Reductive coupling of alkynes by oxobis(diethyldithiocarbamato)molybdenum(IV)-sodium borohydride

Article abstract of DOI:10.1016/S0022-328X(99)00205-3

The reductive coupling of terminal alkynes and the intramolecular cyclization of diynes by oxobis(diethyldithiocarbamato)molybdenum(IV) in the presence of sodium borohydride are reported. The reaction leads to a mixture of products resulting primarily from 'head to tail' coupling of the alkynes. 1,7-Octadiyne undergoes cyclization to afford cycloheptene-3-ylidene in 45% yield. The product distribution appears to be controlled by steric factors associated with the alkyne-molybdenum intermediate.

Full text of DOI:10.1016/S0022-328X(99)00205-3

www.elsevier.nl/locate/jorganchem
Journal of Organometallic Chemistry 585 (1999) 134–140
Reductive coupling of alkynes by
oxobis(diethyldithiocarbamato)molybdenum(IV)–sodium
borohydride
C. Conn *, D. Lloyd-Jones, G.S.K. Kannangara, A.T. Baker
Department of Chemistry, Materials and Forensic Sciences, Uni6ersity of Technology, Sydney, PO Box 123, Broadway, NSW 2007, Australia
Received 22 February 1999; received in revised form 9 April 1999
Abstract
The reductive coupling of terminal alkynes and the intramolecular cyclization of diynes by oxobis(diethyldithiocarbam-
ato)molybdenum(IV) in the presence of sodium borohydride are reported. The reaction leads to a mixture of products resulting
primarily from ‘head to tail’ coupling of the alkynes. 1,7-Octadiyne undergoes cyclization to afford cycloheptene-3-ylidene in 45%
yield. The product distribution appears to be controlled by steric factors associated with the alkyne–molybdenum intermediate.
© 1999 Elsevier Science S.A. All rights reserved.
Keywords: Alkyne coupling; Intramolecular cyclization; Molybdenum; Reductive coupling
Ni(CN)2 [8], PdCl2(PhCN)2 [9], NbCl5 [10] and WCl6
[10]. The major products, linear dimers or substituted
benzenes, formed by these reagents are presumed to
arise via the intermediacy of metallocyclopropene (3),
metallocyclopentadiene (4) and metallocycloheptatriene
(5) complexes. The reaction scheme in Fig. 2 is based
on mechanistic studies by Yamazaki [11], Bianchini [12]
and Wigley [13].
The addition of nucleophiles to metal–alkyne com-
plexes generally produce a cis- or trans-metalloalkene.
From a mechanistic point of view, the two isomers are
believed to arise from different mechanisms. Direct
nucleophilic attack on the alkyne carbon leads to the
trans-metalloalkene, while attack at the metal center,
followed by 1,2-shift of the nucleophile to the alkyne
leads to the cis-metalloalkene [14]. With regard to the
regiochemistry of nucleophilic addition, electrophilic
complexes, such as alkyne–MoO(S2CNEt2)2 or alkyne–
L3RhH+, are under steric control and undergo
Markovnikov addition [15].
1. Introduction
The reversible binding of acetylene to oxobis(di-
ethyldithiocarbamato)molybdenum(IV) (1) (Fig. 1) [1,2]
has been used to explore the role of oxomolybde-
num(IV) in nitrogen fixation by metalloenzymes [2].
The reversible formation of this acetylene–oxomolyb-
denum complex is readily observed spectrophotometri-
cally. The maroon colour of 1 is restored by simply
passing nitrogen through a solution of the yellow
acetylene complex (2). Our interest in alkyne–
MoO(S2CNEt2)2 chemistry arose from the observation
that in the presence of sodium borohydride, the
acetylene adduct of 1 formed ethene, along with small
quantities of 1,3-butadiene [3]. Given this observation
we sought to explore the potential of 1 as a reagent for
the coupling of alkynes.
There are a number of publications, which have
reported the coupling of alkynes using unrelated transi-
tion metal complexes. Some metal complexes used in-
clude CuCl [4], Ni phosphines [5], RhCl(PPh)3 [7],
Probably the closest reported analogous reaction to
that studied here, is the reaction of alkynes with nickel
chloride and Al(i-Bu)3 [16]. In this work a nickel hy-
dride species is formed which then complexes with the
* Corresponding author. Fax: +61-2-95141460.
E-mail address: c.conn@uts.edu.au (C. Conn)
0022-328X/99/$ - see front matter © 1999 Elsevier Science S.A. All rights reserved.
