Rhodium-Catalyzed Cyclocarbonylation of Ketimines via C–H Bond

Mar 9, 2016 - A novel rhodium-catalyzed oxidative cyclocarbonylation of ketimines via cleavage of two C–H bonds was established, which provided a di...
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Rhodium-Catalyzed Cyclocarbonylation of Ketimines via C−H Bond Activation Bao Gao,†,‡ Song Liu,†,§ Yu Lan,*,§ and Hanmin Huang*,† †

State Key Laboratory for Oxo Synthesis and Selective Oxidation, Lanzhou Institute of Chemical Physics, Chinese Academy of Sciences, Lanzhou 730000, People’s Republic of China ‡ University of Chinese Academy of Sciences, Beijing 100049, People’s Republic of China § School of Chemistry and Chemical Engineering, Chongqing University, Chongqing 400030, People’s Republic of China S Supporting Information *

ABSTRACT: A novel rhodium-catalyzed oxidative cyclocarbonylation of ketimines via cleavage of two C−H bonds was established, which provided a direct and reliable method for the synthesis of a wide range of 3-methyleneisoindolin-1-ones with mostly moderate yields. Preliminary experimental mechanistic studies and DFT calculations revealed that this reaction proceeds via imine−enamine tautomerization, N−H cleavage, C−H bond activation, CO insertion, and reductive elimination. The mechanism studies further ruled out an isolated cyclometalated rhodium complex being involved in the present reaction, which was different from many other documented rhodium-catalyzed C−H cyclization reactions.

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INTRODUCTION Transition-metal-catalyzed transformation of aromatic C−H bonds assisted by a directing group represents a burgeoning field in synthetic organic chemistry, because it inherently enables the efficient construction of organic building blocks to prepare a wide range of useful compounds.1 However, the directing group itself in most such reactions remains intact during the reaction and has to be removed after the C−H functionalization process, which leads to lower atom and step economy. One way to circumvent this drawback is developing some certain effective C−H annulation processes, in which the directing group could be utilized as a reactive moiety to be incorporated into the desired product. In this vein, transitionmetal-catalyzed C−H bond activation and subsequent cyclization with alkynes, alkenes, and CO has evolved into one of the most powerful methods in the construction of various heterocycles.2,3 Ketimines are versatile chemicals which have been extensively utilized as effective synthons for transition-metalcatalyzed C−C and C−N bond forming reactions.4 Due to the lower barrier energy, the nucleophilic enamine species II could be facilely formed by tautomerization of ketimine I. The enamine species II would be expected to be trapped by an electrophilic palladium via electrophilic palladation to form an alkylpalladium species. The resulting alkylpalladium complex has proved to be a reactive species to initiate various C−H cyclization reactions that take place between the α-carbon and N atom or the protecting group of the imine (Scheme 1, eq 1).5 As for the rhodium-catalyzed C−H cyclization of ketimines, a cyclometalated rhodium complex was usually generated and proposed as a key active species, which was capable of © XXXX American Chemical Society

Scheme 1. Catalyst-Controlled C−H Cyclization of Ketimines: (1) Palladium-Catalyzed Cyclization of Ketimines, (2) Rhodium-Catalyzed Cyclization of Ketimines, (3) New Strategy for Rhodium-Catalyzed Cyclocarbonylation of Ketimines

cyclization with alkynes or alkenes to form various nitrogenated heterocycles by connecting the N atom with the phenyl ring of the aromatic imines (Scheme 1, eq 2).6 In contrast to the Pdcatalyzed C−H cyclization protocols, the α-carbon of ketimine remained intact in these rhodium-catalyzed cyclizations. As a Special Issue: Organometallics in Asia Received: January 30, 2016

A

DOI: 10.1021/acs.organomet.6b00072 Organometallics XXXX, XXX, XXX−XXX

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Organometallics Table 1. Screening of Reaction Conditionsa

result, the protecting groups attached to the N atom of the imines had to be removed or superstoichiometric amounts of inorganic salts were required to facilitate the cyclization process, which largely reduced the atom economy and appeal of the large-scale applications of these C−H cyclization reactions. To circumvent these problems and in connection with our interests in the area of carbonylation reactions,7 herein we describe a novel strategy to realize a new type of C−H cyclization of ketimines by using rhodium as a catalyst, in which both the C(sp3)−H bond on the α-carbon and the C(sp2)−H bond of ketimines were cleaved. DFT calculations suggested that the C(sp3)−H bond was cleaved prior to the C(sp2)−H bond of the ketimine, which was different from many other Rhcatalyzed C−H cyclization reactions.2 Notably, this protocol provides an efficient and reliable approach to 3-methyleneisoindolin-1-ones, which not only are key structure motifs in a myriad of nature products but also serve as important building blocks for the synthesis of important pharmaceuticals.8

