Synthesis and 13C NMR spectroscopy of 13C-labeled α,ω-diphenylpolyynes

Article abstract of DOI:10.1055/s-0031-1290983

The synthesis of three ¹³C-labeled α,ω- diphenylpolyynes is described. The known positions of the labeled carbon atoms allow assignment of the resonances in the ¹³C NMR spectra and identification of trends in the chemical shifts. Geo

Full text of DOI:10.1055/s-0031-1290983

PAPER
▌1915
13
13
paper
Synthesis and C NMR Spectroscopy of C-Labeled α,ω-Diphenylpolyynes
Rik R. Tykwinski,*a Thanh Luub
a
Department of Chemistry and Pharmacy and Interdisciplinary Center of Molecular Materials (ICMM), University of Erlangen-Nuremberg,
Henkestr. 42, 91054 Erlangen, Germany
b
Department of Chemistry, University of Alberta, Edmonton, AB, T6G 2G2, Canada
E-mail: rik.tykwinski@chemie.uni-erlangen.de
Received: 17.02.2012; Accepted after revision: 28.03.2012
Dedicated to Dr. Tom Nakashima for a lifelong commitment to NMR spectroscopy
ward and efficient protocol for polyyne formation.11 The
Abstract: The synthesis of three 13C-labeled α,ω-diphenylpolyynes
Fritsch–Buttenberg–Wiechell approach is well suited for
is described. The known positions of the labeled carbon atoms allow
the incorporation of 13C labels, using reasonably inexpen-
sive, or easily synthesized precursors, such as carbon tetra-
bromide or benzoic acid, as the source of the 13C labeling.
We report herein the synthesis of diphenylpolyynes with
13C labeling at selected positions of the acetylenic frame-
work. Using these compounds, we outline trends in the
13C NMR chemical shifts as a function of polyyne length.
assignment of the resonances in the 13C NMR spectra and identifi-
cation of trends in the chemical shifts.
Key words: alkynes, carbenes, 13C labeling, polyynes, Fritsch–
Buttenberg–Wiechell rearrangement
α,ω-Diphenylpolyynes (Ph[n], where n is the number of
acetylene units, Scheme 1) were among the first series of
polyynes to be targeted synthetically, and these efforts
emerged with a flurry in the early 1950s.1 The aromatic
stability of terminal phenyl rings, that is, their ability to
tolerate a range of harsh conditions, was ideal for synthe-
ses of the time, since all involved a sequence of addition
and elimination reactions.2 The synthesis and study of di-
phenylpolyynes has continued during the ensuing 60
years, targeting new synthetic methods, physical proper-
ties, or both.3 For example, diphenylpolyynes have been
explored by theory,4 as nonlinear optical (NLO) materi-
als,3d as molecular wires,5 for their electronic structure
(absorption and emission),6 in supramolecular complex-
es,7 and for their chemical reactivity.8
The synthesis of triyne Ph[3] started from the known ke-
tone 1,12 which was first subjected to Ramirez
dibromoolefination13 using a mixture of carbon tetrabro-
mide–13C-labeled carbon tetrabromide (CBr4–13CBr4, ca.
5:1) and triphenylphosphine. This afforded the labeled di-
bromoolefin 2 in 79% yield.14 The 13C NMR spectrum of
2 is consistent with that of the unlabeled analogue and also
confirms the chemical shift of Cα, the labeled carbon, at
107.6 ppm. The identity of Cβ is also revealed at 114.1
ppm, due to the strong coupling observed to Cα, with
1J = 97 Hz.
Fritsch–Buttenberg–Wiechell rearrangement of dibro-
moolefin 2 via reaction with n-butyllithium under stan-
dard conditions15 produced triyne Ph[3] in 62% yield.
Due to the labeling of compound 2 at Cα, rearrangement
of the intermediate alkylidene carbene 3 resulted in only
product Ph[3], that is, the same isotopomer was formed
regardless of which phenylacetylene group migrated in in-
termediate 3 to form triyne Ph[3].
For some time, we have taken an interest in the synthesis
of polyyne molecules, and particularly the evolution of
physical properties as a function of polyyne length. This
is, as one would expect, not a new endeavor. Indeed, the
earliest investigations asked the same question: what hap-
pens to the spectroscopic properties as polyynes become
longer?2 Surprisingly, however, little has been done to
confirm acetylenic NMR resonances via 13C labeling,
even though 13C NMR spectroscopy is a mainstay method
of characterization for polyynes, because the protons
found on terminal end-capping groups change little versus
length. Chemical shifts in triisopropylsilyl end-capped9
and tert-butyl end-capped10 polyynes have been examined
for a handful of molecules, but aside from these examples,
little else is known.
The assignment of the three unique acetylenic carbons of
Ph[3] proved reasonably straightforward based on the
presence of the 13C-enriched sp-carbon at C3, which is ob-
served at 66.4 ppm with 1J = 163 Hz to C2. Carbon C2 is
then identified at 74.4 ppm, based on the doublet with re-
ciprocal one-bond coupling to C3 (1J = 164 Hz), as well as
a doublet resulting from two-bond coupling between
C3↔C2′ with 2J = 20 Hz. The final alkyne carbon, C1, is
assigned at 78.5 ppm, showing a doublet with 2J = 18 Hz
(C1↔C3), as well as a three-bond correlation to HA as ob-
served in the heteronuclear multiple bond correlation
(HMBC) spectrum.16
Many of the polyynes from our studies can be prepared
via the Fritsch–Buttenberg–Wiechell (FBW) rearrange-
ment, which has proven to be a procedurally straightfor-
The predicted chemical shifts of Ph[3] have been report-
ed, calculated using the GIAO-B3LYP/6-31G* method.17
In this study, the calculated chemical shifts of C2 and C3,
at 73.7 and 64.3 ppm, respectively, are quite close to those
measured in solution (74.4 and 66.4 ppm, respectively).
