One-pot synthesis of carbazoles via tandem C–C cross-coupling and reductive amination

Abstract

We have developed a highly efficient synthetic route to carbazoles that employs sequential C–C/C–N bond formation via Suzuki cross-coupling and Cadogan cyclization using commercially available or easily preparable starting materials. The developed method is compatible with electron neutral, rich or deficient substrates. The synthetic utility of this method was demonstrated by the concise syntheses of four natural products (glycozoline, glycozolicine, glycozolidine and clausenalene).

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Introduction

Carbazole is a ubiquitous structural motif in a large number of biologically active natural products and pharmaceuticals.¹ In addition, carbazole derivatives have been widely used as functional organic materials.² Thus, the development of efficient synthetic routes to structurally diverse carbazoles represents an important objective in organic synthesis. Many methods have been developed for the preparation of carbazole.³ The most widely used approaches for the synthesis of the carbazole framework are C–N or C–C bond forming cyclizations from substituted biaryls or N,N-biaryl amines. Representative C–N bond forming reactions for the synthesis of carbazoles are summarized in Scheme 1(a): (A) transition metal free⁴ or palladium catalyzed Buchwald–Hartwig⁵ amination from 2-amino-2′-halo-biphenyls; (B) dehydrogenative C–H/N–H coupling of 2-amino-biphenyls;⁶ (C) iron-mediated oxidative amination of an iron complex;⁷ (D) transition metal mediated double amination of 2,2′-dihalobiphenyls or cyclic diphenyleneiodoniums;⁸ (E) transition metal free⁹ or rhodium catalyzed¹⁰ nitrene insertion of 2-azido-biphenyls; and (F) reductive amination of 2-nitro-biphenyls.¹¹ Similarly, dehydrogenative C–C bond formation of N,N-biaryl amines leads to carbazoles (Scheme 1(b)).¹² Although these methods proceed in good yields and are tolerant of most organic functional groups, they require the preparation of complex starting materials, such as substituted biaryls or N,N-biaryl amines, for the synthesis of diverse carbazoles. Therefore, we investigated the development of a one-pot C–C and C–N bond coupling reaction that utilizes commercially available or easily preparable starting materials.

Scheme 1 Various synthetic approaches to carbazoles.

More recently, one-pot syntheses of carbazoles have been developed (Scheme 1(c)).¹³ Bedford^13a and Ackermann^13b,d reported a palladium catalyzed domino Buchwald–Hartwig amination and C–H activation of 2-chloroanilines with aryl bromides or anilines with dichloroarenes. Jean Jr^13c reported the Pd-catalyzed tandem Suzuki cross-coupling and S_NAr reaction of aniline-derived boronic esters with 2-fluoro-3-halobenzenes. Studer^13f reported a transition metal-free cascade reaction of nitrosoarenes with in situ generated arynes.

We envision a one-pot reaction sequence of C–C cross-coupling and C–N bond forming cyclization to develop a step-economical method to prepare carbazoles. We considered the Suzuki reaction¹⁴ and the Cadogan cyclization¹⁵ for one-pot reaction. Both reactions are the widely used methods for C–C cross-coupling or reductive amination and use similar phosphine reagents for the ligand or reductant.^15d Herein, we present a highly efficient synthetic method to carbazoles that consists of palladium-catalyzed tandem C–C/C–N bond formation via the Suzuki reaction and reductive Cadogan cyclization (Scheme 1).

Results and discussion

Initially, we explored the domino reaction of 2-iodonitrobenzene 1a with phenylboronic acid 2a in the presence of Pd(OAc)₂ and triphenylphosphine in o-DCB at 150 °C, which delivered the carbazole 3a and 2-nitrobiphenyl in 24% and 20% yields (Table 1, entry 1). Based on this result, other 2-halonitrobenzenes were assayed, and it was found that 2-bromonitrobenzene 1b was the most efficient (Table 1, entry 2).

Table 1 Optimization of the reaction conditions^a

Entry	1, X	Catalyst (mol%)	Reductant	T (°C)	Time (h)	Y^b (%)
a Reaction conditions: 1 (0.5 mmol), 2a (0.6 mmol), catalyst (quantity noted), reductant (250 mol%), K2CO3 (200 mol%), o-DCB (1.0 mL) under air in pressure tubes. b Isolated yield by flash column chromatography. c Using a reflux condenser. d 2a (130 mol%).
1	1a, I	Pd(OAc) (2)	PPh3	150	16	24
2	1b, Br	Pd(OAc) (2)	PPh3	150	16	56
3	1c, Cl	Pd(OAc) (2)	PPh3	150	16	31
4	1b, Br	Pd(OAc) (2)	PEt3	150	16	12
5	1b, Br	Pd(OAc) (2)	P(OEt)3	150	16	21
6	1b, Br	Pd2(dba)3 (2)	PPh3	150	16	41
7	1b, Br	Pd(PPh3)4 (2)	PPh3	150	16	29
8	1b, Br	Pd(OAc) (1)	PPh3	150	16	17
9	1b, Br	Pd(OAc) (4)	PPh3	150	16	13
10	1b, Br	Pd(OAc) (2)	PPh3	180	16	72
11	1b, Br	Pd(OAc) (2)	PPh3	180	24	78
12^c	1b, Br	Pd(OAc) (2)	PPh3	Reflux	24	66
⇒13^d	1b , Br	Pd(OAc) (2)	PPh 3	180	24	86

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Thus they were chosen for further studies. When other reductants such as PEt₃ and P(OEt)₃ ^15e were used, the yield of the reaction did not improve (Table 1, entries 4 and 5). Moreover, other catalysts such as Pd₂(dba)₃ and Pd(PPh₃)₄ were not effective in this transformation (Table 1, entries 6 and 7). Reductant and catalyst screening indicated that Pd(OAc)₂ and PPh₃ were the best choices. To improve the yield, the catalyst loading, as well as the reaction temperature and time were surveyed. Increasing and decreasing the catalyst loading were not efficient (Table 1, entries 8 and 9). However, the yield did increase with a higher temperature and longer reaction time (Table 1, entries 10 and 11). The coupling reaction was not efficient at atmospheric pressure (Table 1, entry 12). Using 130 mol% phenylboronic acid 2a gave the best result (Table 1, entry 13).

We next examined the substrate scope with respect to the substituted arylboronic acid (Table 2). Under the optimized conditions, o-bromonitrobenzene 1b was coupled to a diverse range of arylboronic acids 2 to form carbazoles 3a–3o in moderate to excellent yields.

Table 2 Substrate scope of various aryl boronic acids^a

a As given in Table 1, entry 13. b 48 h. c Pd(OAc) (5 mol%), 48 h; yields of the isolated material. See the ESI for details.

