Notes
J . Org. Chem., Vol. 61, No. 23, 1996 8327
Ta ble 2. P r ep a r a tion of 1,2-Dior ga n ylcyclobu ten es via Cr oss-Cou p lin g Rea ction s of 1-Iod o- or 1-Meta lla cyclobu ten es
1,2-diorganylcyclobutene
R′
starting
cyclobutene
organometal or organic halide
catalyst
R
yielda (%)
5a
n-BuLi
none
Me
n-Bu
72
5a
5a
PhZnCl
Pd(PPh3)4
Pd(PPh3)4
Pd(PPh3)4
Pd(PPh3)4
Pd(PPh3)4
Pd(PPh3)4
Pd(PPh3)4
Pd(PPh3)4
Me
Me
Me
allyl
allyl
allyl
allyl
allyl
Ph
75
(E)-n-BuCHdCHAlBu2
n-HexCtCZnCl
(E)-n-BuCHdCHI
(E)-n-BuCHdCHI
PhZnCl
(E)-n-BuCHdCH
n-HexCtC
(E)-n-BuCHdCH
(E)-n-BuCHdCH
Ph
68 (78)
78 (81)
(95)
(62)
(86)
(75)
(68)
5a
4bb
4bc
5b
4bc
4bc
PhI
Ph
n-BuCtC
n-BuCtCZnCl
a
b
Isolated yield. The numbers in parentheses are NMR yields. Generated by treatment of 5b with t-BuLi (2 equiv) followed by addition
of ZnBr2. c Generated in situ via cyclialkylation.
mmol). After 1 h, a solution of 4-octyne (1.45 mL, 10 mmol) in
THF (1 mL) was added, and the mixture was stirred at 0 °C for
2 h.4 The reaction mixture was then cooled to -78 °C, treated
with a solution of I2 (7.62 g, 30 mmol) in THF (20 mL), gradually
warmed to 23 °C and stirred overnight, quenched with 3 N HCl,
extracted with Et2O (2×), washed with aqueous NaHCO3,
Na2S2O3, and NaCl, dried over MgSO4, filtered, and concentrated
in vacuo. Flash chromatography (hexanes) afforded 2.96 g (76%)
of the title compound (>97% Z) as a pale yellow oil: 1H NMR δ
0.90 (t, J ) 7 Hz, 6 H), 1.3-1.65 (m, 4 H), 2.18 (t, J ) 7 Hz, 2
H), 2.48 (t, J ) 7 Hz, 2 H), 2.78 (t, J ) 8 Hz, 2 H), 3.16 (t, J )
8 Hz, 2 H) ppm; 13C NMR δ 1.42, 12.86, 13.95, 21.94, 22.84,
33.80, 42.90, 46.81, 107.84, 143.11 ppm; IR (neat) 2956, 1460
at -78 °C was added n-BuLi (2.5 M in hexanes, 0.66 mL, 1.65
mmol) or t-BuLi (1.7 M in pentane, 1.73 mL, 2.94 mmol). After
45 min, the mixture was warmed to 23 °C, quenched with H2O,
washed with aqueous NH4Cl and NaCl, dried over MgSO4,
filtered, and concentrated. Flash chromatography (hexanes)
afforded 173 mg (87%) of the title compound as a colorless oil:
1H NMR δ 0.89 (t, J ) 7.3 Hz, 6 H), 1.3-1.5 (m, 4 H), 1.96 (t, J
) 7.4 Hz, 4 H), 2.24 (s, 4 H) ppm; 13C NMR δ 14.14, 20.93, 27.51,
30.59, 140.59 ppm; IR (neat) 2958, 1458 cm-1; MS (EI, 70 eV)
m/z (relative intensity) 138 (M+, 100), 123 (8), 109 (60), 95 (59),
81 (72), 67 (62); HRMS calcd for
138.1404.