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RESULTS AND DISCUSSION To validate the feasibility of our hypothesis, we initially synthesized the novel cyclometalated rhodium complex A by treating the ketimine 1a with [Cp*RhCl2]2 in the presence of NaOAc at room temperature for 48 h. The desired fivemembered cyclometalated RhIII complex A was isolated in 82% yield (Scheme 2), whose structure was characterized by HRMS Scheme 2. Formation of Isoindolin-1-one 2a from Ketimine 1a

entry

catalyst

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

[Cp*RhCl2]2 RhCl(PPh3)3 [Rh(OAc)2]2 [Rh(COD)Cl]2 [Cp*RhCl2]2/AgSbF6 [Cp*RhCl2]2/AgOTf [Cp*RhCl2]2/AgBF4 [Cp*RhCl2]2/AgNO3 [Cp*RhCl2]2/AgClO4 [Cp*RhCl2]2/AgNO3 [Cp*RhCl2]2/AgNO3 [Cp*RhCl2]2/AgNO3 [Cp*RhCl2]2/AgNO3 [Cp*RhCl2]2/AgNO3 [Cp*RhCl2]2/AgNO3 [Cp*RhCl2]2/AgNO3 [Cp*RhCl2]2/AgNO3 [Cp*RhCl2]2/AgNO3 [Cp*RhCl2]2/AgNO3 [Cp*RhCl2]2/AgNO3

base (amt (mol %))

yield (%)c

Li2CO3 (20) Na2CO3 (20) K2CO3 (20) Cs2CO3 (20) Ca2CO3 (20) K2CO3 (10) K2CO3 (25) K2CO3 (30) K2CO3 (40) K2CO3 (50) K2CO3 (25)

25 11 14 15 16 13 27 45 25 42 39 56 50 48 49 59 51 47 31 65 (63)d

a Reaction conditions: 1a (0.5 mmol), [Rh] (4 mol %), silver salt (8 mol %), Cu(OAc)2 (1.0 mmol), toluene (1 mL), CO (30 atm), 140 °C, 16 h. bAc2O (10 mol %) was added. cYields determined by GC using n-hexadecane as internal standard. dIsolated yield.

electrophilic rhodium complex. The results showed that a relatively good yield was afforded (45% yield) when 8 mol % of AgNO3 was utilized (Table 1, entry 8). Because the acid released by the C−H cleavage step during the reaction process might decompose the imine moiety, supe stoichiometric amounts of bases (1.0−2.0 equiv), such as NaOAc, K2CO3, K3PO4 and Et3N, were tested and introduced into this reaction. To our disappointment, the reaction was inhibited completely and no target molecule was obtained. We speculated that too great an amount of base may inhibit the C−H cleavage step of ketimines. Thus, we decreased the loading of the base and found that the yield of 2a was indeed increased to 59% when 25 mol % of K2CO3 was added to the reaction system (Table 1, entry 16). Moreover, on addition of 10 mol % of acetic anhydride to the reaction system, the yield of 2a could be further increased to 65% (Table 1, entry 20). The variation of other reaction parameters, such as reaction time, temperature, pressure of CO, and solvent, was unfavorable for this reaction (see the Supporting Information). With the optimized reaction conditions in hand, the oxidative C−H cyclocarbonylation was then carried out with various ketimines to explore the generality and scope of this new reaction. As shown in Table 2, a series of 3-methyleneisoindolin-1-ones could be obtained in moderate to good yields from the corresponding imines derived from substituted anilines and acetophenones. Substrates with electron-donating groups on the phenyl ring of the acetophenones, such as methyl and methoxyl, were compatible with the reaction conditions to give the corresponding products in good yields (Table 2, 2a−c). Interestingly, imine 1e bearing β-hydrogen atoms could participate in the reaction to afford the desired product 2e in

and X-ray crystallography.9 Subsequently, we investigated the stoichiometric reaction of the metal complex A with CO in the presence of AgNO3 (1.0 equiv) and K2CO3 (1.0 equiv) at 140 °C. To our delight, the resulting five-membered RhIII species could react with CO to give the desired product in 38% yield (Scheme 2). Although the reaction conversion was low, this result revealed that the cyclocarbonylation of ketimine 1a with CO via cleavage of two C−H bonds would be indeed possible. Intrigued by this promising result, we sought to establish a catalytic reaction by exploring a suitable oxidant to sustain the catalytic cycle. On the basis of the preliminary investigation above, we initially focused on exploring conditions using readily available rhodium catalysts. As shown in Table 1, the desired product 2a could be obtained with a series of rhodium catalysts, and a relatively good yield (25%) was afforded when the reaction was conducted with [Cp*RhCl2]2 (2 mol %) as the catalyst under a CO atmosphere (30 atm) (Table 1, entry 1). Encouraged by these results, we then investigated the effect of different silver salts, which could act as promoters to remove the chloride anion from the [Cp*RhCl2]2 complex to generate a more active B

