Synthesis of [3H2]-(11S,17R)-11,17-dimethylhentriacontane: A useful tool for the study of the internalisation of communication pheromones of ant Camponotus vagus

Article abstract of DOI:10.1016/S0040-4020(00)00447-6

The convergent synthesis in high enantiomeric and diastereoisomeric purity of [³H₂]-(11S, 17R)-11,17-dimethylhentriacontane, a communication pheromone of ant Camponotus vagus is described. The stereogenic centres were introduced from

Full text of DOI:10.1016/S0040-4020(00)00447-6

TETRAHEDRON
Pergamon
Tetrahedron 56 (2000) 5493±5497
Synthesis of [3H2]-(11S,17R)-11,17-Dimethylhentriacontane:
a Useful Tool for the Study of the Internalisation of
Communication Pheromones of Ant Camponotus vagus
a
Delphine Pempo,a Jean-Christophe Cintrat,b Jean-Luc Parraina, and Maurice Santelli
*
a
Á Â Â Ã
Laboratoire de Synthese Organique, esa CNRS 6009, Faculte des Sciences de Saint-Jerome, F-13397 Marseille Cedex 20, France
b
 Â
Service des Molecules Marquees, Bat 547, CEN saclay, F-91191 Gif/Yvette, France
Received 28 March 2000; accepted 26 May 2000
AbstractÐThe convergent synthesis in high enantiomeric and diastereoisomeric purity of [3H2]-(11S,17R)-11,17-dimethylhentriacontane, a
communication pheromone of ant Camponotus vagus is described. The stereogenic centres were introduced from commercially available
(S)-citronellol and (R)-citronellal and the tritiation step was conducted in the last step of the synthesis with tritium gas over the Wilkinson
catalyst. q 2000 Elsevier Science Ltd. All rights reserved.
Chiral methyl branched subunits are found in several classes
of naturally occurring compounds and are particularly
present in insect pheromones. During the last 15 years,
several total syntheses1 have been performed starting from
natural products (citronellic acid, tartaric acid,¼), or using
selective alkylation reactions of chiral iron complexes2 or
mated and our choice was to localise the tritium atoms
between the two methyl groups.
Our retrosynthetic strategy shown in Scheme 1 is based on a
convergent synthesis coupling two building blocks both
prepared from citronellol. This latter was chosen since
both pure enantiomers are available.10 A combination of
different transformations (ozonolysis, alkylation reactions,
Wittig cross coupling, etc.) on each end of citronellol, had
given a rapid synthesis of all stereoisomers of 11,17-
dimethylhentriacontane. In order to introduce tritium
atoms in the last step of the synthesis and starting from
the (S)-citronellol and (S)-citronellal, we focussed our
attention on the synthesis of the (R,S)-dimethylhentri-
acont-13-ene precursor of the (R,S)-isomer [3H2]-1.
enzymatic resolutions.3,4 A few years ago, Clement et al.
Â
identi®ed, from the ant Camponotus vagus's communica-
tion pheromones, numerous long chain alkanes bearing one,
two or three methyl groups.5,6 Among them, 11,17-
dimethylhentriacontane 1 seems to be one of the most
important compounds with respect to the activity of the
ant.7 In order to determine the in¯uence of dimethylhen-
triacontane and the absolute stereochemistry of the active
pheromone, we synthesised the four possible stereoisomers
of 11,17-dimethylhentriacontane.8 The processes of the
biosynthesis of such long chain alkanes are essentially
achieved, into microsomes of enocytal cells, through
elongation, reduction and decarboxylation process from
acetate, isoleucine, propionate, valine, and equally C16
and C18 fatty acids precursors.9 Nevertheless, the mecha-
nism of the reception of these alkanes is still unclear and
could occur through an active internalisation process
involving a protein. Thus, to better understand how hydro-
carbons are incorporated and metabolised into the organism,
we projected the use of tritiated molecules and notably a
tritiated analogue of 11,17-dimethylhentriacontane. To
facilitate analyses, radioactive labels have to be amalga-
Synthesis of fragment A (Scheme 2) started from (S)-citro-
nellol which was converted by ozonolysis to a 1/1 mixture
of aldehyde 2 and its hemiacetal form 3 in 98% yield.11 The
Wittig ole®nation of the mixture 213 with n-heptylidene-
triphenylphosphorane gave the (Z)-ethylenic alcohol 4 as
the major isomer in 75% yield.12 Reduction of the double
bond under H2 atmospheric pressure over the Wilkinson
catalyst provided 3-methyltridecan-1-ol 5 in 89% yield
without racemisation of the stereocentre.13 The bromination
under the well described conditions (tetrabromomethane/
triphenylphosphine)14 of the alcohol 5 afforded the bromide
6 which was then converted into triphenylphosphonium salt
7 (74% yield from 4).
