Efficient, highly enantioselective synthesis of selina-1,3,7(11)-trien-8-one, a major component of the essential oil of Eugenia uniflora

Article abstract of DOI:10.1021/np000065f

The first synthesis of selina-1,3,7(11)-trien-8-one (1), a major constituent of the essential oil from the leaves of Eugenia uniflora, has been accomplished, with excellent stereo- and regiocontrol, in eight steps and in 12% overall yield from the known octalone derivative 2a.

Full text of DOI:10.1021/np000065f

1292
J . Nat. Prod. 2000, 63, 1292-1294
Efficien t, High ly En a n tioselective Syn th esis of Selin a -1,3,7(11)-tr ien -8-on e, a
Ma jor Com p on en t of th e Essen tia l Oil of Eu gen ia u n iflor a
Alice Kanazawa, Amaury Patin, and Andrew E. Greene*
Universite´ J oseph Fourier de Grenoble Chimie Recherche (LEDSS), 38041 Grenoble Cedex, France
Received February 9, 2000
The first synthesis of selina-1,3,7(11)-trien-8-one (1), a major constituent of the essential oil from the
leaves of Eugenia uniflora, has been accomplished, with excellent stereo- and regiocontrol, in eight steps
and in 12% overall yield from the known octalone derivative 2a .
Sch em e 1a
Eugenia uniflora L. (Myrtaceae) is a shrubby tree
indigenous to Brazil, but now found through exportation
in India, China, Sri Lanka, Egypt, Nigeria, and other
tropical and subtropical regions.1-3 The essential oil derived
from this plant has been used in folk medicine to treat
digestive disorders,4 while tea from the leaves has been
employed against fever and rheumatism;5 wine from the
cherry-like fruit also has been reported to possess medi-
cinial properties.6 Recently, it has been found that the
essential oil obtained from the leaves of E. uniflora exhibits
antimicrobial activity against the Gram-positive bacteria
Sarcina luteu and Mycobacterium phlei and antifungal
activity against Candida albicans and Trichophyton men-
tagrophytes.2
In 1988, Weyerstahl and co-workers1 isolated a major
constituent (17%) from the oxygenated sesquiterpene-rich
essential oil of Nigerian E. uniflora to which they assigned
by NMR the structure and relative stereochemistry shown
in 1. This new selinatrienone has since been found as the
major component in E. uniflora essential oil of Egyptian2
and Brazilian3 origins (20.3 and 48.5%, respectively). We
report herein an efficient, enantioselective approach to (-)-
selina-1,3,7(11)-trien-8-one (1) that establishes the struc-
ture and relative stereochemistry of the natural product.7
Dextrorotatory octalone 2a (Scheme 1), of known8 abso-
based on a second tosylhydrazone transformation, the
lute stereochemistry, was readily secured as previously
Shapiro reaction.12 Toward this end, the octalone derivative
3a was allylically oxidized with the Corey modified13
Collins’ reagent to provide enone 3b (60%), which was then
converted into its tosylhydrazone 3c in essentially quan-
titative yield. Under carefully optimized conditions, 3c was
decomposed with methyllithium in THF to produce the
hexalone derivative 4a (61%) with no detectable formation
of any isomeric diene.
Mild acid treatment of this acetal engendered keto diene
4b (90%), which was converted, albeit in only 10% yield,
into 1 through sequential treatment of the C-7 methoxy-
carbonyl derivative with sodium hydride, methyllithium,
and p-toluenesulfonic acid.14 A more satisfactory procedure
involved the use of ketene dithioacetal 5, easily prepared
in 68% yield from keto diene 4b by treatment with
described8,9 and then recrystallized to afford highly enan-
tioenriched starting material (g98% enantiomer excess).
