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Synthesis 2014; 46(17): 2312-2316
DOI: 10.1055/s-0033-1340192
paper
© Georg Thieme Verlag Stuttgart · New York

Potassium tert-Butoxide Mediated O-Arylation of N-Hydroxyphthalimide and Oximes with Diaryliodonium Salts

Luis C. Misal Castro
Department of Applied Chemistry, Faculty of Engineering, Osaka University, Suita, Osaka 565-0871, Japan   Fax: +81(6)68797396   Email: chatani@chem.eng.osaka-u.ac.jp
,
Naoto Chatani*
Department of Applied Chemistry, Faculty of Engineering, Osaka University, Suita, Osaka 565-0871, Japan   Fax: +81(6)68797396   Email: chatani@chem.eng.osaka-u.ac.jp
› Author Affiliations
Further Information

Publication History

Received: 31 March 2014

Accepted after revision: 30 April 2014

Publication Date:
12 June 2014 (online)

 
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Abstract

A metal-free method for the direct O-arylation of N-hydroxyphthalimide­, pyridine-2-carboxaldehyde oxime, acetophenone oxime, or dimethylglyoxime with diaryliodonium salts under mild reaction conditions and short reaction time in the presence of potassium tert-butoxide is reported. The diaryliodonium counterion salt plays an important role in the reaction when it is carried out at 40 °C or lower temperatures.


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Key words

O-arylation - O-arylhydroxylamines - oximes - N-hydroxyphthalimide - diaryliodonium salts

The development of new synthetic approaches for preparing O-aryloximes is important in organic chemistry, because they are valuable precursors of heterocyclic compounds such as benzofurans[1] and benzoxazoles.[2] Furthermore, O-aryloximes have been reported to be bioactive.[3] The classical method for preparing such compounds involves an SNAr of the conjugated base of N-hydroxy compounds with electron-deficient aromatic molecules (e.g., chloro,[4] fluoro,[1a] nitro,[5] and chromium chloroarene complexes[6]). However, the nature of the arene partner narrows the generalization of the reaction.

The most general route for the synthesis of O-aryloximes 4 would be the arylation of N-hydroxyphthalimide (1), by using 2 equivalents of arylboronic acid, 1 equivalent of copper(I) chloride, and 1.1 equivalents of pyridine at room temperature for 24–48 hours,[7] followed by hydrolysis leading to 3 and aldehyde or ketone condensation (Scheme [1]).

Zoom Image
Scheme 1 Synthesis of O-aryloxime 4

The same conditions have been utilized for the direct O-arylation of oximes by Meyer,[8] and Huang,[9] Cai,[10] and Bora[11] used copper catalysis in the same reaction. However, in most cases the yields are poor or moderate at best. Aryl halides have also been used in such reactions under catalytic conditions. Maitra and Wailes used bromo- or iodoarenes­ with 10 mol% copper(I) iodide and 20 mol% 1,10-phenanthroline for the arylation of oximes.[12] Buchwald and co-workers reported a wide scope for the O-arylation of ethyl acetohydroximate with bromoarenes as coupling partners under palladium/phosphine catalysis.[13] As of this writing, N-phenoxyacetamides (prepared from O-arylhydroxylamines 3) have been used as substrates for regioselective transition-metal-catalyzed ortho-C(sp2)–H bond functionalization.[14]

Diaryliodonium salts have attracted interest in the last few years for its application to catalytic and non-catalytic organic reactions.[15] In addition, the synthesis of hypervalent iodine compounds is now well established.[16] Moreover, such compounds are air- and moisture-stable and have low toxicity. The use of a diaryliodonium salt under metal-free and mild conditions in reactions with different nucleophiles has opened an alternative door to the synthesis of a myriad of organic molecules.[17] In the O-arylation reaction, diphenyliodonium chloride was first used in 1977, but only a single example of the phenylation of N-hydroxyphthalimide (1) has been reported.[18]

