Identification and synthesis of homoterpenoids emitted from elm leaves after elicitation by beetle eggs

Article abstract of DOI:10.1016/S0040-4020(01)01149-8

Egg deposition of the elm leaf beetle Xanthogaleruca luteola on the leaves of the field elm causes the emission of volatiles attracting the parasitoid Oomyzus gallerucae. The present study describes the identification and synthesis of the homoterpenoids:

Full text of DOI:10.1016/S0040-4020(01)01149-8

TETRAHEDRON
Pergamon
Tetrahedron 58 (2002) 315±319
Identi®cation and synthesis of homoterpenoids emitted from elm
leaves after elicitation by beetle eggs
Robert Wegener and Stefan Schulzp
È È
Institut fur Organische Chemie, Technische Universitat Braunschweig, Hagenring 30, D-38106 Braunschweig, Germany
Received 4 July 2001; revised 9 October 2001; accepted 9 November 2001
AbstractÐEgg deposition of the elm leaf beetle Xanthogaleruca luteola on the leaves of the ®eld elm causes the emission of volatiles
attracting the parasitoid Oomyzus gallerucae. The present study describes the identi®cation and synthesis of the homoterpenoids: (E)-2,6-
dimethyl-6,8-nonadien-4-one, (E)-2,6-dimethyl-2,6,8-nonatrien-4-one, and (R,E)-2,3-epoxy-2,6-dimethyl-6,8-nonadiene. These compounds
may be involved in attracting the egg parasitoid. q 2002 Elsevier Science Ltd. All rights reserved.
1. Introduction
2. Results and discussion
The ®eld elm, Ulmus minor, is the food plant of the elm leaf
beetle, Xanthogaleruca luteola (Coleoptera, Chryso-
melidae), which is a known pest species. The beetle deposits
its eggs on the elm leaves which causes the emission of
volatiles guiding a parasitoid wasp, Oomyzus gallerucae
(Hymenoptera, Eulophidae), to these leaves.1 The
parasitoid lays its eggs inside the beetle eggs, which is
bene®cial for the elm. Host plants emitting volatiles in
response to an external cue is a known defense mechanism.2
The gas chromatography±mass spectrometry analysis of
extracts obtained by headspace sampling with a modi®ed
closed-loop-stripping apparatus4 of elm leaves with beetle
eggs revealed 1 as the major homoterpene,3 accompanied by
three minor oxygenated analogues. Isolation of these
components was not possible because of their low concen-
tration in the headspace samples. The mass spectrum of
compound 2 (Fig. 1), is similar to the spectrum of the
related monoterpene epoxyocimene.5 Epoxidation of 1
with 3-chloro-perbenzoic acid (MCPBA)6 proved that this
compound was the epoxyhomoterpene 2, which has
previously been reported as a constituent of several orchid
and cactus scents (e.g. Selenicereus hamatus).7 However,
the stereochemistry of 2 has not been established previously
and no mass spectrum has been published. To elucidate the
enantiomeric composition of natural 2, we synthesized this
epoxide via an asymmetric dihydroxylation route
(Scheme 2). Reaction of 18 with AD-mix-b resulted mainly
in the diol 5. The dihydroxylation mainly takes place at the
isolated trisubstituted double bond, as has been reported for
the related monoterpene ocimene.9 The mesylate 6 was
formed by treatment with 1 equiv. CH3SO2Cl and triethyl-
amine, but was not isolated. However, nuclear magnetic
The homoterpene (E)-4,8-dimethyl-1,3,7-nonatriene
1
(DMNT, Scheme 1) is a typical example of such an
induced volatile; it is produced in response to herbivory
by a variety of plants (e.g. Dicke2). We recently
reported that terpenes are the major volatiles induced in
the elm tree by the egg deposition of X. luteola, and
that sesquiterpenes released after treatment of leaves
with the plant hormone jasmonic acid attract the
parasitoid.3 Nevertheless, the volatile pro®les induced by
jasmonic acid or the eggs are not identical, and, besides
sesquiterpenes, monoterpenes and homoterpenes are
induced as well. In the present paper, we report on the
identi®cation and synthesis of new derivatives of homo-
terpenoids.
Scheme 1.