Aldehyde 8 was obtained in 90% yield from (S)-citronellal
in three steps: addition of dodecylmagnesium bromide,
conversion of alcohol function as tosylate and ozonolysis
of the trisubstituted double bond (Scheme 3). We have
Keywords: pheromone; total synthesis; dimethylhentriacontane; citronellol;
citronellal; tritium.
* Corresponding author. Fax: 133-4-91-98-38-65;
e-mail: jl.parrain@lso.u-3mrs.fr
0040±4020/00/$ - see front matter q 2000 Elsevier Science Ltd. All rights reserved.
PII: S0040-4020(00)00447-6

5494
D. Pempo et al. / Tetrahedron 56 (2000) 5493±5497
Scheme 1. Retrosynthetic pathway.
Scheme 2. Synthesis of fragment A.
chosen to remove the tosylate function after elaboration
of the hydrocarbon skeleton in order to permit easy
separation of 9 from the small amount of symmetric ole®n
(11,16-dimethylhexacos-13-ene) formed by oxidation of the
phosphorane derived from 7.15
the aldehyde. Many attempts to improve the yield of this
cross coupling reaction did not lead to better results.16 The
(11S,17R)-11,17-dimethylhentriacont-13-ene 10 was then
obtained in a pure form in 78% yield by reduction of the
tosylate function with lithium aluminium hydride.17 Finally,
ole®n 10 under tritium atmosphere in the presence of
Wilkinson catalyst furnished 13,14-ditritio-11,17-
dimethylhentriacontane.18 The overall yield was 12%
from (S)-citronellol (8 steps) or 22% from (S)-citronellal
(6 steps).
A Wittig ole®nation between the phosphorane generated
from 7 and the aldehyde 8 led in 28% yield to the required
carbon skeleton. It should be noticed that the low yield of
the reaction could be attributed to the long chain borne by
Scheme 3. Synthesis of [3H2]-(11S,17R)-11,17-dimethylhentriacontane.

D. Pempo et al. / Tetrahedron 56 (2000) 5493±5497
5495
ozone until the red colour disappeared. The yellow solution
was immediately purged of ozone by a stream of argon,
followed by the addition of dimethyl sul®de (1 mL,
15 mmol). The solution was allowed to warm to room
temperature, concentrated and puri®ed by ¯ash chromato-
graphy on silica gel which gave a mixture (1/1) of 2 and its
hemiacetal form 3 (648 mg, 98% yield). Rfˆ0.26 (diethyl
ether/petroleum ether: 1/1). IR (®lm): 3390, 2812, 2750,
1
1719, 1650, 1457, 1375, 1063, 919, 731. H NMR d: 0.89
(3H, d, Jˆ6.2 Hz); 1.35±1.74 (5H, m); 2.43 (1H, dddd,
Jˆ1.7, 6.7, 8.4, 17.3 Hz); 2.47 (1H, dddd, Jˆ1.7, 6.3, 8.5,
17.3 Hz); 3.62±3.73 (2H, m); 9.76 (1H, t, Jˆ1.7 Hz). 13C
NMR d: 19.3; 28.7; 29.2; 31.6; 41.6; 60.6; 203.1; hemi-
acetal 3:1H NMR d: 0.91 (3H, d, Jˆ6.2 Hz); 1.30±1.74
(7H, m); 3.53 (1H, dt, Jˆ3.4, 12.8 Hz); 3.90 (1H, bt,
Jˆ12.8 Hz); 5.14 (1H, dd, Jˆ5.3, 9.2 Hz). 13C NMR d:
23.1; 30.9; 34.0; 36.4; 39.4; 60.2; 96.4.