DOI: 10.1021/acs.organomet.6b00072 Organometallics XXXX, XXX, XXX−XXX

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Organometallics Table 2. Substrate Scope of Iminesa

demonstrated that the yields were not dramatically increased (Table 2, 2q−t). The structures of products 2q,t were confirmed by X-ray crystallography (see the Supporting Information).9 The mechanism of this oxidative C−H cyclocarbonylation was briefly investigated. First, we probed the nature of the aromatic C−H bond activation step by an intramolecular competition experiment using monodeuterated imine D1-1a, which exhibited an inverse KIE of 0.7 (Scheme 3a). This result Scheme 3. H/D Kinetic Isotope Effect Experiments: (a) Intramolecular KIE Effect and (b) Intermolecular KIE Effect

indicated that the C−H bond metalation is reversible.10 On the other hand, an intermolecular competition reaction of ketimine 1a and its pentadeuterated analogue D5-1a exhibited a KIE of 2.4 (Scheme 3b). This result suggested that C−H cleavage at the ortho position of the ketimine might be involved in the rate-limiting step. On the basis of previous reports 5 and preliminary mechanistic studies, two postulated pathways were proposed to account for this Rh-catalyzed C−H bond activation/ cyclocarbonylation of ketimine shown in Figure 1. The catalytic cycle was likely initiated by the removal of chloride of [Cp*RhCl2]2 promoted by Ag+ to generate an active species. In path I, the rhodium species was coordinated with 1a to form the five-membered rhodacycle A via ortho C−H bond

a

Reaction conditions: 1 (0.5 mmol), [Cp*RhCl2]2 (2 mol %), AgNO3 (8 mol %), Cu(OAc)2 (1.0 mmol), K2CO3 (25 mol %), Ac2O (10 mol %), toluene (1 mL), CO (30 atm), 140 °C, 16 h. Isolated yield. bZ/E ratio shown in parentheses was determined by GC and GC-MS analysis.

50% isolated yield with both Z/E isomers (Z/E = 42/58). Moreover, imine 1f derived from 2-acetonaphthone could also be converted into the isoindolin-1-one smoothly, providing the corresponding product 2f in 50% yield. However, substrates with electron-withdrawing groups on the acetophenones were ineffective. Subsequently, the effect of an amino moiety of the ketimines was also investigated (Table 2, 2g−p). The results demonstrated that the reaction of substrates derived from aromatic amines containing electron-donating and -withdrawing functional groups all proceeded smoothly. Generally, substrates with electron-donating groups on the aromatic ring of the amines worked more efficiently than those with electronwithdrawing groups. However, a highly sterically hindered substrate (2h) afforded a relatively low yield. When aliphatic amine 1o was utilized, only a trace amount of the desired product 2o was obtained. Considering the fact that electrondonating groups on the aromatic rings are favorable for this transformation, substrates containing electron-donating groups on both of the two aromatic rings of ketimines were subjected to the reaction conditions. The corresponding results

Figure 1. Plausible reaction mechanism. C

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Figure 2. Free energy profiles and geometry information for the Rh-catalyzed C−H bond activation/carbonylation/cyclization of ketimine. The values given in kcal/mol are the relative free energies calculated by the M11-L method in toluene. The values in parentheses are the relative free energies calculated by the B3LYP method in the gas phase. The values for the bond lengths are given in Å.

shown in Figure 2. In pathway I, the active catalyst CP1, which was set to relative zero, could be coordinated with imine 1a to form the intermediate CP2 with an energy barrier of 15.6 kcal mol−1. The concerted metalation−deprotonation took place via the transition state TS1 with an overall activation free energy barrier of 40.8 kcal mol−1, in which the intermediate CP3 would be endothermically generated. The following deprotonation of the methyl group occurred via the transition state TS2 with an energy barrier of 29.6 kcal mol−1 to form the intermediate CP4, which coordinated with one molecule of carbon monoxide to form the intermediate CP5 irreversibly. The following carbonyl insertion via the transition state TS3 generated the six-membered rhodacycle CP6, which was stabilized by the coordination of another molecule of carbon monoxide. The reductive elimination of intermediate CP7 via the transition state TS4 formed a new C−N bond with an

activation. The following electrophilic deprotonation of the C(sp3)−H bond of the methyl group generated intermediate D. The insertion of CO into the rhodium−carbon bond of intermediate D gave the six-membered rhodacycle E. Reductive elimination afforded the target molecule 2a and Cp*RhI intermediate F, which was oxidized by Cu(OAc)2 to regenerate the active species Cp*RhIIIX2. Alternatively, the key intermediate D could be generated via path II. First, imine 1a could be isomerized to enamine 1a′, which could react with Cp*RhIIIX2 to form intermediate B. Intermediate C could be generated by the following ortho C−H bond activation of intermediate B. Subsequent isomerization offered the intermediate D. Density functional theory (DFT) calculations were employed to further clarify the mechanism for this reaction. The free energy profiles calculated by the newly developed DFT method M11-L11 for the two plausible pathways are D

