1,3-Diethynylallenes: Stable monomers, length-defined oligomers, asymmetric synthesis, and optical resolution

Article abstract of DOI:10.1002/ejoc.200700373

A series of differently substituted 1,3-diethynylallenes (DEAs) have been synthesized, confirming that the previously introduced construction protocols tolerate a variety of functional groups. The new DEAs bear at least one polar group to facilitate enantiomer separations on chiral stationary phases and to allow further functionalization. They are thermally and environmentally stable compounds since bulky substituents next to the cumulene moiety suppress the tendency to undergo [2+2] cyclodimerization. A series of length-defined oligomers were obtained as mixtures of stereoisomers by oxidative coupling of a monomeric DEA under Glaser-Hay conditions. The electronic absorption data indicate a lack of extended π-electron conjugation across the oligomeric backbone due to the orthogonality of the allenic π-systems. Remarkably, even complex mixtures of stereoisomers only yield one single set of NMR signals, which underlines the low stereodifferentiation in acyclic allenoacetylenic structures. Optical resolution of DEAs represents an amazing challenge, and preliminary results on the analytical level are reported. Asymmetric synthesis by Pd-mediated S_N2′-type cross-coupling of an alkyne to an optically pure bispropargylic precursor opens another promising route to optically active allenes with stereoselectivities currently reaching up to 78 % ee. Wiley-VCH Verlag GmbH & Co. KGaA, 2007.

Full text of DOI:10.1002/ejoc.200700373

FULL PAPER
DOI: 10.1002/ejoc.200700373
1,3-Diethynylallenes: Stable Monomers, Length-Defined Oligomers,
Asymmetric Synthesis, and Optical Resolution
Matthijs K. J. ter Wiel,[a][‡] Severin Odermatt,[a][‡] Patrick Schanen,[a][‡] Paul Seiler,[a] and
François Diederich*[a]
Keywords: Allenes / Carbon-rich scaffolds / Enynes / Oligomerization / Stereoselective synthesis
A
series of differently substituted 1,3-diethynylallenes
oligomeric backbone due to the orthogonality of the allenic
(DEAs) have been synthesized, confirming that the pre- π-systems. Remarkably, even complex mixtures of stereoiso-
viously introduced construction protocols tolerate a variety of
functional groups. The new DEAs bear at least one polar
group to facilitate enantiomer separations on chiral station-
ary phases and to allow further functionalization. They are
thermally and environmentally stable compounds since
bulky substituents next to the cumulene moiety suppress the
tendency to undergo [2+2] cyclodimerization. A series of
length-defined oligomers were obtained as mixtures of ste-
reoisomers by oxidative coupling of a monomeric DEA under
Glaser–Hay conditions. The electronic absorption data indi-
cate a lack of extended π-electron conjugation across the
mers only yield one single set of NMR signals, which under-
lines the low stereodifferentiation in acyclic allenoacetylenic
structures. Optical resolution of DEAs represents an amazing
challenge, and preliminary results on the analytical level are
reported. Asymmetric synthesis by Pd-mediated SN2Ј-type
cross-coupling of an alkyne to an optically pure bispropar-
gylic precursor opens another promising route to optically
active allenes with stereoselectivities currently reaching up
to 78% ee.
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2007)
proved however challenging as they tend to quickly dimer-
ize by [2+2] cycloaddition; furthermore, facile isomeriza-
tions have been observed.[6d] We were able to circumvent
these problems by introducing sterically bulky substituents
close to the cumulene moiety.[6b] Following the synthesis of
a first series of stable DEAs, we proceeded with the prepa-
ration of shape-persistent allenoacetylenic macrocycles with
unusual shapes and symmetries and potential host-guesting
properties.[6a,7]
Although 1,3-diethynylallenes are axially chiral, we used
in all previous work racemic mixtures for acetylenic scaf-
folding.[6] The reason for this is the still valid finding that
the optical resolution of the dialkynylated allenes represents
a formidable challenge, even for a research group with large
experience in diverse optical resolutions. As a result, acety-
lenic scaffolding led to complex mixtures of stereoisomers,
with diastereoisomer (but not enantiomer) separation suc-
ceeding only at the stage of the rigid macrocyclic allenoace-
tylenes.[6a] Clearly, a versatile access to enantiomerically
pure DEAs would be highly desirable, in particular since
semi-empirical calculations predict the formation of helical
foldamers with distinct conformational preferences upon
oxidative acetylenic coupling of enantiomerically pure
DEAs.
Introduction
For a long time, since the first discussion by Van’t Hoff,[1]
allenes have been regarded as a curiosity and considered
as unstable. However, the discovery of cumulenic bonds in
natural products has risen the attention given to these struc-
tures.[2] Moreover, allenes are very interesting reactive inter-
mediates.[3] It is therefore not surprising that much progress
has been achieved in the synthesis and the understanding
of the properties of this important class of compounds.[4]
Thus, allenes bearing two different substituents at each of
the two termini (RRЈC=C=CRRЈ) are chiral and the op-
tical stability of enantiomers is high. For 1,3-dimethylallene,
the activation free enthalpy for rotational isomerism leading
to racemization was determined by Roth and co-workers as
∆G϶ = 44.2 kcalmol–1.[5]
Our group has been involved in the exploration of ethyn-
ylated allenes as building blocks for the construction of lin-
ear and macrocyclic carbon-rich scaffolds through oxidative
acetylenic coupling.[6] Particularly interesting in this regard
are 1,3-diethynylallenes (DEAs). The synthesis of DEAs
[a] Laboratorium für Organische Chemie, ETH-Zürich,
Hönggerberg, HCI, 8093 Zürich, Switzerland
Fax: +41-44-632-1109
While the synthesis of optically pure allenes has been
well studied,[4f,8] most of the reported routes seem difficult
to apply to the preparation of enantiomerically pure DEAs,
due to the fact that the two acetylenic substituents provide
E-mail: diederich@org.chem.ethz.ch
[‡] M. K. J. t. W., P. S., and S. O. made equal contributions to this
paper.
Supporting information for this article is available on the
WWW under http://www.eurjoc.org or from the author.
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M. K. J. ter Wiel, S. Odermatt, P. Schanen, P. Seiler, F. Diederich
The synthesis of the new monomeric DEAs followed the
FULL PAPER
only little possibility for stereodifferentiation. Taking into
account mechanistic considerations,[9] it should however be previously established strategy[6b] and started from ynones
possible to synthesize optically pure DEAs via a Pd-cata- 1a–d (Scheme 1). The syntheses of these ynones and their
lyzed SN2Ј-type cross-coupling reaction of alkynes to op- precursors are described with full experimental details in
tically pure bispropargylic precursors, as reported for other the electronic supporting information. Bispropargylic
allenes.[8i,10] Finally, resolution of racemates by high-per- alcohols (Ϯ)-2a–d were obtained by addition of a protected
formance liquid chromatography (HPLC)[11] or separation lithium acetylide in THF. The (iPr)3Si protecting group was
of intermediately prepared diastereoisomers could also chosen as its steric bulk is needed to control the regiochemi-
yield the desired optically pure DEAs, although such ap- stry of the SN2Ј-type Sonogashira cross-coupling used to
proaches have found only limited application in the domain generate the allenes.[6b] The alcohols were then transformed
of allenes.
(NaHDMS, MeOCOCl) into the carbonates (Ϯ)-3a–d fea-
In this work, we present the synthesis of new DEAs with turing the bispropargylic leaving group necessary for form-
polar functional groups introduced with the aim to facili- ing the allenes. The alkyne-protected allenes (Ϯ)-4a–d were
tate enantiomer separations and demonstrate the substan- finally obtained as stable compounds by Pd-catalyzed SN2Ј-
tial scope – in terms of different substitution – of the pre- type reaction of the carbonates with (iPr)3Si-protected cop-
viously reported protocol for the formation of 1,3-dialk- per acetylide.[12] Yields of this reaction ([Pd(PPh3)4], CuI,
ynylated allenes.[6b] We report the synthesis of length-de- Hünig base) were rather low but reproducible; no advantage
fined oligomers by oxidative coupling and demonstrate the was found using the pentafluorobenzoate as a better leaving
lack of extended π-electron delocalization in these systems. group.[13]
Finally, we present our first results in the synthesis and iso-
lation of optically pure DEAs, following both the routes of
enantiomer separations and stereoselective synthesis.
Removal of the alkyne protecting groups with nBu4NF
in THF yielded the more delicate, unprotected DEAs. The
deprotection of the bis(1-methoxy-1-methylethyl) derivative
(Ϯ)-4a proceeded smoothly, although the yield of (Ϯ)-5a
could not be determined and the compound not isolated in
pure form since it is highly volatile and evaporates together
with the solvent. Its formation was however clearly proved
by the appearance of the ethynyl resonance with correct rel-
Results and Discussion
Synthesis of Monomeric 1,3-Diethynylallenes with Polar
Functional Groups
1
ative intensity (2 H) at δ = 3.09 ppm in the H NMR spec-
To assist the synthesis of optically pure allenes, we de- trum in CDCl3, with still some solvent (cyclohexane) from
cided to synthesize allenes bearing at least one polar func- the purification present. Allene (Ϯ)-5b with 1-(4-meth-
tional group. On the one hand, the polar group should fa- oxyphenyl)-1-methylethyl substituents and allene (Ϯ)-5c
cilitate the separation by chiral HPLC. On the other hand, with 1-methyl-1-(3,4,5-trimethoxyphenyl)ethyl substituents
this functional group could also be used for the introduc- were isolated in good yields as stable compounds, which
tion of a chiral auxiliary, leading to the formation of dia- can be stored without decomposition under an inert atmo-
stereoisomers, which could potentially be separated.
sphere at ambient temperature. Crystals of (Ϯ)-5b, suitable
Scheme 1. Formation of monomeric 1,3-diethynylallenes. a) (iPr)3Si–CϵC–Li, THF, –78 °C; b) (i) NaHDMS, THF, –78 °C; (ii) MeOC-
OCl, –78 °C; c) (iPr)3Si–CϵC–H, CuI, [Pd(PPh3)4], Hünig base, ClCH2CH2Cl; d) nBu4NF, THF; e) HCl, THF, H2O. THF = tetra-
hydrofuran; NaHDMS = sodium hexamethyldisilazide.
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1,3-Diethynylallenes
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for X-ray crystallography, were obtained by slow evapora- rivative (Ϯ)-13. Even prolonged stirring in the presence of
tion of n-hexane, and the crystal structure proved the con- nBu4NF in THF did not lead to the cleavage of the tBu-
stitution of the new 1,3-diethynylallene derivative (Fig- Me2Si ether, but only to removal of the alkyne protecting
ure 1). The stable bisphenol derivative (Ϯ)-5d was also ob- group.
tained in high yield by removal of the tetrahydropyran-2-
yl (THP) protecting groups (97%) with HCl in THF/H2O,
followed by alkyne deprotection (91%).
