Polylithiumorganic compounds. Part 28. The reaction of allene and alkyl substituted allenes with lithium metal

Article abstract of DOI:10.1016/S0022-328X(01)01195-0

The reaction of allene (3a) and alkyl substituted allenes 1,2-hexadiene (3b), cyclopropylallene (3c), and vinylidene cyclopropane (3d) with lithium metal was investigated in order to access 2,3-dilithioalkenes 4a-d. These dilithioalkenes 4a-d are very reactive in polar solvents like THF and act as strong bases, either metalation of the starting allene 3a-d, the solvent, or sufficiently acidic intermediates like 8 a-d is observed. The metalation products 5-7 show follow-up reactions like 1,3-H shift to the corresponding 1-lithio-1-alkynes 8 and subsequent metalation to the dilithioalkynes 9. Additionally, lithium hydride elimination and ring-chain rearrangement (for 5c) are observed. 1,2-Hexadiene (3b) can be brought to reaction with lithium metal in the apolar solvent pentane, here the follow-up reactions are much slower due to the insolubility of 4b. In all cases the elucidation of the reaction pathways is hampered by the formation of complex mixtures of, amongst others, regio- and stereoisomeric products upon quenching with simple electrophiles.

Full text of DOI:10.1016/S0022-328X(01)01195-0

Journal of Organometallic Chemistry 642 (2002) 1–8
www.elsevier.com/locate/jorganchem
Polylithiumorganic compounds
Part 28. The reaction of allene and alkyl substituted allenes with
lithium metalꢀ
Adalbert Maercker *, Andrea Tatai, Burkhard Grebe, Ulrich Girreser
Institut fu¨r Organische Chemie, Uni6ersita¨t Siegen, Adolf-Reichwein-Strasse, D-57068 Siegen, Germany
Received 13 February 2001; received in revised form 5 June 2001; accepted 28 August 2001
Abstract
The reaction of allene (3a) and alkyl substituted allenes 1,2-hexadiene (3b), cyclopropylallene (3c), and vinylidene cyclopropane
(3d) with lithium metal was investigated in order to access 2,3-dilithioalkenes 4a–d. These dilithioalkenes 4a–d are very reactive
in polar solvents like THF and act as strong bases, either metalation of the starting allene 3a–d, the solvent, or sufficiently acidic
intermediates like 8 a–d is observed. The metalation products 5–7 show follow-up reactions like 1,3-H shift to the corresponding
1-lithio-1-alkynes 8 and subsequent metalation to the dilithioalkynes 9. Additionally, lithium hydride elimination and ring-chain
rearrangement (for 5c) are observed. 1,2-Hexadiene (3b) can be brought to reaction with lithium metal in the apolar solvent
pentane, here the follow-up reactions are much slower due to the insolubility of 4b. In all cases the elucidation of the reaction
pathways is hampered by the formation of complex mixtures of, amongst others, regio- and stereoisomeric products upon
quenching with simple electrophiles. © 2002 Elsevier Science B.V. All rights reserved.
Keywords: Allenes; Lithium dust; Reductive metalation; Dilithiumorganic compounds; Carbanion rearrangements
1. Introduction
atoms can be explained by assuming fast equilibration
on the NMR time scale [6]. This is also reasonable
according to ab initio calculations on the parent com-
pound, 2,3-dilithiopropene [7]. We were interested in
the preparation of this class of compounds and for-
warded an investigation into the reactivity of allene and
alkyl substituted allenes towards lithium metal. For
butatriene, the next higher homologue of allene, a
different behaviour of phenyl and alkyl substituted
systems towards lithium metal has been observed, the
latter showing 2,3- [8] and even 3,4-addition of lithium
[9] instead of 1,4-addition with the former.
The reductive metalation of unsaturated systems with
lithium metal is one of the best methods to prepare
polylithiumorganic compounds [2]. A most interesting
organodilithium compound 2 with one s- and one
p-bonded lithium is obtained by the addition of lithium
to tetraphenylallene (1) [3] (Scheme 1). The structure of
2 deduced by NMR spectroscopy was controversial at
first [4,5]. However, the equivalence of both lithium
2. Results and discussion
Scheme 1. The known reaction of tetraphenylallene 1 to dilithioallene
2 with one s-bonded and one p-bonded lithium.
2.1. Propadiene (3a)
With the gaseous unsubstituted allene 3a (b.p. −40
°C), only qualitative experiments have been performed.
Allene does not react with lithium metal in apolar
solvents like pentane, the reaction of 3a with lithium
ꢀ Part 27: Ref. [1].
* Corresponding author. Tel.: +49-271-740-4377; fax: +49-271-
740-3270.
E-mail address: maercker@chemie.uni-siegen.de (A. Maercker).
0022-328X/02/$ - see front matter © 2002 Elsevier Science B.V. All rights reserved.
