The Reaction of Ketoximes with Hypervalent Iodine Reagents: Beckmann Rearrangement and Hydrolysis to Ketones

Abstract

We investigated the reaction of ketoximes with hypervalent iodine reagents. A combination of PhI(OAc)₂ and BF₃·Et₂O promoted the Beckmann rearrangement of ketoximes, thus yielding the corresponding amides. From a detailed investigation of the reaction, we determined that the Beckmann rearrangement is preceded by acetylation of the hydroxy group of the ketoxime in situ, accelerating the Beckmann rearrangement. We confirmed that the acetylated ketoxime undergoes the Beckmann rearrangement with BF₃·Et₂O. The reaction of ketoximes with Koser’s reagent [PhI(OH)OTs] in the presence of tetrahydrofuran results in hydrolysis, affording the corresponding ketones in high yields at room temperature.

Oximes are derivatives of carbonyl compounds utilized for the purification and characterization of parent carbonyl compounds, and as carbonyl protector groups.[1] Also, oximes undergo Beckmann rearrangement in the presence of acid, affording the corresponding amides. This rearrangement is one of the most powerful routes for the synthesis of amides; it is widely used in organic syntheses.[2] A Lewis acid is typically used for Beckmann rearrangement for activation of the oxime, along with heating.[3] We have studied the reaction of oximes with hypervalent iodine reagents[4] and observed an interesting transformation that depends on the type of oxime: aldoxime[5] or ketoxime.[6] The reaction of aldoximes with Koser’s reagent [PhI(OH)OTs] in dimethyl sulfoxide–water afforded the corresponding carboxylic acids in good to high yields. The reaction proceeds via hydroxamic acid generated by the oxidation of aldoxime; further oxidation affords a nitroso compound, which undergoes hydrolysis furnishing the carboxylic acid (Scheme [1]).[5] By contrast, we found that the reaction of a ketoxime with a hypervalent iodine reagent showed different reactivity. The combination of PhI(OAc)₂ and a Lewis acid promoted Beckmann rearrangement under mild reaction conditions.[6] In the present paper, we report the scope of substrates, details of the reaction mechanism, and application to the hydrolysis of ketoximes using PhI(OH)OTs under mild conditions (Scheme [1]).

While continuing our studies on hypervalent iodine chemistry,[7] we hypothesized that ketoximes could undergo Beckmann rearrangement with a hypervalent iodine reagent by activating the hydroxy group of ketoxime. However, it has been reported that the eliminated acetate ion attacks the imine group carbon, yielding the parent ketone (Scheme [2]).[8]

Therefore, we hypothesized that capturing the acetate ion via the addition of a Lewis acid could prevent this nucleophilic attack on the carbon of the imine. We first examined the reaction of 4′-methoxyacetophenone oxime (1a) using a combination of PhI(OAc)₂ and BF₃·Et₂O in various solvents. The reaction in tetrahydrofuran (THF) afforded the parent ketone 3a rather than the desired amide 2a (Table [1], entry 1). We then investigated other solvents (entries 2–4); the use of CH₂Cl₂ and CH₃CN gave better results, with the corresponding amide obtained in yields of 52% and 27%, respectively. Without PhI(OAc)₂, the yield of amide was low (entries 5 and 6) despite considering the acid-induced Beckmann rearrangement.

Table 1 Solvent Effect on the Beckmann Rearrangement Using PhI(OAc)₂ and BF₃·Et₂O

Entry	Solvent	Time (h)	Yield (%)
			2a	3a
1	THF	21	–	70
2	TFE	21	3	37
3	CH3CN	20	27	13
4	CH2Cl2	3	52	30
5a	CH3CN	24	3	3
6a	CH2Cl2	21	15	3

^a The reaction was conducted without PhI(OAc)₂.

Unexpectedly, we found that pre-activation of PhI(OAc)₂ with BF₃·Et₂O in CH₃CN was effective, and the yield of 2a improved from 27% to 64%. In contrast, CH₂Cl₂ was ineffective for this pre-activation (Table [2], entries 1 and 2). We then attempted pre-activation at 70 °C for 30 minutes followed by addition of the substrate, stirring for 8 hours; this led to an increase in the yield to 91% (entry 3). High reaction temperatures, like those used for reflux, are typically required for Lewis acid mediated Beckmann rearrangement. However, the present Beckmann rearrangement proceeded at room temperature via pre-activation of the reagents. Heating after the addition of the substrate also greatly enhanced the reaction, which finished within 5 minutes at 70 °C, for a 97% yield (entry 4). Other hypervalent iodine reagents could cause this reaction, but with lower yields (entries 5 and 6). The addition of other Lewis acids (SnCl₄ and ZnCl₂) was not as effective, with longer reaction times observed (entries 7 and 8).

Table 2 Optimization of the Reaction Conditions for Beckmann Rearrangement

Entry	Hypervalent iodine	Pre-activation	Conditions	Yield (%) 2a
1	PhI(OAc)2	rt, 24 h	rt, 8 h	64
2a	PhI(OAc)2	rt, 24 h	rt, 8 h	trace
3	PhI(OAc)2	70 °C, 30 min	rt, 8 h	91
4	PhI(OAc)2	70 °C, 30 min	70 °C, 5 min	97
5	PhI(OCOCF3)2	70 °C, 1.5 h	70 °C, 5 h	67
6	PhI(OH)OTs	70 °C, 1.5 h	70 °C, 5 h	27
7b	PhI(OAc)2	70 °C, 15 min	70 °C, 5 h	88
8c	PhI(OAc)2	70 °C, 24 h	70 °C, 24 h	88

^a CH₂Cl₂ was used as a solvent instead of CH₃CN.