Oligomers
Oligomers and polymers with allenic backbones are only
scarcely investigated.[14] DEAs should be ideally suited for
oligomerization by oxidative acetylenic coupling with for-
mation of oligomers with an allenoacetylenic backbone.
This was first demonstrated with the preparation of a series
of dimeric chromophores starting from the differentially
protected DEAs (Ϯ)-14a–c (Scheme 3). While (Ϯ)-14a had
been previously reported,[6b] the allenes (Ϯ)-14b,c were syn-
Figure 1. ORTEP plot of (Ϯ)-5b at 223(2) K with vibrational ellip-
thesized according to the protocols depicted in Scheme 1
soids shown at the 30% probability level. Arbitrary numbering.
and Scheme 2. Again, a more facile separation of the
formed dimeric stereoisomers was expected as a result of
Selected bond lengths [Å]: C1–C2 1.313(14), C3–C4 1.187(2).
Starting from the ynone 7 with a tBuMe2Si ether func- the introduction of polar ether groups. Selective monode-
tionality, we hoped to prepare a DEA derivative ultimately protection of (Ϯ)-14a–c with K2CO3 in MeOH/THF yielded
featuring a free aliphatic hydroxy group which could then (Ϯ)-15a–c, and oxidative coupling under Hay conditions
be esterified with optically active acids with formation of provided the corresponding “dimers” 16a–c in excellent
separable diastereoisomers. Furthermore, it was of interest, yield. Removal of the (iPr)3Si protecting groups was pos-
in view of acetylenic scaffolding, to introduce different al- sible and deprotection of 16a yielded 17a, which could be
kyne protecting groups. Thus, (iPr)3Si-protected lithium used as an “expanded monomer”[15] in oxidative oligomer-
acetylide was added to ynone 7 (see SI) and the resulting izations (see below). Compound 17c with two free ethynyl
alcohol (Ϯ)-8 was converted into carbonate (Ϯ)-9 residues was obtained as a remarkably stable oil, which
(Scheme 2). Again, SN2Ј-type cross coupling with Et3Si- could be isolated and completely characterized.
protected acetylene with formation of allene (Ϯ)-10 was
Starting from the racemic DEAs (Ϯ)-15a–c, the “dimers”
only low-yielding (8%). Selective removal of the Et3Si pro- should form as a mixture of stereoisomers, a meso and a d/l
1
tecting group with K2CO3 in MeOH/THF afforded mono- form. However, both H and 13C NMR spectroscopy only
deprotected allene (Ϯ)-11 in 90% yield. Attemps to selec- revealed one unique set of resonances! There is, however,
tively cleave the tBuMe2Si ether with pTsOH in wet THF no reason to exclude the existence and formation of both
with formation of alcohol (Ϯ)-12 were unsuccessful; rather, meso-(P,M) and d/l-(PP)/(MM) forms, despite the fact that
the (iPr)3Si group was removed, providing the diethynyl de- we were unable to separate them under various chromato-
Scheme 2. Formation of 1,3-diethynylallene (Ϯ)-13. a) (iPr)3Si–CϵC–Li, THF, –78 °C, 88%; b) (i) NaHDMS, THF, –78 °C, (ii) MeOC-
OCl, 86%; c) Et3Si–CϵC–H, CuI, [Pd(PPh3)4], Hünig base, ClCH2CH2Cl, 8%; d) K2CO3, MeOH, THF, 90%; e) pTsOH, THF or
nBu4NF, THF.
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FULL PAPER
Scheme 3. Formation of DEA dimers. a) K2CO3, MeOH/THF; b) CuCl, TMEDA, air, acetone; c) nBu4NF, THF. TMEDA = N,N,NЈ,NЈ-
tetramethylethylenediamine.
graphic conditions. We have previously encountered iden-
tical NMR spectral behavior as well as practical insepa-
rability of stereoisomeric 1,3-butadiynes bearing stereogenic
elements at the two termini such as chiral allenes[6a] or “chi-
ral” methyl groups.[16] Presumably, the large separation be-
tween the stereogenic elements created by the buta-1,3-di-
yne-1,4-diyl spacer, paired with the great ease of rotation
about this rod-like fragment, prevent the terminal ste-
reogenic elements from influencing each other differentially
in the two diastereoisomeric (meso and d/l) forms, thereby
creating close spectral similarity (or even near-identity) and
leading to practical inseparability.
By crystallization at low temperature, we were able to
grow a small crystal of a meso-diastereoisomer, (P,M)-16a,
which was suitable for X-ray analysis. The ORTEP plot in
Figure 2 shows that a large distance of 10.5 Å is created by
the butadiynediyl spacer between the first points of differ-
ence in the diastereoisomers, namely the terminal allenic
centers C(9) and C(9Ј). Such spatial distance, paired with
the presence of a spacer with no distinct conformational
preferences that could transfer the chiral information from
one stereogenic element to the other, apparently generates
spectral near-identity as well as practical inseparability.
For the synthesis of oligomers by oxidative coupling, we
used the end-capping oligomerization of an “expanded
monomer”, which we had previously applied to the prepa-
ration of poly(triacetylene) (PTA) oligomers with lengths
Figure 2. ORTEP plot of (P,M)-16a at 253(2) K with vibrational
ellipsoids shown at the 30% probability level. Arbitrary numbering.
The distance between C(9) and C(9Ј) in the crystal amounts to
10.5 Å. Selected bond lengths [Å]: C1–C2 1.201(2), C3–C8
1.312(2), C8–C9 1.312(2), C14–C15 1.204(2).
up to 18 nm (24-mer).[15] Dimeric 16a, as a mixture of meso composed of n = 4 (19), 6 (20), 8 (21), and 10 (22) repeat
and d/l forms, was partially deprotected using nBu4NF in units were obtained. The composition of the oligomers was
the presence of o-nitrophenol (Scheme 4), thereby yielding clearly evidenced by the high-resolution matrix-assisted la-
a mixture of starting material, chain propagating (17a), and ser-desorption-ionization mass spectra (HR-MALDI-MS)
end-capping (18) building blocks. This mixture was submit- which showed for each pure oligomer fraction the proton-
ted without purification to oxidative acetylenic coupling ated molecular ion or the [M + Na]+ ion as the base peak.
under Hay conditions. After stirring for a few hours at Again, it can be expected that all these oligomers are
50 °C, complete conversion was observed. By chromatog- formed as mixtures of stereoisomers, including pairs of
raphy on SiO2, followed by gel permeation chromatography enantiomers as well as achiral diastereoisomers. Similar to
1
(GPC) over BioBeads S-X1, oligomers of defined length the findings for dimeric DEAs discussed above, H and 13
C
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1,3-Diethynylallenes
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Scheme 4. Formation of oligomeric DEAs with defined length. a) o-Nitrophenol (1.3 equiv.), nBu4NF (1.1 equiv.), THF, 20 °C; b) CuCl
(0.4 equiv.), equiv. TMEDA (1.4 equiv.), o-dichlorobenzene, air, 50 °C.
NMR analysis does not differentiate between the different coefficient ε [–1 cm–1] with growing length of the oligomer.
diastereoisomers in an oligomeric fraction of defined This spectral behavior is obviously in sharp contrast to the
length: only one set of resonances (as would be expected one observed for poly(triacetylene) oligomers in which the
for a single stereoisomer) was obtained. Also, separation of longest conjugated π-chromophore is extended with each
the different diastereoisomers with same oligomeric length addition of a new enediyne repeat unit. Most importantly,
was unsuccessful.
the successful oligomerization suggests that the proposed
The UV/Vis spectra of the oligomers recorded in cyclo- helical foldamer predicted to form from optically active
hexane are shown in Figure 3. Upon passing from mono- DEA monomers can indeed be prepared in future study.
meric (Ϯ)-23[6b] to the smallest oligomer, dimeric 16a, two
characteristic bands appear at longer wavelength (296 and
316 nm) that are assigned to the newly formed, longest lin-
early π-conjugated ene-diyne-ene fragment. Also, the end-
Towards Optical Resolution of DEAs
absorption shifts bathochromically. In contrast, the posi-
Both the separation of enantiomers by high-performance
tions of the two characteristic longest-wavelength bands liquid chromatography (HPLC) on chiral stationary phases
and the end-absorption are hardly shifted further upon ex- (CSPs) and derivatization to yield a pair of separable dia-
tending the oligomeric length. The maxima are only weakly stereoisomers were pursued on the way to optically active
shifted upon moving from dimeric 16a (296, 316 nm) to tet- DEAs. However, optical resolution by both methods proved
rameric 19 (300, 321), to hexameric 20 (301, 322), to octa- to be a formidable challenge.
meric 21 (301, 323), and decameric 22 (302, 324). This op-
As an example for the latter approach, allenes (Ϯ)-5d
tical behavior proves that there is almost no conjugation and (Ϯ)-6 were treated with (1S)-(–)-camphanic chloride
through the allenic bond in these allenoacetylenic oligo- leading to the formation of esters 24 and 25, in both cases
mers. The longest π-conjugated ene-diyne-ene chromophore as a pair of diastereoisomers (Scheme 5). Unfortunately,
remains the same from the dimer to the decamer, only the these stereoisomers could not be separated chromatographi-
number of these chromophoric fragments increases, which cally on a variety of stationary phases or by recrystalli-
is expressed by the amplification of the molar extinction zation.
Figure 3. UV/Vis spectra of the different allenoacetylenic oligomers in cyclohexane at 20 °C. All oligomers are present as mixtures of
stereoisomers.
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M. K. J. ter Wiel, S. Odermatt, P. Schanen, P. Seiler, F. Diederich
FULL PAPER
Scheme 5. Formation of diastereoisomeric esters for optical resolution. a) (1S)-(–)-Camphanic chloride, Hünig base or Et3N, CH2Cl2.
For the separation by HPLC on polar CSPs, several diffi- Stereoselective Synthesis of Allenes via Optically Active
culties could be foreseen. Most DEAs are highly apolar, so Bispropargylic Pentafluorobenzoates
little interaction with a polar stationary phase is possible.