PII: S0022-328X(01)01195-0

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A. Maercker et al. / Journal of Organometallic Chemistry 642 (2002) 1–8
2.2. 1,2-Hexadiene (3b)
Propylallene (3b) and lithium metal essentially react
in the same way in THF at −40 °C as the unsubsti-
tuted allene 3a (Scheme 2). After 2 h of reaction time
and separation of unreacted lithium metal by filtration,
the addition of dimethyl sulphate to the dark green
solution yielded a complex mixture, consisting of the
following compounds (gas chromatography, n-decane
as internal standard, see also Table 1): 16% of (E,Z)-2-
hexene (13) (1:2) and 2% of 1-hexene (14), then 10% of
3-methyl-1,2-hexadiene (15a) and 3% of 3-heptyne
(16a), both originating from 6b. Furthermore 13% of
(E,Z)-3-heptene (17a) (1:5) and 8% of 3-methyl-1-hex-
ene (18a) were found as derivatives of 7b. The main
product (31% yield) in this reaction was 2-heptyne (19a)
originating from 1-lithio-1-hexyne (8b), while 9b deliv-
ered only 4-methyl-2-heptyne (20a) in 10% yield. Of
unknown products, 7% (less than 1% each) were also
detected by gas chromatography. So in the reaction of
propylallene (3b) with lithium metal in THF a direct
derivative of the primarily formed dilithium compound
4b could not be found (Fig. 1).
Scheme 2. Formation and all possible follow-up reactions of
dilithioalkenes 4a–d.
We were lucky, however, that the reaction of 1,2-
hexadiene (3b) with lithium dust also took place in
boiling pentane, a solvent in which 4b is more stable,
simply due to its insolubility. The excess of lithium
metal could not be filtered off, thus after 12 h of reflux
the pale green reaction mixture was quenched with
dimethyl sulphate. The main reaction products this time
were (E)- and (Z)-3-methyl-3-heptene (21a) (41% 1:1)
as well as 21% of 2,3-dimethyl-1-hexene (22a). Other
products were found in lower yield: 6% of (E,Z)-2-hex-
ene (13) (1:2), 6% of (E,Z)-3-heptene (17a) (1:1), and
4% of 3-methyl-1-hexene (18a), 10% of 2-heptyne (19a),
and 9% of 4-methyl-2-heptyne (20a). Only 3% of un-
known compounds were found and no 14, 15a and 16a
could be detected, demonstrating that in pentane as the
solvent deprotonation in the 3-position of 1,2-hexadi-
ene (3b) to 6b did not occur.
Another run was deuterated after 10 h of reflux in
pentane. Besides starting material 3b and dimers, 6%
each, the following deuterated compounds could be
detected: 62% of (E,Z)-2-hexene-1,2-d2 (21b) and 16%
of 1-hexene-2,3-d2 (22b), both originating from 4b. Ad-
ditionally, 6% of 1-hexyne-1-d1 (19b) arising from 1-
lithio-1-hexyne (8b) was found.
dust in THF requires temperatures of −30 °C and is
indicated by a green coloration of the solution. No
dilithiopropene 4a, however, could be detected among
the reaction products (Scheme 2). The main product
after a reaction time of 1 h at −20 °C was the
dilithiopropyne 9a yielding 57% of 3-heptyne (12) after
derivatization with diethyl sulphate, which was em-
ployed instead of dimethyl sulphate in order to obtain
less volatile products. The s-bonded lithium of the
primarily formed dilithium compound 4a has metalated
the starting material 3a affording allyl lithium (7a),
which is detected as 1-pentene (10). As the amount of
7a (20%) found in the product mixture is rather small,
it was assumed that propadiene (3a) is metalated by
allyl lithium (7a) as well. This could be shown in an
independent experiment by treating propadiene (3a)
with allyl lithium prepared from allyl phenyl ether and
lithium [10], although this time besides metalation (5–
6%) mainly non-volatile products have been obtained.
The primary metalation product 5a undergoes 1,3-hy-
dride shift—a known reaction [11]—to 1-lithiopropyne
(8a), trapped as 2-pentyne (11) in a yield of 23% yield
after quenching with diethyl sulphate. 1-Lithiopropyne
(8a) is mainly metalated once more to the final propar-
gylide 9a—again with one s- and one p-bonded
lithium [2]-affording 3-heptyne (12) after quenching
with diethyl sulphate. So the reaction products ob-
tained in the reaction of propadiene 3a with lithium
metal indicate the intermediate formation of the 2,3-
dilithioalkene 4a, which is not stable under the reaction
conditions but acts as a strong base, starting a cascade
of metalation and rearrangement reactions.
When the reaction mixture of 3b with lithium metal
was quenched with trimethylsilyl chloride in boiling
pentane, the dilithium compound 4b interestingly gave
only (E,Z)-1,2-bis(trimethylsilyl)-2-hexene (21c) (E/
Z=2.2:1) in 53% yield corresponding to 21a and 21b.
