Synthesis of Secondary Aromatic Amides via Pd-Catalyzed

Oct 13, 2017 - Using N-methoxymethyl-N-organylcarbamoyl(trimethyl)silanes as secondary amides source, the direct transformation of aryl halides into t...
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Note Cite This: J. Org. Chem. 2017, 82, 11603-11608

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Synthesis of Secondary Aromatic Amides via Pd-Catalyzed Aminocarbonylation of Aryl Halides Using Carbamoylsilane as an Amide Source Wenting Tong,†,‡ Pei Cao,† Yanhong Liu,† and Jianxin Chen*,† †

College of Chemistry and Materials Science, Shanxi Normal University, Lin fen 041004, PR China Kangda College of Nanjing Medical University, Lianyungang 222000, PR China

‡

S Supporting Information *

ABSTRACT: Using N-methoxymethyl-N-organylcarbamoyl(trimethyl)silanes as secondary amides source, the direct transformation of aryl halides into the corresponding secondary aromatic amides via palladium-catalyzed aminocarbonylation is described. The reactions tolerated a broad range of functional groups on the aryl ring except big steric hindrance of substituent. The types and the relative position of substituents on the aryl ring impact the coupling efficiency.

A

good yields,17 in which an easy and practical method for the introduction of a aminocarbonyl into an organic substrate was provided. To the best of our knowledge, there is only one such publication in the chemical literature describing the direct synthesis of amides by palladium-catalyzed aminocarbonylation of aryl halides using carbamoylsilane as an amide source. However, this approach is limited to the formation of only (tertiary) N,N-dimethyl-substituted amide derivatives, for efficient application within these areas, synthesizing secondary amides are required, but it has never been studied using carbamoylsilane as an amide source. We are interested in exploring the possibility of synthesizing secondary amides. Therefore, carbamoylsilanes containing an amino protecting group are expected to solve this problem. Considering this, the N-methoxymethyl-N-organylcarbamoyl(trimethyl)silanes were selected as an amide source to synthesize secondary amides, wherein methoxymethyl was used as an amino protecting group. To our surprise, the palladium-catalyzed aminocarbonylation of aryl halides with these carbamoylsilanes could directly afford secondary amides in most cases. Here, we report on the successful attempt in this regard, explore the influence of substituents on this transformation and optimize the reaction conditions. When aryl halides 1 were allowed to react with 1.1 equiv of N-methoxymethyl-N-organyl-carbamoyl(trimethyl)silanes (2, 5, 6 or 7)15 under palladium catalysis, good yields of aromatic amides were achieved, generally within a matter of a few hours (Scheme 1). Our study was initiated by examining the effects of solvents and temperature in the model reaction of bromobenzene with N-methoxymethyl-N-methylcarbamoyl(trimethyl)silane catalyzed by [(Ph)3P]4Pd(0). A range of solvents often used for cross-coupling reactions were tested.

mides are a very important class of organic compounds, which have been widely used in pharmaceuticals, petrochemical, polymers, electronics industries and the synthesis of biologically active natural products.1 Due to such interests, numerous methods for the synthesis of amides have been developed, the common routes involve the direct amidation of carboxylic acids or their activated analogues with amines.2 However, these methods generally require harsh conditions and multistep operations.3 Alternate methods include Haller−Bauer and Cannizzaro Reaction,4 oxidation of imines to amides via an oxaziridine,5 modified Staudinger reaction,6 modified Schmidt reaction,7 coupling of carboxylic acids with isocyanides,1e catalyzed oxidative amidation of aldehydes with amines,8 metal-catalyzed aminocarbonylation of aryl halides or aryl tosylates,9 palladium-catalyzed oxidative aminocarbonylation via C(sp3)−H activation,3b and Pd/Ccatalyzed aminocarbonylation of aryl iodides via oxidative C−N bond activation of amines.10 Among them, palladium-catalyzed aminocarbonylation reaction between aryl halides with primary/secondary amines and carbon monoxide is a powerful and most frequently used method in organic synthesis. After the pioneering work of Heck and co-worker in regard to palladium-catalyzed aminocarbonylation in 1974,11 various improved methods were developed using CO as a source of the carbonyl group.12 However, the troublesome handling, storage and transport of hazardous carbon monoxide gas, the reaction setup requiring high-pressure reactors, high temperature and harsh reaction conditions restrict its applications.13,10b Therefore, the development of new CO-free methods for the synthesis of amides is of significant interest among organic chemists.14 Previously, we had developed a straightforward, efficient and practical preparative method of various carbamoylsilanes,15 which are environmentally benign reagents and can be used as amides source.16 Cunico, R. F., et al. have shown that a carbamoylsilane could react with aryl halides catalyzed by palladium catalysts to afford the amides in © 2017 American Chemical Society

