824, 750, 696, 609, 542 cm-1; MS (m/z) 292 (8), 290 (18, M+),
288 (10), 211 (46), 209 (45), 130 (34), 129 (100), 128 (32), 127
(14), 116 (23), 115 (32), 104 (14), 103 (13), 102 (11), 86 (24), 85
(52), 84 (36), 83 (83), 64 (31) 63 (11), 51 (22), 50 (10), 49 (17).
Th er m a l Rin g Op en in g of 1-(1-Br om o-1-p-tolylm eth yl)-
cyclop r op yl Br om id e (1a ) a n d 1-(1-Br om o-1-p h en ylm eth -
yl)cyclop r op yl Br om id e (1b): Gen er a l P r oced u r e. The
cyclopropyl bromides (1a , 1.00 g, 3.29 mmol; or 1b, 1.92 g, 6.62
mmol) were placed in a 5-mL flask and heated at 150 °C for 1
h. After cooling, the products were separated by flash chroma-
tography as colorless oils, (0.51 g of 2a and 0.14 g of 3a , total
yield 65%; and 0.86 g of 2b and 0.29 g of 3b, total yield 60%).
(Z)-2,4-Dibr om o-1-p-tolyl-1-bu ten e (2a ). Rt ) 27.45 min;
Rf 0.18 (pentane);1H NMR (CDCl3) δ 2.38 (s, 3H), 3.13 (t, 2H, J
) 6.8 Hz), 3.66 (t, 2H, J ) 6.8 Hz), 6.84 (s, 1H), 7.20 (“d”, 2H, J
) 8.1 Hz), 7.52 (“d”, 2H, J ) 8.1 Hz); 13C NMR (CDCl3) δ 21.3,
30.5, 46.0, 122.0, 128.82, 128.83, 130.5, 132.5, 138.0; IR (neat) ν
3023, 2955, 2923, 2855, 1642, 1611, 1510, 1441, 1413, 1286,
F IGURE 1. Representation of resonance forms of radical 5.
and the formation of an arylcyclopropylcarbinyl radical
5. It is well-documented that cyclopropylcarbinyl radicals
undergo rapid ring opening to give exclusively butenyl
radicals.8 Radical 5 (Figure 1), however, is stabilized by
the presence of the neighboring benzene ring.8a,b
If 5 is represented as shown in Figure 1, recombination
with a bromine atom leads directly to the observed (Z)-
and (E)-isomers 2 and 3, respectively. Loss of strain of
the three-membered ring in 1 and formation of a styrene
substructure are the driving forces to bring about this
transformation.
1258, 1213, 1185, 1143, 1057, 1009, 913, 865, 803, 759, 682 cm-1
;
MS (m/z) 306 (54), 304 (97, M+), 302 (52), 211 (25), 209 (23),
144 (12), 143 (24), 131 (12), 130 (100), 129 (64), 128 (40), 115
(24), 58 (14), 57 (17), 56 (20); HRMS calcd for C11H1279Br2
301.9306, found 301.9311. Anal. Calcd for C11H12Br2: C, 43.45,
H, 3.97. Found: C, 43.64, H, 3.88.
(E)-2,4-Dibr om o-1-p-tolyl-1-bu ten e (3a ). Rt ) 27.10 min;
Rf 0.29 (pentane); 1H NMR (CDCl3) δ 2.34 (s, 3H), 3.15 (t, 2H, J
) 7.1 Hz), 3.61 (t, 2H, J ) 7.1 Hz), 7.11 (s, 1H), 7.12-7.19 (m,
4H); 13C NMR (CDCl3) δ 21.2, 30.0, 38.9, 125.0, 128.0, 129.3,
133.0, 135.1, 137.6; IR (neat) ν 3025, 2922, 2854, 1630, 1610,
1510, 1444, 1380, 1272, 1212, 1144, 1010, 870, 809, 752, 698
cm-1; MS (m/z) 306 (43), 304 (89, M+), 302 (42), 211 (24), 209
(23), 143 (27), 131 (13), 130 (100), 129 (76), 128 (48), 127 (13),
116 (10), 115 (38), 51 (12); HRMS calcd for C11H1281Br2 303.9286,
found 303.9291.
