An Electrochemical Method for Carboxylic Ester Synthesis from N

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An Electrochemical Method for Carboxylic Ester Synthesis from N‑Alkoxyamides Kripa Subramanian, Subhash L. Yedage, and Bhalchandra M. Bhanage* Department of Chemistry, Institute of Chemical Technology, Mumbai-400019, India S Supporting Information *

ABSTRACT: An electrochemical method for the synthesis of carboxylic as well as hindered esters from N-alkoxyamides has been reported. The electrochemical reaction proceeds through constant current electrolysis (CCE) by taking advantage of the dual role of n-Bu4NI (TBAI) as the redox catalyst as well as the supporting electrolyte. Besides providing mild reaction conditions, the present protocol is free from external oxidants and conducting salts, thereby generating nitrogen as the nonhazardous side product. Additionally, the developed procedure is highly advantageous due to its short reaction time, wide substrate scope, and gram-scale synthesis.

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INTRODUCTION The ester functional group is ubiquitous and a key component of natural products and biologically active molecules (Scheme 1).1 Classical methods reported for ester synthesis from various

Scheme 2. Previous Reports and Present Work for Ester Synthesis from Amides

Scheme 1. Biologically Important Esters

environmental aspects, we see an increasing demand for metaland oxidant-free organic synthesis, albeit such reactions were seldom performed in the past. It is well-known that electrochemistry is one of the benign, energy efficient, and thus sustainable alternatives to conventional redox transformation of organic compounds12 wherein the electron serves as a clean redox reagent, thereby replacing stoichiometric reagents with electric current. Furthermore, indirect/mediated electrosynthesis is a special approach in electroorganic synthesis where a mediator12c,13 acts as both an electron transfer agent and a redox catalyst, thereby avoiding reagent waste along with difficult separation procedures. Hence, the utilization of mediated electrolysis for the synthesis of esters

precursors include functional group interconversions (FGIs).2 However, FGIs of amides have always been a challenge due to the presence of a stable C−N bond.3 Traditionally, esterification of amides has been performed by acid/base2b-mediated processes and metal/enzyme catalysis.4 Among amides, N-alkoxyamides form a special class, useful for the synthesis of a variety of esters. From N-alkoxyamides, esters have been synthesized using Ce(NH4)2(NO2)6,5 NiO2·H2O,5 Ag2O,6 Pb(OAc)4,7,8and tBuOCl/NaN39 as catalysts. Subsequently, Du and co-workers10 used a stoichiometric amount of N-bromosuccinimide for the synthesis of hindered esters. and recently Lan and Lei’s group reported11 the use of Ni(acac)2/DTBP and Cu(OTf)2/DTBP for ester synthesis from amides (Scheme 2). Of late, taking into consideration the © 2017 American Chemical Society

Received: June 14, 2017 Published: September 5, 2017 10025

DOI: 10.1021/acs.joc.7b01473 J. Org. Chem. 2017, 82, 10025−10032

Article

The Journal of Organic Chemistry Table 1. Optimization of Reaction Conditionsa

from N-alkoxyamides seemed to be an attractive alternative to the traditional oxidant/metal-catalyzed approach. Thus, in view of the fact that TBAI is an efficient catalyst14 as well as a supporting electrolyte15 in radical reactions, we expected it to be the ideal candidate as a metal-free redox catalyst in our reactions. Therefore, considering these advantages, we herein report the metal- and oxidant-free electrochemical synthesis of carboxylic and hindered esters from N-alkoxyamides in the presence of TBAI using CCE.

entry 1 2 3

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RESULTS AND DISCUSSION To explore the idea, we initially started with optimization of the reaction by using N-methoxybenzamide 1a as the model substrate, a redox catalyst, and a suitable solvent. CCE was carried out in an undivided cell using a Pt plate anode and Cu plate cathode. As shown in Table 1, a series of experiments were carried out to study the effect of reaction parameters such as catalyst screening, catalyst loading, effect of solvents, electrode materials, and temperature on the yield of the desired product 2a. The progress of the reaction was monitored by using TLC until the starting material was completely consumed. First, various metal-free redox catalysts were screened using N,N-dimethylformamide (DMF) as the solvent and by passing the maximum current possible in each case until the cutoff voltage (10 V) was reached (Table 1, entries 1−8). Of these, TBAI provided superior yield (85%) of the desired product 2a. The use of n-Bu4NBr also resulted in good yield while other catalysts, viz., KI, NaI, Me4NI, and Et4NBr, gave moderate yields of 2a. However, KCl had poor solubility in DMF, leading to conductivity issues and thus produced inferior yield of 2a. The use of molecular I2 as catalyst in 0.1 M tertabutylammonium hexafluorophosphate (TBAPF6) as the electrolyte did not yield the ester. In general, due to their better solubility in most organic solvents, quaternary ammonium halides turned out to better catalysts than metal halides. Out of these quaternary ammonium halides, TBAI proved to be ideal. Furthermore, because TBAI provided necessary conductivity to the reaction mixture, additional conducting salts were not necessary to carry out the reaction. It was observed that on passing 9 mA current (i.e., current density of 1 mA cm−2), the time taken to obtain maximum yield was 90 min. This is equivalent to passing 1 F mol−1 of electric charge which is same as the theoretical amount required for maximum conversion. Thus, for further optimizations the reaction time was fixed to be 90 min at a current density of 1 mA cm−2. Next, the effect of catalyst loading, viz., 5, 10, 15, 20, and 25 mol % of TBAI, at constant reaction time was monitored (Table 1, entries 8−12). Increasing the catalyst concentration from 5 to 10 mol % led to an increase in conductivity of the reaction mixture, leading to a substantial increase in the yield of 2a. Catalyst surge from 10 to 15 and then to 20 mol % led to a gradual increase in yield, and further increase of catalyst loading from 20 to 25 mol % produced little effect on the yield of 2a. Therefore, the concentration of TBAI was fixed to be 20 mol %, which resulted in 94% yield of 2a. The effect of solvents was noteworthy (Table 1, entries 11, 13−16). Out of the various solvents screened, DMF was found to be compatible because it yielded 94% of 2a. Dimethyl sulfoxide (DMSO) gave yields around 78% while C2H5OH and CH3CN gave poor yields of product. Toluene diminished the conductivity of the system drastically and hence did not yield 2a. There was a significant increase in yield when the temperature was increased from

