6.80 (2H, m, ArH), 7.10-7.25 (2H, m, ArH). 13C NMR: δC 34.65,
for 2 h. The 1H NMR spectrum (500 MHz, C6D6) showed
unreacted 14 (74%) (and TTMSS) together with 3,4-dihydro-1H-
quinolin-2-one 19 (18%), 1-ethyl-2-isocyanatobenzene 18 (1%),
and 2,3-dihydroindole-1-carbaldehyde 20 (1.3%). The chemical
shifts of reactant 14 and the products were significantly different
in C6D6 from CDCl3. GC-MS: Peak 10.6, 1-ethyl-2-isocyanato-
benzene 18; Peak 15.1, 2,3-dihydroindole-1-carbaldehyde 20;
Peak 15.6, 3,4-dihydro-1H-quinolin-2-one 19; and Peak 23.1,
1-(2,3-dihydroindol-1-yl)-3,4-dihydro-1H-quinolin-2-one 22. TT-
MSS and other unidentified components (mostly Si compounds)
were also observed.
62.95, 116.20, 119.13, 124.44, 127.50, 130.43, 144.80. IR: 3366
cm-1 (νOH); 2878-2942, 1263 and 1044 cm-1 (νC-NH ).
2
Hydr obr om ide of 1-(2-Br om oeth yl)-2-am in oben zen e (13).
2-(2-Aminophenyl)ethanol (0.24 g, 1.75 mmol) was dissolved in
constant-boiling hydrobromic acid (20 mL, 48% in water) and
refluxed for 4 h. The crystalline precipitate was filtered, washed
with ice-cold hydrobromic acid, and dried in vacuo to yield the
salt as a light gray solid (0.29 g, 82%). Mp 161 °C. 1H NMR
3
(D2O): δH 2.82 (2H, t, CH2, J HH ) 10.6), 3.75 (2H, t, CH2Br,
3J HH ) 10.6), 4.70 (2H, s, NH2), 7.20-7.40 (4H, m, ArH).
1-(2-Br om oeth yl)-2-isocya n a toben zen e (14). To a solution
of the hydrobromide of 2-(2-bromoethyl)aniline in toluene (0.6
g, 21 mmol) was added, at 120 °C over 10 min, a solution of
phosgene in toluene (5 mL of 20%). The solvent and excess of
phosgene were removed in vacuo to give of the title compound
4-Br om obu tyla m in e, Hyd r obr om id e Sa lt. 4-Aminobutan-
1-ol (2 g, 22.4 mmol) was refluxed for 3 h in aqueous hydrobromic
acid (48%). On cooling, the solvent was removed under vacuum,
to afford 3.49 g (68%) of crude hydrobromide salt. δH 1.60-1.71
(2H, m), 1.78-1.83 (2H, m), 2.84-2.90 (2H, m), 3.36-3.40 (2H,
m); δC 25.8, 29.2, 33.8, 39.1; νNH 1500 cm-1 and νNH ) 3490
+
3
(0.4 g, 86%). 1H NMR: δH 3.20 (2H, t, CH2, J HH ) 7.6), 3.57
3
cm-1. M+ 233(1), 210(4), 194(5), 152(100), 135(8), 72(94). Found
C 20.79, H 4.24, N 6.15; C4H11NBr2 requires C 20.62, H 4.76, N
6.01.
3
(2H, t, CH2Br, J HH ) 7.6), 7.10-7.45 (4H, m, ArH). 13C NMR:
δc 31.77, 35.99, 121.59, 124.90, 126.41, 126.74, 128.75, 131.00,
133.22. IR 2271.64 cm-1 (νNCO). Found C 47.82, H 3.57, N 6.20;
C9H8NOBr requires C 47.49, H 3.38, N 6.98.
