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G. Hilt et al.
PRACTICAL SYNTHETIC PROCEDURES
and fractionally distilled with a 10 cm Vigreux column. The regio-
isomeric product mixture (regioisomeric ratio, 1:2 = 78:22) was ob-
tained as a colorless liquid (33.8 g, 222 mmol, 88%); bp 62–64 °C
at 40 mbar.
HRMS: m/z calcd for C13H18: 174.1409; found: 174.1408.
[(5-Bis(methoxymethyl)-1,4-cyclohexadien-1-yl)oxy]trimethyl-
silane (6); Typical Procedure
In a sealed tube CoBr2(dppe) (535 mg, 0.867 mmol, 2.2 mol%),
ZnI2 (1.40 g, 4.39 mmol, 11.0 mol%) and zinc powder (170 mg,
2.60 mmol, 6.5 mol%) were brought to reaction with 2-trimethyl-
silyloxy-1,3-butadiene (6.13 g, 48.5 mmol, 1.2 equiv) and 1,4-
dimethoxy-2-butyne (4.63 g, 40.1 mmol) in anhyd CH2Cl2 (15 mL)
under N2 atmosphere. After stirring 1 h at r.t. the color changed to
deep brown and a very exothermic reaction occurred. The mixture
was stirred at r.t. overnight. The mixture was then filtrated through
a pad of silica (Et2O, 200 mL) and the product (9.44 g, 39.3 mmol,
97%) was obtained as an off-white liquid in good purity after re-
moval of the solvent.
IR (KBr): 3079 (m), 2959 (s), 2932 (s), 2873 (s), 1644 (m), 1466 (s),
1379 (s), 1363 (s), 890 (m), 816 (w) cm–1.
1H NMR (300 MHz, CDCl3): d = 5.22–5.14 (m, 1 H, C=CH), 4.70
(br s, 2 H, C=CH2), 2.69 (d, J = 7.3 Hz, 2 H, C=CHCH2), 2.01 (t,
J = 7.4 Hz, 2 H, C=CCH2), 1.73 (br s, 3 H, CH3), 1.62 (br s, 3 H,
CH3), 1.45–1.28 (m, 4 H, CH2), 0.91 (t, J = 7.1 Hz, 3 H, CH2CH3).
13C NMR (75 MHz, CDCl3): d = 149.7, 132.9, 122.3, 108.8, 36.1,
35.1, 30.2, 25.9, 22.7, 17.8, 14.2.
MS (EI): m/z (%) = 152 (13) [M+], 109 (31), 95 (100).
HRMS: m/z calcd for C11H20: 152.1565; found: 152.1571.
IR (KBr): 2959 (s), 2926 (s), 2894 (s), 2820 (s), 1700 (m), 1669 (m),
1253 (s), 1086 (s), 846 (s) cm–1.
1H NMR (300 MHz, C6D6): d = 4.85–4.79 (m, 1 H, C=CH), 3.73 (br
s, 4 H, 2 × OCH2), 2.98 (s, 3 H, OCH3), 2.97 (s, 3 H, OCH3), 2.93–
2.85 (m, 4 H, 2 × CH2), 0.08 (s, 9 H, 3 × SiCH3).
13C NMR (75 MHz, CDCl3): d = 147.8, 129.62, 129.55, 99.8, 70.8,
70.7, 57.14, 57.10, 33.4, 30.1, 0.0.
1,4-Hydrovinylation of Isoprene with Activated Alkenes: Butyl
(2E)-6-Methyl-2,5-heptadienoate (3) and Butyl (2E,5Z)-5-Meth-
yl-2,5-heptadienoate (4); General Procedure
A 100 mL Schlenk-flask was charged with anhyd ZnI2 (2.62 g, 8.21
mmol, 5.2 mol%), CoBr2(dppe) (1.00 g, 1.62 mmol, 1.0 mol%) and
zinc powder (440 mg, 6.73 mmol, 4.3 mol%) under N2 atmosphere.
The materials were suspended in anhyd CH2Cl2 (20 mL) and iso-
prene (15.0 g, 220 mmol, 1.4 equiv) and butyl acrylate (20.2 g, 158
mmol) were added and the mixture was stirred at r.t. overnight. The
mixture was then fractionally distilled and the regioisomeric prod-
uct mixture (regioisomeric ratio 3:4 = 10:90) was obtained as a col-
orless liquid (27.9 g, 142 mmol, 90%); bp 57 °C at 0.1 mbar.
MS (ESI): m/z (%) = 257 (3) [M + H]+, 279 (86) [M + Na]+.
HRMS (ESI): m/z [M + Na] calcd for C13H24O3NaSi: 279.1392;
found, 279.1382.
HRMS (ESI): m/z [M + H] calcd for C13H25O3Si: 257.1573; found:
257.1605.
IR (KBr): 2961 (s), 2874 (s), 1723 (s), 1651 (s), 982 (s), 816 (s)
cm–1.
Trimethyl{1,4,5-metheno-3-[(trimethylsilyl)ethynyl]-
1,3a,4,5,6,6a-hexahydro-2-pentalenyl}silane (7) ; Typical Pro-
cedure
1H NMR (500 MHz, CDCl3): d = 6.85 (dt, J = 15.6, 6.7 Hz, 1 H,
MeO2CCH=CH), 5.77 (d, J = 15.6 Hz, 1 H, MeO2CCH=CH), 5.32
(q, J = 6.6 Hz, 1 H, C=CHCH3), 4.08 (t, J = 6.8 Hz, 2 H, OCH2),
2.85 (d, J = 6.6 Hz, 2 H, C=CHCH2), 1.63 (s, 3 H, C=CCH3), 1.62–
1.55 (m, 2 H, CH2), 1.52 (d, J = 6.6 Hz, 3 H, C=CHCH3), 1.35 (hex,
J = 7.5 Hz, 2 H, CH2CH3), 0.89 (t, J = 7.5 Hz, 3 H, CH2CH3).
