4a (80 mg) in 5.0 mL of DMF was heated to reflux for 6 h. Then
the solution was cooled to room temperature and 20 mL of
deionized water was added. The mixture was extracted with 15
mL of hexane five times. The combined organic layers were dried
over MgSO4. The solvent was evaporated and the product was
purified by column chromatography with petroleum ether as eluant
to afford a white solid 6a, 80 mg (isolated yield 100%). Mp 104-
105 °C. 1H NMR (CDCl3, SiMe4) δ 1.06 (t, J ) 7.5 Hz, 3H), 1.14-
1.23 (m, 9H), 1.99 (q, J ) 7.5 Hz, 2H), 2.13-2.23 (m, 2H), 2.31-
2.41 (m, 2H), 2.52 (q, J ) 7.5 Hz, 2H), 7.02-7.06 (m, 6H), 7.21-
7.24 (m, 2H); 13C NMR (CDCl3, SiMe4) δ 10.8, 12.5, 12.9, 18.4,
21.0, 21.7, 54.0, 65.1, 70.4, 119.1, 123.6, 125.4, 125.8, 141.8, 153.1.
HRMS calcd for C24H28 316.2191, found 316.2193.
only obtained in 46% yield. No formation of compound 7d was
observed. This result indicated product 7 did not come from
compound 3. Thus, the formation of product 7 was proposed
by the reaction of alkynes with benzyne2n,14 generated from Cp2-
ZrPh2.
In summary, a new and simple method for the preparation
of benzocyclobutadiene derivatives via zirconaindene derivatives
in the presence of CuCl and quinones has been developed, which
provides access to various dimers of benzocyclobutadiene.
Further investigation into the mechanism and the scope of the
reaction is in progress.
1,2,5,8 -Tetrapropyldibenzotricyclo[3.3.0.02,8]octa-3,6-diene (6b).
A white solid (isolated yield 100% from 4b). Mp 111-112 °C. 1H
NMR (CDCl3, SiMe4) δ 0.91 (t, J ) 7.5 Hz, 3H), 0.98-1.06 (m,
9H), 1.36-1.65 (m, 8H), 1.77-1.83 (m, 2H), 1.91-2.01 (m, 2H),
2.16-2.26 (m, 2H), 2.32-2.37 (m, 2H), 6.96-6.99 (m, 6H), 7.12-
7.15 (m, 2H); 13C NMR (CDCl3, SiMe4) δ 15.0, 15.1, 15.3, 19.8,
21.3, 21.5, 28.7, 31.2, 31.7, 53.2, 64.7, 69.9, 119.1, 123.6, 125.3,
125.8, 141.9, 153.1. HRMS calcd for C28H36 372.2817, found
372.2819.
Experimental Section
Typical Procedure for the Preparation of 5,6,6a,10b-Tetra-
ethyl-6a,10b-dihydrobenzo[a]biphenylene (4a). To a solution of
Cp2ZrCl2 (1.0 mmol, 0.292 g) in THF (5.0 mL) was added PhLi
(2.0 M in Bu2O, 2.00 mmol) at 0 °C and the mixture was stirred
for 1 h. To this solution of diphenylzirconocene in THF was added
3-hexyne (228 µL, 2.0 mmol). The reaction mixture was warmed
to room temperature and heated at 80 °C until the solution turned
red (about 24 h). After the solution was cooled to 0 °C, CuCl (0.200
g, 2.00 mmol) was added, and the reaction mixture was stirred for
5 min. Then 5.0 mL of THF followed by 1,4-naphthoquinone (1.2
mmol, 190 mg) was added to the suspension. The mixture was
stirred at room temperature for 12 h and quenched with 3 N HCl
and aqueous layers were extracted with 15 mL of Et2O five times.
The combined organic layers were dried over MgSO4. The solvent
was evaporated and the product was purified by column chroma-
tography with petroleum ether as eluant to afford a colorless liquid
1,2,5,8 -Tetrabutyldibenzotricyclo[3.3.0.02,8]octa-3,6-diene (6c).