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Notably, electron neutral and electron rich arylboronic acids possessing alkyl, aryl, and alkoxy substituents were tolerated in the one-pot reaction (3a–3h, 3m–o), as o-, m- and p-substituted arylboronic acids and 3,4-disubstituted arylboronic acids afforded the corresponding products (3a–3h, 3m–o) in good to high yields. Aryl boronic acids possessing bulky groups at the para position such as t-butyl and phenyl were also converted to carbazoles in excellent yields. As expected, coupling of m-substituted arylboronic acids with o-bromonitrobenzene 1b gave a mixture of corresponding 1- and 3-substituted carbazoles as regioisomers. In these experiments, 3-substituted carbazoles were obtained as the major regioisomer except with 3-tolylboronic acid. In particular, 3,4-(methylenedioxy)phenylboronic acid gave a 5.9 : 1 mixture of 3n and 3n′, demonstrating moderate regioselectivity, while 3-tolylboronic acid and 4-methoxy-3-methylphenylboronic acid gave mixtures with low regioselectivity (3m ¹⁶/m′, 3o ¹⁷/o′).

In addition, we explored the scope of electron deficient arylboronic acids possessing fluorine, chlorine, ketone, and ester moieties and found that they also gave the desired products (3i–3l). Slightly lower yields were observed for electron deficient arylboronic acids except for 4-fluorophenylboronic acid.

In particular, 4-fluoro and 4-chloroboronic acids were tolerated under these coupling conditions. Halogen containing carbazoles are useful for the introduction of additional functionalization. Thus, we examined the further functionalization of 3-chlorocarbazole 3i (Scheme 2). Under modified Suzuki cross-coupling conditions¹⁸ for unprotected N-heterocycles, 3-chlorocarbazole 3i was coupled to a diverse range of arylboronic acids to form functionalized carbazoles (3e, 3ia–3id) in good to excellent yields.

Scheme 2 Further functionalization of 3-chlorocarbazole (3i).

To demonstrate the efficiency of this method, we conducted the gram scale synthesis of carbazole 3a. The coupling reaction of 2-bromonitrobenzene 1b (1 g, 5 mmol) with phenylboronic acid 2a (750 mg, 6.5 mmol) afforded the carbazole 3a in 75% yield.

Next, we turned our attention to the domino reaction of phenylboronic acid with a broad range of substituted o-bromonitrobenzenes (Table 3). Under the optimized conditions, the one-pot reaction of substituted o-bromonitrobenzenes 1 with phenylboronic acid 2a was converted to the corresponding carbazoles in good yields, and similar results with respect to substrate scope of various aryl boronic acids were observed (Table 3, 3g, 3i, 3j, 3m and 3n). These approaches constitute an alternative route that avoids the regioselectivity issue in the synthesis of 1- or 3-substituted carbazoles (3m–3q).

Table 3 Substrate scope of various o-bromonitrobenzenes^a

a As given in Table 1, entry 13. b 48 h. c Pd(OAc) (5 mol%), 48 h; yields of the isolated material. See the ESI for details.

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The scope and limitations of the domino reaction with respect to various substituted o-bromonitrobenzenes and arylboronic acids were next investigated under the optimized conditions (Table 4). Coupling reactions of 1-bromo-4-methoxy-2-nitrobenzene with 3-tolylboronic acid and 4-fluorophenylboronic acid afforded the corresponding carbazoles 3s and 3t in 71% and 66% yields. Likewise, o-bromonitrobenzenes possessing methyl and fluoro substituents were coupled to arylboronic acids to form carbazoles 3u and 3v in 70% and 53% yields. This tandem reaction was applied to the syntheses of four bioactive carbazole alkaloids, glycozoline 3w,¹⁹ glycozolicine 3w′,²⁰ glycozolidine 3x^13a,21 and clausenalene 3y,²² in good yields and moderate regioselectivity.

Table 4 Substrate scope of substituted o-bromonitrobenzenes with aryl boronic acids^a

a As given in Table 1, entry 13. b 48 h; yields of the isolated material. See the ESI for details.

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Conclusions

In conclusion, we have developed highly efficient synthetic methods for carbazoles that are palladium-catalyzed sequential C–C/C–N bond formations via Suzuki cross-coupling and reductive Cadogan cyclization. Electron neutral, rich and deficient substrates were tolerated in this method. The synthetic utility of this method was demonstrated by the concise syntheses of four naturally occurring bioactive carbazole alkaloids, glycozoline 3w, glycozolicine 3w′, glycozolidine 3x and clausenalene 3y, from commercially available simple starting materials. Future studies will focus on further applications of this one-pot strategy to the syntheses of complex natural products.

Experimental

General information

All reactions were run under an atmosphere of air under anhydrous conditions unless otherwise indicated. Dichloromethane (CH₂Cl₂), tetrahydrofuran (THF), dimethylformamide (DMF) and toluene (PhMe) were obtained from the Pure-Solv MD-5 Solvent Purification System (Innovative Technology). Pressure tubes (13 × 100 mm, PYREXPLUS) were dried in an oven overnight and cooled under a stream of nitrogen prior to use. All commercial reagents were used directly without further purification. The progress of the reaction was checked on TLC plates (Merck 5554 Kiesel gel 60 F₂₅₄). Column chromatography was performed on silica gel (Merck 9385 Kiesel gel 60) using hexanes–EtOAc (v/v) or hexanes–acetone (v/v). Infrared spectra were recorded on a Varian 2000 FT-IR. High-resolution mass spectra (EI) were obtained on a Jeol JMS700 HRMS at the Korea Basic Science Center (KBSI), Daegu, Korea. Low-resolution mass spectra (EI) were obtained on a Varian 450-GC/Varian 220-MS and are reported as m/z (relative intensity). Accurate masses are reported for the molecular ion ([M + H]⁺ or [M + Na]⁺). Nuclear magnetic resonance spectra (¹H NMR and ¹³C NMR) were recorded by using a Bruker (300 MHz) spectrometer. Chemical shift values were recorded as parts per million relative to tetramethylsilane as an internal standard unless otherwise indicated, and coupling constants in hertz. The following abbreviations are used: m (multiplet), s (singlet), d (doublet), t (triplet), q (quartet), dd (doublet of doublets), etc.

General procedure for carbazole synthesis

To a re-sealable pressure tube (13 × 100 mm) equipped with a magnetic stir bar were added o-bromonitrobenzene 1 (0.5 mmol, 100 mol%), aryl boronic acid 2 (0.65 mmol, 130 mol%), Pd(OAc) (0.01 mmol, 2 mol%), PPh₃ (1.25 mmol, 250 mol%), K₂CO₃ (1 mmol, 200 mol%) and o-DCB (1 mL, 0.5 M concentration with respect to o-bromonitrobenzene 1). The mixture was heated at 180 °C (oil bath temperature) for 24–48 h, at which point the reaction mixture was allowed to cool to ambient temperature. The reaction mixture was filtered through a pad of celite and the resulting liquor was concentrated in vacuo and purified by flash column chromatography (SiO₂) under the conditions noted to furnish the corresponding product.

