PAPER
Preparation of 1-Bromo-1-chloro-, 1,1-Dibromo- or 1,1-Dichloroalk-1-enes from Ketones
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mmol) at 30°C. After 5 min an exothermic reaction was observed
and the solution became dark. The mixture was stirred at 30°C until
TLC showed the absence of starting material (4 to 24 h). A large
part of isopropenyl acetate was evaporated under vacuum, then
Et2O (30 mL) was added and under stirring at 0°C aq satd Na2CO3
solution (~40 mL) was added slowly until no more gas evolution
was observed . After 30 min at r.t., the aqueous layer was extracted
with Et2O (3 î 30 mL). The organic layers were washed with aq
satd NaHCO3 solution (15 mL) and dried (MgSO4). The residue was
purified by filtration on silica gel using petroleum ether/Et2O/
CH2Cl2 (90:5:5).
(2 î 20 mL). The combined organic layers were washed with aq
satd NaHCO3 solution (15 mL). The organic layer was dried
(MgSO4) and concentrated in vacuo to provide the crude product
which was purified by flash chromatography on silica gel using pe-
troleum ether to give the alkenes 3.
(Bromochloromethylene)cyclohexane (3a)
Yield: 390 mg (93%); colourless oil.
1H NMR (400 MHz, CDCl3): d = 1.79 (m, 6 H), 2.58-2.63 (m, 4 H).
13C NMR (50 MHz, CDCl3): d = 25.95, 26.82, 26.92, 32.04, 34.61,
97.54, 141.67.
IR (neat): n = 2970, 2875, 1450, 1230, 790 cm-1.
1-(Dibromochloromethyl)-1-acetoxycyclohexane (2a)
Yield: 1.65 g (96%); colourless crystals; mp 56-57°C.
Anal. Calcd for C7H10BrCl (209.5): C, 40.13; H, 4.81. Found: C,
40.17; H, 4.77.
1H NMR (400 MHz, CDCl3): d = 1.19-1.27 (m, 2 H), 1.44-1.99
(m, 8 H), 2.14 (s, 3 H), 1.13-2.18 (m, 2 H), 2.84 (d, 1 H, J = 1.2
Hz), 2.87 (s, 1 H).
(Dibromomethylene)cyclooctane (3b)
Yield: 536 mg (95%); colourless oil.
13C NMR (100 MHz, CDCl3): d = 22.81, 22.97, 24.48, 31.54, 75.11,
1H NMR (400 MHz, CDCl3): d = 1.45-1.54 (m, 6 H), 1.73-1.78
(m, 4 H), 2.39-2.42 (m, 4 H).
13C NMR (50 MHz, CDCl3): d = 25.29, 25.70, 27.50, 35.56, 84.47,
147.10.
91.92, 169.17.
IR (neat): n = 2950, 2880, 1750, 1450, 1205, 1020 cm-1.
1-(Tribromomethyl)-1-acetoxycyclooctane (2b)
Yield: 2.1 g (~100%); yellow oil.
1,1-Dibromo-2-propylpent-1-ene (3c)
1H NMR (400 MHz, CDCl3): d = 1.55-1.95 (m, 10 H), 2.12 (s, 3
H), 2.28-2.34 (m, 2 H), 2.96-3.03 (m, 2 H).
13C NMR (100 MHz, CDCl3): d = 22.58, 23.02, 23.62, 27.68, 31.13,
57.77, 93.30, 168.78.
Yield: 502 mg (93%); colourless oil.
1H NMR (400 MHz, CDCl3) d = 0.94 (t, 6 H, J = 7.3 Hz), 1.48 (sext,
4 H, J = 7.6 Hz), 2.22 (t, 4 H, J = 7.6 Hz).
13C NMR (100 MHz, CDCl3): d = 14.06, 20.67, 38.20, 85.66,
143.31.
IR (neat): n = 2940, 2875, 1750, 1470, 1440, 1360, 1210, 1025 cm-1.
IR (neat): n = 2980, 2875, 1470, 810 cm-1.
4-(Tribromomethyl)-4-acetoxyheptane (2c)
Yield: 1.94 g (95%); yellow oil.
Anal. Calcd for C8H14Br2 (270.0) : C, 35.59; H, 5.23. Found: C,
35.73; H, 5.31.
1H NMR (400 MHz, CDCl3): d = 0.96 (t, 6 H, J = 7.2 Hz), 1.52-
1.73 (m, 4 H), 2.12 (s, 3 H), 2.24-2.32 (m, 2 H), 2.43-2.51 (m, 2
1-Bromo-1-chloro-2-pentylhept-1-ene (3d)
Yield: 507 mg (90%); colourless oil.