Exp er im en ta l Section
Syn th esis of (1-p-Tolylm eth ylen e)cyclop r op a n e a n d (1-
P h en ylm eth ylen e)cyclop r op a n e: Gen er a l P r oced u r e. NaH
(5.20 g, 55-65% suspension in oil, 0.12-0.14 mol) was slowly
added to a solution of cyclopropyltriphenylphosphonium bromide
(25.00 g, 0.065 mol) in dry THF (100 mL) and stirred at room
temperature for 12 h. Then, a THF solution of p-tolylaldehyde
or benzaldehyde, respectively (0.070 mol in 5 mL of THF), was
added dropwise and the mixture was refluxed for 6 h. After
cooling, the suspension was filtered and the filtrate was washed
with 10% HCl (3 × 50 mL) and brine (1 × 50 mL) and dried
(MgSO4). After the solvents were removed in vacuo, the products
were purified by bulb-to-bulb distillation.
(1-p-Tolylm eth ylen e)cyclop r op a n e. Yield 59%; bp 75 °C/
0.35 Torr; 1H NMR (CDCl3) δ 1.16-1.23 (m, 2H), 1.40-1.47 (m,
2H), 2.37 (s, 3H), 6.75 (t, 1H, J ) 1.8 Hz), 7.17 (“d”, 2H, J ) 7.8
Hz), 7.46 (“d”, 2H, J ) 8.1 Hz); 13C NMR (CDCl3) δ 0.5, 4.1, 21.2,
118.1, 123.0, 126.5, 129.1, 135.5, 136.3; IR (neat) ν 3048, 3022,
2976, 2953, 2864, 2829, 1611, 1513, 1466, 1259, 1156, 1122,
1042, 909, 833, 734 cm-1; MS (m/z) 144 (30, M+), 143 (14), 130
(10), 129 (100), 128 (49), 127 (14), 115 (12).
(Z)-2,4-Dibr om o-1-p h en yl-1-bu ten e (2b). Rt ) 26.56 min;
1
Rf 0.27 (pentane); H NMR (CDCl3) δ 3.13 (t, 2H, J ) 6.8 Hz),
3.67 (t, 2H, J ) 6.8 Hz), 6.88 (s, 1H), 7.30-7.42 (m, 3H), 7.58-
7.63 (m, 2H); 13C NMR (CDCl3) δ 30.5, 46.0, 122.8, 128.0, 128.1,
128.9, 130.7, 135.4; IR (neat) ν 3056, 3025, 2966, 2926, 1642,
1599, 1492, 1446, 1430, 1417, 1345, 1288, 1258, 1212, 1143,
1080, 1056, 1030, 1009, 919, 849, 749, 693, 618, 555 cm-1; MS
(m/z) 292 (43), 290 (90, M+), 288 (45), 197 (21), 195 (23), 130
(26), 129 (97), 128 (48), 127 (18), 117 (15), 116 (100), 115 (96),
102 (14), 85 (53), 83 (83), 77 (15), 64 (23), 63 (16), 51 (26), 50
(14), 47 (19); HRMS calcd for C10H1079Br2 287.9149, found
287.9152. Anal. Calcd for C10H10Br2: C, 41.42, H, 3.48. Found:
C, 41.64, H, 3.49.
(1-P h en ylm eth ylen e)cyclop r op a n e. Yield 60%; bp 60 °C/
1
0.3 Torr; H NMR (CDCl3) δ 1.16-1.22 (m, 2H), 1.41-1.47 (m,
2H), 6.77 (t, 1H, J ) 2 Hz), 7.20-7.25 (m, 1H), 7.31-7.37 (m,
2H), 7.53-7.58 (m, 2H); 13C NMR (CDCl3) δ 0.5, 4.2, 118.2, 124.3,
126.6, 126.7, 128.4, 138.2; IR (neat) ν 3027, 2977, 2926, 2854,
1599, 1497, 1452, 1082, 1027, 934, 909, 807, 734, 694 cm-1; MS
(m/z) 130 (67, M+), 129 (100), 128 (53), 127 (21), 115 (53), 91 (7),
64 (13), 51 (13).