SYNTHESIS 2012, 44, 1915–1922
Advanced online publication: 14.05.2012
0
0
3
9
-
7
8
8
1
1
4
3
7
-
2
1
0
X
DOI: 10.1055/s-0031-1290983; Art ID: SS-2012-Z0165-OP
© Georg Thieme Verlag Stuttgart · New York

1916
R. R. Tykwinski, T. Luu
PAPER
lyl)ethyne in the presence of the Lewis acid aluminum tri-
chloride (AlCl3). This gave ketone 5, which was
subsequently used in the Ramirez reaction to produce di-
bromoolefin 6 in 35% yield as a pale-yellow oil.18 It is
worth noting that the formation of 6 proceeds more effi-
ciently than the yield would suggest. Unfortunately, how-
ever, extensive purification by column chromatography
Br
Cβ
Br
Cα
*
O
*
CBr4, CBr4
Ph3P, CH2Cl2
Ph
Ph
Ph
Ph
(79%)
2
1
n-BuLi
hexanes
–78 °C
13
was required to remove impurities with C labeling that
* = 13
C
would likely complicate interpretation of the 13C NMR
spectra of the polyyne products in subsequent steps. In the
13C NMR spectrum of 6, the 13C label assigns Cβ at 131.0
ppm, while Cα appears at 103.3 ppm, based on the ob-
served one-bond coupling constant 1J = 88 Hz (Cα↔Cβ).
Br
Li
*
Ph
Ph
3
HA
HA
C1'
Lithium–halogen exchange at –78 °C in hexanes using di-
bromoolefin 6 and n-butyllithium induced the Fritsch–
Buttenberg–Wiechell rearrangement to form diynes 7a,b
as an isotopic mixture. In this reaction, either the alkyne
or the phenyl group can migrate to form either 7a or 7b,
respectively, placing the labeled carbon at either C1 or
C2. The ratio of products is typically close to 1:1.18
C2
C3'
C2'
Ph[3] (62%)
*
C1
C3
HA
HA
Scheme 1 Synthesis of 13C-labeled triyne Ph[3]
Noteworthy, however, is the fact that the predicted shift of
C1 (72.2 ppm) deviates quite significantly from the exper-
imental value determined here (78.5 ppm).
The 13C NMR chemical shifts of the acetylenic carbons of
7a,b can be assigned based on the sequence of C↔C cou-
pling constants. The ipso-carbon (Ci) is observed as two
doublets centered at 121.4 ppm, with 1J = 92 Hz (Ci↔C1
The formation of labeled tetraynes Ph[4]a–c as a mixture
of isotopomers was accomplished from C1-labeled ben-
zoic acid (4) (100% 13C enrichment, Scheme 2). The reac-
tion of 4 with thionyl chloride in dichloromethane gave
the corresponding acid chloride, which underwent
Friedel–Crafts acylation with 1,2-bis(trimethylsi-
2
in 7a) and J = 14 Hz (Ci↔C2 in 7b). This then sets the
chemical shift of C1 as 76.7 ppm based on the observed
common coupling constant to Ci (1J = 92 Hz). The C1 sig-
nal at 76.7 ppm also shows a second doublet with ob-
served 1J = 196 Hz, as a result of C1↔C2 coupling. This
reveals the chemical shift of C2 at 74.2 ppm (C2↔C1,
1J = 203 Hz). The C2 signal shows a second doublet with
1J = 141 Hz, due to one-bond C2↔C3 coupling, identify-
ing the resonance of C3 at 87.8 ppm, which shows a recip-
rocal coupling (1J = 148 Hz). The final resonance at 90.6
ppm, C4, shows a doublet due to two-bond C2↔C4 cou-
pling in 7b (2J = 14 Hz), and a singlet from the isotopomer
7a.19
O
*
O
CBr4
Ph3P
1. SOCl2, CH2Cl2
2. AlCl3, CH2Cl2
OH
*
CH2Cl2
(35%)
SiMe3
C4
4
5
Me3Si
SiMe3
C2
Ci
*
Cα
SiMe3
Br
Br
In the final synthetic steps, desilylation of diynes 7a,b
gave the terminal diynes, which were carried on directly
to an oxidative homocoupling reaction under standard
Hay20 conditions. The result of this reaction is a mixture
of isotopomers Ph[4]a–c, where the labeled carbons are
found at C1/C1′ for Ph[4]a, at C1/C2′ for Ph[4]b, and
C2/C2′ for Ph[4]c.
C1
C3
7a
n-BuLi
hexanes
Cβ
*
–78 °C
(78%)
C2
*
C4
SiMe3
Ci
C1
SiMe3
6
C3
7b
HA
HA
Ci
* = 13
C
Assignment of the resonances of the four unique sp car-
bons C1–C4 of Ph[4]a–c is complicated slightly due to
second order coupling between C1 and C221 and the ap-
proximately equal distribution of the 13C label between C1
and C2. The signal for Ci is observed as two doublets cen-
tered at 120.6 ppm with 1J = 91 Hz and 2J = 14 Hz (both
of equal intensity), as expected for coupling of Ci↔C1
and Ci↔C2, respectively. The reciprocal coupling con-
stants are not, however, evident for the labeled carbons at
77.7 and 74.5 ppm. The lack of a clear coupling pattern
complicates assignment of C1 and C2, although a correla-
tion observed in the HMBC spectrum between HA and the
signal at 77.7 ppm suggests this resonance should be C1.16
C2
C2
C4 C4'
C3'
C2'
Ci
*
*
C1
C3
C3
C1'
HA
Ph[4]a
HA
1. K2CO3
MeOH–THF
C4 C4'
C2'
Ci
C1'
Ci *
*
C1
C3'
2. CuCl, TMEDA
CH2Cl2
Ph[4]b
(100%)
C2
*
C4 C4'
C2'
*
Ci
C1'
Ci
C1
C3
C3'
Ph[4]c
Scheme 2 Synthesis of 13C-labeled tetraynes Ph[4]a–c
Synthesis 2012, 44, 1915–1922
© Georg Thieme Verlag Stuttgart · New York

PAPER
13C-Labeled α,ω-Diphenylpolyynes
1917
Selective homonuclear decoupling, however, provides the
O
O
13
answer.16 Acquisition of a C{1H} spectrum with selec-
1. SOCl2, CH2Cl2
*
OH
tive decoupling (irradiation) of the signal at 77.7 ppm col-
lapses the Ci signal into a singlet and a doublet (2J = 13
Hz), and hence the signal at 77.7 ppm is confirmed as that
of C1. Conversely, the selective decoupling experiment
with irradiation of the signal at 74.5 ppm shows Ci as a
singlet and a doublet (1J = 86 Hz), confirming the chemi-
cal shift of C2 at 74.5 ppm. Irradiation at 77.7 ppm (C1)
also results in a pseudo-doublet at 63.5 ppm (d, J = 158
Hz),16 the consequence of one-bond coupling between
C3↔C2, and thus the chemical shift of C3 is established.