Received: June 5, 2017 Published: October 13, 2017 11603

DOI: 10.1021/acs.joc.7b01028 J. Org. Chem. 2017, 82, 11603−11608

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The Journal of Organic Chemistry Scheme 1. Reaction of Carbamoylsilanes with Aryl Halides

Table 2. Secondary Amides 3 or 4 from Aryl Halides and Carbamoylsilane 2

The reaction proceeded smoothly in all tested solvents. When the reaction was conducted in toluene the product was obtained in high yield and the reaction time was short. Several other solvents, including benzene, acetonitrile, dichloromethane and THF, gave inferior results compared to toluene. The temperature study showed that 100 °C was the optimum temperature to obtain a higher yield of coupling product. Increase or decrease in reaction temperature led to reduce in yield of coupling product (Table 1). Next, model reaction was Table 1. Condition Optimization of Aminocarbonylation of Aryl Halides

entry

catalysta (mol %)

temp (°C)

timeb (h)

yieldc,d (%)

1 2 3 4 5 6 7 8

2.0 2.0 2.0 2.0 1.0 1.5 2.5 3.0

80 90 100 110 100 100 100 100

9.0 7.0 6.0 5.0 7.0 6.0 6.5 7.0

71 75 81 64 58 60 76 66

a

[(Ph)3P]4Pd(0). bTo complete consumption of carbamoylsilane 2. Isolated yield after chromatography on silica gel based on bromobenzene. d1:1.1 mol ratio of bromobenzene and carbamoylsilane. c

run in toluene at 100 °C to examine the effect of catalyst loading, which revealed that 2 mol % of [(Ph)3P]4Pd (relative to 1) was essential for best results. When the amount of catalyst used was less than 2 mol %, low yields of the products were obtained, while increasing the catalyst loading results also in lower yields (entries 5−8). To explore the scope of the palladium-catalyzed aminocarbonylation of aryl halides, a series of (hetero)aryl halides were screened to react with carbamoylsilane 2 in toluene under 2 mol % catalytic loading at 100 °C, and two palladium catalysts were investigated: “A”, tetrakis(triphenylphosphine)palladium(0), and “B”, bis(tri-tert-butylphosphine) palladium(0). The results are listed in Table 2. First, coupling reactions were performed for various halogen substituted benzene 1a−d. We found that chlorobenzene and bromobenzene reacted smoothly catalyzed by A, and good yields of corresponding secondary aryl amides 3a and 3b were achieved directly, the methoxymethyl group had been hydrolyzed and converted into hydrogen atom, bromobenzene exhibited faster reaction rates than chlorobenzene. However, fluorobenzene and iodobenzene did not undergo the coupling reaction under the present conditions catalyzed by A or B. Although aryl iodides are more reactive, the product could not be observed even lengthening reaction time to 46 h, the iodobenzene was

a A = tetrakis(triphenylphosphine)palladium(0); B = bis(tri-tertbutylphosphine)palladium(0). bTo complete consumption of carbamoylsilane 2 in toluene at 100 °C. cIsolated yield based on aryl halides. d 1:1.1 mol ratio of aryl halides and carbamoylsilane.

obtained by separation. While previously Cunico, R. F. reported that the iodobenzene could react with N,N-dimethylcarbamoyl(trimethyl)silane, and chlorobenzene could not react catalyzed by A.17 Next, aryl halides containing different functional groups 11604