This enone was next converted in quantitative yield into
its tosylhydrazone derivative 2b, which underwent double-
bond translocation with concomitant carbonyl reduction
under the “alkene walk” procedure10 to give, in a highly
stereoselective manner, the desired cis-fused octalone
derivative 3a (79% yield). Only 3% of the isomeric trans
product8b,11 was generated in this transformation.
Among the various possibilities examined for the intro-
duction of the remaining double bond, the most effective
in terms of yield and regioselectivity proved to be that
* To whom correspondence should be addressed. Tel.: (33) 4-76-51-46-
86. Fax: (33) 4-76-51-44-94. E-mail: Andrew.Greene@ujf-grenoble.fr.
10.1021/np000065f CCC: $19.00
© 2000 American Chemical Society and American Society of Pharmacognosy
Published on Web 08/02/2000

Notes
J ournal of Natural Products, 2000, Vol. 63, No. 9 1293
NMR (CDCl3, 50 MHz) δ 135.3, 120.1, 109.1, 64.2, 63.5, 46.0,
45.9, 34.0, 33.5, 28.7, 27.2, 26.0, 23.0, 22.5; CIMS m/z 223 (100),
161 (6), 126 (6.5), 108 (8), 99 (36); HREIMS m/z 222.1622 (calcd
for C14H22O2, 222.1620).
lithium hexamethyldisilazane (LHMDS), carbon disulfide,
and methyl iodide.15 In the presence of ethereal methyl-
lithium, 5 experienced clean double addition-elimination15
to produce (-)-selina-1,3,7(11)-trien-8-one (1) (69%), whose
1H and 13C NMR spectra were in excellent agreement with
those of natural 1.
Thus, the first synthesis of this novel selinatrienone has
been accomplished with high stereo- and regiocontrol, in
eight steps and in 12% overall yield from octalone 2a . The
synthesis, although indicating only probable absolute ster-
eochemistry,16 fully confirms the structure and relative
stereochemistry previously proposed for the natural prod-
uct.
(4′a R ,8′a R )-5′,8′a -Dim e t h yl-4′,4′a ,8′,8′a -t e t r a h yd r o-
1′H,3′H-sp ir o([1,3]d ioxola n e-2,2′-n a p h th a len )-7′-on e (3b).
To a suspension of chromic anhydride (800 mg, 8.00 mmol) in
CH2Cl2 (5.0 mL) at 0 °C was added 3,5-dimethylpyrazole
(DMP) (650 mg, 6.76 mmol). After being stirred for 0.5 h at
20 °C, the reaction mixture was cooled to 0 °C, and a solution
of olefin 3a (95 mg, 0.43 mmol) in CH2Cl2 (3.0 mL) was added.
After being stirred for an additional 1 h at 20 °C, the mixture
was poured into pentane-ether (1:1). The resulting mixture
was filtered through Celite, the filtrate concentrated under
reduced pressure and the residue purified by column chroma-
tography on Si gel (pretreated with 2.5% v/v of triethylamine)
with 30% ethyl acetate in cyclohexane to afford 61 mg (60%)
Exp er im en ta l Section
Gen er a l Exp er im en ta l P r oced u r es. Thin-layer chroma-
tography was performed on Merck 60F254 (0.2 mm) sheets,
which were visualized with molybdophosphoric acid in ethanol.
Merck 70-230 Si gel 60 was employed for column chromatog-
raphy. A Nicolet 400 spectrophotometer was used to record
IR spectra (neat or as Nujol film). Bruker AC 200 and AV 300
spectrometers were employed for the NMR spectra (CDCl3
of enone 3b:17 mp 70 °C; [R]20 -32.6° (c 1.0, CHCl3); IR νmax
D
1668, 1640, 1440, 1364, 1265, 1106, 1053, 954 cm-1; 1H NMR
(CDCl3, 300 MHz) δ 5.76 (1H, s), 3.94-3.82 (4H, m), 2.50 (2H,
AB, δa ) 3.16, δb ) 1.84, J ab ) 17.3 Hz), 1.92 (3H, d, J ) 1.4
Hz), 1.90-1.68 (3H, m), 1.64-1.44 (4H, m), 0.95 (3H, s); 13C
NMR (CDCl3, 75 MHz) δ 200.0, 163.2, 125.0, 108.1, 64.4, 63.6,
48.4, 45.7, 44.3, 37.1, 34.7, 28.5, 26.2, 23.3; CIMS m/z 237 (100),
135 (27), 99 (39); anal. C 71.21%, H 8.59%, calcd for C14H20O3,
C 71.16%, H 8.53%.