Scheme 4. [3H2]-Dimethylhentriacontane: fragmentation under 70 eV.
To con®rm the position of tritium atoms, an analysis by
mass spectroscopy was carried out. Mass spectra analysis
of 1 clearly shows that the isotopic enrichment achieved is
close to the theory (52 Ci/mmol compared to a maximum
expected of 58 Ci/mmol) (Scheme 4). The molecular peak is
not observed but there is a peak at m/zˆ453, corresponding
to a loss of a methyl group. Moreover, in this series the
major fragmentation occurs generally in a-position of the
methyl group. Mass spectra of 1, in the ®eld m/zˆ168±170
(west part) and m/zˆ224±228 (east part of 1), shows the
absence of tritium atoms, indicating that the reduction of the
double bond was indeed highly selective and gave no
scrambling at all along the chain, as has been shown using
heterogeneous conditions (palladium on support) for the
reduction of such double bonds.19
Heptyltriphenylphosphonium bromide. To a solution of
1-bromoheptane (17.90 g, 100 mmol) in acetonitrile
(100 mL) was added triphenylphosphine (28.82 g,
110 mmol). After re¯uxing for 24 h, the mixture was
concentrated, the crude product was dissolved into dichloro-
methane (10 mL) then added dropwise to 3 L of diethyl
ether. After stirring for 1 h, the precipitate was ®ltered
and dried under vacuum affording pure white solid
(43.60 g, 99% yield). Rfˆ0.36 (5% methanol/dichloro-
methane). Mp: 1658C. IR (CCl4): 3054, 2984, 2305, 1424,
1
1265, 896. H NMR d: 0.78 (3H, t, Jˆ6.6 Hz); 1.17±1.21
(8H, m); 1.58±1.60 (2H, m); 3.74±3.81 (2H, m); 7.61±7.87
(15H, m). 13C NMR d:13.9; 22.4 (d, JCPˆ4.8 Hz); 22.6 (d,
JCPˆ50.2 Hz); 28.7; 30.1; 30.4; 31.2; 118.0 (3C, d,
JCPˆ85 Hz); 130.5 (6C, d, JCPˆ11.5 Hz); 133.5 (6C, d,
JCPˆ9.5 Hz); 135.1 (3C, d, JCPˆ3.5 Hz).
In conclusion, this total and stereocontrolled synthesis of
[3H2]-(S,R)-dimethylhentriacontane 1 shows the versatile
and powerful worth of (S)-citronellol as chiral building
block. Each end may be used separately to introduce any
lengh of carbon chain with or without a second stereocentre.
Biological tests are currently underway to investigate the
mechanism of internalisation of this pheromone type.
(S,Z)-3-Methyltridec-6-en-1-ol (4). To a suspension of
heptyltriphenylphosphonium bromide (6.53 g, 14.8 mmol)
(previously dried by three azeotropic distillations with
benzene) in tetrahydrofuran (37 mL) was added, at
2408C, n-butyllithium (8.8 mL, 14.1 mmol, 1.6 M in
hexane). The purple solution of ylide was slowly warmed
to room temperature and stirred for 2 h. After cooling to
2808C, mixture of 2 and 3 (490 mg, 3.7 mmol) (previously
dried by three azeotropic distillations with benzene) was
added. The reaction mixture was then allowed to warm to
room temperature, quenched by a saturated solution of
ammonium chloride (10 mL), water (10 mL), petroleum
ether (10 mL) and extracted with diethyl ether (3£10 mL).
The combined organic layers were washed with brine
(3£10 mL) and dried over magnesium sulfate. After
concentration, the crude product was puri®ed by ¯ash
chromatography to give 4 (587 mg, 75% yield) (Z/Eˆ9/1).
Rfˆ0.39 (diethyl ether/petroleum ether: 1/1). IR (®lm):
Experimental
All reactions were carried out under an argon atmosphere.