DOI: 10.1021/acs.organomet.6b00072 Organometallics XXXX, XXX, XXX−XXX

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overall activation free energy of 3.6 kcal mol−1. The coordination of CO and release of product 2a afforded the Cp*RhI intermediate CP9. In path II, the imine−enamine tautomerization of 1a tended to form enamine 1a′. The active catalyst CP1 could be alternatively coordinated with enamine 1a′ to form intermediate CP10 with an energy barrier of 15.0 kcal mol−1. The N−H bond was cleaved via the transition state TS5 with an overall energy barrier of 27.4 kcal mol−1, which led to forming the iminoethylrhodium intermediate CP11. The C(sp2)−H bond was cleaved via the transition state TS6 to form the intermediate CP12. The subsequent isomerization of CP12 offered the common intermediate CP4. In comparison with path I, the relative free energy of transition state TS5 is 13.4 kcal mol−1 lower than that of transition state TS1. Therefore, path II is favorable because the formation of a Rh−C bond is helpful for the metalation−deprotonation. Alternatively, the concerted metalation−deprotonation of CP2 could take place via the transition state TS7 to form the four-membered rhodacycle CP13, which was 22.5 kcal mol−1 higher than that of TS5, indicating that CP2 may not be involved in the present catalytic cycle. On the other hand, the concerted metalation− deprotonation of CP11 could also take place via transition state TS8 to form intermediate CP14. However, the relative free energy of the transition state TS8 was 4.3 kcal mol−1 higher than that of TS6. Therefore, this pathway could also be ruled out. Additionally, the intermediate CP4 can be protonated by acetic acid via transition state TS2 only with an energy barrier of 15.8 kcal mol−1 in the absence of CO. This result indicated that the Rh complex A can be facilely formed by the protonation of intermediate D. Furthermore, the relative free energy of Rh complex A was −3.5 kcal mol−1, which suggested that it could be easily prepared through the stoichiometric reaction of 1a with [Cp*RhCl2]2, but it hardly reacted with CO to furnish the catalytic cycle, as exemplified by the lower yield obtained in the stoichiometric carbonylation reaction (Scheme 1). In summary, the DFT calculations suggested that the mechanism for the reported reaction contains imine−enamine tautomerization, N−H bond cleavage, ortho metalation− deprotonation, CO insertion, C−N bond reductive elimination, and oxidation to regenerate the active catalyst. The computational studies also indicated that the activation barrier of the metalation−deprotonation of the transition state TS6 was only 21.9 kcal mol−1, which was consistent with the inverse KIE of 0.7 (Scheme 3a).