4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 c

21

22d 23e 24f

catalyst (mol %) KI (10) NaI (10) I2/TBAPF6 (10) KCl (10) n-Me4NI (10) n-Bu4NBr (10) n-Et4NBr (10) n-Bu4NI (10) n-Bu4NI (5) n-Bu4NI (15) n-Bu4NI (20) n-Bu4NI (25) n-Bu4NI (20) n-Bu4NI (20) n-Bu4NI (20) n-Bu4NI (20) n-Bu4NI (20) n-Bu4NI (20) n-Bu4NI (20) n-Bu4NI (20) n-Bu4NI (20) n-Bu4NI (20) n-Bu4NI (20) n-Bu4NI (20)

temp (°C)

time (min)

current (mA)

yieldb (%)

DMF DMF DMF

85 85 85

101 105 90

8 6 9

78 78 0

DMF DMF

85 85

105 115

4 7

31 73

DMF

85

101

8

83

DMF

85

146

5.5

76

DMF

85

90

9

85

DMF DMF

85 85

161 90

5 9

48 90

DMF

85

90

9

94

DMF

85

90

9

94

EtOH

85

90

9

10

CH3CN

85

90

9

29

DMSO

85

90

9

78

toluene

85

90

1.5 × 10−3

n.r.

DMF

30

90

9

25

DMF

60

90

9

68

DMF

80

90

9

90

DMF

90

90

9

94

DMF

85

90

9

65

DMF

85

90

9

67

DMF

85

90

9

64

DMF

85

90

9

42

solvent

a

Reaction conditions: N-methoxybenzamide (1a, 0.5 mmol), solvent (15 mL). bGC yield, anode−cathode systems. cGraphite−Cu. dPt−Pt. e Pt−Ni. fPt−C.

room temperature (30 °C) to 60 °C. Further on, we noticed a gradual increase in yield with a rise in temperature to 85 °C. Increase in temperature beyond 85 °C did not affect the yield of 2a (Table 1, entries 11, 17−20). Subsequently, the effect of various electrode materials was also investigated. Changing the anode from platinum to graphite led to a wide reduction in yield of the ester from 94% to 65% (Table 1, entry 21). Apart from copper, the other cathodes, viz., platinum, nickel, and carbon, were comparatively less active for the reaction (Table 1, entries 22−24). From the above observations, we deduced the following optimal reaction conditions: the CCE of 0.5 mmol of N-methoxybenzamide at 1 mA cm−2 in an undivided cell 10026

DOI: 10.1021/acs.joc.7b01473 J. Org. Chem. 2017, 82, 10025−10032

Article

The Journal of Organic Chemistry

respective ester 2m, and the starting material was completely recovered. Interestingly, amides containing external multiple bonds were transformed to the corresponding esters 2n (80%) and 2o (78%) in good yields. Moreover, replacing the phenyl ring of the amide with a heterocyclic furan ring did not hinder the reaction, thereby producing the corresponding ester 2p in 83% yield. However, thiophenyl and pyridynyl N-methoxyamides were stable to electrolysis and thus did not yield any ester (2q, 2r). To further explore the substrate scope of Nalkoxyamides, various N-substituted benzamides were also screened as shown in Table 3. It was noteworthy, that as the OR chain length on nitrogen decreased, the yield of the corresponding esters increased and thus the yield of 4a (62%) was greater than that of 4b (58%) which in turn was greater than 4c (54%). The N-substituted cyclohexylmethoxy and benzyloxy groups, i.e., 3d−f, were well tolerated to produce the respective esters 4d (65%), 4e (73%), and 4f (71%). Interestingly, amides containing N-substituted allyloxy and propargyloxy groups were also transformed to the corresponding esters 4g and 4h in good yields. Notably, when a cyanide containing amide was subjected to optimal reaction conditions, the corresponding product 4i was not obtained and the starting material was recovered. We observed that when N-methoxyamides containing bulky R groups such as phenyl isobutyric or adamantane were electrolyzed, the corresponding esters 6a (83%) and 6b (81%) were obtained in excellent yields, but when R is a 2,6disubstituted group, the corresponding ester 6c (38%) was obtained in low yield. Having successfully achieved the electrochemical transformation of N-alkoxyamides to carboxylic esters, we applied this electrochemical protocol for the synthesis of hindered esters. The synthesis of hindered esters has always been a challenge because bulky substituents always hampered the process and thus not many reports10,16 could be found in this regard. It is worth noting that we were able to successfully synthesize hindered esters in moderate to good yields by applying the standard conditions of electrolysis as shown in Table 4. It was interesting to observe that a bulky R′ group on the amide was also tolerated to produce the corresponding ester 6d in 64% yield. Fortunately, this protocol was also applicable to amides bearing both bulky R and R′ groups as in 6e (61%) even though 6f was not obtained. Control experiments (Scheme 3) were carried out by stirring 0.5 mmol of N-methoxybenzamide with TBAI dissolved in DMF at 85 °C without passing electric current. Here product 2a was not obtained even after 24 h of stirring. This indicated that passing electric current is indispensable for the reaction to be feasible. Further, when reactions were carried out under the standard conditions using N-methoxy-N-methylbenzamide (1s), the corresponding product was not observed. Thus, it was concluded that the N−H bond is necessary for the reaction to be viable. Further, to get insights into the reaction mechanism, the electrolysis was performed under standard conditions in the presence of 40 mol % of a radical scavenger, viz., (2,2,6,6- tetramethylpiperidin-1-yl)oxyl (TEMPO). Here only less than 6% of the ester 2a was isolated. This indicated that the reaction proceeded via a radical mechanism. Additionally, the effect of visible light was also studied. It was found that visible light had no impact on the yield of the desired product, and the reaction proceeded smoothly even in the dark. As shown in Scheme 4, to understand the mechanism further, we carried out crossover experiments under standard

equipped with Pt plate anode and Cu plate cathode using 20 mol % of TBAI and 15 mL DMF at 85 °C for 90 min. With the optimized conditions in hand, we investigated the scope and generality of the reaction for various Nmethoxybenzamide derivatives containing diverse functional groups at the ortho, meta, and para positions of the phenyl ring. The results are summarized in Table 2. In general, electroTable 2. Substrate Scope for Electrochemical Esterification of N-Methoxybenzamide under Standard Conditionsa

a N-Methoxybenzamides 1a−r (0.5 mmol), Pt−Cu electrode in an undivided cell. Yield of isolated pure product.