The final alkyne resonance, C4, is observed as a second
order multiplet in the acquired spectra for Ph[4]a–c cen-
tered at approximately 67.2 ppm.
*
2. AlCl3, CH2Cl2
8
SiMe3
Me3Si
SiMe3
4
2
* = 13
C
Cα
Br
Ci
Br
n-BuLi
Cβ
CBr4, Ph3P
hexanes
C2
*
C1
CH2Cl2
(33%)
–78 °C
(78%)
9
SiMe3
C2
C4
Ci
*
SiMe3
SiMe3
1. K2CO3
MeOH–THF
C1
C3
10a
The synthesis of labeled hexaynes Ph[6]a–c was also ac-
complished starting from 13C-labeled benzoic acid (4)
(100% 13C enrichment, Scheme 3), as previously reported
for the unlabeled analogue.3d Acid 4 was first converted
into the corresponding acid chloride, and this was fol-
lowed by a Friedel–Crafts acylation with 1,4-bis(trimeth-
ylsilyl)butadiyne. This produced ketone 8, which was
quickly carried on without further purification to the di-
bromoolefination reaction. This gave dibromoolefin 9 as
an off-white solid in 33% yield over the three steps from
4. In the 13C NMR spectrum of 9, the 13C label assigns the
Cβ resonance at 129.9 ppm, and Cα appears at 102.6 ppm,
2. CuCl, TMEDA
CH2Cl2
C2
*
C4
C4
Ci
(87%)
C1
C3
10b
C2
C6
Ci
*
*
C1
C3
C3
C5
Ph[6]a
C2
*
C4
C5
C6
Ci
Ci
*
C1
Ph[6]b
1
based on J = 91 Hz coupling (Cα↔Cβ). Subsequent
Fritsch–Buttenberg–Wiechell rearrangement of 9 results
in triynes 10a,b as an approximate 1:1 mixture of isoto-
pomers.
C2
*
C4
C5
C6
*
C1
C3
Ph[6]c
13
The C chemical shifts of the alkyne carbons of triynes
Scheme 3 Synthesis of 13C-labeled tetraynes Ph[6]a–c
10a,b can be assigned using an analysis similar to that em-
ployed for 7a,b. The ipso carbon, Ci, of 10a,b is observed
1
observed as a doublet with 2J = 19 Hz, consistent with that
expected for C4 due to C4↔C2 coupling. The signal at
63.6 ppm shows a weak coupling constant (J = 5 Hz), sug-
gesting assignment as C5, and this leaves the last reso-
nance, a slightly broadened singlet at 64.6 ppm,
assignable as the central carbon C6.
as two doublets centered at 120.8 ppm, with J = 92 Hz
2
(Ci↔C1) and J = 14 Hz (Ci↔C2). The common cou-
pling constant observed for C1↔Ci (1J = 93 Hz) sets C1
as 76.9 ppm. The C1 resonance also shows a doublet with
observed 1J = 197 Hz, as a result of C1↔C2 coupling, re-
vealing the chemical shift of C2 as 74.3 ppm. The C2 sig-
nal shows a second doublet with 1J = 163 Hz, due to one-
bond C2↔C3 coupling, which assigns the resonance at
61.5 ppm (observed 1J = 163 Hz) as C3. While C4 can be
identified by the two doublets centered at 66.8 ppm
(J = 21 Hz and J = 16 Hz), it is not possible to distinguish
C5 and C6.
Table 1 Summary of the Chemical Shifts for Ph[1]–Ph[8]
Chemical shift (ppm, in CDCl3)a
Ph[n]
C1
C2
C3
C4
C5
C6
C7
C8
Ph[1] 89.4
Ph[2] 81.6
Ph[3] 78.5
Ph[4] 77.7
Ph[5] 77.5
Ph[6] 77.5
Ph[8] 77.6
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
Finally, removal of the silyl group and homocoupling un-
der Hay20 conditions converted 10a,b into a mixture of
hexayne isotopomers Ph[6]a–c in excellent yield. In the
13C NMR spectrum of Ph[6]a–c, Ci is observed at 120.1
ppm, again coupling to both labeled C1 (1J = 91 Hz) and
C2 (2J = 14 Hz). Carbon C1 appears at 77.5 ppm, as one
of the two enhanced signals and is identified by an HMBC
correlation to HA.16 The other labeled carbon, C2, is ob-
served at 74.3 ppm, showing one-bond coupling constants
of 198 Hz and 165 Hz to C1 and C3, respectively.21 This
then sets the resonance of C3 at 62.5 ppm because of cou-
pling to C2 (1J = 165 Hz). The resonance at 67.2 ppm is
73.9
–
–
74.4 66.4
74.5 63.7
74.4 62.8
74.3 62.5
74.3 62.6
–
–
67.2
67.3
–
64.5
67.2 63.6 64.6
67.2 63.3 64.5 63.4 63.6
a Values in italic font are tentative assignments. The value Cn for each
Ph[n] used in Figure 3 is highlighted in gray.