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EXPERIMENTAL SECTION

General Experiment Details and Materials. All nonaqueous reactions and manipulations were carried out with standard Schlenk techniques. All solvents before use were dried, degassed by standard methods, and stored under an argon atmosphere. All reactions were monitored by TLC with silica gel coated plates. NMR spectra were recorded on Bruker Avance III (400 MHz) spectrometers. Chemical shifts are reported in parts per million (ppm) downfield from TMS with the solvent resonance as the internal standard. Coupling constants (J) are reported in Hz and referred to apparent peak multiplications. High-resolution mass spectra (HRMS) were recorded on a Bruker MicroTOF-QII mass instrument (ESI). Ketimines used here were known compounds and were synthesized according to the reported methods.12 Synthesis of Rh Complex A Species. N-(1-Phenylethylidene)aniline (1a; 31.8 mg, 0.163 mmol), [Cp*RhCl2]2 (50 mg, 0.08 mmol), PhC(O)Me (9.3 uL, 0.08 mmol), NaOAc (16.5 mg, 0.20 mmol), and CH2Cl2 (8.0 mL) were placed in a 50 mL flame-dried Young-type tube under a nitrogen atmosphere. The mixture was stirred at room temperature for 48 h. The reaction mixture was filtered and concentrated under vacuum. The residue was carefully washed with dried hexane (2 × 5 mL) to remove unreacted materials to give the red Rh complex A (61.0 mg, 82% yield), which was further purified by recrystallization using CH2Cl2/hexane. Complex A was characterized by X-ray and HRMS (see the Supporting Information). General Procedure for Synthesis of 3-Methyleneisoindolin1-ones. A mixture of ketimine 1 (0.5 mmol), [Cp*RhCl2]2 (6.8 mg, 0.01 mmol), AgNO3 (6.8 mg, 8 mol %), K2CO3 (17.3 mg, 25 mol %), Ac2O (4.7 μL, 10 mol %), and toluene (1 mL) was placed in a glass tube which was placed in an autoclave. Then the autoclave was purged three times with CO and charged with CO at 30 atm. The reaction mixture was stirred at 140 °C for 16 h and then cooled to room temperature. After the pressure was carefully released, solvent was removed under reduced pressure. The residue was purified by flash column chromatography on silica gel to give the desired product 2. 3-Methylene-2-phenylisoindolin-1-one (2a). The title compound was prepared according to the general procedure and purified by flash column chromatography to give a pale yellow solid: 69.2 mg, 63% yield; 1H NMR (400 MHz, CDCl3) δ 7.92 (d, J = 7.6 Hz, 1H), 7.75 (d, J = 7.6 Hz, 1H), 7.62 (t, J = 7.6 Hz, 1H), 7.50−7.58 (m, 3H), 7.37−7.43 (m, 3H), 5.23 (d, J = 2.0 Hz, 1H), 4.80 (d, J = 2.4 Hz, 1H); 13 C NMR (100 MHz, CDCl3) δ 166.7, 143.1, 136.3, 134.6, 132.3, 129.8, 129.4, 128.9, 128.1, 128.1, 123.6, 120.1, 90.5; HRMS (ESI) calcd for C15H11NONa [M + Na] 244.0733, found 244.0738. 6-Methyl-3-methylene-2-phenylisoindolin-1-one (2b). The title compound was prepared according to the general procedure and purified by flash column chromatography to give a pale yellow solid: 73.5 mg, 63% yield; 1H NMR (400 MHz, CDCl3) δ 7.73 (s, 1H), 7.63 (d, J = 7.6 Hz, 1H), 7.49−7.53 (m, 2H), 7.37−7.46 (m, 4H), 5.17 (d, J = 2.0 Hz, 1H), 4.75 (d, J = 2.0 Hz, 1H), 2.50 (s, 3H); 13C NMR (100 MHz, CDCl3) δ 166.8, 143.2, 140.2, 134.7, 133.8, 133.3, 129.3, 129.2, 128.1, 128.0, 123.7, 119.9, 89.7, 21.7; HRMS (ESI) calcd for C16H13NONa [M + Na] 258.0889, found 258.0881. 6-Methoxy-3-methylene-2-phenylisoindolin-1-one (2c). The title compound was prepared according to the general procedure and purified by flash column chromatography to give a pale yellow solid: 71.5 mg, 65% yield; 1H NMR (400 MHz, CDCl3) δ 7.64 (d, J = 8.4 Hz, 1H), 7.50−7.54 (m, 2H), 7.37−7.43 (m, 4H), 7.18−7.21 (m, 1H), 5.11 (d, J = 2.0 Hz, 1H), 4.71 (d, J = 2.0 Hz, 1H), 3.91 (s, 3H); 13C NMR (100 MHz, CDCl3) δ 166.6, 161.4, 142.9, 134.7, 130.6, 129.3, 129.0, 128.1, 128.0, 121.4, 120.8, 106.0, 89.3, 55.9; HRMS (ESI) calcd for C16H14NO2 [M + H] 252.1019, found 252.1027. (Z)-3-Ethylidene-2-phenylisoindolin-1-one (2e). The title compound was prepared according to the general procedure and purified by flash column chromatography to give a pale yellow solid: 58.2 mg, 50% yield; 1H NMR (400 MHz, CDCl3) δ 7.88 (d, J = 7.6 Hz, 1H), 7.65 (d, J = 7.6 Hz, 1H), 7.58 (t, J = 7.6 Hz, 1H), 7.35−7.50 (m, 6H), 5.71 (q, J = 7.6 Hz, 1H), 1.35 (d, J = 7.6 Hz, 3H); 13C NMR (100 MHz, CDCl3) δ 167.9, 138.1, 137.1, 135.5, 132.1, 129.2, 128.7, 128.5,

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CONCLUSION In summary, we have developed a novel catalytic protocol for the direct oxidative cyclocarbonylation of ketimines to provide 3-methyleneisoindolin-1-ones through a rhodium-catalyzed C− H bond activation, in which two C−H bonds have been successfully cleaved. This new transformation may be used for a broad range of substrates and thus represents a concise and useful method for the preparation of 3-methyleneisoindolin-1ones that are of interest in synthetic organic chemistry. The DFT calculations disclosed that the C(sp3)−H bond of the αcarbon was cleaved prior to the C(sp2)−H bond of the ketimine, which ruled out the isolated cyclometalated rhodium complex A involved in the present catalytic cycle. Further applications of this strategy in C−H cyclization are in progress. E

