A Route to Cyclooct-2-ynol and Its Functionalization by Mitsunobu Chemistry

Article abstract of DOI:10.1002/ejoc.201301375

A new silver-free synthesis for cyclooctynol is introduced. The obtained alcohol was further functionalized by a Mitsunobu reaction to give an assortment of imide and phenol derivatives. It was also possible to further functionalize the cyclooctyne by treatment with a fluorescein dye. As an interesting application, we used a cyclooctyne-maleimide conjugate as an azide-thiol crosslinker. A new synthesis for cyclooct-2-ynol is presented that does not employ silver salts. The obtained alcohol was further functionalized by Mitsunobu chemistry to afford new cyclooctynes.

Full text of DOI:10.1002/ejoc.201301375

FULL PAPER
DOI: 10.1002/ejoc.201301375
A Route to Cyclooct-2-ynol and Its Functionalization by Mitsunobu Chemistry
Tobias Hagendorn[a] and Stefan Bräse*[a,b]
Keywords: Synthetic methods / Alkynes / Heterocycles / Dyes/pigments
A new silver-free synthesis for cyclooctynol is introduced.
The obtained alcohol was further functionalized by a Mitsu-
nobu reaction to give an assortment of imide and phenol de-
rivatives. It was also possible to further functionalize the cy-
clooctyne by treatment with a fluorescein dye. As an interest-
ing application, we used a cyclooctyne-maleimide conjugate
as an azide-thiol crosslinker.
two (i.e., 3)[11] fluorine atoms in the propargylic position
and an annelated benzene[12] (i.e., 4 and 5) or cyclopropane
ring[13] (i.e., 6). With these modifications, the reaction rate
can be tuned by either electronic effects or ring strain, thus,
enabling a reaction rate that is comparable to the copper-
catalyzed variant. The substituents can also influence the
solubility, which is especially important in the biological
context in which reactions are carried out in water or buffer
solutions.
Introduction
Since Sharpless[1] and Meldal[2] introduced the concept,
the copper-catalyzed azide–alkyne cycloaddition has fast
become a powerful tool in material science,[3] organic syn-
thesis, and chemical biology.[3a,4] A major drawback, how-
ever, arises when it is applied to living organisms, as the
required copper salts are often cytotoxic. A copper-free
variant that overcomes this problem is the strain-promoted
1,3-dipolar cycloaddition (SPAAC) of cyclooctynes with
azides (see Scheme 1). This variation, first introduced by
Bertozzi[5] and based on the pioneering work of Wittig and
Krebs,[6] has now become one of the most important tools
in the field of bioconjugation,[7] as shown by the fact that
various biomolecules or whole cells have been function-
alized by the use of cyclooctynes.[5,8] Besides the biological
applications, cyclooctynes have also found applications in
material science[9] when the absence of copper is required.
Scheme 1. Strain-promoted 1,3-dipolar cycloaddition.
Since its introduction in 2004, the cyclooctyne family has
steadily grown, and various systems presently exist. The
first employed systems were alkynes with a propargylic
ether group (i.e., 1), which are normally synthesized by a
silver-mediated ring-opening reaction (see Figure 1).[5] Fur-
ther variants include systems that contain one (i.e., 2)[10] or
Figure 1. Different generations of cyclooctynes.
During our studies in the field of cyclooctyne chemistry,
we regularly encountered problems with the silver-pro-
moted ring-opening of 8,8-dibromobicyclooctane 7 in the
reaction sequence towards cyclooctynol and its deriva-
tives.[14] Consequently, we tried to establish a silver-free
route to afford cyclooctynol 13. Although the cyclooctynol
derivatives are slow to react in a SPAAC reaction
[1.3ϫ10–3 ms–1 vs. 310ϫ10–3 ms–1 for dibenzoazacyclooct-
[a] Institute of Organic Chemistry, Karlsruhe Institute of
Technology (KIT), Campus South,
Fritz-Haber-Weg 6, 76131 Karlsruhe, Germany
E-mail: braese@kit.edu
Homepage: http://www.ioc.kit.edu/braese/english/index.php
[b] Institute of Toxicology and Genetics, KIT, Campus North,
Hermann-von-Helmholtz-Platz 1, 76344 Eggenstein-
Leopoldshafen, Germany
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejoc.201301375.
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Cyclooct-2-ynol and Its Functionalization by Mitsunobu Chemistry
yne (DIBAC[15])], they are still used.[16] Furthermore, we were identified. Because of this, the amount of LDA was
designed a new synthetic pathway that allows for new sub- decreased to 0.5 equiv. After the elimination reaction, a
stituents in the propargylic position.
mixture was obtained of the reactant and product, which
could not be separated by flash column chromatography.
This mixture then underwent a deprotection step, and after
the removal of the THP protecting group, the resulting
alcohols 11 and 13 could be separated to yield the desired
cyclooct-2-ynol (13).
Results and Discussion
We were interested in a silver-free synthesis of cyclooct-
2-ynol and its derivatives because known procedures require
the use of an excess amount of silver in the form of expens-
ive silver perchlorate. Furthermore, we experienced prob-
lems obtaining the desired (Z)-bromocyclooctenes 8 in
many experiments that used silver salts (see Scheme 2). We
were able to obtain solely the (Z) isomer from our very
first experiment, however, the reproduction failed. Thus, we
carried out the reaction in the dark under various reaction
conditions:
(1) The solvent was either pure methanol or a methanolic
solution in toluene (9:5 v/v).