C10H18 138.1409, found
(E)-2-Meth yl-1,5-d od eca d ien e. To a mixture of 4-iodo-2-
methyl-1-butene (231 mg, 1.18 mmol) and (E)-1-iodo-1-octene
(281 mg, 1.18 mmol) in THF (3 mL) at -78 °C was added t-BuLi
(1.7 M in pentane, 1.4 mL, 2.38 mmol). After 5 h, the reaction
mixture was warmed to 23 °C, stirred for 18 h, quenched with
H2O and 3 N HCl, and dried over Na2SO4. NMR analysis of
the reaction mixture indicated the formation of 1-octene23 (74%),
2-methyl-1,3-butadiene23 (37%), and the title compound (8%),
the identity of which was confirmed by coinjection with an
authentic sample prepared by the Pd-catalyzed cross-coupling
reaction of (E)-1-iodo-1-octene with 3-methyl-3-butenylzinc bro-
mide, which, in turn, was prepared by treatment of 3-methyl-
3-butenyllithium with dry ZnBr2.19 The title compound yielded
the following spectral data: 1H NMR δ 0.88 (t, J ) 7.5 Hz, 3 H),
1.1-1.5 (m, 8 H), 1.71 (s, 3 H), 1.85-2.3 (m, 6 H), 4.65-4.8 (m,
2 H), 5.3-5.5 (m, 2 H) ppm; 13C NMR δ 14.08, 22.46, 22.64,
29.33, 29.56, 30.79, 31.75, 32.57, 37.85, 109.81, 129.57, 130.68,
cm-1
.
(b) (Z)-1,4-Diiod o-3-octen e (1j). To a mixture of (Z)-4-iodo-
3-octen-1-ol (vide infra) (1.12 g, 4.4 mmol), Ph3P (1.50 g, 5.7
mmol), and imidazole (389 mg, 5.7 mmol) in CH2Cl2 (10 mL) at
23 °C was added a solution of I2 (1.45 g, 5.7 mmol) in CH2Cl2
(20 mL).18 After 30 min, the mixture was washed with H2O,
aqueous NH4Cl, and NaCl, dried over MgSO4, filtered, and
concentrated in vacuo. Flash chromatography (hexanes) af-
forded 1.28 g (80%) of the title compound as a light pink oil: 1H
NMR δ 0.91 (t, J ) 7.3 Hz, 3 H), 1.2-1.4 (m, 2 H), 1.4-1.6 (m,
2 H), 2.48 (q, J ) 7.1 Hz, 2 H), 2.71 (q, J ) 6.9 Hz, 2 H), 3.16 (t,
J ) 7.1 Hz, 2 H), 5.55 (t, J ) 6.5 Hz, 1 H) ppm; 13C NMR δ 3.32,
13.84, 21.27, 31.30, 39.95, 44.90, 112.34, 133.03 ppm; IR (neat)
2956, 1170 cm-1. The required starting material (Z)-4-iodo-3-
octen-1-ol was prepared in 27% isolated yield (>97% Z) as a light
brown oil by treatment of 2,3-dihydrofuran (freshly distilled, 2.68
g, 38 mmol) in Et2O (60 mL) at 0 °C with n-BuLi (2.5 M in
hexanes, 32 mL, 80 mmol)6 followed by a solution of I2 (20.3 g,
80 mmol) in THF (50 mL) in -78 °C: 1H NMR δ 0.90 (t, J ) 7.3
Hz, 3 H), 1.2-1.7 (m, 5 H), 2.40 (q, J ) 6.6 Hz, 2 H), 2.48 (t, J
) 7.3 Hz, 2 H), 3.70 (t, J ) 6.5 Hz, 2 H), 5.57 (t, J ) 6.7 Hz, 1
H) ppm; 13C NMR δ 13.84, 21.31, 31.46, 39.76, 45.04, 61.38,
145.61 ppm; IR (neat) 2958, 1458 cm-1
.
1-Iod o-2-m eth ylcyclobu ten e (4a ).1b To 4-bromo-1-butyne
(1.33 g, 10.0 mmol) in pentane (20 mL) was added successively
n-BuLi (2.7 M in hexane, 3.7 mL, 10.0 mmol, -78 °C, 30 min),
Me2AlCl (0.96 mL, 10.0 mmol in CH2Cl2 (5 mL), -78 °C, 30 min),
Cp2ZrCl2 (2.92 g, 10.0 mmol), and Me3Al (1.9 mL, 20 mmol) in
CH2Cl2 (20 mL) (-78 °C). The reaction mixture was warmed
to 23 °C and stirred for 3 h. The reaction mixture was treated
at -78 °C with a solution of I2 (3.81 g, 15.0 mmol) in THF (10
mL), warmed to 0 °C, quenched with a mixture of ice and 3 N
HCl, extracted with ether, washed with aqueous NaHCO3,
Na2S2O3, and NaCl, dried over MgSO4, filtered, and concen-
trated. Distillation over a pinch of 2,6-di-tert-butyl-4-methyl-
phenol afforded 1.1 g (57%) of the title compound as a colorless
112.39, 130.62 ppm; IR (neat) 3334, 2930 cm-1
.
