Copper(II)-Catalyzed O-Arylation of Tertiary Alcohols with Arylbismuth(III) Reagents: A Convenient System for Aryl Transfer

Abstract

Copper(II)-catalyzed O-arylation of tertiary alcohols with various triarylbismuth reagents was investigated. A convenient and efficient system for aryl ether formation of tertiary alcohols has been developed through the in situ oxidation of stable triarylbismuth(III) to triarylbismuth(V) species using PhI(OAc)₂ as the oxidant in the presence of a catalytic amount of copper(II) acetate.

Key words

O-phenylation - O-arylation - arylbismuth - ether - iodobenzene diacetate - tertiary alcohol

References and Notes

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  J. Am. Chem. Soc.  2002,  124:  520 
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• 2c Nicolaou KC. Sarlah D. Wu TR. Zhan W. Angew. Chem. Int. Ed.  2009,  48:  6870 
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• 4e

  The reaction can be also carried out under air as long as moisture is excluded.

• 5a Finet J.-P. Fedorov AY. J. Organomet. Chem.  2006,  691:  2386 
• 5b Combes S. Finet J.-P. Tetrahedron  1998,  54:  4313 
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• 6b Mukaiyama T. Sakurai N. Ikegai K. Chem. Lett.  2006,  35:  1140 
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• 8b Suzuki H. Ogawa T. Komatsu N. Matano Y. Murafuji T. Ikegami T. Organobismuth Chemistry   Elsevier; Amsterdam: 2001. 

9

Triphenylbismuth(V) diacetate(1a) is commercially available from Tokyo Kasei Kogyo, Inc. and used without purification. Triarylbismuth(V) diacetates 1b-i were readily prepared from BiCl₃ as described below.^{5a,8a,¹¹,¹²}

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Synthesis of Triarylbismuth 7b-i:
Method A for the Synthesis of Compounds 7e,i
To a mixture of n-BuLi (9.7 mmol, 1.6 M in hexane) and N,N,N′,N′-tetramethylethylenediamine (9.7 mmol) was added dropwise to a solution of the methoxymethoxy-benzene (9.1 mmol) in anhyd THF (18 mL) at 0 ˚C. After stirring for 6 h at this temperature, a THF solution (9 mL) of BiCl₃ (2.9 mmol) was added slowly at -35 ˚C. The reaction mixture was allowed to warm to r.t., quenched with H₂O (30 mL), extracted with EtOAc (2 × 20 mL), and the combined organic layers were washed with brine and dried over Na₂SO₄. The solvent was removed under reduced pressure, and the residue was purified by column chromatography on silica gel using hexane-EtOAc or recrystallization from MeOH to give the corresponding triarylbismuth(III).
Method B for the Synthesis of Compounds 7b-d,f-h
To an anhyd THF solution (17 mL) of arylmagnesium bromide, prepared from Mg (17 mmol) and aryl bromide (17.5 mmol), was added a THF solution (5 mL) of BiCl₃ (5 mmol) at 0 ˚C. The reaction mixture was allowed to warm to r.t., quenched with H₂O (30 mL), extracted with EtOAc (2 × 20 mL), and the combined organic layers were washed with brine and dried over Na₂SO₄. The solvent was removed under reduced pressure, and the residue was purified by column chromatography on silica gel using hexane-EtOAc or recrystallization from MeOH to give the corresponding triarylbismuth(III).

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Synthesis of Triarylbismuth Diacetate 1b-i Method A for the Synthesis of Compounds 1c-f,i
A mixture of NaBO₃˙H₂O (4.2 mmol) and Ar₃Bi(III) (1.4 mmol) in AcOH (14 mL) was stirred at r.t. for 30 min. The resulting mixture was poured into H₂O (50 mL) and was extracted with CH₂Cl₂ (2 × 30 mL). The combined organic layers were washed with H₂O (2 × 30 mL) and dried over MgSO₄. The solvent was distilled off, and the crude product was precipitated from a mixture of CH₂Cl₂ (1 mL)-hexane (30 mL) to give the corresponding triarylbismuth(V) diacetate. Method B for the Synthesis of Compounds 1b,g,h
A mixture of Ar₃Bi(III) (1.4 mmol) and PhI(OAc)₂ (1.5 mmol) in CH₂Cl₂ (14 mL) was stirred under argon atmosphere for 24 h at r.t. The solvent was distilled off, and the crude product was precipitated from a mixture of CH₂Cl₂ (1 mL)-hexane (30 mL) to give the corresponding triarylbismuth(V) diacetate.