chemical C−N bond cleavage and in situ thermal rearrangement of N-methoxybenzamide gave 2a in 92% yield. It was observed that electron-donating substrates such as CH3, OCH3, and tBu produced good yields of corresponding products 2b−e. But, hindered 2-methyl-N-methoxybenzamide resulted in a lower yield of 2h (52%). Meanwhile, α- and β-Nmethoxynaphthamides were also tolerated to produce the corresponding esters 2f (81%) and 2g (64%), respectively. The lower yield of the esters of N-methoxy-1-naphthamide compared to that of N-methoxy-2-naphthamide may be attributed to the steric hindrance of the former. Next, weakly electron-withdrawing groups such as Cl and Br on the para position resulted in good yields of 2i (81%) and 2j (76%). However, a Cl group in the meta position resulted in a poor yield of 2k (44%) and Cl in the ortho position did not yield the ester 2l. But, a strongly electron-withdrawing group containing amide, viz., N-methoxy-4-nitrobenzamide, did not provide the 10027

DOI: 10.1021/acs.joc.7b01473 J. Org. Chem. 2017, 82, 10025−10032

Article

The Journal of Organic Chemistry Table 3. Substrate Scope for Electrochemical Esterification of N-Substituted Benzamides under Standard Conditionsa

a

N-Substituted benzamides 3a−i (0.5 mmol), Pt−Cu electrode in an undivided cell. Yield of isolated pure product.

Table 4. Substrate Scope for Electrochemical Esterification of Hindered N-Alkoxyamides under Standard Conditionsa

Scheme 3. Control Experiments

a N-Alkoxyamides 5a−f (0.5 mmol), Pt−Cu electrode in an undivided cell. Yield of isolated pure product.

Scheme 4. Experiment To Probe the Proposed Intramolecular Reaction Pathway

electrolytic conditions by taking an equimolar mixture of Nmethoxy (1b) and N-benzyloxy (3e) benzamides. After electrolysis, a 50:50 mixture of the corresponding esters 2b and 4e was obtained with an overall yield of 72% whereas the cross-coupled products 2t and 4j were not observed. This experiment suggested that the process occurs through an intramolecular mechanism. Intending to establish the practicality of the protocol, we scaled up the electrochemical reaction of N-methoxybenzamide for the synthesis of methyl benzoate to gram scale, producing 71% yield under standard conditions as shown in Scheme 5. On the basis of the above observations and former literature reports,5−10 we propose a plausible reaction mechanism for the electrochemical reaction as shown in Scheme 6. Initially, at the anode, the electrochemical oxidation of the iodide ion leads to the formation of an iodine radical which abstracts a proton from N-methoxybenzamide, 1a and converts it to radical

intermediate 2. Being active, 2 immediately undergoes dimerization to form the N−N homodimer 3, thereby liberating HI which further undergoes oxidation to produce iodide ion and H+, and the catalytic cycle continues. The H+ produced at the anode moves toward the cathode, and the expected hydrogen evolution is suppressed due to the presence 10028

DOI: 10.1021/acs.joc.7b01473 J. Org. Chem. 2017, 82, 10025−10032

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The Journal of Organic Chemistry

ELITE-1 column. HRMS were recorded on a micromass ESI TOF (time-of-flight) mass spectrometer. The IR spectra were recorded in ATR (attenuated total reflectance) mode by using a PerkinElmer Spectrum 2 FT-IR spectrometer. All reactions were carried out in oven-dried glassware. Starting materials 1a−r, 3a−i, and 4a−f were synthesized according to reported procedures.18 Other chemicals and solvents were obtained from commercial sources such as SigmaAldrich, Alfa Aesar, and Spectrochem and were used without further purification. Analytical TLC of products was performed with 60F254 silica gel plates (0.25 mm thickness). Products were purified by column chromatography with silica gel (60−120 mesh) using petroleum ether/EtOAc. General Electrochemical Procedure for the Synthesis of Esters from N-Alkoxyamides. A 25 mL pear-shaped three-necked undivided cell equipped with a platinum plate (30 mm × 15 mm) anode and copper plate (30 mm × 15 mm) cathode was connected to a regulated DC power supply. N-Methoxybenzamide (0.5 mmol, 75.6 mg) and TBAI (0.05 mmol, 37 mg) dissolved in 15 mL of DMF were then added into the cell. Electrolysis was carried out under CCE of 1 mA cm−2 at 85 °C until the starting material was completely consumed as determined by TLC. The mixture was constantly stirred during electrolysis. After electrolysis, the reaction mixture was diluted with ethyl acetate and washed twice with water. The organic layer was separated and dried over Na2SO4, filtered, and concentrated in vacuo. The product was then purified by column chromatography. Methyl Benzoate (2a).2g The typical procedure was applied to Nmethoxybenzamide 1a (0.50 mmol, 76 mg). Silica gel chromatography (eluent: petroleum ether/ethyl acetate = 9.5/1) of the product 2a afforded a colorless oil (63 mg, yield 92%): 1H NMR (400 MHz, CDCl3) δH/ppm 7.93 (d, J = 8.4 Hz, 2H), 7.44−7.36 (m, 1H), 7.34− 7.23 (m, 2H), 3.76 (s, 3H). 13C NMR (100 MHz, CDCl3) δC/ppm 166.8, 132.7, 130.1, 129.4, 128.2, 51.8. IR (ATR) ν (cm−1) 2952, 1718, 1435, 1272, 1109, 707. GC-MS (EI, 70 eV) m/z (%) 136.05 (44.40), 106.05 (8.88), 105.05 (100), 77.00 (69.26), 50.95 (28.75). Methyl 4-Methylbenzoate (2b).2g The typical procedure was applied to N-methoxy-4-methylbenzamide 1b (0.50 mmol, 83 mg). Silica gel chromatography (eluent: petroleum ether/ethyl acetate = 9.5/1) of the product 2b afforded a white crystalline solid (59 mg, yield 78%): 1H NMR (400 MHz, CDCl3) δH/ppm 7.90 (d, J = 8.2 Hz, 2H), 7.21 (d, J = 7.2 Hz, 2H), 3.87 (s, 3H), 2.38 (s, 3H). 13C NMR (100 MHz, CDCl3) δC/ppm 167.2, 143.5, 129.6, 129.0, 127.4, 51.9, 21.6. IR (ATR) ν (cm−1) 2925, 1721, 1434, 1275, 1106, 753. GC-MS (EI, 70 eV) m/z (%) 150.05 (43.50), 120.05 (10.35), 119.05 (100), 91.05 (58.49), 77.00 (1.64), 50.95 (4.42). Methyl 4-Methoxybenzoate (2c).2g The typical procedure was applied to N,4-dimethoxybenzamide 1c (0.50 mmol, 91 mg). Silica gel chromatography (eluent: petroleum ether/ethyl acetate = 9.5/1) of the product 2c afforded a white solid (76 mg, yield 91%): 1H NMR (400 MHz, CDCl3) δH/ppm 7.74 (d, J = 8.1 Hz, 2H), 6.66 (d, J = 8.0 Hz, 2H), 3.63 (s, 3H), 3.56 (s, 3H). 13C NMR (100 MHz, CDCl3) δC/ ppm 166.8, 163.3, 131.6, 122.5, 113.6, 55.4, 51.8. IR (ATR) ν (cm−1) 2952, 2843, 1705, 1426, 1280, 1104, 1020, 769. GC-MS (EI, 70 eV) m/z (%) 166.00 (42.42), 136.05 (10.16), 135.05 (100), 107.00 (20.20), 91.95 (16.46), 77.00 (27.75), 63.95 (11.83). Methyl 4-tert-Butylbenzoate (2d).2g The typical procedure was applied to 4-tert-butyl-N-methoxybenzamide 1d (0.50 mmol, 104 mg). Silica gel chromatography (eluent: petroleum ether/ethyl acetate = 9.5/1) of the product 2d afforded a light yellow oil (67 mg, yield 70%): 1H NMR (400 MHz, CDCl3) δH/ppm 7.93 (d, J = 8.5 Hz, 2H), 7.39 (d, J = 8.5 Hz, 2H), 3.84 (s, 3H), 1.28 (s, 9H). 13C NMR (100 MHz, CDCl3) δC/ppm 166.9, 156.4, 129.4, 127.4, 125.2, 51.8, 34.9, 31.0. IR (ATR) ν (cm−1) 2955, 1722, 1435, 1277, 1116, 775, 707. GCMS (EI, 70 eV) m/z (%) 192.00 (21.26), 178.05 (12.74), 177.05 (100), 161.05 (11.85), 149.05 (27.21), 115.00 (11.09), 105.00 (18.89), 91.00 (17.73), 77.00 (9.10), 58.95 (13.17). Methyl 3-Methylbenzoate (2e).2g The typical procedure was applied to N-methoxy-3-methylbenzamide 1e (0.50 mmol, 83 mg). Silica gel chromatography (eluent: petroleum ether/ethyl acetate = 9.5/1) of the product 2e afforded a colorless oil (67 mg, yield 89%): 1 H NMR (400 MHz, CDCl3) δH/ppm 7.81 (d, J = 2.2 Hz, 1H), 7.79

