A versatile synthesis of functionalized pentahelicenes

Article abstract of DOI:10.1021/jo1013977

A general synthetic methodology for the preparation of functionalized (hetero)helicenes has been developed. It employs the sequence of a double propargyl organometallics (Li, Mg, Ga/In) addition to a tolan-2,2′- dialdehyde-type intermediate, a cobalt-catalyzed/cobalt-mediated [2 + 2 + 2] cycloisomerization of a triyne intermediate, and a double silica gel-assisted acetic acid elimination to receive pentahelicene, 1,14-diazapentahelicene, and 3,12-dichloro-, 3,12-dichloro-7-trimethylsilyl-, and 3,12-di-tert- butylpentahelicene. 3,12-Dichloropentahelicene undergoes a Suzuki-Miyaura coupling with aryl boronic acids (or ester) under palladium catalysis to afford 3,12-diarylpentahelicenes.

Full text of DOI:10.1021/jo1013977

pubs.acs.org/joc
A Versatile Synthesis of Functionalized Pentahelicenes
†
†
†
Mısek, Markus B. Schmid, Adrian Kollarovic, Irena G. Stara,*
,†
ꢀ ꢀ
ꢁ
sarova, and Ivo Stary*
ꢀ †
ꢁ
Olivier Songis, Jirı
David Saman, Ivana Cı
´
´
†
,†
ꢁ §
ꢁ
ꢀ
ꢀ
´
†Institute of Organic Chemistry and Biochemistry, Academy of Sciences of the Czech Republic,
Flemingovo naꢁm. 2, 166 10 Prague 6, Czech Republic, and §Department of Inorganic Chemistry,
Charles University, Albertov 2030, 128 40 Prague 2, Czech Republic
stara@uochb.cas.cz; stary@uochb.cas.cz
Received July 22, 2010
A general synthetic methodology for the preparation of functionalized (hetero)helicenes has been
developed. It employs the sequence of a double propargyl organometallics (Li, Mg, Ga/In) addition
to a tolan-2,20-dialdehyde-type intermediate, a cobalt-catalyzed/cobalt-mediated [2 þ 2 þ 2]
cycloisomerization of a triyne intermediate, and a double silica gel-assisted acetic acid elimination to
receive pentahelicene, 1,14-diazapentahelicene, and 3,12-dichloro-, 3,12-dichloro-7-trimethylsilyl-, and
3,12-di-tert-butylpentahelicene. 3,12-Dichloropentahelicene undergoes a Suzuki-Miyaura coupling
with aryl boronic acids (or ester) under palladium catalysis to afford 3,12-diarylpentahelicenes.
Introduction
helquats,3 and helicene-like compounds.4 Its strength consists
of a simultaneous formation of three,1-4 five,5 or six cycles6 in
a single cyclization step, which allows for a rapid construction
of (hetero)helicene backbones. The classical or newly devel-
oped alternative methods7 such as photodehydrocyclization of
stilbene-type precursors,7a Diels-Alder cycloaddition,7b ring-
closing olefin metathesis,7c carbenoid coupling,7d McMurry
reaction,7e Friedel-Crafts cycloacylation7f or cycloalkyl-
ation,7g homolytic aromatic substitution,7h C-H arylation
reaction,7i cycloisomerization of biaryl alkynes,7j Stille-Kelly
reaction,7k rearrangement of benzannulated enediynes,7l aro-
matic oxy-Cope rearrangement,7m cycloaddition of aromatic
arynes,7n binaphthyl bisphosphonium salt conversion,7o and
Stevens rearrangement7p are so far less effective in this regard.
Intramolecular [2 þ 2 þ 2] alkyne cycloisomerization
catalyzed by CoI, Ni0, or RhI has been proven to be a powerful
method for the synthesis of carbohelicenes,1 azahelicenes,2
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DOI: 10.1021/jo1013977
r
Published on Web 09/23/2010
J. Org. Chem. 2010, 75, 6889–6899 6889
2010 American Chemical Society

Songis et al.
JOCArticle
Although remarkable progress in the preparation of helicenes
has recently been accomplished, the modular synthesis of their
functionalized derivatives or heteroanalogues remains a chal-
lenging task.