Herein, we wish to report on the O-arylation of N-hydroxy compounds with diaryliodonium salts in the presence of potassium tert-butoxide. It should also be noted that, during the course of this investigation, Olofsson’s group reported on a similar study in which they demonstrated the feasibility of using these salts for the arylation of N-hydroxyphthalimide (1) and N-hydroxysucccinimide under metal-free conditions and in a short reaction time (0.5–2 h) at 60 °C in N,N-dimethylformamide, as well as in the presence of a base with good to excellent yields in most cases.[19] We independently found that such reactions can be conducted at room temperature and is also amenable for use with oximes to obtain O-aryloximes 4. Our synthesis can be considered to be a complementary methodology to that reported by Olofsson’s group.

Our preliminary studies were carried out with N-hydroxyphthalimide­ (1), diphenyliodonium triflate (1 equiv), and potassium tert-butoxide (1 equiv) at 40 °C for screening different solvents (Table [1]). Among the solvents tested, acetone, acetonitrile, and tetrahydrofuran gave satisfactory yields (entries 4–6). In order to determine whether the counterion of the iodonium salt played a role in the reaction, diphenyliodonium hexafluorophosphate and diphenyliodonium tetrafluoroborate (5a) were used under the optimal conditions found for diphenyl­iodonium triflate (entry 6). With both anions the conversions were higher, and complete conversion occurred with the tetrafluoroborate derivative (entries 7 and 8). Surprisingly, the reaction with diphenyliodonium tetrafluoroborate (5a) reached completion in 30 min when conducted at room temperature (entry 9). The reaction time for this protocol can be visually controlled, because the phenoxide species (PhthNO–) in tetrahydrofuran forms a red suspension that fades to white (or pale yellow) on reaction with the iodonium salts, making it a useful indicator for the completeness of the reaction (see Supporting Information).

Table 1 Optimization of the Reaction Conditions for the O-Arylation of N-Hydroxyphthalimide (1) with Diphenyliodonium Salts 5 a

Entry

Solvent

X

Time (min)

Yield (%)b

 1

toluene

OTf

60

18

 2

CH2Cl2

OTf

60

 9

 3

Et2O

OTf

60

 6

 4

acetone

OTf

60

81

 5

MeCN

OTf

60

82

 6

THF

OTf

60

84

 7

THF

PF6

60

88

 8

THF

BF4

60

99

 9c

THF

BF4

30

99 (90)

10c

THF

BF4

15

71

a Reagents and conditions: 1 (82 mg, 0.5 mmol), 5 (0.5 mmol), t-BuOK (56 mg, 0.5 mmol), solvent (2 mL), 40 °C, air.

b Yield determined by 1H NMR; 1,1,2,2-tetrachloroethane used as internal standard.

c Reaction carried out at r.t. Isolated yield in parentheses.

Several diaryliodonium tetrafluoroborate salts (5b–p)[16c] were tested in the O-arylation of N-hydroxyphthalimide (1) (Table [2]). As expected, the electronic properties of the iodonium salts have an influence on both product yield and reaction time. Halogenated iodonium salts bearing fluoro, chloro, bromo, and iodo groups worked well, with conversions from good to excellent (63–89%, entries 2–9). The reactivities of the halogenated salts differed and were dependent on the position of the halogen atom. For example, when ortho- and para-fluoro-substituted diaryliodonium salts were used, the reaction needed to be carried out at 30 °C for periods of two and three hours, respectively, to give high yields (5c 63%, 5e 86%, entries 2 and 4). In the other hand, when the meta-fluoro salt was used, the reaction was complete within one hour at room temperature, giving an excellent yield (5d, 89%, entry 3). One advantage of using diaryliodonium salts is that whereas N-(2-fluorophenoxy)phthalimide (6c) cannot be produced by using Kelly’s synthesis that uses 2-fluorophenylboronic acid,[7] with this methodology (as in the Olofsson’s work),[19] a compound such as 6c can be synthesized in good yield under milder conditions in a shorter reaction time. For the chloro and bromo salts, the para-substituted derivatives required a longer time than the ortho-substituted salts (entries 5 vs 6 and 7 vs 8). In addition, the para-iododiphenyliodonium salt 5j was also compatible, and after two hours of reaction, a good yield (79%) was obtained (entry 9). Electron-withdrawing groups such as the trifluoromethyl 5b (4-CF3), the ester 5k (4-CO2Me) and the cyano 5l (3-CN) were also tolerated, giving good yields (entries 1, 10 and 11). Weakly electron-donating substituents such as 2- and 3-methyl (5m and 5n) and 1-naphthyl (5p) worked very well at room temperature and in short reaction time (entries 12, 13 and 15). Nevertheless, the electron-rich bis(4-methoxyphenyl)iodonium tetrafluoroborate (5o) remains a challenge in this reaction (as in Olofsson’s method),[19] because at 40 °C and after 24 hours the conversion was poor (entry 14, 34%).