Moreover, stereodifferentiation between the two enantio-
On the basis of reports in the literature,[9,10] it seemed
mers is very low. And finally, low solubility in hexane for possible to synthesize optically pure allenes by stereoselec-
some of the DEAs added another challenge to the study. A tive Pd-catalyzed cross-coupling through anti SN2Ј-type ad-
first series of experiments was conducted with the apolar dition of alkynes to optically pure bispropargylic pentafluo-
allenes (Ϯ)-15a and (Ϯ)-23. However no satisfying results robenzoates. Only two examples of optically active tertiary
could be obtained despite the use of various stationary bispropargylic alcohols have been reported.[17] These com-
phases (the following columns were used: Chiralcel OJ, Chi- pounds could in principle be obtained by asymmetric alk-
ralcel OD-R, Chiralpak OT, Whelk-O 1, CyclobondTM
I
ynylation of propargylic ketones. Despite some recent ex-
SN). Retention times were extremely short, even with pure amples of asymmetric alkynylations of ketones,[18] we
hexane as solvent, showing that there exist indeed only little thought that this approach would not be promising in our
interactions with the stationary phase. The CyclobondTM
I
case due to lacking stereodifferentiation with two similarly
SN column was also used under reversed phase conditions bulky ethynyl residues. We therefore turned to the resolu-
using MeCN/MeOH or MeCN/NaClO4 as eluents, but tion of diastereoisomeric esters of alcohol (Ϯ)-26.[6b] As the
without success.
ester obtained by reaction with (1S)-(–)-camphanic chloride
It was expected that the compounds synthesized in this was not crystalline and not very stable, we first deprotected
study would show somewhat better behavior on the chiral (Ϯ)-26 (Scheme 6). Alcohol (Ϯ)-27 was then esterified to
HPLC columns, as they all feature at least one polar group. give stable, crystalline 28 as a pair of diastereoisomers. Sev-
However, (Ϯ)-4a, (Ϯ)-14b, and (Ϯ)-15b were eluted quickly eral reaction conditions were tried, and finally coupling
even with pure hexane on three different CSPs (Chiralcel with (1S)-(–)-camphanic acid in the presence of DMAP and
OD or OJ and Chiralpak AD). Also (Ϯ)-10 gave no satis- DCC[19] seemed to be the most reproducible, also on a
factory result. It seemed that the introduction of a simple larger scale.
methoxy group was not sufficient to achieve a good separa-
The pure diastereoisomers [Ն98% diastereoisomeric ex-
tion. In the aromatic series, the separation was investigated cess (de)] of ester 28 were obtained by fractional recrystalli-
with silylated allene (Ϯ)-4b, the unprotected DEA (Ϯ)-5b, zation (see Experimental Section for details). By X-ray
and dimers 16b and 17b, which were used as mixtures of analysis, the absolute (R,S,R)-configuration could be as-
meso- and d/l-forms. These experiments showed that the signed to the less soluble isomer (Figure 4). Both isomers
presence of silyl protecting groups needs to be avoided for could also be separated on neutral Al2O3 (activity I), which
successful HPLC separation on a CSD. Both (Ϯ)-4b and allowed purification of the more soluble diastereoisomer.
(Ϯ)-16b were eluted quickly without separation. Also, di-
mer 17b gave only disappointing results as did (Ϯ)-6 and were then hydrolyzed under basic conditions in MeOH/
the camphanic ester 24. THF (Scheme 6). To prove that no racemization occurred
Diastereomerically pure esters (R,S,R)-28 and (S,S,R)-28
Preliminary promising results were obtained with the during the saponification process, part of alcohol (R)-(–)-27
bis(4-methoxyphenyl)-substituted allene (Ϯ)-5b in collabo- was resubmitted to esterification with (1S)-(–)-camphanic
ration with Emile Cavoy (UCB). Complete separation of chloride. The corresponding ester was obtained dia-
the two enantiomers was observed on an analytical Chi- stereomerically pure. The free alkyne was then silylated and
ralcel AD-H column with a 98:2 pentane/MeOH mixture alcohol (S)-(–)-29 transformed into the perfluorobenzoate
for the elution (SI). However, these results could not yet be (S)-30.[6a] As O-silylation was not observed, (S)-(–)-29 was
transferred to a preparative column. This ambitious not isolated but perfluorobenzoyl chloride added directly to
task is currently the subject of a collaboration with Marco the intermediate alkoxide.
Mazzotti (ETH) and will be communicated in due
course.
With the enantiomerically pure precursor (S)-30 in
hands, the cross-coupling to the optically pure allene (P)-
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Scheme 6. Preparation of the optically active bispropargyl pentafluorobenzoate (S)-30. a) K2CO3, MeOH/THF, 63%; b) (1S)-(–)-cam-
phanic acid, DMAP, DCC, CH2Cl2, 59%; c) 1  NaOH aq, MeOH/THF, 20 °C, 94%; d) (i) nBuLi, THF, –78 °C; (ii) (iPr)3SiCl, –78 °C
to 20 °C; e) (i) LiHMDS, THF, 0 °C; (ii) C6F5COCl, 0 °CǞ20 °C; f) (i) nBuLi, THF, –78 °C; (ii) (iPr)3SiCl; (iii) C6F5COCl,
–78 °CǞ20 °C, 30–40%. DMAP = 4-(dimethylamino)pyridine; DCC = dicyclohexylcarbodiimide; LiHMDS = lithium hexamethyldisyl-
azide.
14a, resulting from anti-addition of Me3Si–CϵCH, as pro-
posed in the literature,[9] was investigated (Scheme 7). The
absolute configuration of the allene was assigned based on
the reaction mechanism. The Pd° complex attacks the triple
bond anti to the leaving group. As the acetylene is intro-
duced by a reductive elimination, the overall addition re-
mains anti. Unfortunately, we were not able to prove this
assumption. Different conditions were applied, and the de-
tails of this investigation can be found in the Supporting
Information. To determine the optical purity of DEAs (P)-
14a and mono-deprotected (P)-15a, the latter was trans-
formed into the propargyl-substituted Mosher ketone
(R,P)-31.[20] Reaction with the chloride of the Mosher
acid[21] gave the best results of ketone, but the yields re-
mained low. Optimization of the reaction conditions was
studied with racemic allene, but it was unsuccessful. It pro-
vided, however, proof that both diastereoisomers were
formed at the same rate. H NMR integration of (R,P)-31
Figure 4. ORTEP plot of (R,S,R)-28 at 220 K with vibrational el-
lipsoids shown at the 30% probability level. Arbitrary numbering.
1
Scheme 7. a) Me3Si–CϵC–H, [Pd(PPh3)4], CuI, Cy2NMe (2ϫ0.2 equiv.), toluene, 20 °C, 24 h, 28%; b) K2CO3, MeOH/THF, 98%; c) (i)
nBuLi, THF/hexane; (ii) (R)-MTPA-Cl, –78 °CǞ20 °C, 35%. Cy = cyclohexyl; MTPA = (R)-1-methoxy-1-(trifluoromethyl)phenylacetyl
chloride.
Eur. J. Org. Chem. 2007, 3449–3462
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3455

M. K. J. ter Wiel, S. Odermatt, P. Schanen, P. Seiler, F. Diederich
FULL PAPER
and its minor diastereoisomer (R,M)-31 allowed the deter-
mination of the diastereoisomeric excess. Assuming that no
racemization occurred during SiMe3 deprotection and syn-
thesis of the Mosher ketone, the optical purity of (P)-14a
and (P)-15a could be established.
The best result was obtained in toluene at 20 °C with
Cy2NMe (0.4 equiv.) as base. In this case, the enantiomeric
excess (ee) of the allene was 78%, but the yields were low
with only 25%. At this moment, it is difficult to advance
any conclusions on the parameters influencing the dia-
stereoselectivity. Further research is currently carried out to
get a clearer picture of the reaction.
Experimental Section
Materials and General Methods: Reagents and solvents were pur-
chased at reagent grade from Acros, Aldrich, and Fluka, and used
as received. THF was freshly distilled from Na/benzophenone un-
der N2. Toluene was freshly distilled from Na under N2. CH2Cl2
was freshly distilled from CaH under N2. All reactions were per-
formed under an inert atmosphere by applying a positive pressure
of N2 unless otherwise noted. Flash chromatography (FC) was car-
ried out with SiO2 60 (particle size 0.040–0.063 mm, 230–400 mesh;
Fluka) and distilled technical solvents. Thin-layer chromatography
(TLC) was conducted on aluminum sheets coated with SiO2 60 F254
obtained from Macherey–Nagel; visualization with a UV lamp (254
or 366 nm) and potassium permanganate or cerium molybdate
staining. The chiral stationary phases tested for optical resolutions
of racemic DEAs by HPLC and the solvent mixtures used are
shown in a Table in the electronic supporting information (see also
the footnote on the first page of this paper). Melting points (m.p.)
were measured with a Büchi B-540 melting-point apparatus in open
capillaries and are uncorrected. 1H NMR and 13C NMR spectra
were measured with a Varian Gemini 300, a Varian Mercury 300,
or a Bruker ARX300 at 300 and 75 MHz respectively. Chemical
shifts are reported in ppm relative to the signal of Me4Si. Residual
solvent signals in the 1H and 13C NMR spectra were used as an
internal reference. Coupling constants (J) are given in Hz. The ap-
parent resonance multiplicity is described as s (singlet), br. s (broad
singlet), d (doublet), t (triplet), q (quartet), and m (multiplet). In-
frared spectra (IR) were recorded with a Perkin–Elmer Spectrum
BX instrument. UV/Vis spectra were recorded with a Varian Cary-
5 spectrophotometer. The absorption wavelenghts are reported in
nm with the molar extinction coefficient ε (–1 cm–1) in brackets;
shoulders are indicated as sh. High-resolution (HR) EI-MS spectra
were measured with a Hitachi–Perkin–Elmer VG-Tribrid spectrom-
eter. HR FT-MALDI spectra were measured with an IonSpec Ul-
tima Fourier transform (FT) instrument with [(2E)-3-(4-tert-bu-
tylphenyl)-2-methylprop-2-enylidene]malononitrile (DCTB) or 3-
hydroxypicolinic acid (3-HPA) as matrix. The most important sig-
nals are reported in m/z units with M as the molecular ion. Elemen-
tal analyses were performed at the Laboratorium für Organische
Chemie, ETH Zürich, with a LECO CHN/900 instrument.
Conclusions
This paper demonstrates the substantial scope of our
previously described method to synthesize stable 1,3-dieth-
ynylallenes (DEAs). Many of the new DEAs bear polar
functional groups for further derivatization; furthermore,
such polar groups are required for a successful optical reso-
lution by HPLC on chiral stationary phases. Even with ter-
minally deprotected ethynyl groups, the new derivatives are
stable as a result of the steric bulk around the allene core.
Without bulky substituents directly shielding the allene
core, DEAs are unstable and undergo reactions such as
[2+2] cycloadditions.
Terminally deprotected DEAs are versatile building
blocks for higher-order two- and three-dimensional scaf-
folds by oxidative acetylenic coupling. A range of dimeric
DEAs as well as an oligomeric series with up to ten repeat
units were prepared starting from racemic monomer and
fully characterized. However, stereodifferentiation in these
stable allenoacetylenic chromophores is poor and the vari-
ous stereoisomers could not be separated. As a result of a
lack of diastereodifferentiation, all stereoisomers in oligo-
mers of a given length show identical NMR spectroscopic
1
properties, i.e. the H and 13C NMR spectra only feature
one unique set of resonances. The UV/Vis spectra of the
General Method A, Synthesis of the Bispropargylic Tertiary Alcohol:
different oligomers clearly confirm that π-electron conjuga- nBuLi (1.6  in THF, 1.25 equiv.) was added to a solution of mono-
protected acetylene (1.15 equiv.) in THF (15 mL) at –78 °C. After
stirring for 15 min at –78 °C and 15 min at 20 °C, the solution was
cooled to –78 °C and the ynone (1 equiv., ca 4 mmol) dissolved in
THF (5 mL) added. The mixture was stirred at –78 °C, 0 °C or
20 °C until completion and quenched by adding a saturated aq.