Tetrahydrofuran and diethyl ether were dried and freshly
distilled from sodium/benzophenone. Dichloromethane
was dried by distillation over calcium hydride. Flash chro-
matography was carried out with Merck silica gel (silica gel,
230±400 mesh). 1H NMR and 13C NMR spectra were
recorded on a Bruker AC 200 or a Bruker AMX 400
(nuclear magnetic resonance) spectrometer. Chemical shifts
are given in ppm referring to Me4Si used as internal standard
1
1
for H and 13C NMR spectra (solventˆCDCl3). Coupling
3353, 2924, 2801, 1653, 1460, 1377, 1060, 967. H NMR
d: 0.82±0.89 (6H, m); 1.20±1.40 (11H, m); 1.40±1.61 (2H,
m); 1.95±2.02 (4H, m); 3.60±3.70 (2H, m); 5.28±5.34 (2H,
m). (Z)-isomer: 13C NMR d: 14.1; 19.5; 22.7; 24.7; 27.3;
29.0; 29.2; 29.7; 31.8; 37.2; 39.8; 60.9; 129.7; 130.0; mean-
ingful signals for (E)-isomer: 130.2; 130.4. Anal. Calcd for
C14H28O: C, 79.2; H, 13.3. Found: C, 79.13; H, 13.22.
constants are given in Hertz. The mass spectra were
obtained on a Hewlett Packard apparatus (engine 5989A)
in the GC/MS mode. IR spectra were recorded on a IR-FT
Perkin±Elmer 1600 apparatus and principal patterns are
given in cm21
.
(S)-4-Methyl-6-hydroxyhexanal
(780 mg, 5 mmol) and Sudan Red 7B (0.3 mg) in dichloro-
methane (50 mL) at 2808C were submitted to a stream of
(2).
(S)-Citronellol
(S)-3-Methyltridecan-1-ol (5). To 820 mg (3.9 mmol) of
(S)-3-methyltridec-6-en-1-ol 4 in tetrahydrofuran (20 mL)

5496
D. Pempo et al. / Tetrahedron 56 (2000) 5493±5497
was added Wilkinson catalyst (100 mg, 13% w/w) and
submitted to hydrogen atmosphere. After 3 h, Wilkinson
catalyst (100 mg, 13% w/w) was again added. The reaction
mixture was stirred at room temperature for 18 h under
hydrogen atmosphere. After concentration, the crude
product was puri®ed by ¯ash chromatography on silica gel
to give 5 (740 mg, 89% yield). Rfˆ0.40 (diethyl ether/
pentane: 1/1). IR (®lm): 3353, 2923, 2855, 1465, 1095,
2608C, n-butyllithium (0.62 mL, 1 mmol, 1.6 M in
hexane). The orange solution of ylide was slowly warmed
to room temperature and stirred for 2 h. After cooling to
2808C, the aldehyde 8 (717 mg, 1.6 mmol) (previously
dried by three azeotropic distillations with benzene) was
added. The reaction mixture was then allowed to warm to
room temperature, quenched by saturated solution of
ammonium chloride (15 mL), water (10 mL), petroleum
ether (10 mL) and extracted with diethyl ether (3£10 mL).
The combined organic layers were washed with brine
(3£10 mL) and dried over magnesium sulfate. After
concentration, the crude product was puri®ed by ¯ash
chromatography to give 9 (132 mg, 21% yield) as a 1/1
mixture of diastereoisomers. Rfˆ0.55 (diethyl ether/petro-
leum ether: 1/4). IR (®lm): 2922, 2852, 1599, 1495, 1462,
1366, 1305, 1187, 1176, 1119, 1097, 1020, 967, 894, 814,
723, 688, 665. 1H NMR d: 0.68±0.98 (12H, m); 1.00±1.43
(40H, m); 1.43±1.74 (4H, m); 1.74±2.14 (4H, m); 2.41 (3H,
s); 4.52±4.75 (1H, m); 5.22±5.39 (2H, m); 7.59 (2H, d,
Jˆ7.9 Hz); 7.77 (2H, d, Jˆ8.1 Hz). 13C NMR d: 14.2
(2C), 19.6; 19.3; 21.7; 22.8; 22.7; 24.7; 25.0 (2C); 28.7;
29.4±29.8 (10C); 32.1; 31.9; 33.1; 34.4; 34.6; 36.8; 36.9;
41.8; 82.9; 127.8 (2C); 129.6; 129.8; 135.0; 144.2; mean-
ingful signals for the other diastereoisomer: 29.1; 35.1;
37.3; 83.0; 129.7; 130.3; 135.1; 144.3.