Keywords: homoterpenes; induced volatiles; Sharpless dihydroxylation; terpenes; (E)-4,8-dimethyl-1,3,7-nonatriene; elm; leaf beetle; parasitoid; Ulmus
minor; elm leaf beetle; Oomyzus gallerucae.
Corresponding author. Tel.: 149-531-391-7353; fax: 149-531-391-5272; e-mail: stefan.schulz@tu-bs.de
p
0040±4020/02/$ - see front matter q 2002 Elsevier Science Ltd. All rights reserved.
PII: S0040-4020(01)01149-8

316
R. Wegener, S. Schulz / Tetrahedron 58 /2002) 315±319
Figure 1. Mass spectra of (E)-2,3-epoxy-2,6-dimethyl-6,8-nonadiene (2) and (E)-2,6-dimethyl-2,6,8-nonatrien-4-one (4).
Scheme 2. Reagents and conditions: (a) AD-Mix-b, CH3SO2NH2, tert-BuOH, H2O (1:1), 08C, 65%; (b) CH3SO2Cl, Et3N , CHCl2, room temperature;
2
(c) K2CO3, MeOH, room temperature, 33% (2 steps); (d) 1: O3, 2: (CH3)2S, 53%; (e) acetone, camphorsulfonic acid, room temperature, 70%.
resonance spectra con®rmed that mesylation took place at
the secondary alcohol. Treatment of 6 with a mild base
resulted in enantiomerically pure (S)-epoxide 2. Compari-
son of natural, rac-, and (S)-2 by GC using a chiral cyclo-
dextrine phase showed that 2 from elm leaves was solely
(R)-con®gured. The assignment of enantiomers obtained in
the asymmetric dihydroxylation was based on the Sharpless
model.10 To test this model, the double bonds of 5 were
cleaved by ozonolysis, resulting in the known ketone 7,
whose stereochemisty was con®rmed by NMR.11 We
synthesized 7 by the reported procedure11 and compared it
with the ozonolysis product after transforming both samples
to the acetonide 8 by enantioselective GC. These com-
parisons showed that the con®guration at C-3 was congruent
with the Sharpless model and matched the stereoselectivity
in the dihydroxylation of ocimene.9
readily be identi®ed as the ketone 3 (cyclanthone) by its
MS6 and comparison with an authentic synthetic standard.
This compound was recently identi®ed in the ¯ower scent of
Cyclanthus bipartitus (Cyclanthaceae).6
The last unknown compound showed a very simple mass
spectrum (Fig. 1) with a molecular ion at m/z 164, 2 amu
less than 3 and predominant ion fragments at m/z 55 and 83.
Based on these data we proposed 4 (Scheme 1) as the struc-
ture for this previously uncharacterized homoterpenoid.
Both ketones 3 and 4 were synthesized by a Corey±Seebach
approach at low temperatures (Scheme 3). Addition of
(E)-5-bromo-4-methylpenta-1,3-diene12 at 2788C to the
deprotonated dithianes 1113 and 1214 obtained from
3-methylbutanal 9 and 3-methyl-2-butenal 10, respectively,
resulted in formation of 13 and 14. Since 13 and 14 could
not be separated from 11 and 12 by ¯ash chromatography,
the deprotection of the dithianes was performed with these
The second minor component of the elm samples could
Scheme 3. Reagents and conditions: (a) HS(CH2)3SH, BF3´(CH2CH3)2O, 08C, 92% (11), 97% (12); (b) 1: BuLi, THF, 2408C, 2: (E)-5-bromo-4-methylpenta-
1,3-diene, 2808C; (c) AgNO3, EtOH, H2O (1:1), 17% (2 steps); (d) H5IO6, THF, room temperature, 30% (2 steps).

R. Wegener, S. Schulz / Tetrahedron 58 /2002) 315±319
317
mixtures of mono- and dialkylated dithianes. While 14 was
deprotected with H5IO6, this reaction failed with 13, for
which AgNO3 in ethanol proved effective. Both compounds
were identical with the respective elm tree volatiles. Our
synthesis of 3 and 4 via the dithianes is quick and simple.
