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Typical Procedure: Preparation of the Aryl Triazene 3b
Anhydrous LiCl (8 mmol) was placed in an Ar-flushed flask and dried for 5 min at 130 °C under vacuum (1 mbar). Zinc dust (8 mmol, 2.0 equiv, <10 micron, 98+%, Aldrich) was added under Ar and the mixture was dried again for 10 min at 130 °C under vacuum (1 mbar). The reaction flask was evacuated and refilled with Ar twice. Then THF (4 mL) was added and the zinc dust was activated with BrCH2CH2Br (5 mol%) and Me3SiCl (2 mol%) by warming the reaction mixture with a heat gun for a few minutes. 1-(2-Carbethoxy-4-iodophenylazo)pyrrolidine (2a, 1.5 g, 4 mmol) was added neat at r.t. and the reaction mixture was gradually heated to 50 °C. The insertion reaction was complete after 7 h (checked by GC analysis of reaction aliquots, the conversion was ca. 92%). Titration of an aliquot (1 mL) of the organo-zinc reagent with iodine indicated that the concentration of 1a was ca. 0.88 M. The solution of 1a (3.4 mL, 3 mmol) was carefully separated from the remaining zinc dust by using a syringe and transferred to another Ar-flushed flask. Benzoyl chloride (635 mg, 4.5 mmol) was added at -20 °C, followed by CuCN·2LiCl (3 mL of 1.0 M solution in THF, 3 mmol). The reaction mixture was gradually warmed to r.t. and stirred for 2 h and then quenched with sat. aq NH4Cl solution (5 mL). The aqueous phase was extracted with Et2O (3 × 5 mL) and concentrated in vacuo. Purification by flash chromatography (n-pentane-Et2O = 1:1) furnished the aryl triazene 3b (853 mg, 81%) as a pale red liquid (entry 2 of Table
[1]
). 1H NMR (600 MHz, CDCl3, 25 °C): δ = 8.06 (s, 1 H), 7.85 (d, J = 8.6 Hz, 1 H), 7.76 (d, J = 8.4 Hz, 2 H), 7.57 (t, J = 7.5 Hz, 1 H), 7.52 (d, J = 8.6 Hz, 1 H), 7.44-7.49 (m, 2 H), 4.34 (q, J = 7.1 Hz, 2 H), 3.95 (br s, 2 H), 3.71 (br s, 2 H), 1.98-2.12 (m, 4 H), 1.35 (t, J = 7.1 Hz, 3 H) ppm. 13C NMR (150 MHz, CDCl3, 25 °C): δ = 195.3, 168.0, 153.2, 137.8, 133.1, 132.2, 131.9, 129.8, 128.4, 128.3, 126.4, 118.8, 61.1, 51.3, 46.9, 23.9, 23.5, 14.3 ppm. MS (70 eV, EI): m/z (%) = 351 (5) [M+], 281 (28), 254 (9), 225 (100), 209 (9), 177 (8), 141 (14), 105 (75), 77 (30). IR (neat): ν = 3061 (w), 2977 (w), 2874 (w), 1719 (s), 1651 (vs), 1595 (vs), 1394 (vs), 1302 (s), 1239 (s), 1071 (m), 959 (m) cm-1. HRMS (EI): m/z calcd for C20H21N3O3: 351.1583; found: 352.1651 [M + H]+.
11
Aryl Triazene 3d
Mp 73.8-76.7 °C. 1H NMR (600 MHz, CDCl3, 25 °C): δ = 9.97 (s, 1 H), 8.01 (d, J = 7.9 Hz, 1 H), 7.61-7.66 (m, 2 H), 7.60 (s, 1 H), 7.44 (d, J = 8.2 Hz, 1 H), 7.40 (d, J = 7.9 Hz, 1 H), 7.21 (t, J = 8.2 Hz, 1 H), 3.95-4.01 (m, 2 H), 3.75-3.82 (m, 2 H), 2.00-2.12 (m, 4 H) ppm. 13C NMR (150 MHz, CDCl3, 25 °C): δ = 191.6, 153.6, 143.6, 134.8, 134.1, 133.9, 133.8, 133.6, 130.6, 128.3, 128.1, 117.6, 117.3, 107.4, 51.5, 47.3, 23.9, 23.4 ppm. MS (70 eV, EI): m/z (%) = 304 (43) [M+], 234 (72), 206 (100), 177 (42), 151 (41). IR (KBr): ν = 3057 (w), 2973 (w), 2873 (w), 2748 (w), 2223 (m), 1689 (s), 1596 (m), 1470 (m), 1384 (s), 1307 (s), 1267 (s), 1098 (m), 903 (w) cm-1. HRMS (EI): m/z calcd for C18H16N4O: 304.1324; found: 304.1328.