SCHEME 1. The Synthesis of Pentahelicene 6
The [2 þ 2 þ 2] cycloisomerization approach leads directly to
fully aromatic helicenes1a or to their tetrahydro derivatives,1b,c,8
which have to be oxidized. Even though such an aromatization
-
step can be done with Ph3CþBF4 (refs 1b and 1c) or MnO2
under microwave irradiation,2a an alternative is required as
serious difficulties occasionally occur. Either a lipophilic heli-
cene compound can be difficult to separate from the Ph3CH
side product or the oxidation depends on the MnO2 activity,
which critically varies from batch to batch. Herein, we report
on the innovated synthesis of pentahelicene and its functional-
ized congeners, which demonstrates facile aromatization of the
helical backbone based on an acid-assisted elimination of the
acetic acid. This approach is also an alternative way of assem-
bling the key triyne intermediate, which further extends the
scope of the [2 þ 2 þ 2] alkyne cycloisomerization in the
synthesis of helicenes. Relying on the results described below,
we have recently employed this methodology in the synthesis of
[11]helicene.6
Results and Discussion
Synthesis of Pentahelicene 6. First, we embarked on the
synthesis of the prototypal pentahelicene 6to check the viability
of the proposed approach (Scheme 1). The easily accessible dial-
dehyde 1 (ref 9) was treated with lithiated 1-(triisopropylsilyl)-
propyne to provide triyne 2 as a mixture of diastereomers.
We did not detect homoallenyl alcohols arising through a
propargylic rearrangement in the material purified by column
chromatography. After acetylationof the free hydroxygroups
(2 f 3) and desilylation of the pendant alkyne units (3 f 4),
we attempted the key [2 þ 2 þ 2] cycloisomerization to form
the helical scaffold. Upon applying CoI-catalysis, we obtained
a derivative of tetrahydropentahelicene 5 as a mixture of diaste-
reomers difficult to separate by column chromatography. The last
step of the synthetic sequence proceeded smoothly. The diacetoxy
derivative 5 adsorbed on silica gel underwent spontaneously
acetic acid elimination at elevated temperature to provide pure
pentahelicene 61a,7p in a high yield.
In connection with ongoing projects on helicene-based
materials, we further attempted the preparation of the required
helicene molecules or building blocks employing this newly
developed synthetic methodology described above.
Synthesis of 3,12-Dichloropentahelicene 13. For the sake of
preparing suitable pentahelicene derivatives amenable to sub-
sequent functionalization, we focused on the synthesis of the so-
far unknown 3,12-dichloropentahelicene 13 (Scheme 2).
We reasoned that the aryl chloride moiety would be, on the
one hand, unreactive in order to survive the presence of
organometallics during the synthesis and, on the other hand,
reactive enough to undergo a Suzuki-Miyaura coupling
after the pentahelicene backbone construction. The prepara-
tion of 13 started from commercially available 5-chlorosali-
cylaldehyde 7, which was converted to the corresponding tri-
flate 8.10 Its reaction with gaseous acetylene under PdII/CuI
catalysis smoothly led to dialdehyde 9 but the product was
only sparingly soluble in nonpolar or slightly polar solvents.
Due to this fact, the double addition of LiCH2CtCTIPS in
ether solvents at low temperature was rather difficult to
pursue (cf. reaction 1 f 2) except for a very small quantity
of the starting material 9. Thus, we applied an alternative
method relying on propargyl bromide addition to 9 in the
presence of the stoichiometric amount of gallium and catalytic
amount of indium.11 By adding a hot (50 °C), close-to-saturated
solution of dialdehyde 9 in THF to the preformed organo-
gallium reagent in the same solvent kept at 0 °C, the double
addition proceeded at room temperature. The required
homopropargyl-type triyne 10 was isolated in an acceptable
yield as a mixture of diastereomers. It is worth noting that the
choice of the propargyl organometallics (Li, Mg, Ga), which
were added to the aromatic dialdehydes mentioned in this
study, was on an empirical basis in order to minimize the
Thus, the concept of acetic acid elimination to aromatize
tetrahydrohelicene derivatives has been found to be feasible.