Scheme 5. Electrochemical Gram-Scale Synthesis of Ester from N-Methoxyamide

Scheme 6. Plausible Reaction Mechanism

of n-Bu4N+ ions which eventually get adsorbed on the cathode surface.17 Finally, dimer 3 undergoes in situ thermal rearrangement to produce methyl ester 4. In conclusion, we have developed an efficient electrochemical method for the cleavage of C−N bond of amides for the syntheses of esters by using TBAI as the redox catalyst. The reaction was performed by CCE in an undivided cell containing a platinum anode and copper cathode using DMF as the solvent. The protocol was applicable for the synthesis of a wide range of carboxylic esters and was feasible even for the synthesis of hindered esters. The electrochemical reaction was scalable to gram level, highlighting its practicability. Hitherto, this is a novel and environmentally benign electrochemical approach for the synthesis of esters from amides. This electrochemical protocol has the following benefits: (a) it is free from metal catalysts or oxidizing agents, thereby simplifying the workup and isolation process and leading to a reduction in waste; (b) only a catalytic amount of TBAI is required; (c) no additional supporting electrolyte is required, as TBAI serves the purpose; (d) iodine and its salts have low toxicity and are safe as compared to bromine and other transition-metal-based oxidation catalysts. Hence, TBAI represents the ideal catalyst in this research.

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EXPERIMENTAL SECTION

Instruments and Reagents. Electrolysis was carried out using a regulated DC power supply generated by Metrohm Autolab PGSTAT302N. NMR spectra were recorded with an Agilent Technologies (1H NMR at 500 or 400 MHz, 13C NMR at 125 or 100 MHz) spectrometer. The chemical shifts are reported in ppm relative to TMS as the internal standard and the coupling constant in hertz. A GC-MS-QP 2010 instrument (Rtx-17, 30 m × 25 mm ID, film thickness (df) = 0.25 μm) (column flow 2 mL min−1, 80 to 240 °C at 10 °C min−1 increments) was used for the mass analysis. GC yields were obtained using PerkinElmer Clarus 400 instruments with an 10029