NH4Cl solution (50 mL). The aq. layer was extracted with Et2O
(3ϫ50 mL). The combined organic layers were washed with a satu-
rated aq. NaCl solution (100 mL), dried with Na2SO4, and evapo-
rated under reduced pressure.
tion across allenes with their orthogonal π-systems is
strongly limited: the positions of the longest wavelength
bands are nearly unchanged upon moving from dimeric to
decameric oligomer.
The poor enantiodifferentiation in 1,3-diethynylallenes is
also apparent in the formidable challenge we encountered
in the optical resolution of these compounds. Nevertheless,
promising results have finally been obtained with analytical
samples. Efforts to transfer the conditions to preparative-
scale separations are underway, but remain quite challeng-
ing. Similarly, optical resolutions through the intermediacy
of diastereoisomeric derivatives have so far not been suc-
cessful.
Finally, asymmetric synthesis by Pd-mediated SN2Ј-type
cross-coupling of an alkyne to optically pure bispropargylic
pentafluorobenzoates – scarcely known intermediates –
looks promising and already yielded optically active allenes
with stereoselectivities currently reaching up to 78% ee.
Further work in this direction is currently underway.
General Method B, Synthesis of the Bispropargylic Carbonate from
the Corresponding Tertiary Alcohol: NaHDMS (1  solution in
THF, 1.1 equiv.) was added to a solution of alcohol (1 equiv.) in
THF (15 mL) at –78 °C. After stirring for 15 min at –78 °C and
15 min at 20 °C, the mixture was re-cooled to –78 °C and methyl
chloroformate (1.25 equiv.) added. The mixture was allowed to
reach 20 °C and stirred until completion. It was then quenched by
adding a saturated aq. NH4Cl solution (50 mL). The aq. layer was
extracted with Et2O (3ϫ50 mL). The combined organic layers were
washed with a saturated aq. NaCl solution (100 mL), dried with
Na2SO4, and evaporated under reduced pressure.
3456
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© 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2007, 3449–3462

1,3-Diethynylallenes
FULL PAPER
General Method C, Synthesis of the Allene by Sonogashira Cross-
Coupling: In a small flask, a mixture of CuI (0.1 equiv.) and
[Pd(PPh3)4] (0.1 equiv.) was dried under vacuum to remove all
moisture and oxygen. ClCH2CH2Cl (2.5 mL) was added and Ar
bubbled through the mixture for 5 min. In a Schlenk flask, a solu-
tion containing carbonate (1 equiv., ca 220 µmol) and (iPr)3Si–
as a colorless oil in 49% yield after purification by FC (SiO2; cyclo-
hexane/CH2Cl2, 3:1, Rf = 0.15). H NMR (300 MHz, CDCl3): δ =
1.00 (m, 42 H), 1.44 (s, 6 H), 1.46 (s, 6 H), 3.78 (s, 6 H), 6.78 (d, J
= 9.0 Hz, 4 H), 7.17 (d, J = 9.0 Hz, 4 H) ppm. 13C NMR (75 MHz,
CDCl3): δ = 11.4, 18.7, 28.4, 28.6, 42.6, 55.2, 94.4, 100.3, 104.2,
1
113.1, 127.5, 139.0, 157.6, 214.0 ppm. IR (film): ν = 2940, 2863,
˜
acetylene (12 equiv.) in ClCH2CH2Cl (5 mL) and Hünig base 2359, 2143, 1612, 1151, 1462, 1250, 1182, 1038, 882, 827, 668 cm–1.
(5 mL) was degassed for 5 min. It was then heated to 80 °C, and
the catalyst suspension was added. The mixture was stirred until
all the carbonate was consumed as observed by TLC. It was then
poured into a saturated aq. NH4Cl solution (50 mL), followed by
extraction with CH2Cl2 (3ϫ25 mL). The combined organic layers
were washed with water (50 mL), dried with Na2SO4, and evapo-
rated under reduced pressure.
UV/Vis (n-hexane): λmax (ε) = 227 (39300), 240 (42700), 250
(43100). MS (EI): m/z (%) = 696 (0.7) [M]+, 539 (2.7), 149 (100).
EI-HRMS: m/z calcd. for C45H68O2Si2+: 696.4758, found 696.4756.
C45H68O2Si2 (697.19): calcd. C 77.52, H 9.83; found C 77.46, H
9.69.
(؎)-3,5-Bis[1-(4-methoxyphenyl)-1-methylethyl]hepta-3,4-diene-1,6-
diyne [(؎)-5b]: Following general method E, (Ϯ)-5b was obtained
from (Ϯ)-4b (80 mg, 115 µmol) as a white solid in 79% yield after
purification by FC (SiO2; cyclohexane/EtOAc, 16:1, Rf = 0.25). 1H
NMR (300 MHz, CDCl3): δ = 1.45 (s, 6 H), 1.49 (s, 6 H), 2.92 (s,
2 H), 3.80 (s, 6 H), 6.84 (d, J = 8.6 Hz, 4 H), 7.19 (d, J = 8.6 Hz,
4 H) ppm. 13C NMR (75 MHz, CDCl3): δ = 28.5, 28.6, 42.6, 55.2,
77.2, 81.1, 103.3, 113.2, 127.3, 138.5, 157.7, 213.9 ppm. MS (EI):
m/z (%) = 356 (1), 314 (28), 313 (100). MS (ESI): m/z (%) = 407
[M + Na]+; no exact mass or correct elemental analysis could be
obtained.
General Method D, Selective Et3Si-Alkyne Deprotection with
K2CO3: The allene (1 equiv.) was dissolved in THF (5 mL), and
methanol (5 mL) and K2CO3 (47 equiv.) were added. The mixture
was stirred for 14 h at 20 °C and then poured into water (50 mL).
The aq. layer was extracted with Et2O (3ϫ25 mL), then the com-
bined organic layers were washed with water (3ϫ25 mL), dried
with Na2SO4, and evaporated under reduced pressure.
General Method E, (iPr)3Si-Alkyne Deprotection with nBu4NF: The
allene was dissolved in THF, and a 1.0  solution of nBu4NF in
THF was added. After stirring until completion, water was added
and the mixture extracted with Et2O (3ϫ). The combined organic
layers were washed with water, dried with Na2SO4, and evaporated
under reduced pressure.
(P,M)- and (P,P)/(M,M)-3,5,10,12-Tetrakis(tert-butyl)-1,14-bis(tri-
isopropylsilyl)tetradeca-3,4,10,11-tetraene-1,6,8,13-tetrayne
(16a):[6b] To a solution of 15a[6b] (90 mg, 0.252 mmol, 1.0 equiv.) in
ClCH2CH2Cl (4 mL), a solution of TMEDA (30 µL, 0.206 mmol,
0.8 equiv.) and CuCl (7.4 mg, 0.075 mmol, 0.3 equiv.) in
ClCH2CH2Cl (1 mL) were added. The resulting mixture was stirred
in an open flask for 3 h at 50 °C. Cyclohexane was added and the
organic layer washed twice with a saturated aq. NH4Cl solution.
The combined aq. layers were extracted with cyclohexane. The or-
ganic layer was dried with MgSO4, filtered, and the solvents evapo-
rated. The residue was filtered through SiO2 (cyclohexane). Com-
pound 16a (86 mg, 0.122 mmol, 96%) was obtained as a mixture
of an enantiomeric pair and a diastereoisomeric meso-isomer. Col-
(؎)-6-(4-Methoxyphenyl)-3-[1-(4-methoxyphenyl)-1-methylethyl]-6-
methyl-1-(triisopropylsilyl)hepta-1,4-diyn-3-ol [(؎)-2b]: Following
general method A, (Ϯ)-2b was obtained from 1b (1.42 g,
4.06 mmol) as a colorless oil in 99% yield after purification by flash
chromatography (FC) (SiO2; cyclohexane/EtOAc, 8:1, Rf = 0.45).
1H NMR (300 MHz, CDCl3): δ = 1.09 (m, 21 H), 1.51 (s, 3 H),
1.54 (s, 3 H), 1.62 (s, 6 H), 2.13 (s, 1 H), 3.79 (s, 3 H), 3.80 (s, 3
H), 6.80–6.83 (m, 4 H), 7.38 (d, J = 8.7 Hz, 2 H), 7.51 (d, J =
8.7 Hz, 2 H) ppm. 13C NMR (75 MHz, CDCl3): δ = 11.4, 18.7,
24.3, 24.7, 31.5, 31.6, 35.3, 45.9, 55.17, 55.22, 71.1, 81.6, 85.6, 91.6,
106.9, 112.6, 113.3, 126.5, 129.7, 135.2, 138.7, 157.8, 158.1 ppm.
1
orless solid. Rf = 0.49 (SiO2; hexane); m.p. 110–118 °C. H NMR
(500 MHz, CDCl3): δ = 1.08 (s, 42 H), 1.14 (s, 36 H) ppm. 13C
NMR (125 MHz, CDCl3): δ = 11.3, 18.6, 28.9, 29.0, 35.5, 35.9,
IR (film): ν = 3455, 2940, 2863, 2358, 1611, 1512, 1462, 1382, 1361,
˜
75.3, 76.9, 94.9, 99.6, 102.4, 104.6, 214.2 ppm. IR (KBr): ν = 2963,
˜
1297, 1249, 1181, 1036, 828, 668 cm–1. MS (MALDI): m/z (%) =
555 (45) [M + Na]+, 516 (42), 515 (100), 235. MALDI-HRMS: m/z
calcd. for C34H48NaO3+: 555.3273, found 555.3273. C34H48O3Si
(532.82): calcd. C 76.64, H 9.08; found C 76.75, H 8.97.
2865, 2142, 1464, 1394, 1363, 1241, 1108, 1069, 1018, 996, 883,
863, 754, 678 cm–1. UV/Vis (n-hexane): λmax (ε) = 222, (sh, 40900),
249 (sh, 75400), 255 (sh, 80300), 261 (85400), 277 (25700), 296
(26300), 316 (22400). MS (EI): m/z (%) = 710.5 (52) [M]+, 695.5
(11) [M – Me]+, 667.4 (16) [M – Pr]+, 653.4 (46) [M – tBu]+, 625.4
(11), 553.4 (5) [M – Si(iPr)3]+, 312.3 (12), 157.2 (53) [Si(iPr)3]+,
115.1 (53), 87.1 (32), 73.1 (49), 57.1 (89) [tBu]+, 44.0 (100)
[Pr]+. C48H78Si2 (711.30): calcd. C 81.05, H 11.05; found C 81.03,
H 11.16.