(7) For representative examples, see: (a) Liu, L.; Yang, B.; Katz, T. J.;
Poindexter, M. K. J. Org. Chem. 1991, 56, 3769. (b) Willmore, N. D.; Liu,
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(e) Tanaka, K.; Suzuki, H.; Osuga, H. J. Org. Chem. 1997, 62, 4465.
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(g) Ichikawa, J.; Yokota, M.; Kudo, T.; Umezaki, S. Angew. Chem., Int.
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Chem., Int. Ed. 2006, 45, 2242. (i) Kamikawa, K.; Takemoto, I.; Takemoto,
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3090. (k) Takenaka, N.; Sarangthem, R. S.; Captain, B. Angew. Chem., Int.
Ed. 2008, 47, 9708. (l) Zhang, Y.; Petersen, J. L.; Wang, K. K. Tetrahedron
2008, 64, 1285. (m) Ogawa, Y.; Toyama, M.; Karikomi, M.; Seki, K.; Haga,
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K.; Uyehara, T. Tetrahedron Lett. 2003, 44, 2167. (n) Caeiro, J.; Pena, D.;
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(o) Bestmann, H. J.; Both, W. Angew. Chem., Int. Ed. 1972, 11, 296.
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(p) Stara, I. G.; Stary, I.; Tichy, M.; Zavada, J.; Hanus, V. J. Am. Chem.
Soc. 1994, 116, 5084.
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D. Tetrahedron Lett. 1999, 40, 1993.
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(10) (a)Bengtson,A.;Hallberg,A.;Larhed,M.Org. Lett. 2002,4, 1231. (b) Allen,
C. P.; Benkovics, T.; Turek, A. K.; Yoon, T. P. J. Am. Chem. Soc. 2009, 131, 12560.
(11) Lee, P. H.; Kim, H.; Lee, K. Adv. Synth. Catal. 2005, 347, 1219.
(9) (a) Whitlock, H. W., Jr.; Reed, J. K. J. Org. Chem. 1969, 34, 874.
(b) Orita, A.; Jiang, L.; Tsuruta, M.; Otera, J. Chem. Lett. 2002, 136.
6890 J. Org. Chem. Vol. 75, No. 20, 2010

Songis et al.
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TABLE 1. The Suzuki-Miyaura Coupling between 3,12-Dichloropentahelicene 13 and Arylboronic Acids 19-23
entry
R
conditions (mol %)a
product (%)b
1
H
OH
NH2
CH3;CtC
TIPS;CtC
19 (2.4 equiv), Pd(CH3CN)2Cl2 (25), PCy3 (50), TBAF (6 equiv), 90 °C
20 (4 equiv), Pd(CH3CN)2Cl2 (40), PCy3 (80), TBAF (10 equiv), 85 °C
21 (4 equiv), Pd(OAc)2 (40), 24 (80), Cs2CO3 (9 equiv), dioxane, water, 85 °C
22 (4 equiv), Pd(OAc)2 (40), 24 (80), Cs2CO3 (5 equiv), dioxane, 85 °C
23 (4 equiv), Pd(OAc)2 (10), 24 (20), Cs2CO3 (4 equiv), dioxane, 80 °C
14 (88)
15 (98)
16 (72)
17 (45)
18 (50)
2
3c
4
5
aFree boronic acid was used unless noted otherwise, the reaction period was 20 h. bIsolated yield. cBoronic acid pinacol ester was used.
SCHEME 2. The Synthesis of 3,12-Dichloropentahelicene 13
FIGURE 1. The single-crystal molecular structure of 13.