DOI: 10.1021/acs.joc.7b01473 J. Org. Chem. 2017, 82, 10025−10032

Article

The Journal of Organic Chemistry

1256, 739, 674. GC-MS (EI, 70 eV) m/z (%) 170.05 (35.95), 141.00 (32.18), 139.00 (100), 112.95 (16.52), 110.95 (51.28), 74.95 (30.79), 49.95 (14.46). Methyl Cinnamate (2n).10 The typical procedure was applied to Nmethoxycinnamamide 1n (0.50 mmol, 89 mg). Silica gel chromatography (eluent: petroleum ether/ethyl acetate = 9.5/1) of the product 2n afforded a light yellow oil (65 mg, yield 80%): 1H NMR (400 MHz, CDCl3) δH/ppm 7.67 (d, J = 16.0 Hz, 1H), 7.47 (d, J = 1.9 Hz, 2H), 7.34 (t, J = 1.5 Hz, 3H), 6.42 (d, J = 16.1 Hz, 1H), 3.77 (s, 3H). 13C NMR (100 MHz, CDCl3) δC/ppm 167.4, 144.8, 134.3, 130.3, 128.8, 128.0, 117.8, 51.6. IR (ATR) ν (cm−1) 2950, 1713, 1636, 1434, 1167, 766, 683. GC-MS (EI, 70 eV) m/z (%) 162.00 (52.19), 161.00, (27.82), 156.00 (11.27), 155.00 (91.65), 131.00 (100), 103.00 (65.29), 76.95 (37.45), 50.95 (22.42). Methyl-3-Phenylpropiolate (2o).19 The typical procedure was applied to N-methoxy-3-phenylpropiolamide 1o (0.50 mmol, 88 mg). Silica gel chromatography (eluent: petroleum ether/ethyl acetate = 9.5/1) of the product 2o afforded a pale yellow oil (62 mg, yield 78%): 1 H NMR (500 MHz, CDCl3) δH/ppm δ 7.58−7.52 (m, 2H), 7.44− 7.32 (m, 3H), 3.81 (s, 3H). 13C NMR (125 MHz, CDCl3) δC/ppm 154.4, 133.0, 130.7, 128.6, 119.5, 86.4, 80.4, 52.8. IR (ATR) ν (cm−1). 2954, 2224, 1708, 1434, 1285, 1168, 1003, 756, 688. GC-MS (EI, 70 eV) m/z (%)195.95 (3.77), 165.00 (7.17), 160.00 (31.96), 130.05 (12.18), 129.10 (100), 102.05 (40.00), 101.05 (11.59), 75.00 (16.97), 51.00 (7.62). Methyl Furan-2-carboxylate (2p).20 The typical procedure was applied to N-methoxyfuran-2-carboxamide 1p (0.50 mmol, 71 mg). Silica gel chromatography (eluent: petroleum ether/ethyl acetate = 9.5/1) of the product 2p afforded a pale yellow liquid (52 mg, yield 83%): 1H NMR (500 MHz, CDCl3) δH/ppm 7.54 (d, J = 1.0 Hz, 1H), 7.14 (dd, J = 3.6, 0.6 Hz, 1H), 6.47 (dd, J = 3.5, 1.7 Hz, 1H), 3.86 (s, 3H). 13C NMR (125 MHz, CDCl3) δC/ppm 159.1, 146.3, 144.5, 117.9, 111.8, 51.9. IR (ATR) ν (cm−1) 2956, 1722, 1476, 1299, 1116, 760. GC-MS (EI, 70 eV) m/z (%) 126.05 (38.23), 96.05 (10.21), 95.05 (100), 68.00 (4.23), 67.00 (6.27). Ethyl Benzoate (4a).4d The typical procedure was applied to Nethoxybenzamide 3a (0.50 mmol, 83 mg). Silica gel chromatography (eluent: petroleum ether/ethyl acetate = 9.5/1) of the product 4a afforded a colorless oil (47 mg, yield 62%): 1H NMR (400 MHz, CDCl3) δH/ppm 8.03 (d, J = 6.9 Hz, 2H), 7.65−7.47 (m, 1H), 7.41 (dd, J = 8.3, 6.9 Hz, 2H), 4.35 (q, J = 7.1 Hz, 2H), 1.37 (t, J = 7.1 Hz, 3H). 13C NMR (100 MHz, CDCl3) δC/ppm 166.6, 132.8, 130.4, 129.5, 128.3, 60.9, 14.3. IR (ATR) ν (cm−1) 2982, 1714, 1451, 1270, 1174, 1106, 708. GC-MS (EI, 70 eV) m/z (%) 150.05 (28.24), 122.00 (47.27), 105.95 (14.34), 105.15 (100), 77.00 (69.95), 51.00 (31.44). Propyl Benzoate (4b).4d The typical procedure was applied to Npropoxybenzamide 3b (0.50 mmol, 90 mg). Silica gel chromatography (eluent: petroleum ether/ethyl acetate = 9.5/1) of the product 4b afforded a colorless oil (48 mg, yield 58%): 1H NMR (400 MHz, CDCl3) δH/ppm 8.03 (d, J = 7.0 Hz, 2H), 7.53 (t, J = 7.4 Hz, 1H), 7.42 (dd, J = 8.3, 7.0 Hz, 2H), 4.26 (t, J = 6.7 Hz, 2H), 1.77 (h, J = 7.3 Hz, 2H), 1.01 (t, J = 7.4 Hz, 3H). 13C NMR (100 MHz, CDCl3) δC/ ppm 166.7, 132.8, 130.5, 129.5, 128.3, 66.5, 22.1, 10.5. IR (ATR) ν (cm−1) 2970, 1717, 1452, 1270, 1108, 709. GC-MS (EI, 70 eV) m/z (%) 164.00 (3.15), 123.05 (75.99), 122.05 (51.50), 105.95 (23.03), 105.15 (100), 77.00 (78.83), 51.00 (36.21), 41.05 (10.56). Butyl Benzoate (4c).21 The typical procedure was applied to Nbutoxybenzamide 3c (0.50 mmol, 97 mg). Silica gel chromatography (eluent: petroleum ether/ethyl acetate = 9.5/1) of the product 4c afforded a colorless oil (54 mg, yield 61%): 1H NMR (500 MHz, CDCl3) 8.09−8.00 (m, 2H), 7.58−7.49 (m, 1H), 7.43 (t, J = 7.7 Hz, 2H), 4.32 (t, J = 6.6 Hz, 2H), 1.80−1.70 (m, 2H), 1.52−1.43 (m, 2H), 0.98 (t, J = 7.4 Hz, 3H). 13C NMR (125 MHz, CDCl3) δC/ppm 166.7, 132.8, 130.5, 129.5, 128.3, 64.8, 30.8, 19.3, 13.8. IR (ATR) ν (cm−1) 2960, 2874, 1716, 1452, 1270, 1108, 1027, 707. GC-MS (EI, 70 eV) m/z (%) 178.00 (2.29%), 123.15 (87.32%), 122.05 (28.00%), 106.10 (12.40%), 105.15 (100%), 79.05 (15.30%), 77.05 (64.59%), 56.05 (32.04%), 51.00 (20.73%), 41.00 (10.81%). Cyclohexylmethyl Benzoate (4d).4d The typical procedure was applied to N-(cyclohexylmethoxy)benzamide 3d (0.50 mmol, 117