1-Br om o-4-isocya n a tobu ta n e (25). The hydrobromide salt
of 1-bromo-4-aminobutane (2.15 g, 9.2 mmol) in benzene (30 mL)
was treated with phosgene (10 mL of 20% soln in toluene) at
120 °C for 15 min. The solvent was evaporated and the product
was distilled at 120 °C/10 mmHg, lit.23 84-86 °C/12 mmHg, to
yield the title compound (1.4 g, 89%): δH 1.78 (2H, quin, J )
7.0), 1.98 (2H, quin, J ) 7.0), 3.38 (2H, t, J ) 6.4), 3.44 (2H, t,
J ) 6.7); δC 30.0, 30.1, 34.0, 42.6, 123.2; νNCO ) 2272 cm-1. The
NMR spectra showed contamination by about 9% benzyl bro-
mide.
P h otoch em ica l Rea ction s of 1-Br om o-4-isocya n a tobu -
ta n e (25) w ith Tin a n d Silicon Hyd r id es. A solution of
isocyanate 25 (0.1 g, 0.56 mmol) and tributyltin hydride (0.17
g, 0.56 mmol) in benzene (3 mL) was photolyzed in a quartz tube
with light from a 400-W medium-pressure Hg lamp at ambient
temperature (30 °C) for 3 h. The solution was degassed for 15
min before photolysis. GC-MS analysis showed the following
components: Peak 62, n-butylisocyanate (library fit 947); Peaks
262 and 277, mixture of piperidine-2-one (28) (library fit 937)
and 1-pyrrolidine-carboxaldehyde (29-H) (library fit 794); Peak
438, M+ 168, C9H16N2O (probably dipyrrolidin-1-yl-methanone
or 1-pyrrolidin-1-yl-piperidin-2-one); and Peak 441, M+ 170,
C9H18N2O together with several unidentified components. The
1H NMR spectrum of the whole mixture indicated the expected
resonances for the above components although with major
overlaps of the multiplets. The experiment was repeated but
with similar results.
Bromo-isocyanate 25 (20 mg, 0.1 mmol) and TTMSS (33 mg)
with 1,1′-azobis(cyclohexanecarbonitrile) (3 mg) in deuterioben-
zene (1 mL) were heated at 83 °C for 7 h. The 1H NMR spectrum
showed mainly unreacted starting materials. GC-MS analysis
confirmed that conversion of the bromo-isocyanate was low, but
showed a small amount of piperidine-2-one (28).
Com p u ta tion a l Meth od s. Quantum chemical calculations
were carried out for the 4-isocyanato radicals with the Gaussian
98W package.15 Density functional theory, UB3LYP variant, was
employed. The equilibrium geometries were fully optimized with
respect to all geometric variables, no symmetry being assumed,
with the 6-31G(d,p) and 6-311+G(d,p) basis sets. For the
calculation of thermodynamic properties total energies were
adjusted for zero-point vibrational energies and for thermal
corrections to 298 K.
