Synthesis of Fluoranthene Derivatives via Tandem Suzuki–Miyaura and Intramolecular C–H Arylation Reactions under Both Homogeneous and Heterogeneous Catalytic Conditions

Abstract

A catalytic method for the synthesis of substituted fluoranthenes that operates via tandem Suzuki–Miyaura and intramolecular C–H arylation reactions is reported. The overall reaction sequence works effectively with homogeneous catalysis using Pd(dppf)Cl₂ as well as heterogeneous catalysis using reduced graphene oxide (rGO)-CuPd nanocatalysts with low catalyst loadings. High functional group tolerance is observed under both catalytic conditions where arylboronic acids and esters having electron-withdrawing and electron-donating substituents afforded fluoranthene products in good yields (up to 78%). Moreover, the rGO-CuPd nanocatalysts are demonstrated to be reusable by preserving almost 90% of their initial activity after the third cycle.

Introduction

Fluoranthenes represent an important subclass of polycyclic aromatic hydrocarbons with a broad range of attractive applications.¹ A number of fungal natural products have a fluoranthene core in their structures, such as hortein^2a (1) and daldinone E^2b (2), among others, some of which exhibit important biological activities (Figure 1).² Fluoranthenes have also found widespread applications in materials science, particularly in the area of organic electronics.³ For instance, FLUN-550 (3) was introduced by Goel, Mitra, and co-workers in 2014 as a fluoranthene-based fluorescent probe for selective staining of intracellular lipid droplets.⁴ Structurally related diacenaphthylene-fused benzodithiophenes (4) have recently been developed by Yang, Hartl, Li, and co-workers, and their field-effect mobilities have been investigated (Figure 1).⁵

Figure 1.

Examples of important fluoranthene analogues.

Among the methods available for the synthesis and derivatization of fluoranthenes, Diels–Alder reaction has been the most commonly utilized method,^3a−3c,4,6 whereas transition-metal-catalyzed reactions and various other cyclization strategies have also been employed.^3d,5,7 In 2009, Quimby and Scott reported an effective method for the synthesis of fluoranthenes starting from 1,8-dichloronaphthalenes and arylboronic acids in the presence of a homogeneous Pd catalyst.⁸ However, this reaction requires high catalyst loading (20 mol % Pd₂(dba)₃) and high reaction temperatures (155–175 °C). Total synthesis of the natural product benzo[j]fluoranthene-4,9-diol was accomplished by Dallavalle and co-workers in 2013 wherein the fluoranthene core was assembled by a McMurry ring closure.⁹ More recently, Manabe and co-workers developed an elegant Pd-catalyzed method that enables the three-step synthesis of fluoranthenes via inter- and intramolecular C–H arylation reactions.¹⁰ During the course of our studies on 1,8-diarylnaphthalenes, we have observed that monoaryl as well as symmetrical and unsymmetrical diarylnaphthalenes could be obtained selectively via Suzuki–Miyaura reaction using a tetrakis(triphenylphosphine)palladium (0) (Pd(PPh₃)₄) catalyst starting from 1,8-diiodonaphthalene (5). On the other hand, using a more active Pd catalyst, Pd(dppf)Cl₂ led to the formation of significant amounts of fluoranthene side products, which prompted us to investigate this transformation in detail. Herein, we report a highly effective method for the synthesis of substituted fluoranthenes that can operate under both homogeneous and heterogeneous catalytic conditions.

Results and Discussion

We initiated our study by examining the reaction between 1,8-diiodonaphthalene (5) and 4-fluorophenylboronic acid (6a) in the presence of homogeneous Pd catalysts (Table 1). As mentioned above, the Suzuki–Miyaura monoarylation product was obtained as the major product when Pd(PPh₃)₄ was used as the catalyst with no formation of fluoranthene 6b (entry 1). Pleasingly, Pd(dppf)Cl₂ proved to be an effective catalyst for the desired transformation when used in 5 mol % catalyst loading. Among the carbonate and acetate bases screened, KOAc gave the highest yield of fluoranthene 6b in dimethyl sulfoxide (DMSO) at 90 °C (71%, entries 2–6). Inferior results were obtained when KO^tBu, CsF, and NaOH were examined as bases (entries 7–9). With KOAc as the optimal base, we then performed a solvent screening. Whereas dimethylformamide (DMF) was completely ineffective under the same reaction conditions (entry 10), CH₃CN, dioxane, and N,N-dimethylacetamide (DMA) afforded the desired product 6b, albeit in lower yields (31, 48, and 38%, respectively, entries 11–13). Finally, Pd(OAc)₂/P^tBu₃·HBF₄ and Pd₂(dba)₃/P^tBu₃·HBF₄ combinations were found be catalytically less active compared to Pd(dppf)Cl₂ (entries 14 and 15).

Table 1. Optimization Studies Using Homogeneous Catalysts^a.

entry	catalyst	base	solvent	yield (%)b
1	Pd(PPh3)4	KOAc	DMSO	<5
2	Pd(dppf)Cl2	K2CO3	DMSO	10
3	Pd(dppf)Cl2	Cs2CO3	DMSO	35
4	Pd(dppf)Cl2	Na2CO3	DMSO	28
5	Pd(dppf)Cl2	KOAc	DMSO	71
6	Pd(dppf)Cl2	NaOAc	DMSO	69
7	Pd(dppf)Cl2	KOtBu	DMSO	<5
8	Pd(dppf)Cl2	CsF	DMSO	37
9	Pd(dppf)Cl2	NaOH	DMSO	<5
10	Pd(dppf)Cl2	KOAc	DMF	<5
11c	Pd(dppf)Cl2	KOAc	CH3CN	31
12	Pd(dppf)Cl2	KOAc	dioxane	48
13	Pd(dppf)Cl2	KOAc	DMA	38
14d	Pd(OAc)2/PtBu3·HBF4	KOAc	DMSO	21
15e	Pd2(dba)3/PtBu3·HBF4	KOAc	DMSO	14

^a0.13 mmol 5, 0.15 mmol 6a, 0.52 mmol base, 5 mol % of Pd catalyst, 90 °C, N₂, 24 h.