9H-Carbazole (3a)^6e. Purified by flash column chromatography (SiO₂) using 5% acetone in hexanes as the eluent to give 3a as a white solid (72 mg, 86% yield); ¹H NMR (300 MHz, DMSO) δ 11.33 (s, 1H), 8.12 (d, J = 7.8 Hz, 3H), 7.56 (d, J = 8.1 Hz, 2H), 7.45–7.39 (m, 3H), 7.21–7.16 (m, 3H); ¹³C NMR (75 MHz, DMSO) δ 139.79, 125.54, 122.48, 120.18, 118.53, 110.98; FTIR (neat): ν 3379, 2946, 1450, 1033 cm⁻¹; LRMS m/z (EI) 166.8 (M⁺ − 1), 139.0, 83.4, 62.8.

2-Methyl-9H-carbazole (3b)^23a. Purified by flash column chromatography (SiO₂) using 5% acetone in hexanes as the eluent to give 3b as a white solid (76 mg, 84% yield); ¹H NMR (300 MHz, CDCl₃) δ 8.03 (d, J = 7.8 Hz, 1H), 7.95 (d, J = 7.9 Hz, 2H), 7.42–7.35 (m, 2H), 7.24–7.18 (m, 2H), 7.07 (d, J = 8.0 Hz, 1H), 2.53 (s, 3H); ¹³C NMR (75 MHz, CDCl₃) δ 140.09, 139.59, 136.15, 125.41, 123.58, 121.19, 121.12, 120.14, 120.13, 119.46, 110.86, 110.60, 22.21; FTIR (neat) ν 3394, 2920, 1652, 1530, 1365 cm⁻¹; LRMS m/z (EI) 179.8 (M⁺ − 1), 151.8, 76.8, 62.8.

4-Methyl-9H-carbazole (3c)¹⁰. Purified by flash column chromatography (SiO₂) using 5% acetone in hexanes as the eluent to give 3c as a white solid (79 mg, 87% yield); ¹H NMR (300 MHz, CDCl₃): δ 8.19 (d, J = 7.9 Hz, 1H), 8.09 (br s, 1H), 7.50–7.39 (m, 2H), 7.37–7.31 (m, 1H), 7.32–7.26 (m, 2H), 7.02 (dd, J = 7.3, 0.8 Hz, 1H), 2.89 (s, 3H); ¹³C NMR (75 MHz, CDCl₃): δ 139.54, 139.51, 133.49, 125.77, 125.29, 123.93, 122.68, 121.90, 120.99, 119.44, 110.49, 108.26, 20.92; FTIR (neat) ν 3396, 3200, 2924, 1653, 1521, 1267, 1048 cm⁻¹; LRMS m/z (EI) 181.3 (M⁺), 182.3, 180.4, 177.5, 155.3, 125.8, 93.7.

2-(tert-Butyl)-9H-carbazole (3d)^11d. Purified by flash column chromatography (SiO₂) using 5% acetone in hexanes as the eluent to give 3d as a white solid (94 mg, 84% yield); ¹H NMR (300 MHz, CDCl₃) δ 8.05 (d, J = 7.0 Hz, 1H), 8.00 (d, J = 7.5 Hz, 1H), 7.94 (s, 1H), 7.44 (d, J = 1.6 Hz, 1H), 7.41–7.35 (m, 2H), 7.32 (dd, J = 8.3, 1.4 Hz, 1H), 7.25–7.20 (m, 1H), 1.44 (s, 9H); ¹³C NMR (75 MHz, CDCl₃) δ 149.72, 139.89, 139.82, 125.40, 123.49, 121.03, 120.21, 119.90, 119.41, 117.65, 110.57, 107.25, 35.25, 31.90; FTIR (neat) ν 3194, 2916, 1650, 1525, 1267 cm⁻¹; LRMS m/z (EI) 222.7 (M⁺ − 1), 207.8, 180.0, 167.0, 89.9.

2-Phenyl-9H-carbazole (3e)^6d. Purified by flash column chromatography (SiO₂) using 5% acetone in hexanes as the eluent to give 3e as a white solid (110 mg, 90% yield); ¹H NMR (300 MHz, acetone-d₆) δ 10.50 (s, 1H), 8.19 (d, J = 8.1 Hz, 1H), 8.14 (d, J = 7.7 Hz, 1H), 7.80–7.71 (m, 3H), 7.57–7.32 (m, 6H), 7.21 (td, J = 8.2, 4.3 Hz, 1H); ¹³C NMR (75 MHz, DMSO): δ 141.26, 140.43, 140.35, 137.88, 128.99, 127.12, 127.06, 125.70, 122.23, 121.88, 120.68, 120.32, 118.76, 117.89, 111.06, 108.93; FTIR (neat) ν 3377, 3268, 1692, 1528, 1367, 1227 cm⁻¹; LRMS m/z (EI): 242.8 (M⁺ − 1), 120.3, 76.7, 50.9.

7H-Benzo[c]carbazole (3f)^23b. Purified by flash column chromatography (SiO₂) using 5% acetone in hexanes as the eluent to give 3f as a white solid (91 mg, 84% yield); ¹H NMR (300 MHz, CDCl₃) δ 8.79 (d, J = 8.3 Hz, 1H), 8.58 (d, J = 7.8 Hz, 1H), 8.44 (s, 1H), 8.01 (d, J = 8.1 Hz, 1H), 7.87 (d, J = 8.8 Hz, 1H), 7.75–7.68 (m, 1H), 7.65 (d, J = 8.8 Hz, 1H), 7.59 (d, J = 7.8 Hz, 1H), 7.52–7.43 (m, 2H), 7.43–7.36 (m, 1H); ¹³C NMR (75 MHz, CDCl₃) δ 138.52, 137.16, 130.03, 129.32, 127.55, 127.01, 124.46, 124.09, 123.38, 123.13, 122.16, 120.36, 115.54, 112.71, 111.25; FTIR (neat) ν 3396, 2920, 1876, 1465, 1267, 1120 cm⁻¹; LRMS m/z (EI): 217.7 (M⁺ + 1), 216.8, 188.8, 108.2, 95.3.