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A related one-pot but not in situ copper(II)-catalyzed N-arylation of anilines was reported by Combes and Finet.^5b Barton et al. found that copper(II)-catalyzed N-phenylation of amines by Ph₃Bi(III) occurs smoothly.^4d

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Typical Procedure for the O-Arylation of 2 (Table 3, entry 5)
To a suspension mixture of alcohol 2 (0.22 mmol), Cy₂NMe (0.43 mmol), and powdered MS4A (250 mg) in CH₂Cl₂ (1 mL) was added Cu(OAc)₂ (0.01 mmol). After the mixture was stirred for 30 min, Ar₃Bi (0.33 mmol) and PhI(OAc)₂ (0.41 mmol) were added, and the resulting mixture was kept stirring at r.t. under an oxygen atmosphere (1 atm). Upon completion of the reaction (monitored by TLC), 10% aq NH₃ solution (2 mL) was added to the mixture. The precipitates were filtered off, and the filtrate was extracted with CH₂Cl₂ (2 × 10 mL). The combined extracts were washed with brine, dried over Na₂SO₄, and concentrated under reduced pressure to give an oily residue. Purification by column chromatog-raphy on silica gel using hexane-EtOAc yielded the corresponding aryl ether 3 ^¹4 or 4.

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Spectral Data for the Representative Products 3c,f
Benzyl 2-Methyl-2-(3-methylphenoxy)propionate (3c) Yield: 60 mg (98%). Colorless oil. IR (neat): 2936, 1733, 1488, 1280, 1175, 1137, 959, 695 cm^-¹. ^¹H NMR (400 MHz, CDCl₃): δ = 1.60 (6 H, s, Me), 2.22 (3 H, s, tolyl), 5.21 (2 H, s, Bn), 6.57 (1 H, br d, J = 8.0 Hz, H6′), 6.61 (1 H, br s, H2′), 6.78 (1 H, br d, J = 7.6 Hz, H4′), 7.05 (1 H, dd, J = 8.0, 7.6 Hz, H5′), 7.27-7.33 (5 H, m, Bn). ^¹³C NMR (100 MHz, CDCl₃): δ = 21.5, 25.6, 67.1, 79.1, 115.9, 120.0, 123.0, 128.4, 128.5, 128.6, 128.9, 135.6, 139.3, 153.4, 174.3. HRMS (ESI-FT): m/z calcd for C₁₈H₂₀O₃Na: 307.1310 [M + Na]⁺; found: 307.1307. Benzyl 2-[3-(Methoxymethoxy)phenoxy]-2-methyl-propanoate (3f) Yield: 130 mg (83%). Colorless oil. IR (neat): 2938, 1731, 1600, 1486, 1282, 1138, 1017, 851, 696 cm^-¹. ^¹H NMR (400 MHz, CDCl₃): δ = 1.61 (6 H, s, Me), 3.45 (3 H, s, OMe), 5.09 (2 H, s, OCH₂O), 5.20 (2 H, s, Bn), 6.40 (1 H, ddd, J = 8.0, 2.3, 0.9 Hz, H6′), 6.57 (1 H, dd, J = 2.3, 2.3 Hz, H2′), 6.66 (1 H, ddd, J = 8.3, 2.3, 0.9 Hz, H4′), 7.06 (1 H, dd, J = 8.3, 8.0 Hz, H5′), 7.27-7.45 (5 H, m, Bn). ^¹³C NMR (100 MHz, CDCl₃): δ = 25.5, 56.1, 67.2, 79.3, 94.6, 107.7, 110.1, 112.2, 128.4, 128.6, 129.6, 135.6, 156.6, 158.3, 174.2. HRMS (ESI-FT): m/z calcd for C₁₉H₂₂O₅Na: 353.1365 [M + Na]⁺; found: 353.1361.