Table 2 Scope of the O-Arylation of N-Hydroxyphthalimide (1) with Diaryliodonium Tetrafluoroborate Salts 5 a

Entry

Ar

Time (h)

Yield (%)b

 1

4-F3CC6H4 (5b)

 1

89 (6b)

 2c

2-FC6H4 (5c)

 2

63 (6c)

 3

3-FC6H4 (5d)

 1

89 (6d)

 4c

4-FC6H4 (5e)

 3

86 (6e)

 5

2-ClC6H4 (5f)

 2

77 (6f)

 6

4-ClC6H4 (5g)

 5

81 (6g)

 7

2-BrC6H4 (5h)

 3

74 (6h)

 8

4-BrC6H4 (5i)

 4

75 (6i)

 9

4-IC6H4 (5j)

 2

79 (6j)

10

4-MeO2CC6H4 (5k)

 1

74 (6k)

11

3-NCC6H4 (5l)

 2

78 (6l)

12

2-MeC6H4 (5m)

 1

87 (6m)

13

3-MeC6H4 (5n)

 3

86 (6n)

14d

4-MeOC6H4 (5o)

24

34 (6o)

15

1-Naph (5p)

 2

63 (6p)

a Reagents and conditions: 1 (82 mg, 0.5 mmol), 5 (0.5 mmol), t-BuOK (56 mg, 0.5 mmol), THF (2 mL), air.

b Isolated yield.

c Reaction carried out at 30 °C.

d Reaction carried out at 40 °C.

In order to determine whether or not this synthetic methodology could be also applied to other types of N-hydroxy compounds, the reaction was tested on oxime compounds. Because of our synthetic interest, we used pyridine-2-carboxaldehyde oxime (7) as a model substrate (Table [3]). All reactions were carried out at room temperature, with a reaction time of one hour; the yields obtained for different salts bearing electron-deficient (2-Cl 5f and 4-Br 5h) and electron-donating (2-Me 5m and 3-Me 5n) groups ranged from good to excellent (61–93%, entries 1–5). However, when the electron-rich salt bis(4-methoxyphenyl)iodonium tetrafluoroborate (5o) was used, the resulting product decomposed very easily during purification. We therefore prepared acetophenone oxime (8) and reacted it with salt 5o under standard conditions; in this case, product 10 was obtained in good yield (60%, entry 6). This provides an example of the higher reactivity of the oxime-conjugated base as a nucleophile in the presence of an electron-rich diaryliodonium salt compared to the case of N-hydroxyphthalimide (1).

Table 3 Scope of the O-Arylation of Oximes with Symmetric Diaryliodonium­ Tetrafluoroborate Salts 5 a

Entry

Ar

Substrate

Yield (%)b

1

Ph (5a)

7

93 (9a)

2

2-ClC6H4 (5f)

7

84 (9b)

3

4-BrC6H4 (5h)

7

61 (9c)

4

2-MeC6H4 (5m)

7

76 (9d)

5

3-MeC6H4 (5n)

7

90 (9e)

6

4-MeOC6H4 (5o)

8

60 (10)

a Reagents and conditions: oxime 7 or 8 (0.5 mmol), 5 (0.5 mmol), t-BuOK (56 mg, 0.5 mmol), THF (2 mL), air, 1 h.

b Isolated yield.

