Active sp3 C-H Bonds Oxidation Initiated sp3-sp2 Consecutive C-H

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Active sp3 C−H Bond Oxidation Initiated sp3−sp2 Consecutive C−H Functionalization of N‑Arylglycine Amides: Construction of Isatins Honghe Ji,† Yingzu Zhu,† Yu Shao,§ Jing Liu,† Yu Yuan,*,‡ and Xiaodong Jia*,†,‡ †

College of Chemistry & Chemical Engineering, Northwest Normal University, Lanzhou, Gansu 730070, China School of Chemistry & Chemical Engineering, Yangzhou University, Yangzhou, Jiangsu 225002, China § School of Information Engineering, Yangzhou University, Yangzhou, Jiangsu 225127, China ‡

S Supporting Information *

ABSTRACT: In the presence of catalytic triarylamine radical cation, an sp3−sp2 consecutive C−H functionalization of N-arylglycine amides was achieved, providing a series of isatin derivatives in high yields. In this transformation, the initial aerobic oxidation of the relatively active sp3 C−H bonds triggered the following intramolecular cyclization, in which the aniline group was employed as a removable auxiliary group to enable the consecutive process.

B

ecause of the ubiquitous and diverse nature of C−H bonds in organic compounds, direct functionalization of C−H bonds has been studied for years, and numerous methodologies for constructing complex structures from synthetically available substrates have been developed.1 Compared with sp2 C−H activation, which was generally achieved by the use of transition metal-promoted reactions,2 functionalization of the sp3 C−H bond is still a challenge for organic chemists.3 Recently, Yu and co-workers4 reported a series of elegant examples of sp3 C−H activation by transition metal-catalyzed transformations, in which a directing group is generally crucial for achieving selectivity control and high reaction efficiency. Another approach to realizing the sp3 C−H functionalization is the free radical-mediated process, in which an oxidant is added to oxidize the C−H bonds, providing a radical intermediate followed by further functionalization.5,6 In this area, several model substrates were investigated extensively, such as THIQ, N-arylglycines, N-arylbenzylamines, etc. It is well-known that the C−H bonds adjacent to heteroatoms are relatively active, and the corresponding radical intermediate could be stabilized by p−π conjugation with the lone pair electrons of the heteroatoms. In the cases of Narylglycines, the generated free radicals could also be stabilized by the captodative effect,7 so we questioned whether we could make use of these active C−H bonds to initiate further functionalization of inert C−H bonds through any intramolecular process. Recently, we reported an efficient construction of an isatin skeleton by a novel transformation named the C−H activation relay (CHAR).8 In this reaction, we designed and realized an intramolecular 1,6-hydrogen atom shift, which triggered further activation of inert C−H and C−O bonds in the ester group, providing a series of isatin derivatives from synthetically available N-arylglycine esters (Figure 1, eq 1). In this research, the α-C−H bonds in N-arylglycines were found to be extremely active and could be easily oxidized to the corresponding radical © 2017 American Chemical Society

Figure 1. Different routes to isatin derivatives.

intermediate. Inspired by this work, we hypothesized that in the presence of a radical trapper, for example, a phenyl group, an sp2 C−H functionalization via an intramolecular radical cyclization might be possible (Figure 1, eq 2). If this idea is feasible, the initial sp3 C−H oxidation will act as a trigger to promote the consecutive sp3−sp2 C−H functionalization, and the aniline group will be employed as a removable auxiliary group to enable the consecutive process. Herein, we reported a different version of isatin synthesis through a radical cation saltinduced aerobic oxidation of sp3 C−H bonds in N-arylglycine amides. Isatin is an important pharmacophore and is present in many natural products, synthetic intermediates, and pharmaceuticals.9 It is reported that structures with an isatin skeleton exhibit a variety of biological activities such as anticancer,10 anticonvulsant,11 antifungal,12 anti-HIV,13 anti-inflammatory,14 and other activities.15 Although the first synthesis of isatin was reported as early as 1840,16 considerable effort has been devoted to the Received: June 15, 2017 Published: August 17, 2017 9859

DOI: 10.1021/acs.joc.7b01480 J. Org. Chem. 2017, 82, 9859−9865

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The Journal of Organic Chemistry

Figure 2. Our initial attempts to synthesize isatin.

Table 1. Optimization of Reaction Conditionsa

construction of the isatin motif, and some new methods were developed.17−20 For example, using various oxidants, the oxidative cyclization of 2′-amino acetophenone is an efficient way to construct an isatin skeleton.17 Li and co-workers18 reported a copper-catalyzed intramolecular C−H oxidation/ acylation of formyl-N-arylformamides, using O2 as the terminal oxidant. Lei and co-workers19 have disclosed an elegant method that utilizes readily available anilines for Pd-catalyzed double carbonylation with CO. Other methods involving oxidation of an indole ring or carbon−carbon unsaturated bonds have also been reported.20 Furthermore, construction of spiro- and tetrasubstituted oxoindole skeletons also plays an important role in organic synthesis.21 Although these methods provided different routes to isatin derivatives, some shortcomings such as harsh reaction conditions, a tedious starting material synthesis, and a narrow substrate scope still restricted their broader applications in the synthesis of isatins. Therefore, the diverse synthesis of biologically relevant isatins through facile and applicable methods is still highly desirable. Initially, in the presence of 10 mol % TBPA+• [tris(4bromophenyl)aminium hexachloroantimonate] in MeCN, a series of N-arylglycine amides were employed to confirm the likelihood of our hypothesis (Figure 2, eq 1). Unfortunately, complicated mixtures were obtained, and through crude product analysis, only a trace amount of the desired isatins was detected. Furthermore, other oxidative products, such as a carbonylation product22 and 3,4-dihydroquinazoline,23 were also detected by HPLC−MS. Then, a methyl group was installed on the nitrogen atom to block the undesired side reactions. To our delight, the reaction became cleaner, and the isatin products were isolated in moderate yields. Because the aniline group (colored blue) acts as not only an auxiliary group, activating the sp3 α-C−H bonds, but also a leaving group, different substituents on anilines were then tested. Although the chloro group might increase the likelihood of C−N bond cleavage,24 the electron-withdrawing nature exerts a negative effect on the oxidation of sp3 C−H bonds, resulting in a lower yield of the desired product and an elongated reaction time. The results show that the 4,N-dimethylaniline is a proper removable auxiliary group, giving the desired product in 54% yield. After the removable auxiliary group was established, we started our study on substrate 1aa to determine the best conditions for achieving the efficient synthesis of isatin derivatives (Table 1). The solvent screen was then performed

entry

solvent

temp (°C)

time (h)

yield (%)b

1 2 3 4 5 6 7 8

CH3CN CH2Cl2 CHCl3 DCE MeOPh MeOPh MeOPh MeOPh

60 60 60 60 60 60 60 40

72 72 72 72 36 72 24 72

54 33 46 64 93 68c 88d 55

a

Unless otherwise specified, the reaction was performed with 1aa (0.1 mmol) in the presence of TBPA+• and an anhydrous solvent (1.0 mL). b Yield of crude product 1H NMR using 1,3,5-trimethoxylbenzene as an internal standard. cInduced by 5 mol % TBPA+•. dInduced by 15 mol % TBPA+•.