The product corresponding to 22a and 22b was not
obtained. In addition, 20% of E,Z-17c (1.5:1) deriving
from 7b (one regioisomer only!) as well as 7% of 19c
from 8b and 13% of 20c from 9b could be detected. As

A. Maercker et al. / Journal of Organometallic Chemistry 642 (2002) 1–8
3
products of hydrolysis, 4% of (E,Z)-2-hexene (13) (1:1)
and 3% of 1-hexyne were identified. The main product
in the reaction mixture E-21c was isolated by distilla-
tion in 17% yield.
Deuteration of the THF solution of 4b with D2O
after 1 h yielded 68% of 19b from 8b as well as 27% of
E,Z-21b and 5% of 22b. In diethyl ether as the solvent
the decomposition of 4b also takes place, although
more slowly. Deuteration after 1 h yielded only 24% of
19b besides 67% of E,Z-21b and 9% of 22b.
In order to obtain an NMR spectrum of the primar-
ily formed dilithiumorganic compound 4b, the white
precipitate of 4b in pentane was filtered off and dis-
solved in THF. Unfortunately, again decomposition
took place with the formation of 1-lithio-1-hexyne (8b),
although 1,2-hexadiene (3b) this time was absent and
metalation therefore could not represent the origin of
8b according to Scheme 2 (see also Table 1). A simple
explanation is the assumption that in the absence of the
acidic starting material 3b the dilithiohexene 4b splits
off lithium hydride leading to the same lithioallene 5b,
which is formed by metalation of 1,2-hexadiene (3b).
The other possible product 6b, deprotonated in 3-posi-
tion, is not formed, probably due to the influence of the
alkyl substituent. The reaction corresponds to the for-
mation of vinyl lithium from ethylene and lithium via
1,2-dilithioethane, whereby again lithium hydride is lost
[12–16].
Upon addition of 1,2-hexadiene (3b) to lithium dust
in diethyl ether at room temperature the solution turns
warm and deuterolysis after half an hour yielded only
one deuterated product, namely again 1-hexyne-1-d1
(19b) (28%) besides 16% of (E,Z)-2-hexene (13), 28% of
1-hexene (14) and 9% of 2-hexyne. The same was true
for the reaction in dimethoxyethane (DME) as solvent,
yielding 42% of 19b, 26% of E,Z-13, 6% of 14 and 8%
of 2-hexyne. The latter is the product of isomerization
of the starting material 3b formed via 6b. In both
solvents dimeric products (M=166 g mol−1) could be
detected as well, in 19 and 18% yield, respectively. It
was not excluded experimentally that some of the rear-
rangements observed upon deuterolysis of the reaction
mixtures take place during the work-up under basic
conditions, however, they are in accordance with the
Table 1
Relative amount in % of compounds obtained in the reaction of 3b with lithium metal
Entry
1
2
3
4
5
6
7
8
9
Reaction
conditions
and
derivatization
reagent
THF,
−40 °C
THF,
22 °C
C5H10
40 °C
,
C5H10
40 °C
,
C5H10
40 °C
,
C5H10
40 °C
precipitate
dissolved in
THF, D2O
,
C5H10
40 °C
precipitate
dissolved in
Et2O, D2O
,
Et2O,
r.t.
DME,
r.t.
Me2SO4
Me2SO4
Me2SO4
D2O
Me3SiCl
D2O
D2O
E/Z-13
14
15a
16 (1:2)
2
10
20 (1:1.5)
3
8
6 (1:2)
–
–
–
–
–
4 (1:1)
–
–
–
–
–
–
–
–
16
28
–
26
6
–
16a
3
3
–
–
–
–
–
–
–
E/Z-17a
18a
19a
20a
E/Z-21a
22a
E/Z-21b
22b
19b
E/Z-21c
E/Z-17c
19c
13 (1:5)
–
4
57
–
–
–
–
–
–
–
–
–
–
6 (1:1)
4
10
9
41 (1:1)
21
–
–
–
–
–
–
–
–
–
–
–
–
–
62
16
6
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
27
5
68
–
–
–
–
–
–
–
67
9
24
–
–
–
–
–
–
–
–
–
28
–
–
–
–
–
–
–
–
–
–
–
–
42
–
–
–
–
8
31
10
–
–
–
–
–
–
–
–
53 (2.2:1)
20 (1.5:1)
7
13
–
–
–
–
–
–
–
–
–
–
–
–
20c
Dimeric
products
Other
–
–
6
19
18
7 a
4 a
3 a
6 b
3 c
–
–
9 d
8 d
a Sum of unidentified products, less than 1% each.
b Educt 3b.
c 1-Hexyne.
d 2-Hexyne.