1
solutions, with residual CHCl3 for H NMR and CDCl3 for 13C
NMR as the references). Optical rotations were measured with
a Perkin-Elmer 241 polarimeter. Melting points were taken
on a Bu¨chi-Tottoli apparatus and are not corrected. Mass
spectra were obtained on an AEI MS-30 mass spectrometer
(70 eV, direct insert probe). Microanalyses were performed by
the Central Service of the CNRS.
The reaction mixture was generally poured into water, and
the separated aqueous phase was then thoroughly extracted
with the specified solvent. After being washed with 10%
aqueous HCl and/or NaHCO3 (if required), H2O, and saturated
aqueous NaCl, the combined organic phases were dried over
anhydrous Na2SO4 or MgSO4 and then filtered and concen-
trated under reduced pressure on a Bu¨chi Rotovapor to yield
the crude reaction product. Tetrahydrofuran and ether were
distilled from sodium-benzophenone, and CHCl3, CH2Cl2, and
HMPA were distilled from calcium hydride. All reactions were
carried out under an argon atmosphere.
(4′a R,8′a S)-5′,8′a -Dim eth yl-3′,4′,4′a ,8′a -tetr a h yd r o-1′H-
spir o([1,3]dioxolan e-2,2′-n aph th alen e) (4a). Tosylhydrazide
(66 mg, 0.35 mmol) was added to a solution of enone 3b (50
mg, 0.21 mmol) in THF (0.80 mL), and the mixture was
refluxed for 4 h. Additional tosylhydrazide (30 mg, 0.16 mmol)
was added, and reflux was continued for 1.75 h. The solvent
was then removed under reduced pressure, and the crude
mixture was chromatographed on Si gel with 30% ethyl acetate
in cyclohexane to give 85 mg (99%) of tosylhydrazone 3c (ca.
4:1 mixture of isomers) as a white solid: mp 118 °C (dec); [R]20
D
-42.1° (c 1.0, CHCl3); IR νmax 3210, 1638, 1600, 1448, 1402,
1
1326 cm-1; H NMR (CDCl3, 300 MHz, major isomer) δ 7.54
(4H, AB, δa ) 7.82, δb ) 7.26, J ab ) 8.2 Hz), 5.83 (1H, s), 3.95-
3.75 (4H, m), 2.81 (1H, d, J ) 17.0 Hz), 2.38 (3H, s), 1.78 (3H,
s), 1.95-1.35 (6H, m), 1.35-1.10 (3H, m), 0.85 (3H, s); 13C
NMR (CDCl3, 75 MHz, major isomer) δ 155.4, 148.1, 143.7,
135.6, 129.4, 127.9, 121.2, 108.2, 64.5, 63.6, 47.8, 45.7, 34.9,
30.7, 29.0, 26.8, 26.1, 22.8, 21.5; CIMS m/z 405 (100), 303 (9),
251 (21), 236 (30), 221 (19), 189 (19); anal. C 62.49%, H 7.09%,
N 6.55%, calcd for C21H28N2O4S, C 62.35%, H 6.98%, N 6.93%.
