3-chloro-3-decanoyl-1,7,7 trimethylbicyclo[2.2.1]heptan-2-one.
The oxidation of the alcohols mixture with sodium hypochlorite in pure ethanoic acid produces only 3-a-chloro-3-exo-decanoyl-1,7,7-trimethyl bicyclo[2.2.1]heptan-2-one.
Oxidation with NaClO/ CH3CO2H
0.16 g (0.52 mmol) of the alcohols mixture was stirred for 12 h at 50° C with 1M (2.5 mL) aqueous solution of sodium hypochlorite and pure ethanoic acid (4mL). The products were extracted with ethyl ether (3 x 40 mL) and the organic phase was washed with distilled water and dried with anhydrous sodium sulfate. The organic fractions obtained were concentrated and the products were purified in a liquid column chromatography.
Under the reaction conditions studied the oxidation of the alcohols mixture with hypochlorite in pure ethanoic acid gives only product (8).
Compound (8) is a colorless liquid and the IR spectrum shows two bands at n 1754,9 cm-1 and n 1722,7 cm-1 for the carbonyl groups stretching of this compound.
The 1H-NMR spectrum (Figure 6) and the 1H-1H-COSY shows two groups of signals for the H5 methylenes; at d 3.15 (1H, ddd, J= 7.8, 7.6, 3.9 Hz) for H5-endo and the signal for H5-exo at d 2.51 (1Hb, ddd, J= 7.8, 7.6, 6.5 Hz).
The signals d 198.8 and d 212.0 in the 13C-NMR spectrum assigned to the two carbonyls support structure (8). Moreover the DEPT (135) experiment shows a new chemical shift at d 72.2, while the signal at d 75.77 for the methine (C3) disappears.
13C-NMR experiments help to the signals assignment for all of the carbons of the bicyclic ring and a part of the lateral aliphatic chain. Thus C2 at d 36.9 show coupling with the two signals for the diasterotopic hydrogens which signals appear at d 3.15 and 2.51.
Besides the protons of the syn methyl group at C9 are shielded (d 0.62), because of the proximity to exo carbonylic group at C1'. The signals for the protons at C5 and C6 are very close, H5a and H6a are at d 2.03 and H5b and H6b at d 1.73.
The incorporation of a chlorine atom on the alpha face was postulated due to both the shield induced on protons of one methyl at C7 and the chemical shift of H5a and H6ato lower field due to the fact that they are on the same face with respect to the chlorine.
Figure 6. 1H-NMR of 3-chloro-3-decanoyl-1,7,7 trimethylbicyclo[2.2.1]heptan-2-one.
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A probable explanation for the formation of compound (8) lies on the fact that an acidic solution of sodium hypochlorite has a certain concentration of Cl2 at the thermodynamic equilibrium (figure 8). Chlorine can add to the double bond of the enol structure of the oxidation products.
It is expected that the attack by the chlorine is on the most exposed alpha face of the enol structure, producing the intermediate showed in Figure 8. This intermediate can quickly rearrange to the more stable compound (8).
4H+(ac) + 2 Cl - + 2 ClO -(ac) = 2 Cl2(g) + 2 H2O (l)
Figure 8
3-chloro-3-decanoyl-1,7,7-trimethylbicyclo[2.2.1]heptan-2-one. (8)
1H-NMR : 6.36 (1H, dd, J= 7.76, 7.67 Hz), 2.16-2.08 (2H, m, 1.73-1.60 (2H, m), 1.37 (2H, m, 1.26 (8CH2, s), 0.96 (6H,s), 0.90 (t, J= 8 Hz), 0.78 (s, 3H).
13C-NMR: 207.1, 142.7, 130.5, 57.7, 47.5, 45.9, 31.8, 30.3, 29.3, 28.7, 28.6(2CH2), 26.4, 22.5, 20.4, 18.2, 14.0, 9.1.
MS: 186 (base peak), 312, 297,155, 83, 55.
Anal. Calcd. for C20H33ClO2; C, 70.46; H, 9.76. found. C 70.42; H, 9.77.
Aldolization procedure
Lithium diisopropylamide (LDA) was prepared from diisopropylamine (12.4 mL, 92.1 mmol) with n-butyllithium (51.4 mL of a 1.6 M solution in hexane, 82.24 mmol) in 30.0 mL of dry THF at -78°C. The solution was stirred for 30 min. and then a solution of camphor (12.0 g, 78.9 mmol) in dry THF (52.0 mL) was added dropwise. After the addition, the solution was stirred for 2.5 h, treated with freshly distilled aldehyde (79.0 mmol) and stirred for an additional 20 min. the reaction was quenched at -78°C with a saturated aqueous solution of NH4Cl (200 mL). The cold bath was then removed and the mixture extracted with ethyl ether (3 x 100 mL). The combined organic layers were washed with an aqueous NaCl solution, dried over Na2SO4, and concentrated in vacuum to afford the adduct mixture. The products were purified by liquid column chromatography and the adducts ratio obtained was quantified by 1H-NMR.
3-exo-1-hydroxydecyl-1,7,7-trimethylbicyclo[2.2.1]heptan-2-one. (4)
1H-NMR: 4.15(1H, s), 3.90(1H, m), 2.04(1H, m), 1.97-1.91 (2H, m), 1.76-1.26 (26H, s), 0.94 (3H, s), 0.91 (3H, s), 0.88(3H, s), 0.85 (3H, s).
13C-NMR: 223.6, 73.30, 59.56, 57.84, 46.01, 36.17, 31.90, 29.61-29.31 (7CH2), 24.76, 22.67, 21.67, 20.44, 14.05, 9.04.
Anal. Calcd. for C20H36O2 ; C, 77.87; H, 11.76. found. C, 77.90; H, 11, 79.
3-endo-1-hydroxydecyl-1,7,7-trimethylbicyclo[2.2.1]heptan-2-one. (5)
1H-NMR: 3.92(1H, s), 3.74(1H, m), 2.34 (1H, m), 2.10 (1H, s), 1.77-1.69 (2H, m), 1.47-1.39 (4H, m), 1.27(8CH2, s), 0.98(3H, s), 0.92(3H, s), 0.88(3H,s), 0.85(3H, s).
13C-NMR: 223.90, 73.23, 70.89, 65.77, 59.38, 57.76, 54.88, 46.84, 45.86, 36.05, 34.82, 31.52, 29.56, 29.24, 24.67, 20.81, 19.54, 18.53, 15.20, 9.24
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