4
A. Maercker et al. / Journal of Organometallic Chemistry 642 (2002) 1–8
ether or THF, the same follow-up reactions which were
observed for 3a are found. Interestingly a smaller num-
ber of derivatives are obtained when quenching 4b with
the less reactive trimethylsilyl chloride; due to steric as
well as electronic reasons the reaction occurs preferen-
tially at the terminal end of 4b and 7b.
2.3. Cyclopropylallene (3c)
In order to trap the primarily formed labile dilithium-
organic compound by an intramolecular ring-chain re-
arrangement we replaced the n-propyl group of the
allene 3b with a cyclopropyl group. This method [17]
was already successful, not only with cyclopropyl
alkene [18] and alkyne derivatives [19], but also with
methylenecyclopropane [20] and numerous derivatives
thereof [21,22].
Unfortunately, cyclopropylallene (3c) did not react
with lithium dust in boiling pentane as the solvent, even
on using ultrasonic irradiation. In THF as the solvent
the reaction took place in a similar way as with propyl-
allene (3b), although showing some significant differ-
ences (Scheme 2). Cyclopropylallene (3c) is less reactive
than propylallene (3b) and did not react below −10
°C; the solution after starting of the reaction turned
green, and later orange–brown. The starting material
metalated in the endposition 5c is fairly stable below
0 °C and can be trapped in high yield with dimethyl
sulphate as 26. The allene structure in 26 is retained as
expected [23]. The primarily formed dilithiumorganic
compound 4c does not undergo ring-chain rearrange-
ment as was anticipated, and no allyl lithium derivative
corresponding to 7b could be detected. Presumably 5c
is formed by lithium hydride elimination, which could
not be isolated from the reaction mixture. It has to be
mentioned, however, that the total yield of volatile
products determined by gas chromatography using n-
decane as internal standard was only 32% as a maxi-
mum and some intermediates are lost by
polymerization. Deprotonation of the allenic proton a
to the cyclopropylmethyl group occurs to a high extent
as well, yielding 6c, which is detected as 27 after
quenching with dimethyl sulphate. Isomerization of the
starting material 3c with formation of 29 also takes
place via 6c. The acetylide 8c formed by 1,3-hydride
shift from 5c this time is not metalated a second time to
a propargylide corresponding to 9a and 9b. This
propargylide could be prepared independently from 8c
and butyl lithium and no ring-opening takes place.
Compound 5c, however, undergoes ring-chain rear-
rangement to 24 presumably via 23, even below 0 °C
(Scheme 3). At even higher reaction temperatures,
above 0 °C, 24 is also metalated to the resonance
stabilized pentadienyl dianion 25. Dianion 25 yields
only E,Z-31 upon the reaction with dimethyl sulphate,
while 24 yields E,Z-30 as expected (Fig. 2).
Fig. 1. Products obtained after derivatization of reaction mixtures of
propadiene (3a) and 1,2-hexadiene (3b) with lithium metal.
Scheme 3. Rearrangements observed in the reaction of cyclopropylal-
lene 3c with lithium metal.
Fig. 2. Products obtained upon derivatization with dimethyl sulphate
of the reaction mixture of cyclopropylallene (3c) with lithium metal.
results obtained in the quenching reactions with
dimethyl sulphate where such reactions are impossible.
Thus, in the apolar solvent pentane, direct proof for the
formation of the dilithioalkene 4b is obtained. When
performing the synthesis of 4b in an ethereal solvent or
when dissolving the dilithioalkene 4b in either diethyl

A. Maercker et al. / Journal of Organometallic Chemistry 642 (2002) 1–8
5
Table 2
Products of the reaction of cyclopropylallene (3c) with lithium dust in THF after derivatization with dimethyl sulphate in (%)
Conditions
26
27
28
29
E,Z-30
E,Z-31
Total yield
1 h, −10 °C–0 °C
1 h, 10 °C–20 °C
18 h, room temperature
55
13
–
22
7
6
–
9
60
3
8
19
7
20
2
–
6
2
23
32
13
Three runs of the reaction of cyclopropylallene (3c)
with lithium dust in THF have been performed at three
different temperatures and the results can be taken
from Table 2.
follow-up reactions shown in Scheme 2. The results in
the quenching experiments of 4b presented here, how-
ever, show some selectivity when using less reactive
electrophiles, like trimethylsilyl chloride. In this respect
the use of other electrophiles would be interesting, and
an investigation on triggering the reactivity of the
2.4. Vinylidenecyclopropane (3d)
dilithioalkene
worthwhile.
4
by transmetalation would be
At last vinylidenecyclopropane (3d), the next higher
homologue of methylenecyclopropane [20], was reacted
with lithium dust, whereby again only THF worked as
the solvent, although the reaction took place already at
−40 °C. The results are quite similar to those with the
unsubstituted allene 3a; interestingly no open-chain
products could be obtained. After 1 h at −40 °C, the
excess of lithium was filtered off and dimethyl sulphate
was added as usual. Gas chromatography using n-de-
cane as internal standard showed only two reaction
products in 76% yield: 1-cyclopropyl-1-propyne (29)
and ethylidenecyclopropane (32) in a ratio of about 2:1
(Scheme 4). Only on using n-butyl lithium instead of
lithium, about one half of the acetylide 8d was meta-
lated once more to the propargylide 9d yielding 29 and
33 (1:1) upon the addition of dimethyl sulphate. Even
on the level of the dianion the cyclopropane ring did
not open up.