^bIsolated yields.

^cT = 80 °C.

^dP^tBu₃·HBF₄/Pd(OAc)₂ = 2:1.

^eP^tBu₃·HBF₄/Pd₂(dba)₃ = 4:1. Abbreviations: dppf, 1,1′-bis(diphenylphosphino)ferrocene and dba, dibenzylideneacetone.

Having successfully optimized the fluoranthene synthesis in the presence of homogeneous palladium catalysts, we then turned our attention to the utilization of a heterogeneous catalyst for this transformation, considering the advantages of heterogeneous catalysts over homogeneous ones. As the classical heterogeneous catalysts have limited surface area resulting in low activity, nanocatalysts emerged as highly efficient catalysts for various organic reactions in recent years owing to their high surface-to-volume ratio.¹¹ In this respect, Metin research group has demonstrated that bimetallic Pd nanoparticles (NPs) assembled on reduced graphene oxide (rGO) were highly efficient catalysts in a variety of organic transformations;¹² especially, rGO-assembled CuPd alloy NPs (rGO-CuPd) were shown to be highly efficient heterogeneous catalysts in Sonogashira cross-coupling reactions.^12a By the motivation of these promising results, we selected the rGO-CuPd nanocatalyst as a heterogeneous catalyst to be tested in this transformation.¹³ We first conducted optimization experiments depending on various parameters in the presence of the rGO-CuPd nanocatalyst (Table 2). As can be seen in Table 2, the rGO-CuPd nanocatalyst provided the highest yield by the use of NaOAc as a base and DMSO/H₂O (v/v = 10:1) mixture as a solvent at 120 °C (62%, entry 3). It is worth mentioning that among all tested alloy compositions, the rGO-CuPd catalyst provided the highest yield under the optimized conditions (Table 2, entries 12 and 13). Moreover, the rGO-CuPd nanocatalyst provided a much higher yield than the commercially available Pd/C catalyst (entry 8) and comparable to that of the homogeneous catalyst. To the best of our knowledge, this is the first example of a comparison of the performances of a homogeneous and a heterogeneous catalyst in C–H arylation reactions.

Table 2. Optimization Studies Using Heterogeneous NP Catalysts^a.

entry	catalyst	base	solvent	yield (%)b
1	rGO-CuPd	NaOAc	DMSO	46
2	rGO-CuPd	NaOAc	DMSO/H2Oc	37
3	rGO-CuPd	NaOAc	DMSO/H2Od	62
4e	rGO-CuPd	NaOAc	DMSO/H2Od	51
5f	rGO-CuPd	NaOAc	DMSO/H2Od	44
6	rGO-CuPd	NaOAc	DMF/H2Og	<5
7	rGO-CuPd	NaOAc	DMA/H2Oh	55
8	Pd/Ci	NaOAc	DMSO/H2Od	26
9	rGO-CuPd	KOAc	DMSO/H2Od	43
10	rGO-CuPd	K2CO3	DMSO/H2Od	32
11	rGO-CuPd	Cs2CO3	DMSO/H2Od	21
12	rGO-Cu32Pd68	NaOAc	DMSO/H2Od	19
13j	rGO-Cu75Pd25	NaOAc	DMSO/H2Od	<5

^aReaction conditions: 0.13 mmol 5, 0.15 mmol 6a, 0.65 mmol base, 4.0 mg of nanocatalyst (rGO-CuPd contains 6.5 wt % Pd corresponding to 0.0024 mmol Pd and 1.8 mol % Pd loading), 120 °C, 24 h.

^bIsolated yields.

^cDMSO/H₂O = 5:1.

^dDMSO/H₂O = 10:1.

^e2.0 mg of nanocatalyst was used.

^fT = 100 °C.

^gDMF/H₂O = 10:1.

^hDMA/H₂O = 10:1.

ⁱ10 wt % Pd on carbon (5.0 mg).

^j5.0 mg of catalyst was used.