The O-arylation was successfully applied to the commercially available compound dimethylglyoxime (11); in this case, two equivalents of potassium tert-butoxide and two equivalents of diphenyliodonium tetrafluoroborate (5a) were needed under the same reaction conditions to give the biphenylated product 12 in excellent yield (Scheme [2]).

Zoom Image
Scheme 2 Direct biarylation of dimethylglyoxime (11) with diphenyliodonium tetrafluoroborate (5a)

In conclusion, we report herein a simple method for the base-mediated O-arylation of N-hydroxyphthalimide (1) and oximes 7, 8, and 11 with diaryliodonium tetrafluoro­borate salts under mild reaction conditions. The method tolerates various functional groups such as halogens (F, Cl, Br, I), methoxy groups, esters, and cyano groups. In the majority of cases, the isolated yields range between 60 and 90%.

1H and 13C NMR spectra were recorded on a JEOL ECS-400 spectrometer; samples were prepared in CDCl3, or DMSO-d 6 with TMS as the internal standard. IR spectra were obtained by using a JASCO FT/IR-4200 instrument. High-resolution mass spectra were obtained on a JEOL JMS-DX303 instrument. Column chromatography was performed over silica gel (Silicycle SiliaFlash F60, 230–400 mesh) and Silica Gel 60 (spherical) NH2 (40–50 μm). All known compounds (5a,[16c] 5b,[16c] 5c,[16c] 5d,[20] 5e,[21] 5g,[21] 5h,[20] 5i,[16c] 5j,[21] 5k,[20] 5m,[16c] 5n,[16c] 5o,[16c] 5p,[16c] 6a,[7] 6b,[7] 6c,[19] 6d,[7] 6e,[14a] 6h,[1a] 6i,[7] 6j,[7] 6k,[7] 6m,[7] 6n,[7] 6o,[7] and 10 [11]) were characterized by 1H and 13C NMR spectroscopy, and the data are consistent with the values reported in the literature.


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O-Arylation of N-Hydroxy Compounds; General Procedure

In an oven-dried 5 mL screw-capped vial, the N-hydroxy compound (0.5 mmol) [1 (82 mg), 7 (63 mg), or 8 (68 mg)] was dissolved in THF (2 mL) under atmospheric air. t-BuOK (0.5 mmol, 56 mg) was added and the solution was stirred for 10 min at r.t. The diphenyl­iodonium tetrafluoroborate salt (5a–p, 0.5 mmol) was then added and the solution was again stirred for the indicated time (see Tables 1–3). The mixture was filtered through a Celite pad and concentrated in vacuo. The residue was purified by column chromatography (silica gel, neutral for 6a–p or basic for 9a–e, 10; n-hexane–EtOAc) to afford the desired arylated product.


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Bis(2-chlorophenyl)iodonium Tetrafluoroborate (5f)

White solid; yield: 78% (740 mg).

IR (neat): 1741 (w), 1448 (w), 1055 (s), 994 (s), 759 (m) cm–1.

1H NMR (400 MHz, DMSO-d 6): δ = 7.50 (td, J 1 = 8.0, J 2 = 1.2 Hz, 2 H), 7.71 (td, J 1 = 8.0, J 2 = 1.2 Hz, 2 H), 7.85 (dd, J 1 = 8.0, J 2 = 1.2 Hz, 2 H), 8.54 (dd, J 1 = 8.4, J 2 = 1.2 Hz, 2 H).

13C{1H} NMR (100 MHz, DMSO-d 6): δ = 119.75, 130.26, 130.52, 134.82, 135.98, 138.95.

HRMS: m/z calcd for C12H8Cl2I [M – BF4]: 348.9042; found: 348.9047.


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Bis(3-cyanophenyl)iodonium Tetrafluoroborate (5l)

Tan solid; yield: 27% (245 mg).

IR (neat): 2361 (w), 1741 (s), 1484 (m), 1197 (m), 970 (w), 944 (w), 701 (w) cm–1.