Previously, 3 was synthesized by a longer route using a
Reformatski coupling of 3-methyl-2-butenal and ethyl
4-bromocrotonate as a key step.6
on silica-coated plates (Macherey-Nagel, Polygram SIL G/
UV254). Column chromatography was performed on Merck
silica gel (particle size 0.063±0.2 mm ASTM) unless other-
wise stated. Non-aqueous reactions were conducted in
¯ame-dried glassware and dry nitrogen atmosphere. Dry
tetrahydrofurane was distilled from potassium with benzo-
phenone, dry dichloromethane from CaH2, and dry diethyl
ether from LiAlH4 under nitrogen atmosphere. Solvents
were distilled before use. All other commercially available
reagents were used as received.
In the present study we have con®rmed the presence of
compounds 1, (R)-2, 3, and 4 in the induced volatiles of
the elm tree. Their concentration is highest in leaves on
which the parasitoid laid its eggs, while all other leaf
types (undamaged leaves, arti®cially damaged leaves,
leaves on which the adult beetle was feeding) emit lower
amounts. Cyclanthone 3 is also emitted in similar amounts
during feeding (Wegener, Schulz, Hilker, Meiners,
Hermenau, unpublished results). The synthetic products of
1, (R)-2, 3, and 4 enable electrophysiological studies con-
sidering their function in the tritrophic interactions between
the elm tree, its herbivore, and the parasitoid.
3.1.1. )1)-)R,E)-2,6-Dimethyl-6,8-nonadien-2,3-diol )5).
Methanesulfonamide (0.62 g, 6.5 mmol) was added to a
cooled solution of AD-mix-b (9.31 g) in 75 ml water and
tert-BuOH (v/v 1:1). The mixture was stirred at 08C for 84 h
after adding 1.0 g (6.7 mmol) of (E)-4,8-dimethyl-1,3,7-
nonatriene (1).8 Then Na2SO3 (10 g) was added and the
mixture warmed to room temperature. The aqueous phase
was extracted four times with dichloromethane. The
combined extracts were dried (MgSO4) and the solvent
removed under reduced pressure. Finally, column chroma-
tography (petroleum ether/diethyl ether, 1:1) yielded 0.8 g
1
of 5 (65%). H NMR (CDCl3, 400 MHz) dˆ6.57 (dt, H,
Jˆ16.8, 10.6 Hz, H8), 5.91 (d, H, Jˆ10.9 Hz, H7), 5.11
(dd, H, Jˆ16.8, 1.8 Hz, H9a), 5.00 (dd, H, Jˆ10.2,
1.5 Hz, H9b), 3.35 (dd, H, Jˆ10.4, 2.0 Hz, H3), 2.0±2.4
(m, 2H, H5), 1.4±1.7 (m, 2H, H4), 1.78 (s, 3H, C6-CH3),
1.21 (s, 3H, C2-CH3), 1.16 (s, 3H, C2-CH3). 13C N MR
(CDCl3, 100 MHz) dˆ139.0 (C6), 133.2 (C8), 125.9 (C7),
115.0 (C9), 78.1 (C3), 73.1 (C2), 36.8 (C5), 29.6 (C4), 26.4
(C2-CH3), 23.2 (C2-CH3), 16.5 (C6-CH3). EIMS m/z (%)
184 (1, M1), 167 (2), 166 (15), 123 (8), 108 (3), 95 (32), 94
(35), 93 (21), 82 (32), 81 (30), 72 (16), 71 (27), 67 (31), 59
3. Experimental
3.1. General methods
Headspace samples. Headspace samples were taken 72 h
after starting the induction by closed loop analysis. Using
a modi®ed closed-loop-stripping apparatus,4 samples were
taken 6 h from elm twigs with 10±20 leaves, which carried
15±20 egg masses (i.e. about 1 egg mass per leaf). The
charcoal ®lters (1 mg) used as traps were extracted with
approximately 20 ml dichloromethane.
(100), 53 (13), 43 (28). [a]22 ˆ117.8 (cˆ0.041, CH2Cl2).
D
HRMS, calcd for C11H20O2 184.1463, found 184.1467.