13C NMR (75 MHz, CDCl3): d = 166.8, 146.1, 131.7, 121.72,
121.67, 64.1, 34.5, 30.8, 23.5, 19.2, 13.7, 13.3.
MS (EI): m/z (%) = 95 (100), 123 (22), 140 (15), 196 (2) [M+].
A 100 mL Schlenk-flask was charged with CoBr2(dppe) (406 mg,
0.658 mmol, 2.6 mol%), anhyd ZnI2 (1.00 g, 3.13 mmol, 12.1
mol%) and zinc powder (170 m 2.29 mmol, 8.9 mol%) under N2 at-
mosphere. Then norbornadiene (2.75 g, 29.9 mmol, 1.2 equiv) and
1,4-bistrimethylsilyl-1,3-butadiyne (5.01 g, 25.8 mmol) and anhyd
CH2Cl2 (10 mL) were added. After stirring 30 min at r.t. the color
changed to deep brown and an exothermic reaction was observed
and the mixture was stirred at r.t. overnight. The mixture was then
filtrated through a pad of silica (pentane–Et2O = 5:1, 500 mL). The
product was purified by column chromatography with pentane as
eluent to obtain the desired product in 96% yield (7.11 g, 24.8
mmol; Rf 0.70) as a colorless liquid.7
HRMS: m/z calcd for C12H20O2: 196.1463; found: 196.1452.
Cobalt(I)-Catalyzed Diels–Alder Reactions: 1-(1-Cyclohexen-1-
yl)-4-methyl-1,4-cyclohexadiene (5); Typical Procedure
In a sealed tube CoBr2(dppe) (300 mg, 0.486 mmol, 1.0 mol%), an-
hyd ZnI2 (950 mg, 2.98 mmol, 6.4 mol%) and zinc powder (100 mg,
1.53 mmol, 3.2 mol%) were brought to reaction with isoprene (5.11
g, 75.0 mmol, 1.6 equiv) and 1-ethynyl-1-cyclohexene (4.98 g, 46.9
mmol) in anhyd CH2Cl2 (10 mL) under N2 atmosphere. After stir-
ring for 1 h at r.t. the color changed to deep brown and a very exo-
thermic reaction was observed. The mixture was stirred at r.t.
overnight. The mixture was then filtrated through a pad of silica
(eluent: pentane–Et2O = 20:1; 200 mL) and the product (7.89 g,
45.3 mmol, 96%) was obtained as an off-white solid in good purity
after removal of the solvent.
2-(2-Isopropenyl-5-methyl-1,4-cyclohexadien-1-yl)-4,4,5,5-
tetramethyl-1,3,2-dioxaborolane (9); Typical Procedure
A 100 mL Schlenk-flask was charged with Co(dppe)Br2 (802 mg,
1.29 mmol, 5.0 mol%), Zn dust (255 mg, 3.9 mmol, 15.0 mol%) and
anhyd ZnI2 (1.40 g, 4.38 mmol, 16.8 mol%) under N2 atmosphere.
Then CH2Cl2 (50 mL), the alkynyl boronic ester (5.0 g, 26.0 mmol)
and isoprene (3.6 mL, 36 mmol, 1.4 equiv) were added and the mix-
ture was stirred at r.t. for 3 h. Then the volatiles were removed and
the residue was taken up in Et2O (10 mL), filtered over a small plug
of silica gel (Et2O–pentane, 1:1) and the solvents were removed in
vacuo. The product was purified by column chromatography with
methyl t-butyl ether–pentane (1:99) as eluent to obtain the desired
product in 90% yield (6.11 g, 23.5 mmol; Rf 0.40) as a yellowish oil
(regioisomeric ratio > 95:5).
IR (KBr): 3042 (m), 3022 (m), 2925 (s), 1622 (w), 1445 (s), 820
(w), 798 (w), 774 (m) cm–1.
1H NMR (300 MHz, C6D6): d = 5.79–5.66 (m, 2 H, 2 × C=CH),
5.54–5.44 (m, 1 H, C=CH), 2.93–2.81 (m, 2 H, C=CCH2C=C),
2.67–2.54 (m, 2 H, C=CCH2C=C), 2.25–2.15 (m, 2 H, C=CCH2),
2.12–1.98 (m, 2 H, C=CCH2), 1.73–1.39 (m, 7 H, 2 × CH2, CH3).
13C NMR (75 MHz, C6D6): d = 136.3, 134.3, 130.3, 122.2, 119.7,
118.6, 32.2, 27.8, 26.2, 25.9, 23.5, 23.1, 22.9.
MS (EI): m/z (%) = 91 (92), 131 (75), 159 (47), 174 (100) [M+].
IR (KBr): 2977 (s), 1626 (m), 1298 (s), 1146 (s), 1017 (m) cm–1.
1H NMR (300 MHz, CDCl3): d = 1.20 (s, 12 H, 4 × CH3), 1.62 (s, 3
H, CH3), 1.82 (s, 3 H, CH3), 2.57–2.78 (m, 4 H, 2 × CH2), 4.67–4.71
(m, 1 H, CHH), 4.72–4.77 (m, 1 H, CHH), 5.33–5.38 (m, 1 H, CH).
13C NMR (75 MHz, CDCl3): d = 21.6, 22.8, 24.5, 30.7, 33.6, 82.8,
111.8, 117.8, 130.9, 147.8, 148.7.
Synthesis 2003, No. 4, 634–638 © Thieme Stuttgart · New York