© Georg Thieme Verlag Stuttgart · New York
Synthesis 2012, 44, 1915–1922

1918
R. R. Tykwinski, T. Luu
PAPER
In all cases for the Ph[n] polyynes, HMBC experiments16 capped with triisopropylsilyl groups TIPS[n], the spectra
help to identify carbon C1 due to the correlation between of which have been reported previously (Figure 2).9 Sim-
C1 and HA of the phenyl ring.22,23 Combined with the la- ilar to the Ph[n] polyynes, the resonance of the terminal
beling studies above, it can be seen that the chemical shift carbon of the polyyne chain, C1, is also the most influ-
of C1 shows the most dramatic shift as a function of enced by the polyyne length in the TIPS[n] series, and C1
length, from 89.4 ppm in diphenylacetylene Ph[1] to 77.6 shifts from 82.2 ppm for TIPS[2] to 88.8 ppm for
ppm for Ph[8] (Figure 1, Table 1).24 The chemical shift of TIPS[10].25
carbon C2, on the other hand, shows virtually no change
as a function of polyyne length, appearing at circa 74.3
ppm in all cases except for Ph[2]. The signal for C3 ap-
pears at 66.4 ppm for Ph[3], and then shifts steadily up-
The most striking difference between the two series Ph[n]
and TIPS[n] is the apparent reversal of polarization of the
carbon chain, as evidenced by the relative positions of C1
and C2 in the TIPS[n] polyynes in comparison to those in
field to 63.7 ppm (Ph[4]) and 62.8 ppm (Ph[5]), and holds
Ph[n]. More specifically, within the Ph[n] series, the C1
constant at approximately 62.5 ppm for Ph[6] and Ph[8].
resonance is the most downfield, followed by the reso-
Conversely, the C4 resonance appears consistently at
nance of C2, which appears consistently at approximately
67.3–67.2 ppm.
74 ppm. For the TIPS[n] polyynes, however, the C2 res-
Unambiguous assignment of the resonances for polyyne onance occurs farthest downfield at approximately 90
Ph[8] has not been possible, so the trends for C7–C8 are ppm, followed by C1. It is notable that the C3 and C4 res-
speculative, but a general alternating pattern seems quite onances are also reversed for TIPS[n] versus Ph[n], that
clear. Thus, each additional acetylene unit brings two new is, for the Ph[n] polyynes the C3 resonance appears up-
resonances, and the new ‘odd’ carbon resonance appears field relative to C4, while conversely for TIPS[n], C4 is
slightly upfield from the accompanying ‘even’ resonance, found upfield from C3.
such as for Ph[6], where the C5 and C6 signals are found
at 63.6 and 64.6 ppm, respectively. Continuation of this
trend then places the C7 and C8 signals of Ph[8] at 63.4
and 63.6 ppm, respectively, and suggests that for longer
Ph[n] derivatives, the NMR chemical shift values should
coalesce between 63.4–63.6 ppm, providing an estimate
of the chemical shift of the carbyne.
An interesting trend is observed in the series Ph[n] for the
chemical shift of carbon Cn, that is, the signal of the cen-
tral-most carbon in the polyyne. As can be seen in Figure
3, there is a consistent decrease in chemical shift of Cn as
a function of length. On closer inspection, it is also clear
that the chemical shift values for Cn oscillates along a
mean curve, with shifts of Cn for odd n (n = 3 and 5) that
The chemical shifts of acetylenic carbons in the diphenyl- clearly fall below the trend established by the values for
polyyne series Ph[n] can be compared with the series end- Cn with even n (n = 2, 4, 6 and 8). It is interesting to con-
Figure 1 13C NMR spectra of polyynes Ph[n] with unambiguous assignments shown when possible (CDCl3)24
Synthesis 2012, 44, 1915–1922
© Georg Thieme Verlag Stuttgart · New York

PAPER
13C-Labeled α,ω-Diphenylpolyynes
1919
Figure 2 13C NMR spectra of polyynes TIPS[n] with unambiguous assignments shown when possible (CD2Cl2), from the literature9
than the chemical shift of 63.7 ppm, as suggested from
analysis of the longest series of polyynes reported to date,
the Tr*[n] series (Figure 4).30
(a)
n
Tr*[n]
(b)
Figure 3 Plot of chemical shift of Cn versus n for Ph[n], where n is
the number of acetylene units (see Table 1 for values and Figure 1 for
numbering scheme)
C1 C2 C3 C4
t-Bu[4]
C1 C2 C3 C4 C5
sider if this trend is somehow linked to Hückel aromatici-
ty in polyynes, as suggested by Chauvin and co-workers,26
but this prospect awaits further study.
t-Bu[5]
Figure 4 (a) Chemical structure of ‘super-trityl’ polyynes from refer-
ence 30, and (b) chemical shifts in ppm for the tert-butyl polyynes
from the literature10
Similar to that of the Ph[n] series, for the TIPS[n]
polyynes there seems to be a consistent appearance of new
signals in the narrow range of circa 62–63 ppm suggesting
convergence of the chemical shift values within this
range. The estimates for both Ph[n] and TIPS[n] are in
line with those suggested earlier for other polyynes, such
as those end-capped with platinum,27 dendrimers,28 and
adamantyl groups.29 They are, however, slightly lower
One final observation requires explanation. Members of
both the Ph[n] and TIPS[n] series appear to show an al-
ternating upfield–downfield pattern for the two resonanc-
es of each new acetylene added to the chain, as mentioned
above. For example, excluding C1 and C2, Ph[6] shows a
© Georg Thieme Verlag Stuttgart · New York
Synthesis 2012, 44, 1915–1922

1920
R. R. Tykwinski, T. Luu
PAPER
13C-Labeled 1,6-Diphenylhexa-1,3,5-triyne (Ph[3])
sequence of C4→C6→C5→C3 from high-to-low chemi-
cal shift values. The TIPS[n] series also appears to show
a similar trend for C3→C5/C6→C4, although not defini-
tive because the shifts of C5 and C6 are not known. Con-
versely, the chemical shifts reported for tert-butyl end-
capped polyynes show a consistent trend to lower chemi-
cal shift values such as the resonances for t-Bu[5],
C1→C2→C3→C4→C5 (Figure 4), based on labeling
studies by Bohlmann and Brehm.10 While no labeling
studies have been performed, a similar trend is suggested
for the parent polyyne series, H–(C≡C)n–H based on cou-
pling constants.31 To date, the origin of this difference re-
mains unknown.