4. Experimental
4.1. General
All reactions with air sensitive compounds were
carried out under an atmosphere of dried Ar (99.996%).
Ethereal solvents were purified by adsorptive filtration
over basic aluminium oxide (activity I) and freshly
distilled under Ar from sodium–benzophenone ketyl.
Dimethyl sulphate and diethyl sulphate were distilled in
vacuo and stored over molecular sieve (3 A). Mass
spectra were obtained using GC–MS coupling on a HP
5988A mass spectrometer (hp5 capillary); m/z values
,
3. Conclusions
The highly activated tetraphenylallene
1 reacts
smoothly even at very low temperatures with lithium
metal to the stabilized dilithioallene 2 [2]. When switch-
ing to alkyl substituents, two general effects can be
observed. Firstly, the reaction of the allenes 3a–d with
lithium metal requires higher temperatures, even when
using highly reactive lithium dust containing 2% of
sodium. This might be one reason for the observed
follow-up reactions, especially for 3b in pentane. Sec-
ondly, a polar solvent like THF or diethyl ether is
required to bring about the reaction of 3a,c and 3d with
lithium metal, in these polar solvents the dilithioalkenes
4a–d then simply act as strong bases. So the use of the
least polar solvent is recommended for the investigation
of dilithioalkenes 4. From a synthetic point of view, the
formation of mixtures in quenching the dilithioalkene
4b is the major problem, also in the evaluation of the
Scheme 4. Reaction of vinylidenecyclopropane 4d with lithium metal
and products obtained after quenching with dimethyl sulphate.

6
A. Maercker et al. / Journal of Organometallic Chemistry 642 (2002) 1–8
are reported followed by the relative intensity in paren-
theses. The ten strongest peaks and, if not enclosed, the
intensity of the molecular ion is given. Nuclear mag-
netic resonance (1H and 13C) spectra were recorded on
the Bruker instruments AC 200 and WH 80. Chemical
shifts are reported in parts per million (l) downfield
from an internal TMS reference. Coupling constants (J)
are reported in Hertz (Hz), and spin multiplicities are
indicated by the following symbols: s (singlet), d (dou-
blet), t (triplet), q (quartet), quint (quintet), m (multi-
plet), br (broad signal). Separations of the reaction
mixtures were performed using a preparative gas chro-
matograph (Hupe und Busch, HP 1075c prep. GC). For
analytical gas chromatography a HP 5890 with a SE30
column (25 m) and FID was used.
in the solvent given, with magnetic stirring. A small
amount of the allene was added at a temperature
slightly higher than the stated reaction temperature
until the reaction starts, which was usually noticeable
by a coloration of the reaction mixture. After quench-
ing of the reaction mixture by addition of a solution of
the dialkyl sulphate or the electrophile as a solution in
the solvent employed, the reaction mixture was allowed
to warm to room temperature (r.t.). In order to destroy
the excess of dialkyl sulphate, a concentrated solution
of ammonia was added and the mixture stirred at r.t.
overnight. The aqueous layer was extracted with Et2O,
dried over sodium sulphate, and the solvents were
evaporated using a rotary evaporator. Then the col-
lected solvent was checked by gas chromatography for
the presence of low boiling hydrocarbons deriving from
the allenes.
4.2. Starting materials and reference compounds
Propadiene (3a) was obtained by reaction of 2,3-
dichloro-1-propene with zinc powder [24]. The gas was
condensed at −100 °C and immediately used for fur-
ther reactions. 1,2-Hexadiene (3b) was obtained from
1-hexyne according to Meisters and Swan [25]. Cyclo-
propylallene (3c) was synthesized by addition of dibro-
mocarbene to vinylcyclopropane and subsequent
reaction with methyl lithium [26]. Vinylcyclopropane
itself was obtained by reaction of the p-tosylhydrazone
of cyclopropyl methyl ketone with sodium amide [27].
Vinylidenecyclopropane (3d) was synthesized by addi-
tion of dibromocarbene to methylenecyclopropane [28]
and reaction of the 1,1-dibromospiropentane with
methyl lithium [29]. However, contrary to the reported
method [29], it proved advisable to perform the addi-
tion of methyl lithium at −100 °C and to keep the
reaction mixture below −40 °C throughout, in order
to achieve acceptable yields. Furthermore, the yield
decreased remarkably if the scale of the reaction was
higher than 30 mmol.