(2) Either 2 or 3 equiv. of the silver salt were used with re-
gard to dibromide 7.
(3) The reaction temperature was set at either 0 °C or room
temp.
(4) The mixture was stirred for a reaction time of 30 min or
up to 3 h.
(5) The scale of the reaction was varied with regard to di-
Scheme 3. Reagents and conditions for the cyclooctynol synthesis:
(a) N-bromosuccinimide (NBS), azobis(isobutyronitrile) (AIBN),
CCl4, 2 h, reflux, 51%; then (1) Br2, dichloromethane (DCM),
–40 °C, 1 h; (2) KOtBu, tetrahydrofuran (THF), –50 °C, 3 h, 52%,
see Banert et al.[17]; (b) CuSO4·5H2O, dimethyl sulfoxide (DMSO),
H2O, reflux, 2 h, 51%; (c) Dihydropyran (DHP), Py·TosOH, DCM,
3 h, 99% (THP = tetrahydropyran); d) (1) LDA, THF, –78 °C to
r.t., 12 h; (2) TosOH, MeOH, 2 h, room temp., 36% over two steps.
bromide 7 (between 0.100 and 5.00 g).
(6) Different batches of the silver salt were employed.
With the cyclooct-2-ynol (13) in hand, we decided to
convert the alcohol moiety into imide and phenol func-
tional groups by employing a Mitsunobu reaction (see
Scheme 4).[19] By treating the alcohol with the correspond-
ing nucleophiles in the presence of diisopropyl azodicarbox-
ylate (DIAD) and PPh3 in THF as the solvent, the Mitsu-
nobu reaction was carried out. As a result, we obtained
different cyclooctynes with imide (i.e., 14 and 15), naphthol
(i.e., 16), and phenol (i.e., 17) substitutents.
Scheme 2. Key step in the silver-promoted synthesis of cyclo-
octynes.
In every case, mixtures of (E) and (Z) isomers were
formed, and these were not suitable for further transforma-
tions. When the mixture was treated with NaH to allow for
an elimination reaction, the reactant mixture was isolated
again without the formation of the alkyne. When lithium
diisopropylamide (LDA) was used as the base, only decom-
position took place, and no reaction products could be
identified.
To avoid this problem, we established a route to cyclooct-
2-ynol (13) by starting from cyclooctene (9; see Scheme 3).
The first steps comprised a Wohl–Ziegler bromination fol-
lowed by a sequence of bromination and elimination reac-
tions as described in the literature.[17] Next, the hydrolysis
of dibromocyclooctene 10 to give the corresponding alcohol
11 was carried out by using a DMSO/water mixture.[18]
Alcohol 11 was then protected by treatment with di-
hydropyran to obtain the THP-protected alcohol 12. After
the protection step, the vinylic (E)-bromide 12 could un-
dergo an elimination reaction by treatment with LDA to
yield the corresponding cyclooctyne. When an equimolar
Scheme 4. Reagents and conditions for Mitsunobu reactions:
(a) PPh3, DIAD, phenol or imide derivative, THF, 12 h, room
temp., 44% (14), 38% (15), 65% (16), and 55% yield (17).
The maleimide functionalized cyclooctyne 14 proved es-
amount of bromide 12 and LDA was used, only decomposi- pecially interesting because of its potential use as a
tion of the reactant was observed, and no reaction products crosslinker that can undergo reactions with azides and thi-
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T. Hagendorn, S. Bräse
FULL PAPER
ols. To determine whether the maleimide conjugate was re- tion, and the resulting acid was linked to an amine-func-
active towards azides and thiols, we carried out a click reac- tionalized fluorescein[21] by using standard peptide coupling
tion followed by a subsequent reaction between a thiol and reagents (see Scheme 6).
the maleimide. As an azide we chose ethyl 4-azidobenzoate.
The cycloaddition afforded 18 as a mixture of regioisomers
Conclusions
(8.4:1) that was then used in a further reaction with tert-
butylthiol. The addition of the thiol to maleimide 18
worked out well, and we could, therefore, prove that the
We introduced a new synthesis of cyclooct-2-ynol that
does not require expensive silver salts in the process.
Furthermore, under Mitsunobu conditions, we were able to
substitute the alcohol group of cyclooct-2-ynol with dif-
ferent functionalities such as imides and phenols. We were
also able to synthesize dye-functionalized cyclooctynes by
using this method.
new cyclooctyne-maleimide 14 could be used as
a
crosslinker between azides and thiols (see Scheme 5). Be-
cause cyclooctynol 13 was racemic, we obtained a mixture
of diastereomers when the thiol was treated with the male-
imide.
Experimental Section
General Methods: All organic chemicals were purchased from
ThermoFisher, ABCR, Alfa Aesar, or Sigma Aldrich. The NMR
spectroscopic data were recorded with a Bruker Avance 300
(300 MHz) or Bruker AM 400 (400 MHz) spectrometer, and
CDCl3 or [D6]DMSO was used as the solvent. Mass spectrometry,
FAB-MS and EI-MS, was performed with a Finnigan MAT 90
mass spectrometer. Infrared spectroscopy was carried out with a
Bruker IFS 88 device.