1
1049, 956, 845. H NMR d: 0.76±1.05 (6H, m); 1.00±
1.40 (19H, bs); 1.42±1.68 (2H, m); 3.50 (2H, td, Jˆ4.0;
5.3 Hz). 13C NMR d14.1; 19.7; 22.7; 27.0; 29.2; 29.3;
29.4 (3C); 30.2; 32.1; 37.3; 39.4; 61.2. Anal. Calcd for
C14H30O: C, 78.4; H, 14.1. Found: C, 78.29; H, 14.02.
(S)-1-Bromo-3-methyltridecane (6). To a mixture of 5
(740 mg, 3.5 mmol) and carbon tetrabromide (1.7 g,
5.2 mmol) in anhydrous dichloromethane (18 mL) was
added, at 08C, triphenylphosphine (1.36 g, 5.2 mmol). The
reaction mixture was slowly allowed to warm to room
temperature. The reaction was monitored by TLC. After
3 h, the reaction mixture was concentrated and puri®ed by
¯ash chromatography on silica gel to give 6 (886 mg, 92%
yield). Rfˆ0.73 (diethyl ether/petroleum ether: 1/1). IR
1
(®lm): 2985, 2873, 1456, 1260, 1215, 721. H NMR d:
0.84±0.87 (6H, m); 1.10±1.36 (19H, bs); 1.58±1.70 (2H,
m); 3.31±3.47 (2H, m). 13C NMR d: 14.4; 19.0; 22.8; 27.1;
29.3; 29.5 (3C); 29.7; 31.4; 32.0; 33.5; 36.9; 41.1. Anal.
Calcd for C14H29Br: C, 60.6; H, 10.5. Found: C, 60.35; H,
10.34.
(11S,17R)-11,17-Dimethylhentriacont-13-ene (10). To a
suspension of lithium aluminium hydride (10 mg,
0.2 mmol) in anhydrous diethyl ether (10 mL), 9 (132 mg,
0.2 mmol) was added. After stirring for 10 h at room
temperature, the reaction was monitored by TLC. The reac-
tion was quenched by 3 mL of ethanol, ®ltered on celite 545
and alkene 10 (55 mg, 93% yield) was obtained after
concentration. Rfˆ0.77 (diethyl ether/petroleum ether:
(S)-3-Methyltridecyltriphenylphosphonium bromide (7).
To a solution of 6 (871 mg, 3.2 mmol) in acetonitrile
(31 mL) was added triphenylphosphine (1 g, 3.7 mmol).
After re¯uxing for 48 h, the reaction mixture was concen-
trated and the crude material was chromatographed on silica
gel giving 7 (1.5 g, 91% yield). Rfˆ0.26 (5% methanol/
dichloromethane). IR (®lm): 3053, 2923, 2854, 1483,
1
1/10). IR (®lm): 3026, 2952, 2860, 1475, 1326. H NMR
d: 0.60±0.91 (12H, m); 0.91±1.54 (48H, m); 1.65±2.11
(4H, m); 5.14±5.48 (2H, m). 13C NMR d: 14.2 (2C); 19.6;
19.7; 22.7; 22.8; 25.0; 27.2; 27.3; 29.1±30.3 (14C); 31.9;
32.0; 33.1; 32.5; 34.5; 36.8; 37.1 (2C); 129.8; 131.0. Anal.
Calcd for C33H66: C, 85.6; H, 14.4;. Found: C, 85.84; H,
14.22.
1
1437, 1271, 1190, 1114, 996. H NMR d: 0.73±0.90 (3H,
m); 0.90±1.06 (19H, bs); 1.13±1.40 (11H, m); 1.50±1.71
(2H,m); 3.70±3.86 (2H, m); 7.63±7.93 (15H, m); 13C NMR
d: 13.9; 19.3; 20.5 (1C, d, JCPˆ50.0 Hz); 22.7; 24.5; 27.4±
28.8 (4C); 29.6 (1C, d, JCPˆ5.5 Hz); 31.7 (2C); 33.0 (1C, d,
JCPˆ15.0 Hz); 35.9; 118.5 (3C, d, JCPˆ85.0 Hz); 130.9 (6C,
d, JCPˆ12.5 Hz); 133.5 (6C, d, JCPˆ10.2 Hz); 135.3 (3C, d,
JCPˆ3.3 Hz).