With the optimized conditions in hand, we next investigated the scope of the fluoranthene synthesis reaction under both the homogeneous and heterogeneous catalytic conditions (Table 3). As mentioned above, fluoranthene product 6b was obtained in 71 and 62% yields using methods A and B, respectively (entry 1). The reaction tolerates the presence of nitrile, amide, and ketone groups, affording fluoranthene products 7b, 8b, and 9b in good yields under both conditions (entries 2–4). Whereas −CO₂Me-containing fluoranthene 10b was isolated in 78% yield with method A, method B gave a lower yield (36%, entry 5). 4- and 3-NO₂-substituted boronic acids 11a and 12a both gave the same fluoranthene product 11b in good yields (entries 6 and 7, respectively). The complete regioselectivity observed with substrate 12a is noteworthy to mention. Unsubstituted phenyl- and naphthyl-based boronic acids 13a and 14a are also competent substrates for the reaction under both homogeneous and heterogeneous catalytic conditions (entries 8 and 9, respectively). Gratifyingly, electron-rich 4-OMe-phenylboronic acid 15a afforded fluoranthene 15b in 74 and 63% yields with methods A and B, respectively (entry 10). 3-CF₃-substituted boronic acid 16a reacts regioselectively to give product 16b under both conditions (entry 11). However, 3,5-bis(CF₃)-substituted derivative 16a works only with method A (70% yield), whereas method B did not provide fluoranthene 17b (entry 12). To test a substrate with ortho substitution, boronic acid 18a was examined, and fluoranthene 18b was obtained successfully (entry 13). Finally, in an attempt to synthesize a heteroatom-containing fluoranthene by our methodology, 4-pyridylboronic acid (19a) was tested, and we were pleased to obtain azafluoranthene 19b in 64 and 42% yields with methods A and B, respectively (entry 14). This result underscores the potential of both catalytic conditions to be applied in the preparation of heteroaromatic fluoranthene analogues.

Table 3. Scope of the Fluoranthene Synthesis under Both Homogeneous and Heterogeneous Catalytic Conditions^a.

^aReaction conditions: method A: 1.0 equiv of 5, 1.15 equiv of arylboronic acid or ester, 4.0 equiv of KOAc, 5 mol % of Pd(dppf)Cl₂, DMSO, 90 or 110 °C, N₂, 24 h. Method B: 1.0 equiv of 5, 1.15 equiv of arylboronic acid or ester, 5.0 equiv of NaOAc, 4.0 mg of rGO-CuPd nanocatalyst (1.8 mol % Pd loading), 120 °C, 24 h.

^bT = 90 °C for method A.

^cT = 110 °C for method A.

To gain insights into the mechanism of the C–H arylation reaction, we conducted an intermolecular kinetic isotope effect (KIE) experiment as a preliminary mechanistic study.^14,15 For this purpose, we first prepared deuterated fluoranthene 13b-d₄ along with monoarylnaphthalenes 20 and 20-d₅ independently. When a 1:1 mixture of 20 and 20-d₅ was treated with Pd(dppf)Cl₂ (5 mol %) under the same reaction conditions but with a shorter reaction time (3 h), fluoranthene products 13b and 13b-d₄ were observed to be in a ratio of 1.1 by ¹H NMR spectroscopy (Scheme 1). On the basis of this result, it can be concluded that the C–H activation step is unlikely to be the rate-determining step in the overall intramolecular C–H arylation reaction.

Scheme 1. Intermolecular KIE Experiment.

Reusability is one of the significant criteria for evaluating the performance of heterogeneous catalysts. Therefore, we tested the reusability of rGO-CuPd nanocatalysts in the synthesis of fluoranthene product 6b (Table 3, entry 1). The nanocatalysts were found to be highly reusable, affording the fluoranthene product 6b in 62, 58, and 55% yields in three consecutive cycles (Figure 2a). This means that the rGO-CuPd nanocatalysts preserved almost 90% of their initial catalytic activity after the third run. To get insights into the stability of the rGO-CuPd, we analyzed the rGO-CuPd nanocatalysts by using transmission electron microscopy (TEM) after the three-cycle reusability test. A representative TEM image given in Figure 2b reveals that no considerable change is observable in the overall dispersion and particle size of the CuPd alloy NPs over rGO but there is a minimal deterioration on the morphology of the CuPd NPs realized.

Figure 2.

(A) Three-cycle reusability test for the rGO-CuPd nanocatalysts in the fluoranthene synthesis. (B) Representative TEM image of the rGO-CuPd nanocatalysts after the three-cycle reusability test.

Conclusions

In summary, we have developed a new catalytic method that allows the synthesis of substituted fluoranthene derivatives via tandem Suzuki–Miyaura and intramolecular C–H arylation reactions. The reaction sequence was found to operate effectively under homogeneous catalytic conditions using Pd(dppf)Cl₂ as well as heterogeneous catalytic conditions using rGO-CuPd nanocatalysts. The reaction has a broad substrate scope and functional group tolerance, and fluoranthene products were obtained in good yields (up to 78%) when various arylboronic acids and esters having electron-withdrawing and electron-donating groups with different substitution patterns were used. Moreover, the rGO-CuPd nanocatalysts were found to be reusable heterogeneous catalysts in the presented method. A preliminary mechanistic study has also been conducted through an intermolecular KIE experiment. The reaction developed in this work represents a rare example of a transformation involving a C–H arylation step that can be promoted successfully under both homogeneous and heterogeneous catalytic conditions and therefore is expected to stimulate further research in this area.

Experimental Section

General Information

All reactions under homogeneous catalytic conditions were performed using oven-dried glassware under an inert atmosphere of nitrogen. Reactions were monitored by thin-layer chromatography (TLC) using aluminum-backed plates precoated with silica gel (60 Å, F₂₅₄). UV light and KMnO₄ staining solution were used for TLC visualization. Flash column chromatography was performed on 200–400 mesh flash silica gel. NMR spectra were measured on a Bruker spectrometer at 400 MHz for ¹H NMR spectra and at 100 MHz for ¹³C spectra and calibrated from internal standard (TMS, 0 ppm) or residual solvent signals (chloroform at 7.26 ppm, DMSO at 2.50 ppm for ¹H spectra and chloroform at 77.16 ppm and DMSO at 39.52 for ¹³C spectra). Infrared [Fourier transform infrared (FTIR)] spectra were recorded on a Bruker Alpha-Platinum-ATR spectrometer, with only selected peaks reported. High-resolution mass spectrometry (HRMS) data were obtained using a time-of-flight mass spectrometer. Melting points are uncorrected.