(E)-2-Bromocyclooct-2-enol (11): (E)-1,8-Dibromocyclooct-1-ene
(30.0 g, 0.112 mol, 1.00 equiv.) was dissolved in water (40 mL) and
DMSO (100 mL). Copper sulfate pentahydrate (37.0 g, 0.149 mol,
1.33 equiv.) was added, and the mixture was heated to 100 °C for
2 h. After this time, the reaction mixture was cooled to room tem-
perature, and then water (100 mL) and ethyl acetate (100 mL) were
added. The organic phase was separated and washed with water
(5ϫ 100 mL). After drying the organic phase with Na2SO4, the
solvent was removed, and the crude product was purified using
flash chromatography (silica gel, 20ϫ8 cm; cyclohexane/ethyl acet-
ate, 10:1) to afford 11 (11.7 g, 51% yield) as a colorless liquid; Rf
= 0.20 [cyclohexane (CH)/diethyl ether (EE), 10:1]. 1H NMR
(400 MHz, CDCl3): δ = 6.18 (ddd, 3JH,H = 8.8 Hz, 3JH,H = 8.8 Hz,
Scheme 5. Reagents and conditions: a) 4-azidobenzoate, THF, 12 h,
room temp., 28%; b) tert-butylthiol, DMSO, 12 h, room temp.,
98%.
We also attempted the use of thiols as nucleophiles in the
Mitsunobu reaction of alcohol 13. However, only an ad-
dition reaction between the thiol and alkyne was observed
instead of the desired coupling product (not shown).[20]
As cyclooctyne-dye conjugates are constantly used in cell
labeling, we also wanted to link our cyclooctynol derivative
to a dye molecule. Ester 17 underwent a saponification reac-
3
3
4JH,H = 0.8 Hz, 1 H, CH), 4.65 (dd, JH,H = 11.1 Hz, JH,H
=
4.8 Hz, 1 H, CHOH), 2.27–2.10 (m, 2 H, CH2), 1.93 (br. s, 1 H,
OH), 1.84–1.55 (m, 5 H, CH2), 1.44–1.27 (m, 3 H, CH2) ppm. 13C
NMR (100 MHz, CDCl3): δ = 132.1 (+, CH=CBr), 129.7 (Cquat
,
CBr), 68.8 (+, COH), 36.6 (–, CH2), 30.3 (–, CH2), 28.9 (–, CH2),
26.8 (–, CH2), 23.9 (–, CH2) ppm. IR [attenuated total reflectance
(ATR) platinum diamond): ν = 3383 (m), 2927 (s), 2851 (m), 1636
˜
(w), 1450 (w), 1063 (m) cm–1. MS (EI, 70 eV): m/z (%) = 204/206
(3/3) [M]+. HRMS (EI): calcd. for C8H13OBr 204.0150; found
204.0147.
Scheme 6. Attachment of fluorescein-piperazine amide to acid 20.
Reagents and conditions: (a) NaOH, MeOH/THF/water, 50 °C,
3 h, 65%; b) N,NЈ-diisopropylcarbodiimide (DIC), 1-hydroxy-
benzotriazole (HOBt), N,N-dimethylformamide (DMF), room
temp., 12 h 43%.
(E)-2-[(2-Bromocyclooct-2-en-1-yl)oxy]tetrahydro-2H-pyran
(12):
Alcohol 11 (0.410 g, 2.00 mmol, 1.00 equiv.), 3,4-dihydropyran
(0.252 g, 3.00 mmol, 1.50 equiv.), and pyridinium tosylate (0.050 g,
0.200 mmol, 0.100 equiv.) were stirred in DCM (16 mL) for 2 h.