DOI: 10.1021/acs.joc.7b01028 J. Org. Chem. 2017, 82, 11603−11608

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The Journal of Organic Chemistry were tested, it was revealed that either electron-donating or electron-withdrawing groups on aryl ring at meta or para position were tolerated, offering high isolated yields of coupling products. The electronic properties of the substituent in the phenyl ring influenced the reaction time of aminocarbonylation reaction, the stronger electron-donating the substituent, the shorter the reaction time was (Table 2, entries 5−9). Aryl bromides possessing an electron-withdrawing group, such as a nitro or chloro group, reacted slowly than those possessing electron-donating group, such as a methoxy or methyl group. The aminocarbonylation only selectively occurred at the bromo-terminal for aryl halides containing Br and Cl simultaneously, such as 4-chlorobromobenzene gave exclusively para-chloro aryl amide 3f. 4-Methoxybromobenzene afforded the aryl amide 3h in excellent yield, indicating that a strong electron-donating group affected the coupling process. Furthermore, changing the relative position of substituent on the phenyl ring, it was found that the reaction was highly sensitive to steric factors. Substrate 1j, the relatively minor steric impediment of an ortho methyl inhibiting the reaction, afforded product 3j in low yield with catalyst A. While ortho dimethyl completely inhibited the reaction, as instance 1k gave no desired product due to big steric hindrance catalyzed by A or B. With catalyst A, 2-bromonaphthalene afforded desired product in low yield (12%), while using catalyst B, gave the methoxymethyl-protected product amide 4l in 75% yield, which can be deprotected to transform into secondary amides easily by simple acid hydrolysis.18 As expected, heterocyclic bromide 1m gave the product 3m in high yield catalyzed by A, and 2chloro-5-trifluoropyridine could furnish a good yield of methoxymethyl-protected aryl amide 4n catalyzed by B. Carbamoylsilane 2 could also react with aryl bromides possessing cyano and ester group to give good yields of products, while could not react with aryl bromides possessing carbonyl, amino or hydroxy groups because it can be hydrolyzed by active hydrogen or enolizable α-hydrogens. To further explore the synthetic potential of developed protocol, carbamoylsilanes possessing different groups were selected as secondary amides source, such as N-methoxymethylN-propylcarbamoyl(trimethyl)silane (5), N-cyclohexyl-Nmethoxymethylcarbamoyl(trimethyl)silane (6) and N-benzylN-methoxymethylcarbamoyl(trimethyl)silane (7), to react with aryl bromides bearing different functional groups 1b, 1e, 1g, and 1h under same reaction conditions. The results are listed in Table 3. All carbamoylsilanes reacted smoothly, and aryl bromides bearing an electron-withdrawing and electrondonating group were tolerated, to afford the corresponding amides in moderate yields. Among them, aryl bromide 1e gave the methoxymethyl-protected product 8e, 9e and 10e. Aryl bromide 1b react with carbamoylsilane (5) also afforded methoxymethyl-protected aryl amides 8b. All other reactions directly afforded secondary aryl amides in good yields. The benzyl group of aryl amides 10b, 10e, 10g and 10h can be converted into hydrogen atom easily by deprotection using Pd(OH)2/C and H2, leading to formation of the primary amides.19 A possible route to secondary amides 3 is presented in Scheme 2. The oxidative addition of palladium(0) to aryl halides produce complex I, which undergoes ligand exchange (L = Ph3P) with a nucleophilic carbene arising from a C to O silyl group rearrangement within carbamoylsilane 220 to form II. Loss of trimethylsilyl halide from complex II then gives a carbamoylpalladium intermediate III. The migration of the

Table 3. Reaction of Carbamoylsilanes 5−7 with Aryl Bromides 1b, 1e, 1g and 1h

a A = tetrakis(triphenylphosphine)palladium(0); B = bis(tri-tertbutylphosphine)palladium(0). bTo complete consumption of carbamoylsilane in toluene at 100 °C. cIsolated yield based on aryl halides. d 1:1.2 mol ratio of aryl halides and carbamoylsilane.

carbamoyl function and reductive elimination of PdLn for intermediateIII afford products 4, which can be hydrolyzed in the separation process to form amides 3. In summary, we have developed a novel and highly efficient synthetic method toward secondary aryl amides by palladium11605

DOI: 10.1021/acs.joc.7b01028 J. Org. Chem. 2017, 82, 11603−11608

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The Journal of Organic Chemistry