(entries 1−5), and the results show that anisole is superior, having a greater yield and a shorter reaction time, giving the expected isatin in 93% yield (entry 5). A lower catalyst loading and a lower reaction temperature led to decreased yields and elongated reaction times (entries 6 and 8). When the reaction was initiated by 15 mol % TBPA+•, the reaction time was decreased to 24 h with a slightly lower yield of the desired product (entry 7). With the best reaction conditions established, the scope and limitations of the title procedure were further investigated. First, the substituents on aryl groups were varied to evaluate their effect on reaction efficiency, and the results are compiled in Scheme 1. The substrates with electron-donating groups, such as MeO and Me, at the para position of the aromatic ring underwent this transformation smoothly, producing the desired products in excellent yields (2aa and 2ba). Slightly lower yields were obtained for the halogenated substrates with an elongated reaction time (2ca and 2da), probably because the lower electron density decreases the level of intramolecular cyclization. Similar results were seen with 2,4-disubstituted and unsubstituted analogues (2ea and 2fa). When a m-MeOsubstituted substrate was employed, only one isomer was isolated in 92% yield (2ga), and the cyclization occurred 9860

DOI: 10.1021/acs.joc.7b01480 J. Org. Chem. 2017, 82, 9859−9865

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The Journal of Organic Chemistry Scheme 1. Scope of Aryl Groups on Amidesa

Scheme 2. Scope of Alkyl Groups on Amidesa

a

Reaction conditions: 1 (1 mmol), TBPA+• (10 mol %), anisole (5 mL), 60 °C under O2, 36 h, isolated yield.

selectively at the para position, probably because of steric hindrance. The reaction efficiency was not decreased when ortho substituents existed, and the desired products were obtained in 87% (2ha) and 89% (2ia) yields. The cyclization on the naphthalene ring also proceeded smoothly, giving the expected benzoisatin in 83% yield (2ja). We also employed the 1,2,3,4-tetrahydroquinline-derived amide subjected to the standard reaction conditions, and a tricyclic skeleton was afforded smoothly (2ka), which is an important pharmacophore that exhibits anti-leukemic activity and is present in natural alkaloid.25 Next, various groups on nitrogen were examined to test the reaction scope and functional group tolerance (Scheme 2). All of the alkyl groups performed well with high yields, affording the desired products in good to excellent yields (2ab−2be) in which even the bulky groups (2ac, 2be, and 2bg) did not exert a negative effect on reaction efficiency. Other sensitive groups such as the cyclopropyl ring (2bf) and CC bond (2bh) were completely tolerated under these mild oxidative conditions. In the cases of substrates with other active benzyl C−H bonds, the desired reaction process was partly disturbed, and the yields were lower (2bi and 2bj). Then, the amides derived from diarylamine were tested (2ad−2cd). The symmetric substrates gave the desired products in high yields (2ad and 2cb). When different aryl groups were present, the intramolecular cyclization mainly occurred on the electron-rich ring (2db), and in the case of N-phenyl-N-tolylamide, a 1.4:1 mixture was provided (2cc and 2cd), in which the electron-rich ring exhibited a slightly higher activity, implying the electrophilic nature of the intramolecular cyclization step. To probe the reaction mechanism, we performed several control experiments, and the results are compiled in Scheme 3. In the absence of dioxygen, no reaction occurred and the starting material was fully recovered (eq 1). Then, a radical inhibition experiment was conducted. In the presence of 1 equiv of TEMPO, the reaction was totally inhibited, implying the participation of a free radical intermediate (eq 2). To track the reaction intermediate, we performed HRMS experiments

a

Reaction conditions: 1 (1 mmol), TBPA+• (10 mol %), anisole (5 mL), 60 °C under O2, 36 h, isolated yield.

12 h after the reaction was conducted. We were delighted to observe the signal at m/z 329.0285 (calcd for C16H13BrNO2 + H+, m/z 329.0284), which is demethylated intermediate A (eq 3, path a). The eliminated N-methylaniline was also detected by HRMS (eq 3, path b; calcd for C8H11N + H+, m/z 122.0964; found, m/z 122.0964). These results suggested that the designed intramolecular cyclization was involved in this reaction, and after hydrolysis of generated iminium ion B, the desired isatins were afforded (see Scheme 4 for details). On the basis of the control experiments and previous research,26 a possible mechanism was proposed (Scheme 4). In the presence of dioxygen, the more active C−H bond of glycine amide is oxidized initially, generating a radical intermediate C. Then the electrophilic radical intermediate adds to the electronrich aryl ring, followed by further oxidation and rearomatization. The benzyl C−H bond in intermediate D is more active and oxidized smoothly, providing another radical under the oxidative reaction conditions. Further oxidation leads to the formation of an isatin-derived iminium B, and after aqueous workup, the N-methylaniline is released [detected by HRMS (for details, see Scheme 3, eq 3)], giving the desired isatin product.27 The trace amount of demethylated intermediate observed by HRMS is also derived from iminium E through a demethylation process (see Scheme 3, eq 3). In conclusion, we designed and developed an efficient method for constructing biologically relevant isatin derivatives. In this reaction, the aerobic oxidation of the relatively active sp3 C−H bonds acts as a handle to promote further intramolecular sp2 C−H functionalization, affording a series of isatin derivatives from synthetically available substrates. The mild 9861

DOI: 10.1021/acs.joc.7b01480 J. Org. Chem. 2017, 82, 9859−9865

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The Journal of Organic Chemistry Scheme 3. Control Experiments