1,8-Diiodonaphthalene (5)¹⁶ and rGO-CuPd nanocatalysts^12a were prepared according to reported procedures. All other commercially available reagents were used as received unless stated otherwise.

General Procedure for Fluoranthene Synthesis Using Homogeneous Catalysts (Method A)

A 10 mL oven-dried Schlenk tube was charged with 1,8-diiodonaphthalene (5) (100 mg, 0.26 mmol, 1.0 equiv) and DMSO (2 mL) under a nitrogen atmosphere. Nitrogen gas was bubbled through the solution for 5 min with gentle stirring. Arylboronic acid or pinacol ester (0.30 mmol, 1.1 equiv), Pd(dppf)Cl₂·CH₂Cl₂ (11 mg, 0.013 mmol, 0.05 equiv), and KOAc (100 mg, 1.02 mmol, 4 equiv) were added sequentially to the solution. The Schlenk tube was then sealed with a glass stopper, and the reaction mixture was stirred at 90 or 110 °C for 24 h. The progress of the reaction was monitored by TLC. After cooling to ambient temperature, brine was added to the reaction mixture, and the aqueous phase was extracted with ethyl acetate (2 × 10 mL). The combined organic layer was dried over Na₂SO₄, filtered, and concentrated in vacuo. The viscous crude product was purified by flash column chromatography (silica gel) to afford the desired product.

General Procedure for Fluoranthene Synthesis Using Heterogeneous Catalysts (Method B)

A 10 mL Schlenk tube was charged with the rGO-CuPd nanocatalyst (4.0 mg) and 2 mL of DMSO/H₂O mixture (DMSO/H₂O = 10:1) under air. The suspension was sonicated for 30 min at room temperature. After complete dispersion of the catalyst in the solvent mixture, the Schlenk tube was fitted over a magnetic stirrer. 1,8-Diiodonaphthalene (5) (50 mg, 0.13 mmol, 1.0 equiv), arylboronic acid or pinacol ester (0.15 mmol, 1.1 equiv), and NaOAc·3H₂O (54 mg, 0.65 mmol, 5 equiv) were added sequentially to the mixture with a gentle stirring. The Schlenk tube was then sealed with a glass stopper, and the reaction mixture was stirred at 120 °C for 24 h. The progress of the reaction was monitored by TLC. After cooling to ambient temperature, the reaction mixture was transferred to a centrifuge tube by washing with EtOAc. The mixture was centrifuged for 10 min under 6500 rpm. After complete precipitation of the catalyst, the organic layer was transferred to a separatory funnel and washed with brine. It was then dried over Na₂SO₄, filtered, and concentrated in vacuo. Purification by flash column chromatography (silica gel) gave the desired product.

Procedure for the Recovery of the rGO-CuPd Catalyst

After the completion of the reaction, the reaction mixture was transferred to a centrifuge tube by washing with EtOAc (8 mL). The mixture was centrifuged for 10 min, and the supernatant solution was decanted. The precipitated catalyst was washed additionally with EtOAc (8 mL), EtOH (2 × 8 mL), and acetone (8 mL). Centrifugation and decantation were repeated during each wash to remove any impurities and DMSO completely. The solid catalyst was dried at room temperature and used in the subsequent run for the reusability tests.

8-Fluorofluoranthene (6b)¹⁷

When 1,8-diiodonaphthalene (5) (100 mg, 0.26 mmol) was subjected to method A at 90 °C, fluoranthene 6b was obtained as a white amorphous solid (41 mg, 71%) after purification by column chromatography (hexane only). Application of method B using 1,8-diiodonaphthalene (5) (50 mg, 0.13 mmol) gave 6b in 62% yield (18 mg). R_f = 0.36 (hexane); ¹H NMR (400 MHz, CDCl₃): δ 7.92–7.81 (5H, m), 7.66–7.61 (2H, m), 7.58 (1H, dd, J = 8.8, 2.4 Hz), 7.08 (1H, ddd, J = 9.2, 8.3, 2.4 Hz); ¹³C NMR (100 MHz, CDCl₃): δ 163.2 (d, J_C–F = 245.1 Hz), 141.7 (d, J_C–F = 9.1 Hz), 136.3 (d, J_C–F = 0.6 Hz), 136.2 (d, J_C–F = 2.9 Hz), 135.5 (d, J_C–F = 2.6 Hz), 133.0 (d, J_C–F = 1.2 Hz), 130.1, 128.2, 128.1, 127.5, 126.4 (d, J_C–F = 1.0 Hz), 122.5 (d, J_C–F = 9.2 Hz), 120.7, 120.0 (d, J_C–F = 1.4 Hz), 114.2 (d, J_C–F = 23.4 Hz), 109.2 (d, J_C–F = 22.3 Hz); ¹⁹F NMR (376 MHz, CDCl₃): δ −114.5; FTIR (ATR, solid): 3045, 1580, 1452, 1263, 1172, 1130, 870, 813, 768 cm^–1; GCMS (m/z): 220.1.