134.6, 131.4, 128.6, 126.9, 26.9. Anal. Calcd for C8H9NO: C, 71.09; H, 6.71; N, 10.36. Found: C, 71.12; H, 6.81; N, 10.34%. N-Methyl-4-nitro-benzamide (3e).24 White solid; the eluent composition: petroleum ether/ethyl acetate = 1:2; 71.5 mg, 79.4% yield; mp 141.0−142.5 °C. 1H NMR (600 MHz, DMSO-d6) δ 8.78 (br s, 1H), 8.32−8.06 (m, 4H), 2.82, 2.81 (ss, 3H). 13C NMR (151 MHz, CDCl3) δ 166.1, 145.3, 140.2, 128.0, 123.9, 27.1. Anal. Calcd for C8H8N2O3: C, 53.33; H, 4.48; N, 15.55. Found: C, 53.45; H, 4.43; N, 15.36%. N-Methyl-4-chloro-benzamide (3f).21 White solid; the eluent composition: petroleum ether/ethyl acetate = 2:1; 69.8 mg, 82.3% yield; mp 152.0−153.0 °C. 1H NMR (600 MHz, CDCl3) δ 7.72 (d, J = 8.4 Hz, 2H), 7.41 (d, J = 8.4 Hz, 2H), 6.31 (br s, 1H), 3.02, 3.01 (ss, 3H). 13C NMR (151 MHz, CDCl3) δ 167.2, 137.6, 133.0, 128.8, 128.3, 26.9. Anal. Calcd for C8H8ClNO: C, 56.65; H, 4.75; N, 8.26. Found: C, 56.79; H, 4.73; N, 8.10%. N-Methyl-4-methyl-benzamide (3g).9f White solid; the eluent composition: petroleum ether/ethyl acetate = 2:1; 62.1 mg, 83.3% yield; mp 121.0−122.5 °C. 1H NMR (600 MHz, CDCl3) δ 7.69−7.23 (m, 4H), 6.19, 6.12 (br ss, 1H), 3.04−3.02 (m, 3H), 2.41 (s, 3H). 13C NMR (151 MHz, CDCl3) δ 168.2, 141.7, 131.8, 129.2, 126.8, 26.8, 21.4. Anal. Calcd for C9H11NO: C, 72.46; H, 7.43; N, 9.39. Found: C, 72.18; H, 7.21; N, 9.43%. N-Methyl-4-methoxy-benzamide (3h).9f Yellowish solid; the eluent composition: petroleum ether/ethyl acetate = 1:1; 71.7 mg, 86.8% yield; mp 122.0−123.5 °C. 1H NMR (600 MHz, CDCl3) δ 7.76−6.92 (m, 4H), 6.22 (br s, 1H), 3.86 (s, 3H), 3.01, 3.00 (ss, 3H). 13 C NMR (151 MHz, CDCl3) δ 167.8, 162.0, 129.4, 128.6, 127.0, 113.7, 113.6, 55.4, 26.8. Anal. Calcd for C9H11NO2: C, 65.44; H, 6.71; N, 8.48. Found: C, 65.23; H, 6.53; N, 8.52%. N-Methyl-3-methoxy-benzamide (3i).21 Colorless liquid; the eluent composition: petroleum ether/ethyl acetate = 1:2; 68.1 mg, 82.4% yield. 1H NMR (600 MHz, CDCl3) δ 7.37−7.03 (m, 4H), 6.28 (br s, 1H), 3.86−3.86 (m, 3H), 3.03−3.02 (m, 3H). 13C NMR (151 MHz, CDCl3) δ 168.2, 159.8, 136.1, 129.5, 118.7, 117.5, 112.2, 55.4, 26.9. Anal. Calcd for C9H11NO2: C, 65.44; H, 6.71; N, 8.48. Found: C, 65.39; H, 6.73; N, 8.30%. N-Methyl-2-methyl-benzamide (3j).21 Colorless liquid; the eluent composition: petroleum ether/ethyl acetate = 2:1; 28.6 mg, 38.3% yield. 1H NMR (600 MHz, CDCl3) δ 7.35−7.20 (m, 4H), 5.84 (s, 1H), 3.02−3.00 (m, 3H), 2.46, 2.45 (ss, 3H). 13C NMR (151 MHz, CDCl3) δ 170.8, 136.5, 136.0, 131.0, 129.8, 126.7, 125.6, 26.4, 19.8. Anal. Calcd for C9H11NO: C, 72.46; H, 7.43; N, 9.39. Found: C, 72.18; H, 7.21; N, 9.43%. N-Methoxymethyl-N-methyl-2-naphthalenecarboxamide (4l). Colorless liquid; the eluent composition: petroleum ether/ethyl acetate = 1:1; 86.1 mg, 75.1% yield. 1H NMR (600 MHz, CDCl3) δ 7.93−7.84 (m, 3H), 7.55−7.47 (m, 4H), 5.51, 4.49 (ss, 2H), 3.57, 3.29 (ss, 3H), 3.09, 2.84 (ss, 3H). 13C NMR (151 MHz, CDCl3) δ 172.1, 171.6, 134.4, 133.7, 133.5, 130.0, 129.6, 129.4, 129.2, 128.5, 127.2, 127.1, 126.5, 125.2, 124.9, 124.7, 124.6, 123.8, 82.2, 77.5, 56.4, 55.2, 35.1, 31.8. RI (KBr) υ 1662, 1492, 1456, 1394, 1232, 1097, 1031 cm−1. Anal. Calcd for C14H15NO2: C, 73.34; H, 6.59; N, 6.11. Found: C,73.44; H; 6.38; N, 6.13%. N-Methyl-2-thiophenecarboxamide (3m).21 Yellowish solid; the eluent composition: petroleum ether/ethyl acetate = 1:1; 60.2 mg, 85.3% yield; mp 112.0−113.5 °C. 1H NMR (600 MHz, CDCl3) δ 7.52−7.08 (m, 3H), 6.10 (br s, 1H), 3.02−3.01 (m, 3H). 13C NMR (151 MHz, CDCl3) δ 162.5, 138.9, 129.6, 127.9, 127.6, 26.6. Anal. Calcd for C6H7NOS: C, 51.04; H, 5.00; N, 9.92. Found: C, 51.28; H, 5.16; N, 9.83%. N-Methoxymethyl-N-methyl-5-trifluoromethyl-2-pyridinecarboxamide (4n). Colorless liquid; the eluent composition: petroleum ether/ethyl acetate = 1:1; 97.1 mg, 78.2% yield. 1H NMR (600 MHz, CDCl3) δ 8.89 (d, J = 3.0 Hz, 1H), 8.08 (d, J = 7.2 Hz, 1H), 7.86 (d, J = 8.4 Hz, 1H), 5.03, 4.86 (ss, 2H), 3.46, 3.23 (ss, 3H), 3.21, 3.11 (ss, 3H). 13C NMR (151 MHz, CDCl3) δ 168.7, 168.3, 157.2, 157.0, 145.8, 145.4, 145.3, 145.2, 134.4, 127.5, 127.3, 124.1, 124.0, 123.6, 94.0, 81.8, 78.3, 56.2, 55.4, 35.3, 32.8. RI (KBr) υ 1652, 1608, 1400, 1323, 1129,

