L.T. Phuoc et al. / Tetrahedron 64 (2008) 4835e4851
4843
CDCl3) d 0.86 (3H, s, H18), 1.21e2.52 (18H, m), 2.06 (3H, s,
CH3CO2e), 2.61 (1H, d, J¼12.3 Hz, H6), 2.84 (1H, t,
J¼10.5 Hz, H12b), 3.27 (1H, dd, J¼10.5, 4.8 Hz, H17), 3.36
(3H, s, eOCH2OCH3), 3.69 (3H, s, eCO2CH3), 3.90 (1H,
dd, J¼10.2, 3.9 Hz, H19), 4.22 (1H, ddd, J¼12.0, 9.9,
7.8 Hz, H11), 4.58, 4.66 (2ꢁ1H, ABd, J¼6.7 Hz,
eOCH2OCH3), 7.26 (1H, m, H40), 7.53 (2H, m, H50 and
H60), 8.30 (1H, d, J¼8.2 Hz, H30).
Analysis by TLC showed the absence of starting material.
The mixture was quenched by dropwise addition of water
(30 mL) and extracted with EtOAc (3ꢁ30 mL). The combined
organic layers were washed successively with saturated aq
NaHCO3 solution (30 mL), water (30 mL) and brine
(30 mL), and then dried over MgSO4. Concentration in vacuo
and chromatography on silica gel (EtOAc/hexanes, 1:3) af-
forded the desired product 28 (18.6 mg, 0.038 mmol, 83%)
as an oil and the corresponding 19-ol (3.4 mg, 0.008 mmol,
16%) as an oil.
5.1.13. Methyl ent-11a,13-diacetoxy-19-methoxymethoxy-
17-(2-nitrophenylselenenyl)-19,20-cyclogibberellan-7-oate
(27)
Diacetate 28: IR (Neat) nmax (cmꢀ1): 3078, 2949, 2851,
1
2822, 1738, 1663. H NMR (300 MHz, CDCl3) d 0.86 (3H, s,
A stirred solution of selenenyl ether prepared above
(42 mg, 0.0645 mmol) and pyridine (45 mL, 0.68 mmol) in
CH2Cl2 (10 mL) at 0 ꢂC under nitrogen was treated dropwise
with acetyl chloride (35 mL, 0.45 mmol). After 40 min, the
mixture was allowed to warm to room temperature and stirred
for an additional 2 h. Analysis by TLC showed the absence of
starting material. The reaction mixture was quenched by drop-
wise addition of water (20 mL). After extracting with EtOAc
(3ꢁ20 mL), the combined organic extracts were washed suc-
cessively with saturated aq NH4Cl solution (20 mL), water
(20 mL) and brine (20 mL), and then dried over MgSO4. Con-
centration in vacuo and chromatography on silica gel (EtOAc/
hexanes, 1:2) furnished the desired diacetate 27 (31.7 mg,
0.05 mmol, 71%) as an oil. IR (Neat) nmax (cmꢀ1): 2950,
2852, 1738. 1H NMR (300 MHz, CDCl3) d 0.86 (3H, s,
H18), 1.19e2.66 (16H, m), 2.02 (3H, s, 13-CH3CO2e), 2.05
(3H, s, 11-CH3CO2e), 2.62 (1H, d, J¼12.0 Hz, H6), 2.63
(1H, m, H17), 2.79 (1H, t, J¼11.1 Hz, H12b), 3.35 (3H, s,
eOCH2OCH3), 3.46 (1H, dd, J¼10.8, 4.8 Hz, H017), 3.69
(3H, s, eCO2CH3), 3.92 (1H, dd, J¼10.0, 3.8 Hz, H19),
4.56, 4.65 (2ꢁ1H, ABd, J¼6.7 Hz, eOCH2OCH3), 5.21
(1H, ddd, J¼10.8, 9.0, 8.7 Hz, H11), 7.32 (1H, m, H40),
7.48e7.57 (2H, m, H50 and H60), 8.30 (1H, d, J¼8.5 Hz, H30).
13C NMR (75.5 MHz, CDCl3) d 19.9 (C2), 21.3 (11-
CH3CO2e), 21.8 (13-CH3CO2e), 22.1 (C18), 28.6 (C17),
34.7 (C1), 35.3 (C3), 36.4 (C12), 39.6 (C14), 43.2 (C10),
43.8 (C15), 44.8 (C6), 45.4 (C20), 49.4 (C4), 51.5
(eCO2CH3), 51.9 (C16), 52.0 (C8), 55.3 (C5), 61.3
(eOCH2OCH3), 61.5 (C9), 69.6 (C11), 83.0 (C19), 84.9
(C13), 92.6 (eOCH2OCH3), 125.4 (C30), 126.5 (C40 and
C60), 129.0 (C50), 133.3 (C10), 133.5 (C20), 169.9 (11-
CH3CO2e), 170.1 (13-CH3CO2e), 173.5 (C7). MS (EI) m/z
693 (Mþ, 9%), 663 (9), 491 (100), 431 (19), 371 (71), 327
(82), 309 (38), 295 (34), 267 (60), 223 (30), 186 (22), 91
(20). HRMS (EI) m/z calcd for Mþ, C33H43O10NSe:
693.2052; found: 693.2064.