Fluoranthene-8-carbonitrile (7b)¹⁸

When 1,8-diiodonaphthalene (5) (50 mg, 0.13 mmol) was subjected to method A at 90 °C, fluoranthene 7b was obtained as an off-white solid (21 mg, 70%) after purification by column chromatography (hexane to EtOAc/hexane = 1:19). Application of method B using 1,8-diiodonaphthalene (5) (50 mg, 0.13 mmol) gave 7b in 68% yield (20.4 mg). R_f = 0.40 (EtOAc/hexane = 1:10); ¹H NMR (400 MHz, CDCl₃): δ 8.18 (1H, app s), 8.07 (1H, d, J = 6.9 Hz), 8.03 (1H, d, J = 7.0 Hz), 8.02–7.95 (3H, m), 7.74–7.68 (3H, m); ¹³C NMR (100 MHz, CDCl₃): δ 143.2, 139.8, 135.1, 134.9, 132.7, 131.4, 130.1, 128.5, 128.4, 128.3, 128.0, 124.9, 122.0, 121.9, 121.4, 119.7, 110.5; FTIR (ATR, solid): 2921, 2223, 1736, 1454, 1422, 1259, 1187, 1019, 890, 812 cm^–1; HRMS (APCI⁺): calcd for C₁₇H₁₀N [M + H]⁺, 228.0808; found, 228.0809.

Fluoranthene-8-carboxamide (8b)

When 1,8-diiodonaphthalene (5) (50 mg, 0.13 mmol) was subjected to method A at 90 °C, fluoranthene 8b was obtained as a pale yellow solid (21.7 mg, 67%) after purification by column chromatography (EtOAc/hexane = 1:1 to 4:1). Application of method B using 1,8-diiodonaphthalene (5) (50 mg, 0.13 mmol) gave 8b in 61% yield (19.6 mg). mp 227.4–228.9 °C; R_f = 0.21 (EtOAc/hexane = 3:1); ¹H NMR (400 MHz, DMSO-d₆): δ 8.58 (1H, dd, J = 1.6, 0.6 Hz), 8.22 (1H, d, J = 6.9 Hz), 8.19 (1H, d, J = 6.9 Hz), 8.14 (1H, dd, J = 7.9, 0.6 Hz), 8.09 (1H, br s), 8.04–8.00 (2H, m), 7.98 (1H, dd, J = 7.9, 1.6 Hz), 7.78–7.74 (2H, m), 7.45 (1H, br s); ¹³C NMR (100 MHz, DMSO-d₆): δ 167.9, 141.1, 138.6, 135.6, 135.3, 133.6, 131.9, 129.6, 128.43, 128.37, 127.5, 127.23, 127.17, 121.7, 121.4, 121.1; FTIR (ATR, solid): 3410, 3189, 2923, 2852, 1649, 1610, 1435, 1387, 821, 770 cm^–1; HRMS (APCI⁺): calcd for C₁₇H₁₂NO [M + H]⁺, 246.0913; found, 246.0935.

1-(Fluoranthen-8-yl)ethanone (9b)¹⁹

When 1,8-diiodonaphthalene (5) (100 mg, 0.26 mmol) was subjected to method A at 90 °C, fluoranthene 9b was obtained as a white solid (31.6 mg, 49%) after purification by column chromatography (hexane to EtOAc/hexane = 1:19). Application of method B using 1,8-diiodonaphthalene (5) (50 mg, 0.13 mmol) gave 9b in 57% yield (18.5 mg). R_f = 0.31 (EtOAc/hexane = 1:9); ¹H NMR (400 MHz, CDCl₃): δ 8.50 (1H, dd, J = 1.6, 0.7 Hz), 8.03 (2H, d, J = 6.9 Hz), 8.00–7.95 (2H, m), 7.93 (1H, d, J = 8.2 Hz), 7.90 (1H, d, J = 8.2 Hz), 7.70–7.67 (2H, m), 2.71 (3H, s); ¹³C NMR (100 MHz, CDCl₃): δ 198.1, 143.8, 139.8, 136.5, 136.2, 135.9, 133.3, 130.2, 128.5, 128.4, 128.2, 128.1, 127.4, 121.6, 121.4, 120.9, 27.0; FTIR (ATR, solid): 2924, 1676, 1611, 1428, 1354, 1285, 1239, 816, 772 cm^–1; HRMS (APCI⁺): calcd for C₁₈H₁₃O [M + H]⁺, 245.0961; found, 245.0966.

Methyl Fluoranthene-8-carboxylate (10b)²⁰

When 1,8-diiodonaphthalene (5) (100 mg, 0.26 mmol) was subjected to method A at 90 °C, fluoranthene 10b was obtained as a white solid (53.6 mg, 78%) after purification by column chromatography (EtOAc/hexane = 1:9). Application of method B using 1,8-diiodonaphthalene (5) (50 mg, 0.13 mmol) gave 10b in 36% yield (12.3 mg). R_f = 0.27 (EtOAc/hexane = 1:9); ¹H NMR (400 MHz, CDCl₃): δ 8.5 (1H, dd, J = 1.5, 0.7 Hz), 8.09 (1H, dd, J = 7.9, 1.6 Hz), 8.00 (1H, d, J = 2.5 Hz), 7.98 (1H, d, J = 2.5 Hz), 7.93–7.86 (3H, m), 7.68–7.64 (2H, m), 3.99 (3H, s); ¹³C NMR (100 MHz, CDCl₃): δ 167.4, 143.6, 139.5, 136.2, 135.9, 131.5, 130.1, 129.3, 129.2, 128.3, 128.2, 127.9, 127.2, 122.8, 121.4, 121.2, 120.9, 52.3; FTIR (ATR, solid): 2949, 1716, 1436, 1290, 1245, 1118, 822, 773 cm^–1; HRMS (APCI⁺): calcd for C₁₇H₉O [M – OMe]⁺, 229.0648; found, 229.0714.

