhina, M. A.; Antonov, A. S.; Dyablo, O. V.; Ozeryanskii, V. A.; Pozharskii, A. F. J. Org. Chem. 2011, 76, 7157e7166; (e) Shen, H. C.; Ding, F.-X.; Deng, Q.; Wilsie, L. C.; Krsmanovic, M. L.; Taggart, A. K.; Carballo-Jane, E.; Ren, N.; Cai, T.-Q.; Wu, T.-J.; Wu, K. K.; Cheng, K.; Chen, Q.; Wolff, M. S.; Tong, X.; Holt, T. G.; Waters, M. G.; Hammond, M. L.; Tata, J. R.; Colletti, S. L. J. Med. Chem. 2009, 52, 2587e2602; (f) Aksenova, I. V.; Aksenov, A. V.; Aksenov, N. A. Chem. Heterocycl. Compd. 2009, 45, 117e118; (g)

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7. For the 6p-electrocyclization involving two aromatic p-bonds, see: (a) Saifuddin, M.; Agarwal, P. K.; Kundu, B. J. Org. Chem. 2011, 76, 10122e10128; (b) Choshi, T.; Hibino, S. Heterocycles 2009, 77, 85e97; (c) Tohyama, S.; Choshi, T.; Matsumoto, K.; Yamabuki, A.; Hieda, Y.; Nobuhiro, J.; Hibino, S. Heterocycles 2010, 82, 397e416; (d) Choshi, T.; Hibino, S. Heterocycles 2011, 83, 1205e1239 and further references cited therein. For the related indium-catalyzed 6-exo-dig hydroarylation of o-propargylbiaryls, see: (e) Kwon, Y.; Cho, H.; Kim, S. Org. Lett. 2013, 15, 920e923. 8. When we carried out the reaction of 1a and 2a at 50
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