CoI catalyst led to an unsatisfactory yield). A smooth aroma-
tization by acetic acid elimination completed the synthesis of
3,12-dichloropentahelicene 13, whose structure was unam-
biguously confirmed by a single-crystal analysis (Figure 1).12
Suzuki-Miyaura Couplings of 3,12-Dichloropentahelicene
13. Suzuki-Miyaura coupling chemistry with helicene ha-
lides has practically been unexplored13 and, to the best of our
knowledge, never reported in connection with helicene
chlorides. We found that unactivated dichloropentaheli-
cene 13 reacted with aryl boronic acids 19, 20 (commercially
available), 22,14 and 2315 or boronic acid pinacol ester 21
allene-type byproduct(s) formation and to keep the reaction
partners soluble under the given conditions. After acetyla-
tion (10 f 11), no desilylation step was necessary (cf. 3 f 4)
and the material 11 was subjected directly to CoI-mediated
[2 þ 2 þ 2] cycloisomerization in order to afford functionalized
tetrahydropentahelicene 12 (utilizing a catalytic amount of the
(commercially available) under palladium catalysis in the
presence of electronically rich, bulky phosphines such as
PCy3 or Buchwald’s DavePhos ligand 24 (Table 1).16
Depending on the structure of the aryl boronic acid deriva-
tives, we employed either a solvent-free17 (entries 1 and 2) or
(13) U.S. Patent 6686065.
(14) Madras, B. K.; Meltzer, P. C. Appl. 2003, GB 2380733 A 20030416.
(12) CCDC-784073 and CCDC-784074 contain the supplementary crys-
tallographic data for 13 and 14, respectively. These data can be obtained free
of charge from Cambridge Crystallographic Data Centre via www.ccdc.cam.
ac.uk/data_request/cif or from the Cambridge Crystallographic Data Cen-
tre, 12, Union Road, Cambridge CB2 1EZ, UK; fax þ44(1223) 336033;
e-mail deposit@ccdc.cam.ac.uk.
€
(15) Godt, A.; Unsal, O.; Roos, M. J. Org. Chem. 2000, 65, 2837.
(16) (a) Surry, D. S.; Buchwald, S. L. Angew. Chem., Int. Ed. 2008, 47,
6338. (b) Bellina, F.; Carpita, A.; Rossi, R. Synthesis 2004, 2419. (c) Littke,
A. F.; Fu, G. C. Angew. Chem., Int. Ed. 2002, 41, 4176.
(17) Li, J.-H.; Deng, C.-L.; Xie, Y.-X. Synth. Commun. 2007, 37, 2433.
J. Org. Chem. Vol. 75, No. 20, 2010 6891

Songis et al.
JOCArticle
SCHEME 3. The Synthesis of Silylated 3,12-Dichloropentahe-
licene 28
FIGURE 2. The single-crystal molecular structure of 14 with the
atom numbering scheme. The second part of the molecule is generated
by the operation of its 2-fold axis. Symmetry code (i): 1 - x, y, 0.5 - z.
solution18 (entries 3-5) Suzuki-Miyaura coupling reaction
condition to obtain the products 14-18 in moderate to
excellent yields. The structure of 3,12-diphenylpentahelicene
14 was proven by a single-crystal analysis (Figure 2).12
Synthesis of 3,12-Dichloro-7-trimethylsilylpentahelicene 28.
Aiming at the synthesis of other functionalized pentahelicene
derivatives, we attempted the preparation of TMS-substi-
tuted 3,12-dichloropentahelicene 28 (Scheme 3).
SCHEME 4. The Synthesis of 3,12-Di-tert-butylpentahelicene 35
With the exception of the utilization of an organogallium
reagent derived from silylated propargyl bromide, the syn-
thetic route followed that developed for 13. It is worth noting
that the homopropargyl-type triyne 25 dominated exclu-
sively over the homoallenyl one. After the acetylation and
cycloisomerization steps (25 f 26 f 27), we completed the
synthesis of 28 by silica gel-assisted aromatization. However,
this process was accompanied by a partial desilylation of the
product affording the monosilylated product 28.
Synthesis of 3,12-Di-tert-butylpentahelicene 35 and 1,14-
Diazapentahelicene 41. While the reaction scheme for the
preparation of 3,12-di-tert-butylpentahelicene 35 (Scheme 4)
was the same as that for 13 regardless of the different
electronic nature of the substituents (Cl versus t-Bu) (29 f
35), the synthesis of the heterocyclic analogue 1,14-diaza-
pentahelicene 41 (refs 2a and 19) required a modification
(Scheme 5, 36 f 41). Dialdehyde 37 was practically insoluble
in ether solvents and, therefore, the use of the organogallium
reagent generated from propargyl bromide resulted in a low
yield of 38. However, by treating the suspension of 37 with
propargyl magnesium bromide in a mixture of ether-THF
at low temperature, the homopropargyl-type triyne 38
was readily formed and its acetyl derivative 39 was isolated
in a moderate yield. The cyclized product 40 was subjected to
the final acetic acid elimination by using silica gel either
plain or preferably wetted with triflic acid to afford azahe-
licene 41.