^b SnCl₄ (2.4 equiv) was used instead of BF₃·Et₂O.

^c ZnCl₂ (2.4 equiv) was used instead of BF₃·Et₂O.

Having obtained the optimal reaction conditions, we conducted the Beckmann rearrangement with a variety of ketoximes (Table [3] and Table [4]).

The reactions of acetophenone oximes and aliphatic ketoximes are listed in Table [3]. p-Methoxyacetophenone oxime (1a) underwent the Beckmann rearrangement with a high yield at room temperature (entry 1), but the reaction of o-methoxyacetophenone oxime (1b) resulted in only a 52% yield, even after 24 hours at room temperature (entry 3). Raising the reaction temperature to 70 °C enhanced the reaction, giving the corresponding amides 2b and 2a (entries 4 and 2, respectively), both in 97% yield. Substrates with an electron-donating substituent on the aromatic ring are preferable for this reaction, with the reaction completing faster than for substrates with an electron-withdrawing group on the aromatic ring (entries 5–8). The reaction of ketoxime 1g bearing an indole ring proceeded for 1 hour with a 90% yield (entry 9), while no rearranged product was obtained by the reaction of ketoxime 1h bearing a pyridine ring. Acetylated ketoxime 4h was obtained in 19% yield along with starting material 1h in 52% yield (entry 10). Aliphatic ketoxime 1i also underwent the rearrangement, affording the corresponding amide 2i in a yield of 70% (entry 11). Phenyl isopropyl ketoxime (1j), a mixture of geometric isomers, underwent the Beckmann rearrangement, affording two isomers, 2j and 2j′, according to the ratio of the starting material (entry 12).

Table 3 Beckmann Rearrangement of Acetophenone Oximes and Aliphatic Ketoximes

Entry	Ketoxime 1	Amide 2	Time	Yield (%)
1a	1a	2a	5 min	91
2	1a	2a	8 h	97
3a	1b	2b	24 h	52
4	1b	2b	5 min	97
5	1c	2c	10 min	95
6	1d	2d	30 min	98
7	1e	2e	4 h	97
8b	1f	2f	19 h	79
9	1g	2g	1 h	90
10	1h	2h	24 h	– (19)c
		4h
11	1i	2i	5 h	70
12	1j	2j	30 min	88
		2j′

^a The reaction was conducted at rt.

^b BF₃·Et₂O (4.8 equiv) was used.

^c Yield of 4h in parentheses.

The Beckmann rearrangement of benzophenone oximes also proceeded with high yields under the optimized conditions (Table [4], entries 1–3). Benzophenone oxime (1k) underwent the rearrangement, giving the corresponding amide 2k in 94% yield within 15 minutes (entry 1). The reaction of ketoxime 1l, a 1.0:1.0 mixture of E and Z isomers, afforded two types of amide, 2l and 2l′, in a ratio of 1.0:0.3. The reason for the change in ratio of the product compared to that of the starting material is that isomerization of the starting material occurs after the 4-methoxyphenyl group has been rearranged, giving 2l as the main product (entry 2). In the case of 1m, the products 2m and 2m′ were obtained in a 1.0:0.9 ratio (entry 3). In this case, the two substituents were rearranged as easily as each other. The reaction of oxime 1n, which is derived from fluorenone, did not give a rearranged product, but acetylated ketoxime 4n was obtained in 64% yield (entry 4). Other cyclic ketoximes, i.e., 1o and 1p, did not react under these conditions (entries 5 and 6). On the other hand, 1q underwent the rearrangement, giving the corresponding amide 2q in 71% yield (entry 7). Regarding the reactivity of 1o, it is known that 1o is tolerant to the Lewis acid catalyzed Beckmann rearrangement and no rearranged product was obtained.[9] The reaction was finally allowed to proceed by turning the substrate into indanone oxime mesylate, with limited Lewis acids where the yield depended on the Lewis acid used.[9] We believe that the five-membered ring and six-membered ring are so stable that the rearrangement does not occur under our reaction conditions.

Table 4 Beckmann Rearrangement of Benzophenone Oximes and Cyclic Ketoximes

Entry	Ketoxime 1	Amide 2	Time	Yield (%)
1	1k	2k	15 min	94
2	1l	2l	5 min	95
		2l′
3	1m	2m	30 min	96
		2m′
4	1n	2n	24 h	– (55)a
		4n
5	1o	2o	24 h	–
6	1p	2p	24 h	–
7	1q	2q	3 h	71

^a Yield of 4n in parentheses.

Initially, we assumed that the hypervalent iodine mediated Beckmann rearrangement could proceed by the activation of the hydroxy group of ketoxime with a hypervalent iodine reagent, as well as the Lewis acid preventing nucleophilic attack of the acetate ion. However, when the reaction of 1a was conducted at room temperature, an intermediate was detected via thin-layer chromatography, and disappeared after the reaction. By contrast, the reaction of 1d at room temperature did not complete after 24 hours and its intermediate remained after workup. We then isolated this intermediate, which was found to be acetylated ketoxime 4d (Table [5]).