Scheme 4. Proposed Mechanism

visualization), the reaction was quenched by addition of Na2CO3 in a H2O (10 mL) solution. The mixture was poured into a separator funnel with the addition of excess DCM (10 mL), and then the crude organic solution was extracted three times with water to remove inorganic salts. The organic phase was then dried over anhydrous magnesium sulfate and filtered, and the solvent was removed under reduced pressure. The products were separated by silica gel column chromatography eluted with petroleum ether and acetone [15:1 (v/v)] to afford the products. 5-Methoxy-1-methylindoline-2,3-dione (2aa).18 Compound 2aa was isolated in 90% yield (172 mg, red crystal): mp 170−171 °C; 1H NMR (400 MHz, CDCl3) δ 7.11 (dd, J = 8.5, 2.7 Hz, 1H), 7.07 (d, J = 2.6 Hz, 1H), 6.77 (d, J = 8.5 Hz, 1H), 3.76 (s, 3H), 3.17 (s, 3H); 13C NMR (101 MHz, CDCl3) δ 183.7, 158.3, 156.5, 145.3, 124.5, 117.7, 110.9, 109.55, 55.9, 26.2; EI-MS m/z (relative intensity) 191 (100%), 163 (58.7%), 148 (34.1%), 135 (43.7%), 134 (49.3%), 120 (62.9%), 92 (19.1%). 1,5-Dimethylindoline-2,3-dione (2ba).18 Compound 2ba was isolated in 93% yield (163 mg, red crystal): mp 149−151 °C; 1H NMR (400 MHz, CDCl3) δ 7.33 (m, 2H), 6.72 (d, J = 7.6 Hz, 1H), 3.15 (s, 3H), 2.26 (s, 3H); 13C NMR (101 MHz, CDCl3) δ 183.5, 158.3, 149.2, 138.7, 133.68, 125.5, 117.4, 109.7, 26.1, 20.6; EI-MS m/z (relative intensity) 175 (76.1%), 147 (42.4%), 119 (59.7%), 118 (100%), 91 (34.3%), 77 (17.5%). 5-Chloro-1-methylindoline-2,3-dione (2ca).28 Compound 2ca was isolated in 76% yield (148 mg, red crystal): mp 169−171 °C; 1H

reaction conditions, broad reaction scope, and functional group tolerance make it a facile approach to isatin synthesis. This reaction also provides a conceptually novel way, oxidation of active C−H bonds to initiate sp3−sp2 C−H functionalization, to design and achieve sp2 C−H bond functionalization. Further applications and more designed consecutive reactions are still underway in our laboratory.

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EXPERIMENTAL SECTION

General. Solvents are anhydrous. TBPA+• was purchased from commercial sources and used without treatment. Flash chromatography was performed with silica gel (200−300 mesh). Analytical TLC was performed with silica gel GF254 plates, and the products were visualized by UV detection. 1H NMR (400 or 600 MHz) and 13C NMR (100 or 150 MHz) spectra were recorded in CDCl3. Chemical shifts (δ) are reported in parts per million using TMS as an internal standard, and spin−spin coupling constants (J) are given in hertz. EIMS spectra were recorded by direct inlet at 70 eV. The high-resolution mass spectra (HRMS) were recorded on an electrospray ionization (ESI) apparatus using time-of-flight (TOF) mass spectrometry. Typical Procedure for TBPA+•-Induced Construction of Isatins. A solution of 1 (1 mmol) in anisole (5 mL) was mixed fully, and then TBPA+• (10 mol %) was added dropwise. The reaction solution was stirred at 60 °C under an O2 atmosphere. After the reaction had reached completion as determined by TLC (by UV 9862