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Cyclooct-2-ynol and Its Functionalization by Mitsunobu Chemistry
The solvent was removed, and the crude product was purified by
flash chromatography (silica gel, 20ϫ2 cm; cyclohexane/ethyl acet-
ate, 10:1) to afford a mixture of diastereomers of 12 (0.573 g, 99%
yield) as a colorless liquid; Rf = 0.48 (CH/EE, 10:1). 1H NMR:
1.30 equiv.) and triphenylphosphine (0.440 g, 1.69 mmol,
1.30 equiv.), and the solution was cooled to 0 °C. Then, DIAD
(0.328 g, 1.62 mmol, 1.25 equiv.) was added, and the solution was
warmed to room temperature overnight. The solvent was removed,
and the crude product was purified by flash chromatography (silica
3
3
(400 MHz, CDCl3): δ = 6.29 (dd, JH,H = 8.8 Hz, JH,H = 8.8 Hz,
3
3
0.67 CH=CBr), 6.17 (dd, JH,H = 8.9 Hz, JH,H = 8.9 Hz, 0.06 H, gel, 20ϫ2 cm; cyclohexane/ethyl acetate, 100:1) to afford 14
3
3
CH=CBr), 6.13 (dd, JH,H = 8.8 Hz, JH,H = 8.8 Hz, 0.28 H,
(0.116 g, 44% yield) as a white solid; m.p. 85.7 °C. Rf = 0.23 (CH/
CH=CBr), 4.86–4.78 (m, 1 H, OCHO), 4.66 (dd, JH,H = 7.9 Hz, EE, 20:1). 1H NMR: (300 MHz, CDCl3): δ = 6.65 (s, 2 H,
3
3JH,H = 7.9 Hz, 0.37 H, CHO), 4.56 (dd, JH,H = 4.7 Hz, JH,H
=
CH=CH), 4.99–4.86 (m, 1 H, CHN), 2.44–2.21 (m, 2 H, CH2),
3
3
2.9 Hz, 0.66 H, CHO), 3.94–3.85 (m, 1 H, OCH2), 3.57–3.45 (m, 1 2.21–1.94 (m, 5 H, CH2), 1.82–1.62 (m, 1 H, CH2), 1.53–1.36 (m,
H, OCH2), 2.29–2.09 (m, 2 H, CH2), 1.93–1.83 (m, 1 H, CH2),
1.83–1.59 (m, 7 H, CH2), 1.59–1.47 (m, 3 H, CH2), 1.42–1.28 (m,
1 H, CH2), 1.34–1.37 (m, 1 H, CH2) ppm. 13C NMR (100 MHz,
CDCl3): δ = 169.7 (Cquat, C=O), 134.1 (+, CH), 100.6 (Cquat, C-
3 H, CH2) ppm. 13C NMR (100 MHz, CDCl3): δ = 135.0 (+, alkyne), 88.1 (Cquat, C-alkyne), 44.0 (+, CHN), 40.3 (–, CH2), 34.4
CH=CBr), 131.9 (+, CH=CBr), 127.6 (Cquat, CBr), 127.5 (Cquat
CBr), 97.1 (+, OCHO), 96.3 (+, OCHO), 72.5 (+, CHO), 70.9 (+,
CHO), 62.9 (–, OCH2), 62.1 (–, OCH2), 33.7 (–, CH2), 33.4 (–, 1387 (w), 1360 (w), 1170 (w), 1138 (w) cm–1. MS (EI, 70 eV): m/z
CH2), 30.6 (–, CH2), 30.5 (–, CH2), 30.4 (–, CH2), 30.2 (–, CH2),
(%) = 203 (68) [M]+, 175 (100) [C11H13NO]+. HRMS (EI): calcd.
,
(–, CH2), 29.1 (–, CH2), 28.4 (–, CH2), 20.6 (–, CH2) ppm. IR (ATR
platinum diamond): ν = 2926 (w), 2852 (w), 1700 (s), 1439 (w),
˜
29.1 (–, CH2), 28.9 (–, CH2), 27.0 (–, CH2), 26.9 (–, CH2), 25.5 for C12H13NO2 203.0946; found 203.0947.
(–, CH2), 25.5 (–, CH2), 23.7 (–, CH2), 23.5 (–, CH2), 19.6 (–, CH2),
18.9 (–, CH ) ppm. IR (ATR platinum diamond): ν = 3442 (w),
˜
2
2928 (s), 2852 (m), 1636 (w), 1452 (m) cm–1. MS (EI, 70 eV): m/z
(%) = 209 (7) [M – Br]+, 85 (100) [C5H9O]+. HRMS (EI): calcd.
for C13H21BrO2 288.0725; found 288.0723.
2-(Cyclooct-2-yn-1-yl)isoindoline-1,3-dione (15): To a solution of
alcohol 13 (0.100 g, 0.810 mmol, 1.00 equiv.) in dry THF (8 mL)
under argon were added phthalimide (0.155 g, 1.05 mmol,
1.30 equiv.) and triphenylphosphine (0.276 g, 1.05 mmol,
1.30 equiv.), and the solution was cooled to 0 °C. Then, DIAD
(0.205 g, 1.02 mmol, 1.25 equiv.) was added, and the solution was
warmed to room temperature overnight. The solvent was removed,
and the crude product was purified by flash chromatography (silica
gel, 20ϫ2 cm; cyclohexane/ethyl acetate, 50:1) to afford 15
(0.077 g, 38% yield) as a white solid; m.p. 179.4 °C. Rf = 0.41 (CH/
Cyclooct-2-ynol (13): A solution of LDA (5.72 mmol, 1.00 equiv.)
in THF (8 mL) was cooled to –78 °C, and a solution of protected
alcohol 12 (3.31 g, 11.5 mmol, 2.00 equiv.) in dry THF (10 mL) was
added dropwise under argon. The cooling bath was removed, and
the mixture was stirred overnight. Water (20 mL) was then added,
and the mixture was extracted with ethyl acetate (3ϫ 15 mL). The
organic phase was separated and dried with sodium sulfate, and
the solvent was removed. The residue was purified by flash
chromatography (silica gel; cyclohexane/ethyl acetate, 10:1; Rf =
0.48) to afford a mixture of the protected alkynol and 12. This
mixture was dissolved in methanol (30 mL), and p-toluenesulfonic
acid (0.336 g, 1.77 mmol) was added. The mixture was stirred for
3 h. Water (50 mL) was added, and the aqueous phase was ex-
tracted with ethyl acetate (3ϫ 20 mL). The organic phase was dried
with sodium sulfate, and the crude product was purified by flash
chromatography (silica gel, 40ϫ2 cm; cyclohexane/ethyl acetate,
10:1) to afford 13 (0.336 g, 36% yield over two steps with regard
to 1.00 equiv. of LDA) as a colorless oil; Rf = 0.10 (CH/EE, 10:1).