Dibromoolefin 2 (244 mg, 0.633 mmol) was dissolved in a mixture
of anhyd toluene (4 mL) and anhyd hexanes (4 mL), and the soln
cooled to –78 °C. n-BuLi (2.5 M in hexanes, 1.7 mL, 0.68 mmol)
was added dropwise. The mixture was stirred at –78 °C for 30 min,
and then warmed to r.t. for 30 min. Et2O (10 mL) and sat. aq NH4Cl
soln (10 mL) were added. The organic phase was separated, washed
with brine (2 × 10 mL), and dried over MgSO4. Solvent removal and
purification by column chromatography (silica gel, hexanes) afford-
ed Ph[3] (89 mg, 62%) as a colorless solid. Spectral data were con-
sistent with those published for the unlabeled analogue.3b
13C NMR (100 MHz, CDCl3): δ = 132.9, 129.6, 128.4, 120.9, 78.5
(s and d, 2J = 18 Hz, C1), 74.4 (s and d, 1J = 164 Hz, and d, 2J = 20
Hz, C2), 66.4 (s and d, 1J = 163 Hz, C3*).
13C-Labeled (4,4-Dibromo-3-phenylbut-3-en-1-yn-1-yl)trimeth-
In conclusion, phenyl end-capped polyynes have been
synthesized with incorporation of 13C label(s) in the acet-
ylenic framework. Using NMR spectroscopic techniques,
the chemical shifts of individual carbons are identified,
typically through 13C–13C coupling patterns and con-
stants. Chemical shift trends for Ph[n] polyynes show that
the pattern of resonances is similar to those for TIPS[n]
polyynes, although the polarization of the polyyne chain
appears to be opposite. The chemical shift trend for Ph[n]
polyynes is, however, quite different than those proposed
for H[n] and t-Bu[n] polyynes, which show a consistent
trend in values from higher-to-lower chemical shift mov-
ing from the terminal carbon of the polyyne (C1) toward
the center of the chain Cn.
ylsilane (6)
Dibromoolefin 6 was prepared using the procedure described in the
literature.18
13C-Labeled Trimethyl(phenylbuta-1,3-diyn-1-yl)silanes (7a)
and (7b)
Dibromoolefin 6 (126 mg, 0.352 mmol) was dissolved in anhyd
hexanes (8 mL), the resulting soln cooled to –78 °C and n-BuLi (2.5
M in hexanes, 0.16 mL, 0.40 mmol) added dropwise. The mixture
was stirred at –78 °C for 30 min, and then warmed to r.t. for 30 min.
Et2O (10 mL) and sat. aq NH4Cl soln (10 mL) were added. The or-
ganic phase was separated, washed with brine (2 × 10 mL), and
dried over MgSO4. Solvent removal and purification by column
chromatography (silica gel, hexanes) afforded a ca. 1:1 mixture of
diyne isotopomers 7a and 7b (54.1 mg, 78%) as a yellow oil. Spec-
tral data were consistent with those published in reference 18.
13C NMR (100 MHz, CDCl3): δ = 132.7 (d, J = 2 Hz), 129.3, 128.4
(s and d, J = 6 Hz), 121.4 (d, 1J = 92 Hz and d, 2J = 14 Hz, Ci), 90.6
(d, 2J = 14 Hz, C4), 87.8 (d, 1J = 148 Hz and d, 2J = 18 Hz, C3), 76.7
(d, 1J = 196 Hz and d, 1J = 92 Hz, C1*), 74.2 (d, 1J = 203 Hz and d,
1J = 141 Hz, C2*), –0.4.
Reagent grade reactants and solvents were used without further pu-
rification. All reactions were performed using standard dry glass-
ware under an inert atmosphere of N2 unless otherwise noted
Anhydrous MgSO4 was used as the drying agent after aqueous
work-up. Thin-layer chromatography (TLC) was performed on alu-
minum sheets coated with silica gel F254 (Whatman); visualization
was achieved with UV light or by KMnO4 staining. Column chro-
matography was performed on silica gel-60 (230–400 mesh) ob-
tained from General Intermediates of Canada. Evaporation and
concentration in vacuo was performed at H2O-aspirator pressure.
13C NMR spectra were obtained using Varian Gemini 400 or 500 in-
struments, at r.t. in CDCl3; residual solvent peaks (δ = 7.24 ppm for
1H and δ = 77.0 ppm for 13C) were used as references. The asterisk
(*) refers to 13C-labeled carbons.
13C-Labeled 1,8-Diphenylocta-1,3,5,7-tetraynes (Ph[4]a–c)
A mixture of diynes 7a,b (54.1 mg, 0.279 mmol) was dissolved in
wet THF–MeOH (3 mL, 1:1), K2CO3 (50 mg, 0.36 mmol) was add-
ed, and the resulting soln stirred at r.t. until TLC analysis indicated
complete conversion into the desilylated intermediate. Et2O (10
mL) was added, and the resulting soln washed with sat. aq NH4Cl
soln (2 × 10 mL) and brine (2 × 10 mL), and then dried over MgSO4.
The soln was reduced to ca. 1 mL and added to a soln of the Hay
catalyst [CuCl (50 mg, 0.50 mmol) and TMEDA (0.1 mL) in
CH2Cl2 (5 mL), previously stirred until homogeneous] and a stream
of O2 was bubbled into the reaction mixture until the soln turned
blue. This mixture was stirred at r.t. under O2 until TLC analysis no
longer showed the presence of the starting diynes (ca. 3 h). Et2O (30
mL) and sat. aq NH4Cl soln (2 × 20 mL) were added. The organic
layer was separated, dried over MgSO4, and the solvent removed.
Column chromatography (silica gel, hexanes) afforded Ph[4]a–c
(35 mg, 100%) as a light-yellow crystalline solid. Spectral data
were consistent with those published for the unlabeled analogue.32
13C{1H} NMR (100 MHz, CDCl3): δ = 133.3 (s and d, J = 2 Hz),
130.0, 128.6 (s and d, J = 6 Hz), 120.6 (d, 1J = 91 Hz and d, 2J = 14
Hz, Ci), 77.7 (d, 1J = 207 Hz, C1*; other couplings were obscured
by CDCl3 signals), 74.5 (d, 1J = 198 Hz and d, 1J = 164 Hz, C2*),
67.2 (m, C4), 63.7 (pseudo d, 1J = 167 Hz and d, J = 14 Hz, C3).