DOI: 10.1021/acs.joc.7b01480 J. Org. Chem. 2017, 82, 9859−9865

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The Journal of Organic Chemistry NMR (400 MHz, CDCl3) δ 7.58−7.50 (m, 2H), 6.84 (d, J = 8.2 Hz, 1H), 3.23 (s, 3H); 13C NMR (101 MHz, CDCl3) δ 182.3, 157.6, 149.7, 137.8, 129.6, 125.2, 118.2, 111.2, 26.4; EI-MS m/z (relative intensity) 197 (28.3%), 195 (91.3%), 169 (15.6%), 167 (48.2%), 141 (25.2%), 140 (35.9%), 139 (75.5%), 138 (100%), 112 (25.3%). 5-Bromo-1-methylindoline-2,3-dione (2da).29 Compound 2da was isolated in 84% yield (202 mg, red crystal): mp 169−170 °C; 1H NMR (600 MHz, CDCl3) δ 7.71 (d, J = 8.3 Hz, 1H), 7.68 (s, 1H), 6.81 (d, J = 8.3 Hz, 1H), 3.24 (s, 3H); 13C NMR (101 MHz, CDCl3) δ 182.1, 157.4, 150.1, 140.6, 128.0, 118.5, 116.6, 111.6, 26.3; EI-MS m/z (relative intensity) 241 (98.0%), 239 (100%), 213 (67.5%), 211 (74.5%), 185 (71.3%), 184 (87.2%), 183 (77.7%), 182 (90.9%), 170 (19.0%), 156 (17.6%), 104 (15.4%), 77 (36.9%). 1,5,7-Trimethylindoline-2,3-dione (2ea). Compound 2ea was isolated in 91% yield (172 mg, red crystal): mp 155−156 °C; 1H NMR (600 MHz, CDCl3) δ 7.23 (s, 1H), 7.12 (s, 1H), 3.47 (s, 3H), 2.50 (s, 3H), 2.26 (s, 3H); 13C NMR (151 MHz, CDCl3) δ 184.0, 159.3, 146.7, 142.7, 133.6, 123.6, 121.6, 118.6, 29.6, 20.3, 18.6; EI-MS m/z (relative intensity) 189 (100%), 161 (40.9%), 133 (65.9%), 132 (81.1%), 91 (30.8%); HRMS (ESI-TOF) m/z [M + H]+ calcd for C11H12NO2 190.0863, found 190.0870. 1-Methylindoline-2,3-dione (2fa).28 Compound 2fa was isolated in 90% yield (145 mg, orange crystal): mp 129−131 °C; 1H NMR (600 MHz, CDCl3) δ 7.63−7.56 (m, 2H), 7.12 (t, J = 7.5 Hz, 1H), 6.89 (d, J = 7.8 Hz, 1H), 3.24 (s, 3H); 13C NMR (151 MHz, CDCl3) δ 183.3, 158.2, 151.4, 138.4, 125.3, 123.8, 117.4, 109.9, 26.2; EI-MS m/z (relative intensity) 161 (99.7%), 133 (51.9%), 104 (100%), 78 (33.4%). 6-Methoxy-1-methylindoline-2,3-dione (2ga).30 Compound 2ga was isolated in 92% yield (176 mg, red crystal): mp 197−198 °C; 1H NMR (400 MHz, CDCl3) δ 7.53 (d, J = 8.4 Hz, 1H), 6.52 (d, J = 8.4 Hz, 1H), 6.33 (s, 1H), 3.90 (s, 3H), 3.18 (s, 3H); 13C NMR (101 MHz, CDCl3) δ 180.7, 168.3, 159.6, 154.0, 127.9, 111.1, 107.9, 97.2, 56.2, 26.2; EI-MS m/z (relative intensity) 191 (100%), 163 (48.6%), 148 (33.4%), 135 (21.9%), 134 (28.6%), 120 (60.3%), 92 (22.2%). 1-Methyl-7-phenylindoline-2,3-dione (2ha). Compound 2ha was isolated in 87% yield (206 mg, red crystal): mp 212−213 °C; 1H NMR (600 MHz, CDCl3) δ 7.62 (d, J = 7.3 Hz, 1H), 7.48−7.39 (m, 4H), 7.38−7.33 (m, 2H), 7.13 (t, J = 7.5 Hz, 1H), 2.75 (s, 3H); 13C NMR (151 MHz, CDCl3) δ 183.5, 159.4, 148.0, 141.2, 137.1, 129.6, 128.5, 128.3, 127.4, 124.5, 123.3, 118.6, 30.2; EI-MS m/z (relative intensity) 237 (68.0%), 208 (10.6%), 181 (52.8%), 180 (100%), 152 (15.7%), 139 (9.9%), 90 (8.4%); HRMS (ESI-TOF) m/z [M + H]+ calcd for C15H12NO2 238.0863, found 238.0860. 1,7-Dimethylindoline-2,3-dione (2ia).18 Compound 2ia was isolated in 89% yield (156 mg, red crystal): mp 166−168 °C; 1H NMR (600 MHz, CDCl3) δ 7.43 (d, J = 7.3 Hz, 1H), 7.31 (d, J = 7.7 Hz, 1H), 6.98 (t, J = 7.5 Hz, 1H), 3.50 (s, 3H), 2.55 (s, 3H); 13C NMR (151 MHz, CDCl3) δ 183.7, 159.2, 149.0, 142.2, 123.8, 123.3, 121.9, 118.5, 29.7, 18.8; EI-MS m/z (relative intensity) 175 (100%), 147 (34.6%), 119 (60.0%), 118 (84.7%), 91 (34.1%). 3-Methyl-1H-benzo[e]indole-1,2(3H)-dione (2ja). Compound 2ja was isolated in 83% yield (175 mg, red crystal): mp 208−209 °C; 1 H NMR (400 MHz, CDCl3) δ 8.59 (d, J = 8.4 Hz, 1H), 8.13 (d, J = 8.6 Hz, 1H), 7.78 (d, J = 8.2 Hz, 1H), 7.64 (t, J = 7.7 Hz, 1H), 7.41 (t, J = 7.6 Hz, 1H), 7.12 (d, J = 8.6 Hz, 1H), 3.29 (s, 3H); 13C NMR (151 MHz, CDCl3) δ 182.4, 158.9, 154.7, 140.6, 131.3, 130.2, 129.1, 129.0, 125.5, 123.3, 110.0, 108.9, 26.2; EI-MS m/z (relative intensity) 211 (94.0%), 183 (51.3%), 155 (48.0%), 154 (100%), 140 (14.6%), 127 (25.0%), 113 (10.7%); HRMS (ESI-TOF) m/z [M + H]+ calcd for C13H10NO2 212.0706, found 212.0708. 5,6-Dihydro-4H-pyrrolo[3,2,1-ij]quinoline-1,2-dione (2ka).31 Compound 2ka was isolated in 80% yield (150 mg, red crystal): mp 222−223 °C; 1H NMR (600 MHz, CDCl3) δ 7.36 (d, J = 7.5 Hz, 1H), 7.31 (d, J = 7.6 Hz, 1H), 6.98 (t, J = 7.6 Hz, 1H), 3.77−3.72 (m, 2H), 2.77 (t, J = 6.0 Hz, 2H), 2.06−2.01 (m, 2H); 13C NMR (151 MHz, CDCl3) δ 183.9, 156.9, 147.6, 137.1, 123.2, 123.0, 121.9, 115.7, 38.4, 23.9, 20.2; EI-MS m/z (relative intensity) 187 (81.2%), 159 (80.8%), 158 (46.3%), 131 (64.3%), 130 (100%), 103 (15.7%), 92 (19.1%).

