Copper-Catalyzed N-tert-Butylation of Aromatic Amines under Mild Condi­tions Using tert-Butyl 2,2,2-Trichloroacetimidate

John W. Cran; Dinesh V. Vidhani; Marie E. Krafft

doi:10.1055/s-0033-1339107

Synlett, Inhaltsverzeichnis

Synlett 2014; 25(11): 1550-1554
DOI: 10.1055/s-0033-1339107

letter

Copper-Catalyzed N-tert-Butylation of Aromatic Amines under Mild Conditions Using tert-Butyl 2,2,2-Trichloroacetimidate

John W. Cran*

Department of Chemistry and Biochemistry, Florida State University, Tallahassee, FL 32306-4390, USA Fax: +1(850)6447409 eMail: jcran@chem.fsu.edu

,

Dinesh V. Vidhani

Department of Chemistry and Biochemistry, Florida State University, Tallahassee, FL 32306-4390, USA Fax: +1(850)6447409 eMail: jcran@chem.fsu.edu

,

Marie E. Krafft

Department of Chemistry and Biochemistry, Florida State University, Tallahassee, FL 32306-4390, USA Fax: +1(850)6447409 eMail: jcran@chem.fsu.edu

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Abstract

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Abstract

A variety of aromatic amines have been found to expediently undergo copper-catalyzed N-tert-butylation in the presence of tert-butyl 2,2,2-trichloroactimidate at room temperature.

Key words

anilines - tert-butylation - copper - catalysis - alkylation

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Referenzen

References and Notes

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7 Undistilled MeNO₂ proved to be a less effective medium giving 74% conversion after 24 h with Cu(OTf)₂ as the catalyst. Our previous studies have shown that hydrated MeNO₂ suppressed the catalytic activity of transition metals. See: Cran JW, Krafft ME. Angew. Chem. Int. Ed. 2012; 51: 9398
8 Quenching of the catalyst by electron-rich substrates is also supported by the observation that 1 did not decompose in the presence of 3,4,5-trimethoxy aniline and the catalyst.