Scheme 2. Proposed Mechanism of the Reaction

catalyzed aminocarbonylation of aryl halides using Nmethoxymethyl-N-organylcarbamoyl(trimethyl)silanes as amides source, and investigated the scope and limitation of the aminocarbonylation. In this protocol, the methoxymethyl was used as an amino protecting group and can be easily hydrolyzed for most products in the separation process. The reactions tolerated a broad range of functional groups except big steric hindrance of ortho-substituent on the phenyl ring, and afforded the secondary aryl amides directly in good to excellent yields under mild reaction conditions. We anticipate that the current methodology will prove to be an attractive alternative to the reported methods for aminocarbonylation reactions due to utilizing carbamoylsilanes used as amides source instead of a toxic CO source.

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EXPERIMENTAL SECTION

General Methods. All reactions were carried out using standard Schlenk techniques under a nitrogen atmosphere. Dry toluene was freshly distilled from sodium and benzophenone as a moisture indicator under Ar atmosphere before use. All liquid aryl halides were freshly distilled under Ar atmosphere. Carbamoylsilanes were prepared according to literature procedures.15 Tetrakis(triphenyl- phosphine)palladium(0) and bis(tri-tert-butylphosphine)palladium(0) were obtained from J&K Scientific. 1H (600 MHz) and 13C-{1H} (150.8 MHz) NMR spectra were recorded on Bruker (AV600) NMR spectrometer. All spectra were recorded at room temperature in deuterated chloroform (CDCl3, δ = 7.28 ppm for proton NMR, δ = 77.05 ppm for carbon NMR) unless otherwise stated using tetramethylsilane (TMS) as an internal standard. Chemical shifts are expressed in parts per million (ppm) and coupling constants in Hertz (Hz). Elemental analysis was performed on an EA-1108 analyzer. Melting points were measured with a STUART SMP 10 melting point apparatus and uncorrected. The monitoring of reaction and checking of purity of the product were done using precoated silica gel plates (Merck 60 PF254). Column chromatography was performed using Merck silica gel 200−300mesh and ethyl acetate−petroleum ether elution. Visualization was achieved by UV (254 nm) light detection and iodine staining. General Procedure for Preparation of Secondary Amides 3, 4 and 8−10. A Schlenk tube fitted with a Teflon vacuum stopcock and micro stirbar was flame-heated under vacuum and refilled with Ar. Aryl halides (0.5 mmol) and carbamoylsilane 2 (5, 6 or 7) (0.60 mmol) were charged to the Schlenk tube under argon at ice bath temperature, followed by addition of 0.01 mmol of [(Ph)3P]4Pd(0) and 1.5 mL of dry toluene. The sealed reaction mixture was stirred at 100 °C until no carbamoylsilane could be detected by TLC. Volatiles were removed in vacuum to afford the crude product which was purified by column chromatography on silica gel (petroleum ether/ ethyl acetate combination) to give 3 (4, 8, 9 or 10). N-Methylbenzamide (3b).9f White solid; the eluent composition: petroleum ether/ethyl acetate = 2:1; 54.7 mg, 80.9% yield; mp 78.0− 79.5 °C. 1H NMR (600 MHz, CDCl3) δ 7.79−7.44 (m, 5H), 6.19 (br s, 1H), 3.05, 3.04 (ss, 3H). 13C NMR (151 MHz, CDCl3) δ 168.4, 11606