H).
13C NMR (100 MHz, CDCl3): d = 14.81, 19.23, 22.59, 38.46, 55.71,
92.11, 168.71.
1H NMR (400 MHz, CDCl3): d = 0.88 (t, 6 H, J = 7.0 Hz), 1.28-
1.45 (m, 12 H), 2.18-2.26 (m, 4 H).
13C NMR (50 MHz, CDCl3): d = 14.20, 22.66, 27.08, 31.82, 33.78,
36.13, 100.99, 143.52.
6-(Dibromochloromethyl)-6-acetoxyundecane (2d)
Yield: 1.89 g (90%); yellow oil.
1H NMR (400 MHz, CDCl3): d = 0.89 (t, 6 H, J = 6.8 Hz), 1.25-
1,1-Dibromo-2-phenylbut-1-ene (3e)5
Yield: 430 mg (75%); colourless oil.
1H NMR (200 MHz, CDCl3): d = 0.98 (t, 3 H, J = 7.5 Hz), 2.65 (q,
2 H, J = 7.5 Hz), 7.18 (m, 2 H), 7.32-7.35 (m, 3 H).
13C NMR (50 MHz, CDCl3): d = 11.47, 32.85, 87.65, 127.64,
127.95, 128.36, 140.85, 148.92.
1.55 (m, 12 H), 2.12 (s, 3 H), 2.29-2.34 (m, 2 H), 2.41-2.51 (m, 2
H).
13C NMR (100 MHz, CDCl3): d = 14.14, 22.51, 22.59, 25.24, 36.04,
74.46, 92.76, 168.82.
IR (neat): n = 2980, 2885, 1750, 1465, 1230, 1010, 735 cm-1.
1,1,1-Tribromo-2-phenyl-2-acetoxybutane (2e)
Yield: 1.71 g (80%); colourless oil.
1,1-Dichloroalkenes 6 and 7; General Procedure
A 100 mL two-necked round bottom flask equipped with magnetic
stirrer and a condenser, under N2, was charged with a solution of ke-
tone 4 or 5 (10 mmol) in THF (30 mL). Ph3P (40 mmol, 10.5 g) was
added and the mixture was brought to reflux. CCl4 (25 mL, 240
mmol) was added dropwise in 2 h (the solution turned dark). When
TLC (2-3 h) showed the absence of starting material, the mixture
was cooled to 0°C and hydrolysed with H2O (30 mL). The aqueous
layer was extracted with Et2O (3 î 30 mL) the combined organic
layers were washed with aq satd NaHCO3 solution (20 mL), and
then with brine (20 mL). The organic layer was dried (MgSO4) and
concentrated in vacuo to provide a solid mixture of product and
Ph3PO. The solid was washed several times with pentane and fil-
tered. After the evaporation of pentane the crude product was puri-
fied by flash chromatography on silica gel using petroleum ether to
give the dichloroethylenes 6 or 7.
1H NMR (400 MHz, CDCl3): d = 1.18 (t, 3 H, J = 7.2 Hz), 2.31 (s,
3H), 2.92 (sext, 1 H, J = 7.6 Hz), 3.24 (sext, 1 H, J = 7.6 Hz), 7.34
(m, 3 H), 7.61 (m, 2 H).
13C NMR (100 MHz, CDCl3): d = 11.17, 22.31, 28.47, 55.36, 91.75,
126.99, 128.67, 129.79, 136.52, 168.03.
IR (neat): n = 3180, 2970, 1760, 1495, 1445, 1370, 1220, 1020, 710
cm-1.
1,1-Dihalo-2,2-dialkylethylenes 3; General Procedure
A 100 mL four-necked round bottom flask equipped with mechan-
ical stirrer was charged with a solution of ethylmagnesium bromide
[1.2 M in THF] (6.7 mL, 8 mmol) in THF (10 mL). To this solution
at -95°C was added dropwise a THF solution of the acetate 2 (2
mmol). The mixture was then stirred at -90°C for 30 min, cooled to
-100°C and hydrolysed with aq 1 M HCl (15 mL). The mixture was
then warmed to r.t. and the aqueous layer was extracted with Et2O
1,1-Dichloro-2-propylpent-1-ene (6)
Yield: 2.1g (88%); colourless oil.
Synthesis 2000, No. 1, 109–112 ISSN 0039-7881 © Thieme Stuttgart · New York