338
A. Srikrishna, S. S. V. Ramasastry / Tetrahedron Letters 47 (2006) 335–339
2. Even though different numbering was given to solanas-
cones based on their biogenesis, in the present manuscript
we followed the systematic numbering.
3. Nishikawaji, S.; Fujimori, T.; Matsushima, S.; Kato, K.
Phytochemistry 1983, 22, 1819–1820.
4. Kodama, H.; Fujimori, T.; Kato, K. Agric. Biol. Chem.
1985, 49, 2537–2541.
5. Tazaki, H.; Kodama, H.; Fujimori, T. Agric. Biol. Chem.
1986, 50, 2231–2235.
6. Tazaki, H.; Kodama, H.; Ohnishi, A.; Fujimori, T. Agric.
Biol. Chem. 1989, 53, 3037–3038.
7. Kodama, H.; Fujimori, T.; Tanaka, H.; Kato, K. Agric.
Biol. Chem. 1985, 49, 1527–1528.
Figure 2. ORTEP diagram of the keto-benzoate 36.
8. To the best of our knowledge there is no report on the
synthesis (either racemic or enantioselective) of any of the
hydroxysolanascones. For the enantiospecific synthesis of
the parent solanascone and dehydrosolanascones, see:
Srikrishna, A.; Ramasastry, S. S. V. Tetrahedron Lett.
2005, 46, 7373–7376.
9. (a) Srikrishna, A.; Dethe, D. H. Tetrahedron Lett. 2005,
46, 3381–3383; (b) Srikrishna, A.; Hemamalini, P. Indian
J. Chem. 1990, 29B, 152–153.
10. Smith, J. G. Synthesis 1984, 629–656; Srikrishna, A.;
Ramasastry, S. S. V. Tetrahedron: Asymmetry 2005, 46,
2973–2979.
11. Tsuji, J.; Shimizu, I.; Yamamoto, K. Tetrahedron Lett.
1976, 17, 2975–2976.
LHMDS, trimethylsilyl chloride and triethylamine fol-
lowed by oxidative desilylation14 of the resultant silyl
dienolate with palladium acetate in dry acetonitrile fur-
nished the cross-conjugated dienone 31 in 80% yield.
Reaction of the dienone 31 with lithium dimethylcuprate
in ether at ꢀ30 °C for 1 h furnished the enone 32, which
on photochemical irradiation with a 450 W Hanovia
medium pressure mercury vapor lamp furnished
10-epi-solanascone derivative 33, mp 124–125 °C,15
in 65% yield.
In order to generate the secondary methyl group with
correct stereochemistry, the sequence was altered and
the secondary methyl group was introduced after the
construction of the tetracyclic framework.8 Conse-
quently, irradiation of the enone 30 in methanol with
a 450 W Hanovia medium pressure mercury vapor lamp
for two hours furnished the keto-benzoate 34 in 87%
yield. Treatment of the tetracyclic ketone 34 with
LHMDS, trimethylsilyl chloride and triethylamine fol-
lowed by reaction of the resultant silyl enol ether with
palladium acetate in acetonitrile furnished the enone
35 in 80% yield. Treatment of the enone 35 with lithium
dimethylcuprate at ꢀ30 °C furnished the keto-benzoate
36, mp 168–170 °C, in 63% yield. The stereostructure
of the keto-benzoate 36 was confirmed by X-ray diffrac-
tion analysis (Fig. 2).15 Finally, hydrolysis of the benzo-
ate group in 36 furnished the keto-alcohol15 8, the
aglycone of the glycoside 6, in quantitative yield.
12. Mitsunobu inversion of the alcohols 15 and 22 was
attempted under standard conditions; however it was
unsuccessful probably due to the neopentylic nature of the
alcohols.
13. Belotti, D.; Cossy, J.; Pete, J. P.; Portella, C. Tetrahedron
Lett. 1985, 26, 4591–4594.
14. Ito, Y.; Hirao, T.; Saegusa, T. J. Org. Chem. 1978, 43,
1011–1013.