(11S,17R)-11,17-Dimethyl-13,14-ditritiohentriacontane
(1). To a solution of the alkene 10 (25 mg, 0.054 mmol) in
diethyl ether (5 mL), was added the Wilkinson catalyst
(30 mg). The ¯ask was connected to a Toppler ramp tritium
mannifold in a glove compartment then frozen with liquid
nitrogen and degassed under vacuum during a minute
approximately. The mixture was then placed under a tritium
atmosphere and slowly warmed to room temperature with a
control of the absorption of tritium. The tritium uptaken was
monitored and a constant pressure of 1 atm tritium was
maintained within the reaction vessel. After 16 h at this
temperature, the reaction was stopped by ®ltration on Millex
®lter. The ¯ask and the ®lter were washed and rinsed with
dichloromethane (2£20 mL), then the organic layers are
concentrated, the crude mixture was then diluted with
50 mL of MeOH and the labile tritium is removed. The
crude mixture obtained is ®ltered on silica gel (eluent: pen-
tane) then puri®ed by HPLC using a C18 Nucleosil column
eluting with a mixture of acetone/methanol/H2O (95/2.5/
2.5). radiochemical yield .95%. Speci®c activityˆ52 Ci/
mmole as determined by MS. 1H NMR d: 0.79±0.88 (12H,
(S)-4-Methyl-6-( p-toluenesulfonyloxy)octadecanal (8).
Compound 8 was prepared in three steps from (S)-citronellal
according to Ref. 8. IR (®lm): 2925, 2855, 1724, 1461,
1
1359, 1177, 1097, 897, 737. H NMR d: 0.70±1.00 (6H,
m); 1.00±1.70 (27H, m); 2. 22±2.44 (2H, m); 2.42 (3H,
s);4.52±4.70 (1H, m); 7.28±7.32 (2H, d, Jˆ8.2 Hz);
7.74±7.78 (2H, d, Jˆ8.1 Hz); 9.70 (1H, t, Jˆ1.6 Hz). 13C
NMR d: 14.2; 19.6; 21.6; 22.7; 24.6; 28.3; 28.7; 29.4 (3C);
29.5; 29.7 (3C); 32.0; 35.0; 41.4; 41.6; 82.6; 127.8 (2C);
129.7 (2C); 134.7; 144.5; 202.2; meaningful signals for the
other diastereoisomer: 19.0; 24.5; 28.6; 34.4;41.3; 41.5;
82.4; 202.3.
(11S,17S)-11,17-Dimethyl-19-( p-toluenesulfonyloxy)-
hentriacont-13-ene (9). To a suspension of 7 (500 mg,
0.9 mmol) (previously dried by three azeotropic distillations
with benzene) in tetrahydrofuran (12 mL) was added, at

D. Pempo et al. / Tetrahedron 56 (2000) 5493±5497
5497
 Á
7. Clement, J.-L.; Bagneres, A.-G. Personal communication.
bt); 1.23 (54H, bs). MS (70 eV): m/zˆ453(9); 439(6);
425(3); 327(25); 299(5); 271(23); 243(6); 225(17);
224(29); 169(17); 168(37); 113(20); 99(31); 85(68);
71(85); 57(100).
8. Pempo, D.; Viala, J.; Parrain, J.-L.; Santelli, M. Tetrahedron:
Asymmetry 1996, 7, 1951±1956.
9. Pheromone Biosynthesis, Prestwitch, G. D., Blomquist, G. J.
Eds.; Academic: New York, 1987.
10. Kuwahara, S.; Mori, K. Agric. Biol. Chem. 1983, 47, 2599±
2606.
Acknowledgements
11. Veysoglu, T.; Mitscher, L. A.; Swayze, J. K. Synthesis 1980,
807±810.
Thanks to CNRS and MESR for ®nancial support, Prof.
Â
J.-L. Clement and Dr A.-G. Bagneres for fruitful discussions
and `Conseil Regional PACA' for a grant (DP).
12. Marianof, B. E.; Reitz, A. B. Chem. Rev. 1989, 89, 863±927
(and references therein).
Â
13. The absence of racemisation was controlled by chiral GC
using a Chrompack WCOT fused silica, CP-chirasil-Dex CB,
25 m.
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