12
Aryl Triazene 3e
Mp 120.3-122.2 °C. 1H NMR (600 MHz, CDCl3, 25 °C): δ = 7.60 (s, 1 H), 7.51 (d, J = 8.4 Hz, 1 H), 7.48 (d, J = 8.4 Hz, 1 H), 7.43 (d, J = 8.6 Hz, 2 H), 6.90 (d, J = 8.6 Hz, 2 H), 3.92 (br s, 2 H), 3.83 (s, 3 H), 3.49 (br s, 2 H), 1.95-2.00 (m, 4 H) ppm. 13C NMR (150 MHz, CDCl3, 25 °C): δ = 158.9, 151.5, 136.3, 134.2, 131.3, 131.0, 130.5, 119.6, 117.9, 113.0, 107.7, 55.2, 51.1, 46.9, 23.9, 23.3 ppm. MS (70 eV, EI): m/z (%) = 306 (22) [M+], 236 (11), 208 (100), 193 (32), 177 (6), 165 (19). IR (KBr): ν = 2948 (w), 2879 (w), 2830 (w), 2215 (s), 1595 (m), 1513 (m), 1479 (m), 1383 (s), 1243 (s), 1173 (s), 1030 (m) cm-1. HRMS (EI): m/z calcd for C18H18N4O: 306.1481; found: 306.1483.
13
Aryl Triazene 6
Mp 133.5-135.0 °C. 1H NMR (300 MHz, CDCl3, 25 °C): δ = 7.76 (d, J = 7.1 Hz, 2 H), 7.63 (t, J = 7.1 Hz, 1 H), 7.49-7.53 (m, 2 H), 7.46 (d, J = 7.1 Hz, 2 H), 2.38 (s, 3 H) ppm. 13C NMR (75 MHz, CDCl3, 25 °C): δ = 195.8, 146.8, 139.3, 135.6, 134.7, 134.3, 132.3, 130.4, 128.9, 122.3, 119.1, 92.3, 20.7 ppm. MS (70 eV, EI): m/z (%) = 347 (100) [M+], 270 (22), 220 (34), 190 (11), 165 (6), 115 (15), 105 (98), 77 (40). IR (KBr): n = 3041 (w), 2922 (w), 2852 (w), 2230 (m), 1667 (vs), 1594 (m), 1578 (m), 1448 (m), 1412 (m), 1318 (s), 1212 (m), 1020 (m), 878 (m) cm-1. HRMS (EI): m/z calcd for C15H10INO: 346.9807; found: 346.9789.
14
Aryl Triazene 7
Mp 151.4-152.6 °C. 1H NMR (600 MHz, CDCl3, 25 °C): δ = 7.38 (d, J = 8.4 Hz, 2 H), 7.32-7.36 (m, 4 H), 3.88 (br s, 2 H), 3.78 (br s, 2 H), 3.48 (br s, 2 H), 2.34 (s, 3 H), 1.98-2.03 (m, 4 H), 1.92-1.97 (m, 4 H) ppm. 13C NMR (150 MHz, CDCl3, 25 °C): δ = 150.3, 149.3, 136.5, 135.5, 135.4, 134.4, 133.0, 130.6, 119.5, 119.3, 103.7, 50.8, 46.6, 23.9, 23.8, 23.4, 20.6 ppm. MS (70 eV, EI): m/z (%) = 387 (100) [M+], 348 (11), 289 (59), 277 (53), 262 (49), 219 (65), 205 (12), 191 (72), 165 (13), 152 (25), 116 (10), 70 (19). IR (KBr): ν = 3051 (w), 2974 (w), 2874 (w), 2210 (w)1596 (w), 1397 (s), 1340 (s), 1312 (m), 1218 (m), 1148 (m), 970 (w) cm-1. HRMS (EI): m/z calcd for C22H25N7: 387.2171; found: 387.2174.