1-Ethylindoline-2,3-dione (2ab).32 Compound 2ab was isolated in 86% yield (151 mg, red crystal): mp 160−162 °C; 1H NMR (600 MHz, CDCl3) δ 7.58 (m, 2H), 7.10 (t, J = 7.2 Hz, 1H), 6.90 (d, J = 7.8 Hz, 1H), 3.77 (q, J = 7.0 Hz, 2H), 1.30 (t, J = 7.1 Hz, 3H); 13C NMR (151 MHz, CDCl3) δ 183.7, 157.8, 150.6, 138.4, 125.4, 123.6, 117.5, 110.0, 34.9, 12.5; EI-MS m/z (relative intensity) 175 (100%), 147 (19.8%), 132 (32.5%), 119 (58.2%), 118 (62.1%), 104 (59.4%). 1-Isopropylindoline-2,3-dione (2ac).31 Compound 2ac was isolated in 90% yield (170 mg, red crystal): mp 158−159 °C; 1H NMR (600 MHz, CDCl3) δ 7.59 (d, J = 7.3 Hz, 1H), 7.55 (t, J = 7.8 Hz, 1H), 7.08 (t, J = 7.5 Hz, 1H), 7.02 (d, J = 8.0 Hz, 1H), 4.59−4.47 (m, 1H), 1.52 (s, 6H); 13C NMR (151 MHz, CDCl3) δ 183.8, 157.8, 150.5, 138.1, 125.6, 123.2, 117.9, 111.3, 44.8, 19.4; EI-MS m/z (relative intensity) 189 (85.3%), 147 (13.2%), 146 (100%), 132 (68.5%), 118 (14.1%), 90 (24.9%). 1-Ethyl-7-methylindoline-2,3-dione (2bb). Compound 2bb was isolated in 86% yield (163 mg, red crystal): mp 154−155 °C; 1 H NMR (600 MHz, CDCl3) δ 7.45 (d, J = 7.3 Hz, 1H), 7.32 (d, J = 7.7 Hz, 1H), 6.99 (t, J = 7.5 Hz, 1H), 3.99 (q, J = 7.1 Hz, 2H), 2.51 (s, 3H), 1.32 (t, J = 7.1 Hz, 3H); 13C NMR (151 MHz, CDCl3) δ 184.1, 159.2, 148.4, 142.4, 123.7, 123.5, 121.4, 118.9, 36.9, 18.7, 14.6; EI-MS m/z (relative intensity) 189 (92.6%), 160 (14.2%), 146 (14.9%), 132 (22.7%), 118 (100%), 91 (24.4%); HRMS (ESI-TOF) m/z [M + H]+ calcd for C11H12NO2 190.0863, found 190.0871. 7-Methyl-1-propylindoline-2,3-dione (2bc). Compound 2bc was isolated in 88% yield (179 mg, red crystal): mp 160−161 °C; 1H NMR (600 MHz, CDCl3) δ 7.46 (d, J = 6.9 Hz, 1H), 7.32 (d, J = 7.0 Hz, 1H), 6.99 (t, J = 7.5 Hz, 1H), 3.93−3.82 (m, 2H), 2.49 (s, 3H), 1.78−1.67 (m, 2H), 0.99 (t, J = 7.4 Hz, 3H); 13C NMR (151 MHz, CDCl3) δ 184.1, 159.3, 148.6, 142.4, 123.7, 123.5, 121.4, 118.9, 43.5, 22.7, 18.7, 11.0; EI-MS m/z (relative intensity) 203 (100%), 161 (17.9%), 146 (68.1%), 132 (16.1%), 118 (78.5%), 91 (27.6%); HRMS (ESI-TOF) m/z [M + H]+ calcd for C12H14NO2 204.1019, found 204.1016. 1-Butyl-7-methylindoline-2,3-dione (2bd). Compound 2bd was isolated in 89% yield (193 mg, red crystal): mp 163−164 °C; 1 H NMR (600 MHz, CDCl3) δ 7.45 (d, J = 7.2 Hz, 1H), 7.32 (d, J = 7.7 Hz, 1H), 6.99 (t, J = 7.5 Hz, 1H), 3.94−3.88 (m, 2H), 2.50 (s, 3H), 1.74−1.61 (m, 2H), 1.49−1.36 (m, 2H), 0.96 (t, J = 7.4 Hz, 3H); 13 C NMR (151 MHz, CDCl3) δ 184.1, 159.3, 148.6, 142.4, 123.7, 123.5, 121.4, 118.9, 41.8, 31.5, 19.9, 18.8, 13.7; EI-MS m/z (relative intensity) 217 (80.0%), 189 (22.7%), 175 (20.1%), 160 (32.2%), 146 (100%), 118 (75.2%), 91 (31.9%); HRMS (ESI-TOF) m/z [M + H]+ calcd for C13H16NO2 218.1176, found 218.1184. 1-Isobutyl-7-methylindoline-2,3-dione (2be). Compound 2be was isolated in 89% yield (193 mg, red oil): 1H NMR (600 MHz, CDCl3) δ 7.46 (d, J = 7.3 Hz, 1H), 7.31 (d, J = 7.6 Hz, 1H), 6.99 (t, J = 7.5 Hz, 1H), 3.74 (d, J = 7.4 Hz, 2H), 2.48 (s, 3H), 2.11−1.92 (m, 1H), 0.97 (d, J = 6.7 Hz, 6H); 13C NMR (151 MHz, CDCl3) δ 184.0, 159.5, 148.8, 142.5, 123.8, 123.5, 121.6, 118.9, 49.0, 29.0, 19.8, 18.9; EI-MS m/z (relative intensity) 217 (62.5%), 161 (41.8%), 146 (100%), 118 (25.1%), 91 (24.5%); HRMS (ESI-TOF) m/z [M + H]+ calcd for C13H16NO2 218.1176, found 218.1177. 1-(Cyclopropylmethyl)-7-methylindoline-2,3-dione (2bf). Compound 2bf was isolated in 86% yield (185 mg, red oil): 1H NMR (600 MHz, CDCl3) δ 7.47 (d, J = 6.3 Hz, 1H), 7.34 (d, J = 7.0 Hz, 1H), 7.00 (t, J = 7.4 Hz, 1H), 3.85 (d, J = 6.5 Hz, 2H), 2.59 (s, 3H), 1.16−1.06 (m, 1H), 0.61−0.52 (m, 2H), 0.47 (m, 2H); 13C NMR (151 MHz, CDCl3) δ 184.1, 159.7, 148.9, 142.4, 123.7, 123.6, 121.5, 118.8, 45.9, 19.0, 11.3, 3.8; EI-MS m/z (relative intensity) 215 (40.87%), 185 (13.3%), 173 (8.8%), 160 (100%), 131 (11.4%), 104 (18.8%), 55 (25.4%); HRMS (ESI-TOF) m/z [M + H]+ calcd for C13H14NO2 216.1019, found 216.1020. 1-(Cyclohexylmethyl)-7-methylindoline-2,3-dione (2bg). Compound 2bg was isolated in 87% yield (224 mg, red oil): 1H NMR (600 MHz, CDCl3) δ 7.45 (d, J = 7.3 Hz, 1H), 7.31 (d, J = 7.6 Hz, 1H), 6.99 (t, J = 7.5 Hz, 1H), 3.75 (d, J = 6.8 Hz, 2H), 2.47 (s, 3H), 1.85−1.52 (m, 6H), 1.17 (t, J = 7.9 Hz, 3H), 1.08 (t, J = 10.8 Hz, 2H); 13C NMR (151 MHz, CDCl3) δ 184.1, 159.5, 148.8, 142.5, 123.7, 123.5, 121.6, 118.9, 47.8, 38.2, 30.4, 26.1, 25.7, 19.0; EI-MS m/z 9863