To a solution of tosylhydrazone 3c (500 mg, 1.24 mmol) in
THF (35 mL) at 0 °C was added a 1.6 M solution of methyl-
lithium (3.5 mL, 5.6 mmol) in ether. The reaction mixture was
stirred for 1.5 h at 0 °C and 1 h at 20 °C, after which it was
processed with ethyl acetate in the usual way (see general
experimental procedures) and the crude product was purified
by Si gel chromatography with 30% ethyl acetate in cyclohex-
(4′a R,8′a R)-5′,8′a -Dim eth yl-3′,4′,4′a ,7′,8′,8′a -h exa h yd r o-
1′H-sp ir o([1,3]d ioxola n e-2,2′-n a p h th a len e) (3a ). To a solu-
tion of octalone 2a 8,9 (73 mg, 0.31 mmol) in dry THF (1.1 mL)
was added tosylhydrazide (97 mg, 0.52 mmol), and the reaction
mixture was stirred under reflux for 3.5 h. The solvent was
then removed under reduced pressure, and the residue was
purified by Si gel chromatography with 30% ethyl acetate in
pentane to give 125 mg (100%) of tosylhydrazone 2b as a white
amorphous solid: mp 95-98 °C (dec); [R]20 +127° (c 0.94,
D
CHCl3); IR νmax 3423, 3225, 1706, 1653, 1600, 1340, 1174, 1095,
1
1037 cm-1; H NMR (CDCl3, 200 MHz) δ 7.56 (4H, AB, δa )
7.85, δb ) 7.27, J ab ) 8.2 Hz), 7.58-7.22 (1H, br s), 4.02-3.81
(4H, m), 2.70 (1H, dt, J ) 15.6, 4.0 Hz), 2.40 (3H, s), 2.57-
ane to afford 166 mg (61%) of diene 4a : [R]20 -240° (c 0.8,
D
CHCl3); IR νmax 3035, 1650, 1585, 1448, 1356, 1326, 1258, 1106,
1.85 (3H, m), 1.78 (3H, s), 1.75-1.17 (6H, m), 1.12 (3H, s); 13
C
1053 cm-1 1H NMR (CDCl3, 300 MHz) δ 5.72 (1H, dd, J )
;
NMR (CDCl3, 75 MHz) δ 155.1, 147.8, 143.6, 135.2, 129.2 (2×),
128.0 (2×), 124.8, 108.0, 64.4, 63.4, 48.0, 36.5, 35.6, 34.5, 24.6,
23.6, 21.4, 20.4, 12.4; CIMS m/z 405 (40), 251 (100), 236 (60),
221 (8), 189 (19), 174 (7.3); HREIMS m/z 404.1771 (calcd for
9.3, 5.2 Hz, H-2), 5.57-5.49 (1H, m, H-3), 5.28 (1H, d, J ) 9.3
Hz, H-1), 4.01-3.83 (4H, m, OCH2CH2O), 1.77 (3H, s, H-15),
1.80-1.37 (7H, m, H-5, H-6, H-7, H-9), 0.91 (3H, s, H-14); 13
C
NMR (CDCl3, 75 MHz) δ 138.3 (C-4), 133.7 (C-1), 121.1 (C-3),
116.9 (C-2), 108.7 (C-8), 64.6 (OCH2), 63.7 (OCH2), 46.7 (C-5),
45.6 (C-9), 36.8 (C-10), 34.7 (C-7), 26.8 (C-14), 24.0 (C-6), 22.3
(C-15); CIMS m/z 221(100), 171 (40), 158 (12), 126 (21);
HRFABMS m/z 220.1480 (calcd for C14H20O2, 220.1463).
(4aR,8aS)-5,8a-Dim eth yl-3,4,4a,8a-tetr ah ydr o-1H-n aph -
th a len -2-on e (4b). A solution of diene 4a (250 mg, 1.13 mmol)
in 85% acetic acid (8.5 mL) was heated at 100 °C for 0.5 h.