(E)-2,4-Dibr om o-1-p h en yl-1-bu ten e (3b). Rt ) 26.25 min
(20%); Rf 0.38 (pentane); 1H NMR (CDCl3) δ 3.14 (t, 2H, J ) 7.1
Hz), 3.61 (t, 2H, J ) 7.0 Hz), 7.15 (s, 1H), 7.22-7.40 (m, 5H);
13C NMR (CDCl3) δ 30.0, 38.8, 125.7, 127.7, 128.1, 128.6, 135.1,
135.8; IR (neat) ν 3057, 3025, 2967, 1632, 1600, 1493, 1444, 1430,
Syn th esis of 1-(1-Br om o-1-p-tolylm eth yl)cyclopr opyl Br o-
m id e (1a ) a n d 1-(1-Br om o-1-p h en ylm eth yl)cyclop r op yl
Br om id e (1b): Gen er a l P r oced u r e. Br2 (3.60 g, 0.023 mol)
was slowly added to a solution of (1-tolylmethylene)cyclopropane
and (1-phenylmethylene)cyclopropane, respectively, in CCl4 (50
mL) at 0 °C. After being stirred for 1 h, the mixture was
quenched with 10% Na2SO3 (10 mL) and washed with brine. The
organic phase was dried (MgSO4) and concentrated in vacuo.
The products were purified by bulb-to-bulb distillation.
1-(1-Br om o-1-p-tolylm eth yl)cyclop r op yl Br om id e (1a ).
Yield 88%; bp 100 °C/0.5 Torr; Rt ) 26.65 min; 1H NMR (CDCl3)
δ 1.27-1.33 (m, 1H), 1.35-1.45 (m, 3H), 2.37 (s, 3H), 5.11 (s,
1H), 7.18 (“d”, 2H, J ) 7.8 Hz), 7.42 (“d”, 2H, J ) 8.1 Hz); 13C
NMR (CDCl3) δ 17.4, 17.5, 21.2, 37.3, 61.0, 128.3, 129.0, 136.4,
138.6; IR (neat) ν 3008, 2922, 1612, 1512, 1416, 1265, 1150, 1130,
1031, 824, 807, 754, 739, 580, 568 cm-1; MS (m/z) 306 (28), 304
(53, M+), 302 (25), 225 (32), 223 (32), 211 (13), 209 (13), 144 (31),
143 (47), 142 (13), 141 (11), 131 (11), 130 (80), 129 (100), 128
(66), 127 (17), 117 (10), 115 (36), 80 (11), 71 (21).
1272, 1212, 1147, 1075, 1031, 1010, 919, 863, 753, 700 cm-1
;
MS (m/z) 292 (22), 290 (46, M+), 288 (24), 195 (10), 172 (10),
170 (10), 154 (11), 131 (10), 130 (12), 129 (33), 128 (15), 116 (32),
115 (27), 91 (100), 65 (13), 64 (11), 51 (11); HRMS calcd for
C10H1081Br2 289.9130, found 289.9137.
Ack n ow led gm en t. We thank Ms. S. Felsinger for
the recording of NMR spectra and M. Sc. N. Kokkotas
for performing GC-MS analyses of 2b and 3b. We are
also grateful to Mag. W. Knoll for helpful discussions.
Su p p or tin g In for m a tion Ava ila ble: General experimen-
1
tal information; H and 13C NMR spectra of 2a , 2b, 3a , and
3b; COSY of 2a , 2b, and 3a ; NOESY of 2a , 2b, and 3b; and
HETCOR of 2a , 2b, and 3a . This material is available free of
1-(1-Br om o-1-p h en ylm eth yl)cyclop r op yl Br om id e (1b).
Yield 61%; bp 90 °C/0.5 Torr; Rt ) 25.70 min; 1H NMR (CDCl3)
δ 1.28-1.33 (m, 1H), 1.36-1.47 (m, 3H), 5.11 (s, 1H), 7.31-7.41
(m, 3H), 7.51-7.55 (m, 2H); 13C NMR (CDCl3) δ 17.47, 17.54,
37.2, 60.9, 128.3, 128.4, 128.7, 139.3; IR (neat) ν 3088, 3061,
3029, 3007, 1494, 1451, 1418, 1203, 1151, 1133, 1077, 1030, 906,
J O034431M
(8) (a) Hollis, R.; Hughes, L.; Bowry, V. W.; Ingold, K. U. J . Org.
Chem. 1992, 57, 4284. (b) Bowry, V. W.; Lusztyk, J .; Ingold, K. U. J .
Chem. Soc., Chem. Commun. 1990, 923. (c) Nonhebel, D. C. Chem.
Soc. Rev. 1993, 22, 347.
J . Org. Chem, Vol. 68, No. 18, 2003 7093