DOI: 10.1021/acs.joc.7b01480 J. Org. Chem. 2017, 82, 9859−9865

The Journal of Organic Chemistry

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(relative intensity) 257 (72.0%), 229 (22.4%), 186 (10.8%), 175 (31.4%), 161 (85.7%), 146 (100%), 133 (40.8%), 118 (31.1%), 91 (32.9%); HRMS (ESI-TOF) m/z [M + H]+ calcd for C16H20NO2 258.1489, found 258.1499. 1-Allyl-5-methylindoline-2,3-dione (2bh). Compound 2bh was isolated in 84% yield (169 mg, red oil): 1H NMR (600 MHz, CDCl3) δ 7.41 (s, 1H), 7.36 (d, J = 7.9 Hz, 1H), 6.78 (d, J = 8.0 Hz, 1H), 5.83 (dtd, J = 15.7, 10.5, 5.3 Hz, 1H), 5.33−5.26 (m, 2H), 4.34 (d, J = 5.3 Hz, 2H), 2.32 (s, 3H); 13C NMR (151 MHz, CDCl3) δ 183.5, 158.0, 148.6, 138.7, 133.6, 130.5, 125.7, 118.5, 117.6, 110.7, 42.5, 20.6; EI-MS m/z (relative intensity) 201 (85.8%), 173 (48.6%), 160 (19.6%), 144 (100%), 130 (30.4%); HRMS (ESI-TOF) m/z [M + H]+ calcd for C12H12NO2 202.0863, found 202.0858. 7-Methyl-1-phenethylindoline-2,3-dione (2bi). Compound 2bi was isolated in 75% yield (199 mg, red oil): 1H NMR (400 MHz, CDCl3) δ 7.49 (d, J = 7.2 Hz, 1H), 7.32 (m, 3H), 7.25 (m, 3H), 7.02 (t, J = 7.5 Hz, 1H), 4.23−4.09 (m, 2H), 3.07−2.94 (m, 2H), 2.55 (s, 3H); 13C NMR (101 MHz, CDCl3) δ 183.8, 159.3, 148.4, 142.4, 137.2, 128.8, 128.7, 127.0, 123.8, 123.7, 121.4, 118.9, 43.5, 35.4, 19.0; EI-MS m/z (relative intensity) 265 (52.8%), 231 (9.4%), 161 (16.4%), 158 (27.5%), 146 (100%), 104 (30.0%), 91 (27.1%); HRMS (ESITOF) m/z [M + H]+ calcd for C17H16NO2 266.1176, found 266.1177. 1-Benzyl-7-methylindoline-2,3-dione (2bj). Compound 2bj was isolated in 42% yield (105 mg, red oil): 1H NMR (600 MHz, CDCl3) δ 7.53 (d, J = 7.3 Hz, 1H), 7.34 (t, J = 7.4 Hz, 2H), 7.31−7.23 (m, 2H), 7.20 (d, J = 7.5 Hz, 2H), 7.01 (t, J = 7.5 Hz, 1H), 5.20 (s, 2H), 2.26 (s, 3H); 13C NMR (151 MHz, CDCl3) δ 183.6, 159.6, 148.6, 142.5, 136.2, 129.1, 127.7, 125.6, 124.0, 123.6, 122.0, 118.8, 45.3, 18.6; EI-MS m/z (relative intensity) 251 (67.3%), 194 (19.5%), 160 (100%), 118 (11.3%), 104 (16.9%), 91 (31.0%); HRMS (ESITOF) m/z [M + H]+ calcd for C16H14NO2 252.1019, found 252.1018. 1-Phenylindoline-2,3-dione (2ad).20a Compound 2ad was isolated in 81% yield (181 mg, red crystal): mp 133−135 °C; 1H NMR (600 MHz, CDCl3) δ 7.73−7.66 (m, 1H), 7.60−7.50 (m, 3H), 7.49−7.38 (m, 3H), 7.17 (t, J = 7.5 Hz, 1H), 6.89 (d, J = 8.1 Hz, 1H); 13 C NMR (151 MHz, CDCl3) δ 182.9, 157.3, 151.7, 138.3, 132.9, 129.9, 128.8, 126.0, 125.6, 124.3, 117.5, 111.3; EI-MS m/z (relative intensity) 223 (17.9%), 195 (100%), 167 (32.9%), 139 (6.7%), 92 (6.0%), 77 (10.2%). 5-Methyl-1-(p-tolyl)indoline-2,3-dione (2cd). Compound 2cd was isolated in 93% yield (233 mg, red crystal): mp 138−140 °C; 1H NMR (600 MHz, CDCl3) δ 7.48 (s, 1H), 7.33 (t, J = 7.3 Hz, 3H), 7.30−7.24 (m, 2H), 6.77 (d, J = 8.1 Hz, 1H), 2.42 (s, 3H), 2.34 (s, 3H); 13C NMR (151 MHz, CDCl3) δ 183.3, 157.5, 149.7, 138.7, 138.7, 134.0, 130.5, 130.4, 125.7, 125.7, 117.5, 111.1, 21.2, 20.7; EI-MS m/z (relative intensity) 251 (24.3%), 223 (100%), 208 (20.9%), 194 (23.6%), 180 (12.7%), 134 (13.1%); HRMS (ESI-TOF) m/z [M + H]+ calcd for C16H14NO2 252.1019, found 252.1018. 3-Phenyl-1H-benzo[e]indole-1,2(3H)-dione (2db). Compound 2db was isolated in 83% yield (227 mg, red crystal): mp 216−217 °C; 1 H NMR (400 MHz, CDCl3) δ 8.71 (d, J = 8.4 Hz, 1H), 8.06 (d, J = 8.7 Hz, 1H), 7.79 (d, J = 8.2 Hz, 1H), 7.69 (t, J = 7.6 Hz, 1H), 7.58 (t, J = 7.7 Hz, 2H), 7.53−7.39 (m, 4H), 7.09 (d, J = 8.7 Hz, 1H); 13C NMR (151 MHz, CDCl3) δ 181.9, 158.0, 154.9, 140.4, 132.9, 131.5, 130.4, 130.0, 129.3, 129.0, 128.8, 126.3, 125.8, 123.6, 111.3, 109.3; EIMS m/z (relative intensity) 273 (29.5%), 245 (100%), 217 (21.6%), 189 (7.8%), 108 (12.2%); HRMS (ESI-TOF) m/z [M + H]+ calcd for C18H12NO2 274.0863, found 274.0868. 5-Methyl-1-phenylindoline-2,3-dione (2cc) and 1-(p-Tolyl)indoline-2,3-dione (2cd).20a A mixture of 2cc and 2cd was isolated in 92% yield (218 mg, red oil): 1H NMR (600 MHz, CDCl3) δ 7.66 (d, J = 7.4 Hz, 1H), 7.58−7.46 (m, 5H), 7.41−7.34 (m, 4H), 7.34 (t, J = 6.4 Hz, 3H), 7.31−7.24 (m, 2H), 7.15 (t, J = 7.5 Hz, 1H), 6.86 (d, J = 8.0 Hz, 1H), 6.80 (d, J = 8.1 Hz, 1H), 2.42 (s, 3H), 2.35 (s, 3H); 13C NMR (151 MHz, CDCl3) δ 183.1, 183.0, 157.4 (two 13C), 151.9, 149.5, 138.9, 138.8, 138.3, 134.2, 133.1, 130.5, 130.2, 129.9, 129.6, 128.6, 125.8 (two 13C), 125.5, 124.2, 117.5 (two 13C), 111.3, 111.1, 21.2, 20.7; EI-MS m/z (relative intensity) 237 (23.5%), 209 (100%), 180 (44.3%), 152 (5.6%), 134 (5.8%), 77 (11.1%).