DOI: 10.1021/acs.joc.7b01028 J. Org. Chem. 2017, 82, 11603−11608

Note

The Journal of Organic Chemistry 1080, 1017 cm−1. Anal. Calcd for C10H11F3N2O2: C, 48.39; H, 4.47; N, 11.29. Found: C,48.28; H, 4.36; N, 11.13%. N-Methoxymethyl-N-propylbenzamide (8b). Yellowish liquid; the eluent composition: petroleum ether/ethyl acetate = 5:1; 66.2 mg, 63.9% yield. 1H NMR (600 MHz, CDCl3) δ 7.49−7.42 (m, 5H), 5.03, 4.57 (ss, 2H), 3.56−3.43 (m, 2H), 3.27, 3.18 (ss, 3H), 1.75−1.58 (m, 2H), 1.03−0.77 (m, 3H). 13C NMR (151 MHz, CDCl3) δ 172.3, 136.1, 129.9, 128.3, 127.6, 127.2, 126.5, 81.0, 55.0, 46.9, 21.1, 11.5. RI (KBr) υ 1642, 1419, 1071 cm−1. Anal. Calcd for C12H17NO2: C, 69.54; H, 8.27; N, 6.76. Found: C, 69.28; H, 8.21; N, 6.64%. N-Methoxymethyl-N-propyl-4-nitro-benzamide (8e). Yellowish liquid; the eluent composition: petroleum ether/ethyl acetate = 5:1; 78.8 mg, 62.3% yield. 1H NMR (600 MHz, CDCl3) δ 8.29−7.60 (m, 4H), 5.02, 4.47 (ss, 2H), 3.59−3.46 (m, 2H), 3.22 (s, 3H), 1.76−1.58 (m, 2H), 1.02−0.77 (m, 3H). 13C NMR (151 MHz, CDCl3) δ 170.1, 148.5, 142.1, 128.3, 123.6, 80.9, 55.3, 47.8, 21.3, 11.4. RI (KBr) υ 1652, 1521, 1347, 1080, 843 cm−1. Anal. Calcd for C12H16N2O4: C, 57.13; H, 6.39; N, 11.10. Found: C, 57.25; H, 6.45; N, 11.34%. N-Propyl-4-methyl-benzamide (8g).22 Yellowish solid; the eluent composition: petroleum ether/ethyl acetate = 3:1; 55.1 mg, 62.1% yield; mp 49.5−51.0 °C. 1H NMR (600 MHz, CDCl3) δ 7.68 (d, J = 7.2 Hz, 2H), 7.23 (d, J = 7.2 Hz, 2H), 6.22 (br s, 1H), 3.44−3.41 (m, 2H), 2.41 (s, 3H), 1.67−1.63 (m, 2H), 1.00 (t, J = 7.2 Hz, 3H). 13C NMR (151 MHz, CDCl3) δ 167.6, 141.6, 132.0, 129.2, 128.5, 126.9, 115.7, 41.7, 23.0, 21.4, 11.5. Anal. Calcd for C11H15NO: C, 74.54; H, 8.53; N, 7.90. Found: C, 74.28; H, 8.27; N,7.75%. N-Propyl-4-methoxy-benzamide (8h).22 Yellowish liquid; the eluent composition: petroleum ether/ethyl acetate = 3:1; 53.1 mg, 54.8% yield. 1H NMR (600 MHz, CDCl3) δ 7.75 (d, J = 8.4 Hz, 2H), 6.94 (d, J = 8.4 Hz, 2H), 6.06 (br s, 1H), 3.87 (s, 3H), 3.45−3.42 (m, 2H), 1.68−1.63 (m, 2H), 1.01 (t, J = 7.2 Hz, 3H). 