13C{1H} NMR (100 MHz, CDCl3, irradiation at C1, 77.7 ppm):
δ = 133.1, 129.9, 128.5, 120.4 (s and d, 2J = 13 Hz, Ci), 74.4 (C2*),
67.0 (m, C4), 63.5 (s and pseudo d, 1J = 158 Hz, C3).
13C-Labeled [3-(Dibromomethylene)penta-1,4-diyne-1,5-di-
yl]dibenzene (2)
CBr4 (541 mg, 1.63 mmol), 13CBr4 (109 mg, 0.315 mmol) and Ph3P
(1.02 g, 3.91 mmol) were added to CH2Cl2 (10 mL) at 0 °C and the
resulting soln stirred for ca. 10 min until the mixture turned bright
orange. Ketone 1 (187 mg, 0.814 mmol),12 dissolved in CH2Cl2 (ca.
3 mL), was added in one portion. The mixture was allowed to warm
to r.t. and the progress of the reaction was monitored by TLC anal-
ysis until the ketone was no longer observed (ca. 3 h). When the re-
action was complete, the solvent was reduced to ca. 5 mL, hexanes
(50 mL) was added, the non-homogeneous mixture filtered through
a plug of Celite layered on top of silica gel, and the resulting filtrate
concentrated in vacuo. Column chromatography (silica gel, hex-
anes) gave compound 2 (187 mg, 79%) as a colorless solid. Spectral
data were consistent with those published for the unlabeled ana-
logue.12b
13C{1H} NMR (100 MHz, CDCl3, irradiation at C2, 74.5 ppm):
δ = 133.1, 129.9, 128.5 (s and d, J = 6 Hz), 120.4 (s and d, 1J = 86
Hz, Ci), 77.8 (C1), 67.0 (m, C4), 63.5 (m, C3).
13C NMR (100 MHz, CDCl3): δ = 131.6, 129.1, 128.3, 122.0, 114.1
(s and d, J = 97 Hz, Cβ), 107.6 (s and d, J = 94 Hz, Cα*), 95.7,
85.9.
1
1
Synthesis 2012, 44, 1915–1922
© Georg Thieme Verlag Stuttgart · New York

PAPER
13C-Labeled α,ω-Diphenylpolyynes
1921
13C-Labeled (6,6-Dibromo-5-phenylhexa-5-en-1,3-diyn-1-yl)tri-
methylsilane (9)
mL) and sat. aq NH4Cl soln (2 × 20 mL) were added. The organic
layer was separated, dried over MgSO4, and the solvent removed.
Column chromatography (silica gel, hexanes) afforded Ph[6]a–c
(5.0 mg, 87%) as an orange crystalline solid. Spectral data were
consistent with those published for the unlabeled analogue.3d
13C(1)-benzoic acid (4) (184 mg, 1.49 mmol) was dissolved in
CH2Cl2 (1 mL) and SOCl2 (49 mg, 4.1 mmol) was added. The mix-
ture was stirred overnight and the excess SOCl2 was removed in
vacuo to yield the corresponding acid chloride, which was used di-
rectly in the next step. The acid chloride was dissolved in anhyd
CH2Cl2 (15 mL), 1,4-bis(trimethylsilyl)buta-1,3-diyne (290 mg,
1.49 mmol) added, and the temperature of the soln lowered to
–20 °C. AlCl3 (239 mg, 1.79 mmol) was added portion-wise, and
the mixture warmed to r.t. over 3 h. The reaction was carefully
quenched by addition of the reaction soln to a mixture of 10% HCl
(50 mL) and ice (50 mL). CAUTION: exothermic. Et2O (70 mL)
was added and the organic layer was separated, washed with sat. aq
NaHCO3 soln (2 × 20 mL) and brine (2 × 20 mL), dried over
MgSO4, and the resulting soln reduced to ca. 5 mL to afford the in-
termediate ketone 8 (Rf = 0.2, hexanes–CH2Cl2, 6:1) that was car-
ried on without further purification. CBr4 (744 mg, 2.24 mmol) and
Ph3P (1.17 mg, 4.47 mmol) were added to CH2Cl2 (14 mL) at 0 °C
and the soln stirred for ca. 10 min until the mixture turned bright or-
ange. Ketone 8, dissolved in CH2Cl2 (ca. 3 mL), was added in one
portion. The mixture was allowed to warm to r.t. and the progress
of the reaction monitored by TLC analysis until the ketone was no
longer observed (ca. 3 h). When the reaction was complete, the sol-
vent was reduced to ca. 5 mL, hexanes (50 mL) was added, and the
non-homogeneous mixture filtered through a plug of Celite layered
on top of silica gel. The resulting filtrate was concentrated in vacuo.
Column chromatography (silica gel, hexanes) gave dibromoolefin 9
(190 mg, 33%) as an off-white solid. Spectral data were consistent
with those published for the unlabeled analogue.3d
13C{1H} NMR (125 MHz, CDCl3): δ = 133.5, 130.3, 128.6, 120.1
(d, 1J = 91 Hz and d, 2J = 14 Hz, Ci), 77.5 (d, 1J = 196 Hz, C1; other
couplings were obscured by CDCl3 signals), 74.3 (1J = 198 Hz and
1
2
d, J = 165 Hz, C2), 67.2 (d, J = 19 Hz, C4), 64.6 (C6), 63.6 (d,
J = 5 Hz, C5), 62.5 (d, 1J = 165 Hz and d, 2J = 18 Hz, C3).
Acknowledgment
We are grateful for financial support for this work from the Univer-
sity of Alberta, the Natural Sciences and Engineering Research
Council of Canada (NSERC), and Petro Canada (Young Innovator
Award to R.R.T.). We thank Dr. Alex Scherer for the synthesis and
characterization of TIPS[1].
Supporting Information for this article is available online at
http://www.thieme-connect.com/ejournals/toc/synthesis.SnoIufproi
m
tgioSrantnugIifoop
r
itmnatr
References
(1) For examples, see: (a) Nakagawa, M. Proc. Jpn. Acad.
1950, 26, 38. (b) Bohlmann, F. Chem. Ber. 1951, 84, 785.
(c) Schlubach, H. H.; Franzen, V. Liebigs Ann. Chem. 1951,
572, 116. (d) Schlubach, H. H.; Franzen, V. Liebigs Ann.
