Characterization of Alkoxycarbonyl Radicals
FULL PAPER
SigmaPlot software. In order to avoid depletion of the precursor
and product build-up, a flow cell was used. The concentration of
1a was adjusted so that an optical density of 0.3 was achieved at
the laser wavelength used.
Isopropyl [(9-Fluorenylideneamino)oxycarbonyl]formate (1b): 1H
NMR ([D6]DMSO, 200 MHz): δ ϭ 1.38 (d, 6 H), 5.16 (m, 1 H),
7.37 (t, 1 H), 7.42 (t, 1 H), 7.55 (t, 1 H), 7.61 (t, 1 H), 7.77 (d, 1 H),
7.85 (d, 1 H), 7.88 (d, 1 H), 8.47 (d, 1 H). Ϫ 13C NMR ([D6]DMSO,
50 MHz): δ ϭ 21.39, 71.72, 121.28, 123.01, 129.00, 130.66, 132.83,
133.87, 141.17, 142.13, 154.09, 155.58, 159.81. Ϫ IR (KBr) ν˜ ϭ
2987, 1787, 1631, 1609, 1596, 1453, 1388, 1375, 1357, 1323, 1294,
1229, 1206, 1154, 1095, 1041, 991, 922, 894, 878, 830, 790, 754,
732, 646 cmϪ1. Ϫ MS; m/z: 309, 195, 179, 164, 151, 43. Ϫ
C18H15NO4 (309.3): calcd. C 69.89, H 4.89, N 4.53; found C 69.01,
H 5.03, N 4.32. Ϫ M.p. 99° C.
Calculations: Calculations were performed with a standard density
functional method (UBPW91)[11,12] using
a cc-pVDZ or 6-
311G(d,p) basis set. The calculated vibrational frequencies given
are unscaled. The Gaussian 98 suite of programs[13] was employed
for all calculations.
Product Studies: Photolyses were performed using CCl4 and λexc ϭ
320 nm (Hg low-pressure lamp, Gräntzel, Germany, filtered).
Samples (0.6 m) were purged with Ar for 20 minutes prior to
photolysis. After 30 min photolysis, the solvent was evaporated and
the mixture analyzed by GC-MS (Hewlett-Packard 5890 series II
GC, HP 5972 mass detector, column MDN-5 S, 30 m ϫ 0.25 mm,
0.1 µm film, poly (5% phenyl/95% methylsiloxane). Products were
identified by MS analysis and/or by coinjection with authentic
samples.
tert-Butyl [(9-Fluorenylideneamino)oxycarbonyl]formate (1c): 1H
NMR (CDCl3, 200 MHz): δ ϭ 1.65 (s, 9 H), 7.27 (t, 1 H), 7.30 (t,
1 H), 7.42 (t, 1 H), 7.46 (t, 1 H), 7.56 (d, 1 H), 7.59 (d, 1 H), 7.88
(d, 1 H), 8.46 (d, 1 H). Ϫ 13C NMR (CDCl3, 50 MHz) δ ϭ 27.86,
85.77, 120.24, 120.32, 123.70, 128.51, 128.72, 130.02, 131.00,
132.20, 133.09, 133.80, 141.56, 142.70. Ϫ IR (KBr) ν˜ ϭ 3059, 2986,
2936, 1784, 1749, 1633, 1611, 1598, 1452, 1370, 1306, 1260, 1176,
1158, 1130, 1038, 987, 927, 905, 870, 836, 810, 788, 752, 730, 645
cmϪ1. Ϫ MS; m/z: 323, 195, 179, 164, 151, 76, 57. Ϫ C19H17NO4
(323.3): calcd. C 70.58, H 5.30 N 4.33; found C 70.60, H 5.79, N
4.31. Ϫ M.p. 86 °C.