Analysis. Samples were analyzed by gas chromatography±
mass spectrometry using a Hewlett Packard GC 6890 MSD
5973 with a split/splitless inlet, equipped with a 30 m
HP5MS capillary column (idˆ0.25 mm, ®lm thickness
ˆ0.25 mm). The oven temperature was 508C (for 5 min),
then 58C/min to 3008C. Helium ¯ow rate was set at
1 ml/min in constant ¯ow mode. The mass spectrometer
operated at 70 eV EI ionization mode. Enantiomeric
separations were performed on a ThermoQuest 8000 Top
GC with a ¯ame ionization detector, a 15 m capillary
column (idˆ0.25 mm) coated with heptakis(6-O-TBDMS-
2,3-di-O-acetyl)-b-cyclodextrine (60% OV1701, w/w),15
and hydrogen as carrier gas.
3.1.2. )1)-)S,E)-2,3-Epoxy-2,6-dimethyl-6,8-nonadiene
)S-)2)). Triethylamine (0.09 ml) followed by methane-
sulfonyl chloride (0.037 ml) were added to a cool solution
(08C) of 5 (100 mg, 0.54 mmol) in 1.4 ml dichloromethane.
This solution was stirred during 3 h at room temperature.
After adding 0.2 ml diethyl ether, the solution was ®ltered
through celite and silica and the solvent was removed by
rotary evaporation resulting in 6. NMR showed that the
secondary mesylate had been formed almost exclusively
and 6 was used without further puri®cation. 1H N MR
(CD2Cl2, 400 MHz) dˆ6.58 (dt, H, Jˆ16.6, 10.9 Hz, H8),
5.91 (d, H, Jˆ10.9 Hz, H7), 5.11 (dd, H, Jˆ16.6, 1.6 Hz,
H9a), 5.00 (dd, H, Jˆ10.9, 1.6 Hz, H9b), 4.52 (dd, H,
Jˆ9.5, 2.8 Hz, H3), 3.11 (s, 3H, SO2CH3), 2.05±2.35 (m,
2H, H5), 1.65±1.8 (m, 2H, H4), 1.77 (s, 3H, CH3), 1.24 (s,
3H, CH3), 1.23 (s, 3H, CH3). 13C NMR (CD2Cl2, 100 MHz)
dˆ138.3 (C6), 133.5 (C8), 126.4 (C7), 115.3 (C9), 90.3
(C3), 72.5 (C2), 39.0 (SO2CH3), 36.4 (C5), 29.4 (C4),
27.0 (CH3), 23.7 (CH3), 16.7 (CH3). The crude mesylate
was stirred with 0.146 g K2CO3 in 1.6 ml methanol for
30 min. Most of the methanol was removed by rotary
evaporation, 10 ml water was added before the epoxide
was extracted four times with dichloromethane. The
combined organic extracts were dried (MgSO4), and the
solvent was removed. After column chromatography on
silica (petroleum ether/diethyl ether, 9:1) 30 mg of (S)-2
was obtained (33% for 2 steps). 1H NMR (CDCl3,
Synthesis. Optical rotations were measured on a Dr.
Kernchen Propol digital automatic polarimeter. Proton
nuclear magnetic resonance (1H NMR) spectra were
recorded on a Bruker AM-400 (400 MHz). Chemical shifts
are reported in ppm from tetramethylsilane (dˆ0.00 ppm)
as internal standard. Data are reported as follows:
chemical shift, integration, multiplicity (sˆsinglet, dˆ
doublet, tˆtriplet, qˆquartet, brˆbroadened, mˆmultiplet),
coupling constant(s), and assignment. Carbon nuclear
magnetic resonance (13C NMR) spectra were recorded on
an AM-400 (100 MHz) spectrometer. Chemical shifts are
reported in ppm from tetramethylsilane using the solvent
resonance as an internal standard (CDCl3: dˆ77.0 ppm).
Reactions were monitored by thin layer chromatography

318
R. Wegener, S. Schulz / Tetrahedron 58 /2002) 315±319
400 MHz) dˆ6.57 (dt, H, Jˆ16.7, 10.6 Hz, H8), 5.89 (d, H,
Jˆ10.6 Hz, H7), 5.11 (dd, H, Jˆ16.7, 1.6 Hz, H9a), 5.01
(dd, H, Jˆ10.5, 1.6 Hz, H9b), 2.72 (t, H, Jˆ6.2 Hz, H3),
2.12±2.35 (m, 2H, H5), 1.78 (s, 3H, C6-CH3), 1.61±1.71
(m, 2H, H4), 1.30 (s, 3H, C2-CH3), 1.26 (s, 3H, C2-CH3).