13C NMR (151 MHz, CDCl3) δ 167.1, 162.0, 132.2, 128.7, 128.1, 127.9, 127.7, 127.6, 127.2, 126.8, 125.8, 125.0, 115.7, 113.7, 55.4, 41.7, 23.0, 11.5. Anal. Calcd for C11H15NO2: C, 68.37; H, 7.82; N, 7.25. Found: C, 68.23; H, 7.57; N, 7.12%. N-Cyclohexylbenzamide (9b).9f Yellowish solid; the eluent composition: petroleum ether/ethyl acetate = 3:1; 64.6 mg, 63.4% yield; mp 149.0−151.0 °C. 1H NMR (600 MHz, CDCl3) δ 7.78−7.41 (m, 5H), 6.11 (br s, 1H), 4.00−3.98 (m, 1H), 2.05−1.20 (m, 10H). 13 C NMR (151 MHz, CDCl3) δ 166.6, 135.1, 131.3, 128.5, 126.8, 48.7, 33.3, 25.6, 24.9. Anal. Calcd for C13H17NO: C, 76.81; H, 8.43; N, 6.89. Found: C, 76.70; H, 8.24; N, 6.71%. N-Cyclohexyl-N-methoxymethyl-4-nitro-benzamide (9e). White solid; the eluent composition: petroleum ether/ethyl acetate = 3:1; 75.5 mg, 51.4% yield; mp 128.5−130.0 °C. 1H NMR (600 MHz, CDCl3) δ 8.29−7.56 (m, 4H), 5.00, 4.37 (ss, 2H), 3.47 (s, 1H), 3.32, 3.14 (ss, 3H), 1.94−1.45 (m, 10H). 13C NMR (151 MHz, CDCl3) δ 170.3, 170.1, 148.4, 142.7, 142.1, 132.6, 130.0, 130.0, 128.3, 125.0, 123.9, 123.6, 123.5, 80.9, 55.3, 54.6, 54.5, 47.8, 31.2, 25.9, 25.6, 21.3, 11.4. RI (KBr) υ 1647, 1521, 1424, 1356, 1075 cm−1. Anal. Calcd for C15H20N2O4: C, 61.63; H, 6.90; N, 9.58. Found: C, 61.43; H, 6.83; N, 9.36%. N-Cyclohexyl-4-methyl-benzamide (9g).9f White solid; the eluent composition: petroleum ether/ethyl acetate = 3:1; 54.9 mg, 50.4% yield; mp 100.0−102.0 °C. 1H NMR (600 MHz, CDCl3) δ 7.66 (d, J = 7.8 Hz, 2H), 7.23 (d, J = 7.8 Hz, 2H), 5.98 (br s, 1H), 3.99−3.98 (m, 1H), 2.41 (s, 3H), 2.05−1.23 (m, 10H). 13C NMR (151 MHz, CDCl3) δ 166.5, 141.6, 132.3, 131.2, 129.2, 128.5, 126.8, 48.6, 33.3, 25.6, 24.9, 22.4. Anal. Calcd for C14H19NO: C, 77.38; H, 8.81; N, 6.45. Found: C, 77.19; H, 8.64; N, 6.41%. N-Cyclohexyl-4-methoxy-benzamide (9h).23 Yellowish solid; the eluent composition: petroleum ether/ethyl acetate = 3:1; 60.7 mg, 51.8% yield; mp 152.5−154.0 °C. 1H NMR (600 MHz, CDCl3) δ 7.75−6.90 (m, 4H), 5.98 (br s, 1H), 3.97−3.96 (m, 1H), 3.85, 3.84 (ss, 3H), 2.03−1.23 (m, 10H). 13C NMR (151 MHz, CDCl3) δ 166.2, 162.0, 128.6, 127.4, 113.7, 55.4, 40.6, 33.3, 30.8, 25.9, 25.6, 25.0. Anal. Calcd for C14H19NO2: C, 72.07; H, 8.21; N, 6.00. Found: C, 72.22; H, 8.43; N, 6.20%. N-Benzylbenzamide (10b).8h Yellowish solid; the eluent composition: petroleum ether/ethyl acetate = 3:1; 75.4 mg, 71.3% yield; mp