Table 5 The Beckmann Reaction at Room Temperature

Entry	R	Time (h)	Yield (%)
			2	4
1	OMe (1a)	5 min8	91 (2a)	–
2	H (1d)	24	33 (2d)	11 (4d)

We speculated that the reaction should proceed via acetylated ketoxime and examined the reaction of acetylated ketoxime 4d under various conditions (Table [6]). The reaction of 4d with PhI(OAc)₂ yielded no rearranged product (entry 1), but a combination of PhI(OAc)₂ and BF₃·Et₂O afforded the amide 2d in 89% yield (entry 2). Finally, the use of 5.0 equivalents of BF₃·Et₂O promoted the rearrangement without PhI(OAc)₂, giving 2d in 81% yield (entry 3), thus indicating that 4 is an intermediate in this reaction.

Table 6 The Reaction of O-Acetyl Ketoxime 4d

Entry	PhI(OAc)2	BF3·Et2O	Time (h)	Yield (%)
1	1.2 equiv	–	9	–
2	1.2 equiv	2.4 equiv	24	89
3	–	5.0 equiv	24	81

We show how our proposed reaction mechanism explains the above results (Table [5] and Table [6]) in Scheme [3]. First, PhI(OAc)₂ is activated by BF₃·Et₂O;[10] then, ketoxime reacts with the activated PhI(OAc)₂. Ketoxime 1 can attack the iodine center of activated PhI(OAc)₂ and replace the acetoxy group to afford intermediate A, followed by intramolecular rearrangement giving the acetylated ketoxime 4 (Scheme [3], path a). The acetylated ketoxime 4 may also be obtained via direct attack of ketoxime 1 of the carbonyl carbon of activated PhI(OAc)₂ (Scheme [3], path b). Acetylated ketoxime 4 is more reactive than non-acetylated ketoxime 1 and the acetoxy group is activated by BF₃·Et₂O leading to the Beckmann rearrangement easily, to afford amide 2.

During this study, in contrast to the production of amides, we also found that the use of THF as a solvent was effective for the transformation of ketoxime 1a to ketone 3a with PhI(OAc)₂ and BF₃·Et₂O, in 70% yield (Table [7], entry 1). Moriarty and co-workers have already reported the reaction of ketoxime to ketone with PhI(OAc)₂ in CH₂Cl₂ in a 60% yield when using 1a as a substrate.[8] We attempted the reaction of 1a under Moriarty’s conditions, giving 3a in 53% yield (entry 2); this was difficult to reproduce consistently. Then, we explored the reaction conditions in various solvents without BF₃·Et₂O, but no improvement was observed when using PhI(OAc)₂ as a hypervalent iodine reagent (entries 3–5). The use of PhI(OH)OTs instead of PhI(OAc)₂ significantly improved the yield (entries 6–9), and we obtained a 92% yield of hydrolyzed product 3a when THF was used as a solvent (entry 6). We expected the addition of water to accelerate the reaction, but this was not observed when we used aqueous THF solution as a solvent (THF/H₂O, 1:1 and 10:1). The reaction with PhI(OCOCF₃)₂ afforded 3a in good yield (entry 10), but the yield was lower than with PhI(OH)OTs. We then employed 1.2 equivalents of PhI(OH)OTs in THF at room temperature as the optimized conditions, and investigated the substrate scope (Table [8]).

Table 7 Exploration of the Reaction Conditions for the Transformation to Ketone

Entry	Hypervalent iodine reagent (equiv)	Solvent	Time (h)	Yield (%) 3a
1a	PhI(OAc)2 (1.2)	THF	21	70
2	PhI(OAc)2 (1.2)	CH2Cl2	3	53
3	PhI(OAc)2 (1.2)	CH3CN	0.5	53
4	PhI(OAc)2 (1.2)	THF	3	53
5	PhI(OAc)2 (1.2)	CF3CH2OH	0.5	57
6	PhI(OH)OTs (1.2)	THF	6	92
7	PhI(OH)OTs (1.2)	CH3CN	24	83
8	PhI(OH)OTs (1.2)	CH2Cl2	24	54
9	PhI(OH)OTs (1.2)	CF3CH2OH	24	98 (55)b
10	PhI(OCOCF3)2 (1.2)	THF	24	71

^a BF₃·Et₂O (5.0 equiv) was used.

^b Yield in parentheses indicates the result when the reaction was stopped after 6 h.

Acetophenone oximes 1a and 1c bearing a methoxy group on the aromatic ring underwent hydrolysis to their corresponding ketones in good to high yields (Table [8], entries 1 and 2), as did nonsubstituted acetophenone oxime (1d, entry 3). The reaction of 4′-chloroacetophenone oxime (1e) gave ketone 3e in 96% yield after 19 hours. However, no hydrolyzed product was obtained when using 1f with a nitro group on the aromatic ring, even after 24 hours (entry 5). Increasing the amount of PhI(OH)OTs to 3.0 equivalents promoted the reaction, giving 3f in 59% yield (entry 6). The reaction of ketoxime 1h bearing a pyridine ring afforded the corresponding ketone 3h in a moderate yield (43%, entry 7), which was also improved by increasing the amount of PhI(OH)OTs (entry 8). Other aromatic ketoximes, i.e., 1k, 1n, and 1o, were transformed to their corresponding ketones in good to high yields (entries 9–11). The aliphatic ketoxime 1r was also converted into its parent ketone in high yield (entry 12).

Table 8 Substrate Scope of the Transformation of Ketoxime to Ketone

Entry	Substrate	Time (h)	Yield (%) 3
1	1a	6	94
2	1c	3	72
3	1d	24	82
4	1e	19	96
5	1f	24	trace
6a	1f	24	59
7	1h	24	43
8a	1h	24	57
9	1k	24	80
10	1n	24	62
11	1o	24	78
12	1r	23	93

^a PhI(OH)OTs (3.0 equiv) was used.