P h otoin itia ted Rea ction of 1-(2-Br om oeth yl)-2-isocy-
a n a toben zen e 14 w ith Tr ibu tyltin Hyd r id e. A solution of
14 (0.1 g, 0.44 mmol) and tributyltin hydride (0.13 g, 0.44 mmol)
in benzene (2 mL) was photolyzed in a quartz tube with light
from a 400-W medium-pressure Hg lamp at ambient tempera-
ture (30 °C) for 3 h. The solution was degassed for 15 min before
photolysis. The solution was chromatographed on neutral alu-
mina eluting with hexane/ethyl acetate (1:1). Several prelimi-
nary fractions containing tin residues were obtained followed
by a final fraction containing the products (0.05 g, 77%). The
final fraction was examined by 1H NMR, which showed the
presence of 3,4-dihydro-1H-quinolin-2-one 19 (44%): δH 2.63 (1H,
d, J ) 7.4), 2.66 (1H, d, J ) 5.9), 2.98 (2H, t, J ) 7.6), 6.75 (1H,
d, J ) 7.9), 6.99 (1H, dd, J ) 6.9, 8.5), 7.17 (2H, m), 8.02 (1H, br
s). This spectrum was essentially the same as that reported in
the literature,21 2,3-dihydroindole-1-carbaldehyde 20 (2 isomers,
ratio 3:1). Major isomer (12%): δH 3.16 (2H, m), 4.08 (2H, t, J )
8.7), 7.05-7.4 (4H, m), 8.94 (1H, s). Minor isomer (4%): δH 3.24
(2H, m), 4.13 (2H, m), 8.53 (1H, s). The spectra were essentially
identical with those reported in the literature22 and 2-ethyl
phenylisocyanate 18 (3%): δH 1.15 (3H, t, J ) 7.5), 2.59 (2H, q,
J ) 7.5), 7.2-7.4 (4H, m). Several resonances due to minor
unidentified components were also present. GC-MS: Peak 271
(minor), 2,3-dihydro-1H-indole 11, m/z (%) 118 (100), 91 (21),
65 (6), 59 (9) (library fit 988). Peak 324, 1-ethyl-2-isocyanato-
benzene 18 m/z (%) 147 (49), 132 (100), 119 (26), 104 (8), 77 (21),
63 (7), 51 (15). Peak 399, 2,3-dihydroindole-1-carbaldehyde 20,
m/z (%) 147 (80), 118 (100), 91 (28), 65 (9), 51 (5) (library fit
990). Peak 430, 3,4-dihydro-1H-quinolin-2-one 19, m/z (%) 147
(100), 128 (9), 118 (56), 104 (15), 92 (24), 78 (14), 63 (5), 59 (8)
(library fit 990). Peak 644 (minor), 1-(2,3-dihydroindol-1-yl)-3,4-
dihydro-1H-quinolin-2-one 22, m/z (%) 264 (63), 146 (100), 128
(45), 118 (30), 117 (15), 103 (5), 91 (24), 77 (13), 65(9). Peak 659
(minor), bis(2,3-dihydroindol-1-yl)methanone 23, m/z (%) 264
(65), 147 (6), 132 (10), 118 (100), 91 (15), 77 (7), 65 (3). Ratio of
644:659 was 1.7:1. Reactions of 14 with Bu3SnH were also
carried out with 0.5 and 2.0 equiv of the tin hydride and with
slow addition of the latter to a toluene solution of 14. GC
analyses showed the same products were formed in each case.
The 19:20 ratio was the same, to within the experimental error,
but as expected, the proportion of 18 was reduced in the
experiments with lower Bu3SnH concentrations.
Ack n ow led gm en t. We thank the EPSRC for finan-
cial support (Grant GR/M39640/01).
P h otoin itia ted Rea ction of 1-(2-Br om oeth yl)-2-isocy-
a n a toben zen e (14) w ith Tr is(tr im eth ylsilyl)sila n e. A solu-
tion of 1-(2-bromoethyl)-2-isocyanatobenzene (0.04 g, 0.18 mmol)
and TTMSS (0.052 g, 0.21 mmol) in deuteriobenzene (1 mL) was
heated at 103 °C with 1,1′-azobis(cyclohexanecarbonitrile) (4 mg)
Su p p or tin g In for m a tion Ava ila ble: Gaussian 98 archive
files, table of energies, and images of optimized structures for
radicals 15, 16, 17, 26, 27, and 29. This material is available
(21) Kodera, Y.; Watanabe, S.; Imada, Y.; Murahashi, S.-I. Bull.
Chem. Soc. J pn. 1994, 2542.
J O034002O
(22) Carlier, P. R.; Lockshin, M. P.; Filosa, M. P. Geochemistry 1994,
59, 3232.
(23) Kricheldorf, H. R. Angew. Chem., Int. Ed. Engl. 1979, 18, 689.
J . Org. Chem, Vol. 68, No. 7, 2003 2963