1H NMR: (400 MHz, CDCl3): δ = 4.47–4.39 (m, 1 H, CHOH),
2.37 (br. s, 1 H, OH), 2.28–2.04 (m, 2 H, CH2), 1.97–1.80 (m, 3 H,
CH2), 1.78–1.70 (m, 1 H, CH2), 1.70–1.53 (m, 2 H, CH2), 1.54–
1.27 (m, 2 H, CH2) ppm. 13C NMR (100 MHz, CDCl3): δ = 99.7
(Cquat, C-alkyne), 94.1 (Cquat, C-alkyne), 64.6 (+, COH), 45.2 (–,
CH2), 34.4 (–, CH2), 29.7 (–, CH2), 25.9 (–, CH2), 20.7 (–,
1
EE, 10:1). H NMR: (400 MHz, CDCl3): δ = 7.84–7.78 (m, 2 H,
H-Ar), 7.72–7.67 (m, 2 H, H-Ar), 5.18–5.10 (m, 1 H, CHN), 2.46–
2.31 (m, 2 H, CH2), 2.23–2.00 (m, 5 H, CH2), 1.83–1.66 (m, 1 H,
CH2), 1.56–1.46 (m, 1 H, CH2), 1.38–1.24 (m, 1 H, CH2) ppm. 13
C
NMR (100 MHz, CDCl3): δ = 167.3 (Cquat, CO), 133.9 (+, C-Ar),
131.9 (Cquat, C-Ar), 123.2 (+, C-Ar), 100.4 (Cquat, C-alkyne), 88.4
(Cquat, C-alkyne), 44.1 (+, CHO), 40.2 (–, CH2), 34.5 (–, CH2), 29.2
(–, CH2), 28.5 (–, CH2), 20.7 (–, CH2) ppm. IR (ATR platinum
diamond): ν = 3464 (w), 2929 (w), 2851 (w), 2214 (w), 1775 (w),
˜
1708 (s), 1367 (m), 1329 (m) cm–1. MS (EI, 70 eV): m/z (%) = 254
(67) [M + H]+, 253 (65) [M]+, 225 [M – CO]+, 77 (100). HRMS
(EI): calcd. for C16H15NO2 253.1103; found 253.1100.
2-(Cyclooct-2-yn-1-yloxy)naphthalene (16): To a solution of alcohol
13 (0.080 g, 0.650 mmol, 1.0 equiv.) in dry THF (8 mL) under ar-
gon were added 2-naphthol (0.121 g, 0.850 mmol, 1.30 equiv.) and
triphenylphosphine (0.220 g, 0.840 mmol, 1.30 equiv.), and the
solution was cooled to 0 °C. Then, DIAD (0.205 g, 1.02 mmol,
1.57 equiv.) was added, and the solution was warmed to room tem-
perature overnight. The solvent was removed, and the crude prod-
uct was purified by flash chromatography (silica gel, 20ϫ2 cm; cy-
clohexane/ethyl acetate, 100:1) to afford 13 (0.103 g, 65% yield) as
CH ) ppm. IR (ATR platinum diamond): ν = 3386 (m), 2927 (s),
˜
2
2852 (m), 2211 (w), 1707 (w), 1449 (m) cm–1. MS (EI, 70 eV): m/z
(%) = 125 (3) [M + H]+, 124 (3) [M]+, 95 (100) [C7H11]+. HRMS
(EI): calcd. for C8H12O 124.0888; found 124.0890.
1
a light yellow oil; Rf = 0.77 (CH/EE, 20:1). H NMR: (400 MHz,
CDCl3): δ = 7.73–7.59 (m, 3 H, H-Ar), 7.40–7.31 (m, 1 H, H-Ar),
7.28–7.20 (m, 1 H, H-Ar), 7.17–7.12 (m, 1 H, H-Ar), 7.10–7.04 (m,
1 H, H-Ar), 4.88–4.81 (m, 1 H, CHO), 2.36–2.04 (m, 4 H, CH2),
1.95–1.76 (m, 3 H, CH2), 1.74–1.51 (m, 3 H, CH2) ppm. 13C NMR
1-(Cyclooct-2-yn-1-yl)-1H-pyrrole-2,5-dione (14): To a solution of
alcohol 13 (0.160 g, 1.30 mmol, 1.00 equiv.) in dry THF (15 mL)
under argon were added maleimide (0.164 g, 1.69 mmol,
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T. Hagendorn, S. Bräse
(100 MHz, CDCl3): δ = 155.5 (Cquat, C-O/C-Ar), 134.4 (Cquat, C- (ATR platinum diamond): ν = 2929 (w), 2212 (w), 2058 (w), 1658
FULL PAPER
˜
Ar), 129.3 (+, C-Ar), 129.1 (Cquat, C-Ar), 127.5 (+, C-Ar), 127.0
(s), 1599 (s), 1574 (m), 1449 (w), 1424 (m), 1354 (m), 1305 (w),
(+, C-Ar), 126.2 (+, C-Ar), 123.7 (+, C-Ar), 119.1 (+, C-Ar), 108.2 1244 (s) cm–1. MS (FAB): m/z = 245 [M + H]+, 137 [C7H5O3]+.