8-Nitrofluoranthene (11b)²¹

When 1,8-diiodonaphthalene (5) (50 mg, 0.13 mmol) and 4-nitrophenylboronic acid (11a) (25 mg, 0.15 mmol) were subjected to method A at 90 °C, fluoranthene 11b was obtained as a yellow solid (23.6 mg, 72%) after purification by column chromatography (EtOAc/hexane = 1:5). Application of method B using 1,8-diiodonaphthalene (5) (50 mg, 0.13 mmol) and 4-nitrophenylboronic acid (11a) (25 mg, 0.15 mmol) gave 11b in 70% yield (22.6 mg). The reactions between 1,8-diiodonaphthalene (5) (50 mg, 0.13 mmol) and 3-nitrophenylboronic acid (12a) (25 mg, 0.15 mmol) gave fluoranthene 11b in 64% yield (21 mg) with method A and in 57% yield (18.6) with method B. R_f = 0.32 (EtOAc/hexane = 1:4); ¹H NMR (400 MHz, CDCl₃): δ 8.61 (1H, d, J = 2.1 Hz), 8.21 (1H, dd, J = 8.3, 2.1 Hz), 8.01 (1H, d, J = 7.0 Hz), 7.97 (1H, d, J = 7.0 Hz), 7.96 (1H, d, J = 8.2 Hz), 7.93 (1H, d, J = 8.2 Hz), 7.89 (1H, d, J = 8.3 Hz), 7.71–7.67 (2H, m); ¹³C NMR (100 MHz, CDCl₃): δ 147.5, 144.9, 140.1, 134.9, 134.7, 133.5, 130.1, 128.8, 128.5, 128.4, 128.2, 123.1, 122.4, 121.7, 121.3, 116.8; FTIR (ATR, solid): 2924, 2851, 1517, 1487, 1452, 1338, 821, 772 cm^–1; HRMS (APCI^–): calcd for C₁₆H₉NO₂ [M]⁻, 247.0639; found, 247.0598.

Fluoranthene (13b)

When 1,8-diiodonaphthalene (5) (100 mg, 0.26 mmol) was subjected to method A at 110 °C, fluoranthene 13b was obtained as a pale yellow solid (29 mg, 55%) after purification by column chromatography (hexane only). Application of method B using 1,8-diiodonaphthalene (5) (50 mg, 0.13 mmol) gave 13b in 56% yield (14.7 mg). R_f = 0.36 (hexane); ¹H NMR (400 MHz, CDCl₃): δ 7.97–7.92 (4H, m), 7.86 (2H, d, J = 8.3 Hz), 7.65 (2H, dd, J = 8.2, 6.9 Hz), 7.41–7.39 (2H, m); ¹³C NMR (100 MHz, CDCl₃): δ 139.6, 137.1, 130.22, 130.15, 128.1, 127.7, 126.8, 121.7, 120.2; FTIR (ATR, solid): 3051, 2924, 1454, 1439, 826, 774, 747 cm^–1; GCMS (m/z), 202.2.

Benzo[j]fluoranthene (14b)^7a

When 1,8-diiodonaphthalene (5) (50 mg, 0.13 mmol) was subjected to method A at 110 °C, fluoranthene 14b was obtained as a pale yellow solid (20.6 mg, 62%) after purification by column chromatography (hexane only). Application of method B using 1,8-diiodonaphthalene (5) (50 mg, 0.13 mmol) gave 14b in 59% yield (19.6 mg). R_f = 0.33 (hexane); ¹H NMR (400 MHz, CDCl₃): δ 8.72 (1H, d, J = 8.5 Hz), 8.46 (1H, d, J = 7.0 Hz), 8.06 (1H, d, J = 8.3 Hz), 8.01 (1H, d, J = 6.9 Hz), 7.95–7.92 (1H, m), 7.88–7.86 (2H, m), 7.72–7.60 (3H, m), 7.49 (1H, ddd, J = 8.1, 6.8, 1.1 Hz); ¹³C NMR (100 MHz, CDCl₃): δ 138.0, 137.9, 137.3, 134.4, 134.2, 132.1, 130.8, 129.8, 129.5, 128.5, 128.3, 128.0, 127.5, 127.12, 127.07, 125.4, 124.4, 124.3, 121.0, 120.0.

8-Methoxyfluoranthene (15b)¹⁰

When 1,8-diiodonaphthalene (5) (50 mg, 0.13 mmol) was subjected to method A at 110 °C, fluoranthene 15b was obtained as a yellow solid (22.6 mg, 74%) after purification by column chromatography (hexane to EtOAc/hexane = 1:9). Application of method B using 1,8-diiodonaphthalene (5) (50 mg, 0.13 mmol) gave 15b in 63% yield (19.4 mg). R_f = 0.30 (EtOAc/hexane = 1:9); ¹H NMR (400 MHz, CDCl₃): δ 7.91 (1H, d, J = 6.9 Hz), 7.85–7.76 (4H, m), 7.64–7.58 (2H, m), 7.47 (1H, d, J = 2.4 Hz), 6.92 (1H, dd, J = 8.3, 2.4 Hz), 3.94 (3H, s); ¹³C NMR (100 MHz, CDCl₃): δ 160.2, 141.4, 137.2, 137.0, 133.1, 132.6, 130.1, 128.2, 127.9, 127.1, 125.6, 122.4, 120.1, 119.1, 113.0, 107.9, 55.8; FTIR (ATR, solid): 2920, 2849, 1603, 1455, 1416, 1221, 1173, 1025 cm^–1; HRMS (APCI⁺): calcd for C₁₇H₁₃O [M + H]⁺, 233.0961; found, 233.0963.