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12 General Experimental Methods All commercially available chemicals were used as received. MeNO₂ and CH₂Cl₂ were distilled from CaH₂. Reagent-grade solvents were used for solvent extraction, and organic extracts were dried over anhydrous Na₂SO₄ or MgSO₄. Alumina gel (80–200 mesh) was used for flash chromatography with dry hexane–EtOAc eluent system.¹H NMR spectra were recorded on a 500 MHz Bruker or a 300 MHz Varian spectrometer. ¹³C NMR spectra were recorded on a 125 MHz Bruker or a 75 MHz Varian spectrometer. The proton chemical shifts (δ) are reported as parts per million relative to 7.26 ppm for CDCl₃. The carbon chemical shifts (δ) were reported as parts per million relative to the centerline of the triplet for CDCl₃ at 77.1 ppm. Mass spectra were recorded using a Jeol JMS-600 instrument or an Agilent 6220 TOF-MS (NSF CRIF Grant 0541761). Typical Procedure for tert-Butylation Reaction To a dry round-bottom flask, equipped with a stirrer bar, under argon was added freshly distilled MeNO₂ (2.5 mL), tert-butyl 2,2,2-trichloroacetimidate (0.45 mL, 2.5 mmol), amine (1.0 mmol), and CuOTf (18 mg, 0.05 mmol). The reaction was stirred at r.t. for 2 h, or until the reaction was observed to have gone to completion by TLC or ¹H NMR spectroscopy of small aliquots of the reaction mixture. The reaction mixture was then diluted with EtOAc (25 mL) and washed with aq sat. NaHCO₃ solution (20 mL). The aqueous phase was extracted with an additional portion of EtOAc (20 mL). The combined organic extracts were dried with Na₂SO₄ and filtered through a plug of alumina before being reduced in vacuo. The crude product was purified by flash column chromatography (typically 20:1, hexane–EtOAc).
13 tert-Butylphenylamine (2) Clear oil (125 mg, 0.84 mmol, 84% yield). ¹H NMR (300 MHz, CDCl₃): δ = 7.16 (dd, J = 8.1, 8.1 Hz, 2 H), 6.79–6.73 (m, 3 H), 3.30–2.30 (br s, 1 H), 1.34 (s, 9 H). Compound identified by ¹H NMR spectroscopy by comparison with data previously published in the literature.^1a 4-tert-Butylaminobenzoic Acid Methyl Ester (3) Light yellow oil (208 mg, 1.00 mmol, 99% yield). ¹H NMR (300 MHz, CDCl₃): δ = 7.81 (d, J = 9.0 Hz, 2 H), 6.63 (d, J = 9.0 Hz, 2 H), 4.25–4.00 (br s, 1 H), 3.84 (s, 3 H), 1.40 (s, 9 H). ¹³C NMR (125 MHz, CDCl₃): δ = 167.4, 151.0, 131.3 (2 C), 117,7, 113.7 (2 C), 51.3, 29.7 (3 C). ESI-HRMS: m/z calcd for C₁₂H₁₈NO₂ [MH]⁺: 208.1338; found: 208.1349. 1-(4-tert-Butylaminophenyl)-ethanone (4) Yellow oil (189 mg, 0.99 mmol, 99% yield). ¹H NMR (300 MHz, CDCl₃): δ = 7.78 (d, J = 8.4 Hz, 2 H), 6.63 (d, J = 8.4 Hz, 2 H), 4.32 (br s, 1 H), 2.49 (s, 3 H), 1.41 (s, 9 H). ¹³C NMR (125 MHz, CDCl₃): δ = 196.4, 151.2, 130.6 (2 C), 126.0, 113.5 (2 C), 51.3, 29.7 (3 C), 26.0. ESI-HRMS: m/z calcd for C₁₂H₁₈NO [MH]⁺: 192.1383; found: 192.1374. 4-tert-Butylaminobenzonitrile (5) Light brown oil (165 mg, 0.95 mmol, 95% yield). ¹H NMR (300 MHz, CDCl₃): δ = 7.37 (d, J = 9.0 Hz, 2 H), 6.62 (d, J = 9.0 Hz, 2 H), 4.30-4.10 (br s, 1 H), 1.40 (s, 9 H). Compound identified by ¹H NMR spectroscopy by comparison with data previously published in the literature.