(+, C-Ar), 101.5 (Cquat, C-alkyne), 91.8 (Cquat, C-alkyne), 69.9 (+,
CHO), 42.3 (–, CH2), 34.1 (–, CH2), 29.7 (–, CH2), 26.2 (–, CH2),
HRMS (FAB): calcd. for C15H17O3 245.1178; found 245.1176.
20.7 (–, CH ) ppm. IR (ATR platinum diamond): ν = 3396 (w),
˜
2
3056 (w), 2924 (m), 2849 (m), 2212 (w), 1628 (m), 1598 (m), 1509
(m), 1466 (m), 1447 (m) cm–1. MS (EI, 70 eV): m/z (%) = 250 (8)
[M]+, 84 (100). HRMS (EI): calcd. for C18H18O 250.1358; found
250.1354.
Methyl 4-(Cyclooct-2-yn-1-yloxy)benzoate (17): To a solution of
alcohol 13 (0.100 g, 0.810 mmol, 1.00 equiv.) in dry THF (8 mL)
under argon were added methyl 4-hydroxybenzoate (0.160 g,
1.05 mmol, 1.30 equiv.) and triphenylphosphine (0.276 g,
1.05 mmol, 1.30 equiv.), and the solution was cooled to 0 °C. Then,
DIAD (0.205 g, 1.02 mmol, 1.26 equiv.) was added, and the solu-
tion was warmed to room temperature overnight. The solvent was
removed, and the crude product was purified by flash chromatog-
raphy (silica gel, 20ϫ2 cm; cyclohexane/ethyl acetate, 100:1) to af-
ford 17 (0.114 g, 55% yield) as a white solid; m.p. 49.8 °C. Rf =
0.38 (CH/EE, 20:1). 1H NMR (400 MHz, CDCl3): δ = 8.00–7.95
(m, 2 H, H-Ar), 6.99–6.90 (m, 2 H, H-Ar), 4.86–4.80 (m, 1 H,
CHO), 3.87 (s, 3 H, CH3), 2.33–2.15 (m, 4 H, CH2), 1.98–1.83 (m,
3 H, CH2), 1.81–1.56 (m, 3 H, CH2) ppm. 13C NMR (100 MHz,
CDCl3): δ = 166.9 (Cquat, C=O), 161.5 (Cquat, C-O/C-Ar), 131.5 (+,
C-Ar), 122.8 (Cquat, C-Ar), 114.9 (+, C-Ar), 102.1 (Cquat, C-alk-
yne), 91.0 (Cquat, C-alkyne), 70.1 (+, CHO), 51.9 (+, CH3), 42.2
(–, CH2), 34.1 (–, CH2), 29.7 (–, CH2), 26.1 (–, CH2), 20.7 (–,
9-(2-{4-[4-(Cyclooct-2-yn-1-yloxy)benzoyl]piperazine-1-carbonyl}-
phenyl)-6-hydroxy-3H-xanthen-3-one (21): Acid 20 (0.045 g,
0.184 mmol, 1.00 equiv.), N,N-diisopropylethylamine (DIPEA,
0.038 mL, 0.029 g, 0.223 mmol, 1.21 equiv.), HOBt (0.042 g,
0.274 mmol, 1.49 equiv.), and fluorescein-piperazine amide
(0.110 g, 0.275 mmol, 1.49 equiv.) were dissolved in dry DMF
(5 mL) under argon. DIC (0.042 mL, 0.034 g, 0.271 mmol,
1.47 equiv.) was added, and the solution was stirred at room tem-
perature for 24 h. The solvent was removed, and the crude product
was purified by flash chromatography (silica gel, 20ϫ2 cm; DCM/
MeOH, 40:1–10:1) to afford 21 (0.050 g, 43% yield) as an orange
solid; m.p. 244 °C (decomposition). Rf = 0.28 (DCM/MeOH, 20:1).
1H NMR (400 MHz, CDCl3): δ = 7.93 (br. s, 1 H, OH), 7.62–7.50
(m, 2 H, H-Ar), 7.47–7.38 (m, 1 H, H-Ar), 7.35–7.28 (m, 1 H, H-
Ar), 7.25–7.18 (m, 2 H, H-Ar), 7.03–6.94 (m, 2 H, H-Ar), 6.87–
6.80 (m, 2 H, H-Ar), 6.75–6.66 (m, 4 H, H-Ar), 4.74–4.66 (m, 1 H,
CHO), 3.53–3.16 (m, 8 H, piperazine-H), 2.23–2.04 (m, 4 H, CH2),
1.89–1.76 (m, 3 H, CH2), 1.70–1.46 (m, 3 H, CH2) ppm. 13C NMR
(100 MHz, CDCl3): δ = 175.2 (Cquat, C=O), 170.5 (Cquat, C=O),
167.7 (Cquat, C-Ar), 159.2 (Cquat, C-Ar), 157.4 (Cquat, C-Ar), 151.8
(Cquat, C-Ar), 134.9 (Cquat, C-Ar), 131.6 (Cquat, C-Ar), 130.8 (+,
C-Ar), 130.6 (+, C-Ar), 129.9 (+, C-Ar), 129.6 (+, C-Ar), 129.0 (+,
C-Ar), 127.3 (+, C-Ar), 126.7 (Cquat, C-Ar), 121.9 (+, C-Ar), 115.2
(+, C-Ar), 115.1 (Cquat, C-Ar), 103.9 (+, C-Ar), 102.0 (Cquat, C-
alkyne), 91.1 (Cquat, C-alkyne), 70.0 (+, C-O), 47.4 (–, CH2-piper-
azine), 42.1 (–, CH2), 41.9 (–, CH2-piperazine), 34.0 (–, CH2), 29.6
(–, CH2), 26.0 (–, CH2), 20.6 (–, CH2) ppm. IR (ATR platinum
CH ) ppm. IR (ATR platinum diamond): ν = 2923 (w), 2849 (w),
˜
2
1717 (m), 1603 (m), 1579 (w), 1506 (m), 1437 (m) cm–1. MS (EI,
70 eV): m/z (%) = 258 (17) [M]+, 243 (17) [M – Me]+, 199 (100)
[C14H15O]+. HRMS (EI): calcd. for C16H18O3 258.1256; found
258.1254.
