α-Fluoro-β-lactones
1331
an es18 with vigorous stirrin g over 0.5 h un der dry N2. Th e solution , wh ich con tain ed th e
product, was carefully filtered an d evaporated, an d th e resultin g crude α-fluoro-β-lacton es 3
were th en recrystallized from h exan e.
4,4-Dibenzyl-3-fluorooxetan-2-one (3a). From 0.299 g (1.0 m m ol) of startin g acid 5a, 0.220 g
(82%) of 3a was obtain ed as a wh ite solid; m .p. 97–98 °C (dec.). 1H NMR: 7.39–7.25 m , 8 H;
3
3
2
7.14–7.11 dd, JHH = 7.5, JHF = 2.4, 2 H (arom atic sign als); 5.30 d, JHF = 53, 1 H (CH of th e
2
3
2
2
lacton e rin g); 3.35 dd, JHH = 15, JHF = 2.4, 1 H; 3.20 d, JHH = 15, 1 H; 3.07 dd, JHH = 15,
3JHF = 1.8, 1 H; 2.93 d, JHH = 15, 1 H (ben zylic H’s). 19F NMR: –200.8 d, JHF = 53. 13C NMR:
39.4 d, JCF = 4.5; 40.2; 85.7 d, JCF = 19; 92.6 d, JCF = 228; 127.7; 127.9; 128.9; 129.0;
130.4; 130.7 d, JCF = 1.5; 133.4; 133.9; 164.2 d, JCF = 22. HRMS (EI): [M]• + 270.1056; calcu-
2
2
3
2
1
4
2
lated for C17H15FO2 270.1056. IR (Nujol): 1 826.3 (stron g), 1 865.2.
(R*,R*)-4-Benzyl-3-fluoro-4-phenyloxetan-2-one (3b). From 0.137 g (0.5 m m ol) of 5b, 0.098 g
(76.5%) of product was obtain ed as a wh ite solid; m .p. 89–92 °C (dec.). 1H NMR: 7.34–7.27 m ,
2
3 H; 7.20–7.06 m , 5 H; 6.94–6.87 m , 2 H (arom atic sign als); 5.70 d, JHF = 54, 1 H (CH of th e
2
3
2
lacton e rin g); 3.53 dd, JHH = 14, JHF = 2.1, 1 H; 3.40 d, JHH = 15, 1 H (ben zylic H’s). 19F NMR:
–196.8 d, JHF = 54. 13C NMR: 41.6 d, JCF = 3.6; 87.3 d, JCF = 20; 96.9 d, JCF = 232; 125.3;
127.3; 128.3; 128.6; 128.8; 130.8; 132.8; 137.4; 164.1 d, JCF = 22. HRMS (EI): [M]• +
2
3
2
1
3
256.0896; calculated for C16H13FO2 256.0900. IR (Nujol): 1 854.9 (sh oulder), 1 828.0
(stron g).
(R*,S*)-4-Benzyl-3-fluoro-4-phenyloxetan-2-one (3c). From 0.412 g (1.5 m m ol) of 5c, 0.275 g
(74.8%) of a m ixture of products, con sistin g of 74% lacton e 3c an d 26% 1-fluoroalken e 4c,
from wh ich 3c was obtain ed pure by recrystallization from h exan e; m .p. 77–80 °C (dec.).
2
1H NMR: 7.33–7.25 m , 6 H; 7.15–7.10 m , 2 H (arom atic sign als); 5.53 d, JHF = 54, 1 H (CH
2
3
2
of th e lacton e rin g); 3.48 dd, JHH = 15, JHF = 0.9, 1 H; 3.36 d, JHH = 15, 1 H (ben zylic H’s).
19F NMR: –192.0 d, JHF = 54. 13C NMR: 45.1; 86.5 d, JCF = 20; 93.4 d, JCF = 231; 126.2;
127.9; 128.7; 128.8; 129.0; 130.6; 133.1; 134.8; 163.7 d, JCF = 23. HRMS (EI): [M]• +
2
2
1
3
256.0896; calculated for C16H13FO2 256.0900. IR (Nujol): 1 849.9, 1823.4 (two stron g
ban ds).
(R*,R*)-3-Fluoro-4-methyl-4-phenyloxetan-2-one (3d ). From 0.200 g (1.0 m m ol) of 5d , after
evaporation of th e ch loroform , rin sin g with eth yl acetate, careful filtration an d evaporation
of eth yl acetate, 0.060 g (34%) of product was isolated as a m ixture of products con sistin g of
89% lacton e 3d an d 11% 1-fluoroalken e 4d . Ch aracterization of 3d was don e as th e m ixture.
2
4
1H NMR: 7.10–7.20 m , 5 H; 5.46 d, JHF = 54, 1 H (CH of th e lacton e rin g); 1.81 d, JHF = 3.3
(β-m eth yl). 19F NMR: –194.6 d, JHF = 54. 13C NMR: 22.0 d, JCF = 4.5; 85.1 d, JCF = 21; 96.2 d,
1JCF = 232; 124.3; 128.7; 129.0; 129.1; 139.4; 164.8 d, JCF = 22. IR (Nujol): 1 839.3 (stron g).
2
3
2
3
1-Fluoroalken es 4 from α-Fluoro-β-lacton es 3. Gen eral Procedure
A dry vial, flam e-dried an d purged with dry N2, was ch arged with th e α-fluoro-β-lacton e 3,
sealed tigh tly with a n algen e cap an d teflon , an d h eated at th e specified tem perature over-
n igh t. A yellow oil was form ed in each case. Th e reaction m ixture was cooled with dry ice,
th e vial was open ed, an d th e resultan t oil was dissolved in CDCl3 an d an alyzed by NMR. In
all th e cases a full con version to th e respective 1-fluoroalken e 4 was ach ieved, an d th eir 1H,
19F an d 13C NMR spectra were very clean with n o furth er purification bein g required.
2-Benzyl-1-fluoro-3-phenyl-1-propene (4a ). Heatin g of 100 m g (0.37 m m ol) of 4,4-di-
ben zyl-3-fluorooxetan -2-on e (3a) at 140 °C overn igh t gave 81 m g (97%) of fluoroalken e 4a.
3
3
4
3
1H NMR: 7.23 t, JHH = 7.2, 5 H; 7.17 dd, JHH = 7.2, JHF = 2.2, 2 H; 7.09 td, JHH = 7.2,
Collect. Czech. Chem. Commun. (Vol. 67) (2002)