(؎)-4-(4-Methoxyphenyl)-1-[1-(4-methoxyphenyl)-1-methylethyl]-4-
methyl-1-[(triisopropylsilyl)ethynyl]pent-2-yn-1-yl Methyl Carbonate
[(؎)-3b]: Following general method B, (Ϯ)-3b was obtained from
(Ϯ)-2b (2.00 g, 3.76 mmol) as a colorless oil in 93% yield after puri-
fication by FC (SiO2; cyclohexane/EtOAc, 16:1, Rf = 0.33). 1H
NMR (300 MHz, CDCl3): δ = 1.07 (m, 21 H), 1.49 (s, 3 H), 1.51
(s, 3 H), 1.64 (s, 6 H), 3.72 (s, 3 H), 3.78 (s, 3 H), 3.79 (s, 3 H),
6.77–6.83 (m, 4 H), 7.38 (d, J = 8.7 Hz, 2 H), 7.52 (d, J = 9.0 Hz,
2 H) ppm. 13C NMR (75 MHz, CDCl3): δ = 11.2, 18.5, 24.2, 24.6,
31.3, 31.4, 35.4, 46.0, 54.3, 55.0, 55.1, 76.8, 78.2, 88.1, 93.4, 102.9,
112.3, 113.4, 126.7, 130.1, 135.0, 138.7, 152.6, 158.0, 158.2 ppm.
(؎)-[3,5-Bis(1-methoxy-1-methylethyl)-7-(triethylsilyl)hepta-3,4-
diene-1,6-diyn-1-yl](triisopropyl)silane [(؎)-14b]: Following general
method C, (Ϯ)-14b was obtained from (Ϯ)-3a (301 mg, 687 µmol)
and Et3Si–acetylene as a colorless oil in 28% yield after purifica-
1
tion by FC (SiO2; cyclohexane/EtOAc, 16:1, Rf = 0.43). H NMR
(300 MHz, CDCl3): δ = 0.62 (q, J = 7.9 Hz, 6 H), 1.00 (t, J =
7.9 Hz, 9 H), 1.08 (m, 21 H), 1.36 (s, 3 H), 1.37 (s, 3 H), 1.39 (s, 6
H), 3.24 (s, 3 H), 3.25 (s, 3 H) ppm. 13C NMR (75 MHz, CDCl3):
δ = 4.6, 7.6, 11.4, 18.7, 25.5, 25.7, 25.8, 26.1, 50.9, 51.0, 76.6 (2ϫ),
IR (film): ν = 2927, 2863, 1766, 1512, 1457, 1248, 1181, 1037,
˜
629 cm–1. MS (MALDI): m/z (%) = 629 (30) [M + K]+, 613 (56)
[M + Na]+, 516 (45), 515 (100), 477 (61). MALDI-HRMS: m/z
calcd. for C36H50NaO5Si+: 613.3328, found 613.3331; m/z calcd.
for C36H50KO5Si+: 629.3067, found 629.3083.
95.9, 96.8, 97.9, 98.4, 99.3, 99.7, 215.5 ppm. IR (film): ν = 2943,
˜
2865, 2357, 2340, 2141, 1464, 1378, 1362, 1178, 1112, 1075 cm–1.
EI-HRMS: m/z calcd. for C30H54O2Si2+: 502.3662, found 502.3657.
C48H78O2Si2 (743.30): calcd. C 71.65, H 10.82; found C 71.70, H
10.79.
(؎)-{3,5-Bis[1-(4-methoxyphenyl)-1-methylethyl]-3,4-hepta-1,6-di-
enediyne-1,7-diyl}bis(triisopropylsilane) [(؎)-4b]: Following general
method C, (Ϯ)-4b was obtained from (Ϯ)-3b (283 mg, 0.479 mmol)
Eur. J. Org. Chem. 2007, 3449–3462
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3457

M. K. J. ter Wiel, S. Odermatt, P. Schanen, P. Seiler, F. Diederich
(؎)-[3,5-Bis(1-methoxy-1-methylethyl)hepta-3,4-diene-1,6-diyn-1-yl]- tetraene-1,6,8,13-tetrayne (16c): A mixture of CuCl (124 mg,
FULL PAPER
(triisopropyl)silane [(؎)-15b]: Following general method D, (Ϯ)-15b
was obtained from (Ϯ)-14b (39.0 mg, 77.7 µmol) in 90% yield after
purification by FC. H NMR (300 MHz, CDCl3): δ = 1.07 (m, 21
0.014 mmol) and TMEDA (700 mg, 6.03 mmol) in acetone (10 mL)
was stirred for 5 min at 20 °C. The suspension was filtered, and
1 mL of the resulting blue solution was added to a solution of
allene 15c (36 mg, 66.6 µmol) in acetone (1 mL). After stirring the
1
H), 1.36 (s, 3 H), 1.37 (s, 3 H), 1.38 (s, 3 H), 1.40 (s, 3 H), 3.06 (s,
1 H), 3.24 (s, 3 H), 3.25 (s, 3 H) ppm. 13C NMR (75 MHz, CDCl3): mixture overnight, it was poured into a saturated aq. NH4Cl solu-
δ = 11.2, 18.6, 25.2, 25.4, 25.6, 26.0, 50.9, 51.0, 75.8, 76.6, 81.5
tion (25 mL) and extracted with Et2O (3ϫ15 mL). The organic
layers were collected, dried (Na2SO4), and the residue obtained af-
ter the removal of all organic volatiles was purified by FC (SiO2;
cyclohexane/EtOAc, 16:1, Rf = 0.31) providing the desired com-
pound as a colorless oil (32 mg, 29.6 µmol, 90 %). 1H NMR
(300 MHz, CDCl3): δ = 0.99 (m, 42 H), 1.37 (s, 6 H), 1.468 (s, 6
H), 1.476 (s, 6 H), 1.48 (s, 6 H), 3.77 (s, 6 H), 3.80 (s, 6 H), 6.78
(d, J = 9.1 Hz, 4 H), 6.83 (d, J = 8.8 Hz, 4 H), 7.08 (d, J = 9.1 Hz,
4 H), 7.22 (d, J = 8.8 Hz, 4 H) ppm. 13C NMR (75 MHz, CDCl3):
δ = 11.2, 18.6, 28.0, 28.7 (3 ϫ), 42.8, 43.1, 55.1, 55.2, 75.4, 95.7,
99.5, 103.3, 105.3, 113.2, 113.4, 127.5, 127.6, 138.7, 138.8, 157.8,
(2ϫ), 96.5, 98.0, 98.1, 100.5, 215.4 ppm. IR (film): ν = 2941, 2864,
˜
2141, 1463, 1378, 1362, 1177, 1150, 1074, 882, 668 cm–1. MS (EI):
m/z (%) = 388 (1) [M]+, 373 (5), 73 (100). EI-HRMS: m/z calcd.
for C24H40O2Si+: 388.2802, found 388.2998.
(P,M)- and (P,P)/(M,M)-3,5,10,12-Tetrakis(1-methoxy-1-methyl-
ethyl)-1,14-bis(triisopropylsilyl)tetradeca-3,4,10,11-tetraene-
1,6,8,13-tetrayne (16b): TMEDA (0.70 g, 6.03 mmol) and CuCl
(124 mg, 1.25 mmol) were suspended in acetone (3 mL) and stirred
for 15 min. The resulting suspension was filtered and a solution of
allene 15b (14.3 mg, 36.8 µmol, 1 equiv.) in acetone (1 mL) added.
The mixture was stirred overnight in an open flask and then poured
into a saturated aq. NH4Cl solution (10 mL) and extracted with
Et2O (4ϫ10 mL). The combined organic layers were washed with
water (2ϫ25 mL), dried (Na2SO4), and all volatiles were removed
under reduced pressure. The product 16b (12.8 mg, 16.5 µmol,
90 %) was purified by FC (SiO2; cyclohexane/EtOAc, 8:1, Rf =
157.9, 215.8 ppm, two singlets were not observed. IR (film): ν =
˜
2940, 2862, 2360, 2340, 1511, 1463, 1251, 1182, 1036, 828 cm–1.
MS (MALDI): m/z = 1102 [M + Na]+, 1080 [M + H]+. MALDI-
HRMS: m/z calcd. for C72H95O4Si2+: 1079.677, found 1079.675;
m/z calcd. for C72H94NaO4Si2+: 1101.659, found 1101.656; m/z
calcd. for C72H94KO4Si2+: 1117.633, found 1117.641.
1
0.42). H NMR (300 MHz, CDCl3): δ = 1.07 (m, 42 H), 1.36 (s, 6
(P,M)- and (P,P)/(M,M)-3,5,10,12-Tetrakis[1-(4-methoxyphenyl)-1-
methylethyl]tetradeca-3,4,10,11-tetraene-1,6,8,13-tetrayne (17c):
Following general method E, 17c was obtained from 16c (29 mg,
26.9 µmol) as a colorless oil in 78% yield after purification by FC
(SiO2; cyclohexane/EtOAc, 4:1, Rf = 0.50). 1H NMR (300 MHz,
CDCl3): δ = 1.41 (s, 6 H), 1.46 (s, 6 H), 1.47 (s, 6 H), 1.49 (s, 6 H),
2.93 (s, 2 H), 3.80 (s, 6 H), 3.81 (s, 6 H), 6.82 (d, J = 8.7 Hz, 4 H),
6.84 (d, J = 9.0 Hz, 4 H), 7.14 (d, J = 8.7 Hz, 4 H), 7.20 (d, J =
9.0 Hz, 4 H) ppm. 13C NMR (75 MHz, CDCl3): δ = 28.2, 28.5,
28.6, 28.8, 42.6, 42.9, 55.2, 75.2, 77.6, 81.6, 104.1, 113.3, 113.4,
H), 1.38 (s, 6 H), 1.39 (s, 6 H), 1.40 (s, 6 H), 3.24 (s, 6 H), 3.26 (s,
6 H) ppm. 13C NMR (75 MHz, CDCl3): δ = 11.2, 18.6, 25.1, 25.7,
25.8, 26.2, 51.0, 51.2, 73.9, 76.7, 77.1, 77.8, 97.2, 97.6, 98.5, 101.2,
217.0 ppm. IR (neat): ν = 2979, 2940, 2864, 2141, 1733, 1463, 1378,
˜
1362, 1177, 1074, 668 cm–1. MS (MALDI): m/z (%) = 813
[M + K]+, 798 [M + Na]+, 744, 711, 456. MALDI-HRMS: m/z
calcd. for C48H78NaO5Si+: 797.5341, found 797.5316; m/z calcd.
for C48H78KO5Si+: 813.5080, found 813.5035.