(Cyclooct-2-yn-1-yloxy)benzoic Acid (20): Ester 17 (0.089 g,
0.345 mmol, 1.00 equiv.) was dissolved in THF (3 mL) and meth-
anol (3 mL). Then, sodium hydroxide (0.200 g, 5.00 mmol,
14.5 equiv.) that was dissolved in water (2 mL) was added, and the
mixture was stirred at 50 °C for 3 h. The mixture was then diluted
with water (5 mL), and the aqueous phase was extracted with ethyl
acetate (2ϫ 10 mL). The organic phase was discarded, and the co-
oled aqueous phase was acidified with concentrated HCl to pH =
2. Then, the aqueous phase was extracted with ethyl acetate (2ϫ
10 mL). The organic phase was then dried with sodium sulfate.
Removal of the solvent yielded 20 (0.055 g, 65% yield) as a white
diamond): ν = 2921 (w), 2848 (w), 1632 (m), 1590 (s), 1504 (m),
˜
1454 (m), 1417 (m), 1378 (m), 1237 (s), 1202 (m), 1172 (m) cm–1.
MS (FAB): m/z = 627 [M + H]+. HRMS (FAB): calcd. for
C39H35N2O6 627.2495; found 627.2494.
1
solid; m.p. 161.9 °C. H NMR: (400 MHz, [D6]DMSO): δ = 12.63
(s, 1 H, OH), 7.90–7.85 (m, 2 H, H-Ar), 7.01–6.96 (m, 2 H, H-Ar),
5.09–5.03 (m, 1 H, CHO), 2.29–2.07 (m, 4 H, CH2), 1.89–1.74 (m,
Ethyl 4-[4-(2,5-Dioxo-2,5-dihydro-1H-pyrrol-1-yl)-4,5,6,7,8,9-hexa-
hydro-1H-cycloocta[d]-[1,2,3]triazol-1-yl]benzoate and Regioisomer
3 H, CH2), 1.72–1.51 (m, 3 H, CH2) ppm. 13C NMR (100 MHz, (18): Alkyne 14 (0.050 g, 0.250 mmol, 1.00 equiv.) was dissolved in
[D6]DMSO): δ = 167.0 (Cquat, C=O), 160.8 (Cquat, C-O, C-Ar), THF (10 mL). Ethyl 4-azidobenzoate (0.070 g, 0.370 mmol,
131.2 (+, C-Ar), 123.3 (Cquat, C-Ar), 115.0 (+, C-Ar), 101.8 (Cquat
C-alkyne), 91.5 (Cquat, C-alkyne), 69.5 (+, CHO), 41.7 (–, CH2),
,
1.48 equiv.) was added, and the solution was stirred at room tem-
perature for 12 h. The solvent was removed, and the crude product
33.8 (–, CH2), 29.2 (–, CH2), 25.7 (–, CH2), 19.9 (–, CH2) ppm. IR was purified by flash chromatography (silica gel, 20ϫ2 cm; cyclo-
1284 Eur. J. Org. Chem. 2014, 1280–1286
www.eurjoc.org
© 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Cyclooct-2-ynol and Its Functionalization by Mitsunobu Chemistry
hexane/ethyl acetate, 3:1) to afford 18 (0.027 g, 28% yield) as a
highly viscous oil; Rf = 0.23 (EE/CH, 3:1). 1H NMR (400 MHz,
[D6]DMSO): δ = 8.17 [d, J = 8.4 Hz, 2H (major isomer), H-Ar],
Supporting Information (see footnote on the first page of this arti-
1
cle): Copies of the H and 13C NMR spectra of all key intermedi-
3
ates and final products.
8.02 [d, 3J = 8.4 Hz, 2H (minor isomer), H-Ar], 7.67 [d, 3J =
8.4 Hz, 2H (major isomer), H-Ar], 7.59 [d, 3J = 8.4 Hz, 2H (minor
isomer), H-Ar], 7.06 [s, 2H (major isomer), H-olefin], 6.69 [s, 2H
(minor isomer), H-olefin], 5.36 (dd, 3J = 12.5 Hz, 3J = 3.8 Hz, 1
Acknowledgments
The authors thank the Landesgraduiertenförderung Baden-
Württemberg for financial support.
