Y. Wei et al. / Journal of Fluorine Chemistry 127 (2006) 688–703
701
127.7 (tt, J = 272, 16.1 Hz, CF2, 1C), 100.3 (dt, J = 231,
17.9 Hz, bridgehead C, 1C), 95.2 (dtd, J = 229, 17.4, 3.1 Hz,
bridgehead C, 1C), 76.6 (ddd, J = 13.2, 5.5, 1.8 Hz, C5, 1C),
70.2 (s, OCH2, 1C), 38.3 (dd, J = 20.6, 4.6 Hz, C6, 1C), 31.9 (s,
CH2, 1C), 19.4 (s, CH2, 1C), 13.8 (s, CH3, 1C). IR (neat, cmꢁ1):
2961 (s), 2936 (s), 2875 (s), 1662(w), 1580 (w), 1448 (w), 1366
(s), 1334 (s), 1271, 1156 (s), 1121 (s), 1082, 1043, 995, 952 (s),
891. GC–MS (EI): m/z 238 (M+), 195, 182, 162, 145, 133, 114,
95, 57 (base). HRMS (EI): calcd for C11H13F4O (M ꢁ 1)+
237.0903, found 237.0897.
(neat, cmꢁ1): 2962 (s), 1688 (w), 1446 (w), 1412 (w), 1371 (w),
1335 (w), 1260 (s), 1094 (vs), 1024 (vs), 802 (vs), 701. GC–MS
(EI): m/z 276 (M+), 257, 238, 226, 207, 187, 176, 157, 138
(base, C5F4H2), 119, 88, 75, 59. HRMS (EI): calcd for C10H4F8
(M+) 276.0185, found 276.0182. 19F NMR of 1,4,7,7-
tetrafluoro-2,3-diazabicyclo[2.2.1]hept-5-ene-2,3-dicarboxylic
acid dimethyl ester (40) (CDCl3): d ꢁ137.7 (d, J = 172 Hz,
CF2, 1F), ꢁ148.7 (d, J = 172 Hz, CF2, 1F), ꢁ163.1 (s,
bridgehead Fs, 2F).
4.21. 1,4,7,7-Tetrafluoro-2,3-diazabicyclo[2.2.1]heptane-
2,3-dicarboxylic acid dimethyl ester (41)
4.19. 1,4,5,5-Tetrafluorocyclopentadiene (31)
Flash vacuum pyrolysis (60 mTorr, 8 mm ꢃ 1000 mm
quartz tube) at 600 8C of 0.45 g (1.9 mmol) of endo-5-
butoxy-1,4,7,7-tetrafluorobicyclo[2.2.1]hept-2-ene (36), eva-
porated from a 0 8C reservoir, gave 1,4,5,5-tetrafluorocyclo-
pentadiene (31) in a U-trap cooled to ꢁ196 8C. Acetone (3 mL)
was frozen at the incoming mouth of the U-trap before the
pyrolysis to prevent the dimerization of 31 upon thawing. A
complete conversion of 36 to 31 was obtained. 1,4,5,5-
Tetrafluorocyclopentadiene was allowed to react with dieno-
philes right after it was made. 1H NMR (CDCl3): d 5.51 (br s,
vinyl H, 2H). 19F NMR (CDCl3): d ꢁ141.2 (t, J = 10.8 Hz, 2F),
ꢁ141.6 (t, J = 10.8 Hz, 2F).
In a heavy-walled hydrogenation bottle were placed about
6 mg (0.02 mmol) of 40 in 4 mL of THF and 20 mg of 10% Pd
on carbon. The bottle was mounted on a Parr hydrogenation
apparatus, evacuated and flushed with H2 three times. The
suspension was agitated under 5 atm of H2 for 1d, resulting in
complete conversion to 41. 19F NMR (CDCl3): d ꢁ145.4 (d,
J = 196 Hz, CF2, 1F), ꢁ151.9 (d, J = 196, CF2, 1F). Bridgehead
Fs were not observed at RT because of conformational
interconversion. GC–MS (EI): m/z 286 (M+), 242, 222, 183,
161, 155, 130, 116, 88, 75, 59 (base).