1- and 2-pentene, 1-, 2-, and 3-hexenes and the
corresponding pentynes and hexynes and the various
heptenes are commercially available. 2-Heptyne (19a)
was obtained by base-catalyzed rearrangement of 1-
heptyne [30]. (E,Z)-3-Methyl-3-heptene (21a) was ob-
tained by Wittig reaction of s-butyl triphenyl-
phosphonium bromide [31] with n-butanal [32]. 2,3-
Dimethyl-1-hexene (22a) was made available by subse-
quent alkylation of ethyl acetoacetate, first with propyl
bromide and then with methyl iodide, base-catalyzed
4.4. Reactions of propadiene (3a)
4.4.1. Reaction of propadiene (3a) with lithium
To 0.36 g (52 mmol) of lithium dust in 25 ml of THF
was introduced 3a, generated from 6.02 g (55 mmol) of
2,3-dichloro-1-propene, at −100 °C. The reaction mix-
ture was allowed to warm to −20 °C and kept at this
temperature for 1 h. Then unreacted lithium was
filtered off and the filtrate was quenched with 6.7 ml of
diethyl sulphate. After the usual work-up the following
products were identified using GC–MS coupling and
commercially available reference compounds: 20% of
1-pentene (10), 23% of 2-pentyne (11), and 57% of
3-heptyne (12) [34–36].
4.4.2. Reaction of propadiene (3a) with allyl lithium
Allyl lithium was prepared by addition of freshly
distilled allyl phenyl ether to lithium chunks in THF at
−15 °C with a catalytic amount of biphenyl [10]. After
2 h the solution was filtered off from the formed
lithium phenolate and added dropwise to 3a in an
Et2O–THF mixture at −85 °C. This mixture was
warmed to −40 °C within 90 min, then derivatization
was performed with diethyl sulphate. After the usual
work-up bulb-to-bulb condensation afforded 5% of 1,2-
pentadiene [37] and 1% of 2-pentyne (11) [38]. The
remainder was of polymeric nature.
4.5. Reactions of hexadiene (3b)
cleavage
and
Wittig
reaction
with
methyl
4.5.1. Reaction of 1,2-hexadiene (3b) with lithium
triphenylphosphonium bromide.
To a suspension of 0.18 g (26 mmol) of lithium dust
in 10 ml of n-pentane was added slowly a solution of
1.01 g (12 mmol) of 3b in 3.5 ml of n-pentane. The
reaction mixture was brought to reflux; after 30 min it
turned brownish and a green solid was formed. After
refluxing overnight the mixture was transferred into a
separation funnel and the lithiumorganic compound
4.3. General procedure for the reaction of allenes 3a–d
with lithium and subsequent deri6atization
If not stated otherwise, the allenes were added slowly
as diluted solutions to a suspension of lithium dust [33]

A. Maercker et al. / Journal of Organometallic Chemistry 642 (2002) 1–8
7
was drawn off. The excess lithium stuck to the wall of
the separation funnel. After derivatization with
dimethyl sulphate and the usual work-up the reaction
mixture was purified by bulb-to-bulb condensation and
analyzed by GC–MS coupling after addition of n-de-
cane as standard. Total yield of hydrocarbons was in
the order of 65%. The reaction of 3b in ethereal sol-
vents was performed on the same scale as described
above at the temperatures given in Table 1, the reaction
mixture was separated from unreacted lithium by filtra-
tion. Total yield of hydrocarbons was in the range of
75%. Characterization of the products obtained upon
derivatization with either dimethyl sulphate or D2O was
performed employing reference compounds (see above)
with identical retention times (gas chromatography)
and mass spectra (GC–MS coupling).
mixture was kept for 1 h at the temperature given in
Table 2. After filtration, derivatization with dimethyl
sulphate, work-up, and bulb-to-bulb condensation, the
products were isolated by preparative gas chromatogra-
phy and characterized as follows. 1-Cyclopropyl-1-
propyne (29): 1H- and 13C-NMR spectra were in
accordance with reference data [42,43]; MS (70 eV): m/z
80 [M+, 90], 79(100), 77(72), 65(17), 53(16), 52(26),
51(31), 50(22), 39(29), 28(24). 3-Cyclopropyl-1,2-buta-
1
diene (27): The mass spectrum as well as the H- and
13C-NMR spectrum was in accordance with reference
data [44]. 1-Cyclopropyl-1,2-butadiene (26): The 1H-
NMR spectrum was in accordance with reference data
[45]; MS (70 eV): m/z 94 [M+, 17], 91(25), 79(100),
78(11), 77(83), 65(18), 53(20), 51(16), 39(39), 27(18).
1-Cyclopropyl-2-butyne (28): 1H-NMR (200 MHz,
CDCl3): l 0.2/0.45 (2×m, 2×2H, cyclopropyl-CH2),
0.9 (m, 1H, cyclopropylꢁCH), 1.8 (t, J=2.5 Hz, 3H,
CH3), 2.15 (dq, J=5.9/2.5 Hz, 2H, CH2). 13C-NMR
(50 MHz, CDCl3): l 3.5, 3.8, 9.8, 23.1, 75.6, 77.6.