13C NMR (CDCl3, 100 MHz) dˆ138.3 (C6), 133.2 (C8),
125.9 (C7), 115.1 (C9), 64.0 (C3), 58.4 (C2), 36.4 (C5),
27.3 (C4), 24.8 (C2-CH3), 18.7 (C2-CH3), 16.6 (C6-CH3).
EIMS m/z (%) 166 (2, M1), 151 (2), 148 (3), 123 (14), 95
(39), 94 (22), 93 (49), 85 (40), 81 (53), 79 (100), 71 (59), 59
3.1.5.
propyl)-1,3-dithiane )13) and )E)-2-)2-methyl-2,4-penta-
dienyl)-2-)2-methyl-1-propenyl)-1,3-dithiane )14).
)E)-2-)2-Methyl-2,4-pentadienyl)-2-)2-methyl-
A
solution of 11 (3.25 mmol) in 20 ml dry THF was cooled
to 2408C and 3.2 mmol butyllithium (2.0 ml of 1.6 M
solution in hexane) was added. The mixture was stirred
for 3 h. After cooling to 2808C, 0.52 g (3.25 mmol)
(E)-5-bromo-4-methylpenta-1,3-diene12 was slowly added.
At this temperature, the mixture was stirred for an
additional 4 h before it was poured into 50 ml water. After
extraction with diethyl ether, the combined organic extracts
were dried (MgSO4) and the solvent evaporated. Chromato-
graphy on silica (petroleum ether/diethyl ether, 40:1)
yielded 545 mg of the dialkylated and monoalkylated
dithianes.
(65), 43 (52), 41 (53). [a]22 ˆ117.8 (cˆ0.045, diethyl
D
ether). The enantiomeric excess was determined by GC on
a 15 m fused silica column coated with heptakis(6-O-
TBDMS-2,3-di-O-acetyl)-b-cyclodextrine (60% OV1701,
w/w). The GC oven was 508C for 5 min, then 38C/min to
1808C. The retention times were (S)-2: 22.4 min and (R)-2:
22.9 min. No (R)-enantiomer was detected, ee.99%.
HRMS, calcd for C11H18O 166.1358, found 166.1354.
1
13: H NMR (CDCl3, 400 MHz) dˆ6.55 (dt, H, Jˆ16.8,
10.6 Hz, H40), 5.94 (d, H, Jˆ10.6 Hz, H30), 5.16 (d, H,
Jˆ16.6 Hz, H50a), 5.05 (d, H, Jˆ10.2 Hz, H50b), 2.8±3.0
(m, 4H, H4, H6), 2.74 (s, 2H, H10), 1.8±2.0 (m, 5H, H5,
H100, H200), 1.95 (s, 3H, C20-CH3), 1.02 (d, 6H, Jˆ6.8 Hz,
3.1.3. Ozonolysis of 5. A solution of 5 (0.093 g, 0.50 mmol)
in 5 ml dry dichloromethane was cooled to 2788C. At this
temperature, ozone was bubbled through the solution for
2 h. After adding 0.5 ml dimethyl sul®de, the solution was
warmed to room temperature. A mixture of the ketone
(0.043 g of 7 (53%)) and two hemiacetals was obtained by
chromatography on silica (petroleum ether/diethyl ether,
1:1). For authentication, acetonide 8 was synthesized from
7 according to Brimble et al.11 Its spectral data were found
to be as reported by Brimble et al.11 The ee was determined
by GC on a 15 m fused silica column coated with hep-
takis(6-O-TBDMS-2,3-di-O-acetyl)-b-cyclodextrine (60%
OV1701, w/w). The GC oven temperature was set at
758C. The retention times were (R)-8: 20.4 min and (S)-8:
21.3 min. No (R)-enantiomer was detected in the synthesis
of (S)-8, ee.99%.
13
H300). C NMR (CDCl3, 100 MHz) dˆ134.3 (C20), 132.6
(C40), 131.0 (C30), 115.7 (C50), 53.7 (C2), 49.3 (C10), 47.5
(C100), 30.1 (C4,C6), 26.2 (C5), 24.8 (C200), 21.9 (C200-
(CH3)2), 19.1 (C20-CH3). EIMS m/z (%) 256 (1, M1), 199
(1), 177 (11), 176 (12), 175 (100), 133 (21), 125 (4), 119
(19), 91 (6), 79 (5), 59 (5), 43 (5). Using the procedure
described above, 3.53 mmol dithiane 12 gave 880 mg
crude 14.