Conclusions
(18) Dong, Z.; Liu, X.; Yap, G. P. A.; Fox, J. M. J. Org. Chem. 2007,
In conclusion, we have developed a general synthetic protocol
for the nonphotochemical20 preparation of pentahelicene 6,
its dichloro derivative 13, TMS derivative 28, di-tert-butyl
72, 617.
(19) Staab, H. A.; Zirnstein, M. A.; Krieger, C. Angew. Chem., Int. Ed.
1989, 28, 86.
6892 J. Org. Chem. Vol. 75, No. 20, 2010

Songis et al.
JOCArticle
SCHEME 5. The Synthesis of 1,14-Diazapentahelicene 41
chloroform, loaded into a quartz cup of the direct probe, and
inserted into the ion source. The source temperature was 220 °C.
For exact mass measurement, the spectra were internally cali-
brated with perfluorotri-n-butylamine. ESI mass spectra were
recorded by using the classic ion trap mass spectrometer
equipped with an electrospray ion source. The mobile phase
consisted of methanol/water (9:1), flow rate of 200 μL/min. The
samples were dissolved in chloroform, diluted with the mobile
phase, and injected using a 5-μL loop. The exact mass was
measured using the hybrid mass spectrometer equipped with an
electrospray ion source. The mobile phase consisted of methanol/
water (9:1), flow rate of 100 μL/min. The sample was dissolved
in chloroform and diluted with the mobile phase and injected
using a 2-μL loop. The mass spectra were internally calibrated
using known impurities in the mobile phase. TOF ESI mass
spectra were recorded using the micro mass spectrometer. The
mobile phase consisted of acetonitrile/water (1:1), flow rate of
25 μL/min. Samples dissolved in chloroform were diluted with
the mobile phase and injected using a manual injector (2 μL).
For exact mass measurement, the mass spectra were internally
calibrated using PEG oligomers. Accurate mass measurements
were obtained by the EI, ESI, TOF EI, or TOF ESI MS.
Commercially available catalysts and reagent grade materials
such as phenyl boronic acid 19, 4-hydroxyphenylboronic acid
20, and 4-aminophenylboronic acid pinacol ester 21 were used
as received. 4-Tris(1-methylethyl)silane-acetylene boronic acid
23 was prepared according to the literature procedure.15 Decane
and distilled water were degassed by 3 freeze-pump-thaw
cycles before use; triethylamine was distilled from calcium
hydride under argon; THF was freshly distilled from sodium/
benzophenone under nitrogen, and dioxane was distilled from
calcium hydride and degassed by 3 freeze-pump-thaw cycles
before use. Commercial pure solvents were used directly when
growing crystals for the X-ray analysis. TLC was performed on
silica gel F254-coated aluminum sheets and spots were detected
derivative 35, or diaryl derivatives 14-18, and diaza-
pentahelicene 41. The modular nature of the approach
permits variation of the starting building blocks and the
uniform employment of the sequence of double propargyl
organometallics addition to a tolan-2,20-dialdehyde-type inter-
mediate, a cobalt-catalyzed/cobalt-mediated [2 þ 2 þ 2] cyclo-
isomerization of a triyne intermediate, and a silica gel-assisted
acetic acid elimination to receive a fully aromatic product. 3,12-
Dichloropentahelicene 13 undergoes Suzuki-Miyaura couplings
with aryl boronic acids (or ester) under palladium catalysis
representing the first successful reaction of this type in helicene
chemistry. Thus, we have demonstrated a practical methodol-
ogy for the preparation of various functionalized pentaheli-
cenes, which can serve as a paradigm for the synthesis of higher6
or differently functionalized helicenes. Physical and physico-
chemical studies on the pentahelicene molecules described in
this report are in progress.
by the solution of Ce(SO4)2 4H2O (1%) and H3P(Mo3O10)4
3
(2%) in sulfuric acid (10%). Flash chromatography was per-
formed on silica gel (0.040-0.063 mm or <0.063 mm) or on
silica gel cartridges (0.040-0.063 mm) used in automatic flash
purification systems.
