T. Sastraruji et al. / Tetrahedron 68 (2012) 598e602
601
the general procedure described above from
0.21 mmol), n-butyl butanoate (1 mL), DIB (67.3 mg, 0.21 mmol),
Mg(OAc)2$4H2O (44.8 mg, 0.21 mmol) and TBHP (125.4 L,
0.63 mmol). Separation of the crude reaction products by column
chromatography using gradient elution from 100% EtOAc to MeOH/
EtOAc (1:4) gave 29.0 mg (51%) of 5 and 8.0 mg (13%) of 6.
3
(80.4 mg,
(75.6 mL, 0.39 mmol). Purification by column chromatography using
gradient elution from 100% ether to EtOAc/ether (1:1) gave 15.7 mg
(46%) of 10a. Colourless oil; IR nmax 2931, 2859, 1718, 1271,
m
1112 cmꢁ1
;
1H NMR
d
7.97 (d, J¼7.5 Hz, 2H, ArH2 and 6), 7.48 (t,
J¼7.5 Hz, 1H, ArH4), 7.37 (t, J¼7.5 Hz, 2H, ArH3 and 5), 6.28 (dd,
J¼17.5, 10.5 Hz, 1H, H90), 6.14 (d, J¼17.5 Hz, 1H, H100a), 5.74 (d,
J¼10.5 Hz, 1H, H100b), 4.24 (t, J¼7.0 Hz, 2H, H10), 2.51 (t, J¼7.0 Hz,
2H, H70), 1.70 (tt, J¼7.0, 7.0 Hz, 2H, H20), 1.57 (tt, J¼7.0, 7.0 Hz, 2H,
H60), 1.41e1.38 (m, 2H, H30), 1.34e1.25 (m, 4H, H40 and 50); 13C NMR
Compound 5: pale yellow gum; [
a
]
25 þ23 (c 2.3, CHCl3); IR nmax
D
2966, 2885, 1786, 1664, 1021, 968 cmꢁ1; 1H NMR
d
5.79 (dt, J¼15.5,
6.3 Hz, 1H, H-20), 5.49 (d, J¼15.5 Hz, 1H, H-10), 4.29 (br s, 1H, H-2),
3.47 (br s, 1H, H-9a), 3.13 (ddd, J¼15.5, 10.5, 5.5 Hz, 1H, H-5a), 3.02
(ddd, J¼13.0, 8.5, 5.0 Hz, 1H, H-5b), 2.84 (d, J¼6.0 Hz, 1H, H-7), 2.79
(dq, 1H, J¼11.5, 7.0 Hz, H-10), 2.11e2.06 (m, 2H, H-30), 1.94e1.89 (m,
1H, H-1a), 1.93e1.88 (m, 1H, H-9), 1.86e1.79 (m, 1H, H-6a),
1.80e1.74 (m, 1H, H-1b), 1.77e1.70 (m, 1H, H-6b), 1.27 (d, J¼7.5 Hz,
d
201.1 (C80), 166.8 (COO), 136.7 (C90), 132.9 (ArC4), 130.6 (ArC1),
129.7 (ArC2 and 6), 128.5 (ArC3 and 5), 128.0 (C100), 65.2 (C10), 39.7
(C70), 28.8 (C20), 29.2 (C40 and 50), 26.0 (C30), 24.0 (C60); HRESIMS m/
z 275.1647 [MH]þ, calcd for C17H23O3 275.1642.
3H, H-12), 1.00 (t, J¼7.5 Hz, 3H, H-40); 13C NMR
d
178.4 (C-11), 133.6
4.2.6. (E)-3-Oxohex-4-enyl benzoate (11a). The title compound was
obtained using the general procedure described above from 11
(52.8 mg, 0.26 mmol), n-butyl butanoate (1 mL), DIB (83.8 mg,
0.26 mmol), Mg(OAc)2$4H2O (55.8 mg, 0.26 mmol) and TBHP
(C-20), 126.6 (C-10), 109.3 (C-8), 83.4 (C-3), 81.0 (C-2), 61.1 (C-9a),
51.4 (C-7), 45.8 (C-9), 48.2 (C-5), 35.9 (C-10), 32.5 (C-1), 26.9 (C-6),
25.5 (C-30), 13.6 (C-40), 13.4 (C-12); HRESIMS m/z 276.1604 [MH]þ,
calcd for C16H22NO3 276.1595.