1H NMR (400 MHz, DMSO-d 6): δ = 7.76 (t, J = 8.0 Hz, 2 H), 8.17 (d, J = 8.0 Hz, 2 H), 8.60 (d, J = 8.8 Hz, 2 H), 8.87 (s, 2 H).

13C{1H} NMR (100 MHz, DMSO-d 6): δ = 114.06, 117.01, 132.62, 136.03, 138.64, 139.84.

HRMS: m/z calcd for C14H8N2I [M – BF4]: 330.9727; found: 330.9734.


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N-(2-Chlorophenoxy)phthalimide (6f, Table [2], entry 5)

White solid; yield: 77% (105 mg); mp 187–188 °C.

Rf = 0.23 (hexane–EtOAc, 3:1).

IR (neat): 1740 (s), 1470 (m), 1206 (m), 971 (m), 740 (m), 696 (m) cm–1.

1H NMR (400 MHz, CDCl3): δ = 7.03–7.10 (m, 2 H), 7.20 (td, J 1 = 8.0, J 2 = 1.6 Hz, 1 H), 7.45 (dd, J 1 = 8.0, J 2 = 1.6 Hz, 1 H), 7.83–7.85 (m, 2 H), 7.93–7.95 (m, 2 H).

13C{1H} NMR (100 MHz, CDCl3): δ = 113.83, 121.11, 124.12, 125.08, 127.81, 128.70, 130.99, 135.07, 154.12, 162.53.

HRMS: m/z calcd for C14H8ClNO3: 273.0193; found: 273.0192.


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N-(4-Chlorophenoxy)phthalimide (6g, Table [2], entry 6)

White solid; yield: 81% (111 mg); mp 147–148 °C.

Rf = 0.17 (hexane–EtOAc, 5:1).

IR (neat): 1739 (s), 1484 (m), 1197 (m), 972 (w), 702 (w) cm–1.

1H NMR (400 MHz, CDCl3): δ = 7.14 (d, J = 9.2 Hz, 2 H), 7.31 (d, J = 9.2 Hz, 2 H), 7.82–7.84 (m, 2 H), 7.92–7.94 (m, 2 H).

13C{1H} NMR (100 MHz, CDCl3): δ = 116.12, 124.08, 128.68, 129.68, 129.82, 135.02, 157.42, 162.78.

HRMS: m/z calcd for C14H8ClNO3: 273.0193; found: 273.0194.


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N-(3-Cyanophenoxy)phthalimide (6l, Table [2], entry 11)

White solid; yield: 77% (102 mg); mp 198–199 °C.

Rf = 0.22 (hexane–EtOAc, 3:1).

IR (neat): 2234 (w), 1742 (s), 1357 (m), 1227 (m), 699 (m) cm–1.

1H NMR (400 MHz, CDCl3): δ = 7.42–7.51 (m, 4 H), 7.86–7.88 (m, 2 H), 7.95–7.97 (m, 2 H).

13C{1H} NMR (100 MHz, CDCl3): δ = 113.70, 117.45, 117.79, 119.26, 124.30, 128.35, 128.56, 130.81, 135.28, 158.81, 162.60.

HRMS: m/z calcd for C15H8N2O3: 264.0535; found: 264.0537.


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N-(1-Naphthylphenoxy)phthalimide (6p, Table [2], entry 15)

Yellow solid; yield: 63% (91 mg); mp 114–115 °C.

Rf = 0.27 (hexane–EtOAc, 3:1).

IR (neat): 1738 (s), 1468 (m), 1393 (m), 1281 (m), 1044 (m), 767 (m), 699 (m) cm–1.

1H NMR (400 MHz, CDCl3): δ = 7.03 (d, J = 8.0 Hz, 1 H), 7.03 (t, J = 8.0 Hz, 1 H), 7.54–7.63 (m, 3 H), 7.82–7.87 (m, 3 H), 7.93–7.96 (m, 2 H), 8.44 (d, J = 8.8 Hz, 1 H).