(c) (Z)-1,4-Diiod o-2-m eth yl-1-bu ten e (1k ) a n d Its E Iso-
m er . The Z isomer was prepared from (Z)-4-iodo-3-methyl-3-
buten-1-ol in the same manner as that of (Z)-1,4-diiodo-3-octene
in 62% isolated yield as a colorless oil: 1H NMR δ 1.92 (d, J )
1.3 Hz, 3 H), 2.81 (t, J ) 7.8 Hz, 2 H), 3.21 (t, J ) 7.8 Hz, 2 H),
6.06 (d, J ) 1.1 Hz, 1 H); 13C NMR δ 0.40, 23.06, 42.54, 77.14,
145.81 ppm; IR (neat) 3052, 2966, 1434 cm-1
. (Z)-4-Iodo-3-
1
oil (>97% pure by GLC): bp 78-81 °C (45 mmHg); H NMR δ
methyl-3-buten-1-ol was, in turn, obtained in 57% isolated yield
1.63 (br s, 3 H), 2.72 (br s, 4 H) ppm; 13C NMR δ 16.27, 35.81,
(>97% Z) as a pale yellow oil from the reaction of 3-butyn-1-ol
36.25, 82.71, 154.07 ppm; IR (neat) 1640, 1239 cm-1
. The
19
with Me3Al (3 equiv) and Cp2ZrCl2 (30 mol %) in (CH2Cl)2
required starting compound 4-bromo-1-butyne was prepared by
converting 3-butyn-1-ol to its tosylate via lithiation (1.1 equiv
of n-BuLi) and treatment with p-TsCl followed by bromination
with LiBr in acetone in 72% yield: bp 47-49 °C (91 mmHg); 1H
NMR δ 2.11 (t, J ) 3 Hz, 1 H), 2.75 (dt, J ) 7, 3 Hz, 2 H), 3.45
followed by refluxing for 5 d and treatment with I2 (1.5 equiv)
in THF:20 1H NMR δ 1.54 (br s, 1 H), 1.94 (d, J ) 1.4 Hz, 3 H),
2.52 (t, J ) 6.8 Hz, 2 H), 3.76 (t, J ) 6.8 Hz, 2 H), 5.95-6.05 (m,
1 H) ppm; 13C NMR δ 23.86, 41.64, 60.27, 76.42, 144.38 ppm;
IR (neat) 3342, 3052, 1048 cm-1. (E)-4-Iodo-3-methyl-3-buten-
1-ol was prepared in 65% yield as previously reported.19 Its
conversion to (E)-1,4-diiodo-2-methyl-1-butene in 85% yield was
performed as described above: 1H NMR δ 1.84 (s, 3 H), 2.76
(t, J ) 7.5 Hz, 2 H), 3.22 (t, J ) 7.5 Hz, 2 H), 6.06 (d, J ) 1.0
Hz, 1 H); 13C NMR δ 2.29, 23.10, 43.22, 77.81, 145.85 ppm; IR
(t, J ) 7 Hz, 2 H) ppm; IR (neat) 3325, 2950, 1420, 960 cm-1
.
2-Allyl-1-cyclobu ten ylzin c Der iva tive (4b) a n d 1-Iod o-
2-a llylcyclobu ten e (5b). These compounds were prepared as
follows according to the previously reported method.1b To a
solution of 4-bromo-1-butyne (0.40 g, 3 mmol) in hexane (5 mL)
was added at -78 °C n-BuLi (2.64 M in heptane, 1.1 mL, 3
(neat) 3050, 1234 cm-1
.
P r ep a r a tion of Cyclobu ten es via Cyclia lk yla tion of 1,4-
Diiod o-1-bu ten es. 1,2-Di-n -p r op ylcyclobu ten e (2a ). Rep -
r esen ta tive P r oced u r e. To a solution of (Z)-1,4-diiodo-3-n-
propyl-3-heptene (563 mg, 1.44 mmol) in Et2O (8 mL, or THF)
(23) Pouchert, C. J .; Behnke, J . The Aldrich Library of C and H FT
NMR Spectra, 1st ed.; Aldrich Chemical Co., Inc.: Milwaukee, 1993;
Vol. 1.