Chem. 1951, 573, 105. (e) Jones, E. R. H.; Whiting, M. C.;
Armitage, J. B.; Cook, C. L.; Entwistle, N. Nature (London)
1951, 168, 900. (f) Armitage, J. B.; Entwistle, N.; Jones, E.
R. H.; Whiting, M. C. J. Chem. Soc. 1954, 147.
13C NMR (100 MHz, CDCl3): δ = 137.1 (d, 1J = 58 Hz, Ci), 129.9
(d, 1J = 97 Hz, d, 1J = 91 Hz, and d, 1J = 58 Hz, Cβ*), 128.7, 128.42,
128.38, 102.6 (d, 1J = 91 Hz, Cα), 95.3 (C4), 87.2 (d, J = 4 Hz, C3),
82.0 (d, 2J = 13 Hz, C2), 74.8 (d, 1J = 97 Hz, C1), –0.7.
13C-Labeled Trimethyl(phenylhexa-1,3,5-triyn-1-yl)silanes
(10a) and (10b)
(2) Much of this early work is summarized by Bohlmann, see:
Bohlmann, F. Angew. Chem. 1953, 65, 385.
(3) For some examples, see: (a) Johnson, T. R.; Walton, D. R.
M. Tetrahedron 1972, 28, 5221. (b) Rubin, Y.; Lin, S. S.;
Knobler, C. B.; Anthony, J.; Boldi, A. M.; Diederich, F.
J. Am. Chem. Soc. 1991, 113, 6943. (c) Tobe, Y.; Umeda, R.;
Iwasa, N.; Sonoda, M. Chem.–Eur. J. 2003, 9, 5549. (d) Luu,
T.; Elliott, E.; Slepkov, A. D.; Eisler, S.; McDonald, R.;
Hegmann, F. A.; Tykwinski, R. R. Org. Lett. 2005, 7, 51.
(e) Cataldo, F.; Ursini, O.; Angelini, G.; Tommasini, M.;
Casari, C. J. Macromol. Sci., Pure Appl. Chem. 2010, 47,
739. (f) Rahimi, A.; Schmidt, A. Synthesis 2010, 2621.
(4) Song, J.-W.; Watson, M. A.; Sekino, H.; Hirao, K. Int. J.
Quantum Chem. 2009, 109, 2012.
Dibromoolefin 9 (190 mg, 0.498 mmol) was dissolved in anhyd
hexanes (15 mL), the resulting soln cooled to –78 °C and n-BuLi
(2.5 M in hexanes, 0.24 mL, 0.60 mmol) added dropwise. The mix-
ture was stirred at –78 °C for 30 min, and then warmed to r.t. for 30
min. Et2O (10 mL) and sat. aq NH4Cl soln (10 mL) were added. The
organic phase was separated, washed with brine (2 × 10 mL), and
dried over MgSO4. Solvent removal and purification by column
chromatography (silica gel, hexanes) afforded a ca. 1:1 mixture of
triyne isotopomers 10a and 10b (86.7 mg, 78%) as a yellow oil.
Spectral data were consistent with those published for the unlabeled
analogue.15b
13C NMR (100 MHz, CDCl3): δ = 133.1 (d, J = 2 Hz) 129.8, 128.5
(s and d, J = 6 Hz), 120.8 (d, 1J = 92 Hz and d, 2J = 14 Hz, Ci), 89.0
(d, J = 5 Hz and d, J = 3 Hz), 88.1 (d, J = 6 Hz and d, J = 3 Hz), 76.9
(d, 1J = 197 Hz and d, 1J = 93 Hz, C1*), 74.3 (d, 1J = 197 Hz and
(5) Milani, A.; Lucotti, A.; Russo, V.; Tommasini, M.; Cataldo,
F.; Bassi, A. L.; Casari, C. S. J. Phys. Chem. C 2011, 115,
12836.
1
2
(6) (a) Wahadoszamen, M.; Hamada, T.; Iimori, T.;
Nakabayashi, T.; Ohta, N. J. Phys. Chem. A 2007, 111, 9544.
(b) Nagano, Y.; Ikoma, T.; Akiyama, K.; Tero-Kubota, S.
J. Chem. Phys. 2001, 114, 1775. (c) Kobayashi, M.; Hoshi,
T.; Okubo, J.; Hiratsuka, H.; Harazono, T.; Nakagawa, M.;
Tanizaki, Y. Bull. Chem. Soc. Jpn. 1984, 57, 2905.
(7) (a) Taylor, T. J.; Gabbai, F. P. Organometallics 2006, 25,
2143. (b) Kendall, J.; McDonald, R.; Ferguson, M. J.;
Tykwinski, R. R. Org. Lett. 2008, 10, 2163.
(8) For example, see: (a) Matsuda, T.; Kadowaki, S.;
Yamaguchi, Y.; Murakami, M. Org. Lett. 2010, 12, 1056.
(b) Jiang, M. X.-W.; Rawat, M.; Wulff, W. D. J. Am. Chem.
Soc. 2004, 126, 5970. (c) Shim, S. C.; Lee, T. S. J. Org.
Chem. 1988, 53, 2410. (d) Zschunke, A.; Muegge, C.;
Hintzsche, E.; Schroth, W. J. Prakt. Chem./Chem.-Ztg.
1992, 334, 141.
d, J = 163 Hz, C2*), 66.8 (d, J = 21 Hz and d, J = 16 Hz, C4),
61.5 (d, 1J = 163 Hz and d, 2J = 19 Hz, C3), –0.5.
13C-Labeled 1,12-Diphenyldodeca-1,3,5,7,9,11-hexaynes
(Ph[6]a–c)
A mixture of triynes 10a,b (8.6 mg, 0.387 mmol) was dissolved in
wet THF–MeOH (3 mL, 1:1), K2CO3 (8 mg, 0.06 mmol) was added,
and the resulting soln stirred at r.t. until TLC analysis indicated
complete conversion into the desilylated intermediate. Et2O (10
mL) was added, and the resulting soln washed with sat. aq NH4Cl
soln (2 × 10 mL) and brine (2 × 10 mL), and then dried over MgSO4.