(156.0 mL, 0.78 mmol). Purification bycolumn chromatography using
Compound 6: pale yellow gum; IR nmax 2967, 2914, 1787, 1664,
gradient elution from 100% ether to EtOAc/ether (1:1) gave 12.0 mg
(21%) of 9a, 8.4 mg of 11a (15%) and 15.4 mg of 11b (27%). Compound
11b was spectroscopically identical to that reported.12 Compound
1021, 967 cmꢁ1; [
a
]
25 þ8 (c 1.6, CHCl3); 1H NMR
d
6.80 (d, J¼16.0 Hz,
D
1H, H-10), 6.39 (d, J¼16.0 Hz, 1H, H-20), 4.40 (br s, 1H, H-2), 3.53 (br
s,1H, H-9a), 3.15e3.04 (m, 2H, H-5), 2.94 (d, J¼5.0 Hz,1H, H-7), 2.79
(dq, 1H, J¼12.0, 7.0 Hz, H-10), 2.29 (s, 3H, H-40), 2.04e1.98 (m, 1H,
H-1a), 2.01e1.96 (m, 1H, H-9), 1.88e1.82 (m, 2H, H-6), 1.85e1.79 (m,
11a: colourless oil; 1H NMR
d
8.00 (d, J¼7.0 Hz, 2H, ArH2 and 6), 7.55
(t, J¼7.0 Hz, 1H, ArH4), 7.43 (t, J¼7.0 Hz, 2H, ArH3 and 5), 6.91 (dq,
J¼15.0, 7.0 Hz, 1H, H50), 6.18 (d, J¼15.0 Hz, 1H, H40), 4.64 (t, J¼7.0 Hz,
2H, H10), 3.01 (tt, J¼7.0, 7.0 Hz, 2H, H20),1.92 (d, J¼7.0 Hz, 3H, H60); 13C
1H, H-1b), 1.29 (d, J¼6.5 Hz, 3H, H-12); 13C NMR
d
198.0 (C-30), 177.9
(C-11), 143.5 (C-10), 130.7 (C-20), 109.2 (C-8), 83.5 (C-3), 80.3 (C-2),
61.3 (C-9a), 52.6 (C-7), 45.7 (C-9), 48.3 (C-5), 35.9 (C-10), 32.3 (C-1),
27.9 (C-40), 26.7 (C-6), 13.3 (C-12); HRESIMS m/z 290.1389 [MH]þ,
calcd for C16H20NO4 290.1387.
NMR d
197.2 (C30),166.6 (COO),144.0(C50),132.1 (ArC4 andC40),129.7
(ArC2 and 6), 128.5 (ArC1, 3 and 5), 60.4 (C10), 38.7 (C20), 18.5 (C60);
HRESIMS m/z 219.1029 [MH]þ, calcd for C13H15O3 219.1016.
4.2.7. Oxidation of benzyl-5-hexenyl ether (12). This was achieved
by the general procedure using 12 (42.2 mg, 0.22 mmol), n-butyl
butanoate (1 mL), DIB (70.9 mg, 0.22 mmol), Mg(OAc)2$4H2O
4.2.2. Synthesis of 6 by oxidation of ketone 5. This was achieved by
the general procedure using 5 (6.9 mg, 0.025 mmol), n-butyl buta-
noate (1 mL), DIB (64.4 mg, 8 equiv, 0.20 mmol), Mg(OAc)2$4H2O
(47.2 mg, 0.22 mmol) and TBHP (132.0 mL, 0.66 mmol) to give
(5.4 mg, 1 equiv, 0.025 mmol) and TBHP (120.0
m
L, 24 equiv,
27.2 mg (61%) of 9, 7.8 mg of 9a (16%) and 0.9 mg of 12a (2%) after
column chromatography using gradient elution from 100% ether to
EtOAc/ether (1:9). Compound 12a was spectroscopically identical to
that reported.13
0.60 mmol) to give 2.6 mg (42%) of enone 6 after column chroma-
tography using gradient elution from 100% EtOAc to MeOH/EtOAc
(1:4).