Synthesis and Characterization of the Precursors: The precursor
molecules were synthesized from 9-fluorenone oxime and oxalic
acid monochloride monoesters, which were partly commercially
available, and partly synthesized from the corresponding alcohol
(or acetone oxime) and an excess of oxalyl dichloride. The oxalate
8 was prepared according to a literature procedure.[4,14]
n-Octyl [(9-Fluorenylideneamino)oxycarbonyl]formate (1d): 1H
NMR (CDCl3): δ ϭ 0.86 (t, 2 H), 1.28 (m, 10 H), 1.82 (m, 2 H),
4.41 (t, 2 H), 7.28 (dt, 1 H), 7.31 (dt, 1 H), 7.43 (dt, 1 H), 7.47 (dt,
1 H), 7.57 (dt, 1 H), 7.60 (dt, 1 H), 7.90 (d, 1 H), 8.45 (d, 1 H). Ϫ
13C NMR (CDCl3): δ ϭ 14.04, 22.59, 25.78, 28.37, 29.12, 31.73,
67.75, 120.26, 120.34, 123.74, 128.53, 128.82, 129.94, 131.06,
132.29, 133.18, 133.70, 141.58, 142.74, 154.93, 156.97, 160.72. Ϫ
IR (KBr): ν˜ ϭ 3451, 3060, 2952, 2927, 2860, 1809, 1793, 1758,
1609, 1595, 1471, 1377, 1292, 1228, 1204, 1139, 1126, 1038, 989,
955, 900, 877, 817, 788, 733, 661, 647 cmϪ1. Ϫ MS: m/z: 379, 206,
195, 179, 164, 151, 71, 57, 43, 29. Ϫ C23H25NO4 (379.5): calcd. C
72.8, H 6.64, N 3.69; found C 72.8, H 7.08, N 3.65. Ϫ M.p. 62 °C.
General Procedure for the Conversion of Alcohols to Oxalic Acid
Monoester Monochlorides: The alcohol (10 mmol) was added drop-
wise over 15 min to an excess of oxalyl chloride (20 mmol) at 0 °C.
When the addition was complete, the mixture was allowed to warm
to room temperature. Excess oxalyl chloride was removed by va-
cuum distillation. The product was distilled and kept at 0 °C in
the dark.
General Procedure for the Conversion of Oxalic Acid Monoester
Monochlorides into Alkyl-[(9-fluorenylidenamino)oxycarbonyl]form-
ates: 9-Fluorenone oxime (10 mmol) was suspended in CCl4
(50 mL) at room temperature. To this suspension was added drop-
wise over 15 min a solution of oxalic acid monoester monochloride
(10 mmol) in CCl4 (10 mL). The solution was stirred for 12 h and
filtered, and the solvent was removed. The alkyl-[(9-fluorenylidena-
mino)oxycarbonyl]formates were recrystallized from n-hexane.
Yield: typically ca. 90% (60% for 1f).
Benzyl [(9-Fluorenylideneamino)oxycarbonyl]formate (1e): 1H NMR
(CDCl3, 200 MHz): δ ϭ 5.42 (s, 2 H), 7.10 (t, 1 H), 7.25 (t, 1 H),
7.43 (m, 7 H), 7.54 (d, 1 H), 7.58(d, 1 H), 7.84 (d, 1 H), 8.31(d, 1
H). Ϫ 13C NMR (CDCl3, 50 MHz): δ ϭ 69.18, 120.24, 123.76,
128.53, 128.88, 128.97, 129.11, 129.84, 131.08, 132.29, 133.14,
133.67, 133.97, 141.58, 142.70, 156.67, 160.74. Ϫ IR (KBr): ν˜ ϭ
1800, 1752, 1609, 1595, 1452, 1320, 1286, 1219, 1205, 1136, 1039,
980, 941, 924, 902, 874, 791, 753, 732, 698, 646 cmϪ1. Ϫ MS; m/z:
357, 179, 151, 91, 77, 65, 44. Ϫ C22H15NO4 (357.4): calcd. C 73.94
H 4.23, N 3.92; found C 73.32 H 3.87 N 4.32. Ϫ M.p. 143 °C.