In conclusion, we have developed the hypervalent iodine mediated Beckmann rearrangement of ketoximes in the presence of BF₃·Et₂O under mild reaction conditions. A combination of PhI(OAc)₂ and BF₃·Et₂O generates acetylated ketoxime as an intermediate followed by rearrangement, which is promoted by BF₃·Et₂O. We have also achieved efficient cleavage of ketoximes to ketones by using PhI(OH)OTs, which contains trivalent iodine, in THF, affording the corresponding ketones in good to high yields. Further study of the reactivity of oximes with hypervalent iodine reagents is underway.

All chemicals were obtained from Sigma Aldrich, TCI, Nacalai Chemical, or Fujifilm Wako Chemical as reagent grade and were used as received. TLC was performed on Merck silica gel F254 plates (0.25 mm). ¹H and ¹³C NMR spectra were recorded on JEOL JMN-400, 500, or Bruker AVANCE III 600 spectrometers, in CDCl₃ or DMSO-d ₆. Chemical shifts are expressed in ppm from internal TMS (δ) and coupling constants (J) are in hertz (Hz). Standard abbreviations are used for defining signal multiplicities. High-resolution mass spectra (ESI-MS) were measured using an Exactive Plus mass spectrometer (Thermo Fisher Scientific Inc.).

N-(4-Methoxyphenyl)acetamide (2a);[11] Typical Procedure for the Beckmann Rearrangement of Ketoximes 1 to Amides 2 with PhI(OAc)₂ and BF₃·Et₂O

A solution of PhI(OAc)₂ (155 mg, 0.48 mmol) and BF₃·Et₂O (0.12 mL, 0.96 mmol) in CH₃CN (1.0 mL) was stirred at 70 °C for 30 min. Then, p-methoxyacetophenone oxime (1a) (66 mg, 0.40 mmol) was added to the above mixture and stirred at 70 °C for 5 min. After cooling to room temperature, 0.5% aqueous Na₂SO₃ was added to the reaction mixture which was then extracted with CHCl₃. The combined organic layer was washed with water, dried over Na₂SO₄, and concentrated in vacuo. The residue was purified by silica gel column chromatography (n-hexane/AcOEt, 1:1) and preparative TLC (n-hexane/AcOEt, 5:1) to give N-(4-methoxyphenyl)acetamide (2a) (66 mg, 97%) as a white solid.

¹H NMR (400 MHz, CDCl₃): δ = 7.38 (d, J = 8.8 Hz, 2 H), 7.28 (br, 1 H), 6.85 (d, J = 8.8 Hz, 2 H), 3.78 (s, 3 H), 2.14 (s, 3 H).

N-(2-Methoxyphenyl)acetamide (2b)[12]

2b (64 mg, 97%) was obtained from 1b (66 mg, 0.4 mmol) after purification by silica gel column chromatography (n-hexane/AcOEt, 1:1).

White solid.

¹H NMR (400 MHz, CDCl₃): δ = 8.35 (d, J = 8.0 Hz, 1 H), 7.78 (br, 1 H), 7.03 (t, J = 7.6 Hz, 1 H), 6.95 (t, J = 8.0 Hz, 1 H), 6.87 (d, J = 8.0 Hz, 1 H), 3.87 (s, 3 H), 2.19 (s, 3 H).

N-(3-Methoxyphenyl)acetamide (2c)[13]

2c (63 mg, 95%) was obtained from 1c (66 mg, 0.4 mmol) after purification by silica gel column chromatography (n-hexane/AcOEt, 1:1).

White solid.

¹H NMR (400 MHz, CDCl₃): δ = 7.40 (br s, 1 H), 7.26 (s, 1 H), 7.20 (t, J = 8.4 Hz, 1 H), 6.97 (d, J = 7.6 Hz, 1 H), 6.66 (d, J = 7.2 Hz, 1 H), 3.79 (s, 3 H), 2.16 (s, 3 H).

N-Phenylacetamide (2d)[14]

2d (53 mg, 98%) was obtained from 1d (54 mg, 0.4 mmol) after purification by silica gel column chromatography (n-hexane/AcOEt, 1:1).

White solid.

¹H NMR (400 MHz, CDCl₃): δ = 7.50 (d, J = 8.0 Hz, 2 H), 7.41 (br, 1 H), 7.31 (t, J = 8.0 Hz, 2 H), 7.10 (t, J = 7.2 Hz, 1 H), 2.17 (s, 3 H).

N-(4-Chlorophenyl)acetamide (2e)[15]

2e (64 mg, 97%) was obtained from 1e (66 mg, 0.4 mmol) after purification by silica gel column chromatography (n-hexane/AcOEt, 1:1).

White solid.

¹H NMR (400 MHz, DMSO-d ₆): δ = 10.0 (s, 1 H), 7.59 (d, J = 8.8 Hz, 2 H), 7.32 (d, J = 9.2 Hz, 2 H), 2.03 (s, 3 H).

N-(4-Nitrophenyl)acetamide (2f)[11]

2f (57 mg, 79%) was obtained from 1f (72 mg, 0.4 mmol) after purification by silica gel column chromatography (n-hexane/AcOEt, 1:1) and preparative TLC (n-hexane/AcOEt, 2:1). BF₃·Et₂O (0.25 mL, 1.92 mmol, 4.8 equiv) was used in this case.

Light yellow solid.