Note

ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.joc.7b01480. Copies of all 1H NMR and 13C NMR spectra of all compounds and HRMS spectra of the reaction intermediates (PDF)

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AUTHOR INFORMATION

Corresponding Authors

*E-mail: [email protected]. *E-mail: [email protected]. ORCID

Xiaodong Jia: 0000-0002-0120-8255 Author Contributions

H.J. and Y.Z. contributed equally to this work. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS

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REFERENCES

This work was financially supported by the National Natural Science Foundation of China (NNSFC, 21362030 and 21562038). The authors thank the Jiangsu Provincial Natural Science Foundation (BK20161328) for financial support.

(1) For reviews of C−H activation, see: (a) Alberico, D.; Scott, M. E.; Lautens, M. Chem. Rev. 2007, 107, 174−238. (b) Lyons, T. W.; Sanford, M. S. Chem. Rev. 2010, 110, 1147−1169. (c) Cheng, C.; Hartwig, J. F. Chem. Rev. 2015, 115, 8946−8975. (d) Liu, C.; Yuan, J.; Gao, M.; Tang, S.; Li, W.; Shi, R.; Lei, A. Chem. Rev. 2015, 115, 12138−12204. (2) For recent examples of sp2 C−H activation, see: (a) Zhang, G.; Liu, C.; Yi, H.; Meng, Q.; Bian, C.; Chen, H.; Jian, J.-X.; Wu, L.-Z.; Lei, A. J. Am. Chem. Soc. 2015, 137, 9273−9280. (b) Lee, T.; Wilson, T. W.; Berg, R.; Ryberg, P.; Hartwig, J. F. J. Am. Chem. Soc. 2015, 137, 6742−6745. (c) Kong, W.-J.; Liu, Y.-J.; Xu, H.; Chen, Y.-Q.; Dai, H.X.; Yu, J.-Q. J. Am. Chem. Soc. 2016, 138, 2146−2149. (d) Liu, B.; Huang, Y.; Lan, J.; Song, F.; You, J. Chem. Sci. 2013, 4, 2163−2167. (e) Liang, Y.-F.; Wang, X.; Yuan, Y.; Liang, Y.; Li, X.; Jiao, N. ACS Catal. 2015, 5, 6148−6152. (f) Ye, J.; Lautens, M. Nat. Chem. 2015, 7, 863−870. (3) He, J.; Wasa, M.; Chan, K. S. L.; Shao, Q.; Yu, J.-Q. Chem. Rev. 2017, 117, 8754−8786. (4) (a) He, J.; Shao, Q.; Wu, Q.; Yu, J.-Q. J. Am. Chem. Soc. 2017, 139, 3344−3347. (b) Wu, Y.; Chen, Y.-Q.; Liu, T.; Eastgate, M. D.; Yu, J.-Q. J. Am. Chem. Soc. 2016, 138, 14554−14557. (c) Jain, P.; Verma, P.; Xia, G.; Yu, J.-Q. Nat. Chem. 2016, 9, 140−144. (d) Chen, G.; Gong, W.; Zhuang, Z.; Andra, M. S.; Chen, Y.-Q.; Hong, X.; Yang, Y.-F.; Liu, T.; Houk, K. N.; Yu, J.-Q. Science 2016, 353, 1023−1027. (5) (a) Liu, C.; Liu, D.; Lei, A. Acc. Chem. Res. 2014, 47, 3459−3470. (b) Bonin, H.; Sauthier, M.; Felpin, F.-X. Adv. Synth. Catal. 2014, 356, 645−671. (c) Guo, S.; Kumar, P. S.; Yang, M. Adv. Synth. Catal. 2017, 359, 2−25. (6) (a) Zhang, L.; Hang, Z.; Liu, Z.-Q. Angew. Chem., Int. Ed. 2016, 55, 236−239. (b) Qin, G.; Chen, X.; Yang, L.; Huang, H. ACS Catal. 2015, 5, 2882−2885. (c) Ke, J.; Tang, Y.; Yi, H.; Li, Y.; Cheng, Y.; Liu, C.; Lei, A. Angew. Chem., Int. Ed. 2015, 54, 6604−6607. (d) Zhang, J.; Li, Y.; Zhang, F.; Hu, C.; Chen, Y. Angew. Chem., Int. Ed. 2016, 55, 1872−1875. (e) Wang, Y.; Li, G.-X.; Yang, G.; He, G.; Chen, G. Chem. Sci. 2016, 7, 2679−2683. (f) Huang, H.; Cai, J.; Ji, X.; Xiao, F.; Chen, Y.; Deng, G.-J. Angew. Chem., Int. Ed. 2016, 55, 307−311. 9864