2-Methoxy-9H-carbazole (3g)^16c. Purified by flash column chromatography (SiO₂) using 5% acetone in hexanes as the eluent to give 3g as a white solid (76 mg, 77% yield); ¹H NMR (300 MHz, CDCl₃) δ 7.99 (s, 1H), 7.96 (d, J = 3.4 Hz, 1H), 7.94 (d, J = 8.6 Hz, 1H), 7.41–7.31 (m, 1H), 7.24–7.18 (m, 1H), 6.92 (d, J = 2.1 Hz, 1H), 6.86 (dd, J = 8.5, 2.2 Hz, 1H), 3.91 (s, 1H); ¹³C NMR (75 MHz, CDCl₃) δ 159.21, 140.93, 139.63, 124.69, 123.67, 121.19, 119.70, 119.63, 117.39, 110.44, 108.29, 94.83, 55.77; FTIR (neat) ν 3395, 1336, 1200, 1030 cm⁻¹; LRMS m/z (EI): 197.7 (M⁺ + 1), 196.7, 181.8, 153.8, 127.8.

4-Methoxy-9H-carbazole (3h)^13f. Purified by flash column chromatography (SiO₂) using 5% acetone in hexanes as the eluent to give 3h as a white solid (66 mg, 67% yield); ¹H NMR (300 MHz, CDCl₃) δ 8.34 (d, J = 7.8 Hz, 1H), 8.02 (s, 1H), 7.43–7.38 (m, 2H), 7.34 (d, J = 8.0 Hz, 1H), 7.30–7.21 (m, 1H), 7.04 (d, J = 8.1 Hz, 1H), 6.70 (d, J = 8.0 Hz, 1H), 4.09 (s, 3H); ¹³C NMR (75 MHz, CDCl₃) δ 156.32, 140.92, 138.72, 126.77, 125.01, 123.12, 122.67, 119.70, 112.60, 110.07, 103.62, 100.42, 55.51; FTIR (neat) ν 3386, 2938, 1405, 1248, 1184, 1045 cm⁻¹; LRMS m/z (EI): 197.8 (M⁺ + 1), 196.7, 181.9, 153.9, 128.0.

2-Chloro-9H-carbazole (3i)^6e. Purified by flash column chromatography (SiO₂) using 5% acetone in hexanes as the eluent to give 3i as a white solid (71 mg, 70% yield); ¹H NMR (300 MHz, DMSO) δ 11.43 (s, 1H), 8.12 (d, J = 8.2 Hz, 2H), 7.54–7.49 (m, 2H), 7.40 (t, J = 7.5 Hz, 1H), 7.20–7.14 (m, 2H); ¹³C NMR (75 MHz, DMSO) δ 140.30, 140.08, 129.88, 125.98, 121.81, 121.57, 121.31, 120.35, 119.09, 118.68, 111.23, 110.61; FTIR (neat) ν 3393, 3128, 1636, 1406, 1321, 1178, 754 cm⁻¹; LRMS m/z (EI): 200.7 (M⁺ − 1), 165.7, 138.8, 100.3.

2-Fluoro-9H-carbazole (3j)^11d. Purified by flash column chromatography (SiO₂) using 5% acetone in hexanes as the eluent to give 3j as a white solid (75 mg, 81% yield); ¹H NMR (300 MHz, CDCl₃) δ 8.07 (s, 1H), 8.03–7.97 (m, 2H), 7.44–7.39 (m, 2H), 7.26–7.21 (m, 1H), 7.11 (dd, J = 9.6, 2.2 Hz, 1H), 7.02–6.93 (m, 1H); ¹³C NMR (75 MHz, DMSO) δ 161.18 (d, J = 238.6 Hz), 140.41, 140.28, 125.25, 122.07, 121.46 (d, J = 10.6 Hz), 119.97, 119.20, 119.00, 111.02, 106.49 (d, J = 24.1 Hz), 97.34 (d, J = 26.1 Hz); FTIR (neat) ν 3411, 2919, 1362, 1263 cm⁻¹; LRMS m/z (EI): 186.2 (M⁺ + 1), 185.2, 184.3, 157.3, 92.8.

1-(9H-Carbazole-2-yl)ethan-1-one (3k)^11d. Purified by flash column chromatography (SiO₂) using 7% acetone in hexanes as the eluent to give 3k as a white solid (41 mg, 43% yield); ¹H NMR (300 MHz, DMSO) δ 11.56 (s, 1H), 8.22 (t, J = 8.3 Hz, 2H), 8.08 (s, 1H), 7.79 (d, J = 8.2 Hz, 1H), 7.56 (d, J = 8.1 Hz, 1H), 7.47 (t, J = 7.5 Hz, 1H), 7.21 (t, J = 7.4 Hz, 1H), 2.68 (s, 3H); ¹³C NMR (75 MHz, DMSO) δ 197.86, 141.29, 139.15, 134.10, 127.03, 126.13, 121.59, 121.15, 120.06, 119.12, 118.66, 111.39, 111.35, 26.98; FTIR (neat) ν 3332, 1738, 1366, 1216, 889, 779 cm⁻¹; LRMS m/z (EI): 210.2 (M⁺ + 1), 209.3, 194.3, 166.3, 139.3.

Methyl-9H-carbazole-2-carboxylate (3l)^6e. Purified by flash column chromatography (SiO₂) using 7% acetone in hexanes as the eluent to give 3l as a white solid (69 mg, 61% yield); ¹H NMR (300 MHz, DMSO) δ 11.58 (s, 1H), 8.21 (t, J = 8.8 Hz, 2H), 8.12 (s, 1H), 7.78 (d, J = 8.2 Hz, 1H), 7.57 (d, J = 8.1 Hz, 1H), 7.47 (t, J = 7.5 Hz, 1H), 7.21 (t, J = 7.4 Hz, 1H), 3.89 (s, 3H); ¹³C NMR (75 MHz, DMSO) δ 166.95, 141.10, 139.05, 127.06, 126.30, 126.20, 121.60, 121.10, 120.14, 119.25, 119.16, 112.35, 111.42, 52.05; FTIR (neat) ν 3337, 2937, 1738, 1365, 1216, 888 cm⁻¹; LRMS m/z (EI): 226.2 (M⁺ + 1), 225.2, 194.2, 166.2, 139.2, 97.2, 83.2, 69.7.

3-Methyl-9H-carbazole (3m) and 1-methyl-9H-carbazole (3m′). Purified by flash column chromatography (SiO₂) using 5% acetone in hexanes as the eluent to give 3m/3m′ as a white solid (80 mg, 88% yield, 3m : 3m′ = 1 : 1.2 (determined by using ¹H NMR and a GC-mass spectrometer)). GC (Varian 450-GC, SPB™-680 (30 m × 0.25 mm × 0.25 μm), T₀: 60 °C (hold 4 min), T₁: ramp, 250 °C at 10 °C min⁻¹, carrier: He (1.0 mL min⁻¹), total time 60 min), t_3m′ = 21.95 min, t_3m = 22.32 min, ratio (3m : 3m′ = 1 : 1.2).