(؎)-{3,5-Bis[1-(4-methoxyphenyl)-1-methylethyl]-7-[triethylsilyl]-
hepta-3,4-diene-1,6-diyn-1-yl}(triisopropyl)silane [(؎)-14c]: Follow-
ing general method C, (Ϯ)-14c was obtained from (Ϯ)-3b (153 mg,
0.259 mmol) as a colorless oil in 46 % after purification by FC
127.5, 138.5, 157.9, 215.8 ppm. IR (film): ν = 3283, 2963, 2924,
˜
2360, 2343, 1511, 1251, 1181, 1035, 829, 668 cm–1. MS (MALDI):
m/z (%) = 805 [M + K]+, 789 [M + Na]+, 767 [M + H]+. MALDI-
HRMS: m/z calcd. for C54H55O4+: 767.4103, found 767.4080; m/z
calcd. for C54H54NaO4+: 789.3923, found 789.3914; m/z calcd. for
C54H54KO4+: 806.3662, found 806.3634.
1
(SiO2; cyclohexane/CH2Cl2, 5:2, Rf = 0.27). H NMR (300 MHz,
CDCl3): δ = 0.54 (q, J = 7.8 Hz, 6 H), 0.93 (t, J = 7.8 Hz, 9 H),
0.99 (m, 21 H), 1.41 (s, 3 H), 1.44 (s, 3 H), 1.46 (s, 6 H), 3.77 (s, 3
H), 3.78 (s, 3 H), 6.77 (d, J = 8.7 Hz, 2 H), 6.79 (d, J = 8.7 Hz, 2
H), 7.13 (d, J = 8.7 Hz, 2 H), 7.17 (d, J = 8.7 Hz, 2 H) ppm. 13C
NMR (75 MHz, CDCl3): δ = 4.5, 7.4, 11.2, 18.5, 28.2, 28.3, 28.5,
28.6, 42.6 (2ϫ), 55.1 (2ϫ), 94.5, 95.6, 99.9, 100.3, 104.1, 104.3,
113.1 (2ϫ), 127.6 (2ϫ), 139.0, 139.1, 157.8 (2ϫ), 214.0 ppm. IR
Synthesis of Diethinylallene Oligomers: The dimer 16a (267 mg,
0.375 mmol, 1.0 equiv.) and o-nitrophenol (66 mg, 0.472 mmol,
1.3 equiv.) were dissolved in THF (20 mL) and cooled to 0 °C.
nBu4NF (414 µL of a 1  solution in THF, 0.414 mmol, 1.1 equiv.)
was added, and the solution turned immediately to a bright yellow.
The mixture was allowed to reach 10 °C over a period of 1 h and
stirred at 20 °C for 7.5 h. It was then evaporated under reduced
pressure. The resulting brightly yellow solution was filtered through
SiO2 (hexane, ca. 250 mL). The solvent was evaporated, and a yel-
low oil was obtained (224 mg, quant.). Analysis by GPC showed
that the allene was nearly completely deprotected.
(film): ν = 2953, 2864, 2359, 2140, 1611, 1512, 1462, 1301, 1251,
˜
1038, 883, 827, 631 cm–1. MS (EI): m/z (%) = 654 (1.2) [M]+, 149
(100). EI-HRMS: m/z calcd. for C42H62O2Si2+: 654.4288, found
654.4297.
(؎)-{3,5-Bis[1-(4-methoxyphenyl)-1-methylethyl]hepta-3,4-diene-
1,6-diyn-1-yl}(triisopropyl)silane [(؎)-15c]: Following general
method D, (Ϯ)-15c was obtained from (Ϯ)-14c (200 mg, 306 µmol)
in 97% yield. 1H NMR (300 MHz, CDCl3): δ = 0.99 (m, 21 H),
1.43 (s, 3 H), 1.45 (s, 3 H), 1.46 (s, 3 H), 1.49 (s, 3 H), 2.90 (s, 1
H), 3.79 (s, 6 H), 6.80 (m, 4 H), 7.15 (d, J = 9.0 Hz, 2 H), 7.21 (d,
J = 9.0 Hz, 2 H) ppm. 13C NMR (75 MHz, CDCl3): δ = 11.3, 18.6,
28.25, 28.37, 28.67, 28.71, 42.6 (2ϫ), 55.1, 55.2, 77.5, 80.5, 95.1,
99.8, 102.6, 104.9, 113.12, 113.21, 127.36, 127.44, 138.67, 138.77,
The residue was dissolved in o-dichlorobenzene (10 mL), and a
solution of CuCl (15 mg, 0.153 mmol, 0.4 equiv.) and TMEDA
(76 µL, 0.526 mmol, 1.4 equiv.) in o-dichlorobenzene (1 mL) was
added. The flask was put into a preheated oil bath (50 °C), and the
mixture was stirred for 8 h in an open flask. The mixture was then
filtered through SiO2 (hexane, 10 mL and hexane/CH2Cl2,
100 mL), to separate from the Cu complexes. Analytical GPC (Sho-
dex GPC KF-802.5 and Shodex GPC KF-803L, THF) showed
complete conversion of the dimer and appearance of oligomeric
products. The solution was concentrated under reduced pressure,
157.7 (2ϫ), 213.8 ppm. IR (film): ν = 3282, 2940, 2863, 2360, 2141,
˜
1609, 1512, 1462, 1251, 1182, 1036, 883, 827, 633 cm–1. MS
(MALDI): m/z = 563 (100) [M + Na]+. MALDI-HRMS: m/z calcd.
for C36H48O2Si+: 563.3324, found 563.3308.
(P,M)- and (P,P)/(M,M)-1,14-Bis(triisopropylsilyl)-3,5,10,12-tet- and the o-dichlorobenzene was distilled off under vacuum. A yel-
rakis[1-(4-methoxyphenyl)-1-methylethyl]tetradeca-3,4,10,11- low solid (226 mg) was obtained. The different oligomers could be
3458
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© 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2007, 3449–3462

1,3-Diethynylallenes
FULL PAPER
separated by chromatography (SiO2; hexane/CH2Cl2:100:0 Ǟ 50:1
Ǟ 25:1 Ǟ 20:1 Ǟ 10:1 Ǟ 5:1). The dimer eluted first (43 mg,
60 µmol, 16%), followed by the tetramer (20 mg, 18 µmol, 10%),
hexamer (18 mg, 12 µmol, 10%), octamer (17 mg, 9 µmol, 9%), de-
camer (13 mg, 6 µmol, 7 %), and finally the higher oligomers
(15 mg). The fractions were analyzed by analytical GPC. Further
purification of the oligomers of identical length (but as a mixture
of stereoisomers) was realized by preparative GPC (BioBeads S-
X1, CH2Cl2).
3,5,10,12,17,19,24,26,31,33,38,40,45,47,52,54,59,61,66,68-Icosakis-
(tert-butyl)-1,70-bis(triisopropylsilyl)heptaconta-3,4,10,11,17,18,24,
25,31,32,38,39,45,46,52,53,59,60,66,67-icosaene-1,6,8,13,15,20,22,
27,29,34,36,41,43,48,50,55,57,62,64,69-icosayne (22): Mixture of
stereoisomers; m.p. Ͼ150 °C (slow decomposition). 1H NMR
(500 MHz, C6D6): δ = 1.009 (s, 9 H), 1.013 (s, 9 H), 1.03 (s, 126
H), 1.13 (s, 42 H), 1.14 (s, 18 H), 1.17 (s, 18 H) ppm. 13C NMR
(75 MHz, C6D6): δ = 11.6, 18.8, 28.9, 29.0, 35.7, 36.1, 75.2, 75.6,
76.1, 78.1, 78.5, 78.8, 95.5, 100.3, 103.3, 104.4, 105.1, 214.7, 216.1
ppm. IR (solid): ν = 2956, 2925, 2863, 2139 (w), 1917 (w), 1456,
˜
3,5,10,12,17,19,24,26-Octakis(tert-butyl)-1,28-bis(triisopropylsilyl)-
octacosa-3,4,10,11,17,18,24,25-octaene-1,6,8,13,15,20,22,27-octa-
yne (19): Mixture of stereoisomers; colorless solid; m.p. 95–99 °C.
1H NMR (300 MHz, CDCl3): δ = 1.08 (s, 42 H), 1.139 (s, 18 H),
1.142 (s, 18 H), 1.150 (s, 18 H), 1.154 (s, 18 H) ppm. 1H NMR
(300 MHz, C6D6): δ = 1.00 (s, 18 H), 1.01 (s, 18 H), 1.08 (s, 42 H),
1.13 (s, 18 H), 1.16 (s, 18 H) ppm. 13C NMR (75 MHz, C6D6): δ
= 11.8, 18.9, 29.0, 29.05, 29.1, 35.8, 36.2, 75.2, 75.7, 76.1, 78.1,
78.6, 78.8, 95.4, 100.2, 103.3, 104.2, 104.4, 105.1, 214.4, 215.8 ppm.
1460, 1390, 1362, 1220, 1066, 882, 667 cm–1. UV/Vis (cyclohexane):
λmax (ε) = 254 (sh, 232300), 263 (237800), 281 (197000), 302
(202500), 324 (175700). MS (MALDI): m/z (%) = 2320 (100) [M +
Na]+, 2298 (18) [M + H]+. MALDI-HRMS: m/z calcd. for
C168H222NaSi2+: 2319.6834, found 2319.6859.
(؎)-3-(tert-Butyl)-6,6-dimethylhepta-1,4-diyn-3-ol [(؎)-27]: Alcohol
(Ϯ)-26[6b] (1.667 g, 6.303 mmol, 1.0 equiv.) was dissolved in THF
(40 mL). MeOH (40 mL) and K2CO3 (0.437 g, 3.151 mmol,
0.5 equiv.) were added and the suspension stirred for 5 h under air.
Et2O was then added and the organic layer washed with a saturated
aq. NH4Cl solution. The aq. layer was extracted with Et2O (ca.
50 mL). The combined organic layers were washed with H2O, dried
with Na2SO4, and evaporated under reduced pressure. The re-
sulting oil (1.11 g, 5.77 mmol, 92%) was purified by FC (SiO2; cy-
clohexane/EtOAc, 10:1). Alcohol (Ϯ)-27 was obtained as a volatile
IR (solid): ν = 2962, 2925, 2865, 2899, 2141 (w), 1475, 1458, 1392
˜
(w), 1362, 1072 (w), 995 (w), 882, 668. UV/Vis (cyclohexane): λmax
(ε) = 255 (111900), 264 (sh, 105300), 280 (76300), 300 (75100), 321
(62900). MS (MALDI): m/z (%) = 1244 (23) [M + Na + Si(iPr)2]+,
1130 (100) [M + Na]+, 1108 (46) [M + H]+. MALDI-HRMS: m/z
calcd. for C78H114NaSi2+: 1129.8351, found 1129.8366. C78H114Si2
(1107.93): calcd. C 84.56, H 10.37; found C 84.60, H 10.53.