(E,Z)-4-Hepten-2-yne (30): The 1H-NMR spectrum was
in accordance with reported values [46], the mass spec-
tra of the two isomers were nearly identical. MS (70
eV): m/z 94 [M+, 73], 91(23), 79(80), 78(14), 77(100),
66(11), 65(15), 53(17), 51(17), 39(23). (E,Z)-4-Methyl-2-
4.5.2. Deri6atization with trimethylsilyl chloride on a
preparati6e scale
Starting from 1.50 g (0.22 mol) of lithium metal, 8.21
g (0.10 mol) of 3b in 150 ml of pentane the reaction was
performed as described above with reflux for 10 h.
Then 24.4 g (0.23 mol) of trimethylsilyl chloride were
added dropwise and the mixture was heated to reflux
for another 12 h. After the usual work-up, GC–MS
coupling yielded the composition of the product mix-
ture as given in Table 1. After two consecutive distilla-
tions, the products were characterized as follows.
1-Hexynyltrimethylsilane (19c): b.p. 47–58 °C (10
1
hepten-5-yne (31): The H-NMR spectrum was in ac-
cordance with reported values [47], the mass spectra of
the two isomers were nearly identical. MS (70 eV): m/z
108 [M+, 47], 93(68), 91(79), 79(15), 78(16), 77(100),
65(26), 51(13), 41(18), 39(28).
1
Torr), mass spectrum [39] and H-NMR spectrum [40]
were in accordance with reference data. 2-Hex-
1
enyltrimethylsilane (17c): H- and 13C-NMR spectrum
4.6.2. Reaction of cyclopropylallene (3c) with n-butyl
lithium
in accordance with reference data [41]; MS (70 eV): m/z
156 [M+, 7], 113(3), 99(2), 75(4), 74(9), 73(100), 59(8),
45(6), 43(4), 41(2). 1,3-Bis(trimethylsilyl)-1-hexyne
(20c): MS (70 eV): m/z 226 [M+, 9], 155(13), 139(6),
138(36), 110(5), 109(30), 74(9), 73(100), 59(5), 45(8). As
main product E- and Z-1,2-bis(trimethylsilyl)-2-hexene
(21c) were obtained, the E-isomer was isolated: 3.39 g
(17 mmol, 17%) with b.p. 87–89 °C (10 Torr). 1H-
To 1.50 g (19 mmol) of 3c in 5 ml of Et2O were
added 10 ml of a 2 M solution of n-butyl lithium in
pentane at −30 °C. Then the solution was allowed to
warm to −10 °C within 40 min and was quenched
with dimethyl sulphate. After the usual work-up, which
afforded a total yield of 90%, the following product
composition was obtained: 9% of cyclopropylallene
(3c), 28% of 3-cyclopropyl-1,2-butadiene (27), 11% of
1-cyclopropyl-2-butyne (28), 11% of 1-cyclopropyl-1-
butyne, 22% of 4-cyclopropyl-2-pentyne, 22% not iden-
tified. Characterization of 1-cyclopropyl-1-butyne: The
1H-NMR spectrum was in accordance with reported
values [48]; MS (70 eV): m/z 94 [M+, 27], 91(21),
79(100), 77(94), 66(35), 65(26), 53(25), 50(19), 39(38),
27(15). Characterization of 4-cyclopropyl-2-pentyne:
MS (70 eV): m/z 108 [M+, 2], 93(96), 91(45), 80(100),
NMR (80 MHz, CDCl3): l 0.0 (s, 9H, CH2Si(CH3 3
0.05 (s, 9H, ꢀCSi(CH3)3), 0.9 (t, 3H, CH3), 1.4 (m, 2H,
CH2CH3), 1.7 (d, 2H, CH2
ꢀCCH2), 5.6 (tt, 1H, ꢀCH
6 ) ),
6
6
6
Si(CH3)3), 2.0 (q, 2H,
6
6
). 13C-NMR (20 MHz,
CDCl3): l −1.1, −0.2, 14.0, 20.2, 22.6, 31.6, 137.5,
137.8. MS (70 eV): m/z 228 [M+, 6], 140(17), 125(20),
112(6), 111(5), 75(4), 74(9), 73(100), 59(10), 45(10).
4.6. Reactions of cyclopropylallene (3c)
1
79(84), 77(71), 67(26), 65(35), 41(39), 39(45). H-NMR
4.6.1. Reaction of cyclopropylallene (3c) with lithium
The reactions were performed as described in the
general procedure. To 0.42 g (60 mmol) of lithium dust
in 25 ml of THF were added 1.50 g (19 mmol) of 3c
and the internal standard in 5 ml of THF. The reaction
(200 MHz, CDCl3): l 0.1–0.5 (m, 4 H, cyclo-
propylꢁCH2), 0.7–0.9 (m, 1 H, cyclopropylꢁCH), 1.2
(d, J=6.9 Hz, 3H, CH–CH
6 3), 1.8 (d, J=2.5 Hz, 3H,
ꢀCCH3), 2.1 (m, 1H, CHꢁCH3).
