Synlett 2018; 29(18): 2417-2421
DOI: 10.1055/s-0037-1610298
letter
© Georg Thieme Verlag Stuttgart · New York

Selective Deprotection of N-Tosyl Alkoxyamines Using Bistrifluoromethane Sulfonimide: Formation of Oxime Ethers

Mohamed Salah Azizi
,
Laboratory of Organic Chemistry, Institute of Chemistry, Biology and Innovation (CBI), ESPCI Paris, PSL Research University, CNRS, 10 Rue Vauquelin, 75231 – Paris Cedex 05, France   Email: Janine.Cossy@espci.fr
› Author Affiliations
Further Information

Publication History

Received: 24 July 2018

Accepted after revision: 12 September 2018

Publication Date:
02 October 2018 (online)


Abstract

The detosylation of N-tosyl alkoxyamines was realized by treatment with benzaldehyde and bistrifluoromethane sulfonimide as the catalyst to afford the corresponding oxime ethers. The reaction is chemoselective as N-tosyl amines are not deprotected. A mechanism is proposed for this deprotection.

Supporting Information

 
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  • 16 Compound 9 was isolated as a mixture of E- and Z-isomers in a ratio 96:4.
  • 17 Spectral Data of (E)-9 IR: ν = 2923, 1640, 1446, 1373, 1335, 1210, 1089, 967, 910, 900 cm–1. 1H NMR (400 MHz, CDCl3): δ = 8.06 (s, 1 H), 7.60–7.50 (m, 2 H), 7.40–7.30 (m, 3 H), 5.85 (m, 1 H), 5.04 (dqapp, J = 17.0, 1.8 Hz, 1 H), 4.97 (m, 1 H), 4.32 (m, 1 H), 2.18 (m, 2 H), 1.83 (m, 1 H), 1.59 (m, 1 H), 1.30 (d, J = 6.2 Hz, 3 H). 13C NMR (100 MHz, CDCl3): δ = 145.2, 138.4, 130.8, 129.7, 128.4 (2 C), 126.9 (2 C), 114.6, 79.9, 34.8, 29.7, 19.2. MS (EI): m/z = 203 (13) [M+•], 202 (40), 188 (8), 158 (8), 132 (3), 122 (7), 121 (10), 120 (9), 104 (42), 94 (4), 89 (5), 82 (6), 78 (9), 77 (47), 67 (15), 65 (8), 55 (100), 51 (13).
  • 18 General Procedure for the Synthesis of Oxime Ethers from N-Tosyl Alkoxyamines In a round-bottom flask, a mixture of a solution of N-tosyl alkoxyamide (0.2 mmol, 1 equiv) in anhydrous CH2Cl2 (c = 0.25 M), aldehyde (2 equiv), and a solution of HNTf2 (0.1 equiv) in anhydrous CH2Cl2 was stirred at 40 °C for 18 h. The reaction mixture was cooled to r.t. and saturated aqueous Na2CO3 was added. The two phases were separated, and the aqueous layer was extracted four times with CH2Cl2. The combined organic layers were washed with brine, dried over MgSO4, filtered, and concentrated in vacuo. The crude product was purified by flash chromatography on silica gel (petroleum ether/ethyl acetate) to obtain the desired oxime ether.
  • 19 Spectroscopic Data for 17 1H NMR (400 MHz, CDCl3): δ = 8.02 (s, 1 H), 7.52–7.49 (m, 2 H), 6.90–6.70 (m, 2 H), 5.85 (m, 1 H), 5.04 (dqapp, J = 17.1, 1.8 Hz, 1 H), 4.96 (m, 1 H), 4.29 (m, 1 H), 3.82 (s, 3 H), 2.20–2.15 (m, 2 H), 1.81 (m, 1 H), 1.60 (m, 1 H), 1.29 (d, J = 6.2 Hz, 3 H). 13C NMR (100 MHz, CDCl3): δ = 160.7, 147.5, 138.5, 128.3 (2 C), 125.4, 114.5, 114.1 (2C), 78.7, 55.3, 34.9, 29.7, 19.8. MS (EI): m/z = 233 (22) [M+•], 232 (33), 218 (26), 188 (11), 174 (13), 162 (10), 151 (41), 150 (22), 147 (15), 146 (9), 136 (20), 135 (58), 134 (78), 108 (50), 107 (20), 92 (19), 91 (12), 77 (36), 67 (6), 55 (100), 51 (7). HRMS (ESI): m/z calcd for C14H20NO2 [M + H]+: 234.1489; found: 234.1485.
  • 20 Spectroscopic Data for (E)-18 IR: ν = 3077, 2969, 2936, 2838, 1607, 1572, 1504, 1463, 1438, 1418, 1372, 1311, 1283, 1270, 1208, 1159, 1120, 1107, 1068, 1034, 993, 965 cm–1. 1H NMR (400 MHz, CDCl3): δ = 8.37 (s, 1 H), 7.72 (d, J = 8.6 Hz, 1 H), 6.48 (dd, J = 8.6, 0.5 Hz, 1 H), 6.42 (d, J = 2.3 Hz, 1 H), 5.85 (m, 1 H), 5.03 (dqapp, J = 17.1, 1.8 Hz, 1 H), 4.95 (m, 1 H), 4.28 (m, 1 H), 3.82 (s, 3 H), 3.81 (s, 3 H), 2.17 (m, 2 H), 1.81 (m, 1 H), 1.60 (m, 1 H), 1.29 (d, J = 6.2 Hz, 3 H). 13C NMR (100 MHz, CDCl3): δ = 162.1, 158.7, 143.9, 138.6, 127.2, 114.4, 114.3, 105.3, 98.2, 78.5, 55.5, 55.4, 34.9, 29.7, 19.8. MS (EI) m/z: 263 (M+., 12), 204 (10), 192 (11), 177 (14), 166 (10), 164 (37), 163 (15), 150 (18), 149 (100), 137 (12), 134 (14), 122 (14), 121 (44), 120 (18), 107 (16), 92 (10), 91 (10), 79 (11), 77 (22), 67 (10), 55 (59). HRMS (ESI): m/z calcd for C15H22NO3 [M + H]+: 264.1594; found: 264.1591.
  • 21 Spectroscopic Data for 13 IR: ν = 3073, 2925, 1573, 1448, 1340, 1273, 1210, 1046, 944, 913 cm–1. 1H NMR (400 MHz, CDCl3): δ = 8.09 (s, 1 H), 7.60–7.55 (m, 2 H), 7.40–7.30 (m, 3 H), 5.87 (m, 1 H), 5.06–5.00 (m, 2 H), 4.04 (s, 2 H), 2.17 (dtapp, J = 7.5 Hz, 0.9 Hz, 2 H), 1.43 (m, 10 H). 13C NMR (100 MHz, CDCl3): δ = 147.7, 134.8, 132.5, 129.5, 128.6 (2 C), 126.8 (2 C), 117.3, 79.5, 40.1, 37.2, 32.7 (2 C), 26.2, 21.4 (2 C). MS (EI): m/z = 257 (14), 256 (36), 132 (5), 122 (62), 106 (100), 104 (58), 95 (30), 93 (12), 81 (64), 79 (20), 69 (13), 55 (30), 51 (13).