A white fatty liquid (isolated yield 100% from 4c). 1H NMR
(CDCl3, SiMe4) δ 0.94 (t, J ) 7.5 Hz, 3H), 1.00-1.05 (m, 9H),
1.32-1.39 (m, 4H), 1.44-1.67 (m, 12H), 1.84-1.89 (m, 2H),
1.98-2.06 (m, 2H), 2.22-2.32 (m, 2H), 2.39-2.44 (m, 2H), 7.00-
7.04 (m, 6H), 7.17-7.20 (m, 2H); 13C NMR (CDCl3, SiMe4) δ
14.11 (4C), 23.7, 23.8, 24.0, 26.0, 28.6, 29.0, 30.2, 30.4, 53.0, 64.7,
69.6, 119.1, 123.6, 125.3, 125.8, 142.0, 153.1. HRMS calcd for
C32H44 428.3443, found 428.3444.
1
5,6,11,12-Tetraphenyldibenzo[a,e]cyclooctene (8d).15 A yellow
4a, 98 mg (isolated yield 62%). H NMR (CDCl3, SiMe4) δ 0.93
1
(t, J ) 7.5 Hz, 3H), 1.04 (t, J ) 7.5 Hz, 3H), 1.19-1.28 (m, 6H),
2.13-2.32 (m, 3H), 2.44-2.72 (m, 5H), 7.10-7.14 (m, 1H), 7.18-
7.31 (m, 5H), 7.38-7.41 (m, 1H), 7.57-7.60 (m, 1H); 13C NMR
(CDCl3, SiMe4) δ 11.3, 11.5, 14.2, 15.0, 21.5, 23.7, 25.6, 30.1,
55.8, 59.3, 120.0, 120.6, 123.7, 126.0, 126.2, 126.3, 127.1, 127.5,
131.1, 132.9, 138.3, 138.5, 150.3, 150.7. HRMS calcd for C24H28
316.2191, found 316.2193.
solid (41 mg, isolated yield 16%). Mp 186-190 °C. H NMR
(CDCl3, SiMe4) δ 6.77-6.97 (m, 4H), 7.06-7.10 (m, 20H), 7.16-
7.36 (m, 4H); 13C NMR (CDCl3, SiMe4) δ 126.7, 127.7, 127.9,
128.2, 130.5, 141.2(2C), 143.2. HRMS calcd for C40H28 508.2191,
found 508.2194.
5,6-Diethyl-11,12-diphenyldibenzo[a,e]cyclooctene (8e). Color-
less liquid (125 mg, isolated yield 61%). 1H NMR (CDCl3, SiMe4)
δ 0.95 (t, J ) 7.5 Hz, 6H), 2.42-2.50 (m, 4H), 2.80-2.87 (m,
4H), 7.10-7.19 (m, 10H), 7.29-7.32 (m, 8H); 13C NMR (CDCl3,
SiMe4) δ 13.89, 27.38, 125.85, 126.48, 126.57, 127.08, 127.72,
128.43, 131.06, 139.44, 140.888, 141.60, 143.24, 143.49. HRMS
calcd for C32H28 412.2191, found 412.2193.
5,6,6a,10b-Tetrapropyl-6a,10b-dihydrobenzo[a]biphenylene
(4b). A white fatty liquid (121 mg, isolated yield 65%). H NMR
1
(CDCl3, SiMe4) δ 0.90 (t, J ) 7.5 Hz, 3H), 0.94 (t, J ) 7.5 Hz,
3H), 1.00-1.09 (m, 6H), 1.15-1.39 (m, 4H), 1.45-1.62 (m, 4H),
1.88-2.16 (m, 3H), 2.27-2.56 (m, 5H), 7.05-7.29 (m, 7H), 7.51-
7.54 (m, 1H); 13C NMR (CDCl3, SiMe4) δ 14.4, 14.6, 14.8, 15.3,
19.9, 20.1, 22.67, 23.7, 30.9, 33.9, 356.0, 40.2, 55.5, 59.0, 120.0,
120.4, 123.7, 125.9, 126.1, 126.2, 127.1, 127.5, 129.3, 133.0, 138.0,
138.9, 150.3, 150.8. HRMS calcd for C28H36 372.2817, found
372.2816.
5,6,6a,10b-Tetrabutyl-6a,10b-dihydrobenzo[a]biphenylene (4c).