X-ray Crystallography. Single-crystal diffraction data for 13
and 14 were obtained from the kappa geometry CCD diffract-
ometer by monochromatized Mo KR radiation (λ = 0.71073 A)
at 150(2) K. The structures were solved by direct methods
(SIR92)21 and refined by full-matrix least-squares based on F2
(SHELXL97).22 The hydrogen atoms were found on difference
Fourier maps and recalculated into the idealized position; all
were fixed into their positions (riding model) with assigned
temperature factors Hiso(H) = 1.2Ueq(pivot atom).
Experimental Section
General. 1H NMR spectra were measured at 200.04, 400.13,
and 499.88 or 500.13 MHz, 13C NMR spectra at 100.6 and 125.8
MHz, in CDCl3 with TMS as an internal standard, and in d6-
DMSO. Chemical shifts are given in δ-scale, coupling constants
Jare given in Hz. HMBC experiments were set up for JC-H =5Hz.
For correct assignment of both 1H and 13C NMR spectra of key
compounds, the COSY, HMQC, and HMBC experiments were
performed. IR spectra were measured in CHCl3 or CCl4. EI
mass spectra were determined at an ionizing voltage of 70 eV, m/z
values are given along with their relative intensities (%). Stan-
dard 70 eV spectra were recorded in the positive ion mode. TOF
EI spectra were measured using the orthogonal acceleration
time-of-flight mass spectrometer. The sample was dissolved in
1,10-(Ethyne-1,2-diyldibenzene-2,1-diyl)bis{4-[tris(1-methylethyl)-
silyl]but-3-yn-1-ol} (2). The Schlenk flask was charged with a
solution of 1-triisopropylsilyl-1-propyne (3.0 mL, 12.52 mmol,
2.16 equiv) in THF (30 mL) under argon. The reaction was cooled
to -78 °C, a butyllithium solution (1.6 M in hexanes, 8.0 mL,
12.8 mmol, 2.2 equiv) was added, and the reaction mixture was
stirred at the same temperature for 2 h. Then a solution of
dibenzyl aldehyde 1 (1.358 g, 5.80 mmol) in THF (30 mL) was
added and the reaction mixture was stirred at -78 °C for 1 h and
then at room temperature for another hour. The reaction mix-
ture was poured into a saturated aqueous solution of NH4Cl
(50 mL) and extracted with diethyl ether (5 ꢀ 60 mL), then the
combined organic portions were washed with water (2 ꢀ 20 mL)
and dried over anhydrous MgSO4. The solvents were removed in
(20) The CpCo(CO)2/PPh3 catalyzed [2 þ 2 þ 2] cycloisomerization under
halogen lamp irradiation is not a truly photochemical process with respect to
the triyne substrate. Such an irradiation by visible light usually activates the
catalyst to provide a higher preparative yield of the cyclized product but the
reaction can technically proceed in the absence of light.
(21) Altomare, A.; Cascarano, G.; Giacovazzo, C.; Guagliardi, A.; Burla,
M. C.; Polidori, G.; Camalli, M. J. Appl. Crystallogr. 1994, 27, 435.
€
(22) Sheldrick, G. M. SHELXL97; University of Gottingen, Gottingen,
€
Germany, 1997.
J. Org. Chem. Vol. 75, No. 20, 2010 6893

Songis et al.