H18), 1.14e2.23 (15H, m), 1.96 (3H, s, 13-CH3CO2e), 1.99
(3H, s, 11-CH3CO2e), 2.64 (1H, d, J¼12.0 Hz, H6), 2.93
(1H, dd, J¼12.9, 9.0 Hz, H12b), 3.33 (3H, s, eOCH2OCH3),
3.66 (3H, s, eCO2CH3), 3.92 (1H, dd, J¼10.2, 3.9 Hz, H19),
4.54, 4.63 (2ꢁ1H, ABd, J¼6.7 Hz, eOCH2OCH3), 4.98 (1H,
br s, H17), 5.12 (1H, ddd, J¼10.8, 9.0, 8.7 Hz, H11 overlap-
ped), 5.15 (1H, br s, H017). 13C NMR (75.5 MHz, CDCl3)
d 20.0 (C2), 21.2 (11-CH3CO2e), 22.0 (13-CH3CO2e), 22.2
(C18), 35.4 (C1), 36.7 (C3), 39.7 (C12), 41.2 (C14), 43.9
(C10), 44.1 (C15), 45.4 (C20), 48.8 (C4), 50.3 (C6), 51.7
(eCO2CH3), 51.8 (C8), 55.3 (C5), 58.4 (eOCH2OCH3), 61.5
(C9), 69.7 (C11), 82.2 (C19), 82.9 (C13), 96.1 (eOCH2OCH3),
108.0 (C17), 153.4 (C16), 169.5 (11-CH3CO2e), 169.7 (13-
CH3CO2e), 173.4 (C7). MS (EI) m/z 490 (Mþ, 7%), 459
(17), 430 (95), 388 (100), 370 (88), 343 (38), 326 (74), 308
(53), 283 (47), 267 (43), 249 (34), 223 (43), 181 (24), 105
(27), 91 (31). HRMS (EI) m/z calcd for Mþ, C27H38O8:
490.2567; found: 490.2567.
19-ol: IR (Neat) nmax (cmꢀ1): 3523, 2928, 2851, 2853,
1738, 1663. 1H NMR (300 MHz, CDCl3) d 0.88 (3H, s,
H18), 1.20e2.28 (16H, m), 1.98 (3H, s, 13-CH3CO2e), 2.01
(3H, s, 11-CH3CO2e), 2.66 (1H, d, J¼12.1 Hz, H6), 2.95
(1H, dd, J¼12.8, 9.1 Hz, H12b), 3.69 (3H, s, eCO2CH3),
4.13 (1H, dd, J¼10.9, 4.1 Hz, H19), 5.01 (1H, br s, H17),
5.16 (1H, ddd, J¼11.1, 8.7, 8.4 Hz, H11 overlapped), 5.18
(1H, br s, H017). 13C NMR (75.5 MHz, CDCl3) d 20.2 (C2),
21.3 (11-CH3CO2e), 22.0 (13-CH3CO2e and C18), 34.9
(C1), 39.2 (C3), 39.7 (C12), 41.2 (C14), 43.9 (C10), 44.1
(C15), 45.6 (C20), 48.9 (C4), 50.3 (C6), 51.7 (C8), 51.8
(eCO2CH3), 58.3 (C5), 61.9 (C9), 69.7 (C11), 78.1 (C19),
83.0 (C13), 108.2 (C17), 153.4 (C16), 169.6 (11-CH3CO2e),
169.8 (13-CH3CO2), 173.4 (C7). MS (EI) m/z 445
([MþꢀH], 4%), 386 (27), 344 (100), 326 (67), 285 (34), 267
(25), 241 (18), 223 (31), 167 (39), 105 (27), 149 (93), 71
(33). HRMS (EI) m/z calcd for [MþꢀOCH3], C24H31O6:
415.2120; found: 415.2117.
A stirred solution of 19-ol (257.5 mg, 0.574 mmol) and
pyridine (385 mL, 5.74 mmol) in CH2Cl2 (15 mL) at 0 ꢂC un-
der nitrogen was treated dropwise with acetyl chloride
(360 mL, 4.59 mmol). After 30 min, the mixture was allowed
to warm to room temperature and stirred for an additional
8 h. Analysis by TLC showed the absence of starting material.
The reaction mixture was quenched by dropwise addition of
water (100 mL). After extracting with EtOAc (3ꢁ75 mL),
the combined organic extracts were washed successively
5.1.14. Methyl ent-11a,13-diacetoxy-19-methoxymethoxy-
19,20-cyclogibberell-16-en-7-oate (28) and methyl ent-
11a,13-diacetoxy-19-hydroxy-19,20-cyclogibberell-16-en-
7-oate
A solution of selenenyl ether 27 (31.7 mg, 0.046 mmol) in
THF (4 mL) at 0 ꢂC under nitrogen was treated dropwise with
a solution of 30% H2O2 (2 mL). After 30 min, the mixture was
allowed to warm to room temperature and stirred overnight.