¹⁴ tert-Butyl-(4-nitrophenyl)-amine (6) Yellow oil (192 mg, 0.99 mmol, 99% yield). ¹H NMR (300 MHz, CDCl₃): δ = 8.03 (d, J = 9.0 Hz, 2 H), 6.59 (d, J = 9.0 Hz, 2 H), 4.70–4.50 (br s, 1 H), 1.43 (s, 9 H). Compound identified by ¹H NMR spectroscopy by comparison with data previously published in the literature.^1a tert-Butyl-(2-nitro-4-trifluoromethyl-phenyl)-amine (7) Yellow oil (262 mg, 1.00 mmol, 99% yield). ¹H NMR (300 MHz, CDCl₃): δ = 8.68–8.56 (br s, 1 H), 8.45 (d, J = 2.4 Hz, 1 H), 7.56 (dd, J = 9.0, 2.4 Hz, 1 H), 7.18 (d, J = 15.0 Hz, 1 H), 1.53 (s, 9 H). ¹³C NMR (125 MHz, CDCl₃): δ = 146.3, 133.4, 133.3 (q, J = 3.8 Hz), 125.5 (q, J = 43.8 Hz), 123.7, (q, J = 268.8 Hz), 116.7 (q, J = 30.0 Hz), 116.3, 52.3, 29.6 (3 C). ESI-HRMS: m/z calcd for C₁₁H₁₄N₂O₂F₃ [MH]⁺: 263.1002; found: 263.1002. tert-Butyl-(4-trifluoromethyl-phenyl)-amine (8) Light brown oil (210 mg, 0.97 mmol, 97% yield). ¹H NMR (300 MHz, CDCl₃): δ = 7.37 (d, J = 9.0 Hz, 2 H), 6.69 (d, J = 9.0 Hz, 2 H), 3.97 (s, 1 H), 1.39 (s, 9 H). ¹³C NMR (75 MHz, CDCl₃): δ = 149.7, 126.4 (q, J = 3.4 Hz, 2 C), 125.1 (q, J = 268.7 Hz), 118.5 (q, J = 32.4 Hz), 114.4 (2 C), 51.3, 29.8. ESI-HRMS: m/z calcd for C₁₁H₁₅NF₃ [MH]⁺: 218.1151; found: 218.1153. tert-Butyl-(4-chloro-3-trifluoromethyl-phenyl)-amine (9) Light yellow oil (251 mg, 1.00 mmol, 99% yield). ¹H NMR (300 MHz, CDCl₃): δ = 7.22 (d, J = 9.0 Hz, 1 H), 6.97 (d, J = 3.0 Hz, 1 H), 6.77 (dd, J = 9.0, 3.0 Hz, 1 H), 4.02–3.02 (br s, 1 H), 1.35 (s, 9 H). ¹³C NMR (125 MHz, CDCl₃): δ = 145.6, 131.8, 128.4 (q, J = 31.3 Hz), 123.1 (q, J = 271.3 Hz), 119.3, 119.2 (q, J = 1.3 Hz), 114.7 (q, J = 6.3 Hz), 51.6, 29.8 (3 C). HRMS (EI): m/z calcd for C₁₁H₁₃F₃NCl [M]⁺: 251.0689; found: 251.0690. tert-Butyl-(4-chlorophenyl)-amine (10) Light orange oil (0.181 g, 0.99 mmol, 99% yield). ¹H NMR (300 MHz, CDCl₃): δ = 7.10 (d, J = 9.0 Hz, 2 H), 6.65 (d, J = 9.0 Hz, 2 H), 1.32 (s, 9 H). Compound identified by ¹H NMR spectroscopy by comparison with data previously published in the literature.^1a (2-Bromo-phenyl)-tert-butylamine (11) Pink oil (228 mg, 1.00 mmol, 99% yield). ¹H NMR (300 MHz, CDCl₃): δ = 7.43 (dd, J = 7.8, 1.8 Hz, 1 H), 7.14 (ddd, J = 7.8, 7.8, 1.8 Hz, 1 H), 6.97 (dd, J = 7.8, 1.8 Hz, 1 H), 6.55 (ddd, J = 7.8, 7.8, 1.8 Hz, 1 H), 4.40–4.25 (br s, 1 H), 1.41 (s, 9 H). Compound identified by ¹H NMR spectroscopy by comparison with data previously published in the literature.^4c (2-Bromo-6-methylphenyl)-tert-butylamine (12) Light pink oil (213 mg, 0.88 mmol, 88% yield). ¹H NMR (300 MHz, CDCl₃): δ = 7.39 (d, J = 7.8, 1 H), 7.11 (d, J = 7.8 Hz, 1 H), 6.82 (dd, J = 7.8, 7.8 Hz, 1 H), 3.37–3.29 (br s, 1 H), 2.42 (s, 3 H), 1.26 (s, 9 H). ¹³C NMR (125 MHz, CDCl₃): δ = 143.9, 137.2, 130.5, 130.2, 124.3, 124.2, 56.1, 31.1 (3 C), 21.6. HRMS (EI): m/z calcd for C₁₁H₁₆BrN [M]⁺: 241.0466; found: 241.0476. tert-Butyl-o-tolylamine (13) Light brown oil (98 mg, 0.60 mmol, 60% yield). ¹H NMR (300 MHz, CDCl₃): δ = 7.13–7.04 (m, 2 H), 6.92 (d, J = 8.4 Hz, 1 H), 6.66 (dd, J = 7.2, 7.2 Hz, 1 H), 3.60–3.25 (br s, 1 H), 2.13 (s, 3 H), 1.40 (s, 9 H). Compound identified by ¹H NMR spectroscopy by comparison with data previously published in the literature.