15. Yields refer to isolated and chromatographically pure
compounds. All the compounds exhibited spectral data
(IR, 1H and 13C NMR and mass) consistent with their
structures. Selected spectral data for (1R,2S,4S,5S,7S,
10S,11S)-5,10,11-trimethyl-8-oxotetracyclo[5.3.1.11,4.05,11
]
24
dodecan-2-ol (22): mp: 168–169.5 °C; ½aꢂD +162.8 (c 0.7,
1
CHCl3); IR (thin film): mmax/cmꢀ1 3426, 1670; H NMR
(400 MHz, CDCl3): d 4.23 (1H, dd, J 10.6 and 5.3 Hz),
2.68 (1H, dd, J 16.2 and 10.0 Hz), 2.62–2.50 (1H, m), 2.41
(1H, dd, J 10.8 and 7.4 Hz), 2.05 (1H, d, J 13.2), 2.10–2.00
(2H, m), 1.94 (1H, dd, J 16.0 and 4.8 Hz), 1.75 (1H, d, J
5.3 Hz, H-4), 1.67 (1H, ddd, J 11.7, 3.9 and 1.8 Hz), 1.43
(3H, s), 1.34 (1H, ddd, J 13.2, 5.1 and 3.6 Hz), 1.20 (1H, d,
J 11.6 Hz), 1.15 (3H, s), 1.00 (3H, d, J 6.9 Hz); 13C NMR
(75 MHz, CDCl3): d 218.3 (C), 73.3 (CH), 54.2 (C), 51.0
(CH), 48.5 (C), 45.6 (CH2), 44.2 (C), 43.2 (CH), 35.3
(CH2), 33.1 (CH2), 32.9 (CH2), 27.3 (CH), 19.2 (CH3),
17.9 (CH3), 17.6 (CH3); mass: 234 (M+, 1%), 190 (50), 175
(9), 164 (11), 137 (68), 121 (44), 120 (100), 105 (44), 91
(28); HRMS: m/z calcd for C15H22O2Na (M+Na):
257.1517; Found: 257.1510. For (1R,2R,4S,5S,7S,
In summary, we have accomplished the first total syn-
thesis of the aglycone 8 of the phytoalexin 2b-hydroxy-
solanascone-b-glucopyranoside 6 isolated from flue-
cured tobacco leaves, and its 2,10-diepi- and 2a-epimers,
starting from the readily available monoterpene (R)-
carvone via 3-butenylcarvone.
10S,11S)-5,10,11-trimethyl-8-oxotetracyclo[5.3.1.11,4.05,11
]
Acknowledgements
25
dodec-2-yl benzoate (33): mp: 124–125 °C; ½aꢂD +19.1 (c
1
0.68, CHCl3); IR (neat): mmax/cmꢀ1 1714, 1601; H NMR
We thank the Council of Scientific and Industrial
Research, New Delhi, for the award of a senior research
fellowship to S.S.V.R.
(300 MHz, CDCl3 + CCl4): d 8.01 (2H, d, J 7.2 Hz), 7.56
(1H, t, J 7.2 Hz), 7.44 (2H, t, J 7.2 Hz), 5.22 (1H, d, J
6.6 Hz), 2.80–2.67 (2H, m), 2.60 (1H, dd, J 12.0 and
6.6 Hz), 2.20 (1H, ddd, J 14.7, 6.9 and 2.7 Hz), 2.11 (1H,
dd, J 12.9 and 6.3 Hz), 1.96–1.73 (5H, m), 1.40 (1H, ddd, J
14.4, 4.8 and 2.4 Hz), 1.33 (3H, s), 1.10 (3H, s), 1.17 (3H,
d, J 6.9 Hz); 13C NMR (75 MHz, CDCl3 + CCl4): d 216.1
(C), 166.0 (C), 133.0 (CH), 130.7 (C), 129.6 (2 C, CH),
128.4 (2 C, CH), 76.7 (CH, C-2), 54.4 (C), 50.3 (C), 49.3
(CH), 45.8 (CH2), 44.1 (C), 42.8 (CH), 35.6 (CH2), 33.8
References and notes
1. Fujimori, T.; Kasuga, R.; Keneko, H.; Sakamura, S.;
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564.