Synthesis and Comparison of the Reactivity of Allyl Fluorides and ...

198
Chapter Six
6.5.21 Preparation of 2,2-difluoro-1-(perfluorophenyl)but-3-enyl 4-fluorobenzoate
(173)
The title compound was prepared using a method outlined
by Nakamura et al. [7] A 100 cm 3 , two-necked round-
bottomed flask was equipped with a magnetic stirring bar,
and Rotaflo tap and attached to a Schlenk line. After
flame-drying under high vacuum, the flask was cooled and
filled with nitrogen. The reaction flask was charged with
2,2-difluoro-1-(perfluorophenyl) but-3-en-1-ol (100 mg,
0.37 mmol) and pyridine (1.1 cm 3 ) and cooled to 0 ºC. 4-
Fluorobenzoyl chloride (0.043 cm 3 , x mmol) was added and the reaction mixture warmed to
room temperature and stirred for 2 h. After which the reaction was quenched with brine (6
cm 3 ) and diethyl ether (5 cm 3 ). The organic layer was then separated and washed with HCl
(1 cm 3 , 5 % aqueous solution), saturated brine (10 cm 3 ), saturated NaHCO3 (10 cm 3 ) and
saturated brine (10 cm 3 ) successively, then dried over magnesium sulphate. After removal
of solvent in vacuo the crude product was purified by column chromatography [chloroform:
hexane (50:50)], affording the product as a white solid (137 mg, 95 %). δH 5.62 (1H, d, 3 JHH
= 10.8 Hz, Hb), 5.82 (1H, dt, 3 JHH = 17.2 Hz, 4 JHF = 2.4 Hz, Ha), 6.05 (1H, ddt, 3 JHH = 17.2
Hz, 3 JHF = 12.3 Hz, 3 JHH = 10.8 Hz, Hc), 6.17 (1H, dd, 3 JHF = 14.6 Hz, 3 JHF = 7.9 Hz CHO),
7.16 (2H, tm, 3 JHH = 8.5 Hz, ArH-3), 8.10 (2H, ddm, 3 JHH = 8.8 Hz, 4 JHF = 5.3 Hz, ArH-2);
δC 68.2 (t, 2 JCF = 31.4 Hz, CHCF2), 116.0 (d, 2 JCF = 22.6 Hz, ArCH-3’), 117.6 (t, 1 JCF =
248.9 Hz, CF2), 123.1 (t, 3 JCF = 10.1 Hz, CHCH2), 124.5 (ArC-1’), 128.7 (t, 2 JCF = 25.2 Hz,
CHCH2), 132.8 (d, 3 JCF = 8.8 Hz, ArCH-2’), 163.6 (C=O), 166.4 (d, 1 JCF = 255.3 Hz,
ArCF), [quaternary pentafluoro C-F carbons not visible]. δF -103.2 (1F, s, CF), -105.1 (d,
2 JFF = 245.0 Hz, CF), -110.4 (d, 2 JFF = 251.4 Hz, CF), -138.6 (2F,dm 3 JFF = 21.5 Hz, ArF-2),
-151.2 (1F, t, 3 JFF = 21.5 Hz, ArF-2), -160.9 (2F, m, ArF-3). m/z (EI + ) 396 ([M] + , 25 %),
319 ([M-CF2CH=CH2] + , 75 %). HRMS (EI) 396.03947 (C17H8O2F8 requires 396.03946).