DOI: 10.1021/acs.joc.7b01480 J. Org. Chem. 2017, 82, 9859−9865

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The Journal of Organic Chemistry (7) (a) Viehe, H.; Janousek, Z.; Merényi, R.; Stella, L. Acc. Chem. Res. 1985, 18, 148−154. (b) Bordwell, F. G.; Lynch, T.-Y. J. Am. Chem. Soc. 1989, 111, 7558−7562. (8) Jia, X.-D.; Zhu, Y.-Z.; Yuan, Y.; Zhang, X.-W.; Lu, S.-W.; Zhang, L.; Luo, L.-L. ACS Catal. 2016, 6, 6033−6036. (9) (a) Sumpter, W. C. Chem. Rev. 1944, 34, 393−434. (b) Singh, G. S.; Desta, Z. Y. Chem. Rev. 2012, 112, 6104−6155. (10) Han, K.; Zhou, Y.; Liu, F.; Guo, Q.; Wang, P.; Yang, Y.; Song, B.; Liu, W.; Yao, Q.; Teng, Y.; Yu, P. Bioorg. Med. Chem. Lett. 2014, 24, 591−594. (11) Verma, M. P.; Pandeya, S. N.; Singh, K. N.; Stables, J. P. Acta Pharm. 2004, 54, 49−56. (12) Chohan, Z. H.; Pervez, H.; Rauf, A.; Khan, K. M.; Supuran, C. T. J. Enzyme Inhib. Med. Chem. 2004, 19, 417−423. (13) Jiang, T.; Kuhen, K. L.; Wolff, K.; Yin, H.; Bieza, K.; Caldwell, J.; Bursulaya, B.; Tuntland, T.; Zhang, K.; Karanewsky, D.; He, Y. Bioorg. Med. Chem. Lett. 2006, 16, 2109−2112. (14) Prakash, C. R. R.; Raja, S.; Saravanan, G. International Journal of Pharmaceutical Technology and Biotechnology 2010, 1, 105. (15) (a) Pawar, V.; Lokwani, D.; Bhandari, S.; Mitra, D.; Sabde, S.; Bothara, K.; Madgulkar, A. Bioorg. Med. Chem. 2010, 18, 3198−3211. (b) Lai, Y.; Ma, L.; Huang, W.; Yu, X.; Zhang, Y.; Ji, H.; Tian, J. Bioorg. Med. Chem. Lett. 2010, 20, 7349−7353. (c) Uddin, M. K.; Reignier, S. G.; Coulter, T.; Montalbetti, C.; Granas, C.; Butcher, S.; Krog-Jensen, C.; Felding, J. Bioorg. Med. Chem. Lett. 2007, 17, 2854−2857. (d) Boucherif, A.; Yang, Q. Q.; Wang, Q.; Chen, J. R.; Lu, L. Q.; Xiao, W. J. J. Org. Chem. 2014, 79, 3924−3929. (e) Liu, Y.-L.; Liao, F.-M.; Niu, Y.-F.; Zhao, X.-L.; Zhou, J. Org. Chem. Front. 2014, 1, 742−747. (16) (a) Erdmann, O. L. J. Prakt. Chem. 1840, 19, 321. (b) Laurent, A. Ann. Chim. Phys. 1840, 3, 393. (17) (a) Ilangovan, A.; Satish, G. Org. Lett. 2013, 15, 5726−5729. (b) Liu, Y.; Chen, H.; Hu, X.; Zhou, W.; Deng, G.-J. Eur. J. Org. Chem. 2013, 2013, 4229−4232. (c) Ilangovan, A.; Satish, G. J. Org. Chem. 2014, 79, 4984−4991. (d) Raghavender Reddy, M.; Nageswara Rao, N.; Ramakrishna, K.; Meshram, H. M. Tetrahedron Lett. 2014, 55, 4758−4762. (e) Gao, F.-F.; Xue, W.-J.; Wang, J.-G.; Wu, A.-X. Tetrahedron 2014, 70, 4331−4335. (18) Tang, B.-X.; Song, R.-J.; Wu, C.-Y.; Liu, Y.; Zhou, M.-B.; Wei, W.-T.; Deng, G.-B.; Yin, D.-L.; Li, J.-H. J. Am. Chem. Soc. 2010, 132, 8900−8902. (19) Li, W.; Duan, Z.; Zhang, X.; Zhang, H.; Wang, M.; Jiang, R.; Zeng, H.; Liu, C.; Lei, A. Angew. Chem., Int. Ed. 2015, 54, 1893−1896. (20) (a) Rogness, D. C.; Larock, R. C. J. Org. Chem. 2011, 76, 4980− 4986. (b) Satish, G.; Polu, A.; Ramar, T.; Ilangovan, A. J. Org. Chem. 2015, 80, 5167−5175. (c) Zi, Y.; Cai, Z.-J.; Wang, S.-Y.; Ji, S.-J. Org. Lett. 2014, 16, 3094−3097. (21) (a) Shi, F.; Xing, G.-J.; Zhu, R.-Y.; Tan, W.; Tu, S. Org. Lett. 2013, 15, 128−131. (b) Wang, C.-S.; Zhu, R.-Y.; Zheng, J.; Shi, F.; Tu, S.-J. J. Org. Chem. 2015, 80, 512−520. (c) Dai, W.; Jiang, X.-L.; Wu, Q.; Shi, F.; Tu, S.-J. J. Org. Chem. 2015, 80, 5737−5744. (d) Shi, F.; Tao, Z.-L.; Luo, S.-W.; Tu, S.-J.; Gong, L.-Z. Chem. - Eur. J. 2012, 18, 6885−6894. (e) Dai, W.; Lu, H.; Li, X.; Shi, F.; Tu, S.-J. Chem. - Eur. J. 2014, 20, 11382−11389. (22) Huo, C.; Yuan, Y.; Wu, M.; Jia, X.; Wang, X.; Chen, F.; Tang, J. Angew. Chem., Int. Ed. 2014, 53, 13544−13547. (23) (a) Luo, L.; Zhao, X.; Zhang, L.; Yuan, Y.; Lü, S.; Jia, X.-D. Tetrahedron Lett. 2016, 57, 5830−5833. (b) Rohlmann, R.; Stopka, T.; Richter, H.; Garcı ́a Mancheño, O. J. Org. Chem. 2013, 78, 6050−6064. (24) For reviews of C−N bond cleavage, see: (a) Ouyang, K.; Hao, W.; Zhang, W.-X.; Xi, Z. Chem. Rev. 2015, 115, 12045−12090. (b) Wang, Q.; Su, Y.; Li, L.; Huang, H. Chem. Soc. Rev. 2016, 45, 1257−1272. (25) Lewis, J. R. Nat. Prod. Rep. 1994, 11, 329−332. (26) (a) Richter, H.; Garcı ́a Mancheño, O. Org. Lett. 2011, 13, 6066−6069. (b) Jia, X.-D.; Peng, F.; Qing, C.; Huo, C.; Wang, X. Org. Lett. 2012, 14, 4030−4033. (c) Jia, X.-D.; Wang, Y.; Peng, F.; Huo, C.; Yu, L.; Liu, J.; Wang, X. J. Org. Chem. 2013, 78, 9450−9456. (d) Wang, Y.; Peng, F.; Liu, J.; Huo, C.; Wang, X.; Jia, X.-D. J. Org. Chem. 2015, 80, 609−614.

(27) At present, the cationic cyclization (Friedel−Crafts type reaction) could not be fully ruled out. (28) McAllister, L. A.; McCormick, R. A.; James, K. M.; Brand, S.; Willetts, N.; Procter, D. J. Chem. - Eur. J. 2007, 13, 1032−1046. (29) Beauchard, A.; Ferandin, Y.; Frère, S.; Lozach, O.; Blairvacq, M.; Meijer, L.; Thiéry, V.; Besson, T. Bioorg. Med. Chem. 2006, 14, 6434− 6443. (30) Grougnet, R.; Magiatis, P.; Fokialakis, N.; Mitaku, S.; Skaltsounis, A.-L.; Tillequin, F.; Sévenet, T.; Litaudon, M. J. Nat. Prod. 2005, 68, 1083−1086. (31) Liu, T.; Yang, H.; Jiang, Y.; Fu, H. Adv. Synth. Catal. 2013, 355, 1169−1176. (32) Soltani Rad, M. N.; Khalafi-Nezhad, A.; Babamohammadi, S.; Behrouz, S. Helv. Chim. Acta 2010, 93, 2454−2466.

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DOI: 10.1021/acs.joc.7b01480 J. Org. Chem. 2017, 82, 9859−9865