6

8
A. Maercker et al. / Journal of Organometallic Chemistry 642 (2002) 1–8
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[13] V. Rautenstrauch, Angew. Chem. 87 (1975) 254; Angew. Chem.
Int. Ed. Engl. 14 (1975) 259.
[14] B. Bogdanovic´, B. Wermeckes, Angew. Chem. 93 (1981) 691;
Angew. Chem. Int. Ed. Engl. 20 (1981) 684.
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Ed. Engl. 24 (1985) 262.
[16] N.J.R. van Eikema Hommes, F. Bickelhaupt, G.W. Klumpp,
Angew. Chem. 100 (1988) 1100; Angew. Chem. Int. Ed. Engl. 27
(1988) 1083.
[17] Review: A. Maercker, V.E.E. Daub, A. Deskowski, K.-D. Klein,
K.S. Oeffner, H. Schutz, Macromol. Symp. 134 (1998) 83.
[18] A. Maercker, Liebigs Ann. Chem. 732 (1970) 151.
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Angew. Chem. Int. Ed. Engl. 29 (1990) 667.
4.7. Reactions of 6inylidenecyclopropane (3d)
4.7.1. Reaction of 6inylidenecyclopropane (3d) with
lithium
To 0.26 g (34 mmol) of lithium dust in 15 ml of THF
were added 1.06 g (16 mmol) of 3d in 15 ml of Et2O at
−40 °C. After quenching with dimethyl sulphate and
the usual work-up the total yield of hydrocarbons was
76%, consisting of 39% of ethylidenecyclopropane (32)
and 61% 1-cyclopropyl-1-propyne (29). The mass spec-
trum of 32 was in accordance with a reference spectrum
[49].
[20] A. Maercker, K.-D. Klein, Angew. Chem. 101 (1989) 63; Angew.
Chem. Int. Ed. Engl. 28 (1989) 83.
[21] A. Maercker, K.-D. Klein, J. Organomet. Chem. 410 (1991) C35.
[22] A. Maercker, V.E.E. Daub, Tetrahedron 50 (1994) 2439.
[23] H.J. Reich, J.E. Holladay, T.G. Walker, J.L. Thompson, J. Am.
Chem. Soc. 121 (1999) 9769.
[24] H.N. Cripps, E.F. Kiefer, Org. Synth. Coll. V (1973) 22.
[25] A. Meisters, J.M. Swan, Austr. J. Chem. 18 (1965) 155.
[26] W.R. Roth, T. Schmidt, H. Humbert, Chem. Ber. 108 (1975)
2171.
[27] W. Kirmse, B.-G. von Bu¨low, H. Schepp, Liebigs Ann. 691
(1966) 41.
[28] A. Maercker, R. Sto¨tzel, unpublished results.
[29] J.M. Denis, P. Le Perchec, J.M. Conia, Tetrahedron 33 (1977)
399.
[30] L. Brandsma, Preparative Acetylenic Chemistry, 2nd ed., El-
sevier, Amsterdam, 1988, p. 233.
[31] C. Ru¨chardt, H. Trautwein, Chem. Ber. 98 (1965) 2478.
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Butler, J. Org. Chem. 28 (1963) 372.
4.7.2. Reaction of 6inylidenecyclopropane (3d) with
n-butyl lithium
To a solution of 0.76 g (11 mmol) of 3d in 7 ml of
Et2O and 4 ml of THF were added at −60 °C 5.5 ml
of a 2 M solution of n-butyl lithium in pentane (11
mmol). The reaction mixture was allowed to warm to
−30 °C within 90 min and was then quenched with
dimethyl sulphate. After the usual work-up 0.36 g (5.5
mmol, 50%) of a 1:1 mixture of 1-cyclopropyl-1-
propyne (29) and 1-methyl-1-propynyl-cyclopropane
1
(33) was obtained. The H-NMR spectrum of 33 was in
accordance with reported values [50]. MS (70 eV): m/z
94 (M+, 100), 91(29), 79(88), 77(92), 65(24), 63(9),
53(14), 51(11), 40(9), 39(20).
[33] A. Maercker, M. Theis, Organomet. Synth. 3 (1986) 378.
[34] W. Wagner-Redeker, K. Levsen, H. Schwarz, W. Zummack,
Org. Mass Spectrom. 16 (1981) 361.
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538.
[38] C. Dass, T.M. Sack, M.L. Gross, J. Am. Chem. Soc. 106 (1984)
5780.
Acknowledgements
We thank the Volkswagen-Stiftung and the Fonds
der Chemischen Industrie for financial support.
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