^1a tert-Butyl-m-tolylamine (14) Light brown oil (135 mg, 0.83 mmol, 83% yield). ¹H NMR (300 MHz, CDCl₃): δ = 7.06 (dd, J = 9.0, 9.0 Hz, 1 H), 6.62–6.55 (m, 3 H), 3.20–2.65 (br s, 1 H), 2.28 (s, 3 H), 1.34 (s, 9 H). Compound identified by ¹H NMR spectroscopy by comparison with data previously published in the literature.^1c tert-Butyl-p-tolylamine (15) Light brown oil (132 mg, 0.81 mmol, 81% yield). ¹H NMR (300 MHz, CDCl₃): δ = 6.99 (d, J = 8.4 Hz, 2 H), 6.71 (d, J = 8.4 Hz, 2 H), 3.30–2.40 (br s, 1 H), 2.26 (s, 3 H), 1.30 (s, 9 H). Compound identified by ¹H NMR spectroscopy by comparison with data previously published in the literature.^1a tert-Butyl-(4-methoxyphenyl)-amine (17) Red oil (127 mg, 0.72 mmol, 72% yield). ¹H NMR (300 MHz, CDCl₃): δ = 6.84–6.73 (m, 4 H), 3.76 (s, 3 H), 1.23 (s, 9 H). Compound identified by ¹H NMR spectroscopy by comparison with data previously published in the literature.^1a Biphenyl-4-yl-tert-butylamine (19) Light yellow oil (196 mg, 0.87 mmol, 87% yield). ¹H NMR (300 MHz, CDCl₃): δ = 7.55 (d, J = 7.2 Hz, 2 H), 793 (d, J = 8.4 Hz, 2 H), 7.40 (t, J = 7.5 Hz, 2 H), 7.26 (t, J = 7.5 Hz, 1 H), 6.82 (d, J = 9.0 Hz, 2 H), 4.00–3.20 (br s, 1 H), 1.39 (s, 9 H). Compound identified by ¹H NMR spectroscopy by comparison with data previously published in the literature.¹⁵ tert-Butyl-(4-nitro-naphthalen-1-yl)-amine (20) Yellow oil (203 mg, 0.83 mmol, 83% yield). ¹H NMR (300 MHz, CDCl₃): δ = 9.05 (d, J = 9.0 Hz, 1 H), 8.46 (d, J = 9.0 Hz, 1 H), 7.76 (d, J = 9.0 Hz, 1 H), 7.67 (dd, J = 7.8, 7.8 Hz, 1 H), 7.51 (dd, J = 7.8, 7.8 Hz, 1 H), 6.78 (d, J = 9.0 Hz, 1 H), 5.38–5.31 (br s, 1 H), 1.58 (s, 9 H). ¹³C NMR (75 MHz, CDCl₃): δ = 148.5, 134.1, 129.5, 129.1, 128.1, 125.7, 125.0, 122.5, 120.1, 103.5, 52.2, 29.4 (3 C). HRMS (EI): m/z calcd for C₁₄H₁₆O₂N₂ [M]⁺: 244.1212; found: 244.1212. tert-Butyl-naphthalen-2-yl-amine (22) Red oil (123 mg, 0.62 mmol, 62% yield). ¹H NMR (300 MHz, CDCl₃): δ = 7.66 (d, J = 8.4 Hz, 1 H), 7.61 (d, J = 8.4 Hz, 2 H), 7.36 (dd, J = 7.5, 7.5 Hz, 1 H), 7.20 (dd, J = 7.5, 7.5 Hz, 1 H), 7.04 (d, J = 2.4 Hz, 1 H), 6.90 (dd, J = 9.0, 2.4 Hz, 1 H), 4.00–3.20 (br s, 1 H), 1.43 (s, 9 H). Compound identified by ¹H NMR spectroscopy by comparison with data previously published in the literature.¹⁶
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15 Gassman PG, Campbell GA, Fredrick RC. J. Am. Chem. Soc. 1972; 94: 3884
16 Cortright SB, Huffman JC, Yoder RA, Coalter III JN, Johnston JN. Organometallics 2004; 23: 2238

Copper-Catalyzed N-tert-Butylation of Aromatic Amines under Mild Condi­tions Using tert-Butyl 2,2,2-Trichloroacetimidate

Copper-Catalyzed N-tert-Butylation of Aromatic Amines under Mild Conditions Using tert-Butyl 2,2,2-Trichloroacetimidate