The soln was reduced to ca. 1 mL and added to a soln of the Hay
catalyst [CuCl (8 mg, 0.08 mmol) and TMEDA (0.1 mL) in CH2Cl2
(3 mL), previously stirred until homogeneous] and a stream of O2
was bubbled into the reaction mixture until the soln turned blue.
This mixture was stirred at r.t. under O2 until TLC analysis no lon-
ger showed the presence of the starting triynes (ca. 3 h). Et2O (30
© Georg Thieme Verlag Stuttgart · New York
Synthesis 2012, 44, 1915–1922

1922
R. R. Tykwinski, T. Luu
PAPER
(9) Eisler, S.; Slepkov, A. D.; Elliott, E.; Luu, T.; McDonald, R.;
Hegmann, F. A.; Tykwinski, R. R. J. Am. Chem. Soc. 2005,
127, 2666.
(10) Bohlmann, F.; Brehm, M. Chem. Ber. 1979, 112, 1071.
(11) (a) Chalifoux, W. A.; Tykwinski, R. R. Chem. Rec. 2006, 6,
169. (b) Jahnke, E.; Tykwinski, R. R. Chem. Commun. 2010,
46, 3235.
(12) (a) Wadsworth, D. H.; Geer, S. M.; Detty, M. R. J. Org.
Chem. 1987, 52, 3662. (b) Philp, D.; Gramlich, V.; Seiler,
P.; Diederich, F. J. Chem. Soc., Perkin Trans. 2 1995, 875.
(13) Ramirez, F.; Desai, N. B.; McKelvie, N. J. Am. Chem. Soc.
1962, 84, 1745.
(14) Unlabeled compound 2 has been synthesized previously by
a slightly different route, see reference 12b.
(15) (a) Eisler, S.; Tykwinski, R. R. J. Am. Chem. Soc. 2000, 122,
10736. (b) Eisler, S.; Chahal, N.; McDonald, R.; Tykwinski,
R. R. Chem.–Eur. J. 2003, 9, 2542.
(16) See Supporting Information for the HMBC spectrum.
(17) Hisaki, I.; Sonoda, M.; Tobe, Y. Eur. J. Org. Chem. 2006,
833.
ppm for C1–C4, respectively, see: Mabry, J.; Johnson, R. P.
J. Am. Chem. Soc. 2002, 124, 6497.
(24) The syntheses of unlabeled Ph[3] and Ph[4] were analogous
to those reported herein for the labeled compounds.
Unlabeled Ph[4], Ph[6], and Ph[8] were synthesized as
reported in reference 3d. The synthesis of unlabeled Ph[5]
has been reported (see references 3b and 3e) and is also
described in the Supporting Information.
(25) The resonance for the two degenerate acetylenic carbons of
Ph[1] (δ = 89.4) and TIPS[1] (δ = 112.5, see Supporting
Information for spectrum) shows the most dramatic
chemical shift deviation from the trend within each series,
which presumably results from the influence of the end-
capping groups. The position of this resonance relative to
others in the series suggests that the distal end-group has a
more significant influence on the chemical shift than the
proximal group, that is, in the hypothetical case R–C1≡C1′–
R′, the chemical shift of C1 is influenced mainly by R′, and
reciprocally C1′ by R. We thank a reviewer for pointing out
this observation.
(18) Bichler, P.; Chalifoux, W. A.; Eisler, S.; Shi Shun, A. L. K.;
Chernick, E. T.; Tykwinski, R. R. Org. Lett. 2009, 11, 519.
(19) The assignment of C3 and C4 in the present study is reversed
from that reported earlier, see: Klusener, P. A. A.;
Hanekamp, J. C.; Brandsma, L.; von Ragué Schleyer, P.
J. Org. Chem. 1990, 55, 1311.
(26) Chauvin, R.; Lepetit, C.; Maraval, V.; Leroyer, L. Pure
Appl. Chem. 2010, 82, 769.
(27) Zheng, Q.; Bohling, J. C.; Peters, T. B.; Frisch, A. C.;
Hampel, F.; Gladysz, J. A. Chem.–Eur. J. 2006, 12, 6486.
(28) Gibtner, T.; Hampel, F.; Gisselbrecht, J. P.; Hirsch, A.
Chem.–Eur. J. 2002, 8, 408.
(20) Hay, A. S. J. Org. Chem. 1962, 27, 3320.
(21) Coupling patterns for C1 and C2 for Ph[4] and Ph[6] are
observed as AB quartets (δν/J = 1.6).
(29) (a) Tykwinski, R. R.; Chalifoux, W.; Eisler, S.; Lucotti, A.;
Tommasini, M.; Fazzi, D.; Del Zoppo, M.; Zerbi, G. Pure
Appl. Chem. 2010, 82, 891. (b) Chalifoux, W. A.; Ferguson,
M. J.; McDonald, R.; Melin, F.; Echegoyen, L.; Tykwinski,
R. R. J. Phys. Org. Chem. 2011, 25, 69.
(30) Chalifoux, W. A.; Tykwinski, R. R. Nature Chem. 2010, 2,
967.
(31) Wakabayashi, T.; Tabata, H.; Doi, T.; Nagayama, H.;
Okuda, K.; Umeda, R.; Hisaki, I.; Sonoda, M.; Tobe, Y.;
Minematsu, T.; Hashimoto, K.; Hayashi, S. Chem. Phys.
Lett. 2007, 433, 296.
(22) The 1H NMR chemical shift of HA, which might be
influenced ‘through space’ by the electronic nature of the
polyyne chain, shifts only slightly downfield as a function of
length for Ph[1]–Ph[6] and Ph[8] (i.e., a multiplet centered
at 7.54, 7.52, 7.52, 7.53, 7.53, 7.55, and 7.56 ppm,
respectively).
(23) For Ph[2], the assignment of C1 and C2 is confirmed by 13
labeling studies of Ph–C1C2–C3C4–C6H4Me, which
shows acetylenic resonances at 81.2, 74.1, 73.3, and 81.9
C
(32) Heuft, M. A.; Collins, S. K.; Yap, G. P. A.; Fallis, A. G. Org.
Lett. 2001, 3, 2883.
Synthesis 2012, 44, 1915–1922
© Georg Thieme Verlag Stuttgart · New York