A colorless liquid (124 mg, isolated yield 58%). 1H NMR (CDCl3,
SiMe4) δ 0.81-0.99 (m, 12H), 1.15-1.33 (m, 8H), 1.43-1.54 (m,
8H), 1.90-2.17 (m, 3H), 2.27-2.54 (m, 5H), 7.00-7.19 (m, 6H),
7.23-7.26 (m, 1H), 7.46-7.49 (m, 1H); 13C NMR (CDCl3, SiMe4)
δ 13.91, 13.96, 14.00, 14.1, 23.2, 23.4, 23.6, 23.9, 28.5, 28.7, 29.0,
31.2, 31.6, 32.5, 33.3, 37.8, 55.4, 58.9, 120.0, 120.5, 123.7, 125.9,
126.1, 126.2, 127.1, 127.5, 129.3, 133.1, 137.9, 138.8, 150.3, 150.8.
HRMS calcd for C32H44 428.3443, found 428.3442.
5,6-Dibutyl-11,12-diphenyldibenzo[a,e]cyclooctene (8f).3a
A
1
white crystal (147 mg, isolated yield 63%). Mp 109-111 °C. H
NMR (CDCl3, SiMe4) δ 0.77 (t, J ) 7.2 Hz, 6H), 1.20-1.29 (m,
4H), 2.36-2.47 (m, 4H), 2.74 (t, J ) 7.6 Hz, 4 H), 7.02-7.19 (m,
10H), 7.23-7.30 (m, 8H); 13C NMR (CDCl3, SiMe4) δ 13.89, 23.28,
31.56, 34.55, 125.70, 126.42, 126.63, 127.11, 127.72, 128.52,
131.12, 138.53, 140.80, 141.52, 143.41, 143.50. HRMS calcd for
C36H36 468.2817, found 468.2815.
9,10-Diethylphenanthrene (7a).10 A white solid (28 mg, isolated
yield 12%). Mp 104-106 °C. 1H NMR (CDCl3, SiMe4) δ 1.38 (t,
J ) 7.5 Hz, 6H), 3.18 (t, J ) 7.5 Hz, 4H), 7.56-7.62 (m, 4 H),
8.06-8.13 (m, 2 H), 8.69-8.72 (m, 2H); 13C NMR (CDCl3, SiMe4)
δ 15.2, 22.3, 123.1, 124.8, 125.6, 126.8, 130.0, 131.2, 135.0. HRMS
calcd for C18H18, 234.1409, found. 234.1411.
Typical Procedure for the Preparation of 1,2,5,8-Tetra-
9,10-Dipropylphenanthrene (7b).10 A white solid (37 mg,
ethyldibenzotricyclo[3.3.0.02,8]octa-3,6-diene (6a). A solution of
1
isolated yield 14%). Mp 94-95 °C. H NMR (CDCl3, SiMe4) δ
1.20 (t, J ) 7.5 Hz, 6H), 1.78 (m, 4H), 3.18 (t, J ) 8.4 Hz, 4H),
(14) Selected papers for phenanthrenes formed from one alkyne and two
benzynes: (a) Pena, D.; Escudero, S.; Perez, D.; Guitian, E.; Castedo, L.
Angew. Chem., Int. Ed. 1998, 37, 2659. (b) Pena, D.; Perez, D.; Guitian,
E.; Castedo, L. Org. Lett. 1999, 1, 1555. (c) Pena, D.; Perez, D.; Guitian,
E.; Castedo, L. J. Am. Chem. Soc. 1999, 121, 5827. (d) Radhakrishnan, K.
V.; Yoshikawa, E.; Yamamoto, Y. Tetrahedron Lett. 1999, 40, 7533. (e)
Yoshikawa, E.; Radhakrishnan, K. V.; Yamamoto, Y. J. Am. Chem. Soc.
2000, 122, 7280.
7.62-7.65 (m, 4 H), 8.13-8.16 (m, 2 H), 8.74-8.77 (m, 2H); 13
C
NMR (CDCl3, SiMe4) δ 14.8, 24.0, 31.5, 122.9, 124.7, 125.3, 126.5,
129.8, 131.3, 133.8. HRMS calcd for C20H22 262.1722, found
262.1725.
(15) Holland, J. M.; Jones, D. W. J. Chem. Soc. C 1971, 608.
J. Org. Chem, Vol. 71, No. 14, 2006 5375