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Organometallics

127.8, 123.7, 120.2, 90.7, 52.3; HRMS (ESI) calcd for C17H13NO3Na [M + Na] 302.0788, found 302.0791. 2-(4-Chlorophenyl)-3-methyleneisoindolin-1-one (2m). The title compound was prepared according to the general procedure and purified by flash column chromatography to give a pale yellow solid: 52.2 mg, 41% yield; 1H NMR (400 MHz, CDCl3) δ 7.91 (d, J = 7.6 Hz, 1H), 7.76 (d, J = 8.0 Hz, 1H), 7.64−7.68 (m, 1H), 7.55−7.59 (m, 1H), 7.47−7.51 (m, 2H), 7.32−7.35 (m, 2H), 5.25 (d, J = 2.4 Hz, 1H), 4.80 (d, J = 2.4 Hz, 1H); 13C NMR (100 MHz, CDCl3) δ 166.6, 142.8, 136.2, 133.8, 133.1, 132.5, 129.9, 129.6, 129.4, 128.7, 123.7, 120.2, 90.5; HRMS (ESI) calcd for C15H10ClNONa [M + Na] 278.0343, found 278.0347. 2-(3-Chlorophenyl)-3-methyleneisoindolin-1-one (2n). The title compound was prepared according to the general procedure and purified by flash column chromatography to give a pale yellow solid: 62.5 mg, 49% yield; 1H NMR (400 MHz, CDCl3) δ 7.91 (d, J = 7.2 Hz, 1H), 7.76 (d, J = 7.6 Hz, 1H), 7.64−7.68 (m, 1H), 7.55−7.59 (m, 1H), 7.39−7.48 (m, 3H), 7.29−7.31 (m, 1H), 5.26 (d, J = 2.4 Hz, 1H), 4.83 (d, J = 2.0 Hz, 1H); 13C NMR (100 MHz, CDCl3) δ 166.4, 142.7, 136.2, 135.8, 134.8, 132.6, 130.3, 129.9, 128.6, 128.4, 128.3, 126.4, 123.7, 120.2, 90.7; HRMS (ESI) calcd for C15H10ClNONa [M + Na] 278.0343, found 278.0339. 6-Methoxy-3-methylene-2-(o-tolyl)isoindolin-1-one (2q). The title compound was prepared according to the general procedure and purified by flash column chromatography to give a pale yellow solid: 83.8 mg, 63% yield. 1H NMR (400 MHz, CDCl3) δ 7.64 (d, J = 8.4 Hz, 1H), 7.30−7.40 (m, 4H), 7.18−7.24 (m, 2H), 5.05 (d, J = 2.0 Hz, 1H), 4.39 (d, J = 2.0 Hz, 1H), 3.90 (s, 3H), 2.16 (s, 3H); 13C NMR (100 MHz, CDCl3) δ 166.4, 161.4, 142.7, 137.3, 133.4, 131.2, 130.9, 129.3, 129.1, 129.1, 126.9, 121.5, 120.7, 106.0, 89.3, 55.9, 17.8; HRMS (ESI) calcd for C17H15NO2Na [M + Na] 288.0995, found 288.1006. 2-(4-Ethylphenyl)-6-methoxy-3-methyleneisoindolin-1-one (2r). The title compound was prepared according to the general procedure and purified by flash column chromatography to give a pale yellow solid: 82.3 mg, 59% yield; 1H NMR (400 MHz, CDCl3) δ 7.63 (d, J = 8.4 Hz, 1H), 7.38 (d, J = 2.4 Hz, 1H), 7.26−7.35 (m, 4H), 7.17−7.19 (m, 1H), 5.09 (d, J = 2.0 Hz, 1H), 4.70 (d, J = 2.0 Hz, 1H); 3.90 (s, 3H), 2.69 (q, J = 7.6 Hz, 2H), 1.29 (t, J = 7.6 Hz, 3H); 13C NMR (100 MHz, CDCl3) δ 166.7, 161.4, 144.2, 143.1, 132.1, 130.7, 129.0, 128.8, 127.9, 121.3, 120.7, 105.9, 89.3, 55.9, 28.6, 15.4; HRMS (ESI) calcd for C18H17NO2Na [M + Na] 302.1151, found 302.1158. 6-Methoxy-2-(4-methoxyphenyl)-3-methyleneisoindolin-1-one (2s). The title compound was prepared according to the general procedure and purified by flash column chromatography to give a pale yellow solid: 76.9 mg, 55% yield; 1H NMR (400 MHz, CDCl3) δ 7.63 (d, J = 8.4 Hz, 1H), 7.38 (d, J = 2.4 Hz, 1H), 7.26−7.29 (m, 2H), 7.17−7.19 (m, 1H), 7.02−7.04 (m, 2H), 5.08 (d, J = 2.0 Hz, 1H), 4.66 (d, J = 2.0 Hz, 1H); 3.90 (s, 3H), 3.86 (s, 3H); 13C NMR (100 MHz, CDCl3) δ 166.9, 161.4, 159.2, 143.3, 130.7, 129.3, 129.0, 127.2, 121.3, 120.7, 114.6, 105.9, 89.2, 55.8, 55.5; HRMS (ESI) calcd for C17H15NO3Na [M + Na] 304.0944, found 304.0945. 2-(3,4-Dimethoxyphenyl)-6-methoxy-3-methyleneisoindolin-1one (2t). The title compound was prepared according to the general procedure and purified by flash column chromatography to give a pale yellow solid: 75.0 mg, 48% yield; 1H NMR (400 MHz, CDCl3) δ 7.62−7.65 (m, 1H), 7.37 (s, 1H), 7.17−7.20 (m, 1H), 6.88−7.00 (m, 3H), 5.10 (d, J = 2.0 Hz, 1H), 4.69 (d, J = 1.6 Hz, 1H); 3.88−3.94 (m, 9H); 13C NMR (100 MHz, CDCl3) δ 166.8, 161.4, 149.4, 148.8, 143.3, 130.6, 128.9, 127.3, 121.4, 120.7, 120.6, 111.5, 111.3, 105.9, 89.3, 56.1, 56.0, 55.8; HRMS (ESI) calcd for C18H18NO4 [M + H] 312.1230, found 312.1228.