¹H NMR (400 MHz, DMSO-d ₆): δ = 10.55 (s, 1 H), 8.20 (d, J = 8.8 Hz, 2 H), 7.81 (d, J = 8.4 Hz, 2 H), 2.11 (s, 3 H).

N-[1-(Phenylsulfonyl)-1H-indol-3-yl]acetamide (2g)[14]

2g (113 mg, 90%) was obtained from 1g (126 mg, 0.4 mmol) after purification by silica gel column chromatography (n-hexane/AcOEt, 1:1) and preparative TLC (CHCl₃/MeOH, 20:1).

White solid.

¹H NMR (400 MHz, DMSO-d ₆): δ = 10.22 (s, 1 H), 8.09 (s, 1 H), 7.97–7.86 (m, 4 H), 7.65 (t, J = 7.6 Hz, 1 H), 7.55 (t, J = 8.0 Hz, 2 H), 7.40 (t, J = 7.6 Hz, 1 H), 7.31 (t, J = 7.6 Hz, 1 H), 2.13 (s, 3 H).

1-(Pyridin-3-yl)ethanone O-Acetyloxime (4h)

4h (6.8 mg, 19%) was obtained from 1h (27 mg, 0.2 mmol) after purification by silica gel column chromatography (n-hexane/AcOEt, 1:2) and preparative TLC (CHCl₃/MeOH, 20:1).

Light yellow oil.

¹H NMR (400 MHz, CDCl₃): δ = 8.95 (s, 1 H), 8.69 (d, J = 4.4 Hz, 1 H), 8.12 (d, J = 8.0 Hz, 1 H), 7.37 (dd, J = 4.8, 8.0 Hz, 1 H), 2.43 (s, 3 H), 2.29 (s, 3 H).

¹³C NMR (400 MHz, CDCl₃): δ = 168.4, 160.0, 151.1, 147.8, 134.3, 130.7, 123.3, 19.6, 14.0.

HRMS (ESI+): m/z [M + Na]⁺ calcd for C₉H₁₀N₂O₂Na: 201.0640; found: 201.0634.

N-(2-Phenylethyl)acetamide (2i)[15]

2i (23 mg, 70%) was obtained from 1i (33 mg, 0.2 mmol) after purification by silica gel column chromatography (n-hexane/AcOEt, 1:1) and preparative TLC (n-hexane/AcOEt, 1:8).

White solid.

¹H NMR (400 MHz, CDCl₃): δ = 7.33–7.19 (m, 5 H), 5.50 (br, 1 H), 3.52 (q, J = 6.8 Hz, 2 H), 2.82 (t, J = 6.8 Hz, 2 H), 1.94 (s, 3 H).

2-Methyl-N-phenylpropanamide (2j)[13]

2j and 2j′ (57 mg, 88%) were obtained as a 1.0:0.8 mixture from 1j (65 mg, 0.4 mmol) after purification by silica gel column chromatography (n-hexane/AcOEt, 6:1).

White solid.

¹H NMR (400 MHz, CDCl₃): δ = 7.54 (d, J = 8.0 Hz, 2 H), 7.36 (br, 1 H), 7.33–7.29 (m, 2 H), 7.09 (t, J = 7.2 Hz, 1 H), 2.52 (sept, J = 6.8 Hz, 1 H), 1.24 (d, J = 6.8 Hz, 6 H).

N-(1-Methylethyl)benzamide (2j′)[13]

White solid.

¹H NMR (400 MHz, CDCl₃): δ = 7.75 (d, J = 7.6 Hz, 2 H), 7.50–7.40 (m, 3 H), 5.95 (br, 1 H), 4.35–4.24 (m, 1 H), 1.27 (d, J = 6.4 Hz, 6 H).

N-Phenylbenzamide (2k)[16]

2k (74 mg, 94%) was obtained from 1k (79 mg, 0.4 mmol) after purification by silica gel column chromatography (CHCl₃/MeOH, 20:1).

White solid.

¹H NMR (400 MHz, DMSO-d ₆): δ = 10.25 (s, 1 H), 7.95 (d, J = 7.6 Hz, 2 H), 7.78 (d, J = 8.0 Hz, 2 H), 7.60–7.50 (m, 3 H), 7.35 (t, J = 8.0 Hz, 2 H), 7.09 (t, J = 7.6 Hz, 1 H).

N-(4-Methoxyphenyl)benzamide (2l) and 4-Methoxy-N-phenylbenzamide (2l′)[16]

2l and 2l′ (86 mg, 95%) were obtained as a 1.0:0.3 mixture from 1l (91 mg, 0.4 mmol) after purification by silica gel column chromatography (n-hexane/AcOEt, 1:1).

White solid.

¹H NMR (400 MHz, DMSO-d ₆): δ = 10.11 (s, NH, 0.74 H), 10.07 (s, 0.26 H), 7.96–7.92 (m, 2 H), 7.75 (d, J = 8.0 Hz, 0.52 H), 7.66 (d, J = 8.4 Hz, 1.48 H), 7.59–7.49 (m, 2.22 H), 7.33 (t, J = 8.0 Hz, 0.52 H), 7.09–7.04 (m, 0.78 H), 6.92 (d, J = 8.8 Hz, 1.48 H), 3.83 (s, 0.78 H), 3.74 (s, 2.22 H).

N-(4-Chlorophenyl)benzamide (2m) and 4-Chloro-N-phenylbenzamide (2m′)[16]

2m and 2m′ (90 mg, 96%) were obtained as a 1.0:0.9 mixture from 1m (93 mg, 0.4 mmol) after purification by silica gel column chromatography (CHCl₃).

