3-Trimethylsilyl-bromobenzene:
A mixture of 1,3-dibromobenzene (25.0 g, 106.4 mmol) and
trimethylsilylchloride (11.6 g, 106.4 mmol) in diethyl ether (50 ml) was added
dropwise in 1.5 hours on magnesium (2.59 g, 106.4 mmol) in diethyl ether
(25 ml). Then the mixture was refluxed for 18 hours, cooled to 0°C, treated
with 4 N HCl (75 ml). The organic layer was separated, washed with water,
brine, dried over MgSO 4 and concentrated. 3-Trimethylsilylbromobenzene was
obtained by fractional distillation as a colorless oil (13.4 g, 55% yield, b.p.:
55-62°C/0.8 mmHg.
2,2,2-Trifluoro-1-(3-trimethylsilylphenyl)ethanone:
To a solution of 3-trimethylsilylbromobenzene (7.62 g, 33.3 mmol) in diethyl
ether (35 ml) was added 1.5 M n-butyl lithium in hexane (22.2 ml, 33.3
mmol) at 0°C over 10 min. Then the mixture was allowed to react 15 min at
room temperature, cooled to -78°C and ethyl trifluoroacetate (14.2 g, 100
mmol) was added over 5 min. Then the mixture was allowed to react 15 min
at -78°C, the cooling bath was removed and when the temperature rose to
0°C. 3 N HCl (35 ml) was added dropwise. The organic layer was separated,
washed with water, brine, dried over MgSO 4 and concentrated.
Chromatography (silica gel, cyclohexane/diethyl ether: 90/10) followed by
distillation under reduced pressure afforded the expected compound
(zifrosilone) as a colorless oil (4.32 g, 53% yield), boiling point 120°C/0.8 mm
Hg; Rf: 0.28 (cyclohexane/diethyl ether: 95/5).