PII: S0022-328X(99)00205-3

C. Conn et al. / Journal of Organometallic Chemistry 585 (1999) 134–140
135
no reaction took place in the absence of borohydride.
Mechanistically, it was of interest to determine the
isomeric composition of the dienes and the aromatic
components. The 1-hexyne reaction was selected for this
purpose. Unfortunately, we were unable to separate the
products formed by thin layer chromatography using
either silica, boric acid or silver nitrate impregnated
silica. However we were able to separate the dienes and
the aromatic components from the other products, and
this relatively pure mixture was analysed by 2D-NMR.
GC–MS analysis of this mixture showed it to consist of
a mixture of three isomeric dienes and two aromatic
components. The 1H-NMR spectrum of the mixture
displayed four aromatic resonances, which corresponded
to that expected from two trialkylbenzenes: a 1,2,4- and
a 1,3,5-trialkylbenzene. Thus the 1,2,4-tributylbenzene
produced a doublet at l 7.07 (J=7.6 Hz), a doublet at
6.95 (J=1.5 Hz) and a doublet of doublets at 6.93
(J=7.6 and 1.5 Hz). The fourth aromatic signal was a
singlet at l 6.81 corresponding to a symmetrically
substituted trialkylbenzene. These four resonances corre-
lated to literature values for the corresponding triethyl-
benzenes [17]. Integration showed the ratio of these peaks
corresponded to a ratio of 1:0.4 for the 1,3,5-tributylben-
zene to the 1,2,4-tributylbenzene, a value confirmed by
GC–MS analysis. This ratio is larger than that expected
from simply a random coupling, suggesting that, as was
expected, steric effects influence the regiochemical com-
position.
Fig. 1. Complexation of (1) with acetylene.
alkyne. A mechanism analogous to that shown in Fig.
2 was postulated based on extensive deuterolysis exper-
iments. Products similar to those found here, that is
arenes and dienes, were reported.
2. Results and discussion
In our initial investigations, we used 1-hexyne and
1-dodecyne as substrates. The latter proved somewhat
more convenient in elucidating the scope of the reaction
given the volatile nature of some of the products formed
from the reaction with 1 and sodium borohydride. This
was due to the formation of significant amounts of
volatile alkenes, presumably formed by direct reduction
and hydrolysis of the alkyne complex 2. In all experi-
ments the reaction mixtures were extracted and analysed
by GC–MS.
A number of variables were examined including sol-
vent, ratio of alkyne to 1 and the ratio of NaBH4 to
alkyne. A summary of these studies is shown in Tables
1 and 2. From these studies a number of trends can be
seen. Firstly, the yield of dienes tend to increase with
increasing amounts of reducing agent and 1, and sec-
ondly the more water present, the greater the yield of the
dimeric product. This latter point may simply reflect the
improved solubility of NaBH4. Another trend to emerge
was that increasing the amount of the alkyne relative to
1, leads to more aromatic products as expected given the
mechanism shown in Fig. 2. It should also be noted that
For identification of the dienes formed, it proved
convenient to synthesise some of the expected dienes.
Apart from geometrical isomers, three positional isomers
are possible, that is, 1,4-dibutylbuta-1,3-diene, 1,3-
dibutylbuta-1,3-diene and 2,3-dibutylbuta-1,3-diene.1
Given that steric effects on the product composition were
evident for the aromatic products, they would also be
expected to influence the regioisomeric distribution of the
diene products.
In any case, we synthesised two of the geometric
isomers of dodeca-5,7-dienes, specifically the (E,E)- and
the (E,Z)-isomers by literature procedures [18,19]. The
former was synthesized by in situ copper(I) catalysed
oxidative coupling of the (E)-hex-1-enyl-1-diisobutylalu-
minium and the latter by in situ oxidative coupling of
1
(E)-hex-1-enyl-1-thexylborate. Comparison of the H-
NMR of the diene/arene mixture with these isomers
indicated that the (E,E)-isomer was the main dodeca-5,7-
diene formed. Only traces of the (E,Z)-isomer were
detected and no (Z,Z)-isomer was found.
The structures of the other two isomeric dienes formed
1
in the reaction were readily determined from the H-
NMR spectrum after taking into consideration the
presence of the (E,E)-isomer. The NMR showed four
broad singlets due to the presence of two pairs of olefinic
Fig. 2. Mechanism for the reductive coupling of alkynes with transi-
tion metals.
1 Trivial nomenclature has been used in the discussion for these
dienes for convenience.