The solvent was removed under reduced pressure, and the
product was processed with ether in the normal manner (see
general experimental procedures) and then filtered rapidly
through a short Si gel column to afford 181 mg (90%) of keto
diene 4b: [R]20D -197° (c 0.8, CHCl3); IR νmax 3028, 1718, 1645,
1584, 1443, 1363, 1299, 1238 cm-1; 1H NMR (CDCl3, 300 MHz)
δ 5.76 (1H, dd, J ) 9.3, 5.2 Hz), 5.64-5.54 (1H, m), 5.26 (1H,
d, J ) 9.3 Hz), 2.33-2.18 (4H, m), 2.05-1.93 (2H, m), 1.80
C
21H28N2O4S, 404.1770).
Catecholborane (0.500 mL, 0.562 g, 4.69 mmol) was added
to a solution of tosylhydrazone 2b (1.06 g, 2.62 mmol) in freshly
distilled CHCl3 (26 mL) at 0 °C, and the reaction mixture was
stirred at 0 °C for 0.5 h. Sodium acetate trihydrate (4.34 g,
31.9 mmol) was then added, and the mixture was heated at
65 °C for 0.75 h. After being cooled to 20 °C, the mixture was
treated with saturated aqueous NaHCO3 solution, and the
product was isolated with ether in the usual way (see general
experimental procedures) and purified by Si gel chromatog-
raphy with 20% ethyl acetate in pentane to yield 0.460 g (79%)
of olefin 3a : [R]20 -27° (c 0.88, CHCl3); IR νmax 3040, 1448,
D
1356, 1113, 1091 cm-1; 1H NMR (CDCl3, 200 MHz) δ 5.26 (1H,
br s), 4.22-3.80 (4H, m), 2.04-1.77 (4H, m), 1.72-1.55 (5H,
m), 1.52-1.30 (4H, m), 1.07-0.95 (1H, m), 0.89 (3H, s); 13C

1294 J ournal of Natural Products, 2000, Vol. 63, No. 9
Notes
(3H, s), 1.72-1.53 (1H, m), 0.99 (3H, s); 13C NMR (CDCl3, 75
MHz) δ 210.6, 139.0, 130.8, 123.6, 117.7, 52.2, 45.9, 41.1, 40.9,
26.5, 26.4, 22.2; CIMS m/z 194 (46), 177 (38), 159 (11), 119
(100), 105 (5); HREIMS m/z 176.1203 (calcd for C12H16O,
176.1201).
(C-3), 118.0 (C-2), 53.4 (C-9), 46.1 (C-5), 38.4 (C-10), 29.8 (C-
6), 26.7 (C-14), 22.6 (C-15), 22.2 (C-12 or C-13), 21.7 (C-12 or
C-13); EIMS m/z 216 (5), 149 (10), 110 (19), 97 (30), 69 (29),
57 (78), 43 (100); HREIMS m/z 216.1514 (calcd for C15H20O,
216.1514).
(4a R,8a S)-(Bis-m et h ylsu lfa n yl-m et h ylen e)-d im et h yl-
3,4,4a ,8a -tetr a h yd r o-1H-n a p h th a len -2-on e (5). To a stirred
solution of keto diene 4b (48.5 mg, 0.28 mmol) in THF (1.00
mL) and HMPA (0.050 mL) at -78 °C was added a 1.0 M
solution of LHMDS in THF (0.30 mL, 0.30 mmol) and, after
0.5 h, carbon disulfide (0.020 mL, 25 mg, 0.33 mmol). The
reaction mixture was allowed to warm to 0 °C over 2 h, and
then cooled to -78 °C and treated with an additional 0.30 mL
(0.30 mmol) of the 1.0 M LHMDS solution. After being stirred
at -78 °C for 0.5 h, the solution was treated with methyl iodide
(0.090 mL, 205 mg, 1.44 mmol), allowed to warm to 20 °C over
1 h, and then stirred at this temperature for 1 h. The crude
product was isolated with ether in the usual manner (see
general experimental procedures) and purified by Si gel
chromatography with 10% ether in pentane to afford 52.5 mg
Ack n ow led gm en t. We thank Prof. Y. Yalle´e, Prof. E.