White solid.

¹H NMR (400 MHz, DMSO-d ₆): δ = 10.36 (s, NH, 0.47 H), 10.30 (s, NH, 0.53 H), 7.98–7.93 (m, 2 H), 7.82–7.74 (m, 2 H), 7.61–7.51 (m, 2.53 H), 7.41–7.33 (m, 2 H), 7.10 (t, J = 7.6 Hz, 0.47 H).

9-Fluorenone O-Acetyloxime (4n)[17]

4n (26 mg, 55%) was obtained from 1n (39 mg, 0.2 mmol) after purification by silica gel column chromatography (CHCl₃) and preparative TLC (CHCl₃/MeOH, 100:1).

Yellow solid.

¹H NMR (400 MHz, CDCl₃): δ = 8.25 (d, J = 7.6 Hz, 1 H), 7.92 (d, J = 8.0 Hz, 1 H), 7.63 (d, J = 8.0 Hz, 1 H), 7.59 (d, J = 8.0 Hz, 1 H), 7.48 (t, J = 7.6 Hz, 1 H), 7.43 (t, J = 7.6 Hz, 1 H), 7.35–7.27 (m, 2 H), 2.42 (s, 3 H).

3,4,5,6-Tetrahydro-1H-1-benzazocin-2-one (2q)[18]

2q (25 mg, 71%) was obtained from 1q (35 mg, 0.2 mmol) after purification by silica gel column chromatography (CHCl₃/MeOH, 30:1) and preparative TLC (CHCl₃/MeOH, 30:1).

White solid.

¹H NMR (400 MHz, CDCl₃): δ = 7.79 (br, 1 H), 7.30–7.19 (m, 3 H), 7.09 (d, J = 7.2 Hz, 1 H), 2.90–1.30 (m, 8 H).

Acetophenone O-Acetyloxime (4d)[19] by the Beckmann Reaction of 1d at Room Temperature (Table [5], Entry 2)

A solution of PhI(OAc)₂ (77 mg, 0.24 mmol) and BF₃·Et₂O (0.06 mL, 0.48 mmol) in CH₃CN (0.5 mL) was stirred at 70 °C for 30 min. Then, acetophenone oxime (1d) (27 mg, 0.20 mmol) was added to the above mixture and stirred at rt for 24 h. After cooling to room temperature, 0.5% aqueous Na₂SO₃ was added to the reaction mixture which was then extracted with CHCl₃. The combined organic layer was washed with water, dried over Na₂SO₄, and concentrated in vacuo. The residue was purified by silica gel column chromatography (n-hexane/AcOEt, 1:1) and preparative TLC (n-hexane/AcOEt, 4:1) to give acetophenone O-acetyloxime (4d) (4.7 mg, 11%) as a white solid.

¹H NMR (400 MHz, CDCl₃): δ = 7.74 (dd, J = 1.4, 8.2 Hz, 2 H), 7.45–7.38 (m, 3 H), 2.39 (s, 3 H), 2.27 (s, 3 H).

4′-Methoxyacetophenone (3a);[20] Typical Procedure for the Hydrolysis of Ketoximes 1 to Ketones 3 with PhI(OH)OTs in THF

To a solution of p-methoxyacetophenone oxime (1a) (50 mg, 0.30 mmol) in THF (0.75 mL) was added PhI(OH)OTs (141 mg, 0.36 mmol) and the mixture was stirred at rt for 6 h. 3% Aqueous Na₂SO₃ was added to the reaction mixture which was then extracted with Et₂O. The combined organic layer was dried over Na₂SO₄ and concentrated in vacuo. The residue was purified by silica gel column chromatography (n-hexane/AcOEt, 20:1) to give 4′-methoxyacetophenone (3a) (42 mg, 94%) as a yellow oil.

¹H NMR (400 MHz, CDCl₃): δ = 7.94 (d, J = 8.8 Hz, 2 H), 6.93 (d, J = 8.8 Hz, 2 H), 3.87 (s, 3 H), 2.56 (s, 3 H).

3′-Methoxyacetophenone (3c)[20]

3c (32 mg, 72%) was obtained from 1c (50 mg, 0.3 mmol) after purification by silica gel column chromatography (n-hexane/AcOEt, 10:1).

Yellow oil.

¹H NMR (400 MHz, CDCl₃): δ = 7.54 (d, J = 7.2 Hz, 1 H), 7.494–7.488 (m, 1 H), 7.39–7.35 (m, 1 H), 7.11 (dd, J = 2.4, 8.4 Hz, 1 H), 3.86 (s, 3 H), 2.60 (s, 3 H).

Acetophenone (3d)[20]

3d (110 mg, 82%) was obtained from 1d (150 mg, 1.1 mmol) after purification by silica gel column chromatography (n-hexane/AcOEt, 10:1).

Yellow oil.

¹H NMR (400 MHz, CDCl₃): δ = 7.97–7.95 (m, 2 H), 7.59–7.55 (m, 1 H), 7.49–7.45 (m, 2 H), 2.61 (s, 3 H).

4′-Chloroacetophenone (3e)[20]

3e (43 mg, 96%) was obtained from 1e (50 mg, 0.29 mmol) after purification by silica gel column chromatography (n-hexane/AcOEt, 20:1).

Yellow oil.

¹H NMR (400 MHz, CDCl₃): δ = 7.91–7.88 (d, J = 8.8 Hz, 2 H), 7.45–7.43 (d, J = 8.4 Hz, 2 H), 2.59 (s, 3 H).