1
14: H NMR (CDCl3, 400 MHz) dˆ6.56 (dt, H, Jˆ16.7,
10.6 Hz, H40), 5.97 (d, H, Jˆ10.7 Hz, H30), 5.52 (m, H,
H100), 5.14 (dd, H, Jˆ16.9, 1.8 Hz, H50a), 5.04 (dd, H,
Jˆ10.2, 1.7 Hz, H50b), 2.75±2.99 (m, 4H, H4, H6), 2.82
(s, 2H, H10), 1.9±2.1 (m, 2H, H5), 1.95 (d, 3H, Jˆ1.4 Hz,
C200-CH3), 1.86 (s, 3H, C20-CH3), 1.77 (d, 3H, Jˆ1.3 Hz,
13
3.1.4. 2-)2-Methylpropyl)-1,3-dithiane )11) and 2-)2-
methyl-1-propenyl)-1,3-dithiane )12). The respective
aldehyde (26.7 mmol, 3-methylbutanal and 3-methyl-2-
butenal) was dissolved in 1.5 ml dry diethyl ether. 1,3-
Propanedithiol (3.04 g, 28.1 mmol) was added at 08C.
After stirring for 10 min, 1.7 ml of BF3´O(CH2CH3)2 was
added very carefully. The solution was stirred for an
additional 10 min at 08C. The solvent was evaporated
under reduced pressure to get the dithianes.
C200-CH3). C NMR (CDCl3, 100 MHz) dˆ138.4 (C200),
134.2 (C20), 132.8 (C40), 130.9 (C30), 127.9 (C100), 115.2
(C50), 53.1 (C2), 50.6 (C10), 27.8 (C4, C6), 27.6 (C200-Me),
25.3 (C5), 19.2 (C200-Me), 18.4 (C20-Me). EIMS m/z (%)
254 (1, M1), 179 (3), 175 (9), 174 (10), 173 (100), 133 (1),
117 (1), 111 (1), 105 (4), 99 (19), 91 (5), 65 (4), 55 (3), 45
(2), 41 (7), 39 (3).
3.1.6. )E)-2,6-Dimethyl-6,8-nonadien-4-one )3). A solu-
tion of 0.5 g AgNO3 in 2.5 ml water was added to a stirred
solution of 0.148 g of crude 13 in 25 ml ethanol. The
mixture was stirred for 3 h at 408C before it was poured
into 50 ml water. The solution was extracted three times
with diethyl ether, the extracts were combined, washed
with brine, dried with MgSO4, and ®nally the solvent was
removed under reduced pressure. Chromatography on
ALOX Ndeactivated with 10% water, using petroleum
ether as eluent, gave 25 mg pure 3 (17% over two steps).
1H NMR (C6D6, 400 MHz) dˆ6.48 (dt, H, Jˆ16.6, 10.6 Hz,
H8), 5.81 (d, H, Jˆ10.7 Hz, H7), 5.10 (d, H, Jˆ16.6 Hz,
H9a), 4.99 (d, H, Jˆ10.5 Hz, H9b), 2.72 (s, 2H, H5),
2.2±2.0 (m, H, H2), 1.92 (d, 2H, Jˆ7.8 Hz, H3), 1.60 (s,
1
11: yield 92%. H NMR (CDCl3, 400 MHz) dˆ4.08 (t, H,
Jˆ7.5 Hz, H2), 2.75±3 (m, 4H, H4, H6), 1.8±2.2 (m, 3H,
H5, H20), 1.59 (t, 2H, Jˆ7.3 Hz, H10), 0.93 (d, 6H,
Jˆ6.6 Hz, C20(CH3)2). 13C N MRdˆ45.5 (C2), 44.1
(C10), 30.3 (C4,C6), 26.0 (C5), 24.8 (C20), 22.2 (C20-Me).
EIMS m/z (%) 176 (56, M1), 161 (2), 133 (15), 121 (10),
119 (100), 101 (8), 91 (6), 87 (9), 73 (11), 69 (12), 59 (7), 45
(12), 41 (14), 39 (6).