128.2, 127.8, 123.5, 118.9, 104.1, 12.6; HRMS (ESI) calcd for C16H14NO [M + H] 236.1070, found 236.1066. 3-Methylene-2-phenyl-2,3-dihydro-1H-benzo[f ]isoindol-1-one (2f). The title compound was prepared according to the general procedure and purified by flash column chromatography to give a pale yellow solid: 67.7 mg, 50% yield; 1H NMR (400 MHz, CDCl3) δ 8.44 (s, 1H), 8.18 (s, 1H), 7.96−8.03 (m, 2H), 7.52−7.63 (m, 4H), 7.41− 7.44 (m, 3H), 5.29 (d, J = 2.4 Hz, 1H), 4.76 (d, J = 2.0 Hz, 1H); 13C NMR (100 MHz, CDCl3) δ 166.6, 143.1, 135.5, 134.8, 133.8, 132.0, 129.9, 129.4, 128.8, 128.2, 128.1, 128.1, 127.0, 126.9, 124.2, 119.4, 88.7; HRMS (ESI) calcd for C19H13NONa [M + Na] 294.0889, found 294.0884. 3-Methylene-2-(p-tolyl)isoindolin-1-one (2g). The title compound was prepared according to the general procedure and purified by flash column chromatography to give a pale yellow solid: 65.3 mg, 56% yield; 1H NMR (400 MHz, CDCl3) δ 7.91 (d, J = 7.6 Hz, 1H), 7.75 (d, J = 7.6 Hz, 1H), 7.62−7.66 (m, 1H), 7.54−7.58 (m, 1H), 7.31 (d, J = 8.0 Hz, 2H), 7.25−7.27 (m, 2H), 5.21 (d, J = 2.0 Hz, 1H), 4.78 (d, J = 2.0 Hz, 1H), 2.42 (s, 3H); 13C NMR (100 MHz, CDCl3) δ 166.8, 143.3, 138.0, 136.3, 132.2, 131.9, 130.0, 129.7, 129.0, 127.9, 123.6, 120.0, 90.3, 21.3; HRMS (ESI) calcd for C16H14NO [M + H] 236.1070, found 236.1079. 3-Methylene-2-(o-tolyl)isoindolin-1-one (2h). The title compound was prepared according to the general procedure and purified by flash column chromatography to give a pale yellow solid: 43.0 mg, 37% yield; 1H NMR (400 MHz, CDCl3) δ 7.93 (d, J = 7.6 Hz, 1H), 7.76 (d, J = 7.6 Hz, 1H), 7.63−7.67 (m, 1H), 7.55−7.59 (m, 1H), 7.30− 7.39 (m, 3H), 7.22−7.26 (m, 1H), 5.18 (d, J = 2.0 Hz, 1H), 4.48 (d, J = 2.0 Hz, 1H), 2.16 (s, 3H); 13C NMR (100 MHz, CDCl3) δ 166.5, 142.9, 137.3, 136.4, 133.4, 132.2, 131.2, 129.7, 129.3, 129.1, 127.0, 123.6, 120.2, 90.4, 17.8; HRMS (ESI) calcd for C16H13NONa [M + Na] 258.0889, found 258.0876. 2-(4-Ethylphenyl)-3-methyleneisoindolin-1-one (2i). The title compound was prepared according to the general procedure and purified by flash column chromatography to give a pale yellow solid: 70.5 mg, 57% yield; 1H NMR (400 MHz, CDCl3) δ 7.91 (d, J = 7.6 Hz, 1H), 7.74 (d, J = 7.6 Hz, 1H), 7.60−7.64 (m, 1H), 7.52−7.56 (m, 1H), 7.25−7.35 (m, 4H), 5.21 (d, J = 2.0 Hz, 1H), 4.79 (d, J = 2.0 Hz, 1H), 2.68 (q, J = 7.6 Hz, 2H), 1.28 (t, J = 7.6 Hz, 3H); 13C NMR (100 MHz, CDCl3) δ 166.8, 144.2, 143.3, 136.3, 132.2, 132.0, 129.7, 129.0, 128.8, 127.9, 123.5, 120.1, 90.4, 28.6, 15.5; HRMS (ESI) calcd for C17H16NO [M + H] 250.1226, found 250.1222. 