136
C. Conn et al. / Journal of Organometallic Chemistry 585 (1999) 134–140
Table 1
Reaction of 1-hexyne with 1
Hexyne:(1) ratio
Solvent
(DMF:H2O)
NaBH4
Temperature (°C)/time
(h)
Recovered
hexyne
Hexane
Hexene
Dienes
Arenes
Others
0.44
0.29
0.25
0.18
0.19
1.0
4:1
1.5
2
2.1
1.4
1.2
4.7
30/4
30/4
30/4
30/4
35/23
22/18
5
11
14
67
25
1
1
16
19
3
7
0
2
27
29
15
0
46
44
35
11
39
62
13
2
1
3
28
13
24 c, 6 d
1 c, 1 d
1 c, 1 d
1 c, 1 d
1 d
4:1 a
1:1 a
b
11:1 a
6:1
0
1 d
a THF used in place of DMF.
b Anhydrous DMF.
c Unidentified trimers.
d Unidentified dodecenes.
ucts are likely to arise via hydride reduction, followed
by hydrolysis of the metallocycopentadienes (6–8) (Fig.
4; note the oxidation state and the presence of ligands
is not specified). GC–MS analysis also showed the
presence of compounds with a molecular weight of 250.
While their GC retention times were close to those
observed for aromatic components, these products were
assumed to be trimers, not cyclohexadienes. The trimers
would arise by reduction, followed by hydrolysis of the
metallocycloheptatriene intermediate (5). It is not possi-
ble to rationalize the formation of cyclohexadienes,
given the likelihood that the mechanism in Fig. 2
operates. Once again, the isomeric composition of these
compounds was not pursued, given their presence in
trace amounts.
Berg and Hodgson reported that Mo2O3(S2CNEt2)4,
an oxo-bridged dimer, equilibrates in solution to
MoO(S2CNEt2)2 and MoO2(S2CNEt2)2 [21]. This
prompted us to explore the potential of using this
Mo(V) complex as a less oxygen-sensitive substitute for
MoO(S2CNEt2)2. Thus when Mo2O3(S2CNEt2)4 was
used in excess in place of MoO(S2CNEt2)2 the same
yields and product proportions were obtained for re-
ductive coupling of 1-hexyne. While we did not explore
this further, it does suggest a convenient alternative
procedure for reductive coupling, given the air stability
of this Mo(V) complex.
methylene resonances at l 4.84 and 4.87, and l 4.91
and 5.05. Calculation of the predicted shift for the first
pair using Pascual, Meier and Simon’s rule [20] showed
that these corresponded to the shifts and coupling
expected for (E)-2,4-dibutylbuta-1,3-diene2 (l 4.81 and
4.95), the product of ‘head to tail’ coupling. In addition
to these olefinic resonances, a doublet of triplets (l
5.73, J=15.7, 7.1 Hz) was also present. This corre-
sponded to an olefinic proton coupling to a (E)-olefinic
proton and geminal coupling to an allylic methylene.
1
This was confirmed by H–1H-COSY experiments, as
were all assignments. The remaining olefinic resonances
corresponded to the product of tail to tail coupling,
that is, the 2,3-dibutyl-1,3-butadiene. Once again the
1H-NMR integration based on these assignments corre-
lated well with the GC–MS analysis, which showed the
diene ratio to be 10:7:1 for (E)-1,3-dibutylbutadiene:
(E,E)-1,4-dibutylbutadiene: 2,3-dibutylbutadiene.
This product distribution is likely to arise from steric
constraints on the coupling reaction, during the forma-
tion of oxomolybdenumcyclopentadiene (4) (Fig. 2).
Steric factors are likely to control the orientation of
insertion of the second alkyne into the C–Mo bond.
Thus a ‘head to tail’ insertion leads to the least hin-
dered metallocyclopentadiene (6) (Figs. 3 and 4) with
alkyl groups oriented away from one another. Insertion
in a ‘head to head’ fashion leads to 7 and ‘tail to tail’
fashion leads to 8. Thus formation of 8 is least fa-
voured, while the formation of 6 versus 7 may be
further controlled by electronic factors.