8-(Trifluoromethyl)fluoranthene (16b)¹⁰

When 1,8-diiodonaphthalene (5) (100 mg, 0.26 mmol) was subjected to method A at 90 °C, fluoranthene 16b was obtained as a white solid (37 mg, 52%) after purification by column chromatography (hexane only). Application of method B using 1,8-diiodonaphthalene (5) (50 mg, 0.13 mmol) gave 16b in 58% yield (20.6 mg). R_f = 0.32 (hexane); ¹H NMR (400 MHz, CDCl₃): δ 8.11–8.10 (1H, m), 7.97–7.88 (5H, m), 7.67–7.62 (3H, m); ¹³C NMR (100 MHz, CDCl₃): δ 142.5, 139.8, 135.7, 135.6, 132.9, 130.1, 129.5 (q, J_C–F = 32.0 Hz), 128.3, 128.2, 127.9, 127.6, 124.6 (q, J_C–F = 3.9 Hz), 121.5, 121.4, 121.0, 118.4 (q, J_C–F = 3.9 Hz); ¹⁹F NMR (376 MHz; CDCl₃): δ −61.9; FTIR (ATR, solid): 1458, 1431, 1325, 1262, 1157, 1113 cm^–1; GCMS (m/z): 270.1.

7,9-Bis(trifluoromethyl)fluoranthene (17b)

When 1,8-diiodonaphthalene (5) (100 mg, 0.26 mmol) was subjected to method A at 110 °C, fluoranthene 17b was obtained as a white solid (31 mg, 70%) after purification by column chromatography (hexane only). mp 138.9–140.7 °C; R_f = 0.32 (hexane); ¹H NMR (400 MHz, CDCl₃): δ 8.36 (1H, d, J = 7.2 Hz), 8.30 (1H, s), 8.05 (1H, d, J = 7.0 Hz), 8.01 (1H, d, J = 8.2 Hz), 7.98 (1H, d, J = 8.2 Hz), 7.93 (1H, s), 7.77–7.69 (2H, m); ¹³C NMR (100 MHz, CDCl₃): δ 141.9, 134.0, 132.9, 132.6, 130.1, 129.3, 128.8, 128.1, 126.6 (q, J_C–F = 4.9 Hz), 125.4, 122.7, 121.7–121.5 (m), 121.3–121.2 (m); ¹⁹F NMR (376 MHz, CDCl₃): δ −62.2, −63.0; FTIR (ATR, solid): 1583, 1444, 1357, 1299, 1277, 1161, 1119 cm^–1; HRMS (APCI^–): calcd for C₁₈H₈F₆ [M]⁻, 338.0536; found, 338.0532.

7-Fluorofluoranthene (18b)¹⁷

When 1,8-diiodonaphthalene (5) (100 mg, 0.26 mmol) was subjected to method A at 90 °C, fluoranthene 18b was obtained as a white amorphous solid (37.9 mg, 65%) after purification by column chromatography (hexane only). Application of method B using 1,8-diiodonaphthalene (5) (50 mg, 0.13 mmol) gave 18b in 46% yield (13.4 mg). R_f = 0.36 (hexane); ¹H NMR (400 MHz, CDCl₃): δ 8.11 (1H, d, J = 6.9 Hz), 7.95 (1H, d, J = 6.9 Hz), 7.88 (1H, d, J = 8.2 Hz), 7.87 (1H, d, J = 8.2 Hz), 7.71–7.63 (3H, m), 7.34 (1H, ddd, J = 8.2, 7.5, 5.1 Hz), 7.11 (1H, ddd, J = 9.7, 8.3, 0.7 Hz); ¹³C NMR (100 MHz, CDCl₃): δ 159.3 (d, J_C–F = 250.2 Hz), 142.3 (d, J_C–F = 6.4 Hz), 136.5 (d, J_C–F = 2.1 Hz), 134.0 (d, J_C–F = 1.6 Hz), 132.1, 130.1, 129.1 (d, J_C–F = 7.3 Hz), 128.4, 128.0, 127.4, 126.9, 125.8 (d, J_C–F = 16.1 Hz), 123.7 (d, J_C–F = 4.0 Hz), 121.0, 117.6 (d, J_C–F = 2.9 Hz), 114.9 (d, J_C–F = 20.2 Hz); ¹⁹F NMR (376 MHz, CDCl₃): δ −118.3; FTIR (ATR, solid): 3045, 1572, 1445, 1236, 1178, 823, 794, 769 cm^–1; GCMS (m/z): 220.1.