4′-Nitroacetophenone (3f)[21]

3f (27.4 mg, 59%) was obtained from 1f (50 mg, 0.28 mmol) after purification by silica gel column chromatography (benzene).

Yellow oil.

¹H NMR (400 MHz, CDCl₃): δ = 8.32 (d, J = 8.2 Hz, 2 H), 8.11 (d, J = 8.2 Hz, 2 H), 2.68 (s, 3 H).

3-Acetylpyridine (3h)[22]

3h (25.6 mg, 57%) was obtained from 1h (50 mg, 0.37 mmol) after purification by silica gel column chromatography (AcOEt).

Yellow oil.

¹H NMR (400 MHz, CDCl₃): δ = 9.18–9.17 (m, 1 H), 8.80 (dd, J = 1.2, 4.8 Hz, 1 H), 8.24 (dt, J = 1.8, 7.8 Hz, 1 H), 7.45–7.41 (dd, J = 4.8, 7.8 Hz, 1 H), 2.65 (s, 3 H).

Benzophenone (3k)[23]

3k (37 mg, 80%) was obtained from 1k (50 mg, 0.25 mmol) after purification by silica gel column chromatography (n-hexane/CHCl₃, 4:1).

Yellow oil.

¹H NMR (400 MHz, CDCl₃): δ = 7.82–7.80 (m, 4 H), 7.59 (t, J = 7.2 Hz, 2 H), 7.50–7.47 (m, 4 H).

9-Fluorenone (3n)[23]

3n (29 mg, 62%) was obtained from 1n (50 mg, 0.26 mmol) after purification by silica gel column chromatography (n-hexane/AcOEt, 10:1).

Yellow oil.

¹H NMR (400 MHz, CDCl₃): δ = 7.66 (d, J = 7.2 Hz, 2 H), 7.54–7.47 (m, 4 H), 7.31–7.28 (m, 2 H).

1-Indanone (3o)[24]

3o (35 mg, 78%) was obtained from 1o (50 mg, 0.34 mmol) after purification by silica gel column chromatography (n-hexane/AcOEt, 5:1).

Yellow oil.

¹H NMR (400 MHz, CDCl₃): δ = 7.76 (d, J = 8.0 Hz, 1 H), 7.60–7.55 (m, 1 H), 7.48 (d, J = 8.0 Hz, 1 H), 7.41–7.35 (m, 1 H), 3.14 (t, J = 5.8 Hz, 2 H), 2.71–2.68 (m, 2 H).

2-Octanone (3r)[21]

3r (42 mg, 93%) was obtained from 1r (50 mg, 0.35 mmol) after purification by silica gel column chromatography (CHCl₃).

Yellow oil.

¹H NMR (400 MHz, CDCl₃): δ = 2.41 (t, J = 7.4 Hz, 2 H), 2.13 (s, 3 H), 1.60–1.55 (m, 2 H), 1.32–1.22 (m, 6 H), 0.88 (t, J = 6.8 Hz, 3 H).

Conflict of Interest

The authors declare no conflict of interest.

Acknowledgment

We thank the Kindai University Joint Research Center for use of their facilities.

• References

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Corresponding Authors

Publication History

Received: 12 March 2022

Accepted after revision: 26 April 2022

Accepted Manuscript online:
26 April 2022

Article published online:
08 June 2022

© 2022. Thieme. All rights reserved

Georg Thieme Verlag KG
Rüdigerstraße 14, 70469 Stuttgart, Germany

• References

• 1 Wuts PG. M. Greene’s Protective Groups in Organic Synthesis, 5th ed. John Wiley & Sons, Inc; Hoboken, NJ: 2014: 661
  CrossrefSearch in Google Scholar
• 2a Craig D. The Beckmann and Related Reactions . In Comprehensive Organic Synthesis, Vol. 7. Trost BM, Fleming I. Pergamon Press; Oxford: 1991: 689-702
  CrossrefSearch in Google Scholar
• 2b Gawley RE. Org. React. 1988; 35: 1
  Search in Google Scholar
• 3a Ghiaci M, Imanzadeh GH. Synth. Commun. 1998; 28: 2275
  CrossrefSearch in Google Scholar
• 3b Thomas B, Sugunan S. Microporous Mesoporous Mater. 2006; 96: 55
  CrossrefSearch in Google Scholar
• 3c Sugamoto K, Matsushita Y, Matsui T. Synth. Commun. 2011; 41: 879
  CrossrefSearch in Google Scholar
• 3d An N, Pi H, Liu L, Du W, Deng W. Chin. J. Chem. 2011; 29: 947
  CrossrefSearch in Google Scholar