The other simple alkyne which was subjected to
reductive coupling with oxobis(diethyldithiocarbam-
ato)molybdenum(IV) was 2-pentyne. This was of inter-
est as it further enabled steric effects to be evaluated. In
contrast to palladium [9] and nickel [6] catalysts which
form arenes from internal alkynes, no aromatic prod-
ucts were formed, supporting the importance of steric
factors in the current case. The only products detected
by GC–MS analysis were three isomeric dienes. 1H-
NMR analysis of this mixture was not straightforward;
Other minor products that were detected had molec-
ular weights that corresponded to reduced dienes, that
is dodecenes. The isomeric composition of these minor
components was not further investigated. These prod-
2 See footnote 1.

C. Conn et al. / Journal of Organometallic Chemistry 585 (1999) 134–140
137
Table 2
Reaction of 1-dodecyne with 1
Dodecyne:1 ratio Solvent
NaBH4 Temperature (°C)/ Recovered
Dodecane Dodecene Dienes Arenes Others a
(DMF:H2O)
time (h)
dodecyne
1.0
1.0
1.0
1.0
0.30
1.0
10:1
10:1
6.7
4.0
1.0
5.0
3.0
1.0
22/20
22/20
30/4
22/20
22/20
22/20
14
12
18
69
0
4
16
5
11
0
10
26
9
9
0
45
43
37
3
88
44
9
0
13
0
0
2
5 c
1 c
3 c
0
10:1
20:1 b
2.3:1
7:1
7 c
2 c
36
6
9
a 1-Dodecanethiol found (1.3–3.5%).
b THF used in place of DMF.
c Unidentified eicostetraenes.
The reduction of oximes [25] and nitroarenes [26] using
mixtures of molybdenum oxides or complexes and boro-
hydrides has been previously reported. While these
workers do not address the precise nature of the molyb-
denum species involved, more recent work has demon-
strated the formation of low mixed valency molybdenum
species, formed on treatment of molybdate with potas-
sium borohydride [27]. Given that in the absence of
sodium borohydride no reaction took place, it is likely
that a low valent molybdenum species is involved in the
couplingstepdescribedhere. Thefateofthemolybdenum,
and the diethylthiocarbamate ligand, remains undeter-
mined at this stage.
however, given the formation of only (E,E)-isomers in the
case of both 1-hexyne and 1-dodecyne coupling, the same
(E,E)-geometry is likely here. The structures tentatively
assigned to the products are shown in Fig. 5. The ratio
oftheproducts, 13, 14andbyGC–MSwasapproximately
1:1:0.3, based on analogy with the previous results.
The final alkyne to be examined was of particular
interest from a synthetic point of view. Intramolecular
coupling of diynes has been reported for a range of
catalysts. While the majority of the literature concerns
intramoleculareneynecyclizations(forexampleCp2ZrCl2
[22] and Pd(II) [23]), there are relatively few simple
intramolecular diyne cyclizations (for example Pd(II)
[24]). While these other complexes accomplish this task
efficiently, providing good yields, the possibility of using
oxomolybdenumdithiocarbamates would have the ad-
vantage of providing a relatively cheap alternative cycliza-
tion reagent. The observations made concerning the
reactions of simple alkynes, suggest that the intramolec-
ular cyclization of 1,7-octadiyne may lead to three
possible products (Fig. 6). In the event, reaction of
1,7-octadiyne led to problems due to the volatility of the
products resulting in poor recoveries. Thus the yields
quoted do not necessarily reflect the efficacy of the
reaction. The mixture of products was again identified
using 1H-NMR, COSY and GC–MS. As expected from
the results obtained for intermolecular coupling, the
major product was the result of ‘head to tail’ coupling,
cyclohept-1-ene-3-ylidene (16), formed in 37% yield,
along with oct-1-en-7-yne formed in 25% yield (Fig. 6).
The remainder of the reaction product consisted of
unidentified dimers (22%) and recovered 1,7-octadiyne
(15%). Traces of a product tentatively identified as the
result of 1,8-cyclization, that is cycloocta-1,3-diene (15),
were also detected. Thus while the yield is poor, in-
tramolecular cyclization is highly selective in this case.
While ‘head to tail’ coupling was the main mode of
cyclization for 1,7-octadiyne, other diynes may well form
products via ‘head to head’ coupling. This cyclization
mode may predominate as the distance between the
alkynes increases.
3. Conclusions
Alkynes are reductively coupled in the presence of
oxomolybdenumdiethydithiocarbamate and sodium
borohydride. The major products of intermolecular cou-
pling of unsymmetrical alkynes arise via ‘head to tail’
coupling. Terminal alkynes afford dienes along with
arenes, while internal alkynes form only dienes. In-
tramolecular cyclization of 1,7-octadiyne led predomi-
nantly to cyclohept-1-ene-3-ylidene in 44% yield based on
recovered staring material. These yields are unacceptable
from a synthetic viewpoint, however the results suggest
that the use of more sterically demanding ligands may
lead to greater selectivity in the mode of coupling.