3
H, CH), 4.36 (q, J = 7.0 Hz, 2 H, CH2CH3), 3.16–2.99 (m, 1 H,
CH2), 2.87–2.68 (m, 1 H, CH2), 1.98–1.86 (m, 1 H, CH2), 1.86–
3
1.50 (m, 4 H, CH2), 1.58–1.42 (m, 2 H, CH2), 1.35 (t, J = 7.1 Hz,
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3 H, CH2CH3) ppm. 13C NMR (100 MHz, [D6]DMSO): δ = 170.6
(Cquat, CO2Et), 169.1 (Cquat, CO2Et), 164.8 (Cquat, C-imid), 164.8
(Cquat, C-imid), 144.7 (Cquat, C-Ar), 142.6 (Cquat, C-Ar), 139.6
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C-Ar), 133.9 (+, C-olefin), 132.2 (Cquat, C-Ar), 130.8 (Cquat, C-Ar),
130.6 (+, C-Ar), 130.3 (+, C-Ar), 125.9 (+, C-Ar), 125.8 (+, C-Ar),
61.3 (–, CO2CH2CH3), 61.2 (–, CO2CH2CH3), 46.6 (+, CH), 44.1
(+, CH), 29.5 (–, CH2), 29.4 (–, CH2), 26.3 (–, CH2), 25.6 (–, CH2),
24.6 (–, CH2), 24.4 (–, CH2), 24.3 (–, CH2), 23.9 (–, CH2), 20.9
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˜
2
3
2925 (w), 2854 (w), 1702 (m), 1606 (m), 1513 (w), 1475 (w), 1445
(w), 1387 (m), 1354 (m), 1272 (m), 149 (m), 1100 (m), 1019 (m),
1003 (m) cm–1. MS (EI, 70 eV): m/z (%) = 395 (100) [M + H]+, 270
(35) [C17H20NO2]+. HRMS (EI): calcd. for C21H23O4N4 395.1714;
found 395.1712.
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hexahydro-1H-cycloocta[d][1,2,3]triazol-1-yl}benzoate (19): Triazole
18 (0.020 g, 0.051 mmol, 1.00 equiv.) was dissolved in DMSO
(2 mL) and tert-butylthiol (0.006 g, 0.066 mmol, 1.30 equiv.), and
the resulting mixture was stirred for 12 h. After this time, the excess
amount of thiol was removed under high vacuum. The DMSO
solution was then diluted with water (5 mL), and the aqueous
phase was extracted with ethyl acetate (2ϫ 2 mL). The organic
phase was washed thoroughly with water (10ϫ 2 mL). The organic
phase was dried with sodium sulfate, and the solvent was removed
to yield pure product 19 (0.024 g, 98% yield, complex mixture of
1
regioisomers and diastereomers) as a highly viscous oil. H NMR
(400 MHz, [D6]DMSO): δ = 8.24–8.12 (m, 2 H, H-Ar), 7.72–7.56
3
(m, 2 H, H-Ar), 5.47–5.26 (m, 1 H, CHN), 4.37 (q, J = 7.1 Hz, 2
H, CO2CH2), 4.15–4.04 (m, 1 H, CHS), 3.39–3.27 (m, 1 H,
NCOCH2), 3.23–3.04 (m, 1 H, NCOCH2), 2.94–2.68 (m, 2 H,
CH2), 2.65–2.54 (m, 1 H, CH2), 1.93–1.46 (m, 7 H, CH2), 1.46–
1.28 (m, 11 H, CH3), 1.28–1.12 (m, 1 H, CH3) ppm. 13C NMR
(100 MHz, [D6]DMSO): δ = 176.2 (Cquat, CO2Et), 176.1 (Cquat
CO2Et), 174.5 (Cquat, C-imid), 164.8 (Cquat, C-imid), 141.8 (Cquat
,
,
C-Ar), 141.8 (Cquat, C-Ar), 139.07 (Cquat, C-Ar), 134.5 (Cquat, C-
Ar), 130.8 (Cquat, C-Ar), 130.7 (+, C-Ar), 125.77 (+, C-Ar), 61.2
(–, CO2CH2), 47.6 (+, CHN), 44.4 (Cquat, CS), 44.4 (Cquat, CS),
38.9 (–, CH2CHS), 38.8 (+, CHS), 31.0 [+, CH3(tert-butyl)], 31.0
[+, CH3(tert-butyl)], 28.0 (–, CH2), 28.0 (–, CH2), 25.6 (–, CH2),
25.6 (–, CH2), 24.4 (–, CH2), 24.3 (–, CH2), 24.3 (–, CH2), 20.8
(–, CH2), 14.1 [+, CH3(ester)] ppm. IR (ATR platinum diamond):
ν = 2924 (vw), 2862 (vw), 1776 (vw), 1702 (w), 1607 (vw), 1513
˜
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(vw) cm–1. MS (EI, 70 eV): m/z (%) = 484 (33) [M]+, 456 (57) [M –
N2]+, 270 (100) [C17H20NO2]+. HRMS (EI): calcd. for
C25H32O4N4S 484.2139; found 484.2138.
Eur. J. Org. Chem. 2014, 1280–1286
© 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
1285

T. Hagendorn, S. Bräse
FULL PAPER
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Received: September 10, 2013
Published Online: December 16, 2013
1286
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© 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2014, 1280–1286