Synthesis of 1g: 9-Fluorenone oxime (4.1 g, 21 mmol) was sus-
pended in CCl4 (350 mL) at room temperature. To this suspension
was added dropwise
a solution of oxalyl dichloride (1 mL,
2-Propylideneamino [(9-Fluorenylideneamino)oxycarbonyl]formate
(1f): H NMR (CDCl3): δ ϭ 2.09 (s, 3 H), 2.14 (s, 3 H), 7.27(td, 1
1
10 mmol) in CCl4 (10 mL). The solution was stirred for 12 h and
filtered, and the solvent was removed. The product was recrystal-
lized from toluene (1700 mL). Yield: 4.0 g (86%), dec. 221 °C.
H), 7.29 (td, 1 H), 7.42 (td, 1 H), 7.46(td, 1 H), 7.55 (d, 1 H), 7.59
(d, 1 H), 7.84 (d, 1 H) 8.40 (d, 1 H). Ϫ 13C NMR (CDCl3): δ ϭ
17.44, 21.80, 120.30, 120.34, 123.62, 128.51, 128.88, 129.80, 131.08,
132.31, 133.24, 133.66, 141.58, 142.70, 160.39, 166.81. Ϫ IR (KBr):
ν˜ ϭ 1787, 1732, 1637, 1610, 1597, 1452, 1370, 1321, 1277, 1249,
1204, 1157, 1129, 1038, 983, 915, 866, 840, 792, 783, 755, 730, 644
cmϪ1. Ϫ MS; m/z: 322, 179, 164, 151, 76, 56, 44. Ϫ HRMS: found
322.096000, calcd. 322.095357. Ϫ M.p. 215 °C (dec.).
Ethyl [(9-Fluorenylideneamino)oxycarbonyl]formate (1a): 1H NMR
(CDCl3): δ ϭ 8.43 (d, 1 H), 7.88 (d, 1 H), 7.57 (d, 1 H), 7.55 (d, 1
H), 7.46 (t, 1 H), 7.42 (t, 1 H), 7.31 (t, 1 H), 7.26 (t, 1 H), 4.48 (q,
2 H), 1.47 (t, 3 H). Ϫ 13C NMR (CDCl3): δ ϭ 160.76, 156.84,
154.89, 142.72, 141.58, 133.66, 133 16, 132.27, 131.08, 129.92,
128.88, 128.51, 123.72, 120.32, 120.24, 63.65, 13.98. Ϫ IR (KBr)
ν˜ ϭ 3400, 2990, 1785, 1749, 1612, 1597, 1497, 1367, 1324, 1291,
9-Fluorenylideneamino
[(9-Fluorenoneamino)oxycarbonyl]formate
1207, 1164, 1152, 1109, 1039, 1017, 985, 945, 912, 874, 814, 786, (1g): IR (KBr): ν˜ ϭ 1770, 1631, 1593, 1452, 1319, 1207, 1158, 1121,
733, 647 cmϪ1. Ϫ MS; m/z: 295, 232, 195, 178, 164, 151, 29. Ϫ
HRMS: found 295.084458, calcd. 295.085100. Ϫ C17H13NO4
(295.3): calcd. C 69.15, H 4.44, N 4.74; found C 69.25, H 4.54, N
4.66. Ϫ M.p. 116 °C.
1101, 1039): 989, 969, 880, 858, 827, 788, 730, 648 cmϪ1. Ϫ MS:
m/z: 444, 372, 356, 327, 206, 195, 179, 164, 151, 91, 76, 63, 44. Ϫ
HRMS: found 444.111200, calcd. 444.111007. Ϫ M.p. 221 °C
(dec.).
Eur. J. Org. Chem. 2001, 545Ϫ552
551