Barreiro, and Dr. E. Muri for their interest in our work and
Prof. P. Weyerstahl and Prof. H. Marschall-Weyerstahl for
spectra and useful information. In addition, Prof. A. A.
Craveiro is thanked for a helpful exchange. A fellowship award
from MRES to A.P. and financial support from the CNRS
(UMR 5616) and the Universite´ J oseph Fourier are gratefully
acknowledged.
Refer en ces a n d Notes
(1) Weyerstahl, P.; Marschall-Weyerstahl, H.; Christiansen, C.; Ogun-
timein, B. O.; Adeoye, A. O. Planta Med. 1988, 54, 546-549.
(2) El-Shabrawy, A. O. Bull. Fac. Pharm. Cairo Univ. 1995, 33, 17-21.
(3) de Morais, S. M.; Craveiro, A. A.; Machado, M. I. L.; Alencar, J . W.;
Matos, F. J . A. J . Essent. Oil Res. 1996, 8, 449-451. The indicated
trans stereochemistry is incorrect and should be cis (A. A. Craveiro,
private communication).
(4) (a) Adebajo, A. C. Fitoterapia 1989, 60, 451-455. Fadeyi, M. O.;
Akpan, U. E. Phytother Res. 1989, 3, 154-155. (b) Gildemeister, E.;
Hoffmann, F. Die A¨ therischen O¨ le; Akademie Verlag: Berlin, 1961;
Vol. 18, pp 118, 121.
(68%) of dithioacetal 5: [R]20 -197° (c 1.1, CHCl3); IR νmax
D
3026, 1691, 1669, 1500, 1433, 1249 cm-1; 1H NMR (CDCl3, 300
MHz) δ 5.74 (1H, dd, J ) 9.4, 5.3 Hz), 5.64-5.59 (1H, m), 5.30
(1H, d, J ) 9.4 Hz), 2.85 (2H, AB of ABX, δa ) 3.18, δb ) 2.53,
J ab ) 15.2 Hz, J ax ) 4.9 Hz, J bx ) 10.4 Hz), 2.43 (2H, AB, δa
) 2.57, δb ) 2.28, J ab ) 14.7 Hz), 2.31 (6H, s), 2.10-1.97 (1H,
X of ABX, J ax ) 4.9 Hz, J bx ) 10.4 Hz), 1.84 (3H, s), 1.03 (3H,
s); 13C NMR (CDCl3, 75 MHz) δ 199.7, 143.0, 140.0, 137.8,
131.5, 123.1, 118.1, 52.7, 46.3, 38.4, 33.3, 26.6, 22.2, 18.0 (2×);
CIMS m/z 281 (100), 175 (19), 159 (17); HRFABMS m/z
280.0961 (calcd for C15H20OS2, 280.0956).
(5) Neves, L. D. J .; Donato, A. M. Bradea 1989, 5, 275-284.
(6) Popenol, E. Manual of Tropical and Subtropical Fruits; Ann Arbor,
University Microfilms: 1934 (reprint 1970); p 285.
(7) Homoannular eudesmadienes are rather uncommon. For other
examples, see: Dictionary of Terpenoids; Connolly, J . D., Hill, R. A.,
Eds.; Chapman and Hall: New York, 1991; Vol. 1, pp 317-391.
(8) (a) J abin, I.; Revial, G.; Melloul, K.; Pfau, M. Tetrahedron: Asym-
metry, 1997, 8, 1101-1109. (b) Muri, E.; Kanazawa, A.; Barreiro, E.;
Greene, A. E. J . Chem. Soc., Perkin Trans. 1 2000, 731-735. The
antipode used in the present work was arbitrarily chosen.
(9) Sequeira, L. C., Ph.D. Thesis, Universidade Federal do Rio de J aneiro,
1996.