Fig. 3. Regiochemistry of coupling of unsymmetrical alkynes with 2.

138
C. Conn et al. / Journal of Organometallic Chemistry 585 (1999) 134–140
Fig. 6. Possible cyclization modes of 1,7-octadiyne.
min−1; 220°C, 1 min; 220–290°C at 8°C min−1; 290°C,
4 min. Helium was used as the carrier gas, a 25:1 split
ratio was employed with an inlet pressure of 275 kPa.
1
Mass spectra were obtained at 70 eV. H-NMR and all
13C-NMR were recorded on Bruker DRX 300 operat-
ing at 300.166 and 75.47 MHz, or a Bruker DRX 500
operating at 500.132 MHz. Deuterated chloroform was
used as the solvent. Preparative thin layer chromatogra-
phy (TLC) was performed using Merck Silica Gel
60F254. Flash chromatography was performed using
BDH Silica Gel (40–63 mm). All solvents used with
MoO(S2CNEt2)2 were purged with nitrogen for 30 min
before use.
4.2. Dioxobis(diethyldithiocarbamato)molybdenum(VI)
Hydrochloric acid (2 M) was slowly added to a
rapidly stirring solution of sodium diethyldithiocarba-
mate trihydrate (14.0 g, 62.1 mmol), sodium acetate
trihydrate (35.0 g) and sodium molybdate(VI) dihydrate
(15.0 g, 62.0 mmol) in water (150 ml), until pH 5.5 was
reached. The rusty-brown precipitate became yellow as
the pH approached 5.5. The yellow solid was isolated
by vacuum filtration, washed with water, ethanol and
ether and dried at the pump. The product (15.2 g, 58%)
was used without further purification. IR 878, 912
Fig. 4. Mechanism for the formation of butadienes from metallo-
cyclopentadienes.
4. Experimental
cm−1
.
4.1. General
4.3. Oxobis(diethyldithiocarbamato)molybdenum(IV)
All infrared spectra were recorded on a Bio-Rad
FTS-7 FT spectrophotometer as Nujol mulls. UV–vis
spectra were obtained on a Shimadzu W-2 101 PC
UV–vis scanning spectrophotometer. Solid probe mass
spectra were obtained at 70 eV using a Jeol JMS
DX303 Mass Spectrometer. All GC–MS analyses were
performed using a HP5 column (0.25 mm ID×30 m
fused silica capillary column coated with 0.25 mm of 5%
phenyl-silicone–95% methyl-silicone). The GC oven
program consisted of 70°C, 1 min; 70–220°C at 16°C
To MoO2(S2CNEt2)2 (5.0 g, 11.8 mmol) in 1,2-
dichloroethane (50 ml) in a Schlenk flask was added
triphenylphosphine (7.0 g, 26.7 mmol) in 1,2-
dichloroethane (20 ml) and the mixture was refluxed for
60 min under nitrogen. After the solvent was removed
under vacuum and the residue was triturated with cold
ethanol (250 ml) and filtered under nitrogen. The
residue was washed with ethanol then ether and dried,
1
affording maroon crystals (yield 4.0 g, 88%). H-NMR:
l 1.36, br t (J=7.1 Hz), 4×CH3; 3.86 and 3.94, each
br sex (J=7.1 Hz), 2×CH2. IR: 957, 1524 cm−1
.
5. Coupling reactions
The following method is representative of coupling
reactions carried out using oxobis(diethyldithiocarbam-
ato)molybdenum (IV). For the intramolecular coupling
Fig. 5. Butadienes from the reaction of 1 with 2-pentyne.

C. Conn et al. / Journal of Organometallic Chemistry 585 (1999) 134–140
139
of 1,7-octadiyne, 9:1 dimethylformamide–water was
used as the solvent and the concentration of the diyne
was 0.01 M. All transfer steps were carried out in a
nitrogen filled dry-box.
thexylborane in tetrahydrofuran (0.5 M, 2.9 ml, 1.4
mmol) at 0°C. The solution was stirred for 1 h at
0–5°C and then trimethylamine N-oxide dihydrate
(138 mg, 1.24 mmol) was added at 0°C and stirred at
this temperature for a further 1 h. The resulting solu-
tion was treated with sodium hydroxide solution (3 M,
1.2 ml), followed by iodine (310 mg) in tetrahydro-
furan (1.5 ml). Excess iodine was decomposed by addi-
Oxobis(diethyldithiocarbamato)molybdenum
(IV)
(30 mg, 0.88 mmol) in 4:1 dimethylformamide–water
(25 ml) was stirred for 5 min to dissolve the complex.