For reviews see:
• 4a Hypervalent Iodine Chemistry. Modern Developments in Organic Synthesis. In Topics in Current Chemistry, Vol. 224. Wirth T. Springer; Berlin: 2003
  Search in Google Scholar
• 4b Tohma H, Kita Y. Adv. Synth. Catal. 2004; 346: 111
  Search in Google Scholar
• 4c Moriarty RM. J. Org. Chem. 2005; 70: 2893
  CrossrefPubMedSearch in Google Scholar
• 4d Wirth T. Angew. Chem. Int. Ed. 2005; 44: 3656
  CrossrefPubMedSearch in Google Scholar
• 4e Zhdankin VV, Stang PJ. Chem. Rev. 2008; 108: 5299
  CrossrefPubMedSearch in Google Scholar
• 4f Ochiai M. Synlett 2009; 159
• 4g Dohi T, Kita Y. Chem. Commun. 2009; 2073
  CrossrefPubMed
• 4h Duschek A, Kirsch SF. Angew. Chem. Int. Ed. 2011; 50: 1524
  CrossrefPubMedSearch in Google Scholar
• 4i Merritt EA, Olofsson B. Synthesis 2011; 517
• 4j Silva LF, Olofsson B. Nat. Prod. Rep. 2011; 28: 1722
  Search in Google Scholar
• 4k Yoshimura A, Zhdankin VV. Chem. Rev. 2016; 116: 3328
  Search in Google Scholar
• 4l Hypervalent Iodine Chemistry. In Topics in Current Chemistry, Vol. 373. Wirth T. Springer; Switzerland: 2016
  Search in Google Scholar
• 5 Nakamura A, Kanou H, Tanaka J, Imamiya A, Maegawa T, Miki Y. Org. Biomol. Chem. 2018; 16: 541
  CrossrefPubMedSearch in Google Scholar
• 6 Oishi R, Segi K, Hamamoto H, Nakamura A, Maegawa T, Miki Y. Synlett 2018; 29: 1465
  Thieme ConnectPubMedSearch in Google Scholar
• 7a Hamamoto H, Umemoto H, Umemoto M, Ohta C, Doshita M, Miki Y. Synlett 2010; 2593
• 7b Hamamoto H, Hattori S, Takemaru K, Miki Y. Synlett 2011; 1563
• 7c Miki Y, Umemoto H, Doshita M, Hamamoto H. Tetrahedron Lett. 2012; 53: 1924
  CrossrefSearch in Google Scholar
• 7d Hamamoto H, Umemoto H, Umemoto M, Ohta C, Fujita E, Nakamura A, Maegawa T, Miki Y. Heterocycles 2015; 91: 561
  CrossrefSearch in Google Scholar
• 7e Nakamura A, Tanaka S, Imamiya A, Takane R, Ohta C, Fujimura K, Maegawa T, Miki Y. Org. Biomol. Chem. 2017; 15: 6702
  CrossrefPubMedSearch in Google Scholar
• 7f Shibata A, Kitamoto S, Fujimura K, Hirose Y, Hamamoto H, Nakamura A, Miki Y, Maegawa T. Synlett 2018; 29: 2275
  Thieme ConnectSearch in Google Scholar
• 7g Nakamura A, Takane R, Tanaka J, Morimoto J, Maegawa T. Heterocycles 2018; 97: 785
  CrossrefSearch in Google Scholar
• 8 Moriarty RM, Prakash O, Vavilikolanu PR. Synth. Commun. 1986; 16: 1247
  CrossrefPubMedSearch in Google Scholar
• 9 Torisawa Y, Nishi T, Minamikawa J. Bioorg. Med. Chem. 2003; 11: 2205
  CrossrefPubMedSearch in Google Scholar
• 10 Izquierdo S, Essafi S, Rosal I, Vidossich P, Pleixats R, Vallribera A, Ujaque G, Lledós A, Shafir A. J. Am. Chem. Soc. 2016; 138: 12747
  CrossrefPubMedSearch in Google Scholar
• 11 Prakash GK. S, Moran MD, Mathew T, Olah GA. J. Fluorine Chem. 2009; 130: 806
  CrossrefPubMedSearch in Google Scholar
• 12 Dooleweerdt K, Fors BP, Buchwald SL. Org. Lett. 2010; 12: 2350
  CrossrefPubMedSearch in Google Scholar
• 13 Furuya Y, Ishihara K, Yamamoto H. J. Am. Chem. Soc. 2005; 127: 11240
  CrossrefPubMedSearch in Google Scholar
• 14 Roy S, Gribble GW. Heterocycles 2006; 70: 51
  CrossrefPubMedSearch in Google Scholar
• 15 Sakai N, Moriya T, Konohara T. J. Org. Chem. 2007; 72: 5920
  CrossrefPubMedSearch in Google Scholar
• 16 Wang Y, Zhu D, Tang L, Wang S, Wang Z. Angew. Chem. Int. Ed. 2011; 50: 8917
  CrossrefPubMedSearch in Google Scholar
• 17 Liu S, Yu Y, Liebeskind LS. Org. Lett. 2007; 9: 1947
  CrossrefPubMedSearch in Google Scholar
• 18 Witosiñska A, Musielak B, Serda P, Owiñska M, Rys B. J. Org. Chem. 2012; 77: 9784
  CrossrefPubMedSearch in Google Scholar
• 19 Huang K, Li S, Chang M, Zhang X. Org. Lett. 2013; 15: 484
  CrossrefPubMedSearch in Google Scholar
• 20 Muthaiah S, Hong SH. Adv. Synth. Catal. 2012; 354: 3045
  CrossrefPubMedSearch in Google Scholar
• 21 Moriyama K, Takemura M, Togo H. J. Org. Chem. 2014; 79: 6094
  CrossrefPubMedSearch in Google Scholar
• 22 Chudinov YB, Gashev SB, Firgang SI, Semenov VV. Russ. Chem. Bull. 2007; 56: 1612
  CrossrefSearch in Google Scholar
• 23 Fernandes RA, Bethi V. RSC Adv. 2014; 4: 40561
  CrossrefSearch in Google Scholar
• 24 Ou-yang J, Zhang W, Qin F, Zuo Q, Xu S, Wang Y, Qin B, You S, Jia X. Org. Biomol. Chem. 2017; 15: 7374
  CrossrefPubMedSearch in Google Scholar

• Supplementary Material