4.2.3. Oxidation of stemofoline 7. This was achieved by the general
procedure using 7 (19.3 mg, 0.05 mmol), n-butyl butanoate (1 mL),
DIB (16.1 mg, 0.05 mmol), Mg(OAc)2$4H2O (10.7 mg, 0.05 mmol)
4.2.8. 3-Phenylpropyl acrylate (13a). The title compound was ob-
tained using the general procedure described above from 13
(108 mg, 0.61 mmol), ethyl acetate (1 mL), DIB (296 mg, 1.5 equiv,
0.92 mmol), Mg(OAc)2$4H2O (131 mg, 0.61 mmol) and TBHP
and TBHP (30.0 mL, 0.15 mmol) to give 8.0 mg (58%) of the known
lactone 8, after column chromatography using gradient elution
from 100% EtOAc to MeOH/EtOAc (1:4). The product was spectro-
scopically identical to that reported.2
(549 mL, 4.5 equiv, 2.75 mmol) to give 104 mg (90%) of 13a after
column chromatography using gradient elution from 100% ether to
EtOAc/ether (1:9). Compound 13a was spectroscopically identical
to that reported.14
4.2.4. 4-Oxohex-5-enyl benzoate (9a). The title compound was
obtained using the general procedure described above from 9
(22.2 mg, 0.11 mmol), n-butyl butanoate (1 mL), DIB (34.8 mg,
0.11 mmol), Mg(OAc)2$4H2O (23.2 mg, 0.11 mmol) and TBHP
4.2.9. 3-Phenylpropyl benzoate (14a). The title compound was ob-
tained using the general procedure described above from 14 (103 mg,
0.45 mmol), ethyl acetate (1 mL), DIB (217 mg,1.5 equiv, 0.68 mmol),
(64.8
EtOAc/ether (15:85) as eluent gave 16.9 mg (72%) of 9a. Colourless
oil; IR nmax 2959, 2902, 1716, 1675, 1270, 1110 cmꢁ1; 1H NMR
8.03
m
L, 0.33 mmol). Purification by column chromatography using
Mg(OAc)2$4H2O (96.5 mg, 0.45 mmol) and TBHP (405 mL, 4.5 equiv,
2.03 mmol)togive103 mg(95%)of14a aftercolumnchromatography
using gradient elution from 100% ether to EtOAc/ether (1:9). Com-
pound 14a was spectroscopically identical to that reported.15
d
(d, J¼7.0 Hz, 2H, ArH2 and 6), 7.56 (t, J¼7.0 Hz, 1H, ArH4), 7.44 (t,
J¼7.0 Hz, 2H, ArH3 and 5), 6.38 (dd, J¼17.5, 7.5 Hz, 1H, H50), 6.25 (d,
J¼17.5 Hz, 1H, H60a), 5.85 (d, J¼7.5 Hz, 1H, H60b), 4.37 (t, J¼7.0 Hz,
2H, H10), 2.77 (t, J¼7.0 Hz, 2H, H30), 2.15e2.12 (m, 2H, H20); 13C NMR
4.2.10. Hexyl benzoate (15a). The title compound was obtained us-
ing the general procedure described above from 15 (109 mg,
0.57 mmol), ethyl acetate (1 mL), DIB (277 mg,1.5 equiv, 0.86 mmol),
d
199.7 (C40), 166.7 (COO), 136.6 (C50), 133.1 (ArC4), 129.7 (ArC2 and
6),128.6 (C60),128.5 (ArC1, 3 and 5), 64.3 (C10), 36.1 (C30), 23.2 (C20);
Mg(OAc)2$4H2O (122 mg, 0.57 mmol) and TBHP (684 mL, 6.0 equiv,
HRESIMS m/z 219.1028 [MH]þ, calcd for C13H15O3 219.1016.
3.42 mmol) to give 109 mg (93%) of 15a after column chromatogra-
phy using gradient elution from 100% ether to EtOAc/ether (1:9).
Compound 15a was spectroscopically identical to that reported.16
4.2.5. 8-Oxodec-9-enyl benzoate (10a). The title compound was
obtained using the general procedure described above from 10
(32.8 mg, 0.13 mmol), n-butyl butanoate (1 mL), DIB (40.6 mg,
0.13 mmol), Mg(OAc)2$4H2O (27.0 mg, 0.13 mmol) and TBHP
4.2.11. Hexyl acrylate (16a). The title compound was obtained us-
ing the general procedure described above from 16 (70.3 mg,