1-Hexyne (0.23 ml, 2.0 mmol) was added and the
solution stirred for 30 min. Sodium borohydride (110
mg, 2.9 mmol in water (1 ml) was then added and the
mixture stirred at room temperature for 20 h. The
reaction mixture was extracted with n-pentane (4×50
ml) and the combined organic extracts washed with
water (2×50 ml) followed by saturated sodium chlo-
ride solution (2×20 ml). The organic phase was con-
centrated under reduced pressure and purified by
passing through a short silica gel column capped with
anhydrous sodium sulfate, eluting with n-pentane. Re-
moval of the solvent under vacuum afforded an oil
which was further purified by preparative TLC using
petroleum spirits (40–60°C): dichloromethane (9:1) as
the mobile phase. The major band, which consisted of
a mixture of dimers and trimers was then analysed by
tion of
a
small amount of aqueous sodium
thiosulphate. The reaction mixture was extracted with
petroleum spirit (30–40°C, 5×50 ml) and the com-
bined organic extracts were concentrated under re-
duced pressure and purified by flash chromatography
on a short silica gel column, eluting with petroleum
spirit 30–40°C. Removal of the solvent under vacuum
yielded a colourless oil (231 mg, 92%) determined to be
1
86% pure by GC. H-NMR: l 0.93, t (J=7.2 Hz), 1-
and 12-CH3; 1.40, m, 2-, 3-, 10- and C11-CH2; 2.13,
2,15 each dt (J=7.2, 7.2 Hz), 4- and 9-CH2; 5.31, dt,
(J=10.8 and 7.5 Hz) 5-CH; 5.68, dt (J=14.9, 7.5 Hz);
5.97, dd (J=10.8, 10.8 Hz), 7-CH. 6.33, ddt (J=15.1,
10.8 and 1 Hz) 6-CH. 13C{1H}-NMR: 13.9, 22.3, 27.4,
31.6, 32.0, 32.6, 125.7, 128.7, 129.9 and 134.5. MS:
m/z=166 (M+., 19%), 123 (10), 109 (10), 95 (17), 81
(62), 67 (100), 54 (28), 41 (52), 27 (31).
1
GC–MS and H-NMR.
5.1. (E,E)-Dodeca-5,7-diene
1-Hexyne (0.27 ml, 2.4 mmol) and 0.7 M di-isobutyl-
aluminium hydride (0.7 M in toluene, 3.3 ml, 2.3
mmol) was added, while maintaining the temperature
at 25°C with cooling in a water bath. The solution was
stirred at room temperature for 30 min and then
heated at 50°C for 4 h. The solvent was removed under
vacuum and dry THF (2 ml) was added. Copper(I)
chloride (285 mg, 2.9 mmol) was added and the black
suspension was stirred at room temperature for 30 min
and then heated to 50°C for 4 h. The reaction mixture
was poured slowly into dilute sulfuric acid (5%, 10 ml)
and then extracted with n-pentane (5×10 ml). The
combined organic extracts were washed with saturated
aqueous sodium hydrogen carbonate (50 ml) and dried.
The solvent was then removed under reduced pressure
and the residue was subjected to chromatography short
column of silica gel, eluting with petroleum spirits
(30–40°C). Removal of the solvent under vacuum af-
forded the diene (127 mg, 59%) as a colourless oil.
1H-NMR: l 0.89, t (J=7.2 Hz), 1- and 12-CH3; 1.33,
m, 2-, 3-, 10- and 11-CH2; 2.05, dt (J=7.2, 7.2 Hz), 4-
and 9-CH2; 5.56, m, 5- and 8-CH; 6.00, m, 6- and
7-CH. 13C{1H}-NMR: 13.9, 22.3, 31.6, 32.3, 130.3,
132.4. MS: m/z=166 (M+., 20%), 123 (10), 109 (10),
95 (18), 81 (62), 67 (100), 54 (23), 41 (48), 27 (24).
Acknowledgements
We gratefully acknowledge the assistance of Dr Pe-
ter Barron of Bruker Australia in allowing us access to
the Bruker DRX500 spectrometer and financial sup-
port from the UTS Internal Grants Scheme.
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