3-Methyl-9H-carbazole (3m)^6e. ¹H NMR (300 MHz, DMSO) δ 11.10 (s, 1H), 8.05 (d, J = 7.7 Hz, 1H), 7.89 (s, 1H), 7.45 (d, J = 8.1 Hz, 1H), 7.39–7.32 (m, 2H), 7.20 (d, J = 8.0 Hz, 1H), 7.12 (t, J = 7.4 Hz, 1H), 2.46 (s, 3H): ¹³C NMR (75 MHz, DMSO) δ 139.98, 137.96, 127.08, 126.82, 125.29, 122.54, 122.22, 120.02, 119.90, 118.23, 110.85, 110.63, 21.10; FTIR (neat) ν 3442, 1701, 1371, 1207 cm⁻¹; LRMS m/z (EI): 182.2 (M⁺ + 1), 181.2, 180.3, 152.3, 90.2, 77.2, 63.2, 51.1.

1-Methyl-9H-carbazole (3m′)^13f. ¹H NMR (300 MHz, DMSO) δ 11.16 (s, 1H), 8.08 (d, J = 7.8 Hz, 1H), 7.93 (d, J = 7.7 Hz, 1H), 7.50 (d, J = 8.1 Hz, 1H), 7.38–7.34 (m, 1H), 7.20–7.10 (m, 2H), 7.10–7.02 (m, 1H), 2.55 (s, 3H); ¹³C NMR (75 MHz, DMSO) δ 139.79, 139.04, 125.94, 125.29, 122.79, 121.95, 120.17, 120.05, 118.62, 118.46, 117.60, 111.03, 17.00; FTIR (neat) ν 3442, 1701, 1371, 1207 cm⁻¹; LRMS m/z (EI): 181.2 (M⁺), 180.2, 152.3, 135.2, 77.2, 63.2, 51.1.

5H-[1,3]Dioxolo[4,5-b]carbazole (3n) and 5H-[1,3]dioxolo[4,5-a]carbazole (3n′). Purified by flash column chromatography (SiO₂) using 5% acetone in hexanes as the eluent to give 3n/3n′ as a white solid (90 mg, 87% yield, 3n : 3n′ = 5.9 : 1 (determined by using ¹H NMR and a GC-mass spectrometer)). GC (Varian 450-GC, SPB™-680 (30 m × 0.25 mm × 0.25 μm), T₀: 60 °C (hold 4 min), T₁: ramp, 250 °C at 10 °C min⁻¹, carrier: He (1.0 mL min⁻¹), total time 60 min), t_3n′ = 25.38 min, t_3n = 26.90 min, ratio (3n : 3n′ = 5.9 : 1).

5H-[1,3]Dioxolo[4,5-b]carbazole (3n)^23c. ¹H NMR (300 MHz, DMSO) δ 11.08 (s, 1H), 7.96 (d, J = 7.7 Hz, 1H), 7.62 (s, 1H), 7.40 (d, J = 8.0 Hz, 1H), 7.24 (t, J = 7.5 Hz, 1H), 7.09–7.02 (m, 2H), 6.03 (s, 2H); ¹³C NMR (75 MHz, DMSO) δ 146.72, 141.52, 139.56, 135.14, 123.76, 122.83, 119.26, 118.20, 115.40, 110.79, 100.69, 99.36, 92.16; FTIR (neat) ν 3397, 1710, 1266, 1043, 936, 748 cm⁻¹; LRMS m/z (EI): 212.0 (M⁺ + 1), 211.2.

5H-[1,3]Dioxolo[4,5-a]carbazole (3n′). ¹H NMR (300 MHz, DMSO) δ 11.35 (s, 1H), 8.01 (d, J = 7.7 Hz, 1H), 7.67 (d, J = 15.0 Hz, 1H), 7.42 (d, J = 8.3 Hz, 1H), 7.38–7.30 (m, 1H), 7.16–7.06 (m, 1H), 6.86 (d, J = 8.2 Hz, 1H), 6.13 (s, 2H); FTIR (neat) ν 3397, 1710, 1266, 1043, 936, 748 cm⁻¹; LRMS m/z (EI): 211.9 (M⁺ + 1), 211.1, 154.2.

3-Methoxy-2-methyl-9H-carbazole (3o)^12k. Purified by flash column chromatography (SiO₂) using 7% acetone in hexanes as the eluent to give 3o as a yellow solid (54 mg, 51% yield); ¹H NMR (300 MHz, acetone-d₆) δ 10.10 (s, 1H), 7.96 (d, J = 7.7 Hz, 1H), 7.81 (s, 1H), 7.42 (d, J = 8.1 Hz, 1H), 7.28–7.23 (m, 1H), 7.13–7.08 (m, 1H), 7.02 (s, 1H), 3.90 (s, 3H), 2.31 (s, 3H); ¹³C NMR (75 MHz, acetone-d₆) δ 158.18, 140.73, 140.68, 124.60, 124.12, 121.94, 119.79, 119.42, 118.89, 116.68, 111.28, 93.30, 55.67, 16.92; FTIR (neat) ν 3313, 3069, 1783, 1689, 1404, 1270, 1169 cm⁻¹; LRMS m/z (EI): 212.2(M⁺ + 1), 211.3, 196.6, 195.7, 167.5.

1-Methoxy-2-methyl-9H-carbazole (3o′)^23e. Purified by flash column chromatography (SiO₂) using 5% acetone in hexanes as the eluent to give 3o′ as a yellow solid (29 mg, 27% yield); ¹H NMR (300 MHz, acetone-d₆) δ 10.16 (s, 1H), 7.99 (d, J = 7.7 Hz, 1H), 7.89 (d, J = 8.5 Hz, 1H), 7.43 (d, J = 8.0 Hz, 1H), 7.32–7.25 (m, 1H), 7.19–7.10 (m, 1H), 6.90 (d, J = 8.5 Hz, 1H), 3.91 (s, 3H), 2.40 (s, 3H); ¹³C NMR (75 MHz, acetone-d₆) δ 156.86, 141.66, 141.42, 125.16, 124.60, 120.13, 119.56, 118.53, 118.01, 111.33, 107.65, 104.63, 56.46, 10.15; FTIR (neat) ν 3313, 3069, 1783, 1689, 1404, 1270, 1169 cm⁻¹; LRMS m/z (EI): 212.3 (M⁺ + 1), 211.4, 196.6, 195.7, 167.7.