(s, 1H), 7.28 (d, J = 4.3 Hz, 1H), 7.24 (dd, J = 7.7, 2.3 Hz, 1H), 3.85 (s, 3H), 2.33 (s, 3H). 13C NMR (100 MHz, CDCl3) δC/ppm 167.1, 138.0, 133.6, 130.0, 128.2, 126.6, 51.9, 21.1. IR (ATR) ν (cm−1) 2952, 1718, 1436, 1279, 1201, 1106, 743. GC-MS (EI, 70 eV) m/z (%) 150.20 (41.11), 119.15 (100), 91.10 (61.80), 65.05 (19.09), 39.05 (7.40). Methyl 2-Naphthoate (2f).2e The typical procedure was applied to N-methoxy-2-napthamide 1f (0.50 mmol, 101 mg). Silica gel chromatography (eluent: petroleum ether/ethyl acetate = 9.5/1) of the product 2f afforded a white solid (75 mg, yield 81%): 1H NMR (400 MHz, CDCl3) δH/ppm 8.60 (s, 1H), 8.05 (d, J = 8.7 Hz, 1H), 7.93 (d, J = 8.1 Hz, 1H), 7.86 (d, J = 8.2 Hz, 2H), 7.55 (m, 2H), 3.97 (s, 3H). 13C NMR (100 MHz, CDCl3) δC/ppm 167.2, 135.5, 132.5, 131.0, 129.3, 128.2, 128.1, 127.7, 127.4, 126.6, 125.2, 52.2. IR (ATR) ν (cm−1) 1706, 1438, 1294, 1201, 1130, 768, 484. GC-MS (EI, 70 eV) m/z (%) 186.00 (47.57), 156.00 (11.27), 155.00 (91.65), 127.05 (100), 101.00 (9.62), 77.05 (20.64), 63.15 (17.61), 51.00 (10.32). Methyl 1-Naphthoate (2g).2e The typical procedure was applied to N-methoxy-1-napthamide 1g (0.50 mmol, 101 mg). Silica gel chromatography (eluent: petroleum ether/ethyl acetate = 9.5/1) of the product 2g afforded a colorless oil (60 mg, yield 64%): 1H NMR (400 MHz, CDCl3) δH/ppm 9.01 (d, J = 8.6 Hz, 1H), 8.18 (d, J = 7.3 Hz, 1H), 7.95 (d, J = 8.2 Hz, 1H), 7.83 (d, J = 8.2 Hz, 1H), 7.67−7.57 (m, 1H), 7.56−7.47 (m, 1H), 7.47−7.39 (m, 1H), 3.97 (s, 3H). 13C NMR (100 MHz, CDCl3) δC/ppm 167.9, 133.8, 133.4, 131.4, 130.3, 128.6, 127.8, 127.0, 126.2, 125.9, 124.5, 52.1. IR (ATR) ν (cm−1) 2950, 1711, 1435, 1243, 1133, 778. GC-MS (EI, 70 eV) m/z (%) 185.95 (62.28), 155.00 (100), 127.05 (89.67), 101.00 (7.26), 77.00 (13.65), 63.10 (11.71), 50.95 (6.77). Methyl 2-Methylbenzoate (2h).2g The typical procedure was applied to N-methoxy-2-methylbenzamide 1h (0.50 mmol, 83 mg). Silica gel chromatography (eluent: petroleum ether/ethyl acetate = 9.5/1) of the product 2h afforded a colorless oil (39 mg, yield 52%): 1 H NMR (400 MHz, CDCl3) δH/ppm 7.85 (d, J = 8.2 Hz, 1H), 7.29 (d, J = 1.7 Hz, 1H), 7.15 (dd, J = 9.0, 5.3 Hz, 2H), 3.79 (s, 3H), 2.54 (s, 3H). 13C NMR (100 MHz, CDCl3) δC/ppm 167.8, 140.1, 131.8, 131.6, 130.5, 129.4, 125.6, 51.5, 21.6. IR (ATR) ν (cm−1) 2952, 1718, 1435, 1254, 1082, 735. GC-MS (EI, 70 eV) m/z (%) 150.05 (59.43), 120.05 (9.36), 119.05 (100), 91.00 (89.65), 76.95 (9.73), 64.95 (34.61). Methyl 4-Chlorobenzoate (2i).2g The typical procedure was applied to 4-chloro-N-methoxybenzamide 1i (0.50 mmol, 93 mg). Silica gel chromatography (eluent: petroleum ether/ethyl acetate = 9.5/1) of the product 2i afforded a colorless oil (69 mg, yield 81%): 1 H NMR (400 MHz, CDCl3) δH/ppm 7.95 (d, J = 8.4 Hz, 2H), 7.39 (d, J = 7.7 Hz, 2H), 3.89 (s, 3H). 13C NMR (100 MHz, CDCl3) δC/ ppm 166.1, 139.3, 130.9, 128.6, 128.5, 52.2. IR (ATR) ν (cm−1) 1675, 1400, 1276, 1090, 759, 522. GC-MS (EI, 70 eV) m/z (%) 170.10, (30.46), 141.10 (32.38), 139.10 (100), 113.10 (13.13), 111.05 (40.31), 75.05 (25.11), 50.00 (10.87). Methyl 4-Bromobenzoate (2j).2g The typical procedure was applied to 4-bromo-N-methoxybenzamide 1j (0.50 mmol, 115 mg). Silica gel chromatography (eluent: petroleum ether/ethyl acetate = 9.5/1) of the product 2j afforded a white solid (82 mg, yield 76%): 1H NMR (400 MHz, CDCl3) δH/ppm 7.87 (d, J = 8.6 Hz, 2H), 7.56 (d, J = 8.6 Hz, 2H), 3.89 (s, 3H). 13C NMR (100 MHz, CDCl3) δC/ppm 166.3, 131.7, 131.1, 129.0, 128.0, 52.3. IR (ATR) ν (cm−1) 2950, 1714, 1581, 1433, 1190, 848, 755, 572. GC-MS (EI, 70 eV) m/z (%) 213.85 (36.40), 184.85 (94.97), 182.85 (100), 156.90 (42.22), 154.90, (43.86), 135.00 (13.02), 104.00 (8.08), 76.00 (57.96), 75.00 (59.48), 73.95 (31.75), 49.95 (58.79). Methyl 3-Chlorobenzoate (2k).2e The typical procedure was applied to 3-chloro-N-methoxybenzamide 1k (0.50 mmol, 93 mg). Silica gel chromatography (eluent: petroleum ether/ethyl acetate = 9.5/1) of the product 2k afforded a colorless oil (38 mg, yield 44%): 1 H NMR (400 MHz, CDCl3) δH/ppm 7.99 (s, 1H), 7.89 (d, J = 7.5 Hz, 1H), 7.49 (d, J = 8.0 Hz, 1H), 7.41−7.29 (m, 1H), 3.90 (s, 3H). 13 C NMR (100 MHz, CDCl3) δC/ppm 165.7, 134.4, 132.8, 131.8, 129.56, 129.62, 127.6, 52.3. IR (ATR) ν (cm−1) 2925, 1726, 1437, 10030