Acenaphtho[1,2-c]pyridine (19b)

When 1,8-diiodonaphthalene (5) (100 mg, 0.26 mmol) was subjected to method A at 110 °C, azafluoranthene 19b was obtained as a pale green sticky solid (34.7 mg, 64%) after purification by column chromatography (EtOAc/hexane = 1:1 to 4:1). Application of method B using 1,8-diiodonaphthalene (5) (50 mg, 0.13 mmol) gave 19b in 42% yield (11.4 mg). R_f = 0.18 (EtOAc/hexane = 2:1); ¹H NMR (400 MHz, CDCl₃): δ 9.16 (1H, s), 8.64 (1H, d, J = 5.0 Hz), 8.03 (1H, d, J = 7.0 Hz), 8.01 (1H, d, J = 6.9 Hz), 7.97 (1H, d, J = 8.2 Hz), 7.89 (1H, d, J = 8.2 Hz), 7.78 (1H, dd, J = 5.0, 1.1 Hz), 7.70–7.64 (2H, m); ¹³C NMR (100 MHz, CDCl₃): δ 148.8, 146.3, 143.0, 134.70, 134.69, 134.3, 132.4, 130.2, 129.2, 128.4, 128.1, 127.5, 122.6, 121.5, 116.5; FTIR (ATR, solid): 3010, 3000, 1633, 1600, 1454, 1422, 1187, 820, 773 cm^–1; HRMS (ESI⁺): calcd for C₁₅H₁₀N [M + H]⁺, 204.0808; found, 204.0816.

1-Iodo-8-phenylnaphthalene (20)²²

A 10 mL oven-dried Schlenk tube was charged with 1,8-diiodonaphthalene (5) (100 mg, 0.26 mmol, 1.0 equiv) and DMF (2 mL) under a nitrogen atmosphere. Nitrogen gas was bubbled through the solution for 5 min with gentle stirring. Phenylboronic acid (13a) (41 mg, 0.33 mmol, 1.3 equiv), Pd(PPh₃)₄ (15 mg, 0.013 mmol, 0.05 equiv), and K₂CO₃ (140 mg, 1.0 mmol, 4 equiv) were added sequentially to the solution. The reaction mixture was stirred at 80 °C for 24 h. The progress of the reaction was monitored by TLC. After cooling to ambient temperature, brine was added to the reaction mixture, and the aqueous phase was extracted with ethyl acetate (2 × 10 mL). The combined organic layer was dried over Na₂SO₄, filtered, and concentrated in vacuo. The viscous crude product was purified by flash column chromatography (hexane only) to afford product 20 (31 mg, 36%) as a colorless oil. R_f = 0.38 (hexane); ¹H NMR (400 MHz, CDCl₃): δ 8.22 (1H, dd, J = 7.3, 1.3 Hz), 7.92 (1H, dd, J = 8.1, 1.2 Hz), 7.86 (1H, dd, J = 7.3, 2.2 Hz), 7.53–7.42 (5H, m), 7.35–7.33 (2H, m), 7.11 (1H, t, J = 7.7 Hz); ¹³C NMR (100 MHz, CDCl₃): δ 142.5, 141.7, 141.5, 135.7, 131.6, 131.24, 131.15, 129.9, 129.2, 127.9, 127.5, 126.7, 125.3, 92.2; GCMS (m/z): 330.0.

20-d₅

Compound 20-d₅ was synthesized via the same procedure used for compound 20 starting from 1,8-diiodonaphthalene (5) and the commercially available phenyl-d₅-boronic acid. The crude reaction mixture was purified by flash column chromatography (hexane only) to afford the product 20-d₅ (25 mg, 28%) as a colorless oil. R_f = 0.38 (hexane); ¹H NMR (400 MHz, CDCl₃): δ 8.23 (1H, dd, J = 7.3, 1.0 Hz), 7.92 (1H, d, J = 8.1 Hz), 7.87 (1H, dd, J = 7.3, 2.2 Hz), 7.53–7.48 (2H, m), 7.11 (1H, t, J = 7.7 Hz); ¹³C NMR (100 MHz, CDCl₃): δ 142.5, 141.7, 141.3, 135.7, 131.2, 129.9, 129.2, 126.7, 125.3, 92.2; GCMS (m/z): 335.1.

Fluoranthene-d₄ (13b-d₄)

R_f = 0.36 (hexane); ¹H NMR (400 MHz, CDCl₃): δ 7.95 (2H, dd, J = 7.0, 0.5 Hz), 7.85 (2H, dd, J = 8.3, 0.6 Hz), 7.64 (2H, dd, J = 8.2, 6.9 Hz); GCMS (m/z): 206.2.

Intermolecular KIE Study

A 10 mL oven-dried Schlenk tube was charged with 20 (20 mg, 0.06 mmol) and 20-d₅ (20 mg, 0.06 mmol), followed by the addition of DMSO (2 mL) under a nitrogen atmosphere. Nitrogen gas was bubbled through the solution for 5 min with gentle stirring. Pd(dppf)Cl₂·CH₂Cl₂ (5 mg, 0.006 mmol) and KOAc (50 mg, 0.5 mmol) were added sequentially to the reaction mixture. The Schlenk tube was then sealed with a glass stopper, and the reaction mixture was stirred at 90 °C for 3 h. After cooling to ambient temperature, brine was added to the reaction mixture, and the aqueous phase was extracted with ethyl acetate (2 × 10 mL). The combined organic layer was dried over Na₂SO₄, filtered, and concentrated in vacuo. The crude reaction mixture was purified by flash column chromatography (hexane only) to afford a mixture of the products 13b and 13b-d₄ (7.3 mg, 30%) as a viscous oil. The ratio of the two products was determined by ¹H NMR spectroscopy where the intermolecular KIE k(H)/k(D) was found to be 1.1 based on integration analysis. This experiment was repeated twice, and the same result was obtained in both experiments.

Supporting Information Available

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acsomega.7b01566.

• TEM and X-ray diffraction images and NMR spectra (PDF)

The authors declare no competing financial interest.