3-Methoxy-9H-carbazole (3p)^6e. Purified by flash column chromatography (SiO₂) using 5% acetone in hexanes as the eluent to give 3p as a brown solid (59 mg, 60% yield); ¹H NMR (300 MHz, CDCl₃) δ 8.02 (d, J = 7.8 Hz, 1H), 7.85 (s, 1H), 7.54 (d, J = 2.4 Hz, 1H), 7.44–7.30 (m, 2H), 7.28–7.12 (m, 2H), 7.05 (dd, J = 8.7, 2.4 Hz, 1H), 3.91 (s, 3H); ¹³C NMR (75 MHz, CDCl₃) δ 153.88, 140.32, 134.42, 125.89, 123.76, 123.34, 120.34, 119.10, 115.16, 111.46, 110.88, 103.13, 56.14; FTIR (neat) ν 3405, 1788, 1685, 1400, 1260, 1031 cm⁻¹; LRMS m/z (EI): 198.3 (M⁺ + 1), 197.4, 182.7, 181.7, 154.3, 101.5.

2,3-Dimethoxy-9H-carbazole (3q)^23d. Purified by flash column chromatography (SiO₂) using 7% acetone in hexanes as the eluent to give 3q as a white solid (70 mg, 62% yield); ¹H NMR (300 MHz, DMSO) δ 10.98 (s, 1H), 7.99 (d, J = 7.7 Hz, 1H), 7.66 (s, 1H), 7.43 (d, J = 8.0 Hz, 1H), 7.26 (t, J = 7.6 Hz, 1H), 7.08 (t, J = 7.4 Hz, 1H), 7.04 (s, 1H), 3.86 (s, 3H), 3.85 (s, 3H); ¹³C NMR (75 MHz, DMSO₃) δ 149.18, 143.71, 139.56, 134.63, 123.67, 123.00, 119.26, 118.12, 114.30, 110.72, 103.33, 94.62, 56.21, 55.63; FTIR (neat) ν 3337, 2917, 1402, 1186, 1090 cm⁻¹; LRMS m/z (EI): 228.2 (M⁺ + 1), 227.5, 212.7, 211.7, 184.5.

2-Methoxy-7-methyl-9H-carbazole (3s)^20d. Purified by flash column chromatography (SiO₂) using 5% acetone in hexanes as the eluent to give 3s as a white solid (75 mg, 71% yield); ¹H NMR (300 MHz, DMSO) δ 10.98 (s, 1H), 7.88 (d, J = 8.5 Hz, 1H), 7.84 (d, J = 7.9 Hz, 1H), 7.21 (s, 1H), 6.96–6.88 (m, 2H), 6.73 (dd, J = 8.5, 2.2 Hz, 1H), 3.82 (s, 3H), 2.44 (s, 3H); ¹³C NMR (75 MHz, DMSO) δ 158.14, 141.07, 140.22, 133.50, 120.54, 120.44, 120.03, 119.02, 116.32, 110.73, 107.42, 94.53, 55.25, 21.65; FTIR (neat) ν 3394, 1726, 1366, 1219, 1091 cm⁻¹; LRMS m/z (EI): 212.5 (M⁺ + 1), 211.6, 196.6, 195.7, 168.5.

2-Fluoro-7-methoxy-9H-carbazole (3t). Purified by flash column chromatography (SiO₂) using 5% acetone in hexanes as the eluent to give 3t as a white solid (71 mg, 66% yield); ¹H NMR (300 MHz, CDCl₃) δ 7.97 (br s, 1H), 7.87 (d, J = 8.5 Hz, 1H), 7.85 (d, J = 8.3 Hz, 1H), 7.06 (dd, J = 9.5, 2.3 Hz, 1H), 6.98–6.93 (m, 1H), 6.90 (d, J = 2.2 Hz, 1H), 6.86 (dd, J = 8.5, 2.2 Hz, 1H), 3.90 (s, 1H); ¹³C NMR (75 MHz, CDCl₃) δ 158.87, 141.31, 120.78, 120.38, 120.25, 116.91, 108.55, 107.82, 107.50, 97.63, 97.27, 95.02, 55.78; FTIR (neat) ν 3192, 2843, 1539, 1406, 1155 cm⁻¹; LRMS m/z (EI): 216.5 (M⁺ + 1), 215.5, 200.6, 199.7, 172.5, 171.5; HRMS m/z (EI): calcd For C₁₃H₁₀FNO (M⁺) 215.0747, found 215.0746.

10-Methyl-7H-benzo[c]carbazole (3u)^23f. Purified by flash column chromatography (SiO₂) using 5% acetone in hexanes as the eluent to give 3u as a white solid (81 mg, 70% yield); ¹H NMR (300 MHz, CDCl₃) δ 8.79 (d, J = 8.3 Hz, 1H), 8.37 (s, 1H), 8.31 (s, 1H), 8.01 (d, J = 8.1 Hz, 1H), 7.84 (d, J = 8.8 Hz, 1H), 7.72 (t, J = 7.6 Hz, 1H), 7.59 (d, J = 8.8 Hz, 1H), 7.52–7.44 (m, 2H), 7.29 (d, J = 8.4 Hz, 1H), 2.64 (s, 3H); ¹³C NMR (75 MHz, CDCl₃) δ 137.41, 136.78, 130.09, 129.60, 129.27, 127.27, 126.90, 125.87, 124.27, 123.39, 122.98, 122.06, 115.22, 112.79, 110.88, 21.96; FTIR (neat) ν 3470, 2897, 1696, 1542, 1267, 1152 cm⁻¹; LRMS m/z (EI): 232.7 (M⁺ + 1), 231.2, 230.2, 228.8, 197.2, 118.8.

2-(tert-Butyl)-7-fluoro-9H-carbazole (3v). Purified by flash column chromatography (SiO₂) using 5% acetone in hexanes as the eluent to give 3v as a yellow solid (64 mg, 53% yield); ¹H NMR (300 MHz, DMSO) δ 11.24 (s, 1H), 8.04 (dd, J = 8.5, 5.7 Hz, 1H), 7.97 (d, J = 8.3 Hz, 1H), 7.43 (s, 1H), 7.23 (dd, J = 10.3, 2.1 Hz, 2H), 6.99–6.91 (m, 1H), 1.36 (s, 9H); ¹³C NMR (75 MHz, DMSO) δ 160.94 (d, J = 237.8 Hz), 148.29, 140.61, 140.44, 121.08 (d, J = 10.5 Hz), 119.71, 119.50, 119.20, 117.01, 107.26, 106.27 (d, J = 24.1 Hz), 97.30 (d, J = 26.0 Hz), 34.76, 31.60; FTIR (neat) ν 3475, 3187, 1741, 1598, 1266 cm⁻¹; LRMS m/z (EI): 242.1 (M⁺ + 1), 241.1, 227.4, 226.5, 198.2; HRMS m/z (EI): calcd For C₁₆H₁₆FN (M⁺) 241.1268, found 241.1267.