DOI: 10.1021/acs.joc.7b01473 J. Org. Chem. 2017, 82, 10025−10032

Article

The Journal of Organic Chemistry

colorless oil (79 mg, yield 81%): 1H NMR (500 MHz, CDCl3) δH/ ppm 3.62 (s, 3H), 1.98 (s, 3H), 1.86 (d, J = 3.0 Hz, 6H), 1.75−1.62 (m, 6H). 13C NMR (125 MHz, CDCl3) δC/ppm 178.2, 51.5, 40.6, 38.8, 36.5, 27.9. IR (ATR) ν (cm−1) 2905, 2852, 1728, 1452, 1233, 1184, 1076. GC-MS (EI, 70 eV) m/z (%) 194.10 (13.97), 136.20 (12.07), 135.20 (100), 107.10 (9.55), 93.10 (14.92), 79.05 (13.96), 41.00 (3.47). Methyl 2,6-Dimethoxybenzoate (6c).25 The typical procedure was applied to N,2,6-trimethoxybenzamide 5c (0.50 mmol, 106 mg). Silica gel chromatography (eluent: petroleum ether/ethyl acetate = 9.5/1) of the product 6c afforded off white solid (37 mg, yield 38%): 1H NMR (500 MHz, CDCl3) δH/ppm 7.27 (t, J = 8.5 Hz, 1H), 6.55 (d, J = 8.4 Hz, 2H), 3.90 (s, 3H), 3.80 (s, 6H). 13C NMR (125 MHz, CDCl3) δC/ ppm 167.1, 157.3, 131.1, 112.9, 103.9, 77.3, 77.0, 76.8, 56.0, 52.4. IR (ATR) ν (cm−1) 3006, 2921, 2850, 1731, 1594, 1475, 1251, 1104. GCMS (EI, 70 eV) m/z (%) 196.00 (42.37), 166.00 (10.17), 165.00 (100), 150.05 (25.19), 136.05 (12.62), 122.00 (9.62), 107.00 (22.59), 79.00 (5.47), 77.00 (7.89), 51.00 (4.12). Isobutyl Benzoate (6d).4d The typical procedure was applied to Nisobutoxybenzamide 5d (0.50 mmol, 97 mg). Silica gel chromatography (eluent: petroleum ether/ethyl acetate = 9.5/1) of the product 6d afforded a colorless oil (54 mg, yield 61%): 1H NMR (500 MHz, CDCl3) δH/ppm 8.10−8.02 (m, 2H), 7.58−7.50 (m, 1H), 7.46−7.40 (m, 2H), 4.11 (d, J = 6.6 Hz, 2H), 2.15−2.03 (m, 1H), 1.02 (d, J = 6.7 Hz, 6H). 13C NMR (125 MHz, CDCl3) δC/ppm 166.6, 132.8, 130.5, 129.5, 128.3, 71.0, 27.9, 19.2. IR (ATR) ν (cm−1) 2963, 2875, 1717, 1451, 1268, 1109, 1026, 708. GC-MS (EI, 70 eV) m/z (%)178.05 (0.05%), 124.10 (8.37%), 123.15 (81.71%), 106.05 (14.43%), 105.15 (100%), 79.05 (7.67%), 77.05 (63.38%), 56.05 (45.73%), 51.00 (20.65%), 41.00 (12.11%). (3r,5r,7r)-tert-Butyl Adamantane-1-carboxylate (6e).10 The typical procedure was applied to (3r,5r,7r)-N-(tert-butoxy)adamantane-1carboxamide 5e (0.50 mmol, 126 mg). Silica gel chromatography (eluent: petroleum ether/ethyl acetate = 9.5/1) of the product 6e afforded a colorless oil (72 mg, yield 61%): 1H NMR (500 MHz, CDCl3) δH/ppm 2.02 (d, J = 3.2 Hz, 4H), 1.90 (d, J = 2.9 Hz, 8H), 1.83 (d, J = 2.9 Hz, 1H), 1.77−1.65 (m, 9H), 1.42 (s, 2H). 13C NMR (125 MHz, CDCl3) δC/ppm 184.2, 40.5, 38.8, 38.5, 36.4, 28.0, 27.8. IR (ATR) ν (cm−1). 2905, 2852, 1695, 1453, 1247, 1169, 1079. GC-MS (EI, 70 eV) m/z (%) 180.05 (4.84), 136.15 (11.57), 135.15 (100), 107.05 (9.06), 93.05 (13.68), 79.05 (12.57), 57.05 (6.22), 41.00 (3.85). Procedure for the Gram-Scale Synthesis of Methyl Benzoate. A 250 mL round-bottomed flask with detachable threeneck lid equipped with a cylindrical platinum gauze (d = h = 4.5 cm) anode and copper plate (4.5 cm × 6.0 cm) cathode was connected to a regulated DC power supply. N-Methoxybenzamide (7.0 mmol, 1.06 g) and TBAI (1.4 mmol, 2.6 g) dissolved in 150 mL of DMF were then added to the cell. Electrolysis was carried out under CCE of 1 mA cm−2 at 85 °C for 90 min until 1 F mol−1 charge was consumed. The mixture was constantly stirred during electrolysis. After electrolysis, the reaction mixture was diluted with ethyl acetate and washed thrice with water. The organic layer was separated and dried over Na2SO4, filtered, and concentrated in vacuo. The product was then purified by column chromatography.