13C{1H} NMR (100 MHz, CDCl3): δ = 106.66, 121.44, 123.36, 124.00, 124.22, 125.08, 126.18, 126.90, 127.49, 128.82, 134.54, 134.91, 154.12, 162.88.

HRMS: m/z calcd for C18H11NO3: 289.0739; found: 289.0737.


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Pyridine-2-carboxaldehyde O-Phenyloxime (9a, Table [3], entry 1)

Yellow solid; yield: 93% (92 mg); mp 45–46 °C.

Rf = 0.41 (hexane–EtOAc, 3:1).

IR (neat): 1591 (m), 1490 (m), 1213 (s), 943 (s), 753 (m), 690 (m) cm–1.

1H NMR (400 MHz, CDCl3): δ = 7.07 (t, J = 7.2 Hz, 1 H), 7.28–7.38 (m, 5 H), 7.76 (td, J 1 = 8.0, J 2 = 2.0 Hz, 1 H), 8.02 (d, J = 8.0 Hz, 1 H), 8.51 (s, 1 H), 8.67 (d, J = 5.2 Hz, 1 H).

13C{1H} NMR (100 MHz, CDCl3): δ = 114.64, 121.25, 122.71, 124.56, 129.33, 136.53, 149.78, 151.09, 152.25, 159.14.

HRMS: m/z calcd for C12H10N2O: 198.0793; found: 198.0795.


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Pyridine-2-carboxaldehyde O-(2-Chlorophenyl)oxime (9b, Table­ [3], entry 2)

White solid; yield: 84% (98 mg); mp 77–78 °C.

Rf = 0.16 (hexane–EtOAc, 10:1).

IR (neat): 1586 (m), 1471 (s), 1231 (m), 934 (m), 737 (m) cm–1.

1H NMR (400 MHz, CDCl3): δ = 7.02 (td, J 1 = 8.0, J 2 = 1.2 Hz, 1 H), 7.27 (m, 1 H), 7.34–7.41 (m, 2 H), 7.58 (dd, J 1 = 8.0, J 2 = 1.2 Hz, 1 H), 7.77 (td, J 1 = 8.0, J 2 = 1.2 Hz, 1 H), 7.99 (d, J = 8.0 Hz, 1 H), 8.63 (s, 1 H), 8.69 (d, J = 4.4 Hz, 1 H).

13C{1H} NMR (100 MHz, CDCl3): δ = 116.48, 120.64, 121.58, 123.42, 124.83, 127.69, 130.15, 136.60, 149.97, 150.64, 153.55, 154.61.

HRMS: m/z calcd for C12H9ClN2O: 232.0403; found: 232.0404.


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Pyridine-2-carboxaldehyde O-(4-Bromophenyl)oxime (9c, Table­ [3], entry 3)

White solid; yield: 61% (85 mg); mp 58–59 °C.

Rf = 0.30 (hexane–EtOAc, 3:1).

IR (neat): 1583 (m), 1480 (s), 1215 (s), 941 (s), 822 (m), 775 (m), 742 (w) cm–1.

1H NMR (400 MHz, CDCl3): δ = 7.17 (d, J = 8.8 Hz, 2 H), 7.33–7.36 (m, 1 H), 7.44 (d, J = 8.8 Hz, 2 H), 7.77 (td, J 1 = 8.0, J 2 = 1.6 Hz, 1 H), 7.99 (d, J = 8.0 Hz, 1 H), 8.49 (s, 1 H), 8.67 (d, J = 5.2 Hz, 1 H).

13C{1H} NMR (100 MHz, CDCl3): δ = 114.91, 116.35, 121.38, 124.76, 132.18, 136.60, 149.86, 150.73, 152.69, 158.21.

HRMS: m/z calcd for C12H9BrN2O: 275.9898; found: 275.9895.


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Pyridine-2-carboxaldehyde O-2-Tolyloxime (9d, Table [3], entry 4)

Yellow liquid; yield: 76% (81 mg).

Rf = 0.37 (hexane–EtOAc, 3:1).