105.5−107.0 °C. 1H NMR (600 MHz, CDCl3) δ 7.82−7.31 (m, 10H), 6.77, 6.72 (br ss, 1H), 4.64, 4.63 (ss, 2H). 13C NMR (151 MHz, CDCl3) δ 167.5, 138.3, 134.4, 131.6, 128.8, 128.6, 127.9, 127.6, 127.1, 44.1. Anal. Calcd for C14H13NO: C, 79.59; H, 6.20; N, 6.63. Found: C, 79.31; H, 6.41; N, 6.34%. N-Benzyl-N-methoxymethyl-4-nitro-benzamide (10e). Yellowish liquid; the eluent composition: petroleum ether/ethyl acetate = 3:1; 77.1 mg, 51.3% yield. 1H NMR (600 MHz, DMSO-d6) δ 8.33−7.30 (m, 9H), 4.74−4.49 (m, 4H), 3.25−3.10 (m, 3H). 13C NMR (151 MHz, CDCl3) δ 170.1, 164.9, 148.7, 141.6, 136.6, 136.0, 135.8, 128.8, 128.7, 128.6, 128.5, 128.4, 128.3, 128.1, 127.9, 127.8, 123.7, 79.6, 78.7, 78.5, 73.7, 56.5, 55.9, 55.6, 54.9, 49.4, 48.0, 46.3, 45.9. RI (KBr) υ 1649, 1524, 1344, 1089, 852 cm−1. Anal. Calcd for C16H16N2O4: C, 63.99; H, 5.37; N, 9.33. Found: C, 64.12; H, 5.43; N, 9.39%. N-Benzyl-4-methyl-benzamide (10g).12d White solid; the eluent composition: petroleum ether/ethyl acetate = 3:1; 70.2 mg, 62.2% yield; mp 107.0−109.0 °C. 1H NMR (600 MHz, CDCl3) δ 7.82−7.23 (m, 9H), 6.58, 6.52 (br ss, 1H), 4.67−4.65 (m, 2H), 2.41 (s, 3H). 13C NMR (151 MHz, CDCl3) δ 167.5, 167.4, 141.9, 138.4, 138.3, 134.4, 131.5, 129.2, 129.1, 128.7, 128.6, 128.3, 127.9, 127.6, 127.5, 127.1, 44.1, 44.0, 21.5. Anal. Calcd for C15H15NO: C, 79.97; H, 6.71; N, 6.22. Found: C, 80.18; H, 6.46; N, 6.33%. N-Benzyl-4-methoxyl-benzamide (10h).8h Yellowish solid; the eluent composition: petroleum ether/ethyl acetate = 3:1; 74.1 mg, 61.3% yield; mp 122.0−123.5 °C. 1H NMR (600 MHz, CDCl3) δ 7.79−6.92 (m, 9H), 6.48 (br s, 1H), 4.65, 4.64 (ss, 2H), 3.86 (s, 3H). 13 C NMR (151 MHz, CDCl3) δ 166.9, 162.2, 138.5, 128.8, 128.7, 127.9, 127.6, 126.7, 113.8, 55.4, 44.1. Anal. Calcd for C15H15NO2: C, 74.67; H, 6.27; N, 5.81. Found: C, 74.58; H, 6.21; N, 5.76%.

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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.joc.7b01028. 1 H and 13C NMR spectroscopic of 3a, 3e−j, 3n−p, 8b− 10b, 8e−10e, 8g−10g, and 8h−10h. (PDF)

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Tel.: +86-0357-2051192. ORCID

Jianxin Chen: 0000-0002-1064-8439 Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This research was supported by Shanxi Province Foundation for Returness (No. 0713), the Natural Science Foundation of Shanxi Province (No. 2012011046-9) and Foundation of Shanxi Normal University (No. SD2015CXXM-83), China.

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REFERENCES

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