1
colorless liquid (0.738 g, 3.838 mmol, 61%). H NMR (300 MHz,
3,5,10,12,17,19,24,26,31,33,38,40-Dodecakis(tert-butyl)-1,42-bis-
(triisopropylsilyl)dotetraconta-3,4,10,11,17,18,24,25,31,32,38,39-do-
decaene-1,6,8,13,15,20,22,27,29,34,36,41-dodecayne (20): Mixture
of stereoisomers; colorless solid; m.p. Ͼ130 °C (with decomposi-
tion). 1H NMR (300 MHz, CDCl3): δ = 1.08 (s, 42 H), 1.138 (s, 18
H), 1.141 (s, 18 H), 1.15 (s, 72 H) ppm. 1H NMR (300 MHz, C6D6):
δ = 1.004 (s, 9 H), 1.007 (s, 9 H), 1.024 (s, 27 H), 1.026 (s, 27 H),
1.12 (s, 42 H), 1.13 (s, 18 H), 1.17 (s, 18 H) ppm. 13C NMR
(125 MHz, C6D6): δ = 11.7, 18.8, 28.92, 28.98 (2ϫ), 29.1, 35.7,
36.11, 36.14, 75.1, 75.59, 75.64, 75.71, 76.1, 78.1, 78.5, 78.62, 78.64,
78.8, 95.5, 100.3, 103.3, 104.3, 104.41, 104.42, 104.45, 105.1, 214.7,
CDCl3): δ = 1.11 (s, 9 H); 1.23 (s, 9 H), 2.31 (br. s, 1 H), 2.50 (s, 1
H). 13C NMR (75 MHz, CDCl3): δ = 24.7, 27.4, 30.8, 39.9, 70.6,
71.7, 78.1, 84.0, 92.9 ppm. IR (film): ν = 3466 (w br.), 3311 (w),
˜
2968, 2930, 2870, 2244 (w), 1728 (w), 1477, 1459, 1363, 1264, 1064,
999, 964, 882, 649, 631 cm–1. MS (EI): m/z (%) = 191 (Ͻ1) [M]+,
177 (12) [M – Me]+ , 136 (53) [M + H – tBu]+ , 135 (52)
[M – tBu]+, 69 (100), 57 (88) [tBu]+. EI-HRMS: m/z calcd. for
C
12H17O+: 177.1279, found 177.1276. C13H20O (192.30): calcd.
C 81.20, H 10.48, O 8.32; found C 81.37, H 10.44, O 8.35.
(1R)-1-tert-Butyl-1-ethynyl-4,4-dimethylpent-2-yn-1-yl (1S,4R)-
4,7,7-Trimethyl-3-oxo-2-oxabicyclo[2.2.1]heptane-1-carboxylate
[(R,S,R)-28] and (1S)-1-tert-Butyl-1-ethynyl-4,4-dimethylpent-2-yn-
1-yl (1S,4R)-4,7,7-Trimethyl-3-oxo-2-oxabicyclo[2.2.1]heptane-1-
carboxylate [(S,S,R)-28]: Alcohol (Ϯ)-27 (1.5 g, 7.8 mmol,
1.0 equiv.) was dissolved in dry CH2Cl2 (15 mL). DMAP (480 mg,
0.5 equiv.) and (1S)-(–)-camphanic acid (1.7 g, 1.1 equiv.) were
added, and the mixture was cooled to 0 °C. A solution of DCC
(1.92 g, 1.2 equiv.) in CH2Cl2 (15 mL) was added. The mixture was
stirred at 20 °C for 16 h. Then, the solids were removed by fil-
tration. The filtrate was washed twice with 0.2  HCl and twice
216.04, 216.06, 216.08, 216.10 ppm. IR (solid): ν = 2961, 2926,
˜
2864, 2899, 2141 (w), 1915 (w), 1474, 1460, 1362, 1392, 1220, 1071,
882, 750, 678, 665 cm–1. UV/Vis (cyclohexane): λmax (ε) = 256
(147800), 266 (sh, 140600), 281 (112400), 301 (113800), 322
(97200). MS (MALDI): m/z (%) = 1641 (23) [M + Na + Si-
(iPr)2]+, 1527 (78) [M + Na]+, 1505 (100) [M + H]+. MALDI-
HRMS: m/z calcd. for C108H150NaSi2+: 1527.1199, found
1527.1216.
3,5,10,12,17,19,24,26,31,33,38,40,45,47,52,54-Hexadecakis(tert-bu-
tyl)-1,56-bis(triisopropylsilyl)hexapentaconta-3,4,10,11,17,18,24,25,
31,32,38,39,45,46,52,53-hexadecaene-1,6,8,13,15,20,22, with H2O. The organic layer was dried with MgSO4 and evaporated
27,29,34,36,41,43,48,50,55-hexadecayne (21): Mixture of stereoiso-
mers; colorless solid; m.p. Ͼ140° (with decomposition). H NMR
under reduced pressure. The product was purified by FC (SiO2;
cyclohexane/EtOAc, 10:0Ǟ10:1) and obtained as a mixture of 2
1
(500 MHz, C6D6): δ = 1.006 (s, 9 H), 1.009 (s, 9 H), 1.026 (s, 27 diastereoisomers (R,S,R)- and (S,S,R)-28 (1.72 g, 4.62 mmol, 59%).
H), 1.030 (s, 63 H), 1.12 (s, 42 H), 1.14 (s, 18 H), 1.17 (s, 18 H) The esters were dissolved in a small amount of CH2Cl2, and cyclo-
ppm. 13C NMR (75 MHz, C6D6): δ = 11.6, 18.8, 28.89, 28.96,
29.05, 35.7, 36.10, 36.13, 75.2, 75.67, 75.74, 76.1, 78.1, 78.5, 78.6,
78.8, 95.5, 100.3, 103.3, 104.3, 104.4, 105.1, 214.7, 216.1 ppm. IR
hexane was added. Slow evaporation of the solvent gave colorless
needles. The supernatant was pipetted off and the crystals
[841 mg,Ն98% de of (R,S,R)-isomer] were washed with a little cy-
clohexane or pentane. Further evaporation of the mother liquid
gave crystals enriched in the other isomer [76% de of the (S,S,R)-
(solid): ν = 2961, 2925, 2865, 2899, 2141 (w), 1917 (w), 1473, 1460,
˜
1393, 1362, 1220, 1066, 882, 750, 678, 665 cm–1. UV/Vis (cyclohex-
ane): λmax (ε) = 258 (202500), 262 (202900), 281 (162700), 301 isomer]. The resulting mother liquid was enriched in the (S,S,R)-
(166800), 323 (144900). MS (MALDI): m/z (%) = 2037 (25) [M + isomer (68% de). Repeated fractional recrystallization led to dia-
Na + Si(iPr)2]+, 1923 (100) [M + Na]+, 1901 (66) [M + H]+, 1843 stereomerically pure product (Ն98 % de, as determined by 1H
(24) [M – tBu]+, 1787 (36) [M – 2 tBu]+, 1731 (27) [M – 3 tBu]+.
MALDI-HRMS: m/z calcd. for C138H186NaSi2+: 1923.4017, found
1923.4040.
NMR of the alkyne proton). Alternatively, fractions enriched in
(S,S,R)-isomer could be separated into the two isomers by FC over
Al2O3 N (activity I, cyclohexane/EtOAc, 10:1).
Eur. J. Org. Chem. 2007, 3449–3462
© 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
3459

M. K. J. ter Wiel, S. Odermatt, P. Schanen, P. Seiler, F. Diederich
FULL PAPER
(R,S,R)-28: Colorless crystals. [α]D = –27 (CHCl3, c = 1.0); m.p.
154–157 °C. H NMR (300 MHz. CDCl3): δ = 1.00 (s, 3 H), 1.06
(Al2O3, activity III, hexane). Rf = 0.5 (Al2O3, hexane); [α]D = –83.
1H NMR (300 MHz, CDCl3): δ = 1.22 (s, 9 H), 1.18 (s, 9 H), 1.08
(s, 21 H) ppm. 13C NMR (75 MHz, CDCl3): δ = 11.4, 18.7, 25.0,
27.7, 30.6, 40.5, 74.5, 78.0, 88.3, 95.9, 102.3, 109.1, 136.4, 139.0,
141.7, 144.2, 146.6, 156.0 ppm. 19F NMR (282 MHz, CDCl3): δ =
1
(s, 3 H), 1.11 (s, 3 H), 1.17 (s, 9 H), 1.22 (s, 9 H), 1.67 (ddd, J =
4.2, 9.3, 13.2 Hz, 1 H), 1.91 (ddd, J = 4.8, 10.8, 13.2 Hz, 1 H), 2.04
(ddd, J = 4.5, 9.3, 13.5 Hz, 1 H), 2.46 (ddd, J = 4.2, 10.8, 13.5 Hz,
1 H), 2.61 (s, 1 H) ppm. 13C NMR (75 MHz, CDCl3): δ = 9.8,
16.89, 16.93, 24.9, 27.6, 29.0, 30.1, 30.6, 40.7, 54.7, 54.9, 74.09,
–161.1 (m), –139.1 (m), –150.1 (m) ppm. IR (film): ν = 2926, 2865,
˜
1756, 1651, 1521, 1505, 1463, 1327, 1207, 1001, 955, 882 cm–1. MS
(EI): m/z (%) = 542 (21) [M]+, 325 (29), 289 (40), 189 (100).
C29H39F5O2Si (542.70): calcd. C 64.18, H 7.24, F 17.50; found C
64.43, H 7.49, F 17.43.
74.15, 75.5, 79.4, 91.0, 95.2, 164.3, 178.2 ppm. IR (solid): ν = 3253,
˜
2971, 2239 (w), 2114 (w), 1774 (s), 1758 (s), 1476, 1310, 1259, 1111,
1052 (s), 934, 885, 739, 701 cm–1. MS (EI): m/z (%) = 372 (20)
[M]+, 357 (19) [M – Me]+, 182 (68), 164 (55), 136 (100), 83 (77), 57
(67) [tBu]+. EI-HRMS: m/z calcd. for C23H32O4+: 372.2301, found
372.2302. C23H32O4 (372.50): calcd. C 74.16, H 8.66, O 17.18;
found C 74.14, H 8.48, O 17.21.
(2R,P)-6,8-Bis(tert-butyl)-1,1,1-trifluoro-10-triisopropylsilyl-2-meth-
oxy-2-phenyldeca-6,7-dien-4,9-diyn-3-one [(2R,P)-31]: Allene (P)-
15a (19.5 mg, 55 µmol, 1.0 equiv., [α]D = –82°) was dissolved in dry
THF (0.5 mL) and hexane (0.5 mL) and cooled to –60 °C. nBuLi
(36 µL of a 1.6  solution in hexane, 58 µmol, 1.05 equiv.) was
(S,S,R)-28: Colorless crystals. [α]D = –13 (CHCl3, c = 1.0); m.p.