(4a R,8a S)-3-Isop r op ylid en e-5,8a -d im et h yl-3,4,4a ,8a -
tetr a h yd r o-1H-n a p h th a len -2-on e (1). To a stirred suspen-
sion of copper iodide (40 mg, 0.21 mmol) in anhydrous ether
(1.5 mL) at 0 °C was added a 1.6 M solution of methyllithium
in ether (0.26 mL, 0.42 mmol). The solution was cooled to -78
°C, and treated dropwise with a solution of dithioacetal 5 (30
mg, 0.11 mmol) in ether (1.5 mL). The reaction mixture was
stirred for 0.5 h at -78 °C and then quenched with CH3OH.
The reaction mixture was then processed with ether in the
normal manner (see general experimental procedures), and the
crude product was purified by Si gel column chromatography
(10) (a) Kabalka, G. W.; Yang, D. T. C.; Baker, J . D., J r. J . Org. Chem.
1976, 41, 574-575. (b) See also: Hutchins, R. O.; Kacher, M.; Rua,
L. J . Org. Chem. 1975, 40, 923-926.
(11) Goldsmith, D. J .; Sakano, I. J . Org. Chem. 1976, 41, 2095-2098.
(12) For a review of the Shapiro reaction, see: Shapiro, R. H. Org. React.
1976, 23, 405-507.
(13) (a) Corey, E. J .; Fleet, G. W. J . Tetrahedron Lett. 1973, 4499-4501.
(b) Salmond, W. G.; Barta, M. A.; Havens, J . L. J . Org. Chem. 1978,
43, 2057-2059.
(14) (a) Coates, R. M.; Shaw, J . E. J . Am. Chem. Soc. 1970, 92, 5657-
5664. (b) Banerjee, A. K.; Laya-Mimo, M. Synth. Commun. 1995, 25,
1035-1044.
with 10% ether in pentane to yield 16 mg (69%) of 1: [R]20
D
-258° (c 1.0, CHCl3); IR νmax 3026, 1687, 1620, 1444, 1373,
1293, 1266 cm-1; 1H NMR (CDCl3, 300 MHz) δ 5.75 (1H, dd, J
) 9.5, 4.8 Hz, H-2), 5.64-5.58 (1H, m, H-3), 5.30 (1H, d, J )
(15) (a) Corey, E. J .; Chen, R. H. K. Tetrahedron Lett. 1973, 3817-3820.
(b) Dieter, R. K. J . Org. Chem. 1981, 46, 5031-5033.
(16) The reported1 optical rotation of the natural material is considerably
different from that of our synthetic substance (-6 vs. -258°). This
may be due to the small amount of the natural material that was
available and/or the questionable polarimeter readings at the time
of the isolation (private communication, P. Weyerstahl).
(17) HPLC (Chiracel OD-H, 5 µm, hexane-2-propanol (7:3), 0.5 cm3/min,
tR 11.32 min (versus 12.90 min)) indicated an enantiomeric excess
for enone 3b of g98%.
9.5 Hz, H-1), 2.45 (2H, AB of ABX, δa ) 2.63, δb ) 2.26, J ab
15.0 Hz, J ax ) 4.5 Hz, J bx ) 10.1 Hz, H-6), 2.36 (2H, AB, δa )
2.45, δb ) 2.28, J ab ) 14.6 Hz, H-9), 1.98 (1H, X of ABX, J ax
)
)
4.5 Hz, J bx ) 10.1 Hz, H-5), 1.92 (3H, d, J ) 1.8 Hz, H-12 or
H-13), 1.83 (3H, s, H-15), 1.76 (3H, d, J ) 1.0 Hz, H-12 or
H-13), 1.02 (3H, s, H-14); 13C NMR (CDCl3, 75 MHz) δ 203.8
(C-8), 139.5 (C-11), 138.3 (C-4), 132.6 (C-7), 131.7 (C-1), 123.0
NP000065F