mg). Silica gel chromatography (eluent: petroleum ether/ethyl acetate = 9.5/1) of the product 4d afforded a colorless oil (71 mg, yield 65%): 1 H NMR (400 MHz, CDCl3) δH/ppm 8.03 (dd, J = 8.4, 1.4 Hz, 2H), 7.64−7.48 (m, 1H), 7.42 (dd, J = 8.4, 7.0 Hz, 2H), 4.12 (d, J = 6.3 Hz, 2H), 1.86−1.62 (m, 5H), 1.41−0.83 (m, 6H). 13C NMR (100 MHz, CDCl3) δC/ppm 166.6, 132.8, 130.5, 129.5, 128.3, 70.0, 37.2, 29.7, 26.4, 25.7. IR (ATR) ν (cm−1) 2924, 2853,1717, 1450, 1268, 1176, 1113, 708. GC-MS (EI, 70 eV) m/z (%) 218.15 (0.03), 123.00 (20.15), 105.00 (99.61), 96.10 (100), 81.05 (94.42), 77.00 (63.31), 68.05 (23.36), 67.05 (42.26), 55.05 (33.11), 54.05 (15.83), 51.00 (17.12), 41.05 (23.24). Benzyl Benzoate (4e).4d The typical procedure was applied to N(benzyloxy)benzamide 3e (0.50 mmol, 114 mg). Silica gel chromatography (eluent: petroleum ether/ethyl acetate = 9.5/1) of the product 4e afforded a colorless oil (77 mg, yield 73%): 1H NMR (400 MHz, CDCl3) δH/ppm 8.12−8.05 (m, 2H), 7.60−7.51 (m, 1H), 7.49−7.31 (m, 5H), 5.37 (s, 3H). 13C NMR (100 MHz, CDCl3) δC/ ppm 166.4, 136.0, 133.2, 130.1, 129.7, 128.6, 128.4, 128.2, 128.2, 66.7. IR (ATR) ν (cm−1) 1716, 1451, 1266, 1175, 708. GC-MS (EI, 70 eV) m/z (%) 212.00 (38.42), 194.00 (22.16), 167.05 (11.92), 105.95 (19.66), 105.15 (100), 91.05 (82.23), 79.05 (12.98), 77.00 (63.57), 65.05 (25.60), 51.00 (31.53), 39.00 (11.98). 3-Chlorobenzyl Benzoate (4f).2f The typical procedure was applied to N-((3-chlorobenzyl)oxy)benzamide 3f (0.50 mmol, 131 mg). Silica gel chromatography (eluent: petroleum ether/ethyl acetate = 9.5/1) of the product 4f afforded a colorless oil (87 mg, yield 71%): 1H NMR (400 MHz, CDCl3) δH/ppm 8.07 (d, J = 6.9 Hz, 2H), 7.56 (t, J = 7.4 Hz, 1H), 7.44 (t, J = 7.7 Hz, 3H), 7.30 (d, J = 1.4 Hz, 3H), 5.32 (s, 2H). 13C NMR (100 MHz, CDCl3) δC/ppm 166.2, 138.0, 134.4, 133.2, 129.9, 129.8, 129.7, 128.4, 128.4, 128.1, 126.1, 65.7. IR (ATR) ν (cm−1) 1718, 1451, 1265, 1176, 1107, 709, 538. GC-MS (EI, 70 eV) m/z (%) 245.90 (22.44), 127.00 (11.07), 125.00 (34.50), 105.95 (22.88), 89.00 (19.85), 105.15 (100), 77.00 (50.16), 51.00 (18.15). Prop-2-en-1-yl Benzoate (4g).22 The typical procedure was applied to N-(prop-2-en-1-yloxy)benzamide 3g (0.50 mmol, 89 mg). Silica gel chromatography (eluent: petroleum ether/ethyl acetate = 9.5/1) of the product 4g afforded a colorless oil (60 mg, yield 74%): 1H NMR (400 MHz, CDCl3) δH/ppm 8.05 (d, J = 7.0 Hz, 2H), 7.61−7.49 (m, 1H), 7.42 (dd, J = 8.6, 6.9 Hz, 2H), 6.11−5.91 (m, 1H), 5.45−5.22 (m, 2H), 4.81 (d, J = 5.6 Hz, 2H). 13C NMR (100 MHz, CDCl3) δC/ ppm 166.2, 133.0, 132.2, 130.1, 129.6, 128.3, 118.2, 65.5. IR (ATR) ν (cm−1) 1717, 1649, 1452, 1266, 1176, 1108, 708. GC-MS (EI, 70 eV) m/z (%) 162.00 (10.69), 117.05 (9.70), 105.95 (47.59), 105.05 (100), 77.00 (75.98), 51.00 (34.27), 50.00 (10.50), 41.00 (16.54), 39.00 (18.26). Prop-2-yn-1-yl Benzoate (4h).23 The typical procedure was applied to N-(prop-2-yn-1-yloxy)benzamide 3h (0.50 mmol, 88 mg). Silica gel chromatography (eluent: petroleum ether/ethyl acetate = 9.5/1) of the product 4h afforded a colorless oil (58 mg, yield 73%): 1H NMR (400 MHz, CDCl3) δH/ppm 8.04 (d, J = 8.4 Hz, 2H), 7.53 (td, J = 7.4, 1.4 Hz, 1H), 7.41 (t, J = 7.0 Hz, 2H), 4.89 (d, J = 1.6 Hz, 2H), 2.51 (t, J = 2.4 Hz, 1H). 13C NMR (100 MHz, CDCl3) δC/ppm 165.7, 133.3, 129.8, 129.3, 128.4, 77.7, 75.1, 52.4. IR (ATR) ν (cm−1) 3296, 1720, 1452, 1262, 1095, 707, 568. GC-MS (EI, 70 eV) m/z (%) 159.95 (12.92), 115.00 (24.70), 105.95 (42.58), 105.05 (100), 77.05 (79.87), 50.95 (43.83), 50.00 (14.39), 39.00 (24.75). Methyl 2-Methyl-2-phenylpropanoate (6a).24 The typical procedure was applied to N-methoxy-2-methyl-2-phenylpropanamide 5a (0.50 mmol, 97 mg). Silica gel chromatography (eluent: petroleum ether/ethyl acetate = 9.5/1) of the product 6a afforded a white solid (74 mg, yield 83%): 1H NMR (500 MHz, CDCl3) δH/ppm 7.5−7.16 (m, 5H), 3.66 (s, 3H), 1.61 (d, J = 1.6 Hz, 6H). 13C NMR (125 MHz, CDCl3) δC/ppm 177.3, 144.7, 128.4, 126.7, 125.6, 52.2, 46.5, 26.6. IR (ATR) ν (cm−1) 2977, 1730, 1434, 1255, 1144, 697. GC-MS (EI, 70 eV) m/z (%) 178.05 (21.95), 120.15 (11.91), 119.15 (100), 103.05 (6.98), 91.10 (56.70), 77.05 (8.33), 51.00 (4.49), 41.00 (11.61). (3r,5r,7r)-Methyl Adamantane-1-carboxylate (6b).10 The typical procedure was applied to (3r,5r,7r)-N-methoxyadamantane-1-carboxamide 5b (0.50 mmol, 105 mg). Silica gel chromatography (eluent: petroleum ether/ethyl acetate = 9.5/1) of the product 6b afforded a

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*E-mail: [email protected]; bm.bhanage@gmail. com. 10031

DOI: 10.1021/acs.joc.7b01473 J. Org. Chem. 2017, 82, 10025−10032

Article

The Journal of Organic Chemistry ORCID

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Bhalchandra M. Bhanage: 0000-0001-9538-3339 Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS K.S. thanks the University Grants Commission of India (UGC) for providing a Basic Scientific Research (BSR) fellowship. S.L.Y. thanks the Council of Scientific and Industrial Research (CSIR), Govt. of India, for providing a Senior Research Fellowship (SRF).

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DOI: 10.1021/acs.joc.7b01473 J. Org. Chem. 2017, 82, 10025−10032