Notes
J . Org. Chem., Vol. 66, No. 10, 2001 3629
1,3,5-Tr ip en tylben zen e (2b). 1H NMR δ 0.864-0.898 (t,
3H), 1.236-1.322 (m, 4H), 1.552-1.605 (m, 2H), 2.375 (t, 2H),
6.383 (s, 3H); 13C NMR δ 13.9, 22.4, 27.2, 30.8, 39.9, 120.3, 137.7;
MS m/z 266, 262, 241, 227, 205, 192, 171, 149, 135, 113, 99, 91,
77, 55, 41, 29.
1,3,5-Tr ih exylben zen e (2c). 1H NMR δ 0.851-0.885 (t, 3H),
1.236-1.300 (m, 6H), 1.542-1.577 (m, 2H), 2.356-2.393 (t, 3H),
6.381 (s, 3H); 13C NMR δ 14.0, 22.5, 27.5, 28.3, 31.5, 39.9, 120.3,
137.7; MS m/z 292, 290, 269, 248, 219, 206, 185, 163, 149, 135,
109, 91, 79, 55, 43, 29.
1,3,5-Tr i(ter t-bu tyl)ben zen e (2d ). Solid, mp 70-73 °C (lit.20
mp 73 °C);1H NMR δ 1.207 (s, 27H), 6.523 (s, 3H); 13C NMR δ
28.9, 39.2, 117.9, 148.0; MS m/z 246 (M+), 234, 219, 202, 199,
183, 163, 157, 143, 123, 107, 91, 77, 65, 57, 41, 29.
cyclotrimerization of unsymmetrical alkynes. When R3
) alkyl or p-ClPh or p-MePh, R4 ) H and R3 ) alkyl, R4
) alkyl in Scheme 2, there is less steric hindrance in 6a
during the ring-closure process, and the products of the
cyclotrimerization are symmetrical benzene derivatives.
When R3 ) Ph, R4 ) Me, 6a is more sterically hindered,
holding back the ring-closure process more than 6b, so
the more highly sterically strained product was obtained.
The reason why cyclotrimerization of diphenylacet-
ylene and phenylacetylene did not give benzene deriva-
tives is under investigation.18
Con clu sion
1,2,4-Tr i(p -m et h ylp h en yl)b en zen e (2e). Solid, mp 173-
175 °C (lit.21 mp 178 °C); 1H NMR δ 2.369 (s, 9H), 7.175-7.196
(d, 6H), 7.271 (s, 3H), 7.592-7.6130 (d, 6H); 13C NMR δ 21.2,
121.2, 126.5, 129.2, 134.9, 135.9, 139.3; MS m/z 348 (M+), 333,
317, 302, 267, 252, 232, 215, 189, 163, 151,133, 107, 101, 89,
65, 51, 39, 27.
In conclusion, we reported a novel regioselective and
highly chemoselective procedure for the synthesis of
benzene derivatives. The effect of CuCl2 and the solvent
on the Pd(II)-catalyzed cyclotimerization of alkynes was
also discussed.
1,3,5-Tr i(p-ch lor op h en yl)ben zen e (2f). Solid, mp 242-245
1
°C (lit.21 mp 246 °C); H NMR δ 7.264 (s, 3H), 7.345-7.366 (d,
6H), 7.628-7.650 (d, 6H); 13C NMR δ 122.1, 127.8, 128.7, 135.3,
135.9; MS m/z 348, 344, 333, 307 (- 37Cl-), 272 (- 35Cl-), 236
(- 37Cl-), 202, 185, 161, 136, 118, 100, 87, 75, 66, 51, 36.
Exp er im en ta l Section
All 1H NMR and 13C NMR spectra were recorded at 400 MHz
using CDCl3 as solvent. TLC was performed using commercially
prepared 100-400 mesh silica gel plates (HF254), and visualiza-
tion was effected at 254 nm. CuCl2 was dried at 130 °C under
HCl gas. All other reagents were used directly as obtained
commercially. All melting points are uncorrected.
1,2,4-Tr im eth yl-3,5,6-tr iph en ylben zen e (3). Solid, mp 220-
222 °C (lit.11f mp 224 °C); 1H NMR δ 1.705 (s, 6H), 2.030 (s, 3H),
6.964-7.438 (m, 15H); 13C NMR δ 1.0, 15.2, 121.8, 128.4, 129.2,
132.5; MS m/z 348 (M+), 333, 318, 302, 289, 271, 255, 241, 215,
191, 178, 165, 151, 105, 91, 77, 65, 51, 43.
Gen er a l P r oced u r e for th e Cyclotr im er iza tion of Ter -
m in a l Alk yn es. To a mixture of PdCl2 (0.056 mmol) and CuCl2
(2 mmol) in C6H6 (10 mL)-BuOH (0.6 mL) was added alkyne (1
mmol). The reaction was stirred at the desired temperature.
After complete conversion of acetylenes as monitored by GC
analyses, the mixture was filtered, and the benzene was removed
by rotary evaporation to give crude products. The products were
then purified by preparative TLC on silica gel (light petroleum
ether-ethyl ether). The conversions were measured by GC
analyses using an internal standard.
Ack n ow led gm en t. We are grateful to the National
Natural Science Foundation of China for financial
support (Grants 29772036 and 29872039). We also
thank Dr. Fanglu¨ Huang and Professor Xiyan Lu
(Shanghai Institute of Organic Chemistry, Chinese
Academy of Sciences) for helpful discussion.
Su p p or tin g In for m a tion Ava ila ble: Spectral data (1H,
13C, MS) of all the compounds. This material is available free
Hexa p r op ylben zen e (2a ). Solid, mp 100-103 °C (lit.19 mp
102-102.5 °C); 1H NMR δ 1.030-1066 (t, 3H), 1.526 (m, 2H),
2.454-2.495 (t, 2H); 13C NMR δ 15.2, 24.8, 32.2, 136.7; MS m/z
330 (M+), 301, 287, 273, 259, 245, 229, 217, 187, 175, 159, 145,
133, 105, 91, 80, 69, 55, 43, 29.
J O0017382
(18) The products are red oils. We cannot confirm the construction
of the products by 1H NMR, 13C NMR, and MS.
(19) Hopff, H.; Gati, A. Helv. Chim. Acta 1965, 48(3), 509.
(20) Mccaulay, D. A.; Line, A. P. J . Am. Chem. Soc. 1953, 75, 2411.
(21) Lyle, R. E.; Dewitt, E. J .; Nichols, N. M.; Cleland, W. J . Am.
Chem. Soc. 1953, 75, 5959.