4.22. 1,7,10,10-Tetrafluoro-4-thia-2,6-
diazatricyclo[5.2.1.02,6]dec-8-ene-3,5-dione (43)
4.20. 1,1,2,4,7,7a,8,8-Octafluoro-3a,4,7,7a-tetrahydro-1H-
4,7-methanoindene (37)
A 1,3,4-thiadiazole-2,5-dione (42) acetone solution was
prepared as follows. 1,3,4-Thiadiazolidine-2,5-dione [29]
(0.62 g, 5.2 mmol) was stirred with 0.62 mL (5.2 mmol) of
tert-butyl hypochlorite in 10 mL of acetone for 3 h at ꢁ78 8C in
a three-necked round-bottomed flask equipped with stir bar,
dropping funnel and connection to a nitrogen bubbler. 1,4,5,5-
Tetrafluorocyclopentadiene (31, 0.55 g, 4.0 mmol) in 4 mL of
acetone was added to the flask via the dropping funnel. After the
addition was complete, the reaction solution was allowed to
warm up slowly to RT. The solvent was removed by roto-
evaporation, and 0.98 g (3.9 mmol, 97%) of 43 was obtained as
This experiment was intended to yield the Diels–Alder
adduct 40 of 31 with dimethyl azodicarboxylate, but gave
predominantly instead the cyclopentadiene dimer 37. To a
20 mL pressure tube with a threaded Teflon stopper was added a
solution of 2.00 g (13.6 mmol) of dimethyl azodicarboxylate in
5 mL of benzene. The solution was exposed for 2 h to filtered
UV irradiation (filter plate Corning C.S. no. 0–53) from a
450 W Hanovia medium pressure mercury lamp. Then a
1,4,5,5-tetrafluorocyclopentadiene benzene solution which was
obtained from the complete pyrolysis of 0.15 g (0.62 mmol) of
endo-5-butoxy-1,4,7,7-tetrafluorobicyclo[2.2.1]hept-2-ene was
added. The tube was totally immersed in an oil bath heated to
100 8C and irradiation was continued for another 12 h. 19F
NMR showed that the cyclopentadiene dimer 37 and the Diels–
Alder adduct 40 were obtained in a ratio of 19:1. After the
solvent was roto-evaporated, the yellow product was treated
with 4 g activated basic alumina to decompose excess dimethyl
azodicarboxylate. The alumina/product mixture was placed on
a silica gel (30 g) column and eluted first with hexanes, yielding
1
an oil. H NMR (CDCl3): d 6.87 (dt, J = 4.0, 2.5 Hz, vinyl H,
1
2H). H NMR (CD3OD): d 7.12 (dt, J = 4.0, 2.5 Hz, vinyl H,
2H). 19F NMR (CDCl3): d ꢁ133.5 (d, J = 173 Hz, CF2, 1F),
ꢁ144.2 (d, J = 173 Hz, CF2, 1F), ꢁ174.1 (s, bridgehead F, 2F).
13C NMR (CD3OD, 19F decoupled): d 171.1 (s, CO, 2C), 131.2
1
(d, JCH = 191 Hz, vinyl C, 2C), 120.4 (s, CF2, 1C), 104.8 (t,
J = 6.4 Hz, bridgehead C, 2C). IR (neat, cmꢁ1): 2963, 1756,
1714 (s), 1361, 1234, 1187, 1118, 1087, 1027, 945, 786, 685,
677. GC–MS (EI): m/z 254 (M+), 194, 175, 152, 138 (base), 88,
60. HRMS (EI): calcd for C7H2F4N2O2S (M+) 253.9773, found
254.0004.
1,4,5,5-tetrafluorocyclopentadiene
dimer
(37,
78 mg,
0.28 mmol, 90%), and then with hexanes/CH2Cl2 (1:1),
yielding a small amount of adduct 40. 1H NMR of 37 (CDCl3):
d 6.40 (m, vinyl H, 1H), 6.22 (m, vinyl H, 1H), 5.65 (m, vinyl H,
1H), 3.69 (m, bridgehead H, 1H). 19F NMR (CDCl3): d ꢁ108.5
(d, J = 277 Hz, CF2, 1F), ꢁ117.9 (d, J = 277 Hz, CF2, 1F),
ꢁ129.1 (dd, J = 169, 24 Hz, CF2, 1F), ꢁ131.4 (s, vinyl F, 1F),
ꢁ142.7 (d, J = 169 Hz, CF2, 1F), ꢁ191.1 (s, bridgehead F, 1F),
ꢁ100.1 (s, bridgehead F, 1F), ꢁ207.9 (s, bridgehead F, 1F). IR
4.23. 1,7,10,10-Tetrafluoro-4-thia-2,6-
diazatricyclo[5.2.1.02,6]decane-3,5-dione (44)
In a heavy-walled hydrogenation bottle were placed 0.45 g
(1.8 mmol) of 43 in 10 mL of THF and 0.90 g of 5% Pd-on-
alumina. The bottle was mounted on a Parr hydrogenation
apparatus, evacuated and flushed with H2 three times. The