Glycozoline (3w)^19d. Purified by flash column chromatography (SiO₂) using 5% acetone in hexanes as the eluent to give 3w as a yellow solid (37 mg, 35% yield); ¹H NMR (300 MHz, CDCl₃) δ 7.85 (s, 1H), 7.77 (s, 1H), 7.54 (d, J = 2.4 Hz, 1H), 7.31–7.21 (m, 3H), 7.06 (dd, J = 8.7, 2.5 Hz, 1H), 3.94 (s, 3H), 2.54 (s, 3H); ¹³C NMR (75 MHz, CDCl₃) δ 153.87, 138.69, 134.89, 128.45, 127.32, 123.76, 123.64, 120.25, 115.01, 111.41, 110.56, 103.23, 56.19, 21.54; FTIR (neat) ν 3410, 2894, 1706, 1492, 1266, 1131 cm⁻¹; LRMS m/z (EI): 212.1 (M⁺ + 1), 211.2, 197.2, 196.3, 168.2, 167.2.

Glycozolicine (3w′)^20d. Purified by flash column chromatography (SiO₂) using 5% acetone in hexanes as the eluent to give 3w′ as a yellow solid (41 mg, 39% yield); ¹H NMR (300 MHz, CDCl₃) δ 8.17 (s, 1H), 7.87 (s, 1H), 7.67 (d, J = 7.8 Hz, 1H), 7.34 (d, J = 8.2 Hz, 1H), 7.24 (d, J = 8.2 Hz, 1H), 7.16 (t, J = 7.8 Hz, 1H), 6.89 (d, J = 7.8 Hz, 1H), 4.00 (s, 3H), 2.54 (s, 3H); ¹³C NMR (75 MHz, CDCl₃) δ 145.79, 137.57, 130.24, 128.76, 127.19, 124.32, 123.96, 120.54, 119.61, 112.94, 110.71, 105.87, 55.59, 21.56; FTIR (neat) ν 3410, 2894, 1706, 1492, 1266, 1131 cm⁻¹; LRMS m/z (EI): 212.2 (M⁺ + 1), 211.3, 197.2, 196.3, 169.1, 168.2, 142.1.

Glycozolidine (3x)^20d. Purified by flash column chromatography (SiO₂) using 7% acetone in hexanes as the eluent to give 3x as a white solid (56 mg, 46% yield); ¹H NMR (300 MHz, CDCl₃) δ 7.76 (s, 1H), 7.56 (s, 1H), 7.46 (d, J = 2.2 Hz, 1H), 7.15 (d, J = 8.7 Hz, 1H), 6.96 (dd, J = 8.6, 2.3 Hz, 1H), 6.63 (s, 1H), 3.92 (s, 3H), 3.83 (s, 3H), 2.37 (s, 3H); ¹³C NMR (75 MHz, CDCl₃) δ 157.50, 153.90, 140.10, 134.23, 123.96, 121.47, 118.98, 116.17, 113.10, 111.10, 102.53, 92.53, 56.14, 55.52, 16.87; FTIR (neat) ν 3389, 3066, 1787, 1637, 1509, 1365, 1270 cm⁻¹; LRMS m/z (EI): 242.3 (M⁺ + 1), 241.3, 227.2, 226.3, 198.2, 183.2, 154.1.

2,6-Dimethoxy-1-methyl-9H-carbazole (3x′). Purified by flash column chromatography (SiO₂) using 5% acetone in hexanes as the eluent to give 3x′ as a white solid (27 mg, 22% yield). ¹H NMR (300 MHz, DMSO) δ 10.76 (s, 1H), 7.85 (d, J = 8.5 Hz, 1H), 7.56 (d, J = 2.4 Hz, 1H), 7.31 (d, J = 8.7 Hz, 1H), 6.91 (dd, J = 8.7, 2.5 Hz, 1H), 6.84 (d, J = 8.6 Hz, 1H), 3.85 (s, 3H), 3.82 (s, 3H), 2.33 (s, 3H); ¹³C NMR (75 MHz, DMSO). δ 155.44, 153.04, 141.29, 135.08, 123.59, 117.97, 116.79, 113.20, 111.23, 106.54, 103.49, 102.67, 56.08, 55.56, 10.24; FTIR (neat) ν 3389, 3066, 1787, 1637, 1509, 1365, 1270 cm⁻¹; LRMS m/z (EI): 242.3 (M⁺ + 1), 241.3, 227.2, 226.3, 198.2, 197.2, 183.2, 154.1.

Clausenalene (3y) and 7-methyl-10H-[1,3]dioxolo[4,5-a]carbazole (3y′). Purified by flash column chromatography (SiO₂) using 5% acetone in hexanes as the eluent to give 3y/3y′ as a white solid (61 mg, 80% yield, 3y : 3y′ = 5.3 : 1 (determined by using ¹H NMR and a GC-mass spectrometer)). GC (Varian 450-GC, SPB™-680 (30 m × 0.25 mm × 0.25 μm), T₀: 60 °C (hold 4 min), T₁: ramp, 250 °C at 10 °C min⁻¹, carrier: He (1.0 mL min⁻¹), total time 60 min), t_3y′ = 26.98 min, t_3y = 28.69 min, ratio (3y : 3y′ = 5.3 : 1).

Clausenalene (3y)^22c. Purified by recrystallization from dichloromethane and hexanes to give 3y as a white solid. ¹H NMR (300 MHz, acetone-d₆) δ 10.09 (s, 1H), 7.76 (s, 1H), 7.50 (s, 1H), 7.31 (d, J = 8.2 Hz, 1H), 7.09 (dd, J = 8.2, 1.2 Hz, 1H), 6.98 (s, 1H), 6.00 (s, 2H), 2.45 (s, 3H); ¹³C NMR (75 MHz, acetone-d₆) δ 147.94, 142.82, 139.11, 136.64, 128.26, 126.07, 124.45, 119.77, 116.76, 111.26, 101.66, 99.82, 92.85, 21.48; FTIR (neat): ν 3400, 3009, 1728, 1366, 1219, 1093, 533 cm⁻¹; LRMS m/z (EI): 225.9 (M⁺ + 1), 225.2.

7-Methyl-10H-[1,3]dioxolo[4,5-a]carbazole (3y′). ¹H NMR (300 MHz, acetone-d₆) δ 10.17 (s, 1H), 7.81 (s, J = 0.6 Hz, 2H), 7.61–7.57 (m, 1H), 7.36 (d, J = 8.2 Hz, 1H), 7.17 (dd, J = 8.2, 1.2 Hz, 1H), 6.80 (d, J = 8.2 Hz, 1H), 6.07 (s, 2H), 2.46 (s, 3H); FTIR (neat) ν 3400, 3009, 1728, 1366, 1219, 1093, 533 cm⁻¹; LRMS m/z (EI): 225.9 (M⁺ + 1), 225.2.