116.7–118.9 °C. 1H NMR (300 MHz, CDCl3): δ = 1.00 (s, 3 H), added, followed by Mosher acid chloride [(R)-MTPA-Cl, 20 µL,
1.05 (s, 3 H), 1.11 (s, 3 H), 1.17 (s, 9 H), 1.2 (s, 9 H), 1.67 (ddd, J 107 µmol, 1.9 equiv.] after a few minutes. The solution was slowly
= 4.2, 9.3, 13.5 Hz, 1 H), 1.91 (ddd, J = 4.5, 10.8, 13.2 Hz, 1 H),
2.04 (ddd, J = 4.5, 9.3, 13.5 Hz, 1 H), 2.48 (ddd, J = 4.2, 10.8,
warmed to 0 °C then to 20 °C. Cyclohexane was added, and the
solution was washed twice with H2O. The organic layer was dried
13.5 Hz, 1 H), 2.62 (s, 1 H) ppm. 13C NMR (75 MHz, CDCl3): δ with Na2SO4 and evaporated under reduced pressure. The resulting
= 9.8, 16.89, 16.93, 24.9, 27.6, 29.0, 30.1, 30.6, 40.7, 54.7, 54.9, oil (quant.) was purified by flash-chromatography (SiO2; cyclohex-
74.09, 74.15, 75.5, 79.4, 91.0, 95.2, 164.3, 178.2 ppm. IR (solid): ν
ane/CH2Cl2, 10:0Ǟ10:1). Ketone 31 was obtained as an almost
colorless oil (12 mg, 21 µmol, 39%). The 1H NMR spectrum in
C6D6 showed two distinct signals for the methoxy-groups of the 2
diastereoisomers. 1H NMR (300 MHz, CDCl3): δ = 0.966 and
˜
= 3241, 2967, 1780 (s), 1749 (s), 1457, 1312, 1263 (s), 1100 (s), 1051
(s), 928, 884, 733 cm–1. MS (EI): m/z (%) = 372 (9) [M]+, 357 (6)
[M – Me]+, 316 (6) [M + H – tBu]+, 182 (48), 164 (30), 136 (30),
83 (24), 57 (28) [tBu]+, 17.97 (100) [H2O]+. EI-HRMS: m/z calcd. 0.969 (s, 9 H), 1.070 and 1.073 (s, 21 H), 1.10 (s, 9 H), 3.66–3.69
for C23H32O4+: 372.2301, found 372.2289. C23H32O4 (372.50): (m, 3 H), 7.38–7.41 (m, 3 H), 7.53–7.57 (m, 2 H) ppm. H NMR
1
calcd. C 74.16, H 8.66, O 17.18; found C 74.11, H 8.50, O 17.14.
(300 MHz, C6D6): δ = 0.938 and 0.942 (s, 9 H), 1.086 and 1.092
and 1.097 (s, 21 H), 1.11 (s, 9 H), 3.40–3.41 and 3.47–3.48 (m, 3
H), 7.00–7.04 (m, 3 H), 7.60–7.64 (m, 2 H) ppm. 13C NMR
(75 MHz, C6D6): δ = 11.8, 19.0, 28.8, 29.0, 35.9, 36.0, 55.8, 87.5,
89.7 and 89.8, 90.1, 97.4, 98.9 and 99.0, 101.88 and 101.94, 105.8
and 105.9, 124.2 (q, J = 287 Hz), 128.6, 129.6, 132.7, 179.9, 215.6
(3R)-3-tert-Butyl-6,6-dimethylhepta-1,4-diyn-3-ol [(R)-27]: (R,S,R)-
28 (313 mg, 0.840 mmol, Ն 98% de) was dissolved in THF (5 mL),
and a 1  solution of NaOH (1 mL) and MeOH (2 mL) were
added. The mixture was stirred for 2 h under air. More NaOH
solution (0.1 mL) was added, and after 40 min the solution was
diluted with Et2O and washed with a saturated aq. NH4Cl solution
and H2O. The organic layer was dried with Na2SO4 and evaporated
under reduced pressure to yield a slightly yellow oil, which was
filtered through SiO2 (cyclohexane/EtOAc, 10:1). Evaporation gave
a colorless liquid (154 mg, 0.801 mmol, 95%), which became solid
after storage at 4 °C. Colorless solid. [α]D = –1.8 (CHCl3, c = 1.0);
m.p. 39.1–40.2 °C.
ppm. IR (film): ν = 2963, 2866, 2187, 1922 (w), 1683, 1461, 1273,
˜
1168 (s), 1070 (s) cm–1. MS (EI): m/z (%) = 573 (1) [M + H]+,
563.94 (3), 529.28 (11) [M – iPr]+, 383.26 (51), 57.07 (100) [tBu]+.
EI-HRMS: m/z calcd. for C34H48O2Si+: 573.3376, found 573.3314.
X-ray Analysis: The structures were solved by direct methods
(SIR92)[22] and refined by full-matrix least-squares analysis
(SHELXL-97),[23] using an isotropic extinction correction. All non
H-atoms were refined anisotropically; H-atoms were refined iso-
tropically, whereby H-positions are based on stereochemical con-
siderations.
(3S)-3-(tert-Butyl)-6,6-dimethylhepta-1,4-diyn-3-ol [(S)-27]: (S,S,R)-
28 (108 mg, 0.289 mmol, Ն 98% de) was dissolved in THF (2 mL)
and a 1  aq. NaOH solution (1 mL) and MeOH (1 mL) were
added. The mixture was stirred for 2 h under air. More NaOH X-ray Crystal Structure of (؎)-5b: Crystal data at 223(2) K for
solution (0.5 mL) was added, and after 4 h the solution was diluted
with Et2O and washed with a saturated aq. NH4Cl solution and
H2O. The organic layer was dried with Na2SO4 and evaporated
under reduced pressure to yield a slightly yellow oil (54 mg,
0.281 mmol, 97%), which became solid after storage at 4 °C. Color-
less solid. [α]D = 1.7 (CHCl3, c = 1.0); m.p. 39.0–39.9 °C.
C27H28O2, Mr = 384.49, monoclinic, space group C 2/c (no.15),
Dcalcd. = 1.128 gcm–3, Z = 4, a = 13.8290(3) Å, b = 6.5589(2) Å, c
= 25.4813(7) Å, β = 101.615(1)°, V = 2263.90(11) Å3; Bruker-
Nonius Kappa-CCD diffractometer, Mo-Kα radiation,
λ =
0.7107 Å,
µ
=
0.069 mm–1. Approximate crystal dimensions
0.23ϫ0.19ϫ0.15 mm. Numbers of measured and unique reflec-
tions are 3675 and 2220, respectively (Rint = 0.017). Final R(F) =
0.051, wR(F2) = 0.169 for 153 parameters and 1797 reflections with
IϾ2σ(I) and 3.01ϽθϽ26.02° (corresponding R values based on all
2220 reflections are 0.064 and 0.187 respectively).
(1S)-1-tert-Butyl-1-ethynyl-4,4-dimethylpent-2-yn-1-yl Pentafluo-
robenzoate [(S)-30]: Alcohol (R)-(–)-27 was dissolved in THF and
cooled to –78 °C. nBuLi (2.1 equiv.) was added and the mixture
stirred for 15 min at –78 °C and 15 min at 20 °C. The solution was
cooled to –78 °C, and (iPr3)SiCl (1.5 equiv.) was added. The mix-
ture was stirred until TLC showed complete consumption of the
starting material. Pentafluorobenzoyl chloride was added and the
mixture stirred at 0 °C for 2 h. The reaction was quenched by the
addition of a saturated aq. NH4Cl solution. The aq. layer was ex-
tracted with Et2O. The organic layer was washed with H2O, dried
with MgSO4, filtered and the solvents evaporated. The desired
product was obtained in 30–40% yield after purification by FC
X-ray Crystal Structure of (P,M)-16a: Crystal data at 253(2) K for
C48H78Si2, Mr = 711.28, orthorhombic, space group Pbca (no.61),
Dcalcd. = 0.940 gcm–3, Z = 4, a = 9.2960(11) Å, b = 11.6725(12) Å,
c = 46.3312(25) Å, V = 5027.3(9) Å3; Bruker-Nonius Kappa-CCD
diffractometer, Mo-Kα radiation, λ = 0.7107 Å, µ = 0.097 mm–1.
Approximate crystal dimensions 0.3ϫ0.3ϫ0.03 mm. Number of
measured and unique reflections are 7684 and 4223, respectively
(Rint = 0.022). Final R(F) = 0.047, wR(F2) = 0.114 for 266 param-
3460
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Eur. J. Org. Chem. 2007, 3449–3462

1,3-Diethynylallenes
FULL PAPER
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respectively).
[7]
[8]
X-ray Crystal Structure of (R,S,R)-28: Crystal data at 120(2) K for
C23H32O4, Mr = 372.49, orthorhombic, space group P212121
(no.19), Dcalcd. = 1.085 gcm–3, Z = 4, a = 9.8869(13) Å, b =
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=
0.073 mm–1.
A colorless crystal (linear dimensions ca.
0.2ϫ0.18ϫ0.16 mm) was obtained by evaporation of a hexane/
pentane solution. Number of measured and unique reflections are
4390 and 2486, respectively (Rint = 0.030). Final R(F) = 0.045,
wR(F2) = 0.097 for 280 parameters and 2247 reflections with
IϾ2σ(I) and 6.46ϽθϽ26.02° (corresponding R-values based on all
2486 reflections are 0.053 and 0.102, respectively).
CCDC-641333 (for 5b), -641331 (for 16a), and -641332 (for 28)
contain the supplementary crystallographic data for this paper.
These data can be obtained free of charge from The Cam-
bridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/
data_request/cif.
Supporting Information (see also the footnote on the first page of
this article): The synthesis and characterization of ynones 1a–d,
their precursors, and of compounds 2a,c,d-(Ϯ) to 6a,c,d, 8-(Ϯ)-13,
24, and 25, a GPC chromatogram of the oligomers, partial NMR
spectra of 28, details on the HPLC experiments, and experimental
details on the stereoselective synthesis.
[9]
[10]
Acknowledgments
This research was supported by the ETH Research Council. We
thank Dr. Carlo Thilgen (ETH Zürich) for help with the nomencla-
ture. The authors would like to thank Dr. Emile Cavoy and Aurélie
Brémaud at UCB, Global Chemistry R&D, Braine l’Alleud, Bel-
gium, for their help in the screening of the various chiral stationary
phases in the HPLC separation and for the analytical resolution of
allene (Ϯ)-5b.
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Received: April 26, 2007
Published Online: June 5, 2007
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Eur. J. Org. Chem. 2007, 3449–3462