IR (neat): 1744 (w), 1585 (m), 1484 (s), 1223 (s), 1112 (s), 947 (s), 754 (s), 701 (m) cm–1.

1H NMR (400 MHz, CDCl3): δ = 2.32 (s, 3 H), 6.99 (dt, J 1 = 8.0, J 2 = 1.2 Hz, 1 H), 7.19–7.23 (m, 2 H), 7.32–7.35 (m, 1 H), 7.46 (d, J = 8.0 Hz, 1 H), 7.76 (td, J 1 = 8.0, J 2 = 1.6 Hz, 1 H), 8.02 (d, J = 8.0 Hz, 1 H), 8.56 (s, 1 H), 8.67 (d, J = 5.2 Hz, 1 H).

13C{1H} NMR (100 MHz, CDCl3): δ = 15.97, 114.65, 121.24, 122.65, 124.52, 125.03, 126.83, 130.78, 136.54, 149.80, 151.20, 152.28, 157.14.

HRMS: m/z calcd for C13H12N2O: 212.0950; found: 212.0951.


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Pyridine-2-carboxaldehyde O-3-Tolyloxime (9e, Table [3], entry 5)

Yellow liquid; yield: 90% (95 mg).

Rf = 0.40 (hexane–EtOAc, 3:1).

IR (neat): 1745 (w), 1584 (s), 1484 (s), 1250 (s), 1143 (s), 957 (s), 777 (s), 745 (m), 689 (w) cm–1.

1H NMR (400 MHz, CDCl3): δ = 2.38 (s, 3 H), 6.89 (d, J = 8.0 Hz, 1 H), 7.08–7.12 (m, 2 H), 7.23 (t, J = 8.0 Hz, 1 H), 7.32–7.35 (m, 1 H), 7.76 (t, J = 8.0 Hz, 1 H), 8.02 (d, J = 8.0 Hz, 1 H), 8.50 (s, 1 H), 8.67 (d, J = 5.2 Hz, 1 H).

13C{1H} NMR (100 MHz, CDCl3): δ = 21.54, 111.71, 115.24, 121.29, 123.52, 124.54, 129.09, 136.53, 139.48, 149.79, 151.14, 152.13, 159.13.

HRMS: m/z calcd for C13H12N2O: 212.0950; found: 212.0949.


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Dimethyl-O,O′-diphenylglyoxime (12, Scheme [2])

Yellow solid; yield: 86% (115 mg); mp 121–122 °C.

Rf = 0.53 (hexane–EtOAc, 20:1).

IR (neat): 1589 (m), 1479 (s), 1213 (s), 923 (s), 752 (s), 688 (m) cm–1.

1H NMR (400 MHz, CDCl3): δ = 2.37 (s, 6 H), 7.07 (t, J = 7.6 Hz, 2 H), 7.27 (d, J = 8.4 Hz, 4 H), 7.35 (t, J = 9.2 Hz, 4 H).

13C{1H} NMR (100 MHz, CDCl3): δ = 10.89, 114.68, 122.69, 129.33, 156.60, 159.20.

HRMS: m/z calcd for C16H16N2O2: 268.1212; found: 268.1211.


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Acknowledgment

This work was supported, in part, by a Grant-in-Aid for Scientific Research on Innovative Areas “Molecular Activation Directed toward Straightforward Synthesis” from Monbusho (The Ministry of Education, Culture, Sports, Science and Technology) and by JST Strategic Basic Research Programs “Advanced Catalytic Transformation Program for Carbon Utilization (ACT-C)” from the Japan Science and Technology Agency.

Supporting Information

    for this article is available online at http://www.thieme-connect.com.accesdistant.sorbonne-universite.fr/products/ejournals/journal/ 10.1055/s-00000084.
  • Supporting Information


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Zoom Image
Scheme 1 Synthesis of O-aryloxime 4
Zoom Image
Scheme 2 Direct biarylation of dimethylglyoxime (11) with diphenyliodonium tetrafluoroborate (5a)