General procedure for Suzuki coupling of 3-chlorocarbazole (3i)

To a re-sealable pressure tube (13 × 100 mm) equipped with a magnetic stir bar were added 2-chloro-9H-carbazole 3i (0.1 mmol, 100 mol%), aryl boronic acid 2 (0.15 mmol, 150 mol%), Pd₂(dba)₃ (0.01 mmol, 10 mol%), PCy₃ (0.25 mmol, 25 mol%), K₃PO₄ (1.27 M in water, 0.34 mmol) and dioxane (2 mL, 0.05 M concentration with respect to 2-chloro-9H-carbazole 3i). The slurry was sealed and purged with argon gas for 5 minutes. The mixture was heated at 100 °C (oil bath temperature) for 2 h, at which point the reaction mixture was allowed to cool to ambient temperature. The reaction mixture was treated with saturated sodium bicarbonate solution and extracted with dichloromethane (3x). The combined organic layers were dried with magnesium sulfate, filtered, and concentrated in vacuo and purified by flash column chromatography (SiO₂) and recrystallization from dichloromethane and hexanes under the conditions noted to furnish the corresponding product.

2-([1,1′-Biphenyl]-4-yl)-9H-carbazole (3ia). Purified by recrystallization from dichloromethane and hexanes to give 3ia as a white solid (23 mg, 72% yield); ¹H NMR (300 MHz, DMSO) δ 11.35 (s, 1H), 8.20 (d, J = 8.1 Hz, 1H), 8.14 (d, J = 7.8 Hz, 1H), 7.86 (d, J = 8.1 Hz, 1H), 7.85 (s, 1H), 7.82–7.71 (m, 5H), 7.55–7.46 (m, 4H), 7.44–7.36 (m, 2H), 7.18 (t, J = 7.4 Hz, 1H); ¹³C NMR (75 MHz, DMSO) δ 140.41, 140.33, 140.20, 139.70, 138.77, 137.20, 129.03, 127.50, 127.21, 126.56, 125.70, 122.19, 121.94, 120.70, 120.30, 118.74, 117.72, 111.03, 108.74; FTIR (neat) ν 3403, 3101, 1753, 1691, 1530, 1368, 1206, 763 cm⁻¹; HRMS m/z (EI): calcd For C₂₄H₁₇N (M⁺) 319.1361, found 319.1360.

2-(4-Fluorophenyl)-9H-carbazole (3ib). Purified by flash column chromatography (SiO₂) using 5% acetone in hexanes as the eluent to give 3ib as a yellow solid (23 mg, 88% yield); ¹H NMR (300 MHz, CDCl₃) δ 8.12 (d, J = 7.8 Hz, 1H), 8.10 (s, 1H), 8.09 (d, J = 7.4 Hz, 1H), 7.68–7.61 (m, 2H), 7.58 (s, 1H), 7.46–7.40 (m, 3H), 7.30–7.22 (m, 1H), 7.19–7.11 (m, 2H); ¹³C NMR (75 MHz, acetone-d₆) δ 163.17 (d, J = 243.9 Hz), 141.61, 141.56, 139.27 (d, J = 3.2 Hz), 138.56, 129.87 (d, J = 8.0 Hz), 126.59, 123.71, 123.33, 121.34, 121.00, 119.91, 119.11, 116.33 (d, J = 21.5 Hz), 111.80, 109.96; FTIR (neat) ν 3400, 1650, 1367, 1223, 724 cm⁻¹; LRMS m/z (EI): 262.2 (M⁺ + 1), 262.2; HRMS m/z (EI): calcd For C₁₈H₁₂FN (M⁺) 261.0954, found 261.0953.

Methyl 4-(9H-carbazol-2-yl)benzoate (3ic). Purified by recrystallization from dichloromethane and hexanes to give 3ic as a white solid (21 mg, 70% yield); ¹H NMR (300 MHz, DMSO) δ 11.39 (s, 1H), 8.22 (d, J = 8.2 Hz, 1H), 8.15 (d, J = 7.7 Hz, 1H), 8.07 (d, J = 8.4 Hz, 2H), 7.92 (d, J = 8.4 Hz, 2H), 7.81 (d, J = 1.3 Hz, 1H), 7.54 (dd, J = 8.2, 1.5 Hz, 1H), 7.52 (d, J = 8.1 Hz, 1H), 7.41 (td, J = 8.1, 0.9 Hz, 1H), 7.18 (td, J = 7.7, 0.5 Hz, 1H), 3.89 (s, 3H); ¹³C NMR (75 MHz, DMSO) δ 166.18, 145.77, 140.47, 140.28, 136.26, 129.86, 128.01, 127.21, 125.98, 122.59, 122.03, 120.83, 120.47, 118.85, 117.91, 111.11, 109.26, 52.16; FTIR (neat) ν 3388, 2139, 1719, 1363, 1218, 1095, 702 cm⁻¹; HRMS m/z (EI): calcd For C₂₀H₁₅NO₂ (M⁺) 301.1103, found 301.1103.

2-(2-Methoxyphenyl)-9H-carbazole (3id). Purified by recrystallization from dichloromethane and hexanes to give 3id as a white solid (26 mg, 95% yield); ¹H NMR (300 MHz, acetone-d₆) δ 10.34 (s, 1H), 8.12 (d, J = 8.2 Hz, 2H), 7.67 (d, J = 0.6 Hz, 1H), 7.52 (d, J = 8.1 Hz, 1H), 7.43–7.39 (m, 2H), 7.37–7.30 (m, 2H), 7.22–7.16 (m, 1H), 7.11 (d, J = 8.0 Hz, 1H), 7.05 (td, J = 7.4, 0.9 Hz, 1H), 3.81 (s, 3H); ¹³C NMR (75 MHz, DMSO) δ 156.58, 140.45, 140.02, 136.01, 131.16, 131.07, 129.05, 125.98, 122.63, 121.60, 121.27, 120.82, 120.53, 119.99, 119.10, 112.23, 112.02, 111.32, 55.90; FTIR (neat) ν 3409, 3012, 1733, 1599, 1247, 1032, 866, 748 cm⁻¹; LRMS m/z (EI): 273.2 (M⁺), 273.9, 258.3; HRMS m/z (EI): calcd C₁₉H₁₅NO (M⁺) 273.1155, found 273.1154.

Acknowledgements

This work was supported by the 2013 Research Fund of University of Ulsan.

Notes and references

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Footnote

† Electronic supplementary information (ESI) available: Details of experimental procedures and spectroscopic data for all new compounds (¹H NMR, ¹³C NMR, IR, MS), including images of NMR spectra. See DOI: 10.1039/c5ob01952d

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