12: yield 97%. 1H NMR (CDCl3, 400 MHz) dˆ5.14 (m, H,
H10), 4.87 (d, H, Jˆ10.0 Hz, H1), 2.75±3 (m, 4H, H4, H6),
1.8±2.2 (m, 2H, H5), 1.74±1.76 (m, 6H, 2CH3). 13C N MR
(CDCl3, 100 MHz) dˆ137.7 (C20), 121.1 (C10), 44.4 (C2),
30.5 (C4,C6), 25.6 (CH3), 24.9 (C5), 18.3 (CH3). EIMS m/z
(%) 174 (100, M1), 159 (8), 141 (7), 127 (4), 117 (11), 109
(19), 100 (29), 99 (83), 85 (86), 67 (15), 65 (12), 59 (8), 45
(18), 41 (20).
3H, C6-CH3), 0.76 (d, 6H, Jˆ7.6 Hz, H1). 13C N MR (CD6,
6
100 MHz) dˆ206.1 (C4), 133.2 (C8), 132.8 (C6), 129.9
(C7), 116.2 (C9), 54.3 (C5), 50.3 (C3), 24.0 (C2), 22.5
(C1), 16.9 (C6-CH3). EIMS m/z (%) 166 (13), 86 (4), 85
(69), 81 (11), 79 (8), 67 (3), 58 (5), 57 (100), 55 (3), 43 (9),

R. Wegener, S. Schulz / Tetrahedron 58 /2002) 315±319
319
2. Dicke, M. J. Plant Physiol. 1994, 143, 465±472.
3. Wegener, R.; Schulz, S.; Meiners, T.; Hadwich, K.; Hilker, M.
J. Chem. Ecol. 2001, 27, 499±515.
41 (27), 39 (9). HRMS, calcd for C11H18O 166.1358, found
166.1357.
3.1.7. )E)-2,6-Dimethyl-2,6,8-nonatrien-4-one )4). A solu-
tion of 0.43 g of crude dithiane 14 in 25 ml dry diethyl ether
and 10 ml dry THF was cooled to 08C. At this temperature,
0.78 g (3.4 mmol) H5IO6 in 10 ml dry THF was added drop-
wise during 3 min. After 15 min of stirring at room tempera-
ture, the reaction mixture was washed with a saturated
solution of sodium sul®te in water. The aqueous phase
was extracted four times with diethyl ether, the organic
extracts were combined and dried (MgSO4), and the solvent
was removed under reduced pressure. Chromatography on
ALOX Ndeactivated with 10% water (petroleum ether/
diethyl ether, 9:1) yielded 87 mg (30% over 2 steps) of 4.
1H N MR (6CD6, 400 MHz), dˆ6.49 (dt, H, Jˆ16.8,
10.6 Hz, H8), 5.8±5.9 (m, 2H, H3, H7), 5.08 (d, H,
Jˆ16.8 Hz, H9a), 4.96 (d, H, Jˆ10.3 Hz, H9b), 2.90 (s,
2H, H5), 2.07 (s, 3H, C2-CH3), 1.65 (s, 3H, C6-CH3),
1.39 (s, 3H, C2-CH3). 13C NMR (C6D6, 100 MHz)
dˆ196.8 (C4), 155.1 (C2), 133.5 (C6), 133.4 (C8), 129.8
(C3), 123.1 (C7), 116.1 (C9), 55.6 (C5), 27.2 (C2-CH3),
20.5 (C2-CH3), 16.8 (C6-CH3). EIMS m/z (%) 164 (3), 84
(6), 83 (100), 81 (1), 79 (2), 77 (2), 65 (1), 56 (1), 55 (28), 54
(1), 53 (6), 51 (1), 41 (3), 40 (1), 39 (8). HRMS, calcd for
C11H16O 164.1201, found 164.1205.
4. Boland, W.; Ney, P.; JaÈnicke, L.; Gassmann, G. A Closed-
Loop-Stripping Technique as a Versatile Tool for Metabolic
Studies of Volatiles. In Analysis of Volatiles: Method, Appli-
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380.
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gemeinschaft and the Fonds der chemischen Industrie is
gratefully acknowledged.
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È
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