2-(4-(tert-Butyl)phenyl)-3-methyleneisoindolin-1-one (2j). The title compound was prepared according to the general procedure and purified by flash column chromatography to give a pale yellow solid: 79.8 mg, 58% yield; 1H NMR (400 MHz, CDCl3) δ 7.92 (d, J = 7.2 Hz, 1H), 7.75 (d, J = 7.6 Hz, 1H), 7.62−7.66 (m, 1H), 7.51−7.57 (m, 3H), 7.28−7.31 (m, 2H), 5.23 (d, J = 2.0 Hz, 1H), 4.83 (d, J = 2.0 Hz, 1H), 1.37 (s, 9H); 13C NMR (100 MHz, CDCl3) δ 166.8, 150.9, 143.2, 136.3, 132.2, 131.8, 129.7, 129.1, 127.5, 126.3, 123.6, 120.0, 90.5, 34.7, 31.4; HRMS (ESI) calcd for C19H19NONa [M + Na] 300.1359, found 300.1357. 2-(4-Methoxyphenyl)-3-methyleneisoindolin-1-one (2k). The title compound was prepared according to the general procedure and purified by flash column chromatography to give a pale yellow solid: 74.9 mg, 60% yield; 1H NMR (400 MHz, CDCl3) δ 7.91 (d, J = 7.6 Hz, 1H), 7.74 (d, J = 8.0 Hz, 1H), 7.62−7.66 (m, 1H), 7.53−7.57 (m, 1H), 7.26−7.31 (m, 2H), 7.01−7.05 (m, 2H), 5.21 (d, J = 2.0 Hz, 1H), 4.75 (d, J = 2.0 Hz, 1H), 3.86 (s, 3H); 13C NMR (100 MHz, CDCl3) δ 166.9, 159.2, 143.6, 136.2, 132.2, 129.7, 129.3, 129.0, 127.1, 123.5, 120.1, 114.7, 90.3, 55.5; HRMS (ESI) calcd for C16H13NO2Na [M + Na] 274.0838, found 274.0848. Methyl 4-(1-Methylene-3-oxoisoindolin-2-yl)benzoate (2l). The title compound was prepared according to the general procedure and purified by flash column chromatography to give a pale yellow solid: 61.5 mg, 44% yield; 1H NMR (400 MHz, CDCl3) δ 8.18−8.21 (m, 2H), 7.92 (d, J = 7.6 Hz, 1H), 7.77 (d, J = 7.6 Hz, 1H), 7.65−7.69 (m, 1H), 7.56−7.60 (m, 1H), 7.49−7.52 (m, 2H), 5.29 (d, J = 2.4 Hz, 1H), 4.88 (d, J = 2.4 Hz, 1H), 3.95 (s, 3H); 13C NMR (100 MHz, CDCl3) δ 166.4, 142.4, 138.8, 136.3, 132.6, 130.7, 130.0, 129.4, 128.6,

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DOI: 10.1021/acs.organomet.6b00072 Organometallics XXXX, XXX, XXX−XXX

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Compound characterization and DFT calculation data for products (PDF) All computed molecule Cartesian coordinates (XYZ) Crystallographic data for complex A (CCDC 1439528)(CIF) Crystallographic data for product 2q (CCDC 1439514) (CIF) Crystallographic data for product 2t (CCDC 1439517) (CIF)

AUTHOR INFORMATION

Corresponding Authors

*E-mail for Y.L.: [email protected]. *E-mail for H.H.: [email protected]. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This research was supported by the Chinese Academy of Sciences and the National Natural Science Foundation of China (21222203 and 21133011). We acknowledge the generous allocation of computer time at the Chinese Academy of Sciences supercomputing Lanzhou subcenter.

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DOI: 10.1021/acs.organomet.6b00072 Organometallics XXXX, XXX, XXX−XXX

Article

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DOI: 10.1021/acs.organomet.6b00072 Organometallics XXXX, XXX, XXX−XXX