JOCArticle
vacuo and the residue was purified by flash chromatography on
silica gel (petroleum ether-diethyl ether 90:10 to 85:15) to
provide triyne 2 (2.127 mg, 59%) as an oil. 1H NMR (500
MHz, CDCl3): 1.05 (42 H, m), 2.72 (2 H, dd, J = 17.0, 3.2), 2.74
(2 H, dd, J = 17.0, 3.2), 3.04 (4 H, dd, J = 17.0, 4.7), 5.37 (2 H,
m), 7.27 (2 H, dt, J = 7.7, 7.7, 1.0), 7.38 (2 H, dt, J = 7.6, 7.6,
1.4), 7.52 (2 H, dd, J = 7.7, 1.4), 7.62 (2 H, d, J = 7.7). 13C NMR
(125 MHz, CDCl3): 11.2 (q), 18.6 (q), 29.97 (t), 30.04 (t), 70.4 (d),
84.3 (s), 92.2 (s), 104.1 (s), 120.4 (s), 125.5 (d), 127.5 (d), 128.8
(d), 132.6 (d), 143.8 (s). IR (CCl4): 3615 w, 3560 w, 3097 vw, 3070
w, 3030 w, 2866 vs, 2170 m, 1601 vw, 1489 w, 1463 m, 1451 m,
1383 w, 1367 w, 1332 w, 1309 w, 1194 w, 1160 vw, 1106 w, 1057
m, 1019 m, 996 m, 883 m, 678 s, 663 m, 607 w, 458 w cm-1. EI
MS: 626 (Mþ•, 4), 608 (40), 565 (16), 431 (100), 413 (52), 387 (40),
329 (7), 283 (12), 257 (29), 235 (39), 178 (22), 153 (47), 115 (64),
75 (69), 59 (93). HR EI MS: calcd for C40H58O2Si2 626.3975,
found 626.3994.
s, 639 s, 608 w, 566 w, 514 w, 448 w cm-1. EI MS: 398 (Mþ•, 0.4),
356 (1), 314 (1), 295 (10), 278 (44), 257 (100), 239 (26), 228 (68),
215 (6), 202 (14), 189 (6), 178 (12), 43 (85). HR EI MS: not
recorded due to a low intensity of the molecular ion.
5,6,9,10-Tetrahydropentahelicene-5,10-diyl Diacetate (5). A
two-necked Schlenk flask was charged with triyne 4 (105 mg,
0.264 mmol) and flushed with argon. Decane (2.5 mL) was
added and then a solution of PPh3 (28.0 mg, 0.107 mmol, 40 mol
%) in decane (0.5 mL) and a solution of CpCo(CO)2 (7.0 μL,
0.053 mmol, 20 mol %) in decane (0.5 mL) were added. The
reaction mixture was heated at 140 °C for 2 h under simulta-
neous irradiation with a halogen lamp. The solvent was removed
in vacuo and the crude product was chromatographed on silica
gel (hexane-diethyl ether 100:0 to 80:20) to provide the tetra-
hydro [5[helicene derivative 5 (86.4 mg, 82%) as an amorphous
solid. 1H NMR (200 MHz, CDCl3): 1.96 (3 H, br s), 2.32 (3 H, br
s), 2.65-3.37 (6 H, m), 5.89-6.26 (2 H, m), 7.00-7.59 (10 H, m).
IR (CHCl3): 3104 w, 3067 w, 3029 m, 1730 vs, 1605 w, 1572 w,
1490 m, 1435 m, 1423 m, 1374 s, 1329 w, 1246 vs, 1175 m, 1161 w,
1136 w, 1113 w, 1038 s, 1023 s, 990 s, 948 m, 813 m, 686 w, 611 m,
536 w, 510 w cm-1. EI MS: 398 (Mþ•, 20), 338 (7), 278 (100), 263
(13), 252 (11), 178 (7), 138 (17), 97 (7), 71 (12), 57 (13), 45 (11).
HR EI MS: calcd for C26H22O4 398.1518, found 398.1521.
Pentahelicene (6). To a solution of tetrahydro [5]helicene
derivative 5 (72.0 mg, 0.181 mmol) in dichloromethane (5 mL)
was added silica gel (3.6 g). The solvent was evaporated in vacuo
and the solvent-free mixture was heated at 110 °C for 30 min.
The product was extracted from silica gel by dichloromethane
(100 mL). Removal of the solvent in vacuo led to pentahelicene
6 (46.8 mg, 93%) as an amorphous solid.1a,7p
Ethyne-1,2-diylbis{benzene-2,1-diyl-1-[tris(1-methylethyl)silyl]-
but-1-yne-4,4-diyl} Diacetate (3). To a solution of dihydroxy
derivative 2 (512 mg, 0.817 mmol) in pyridine (6 mL) was added
acetanhydride (620 μL, 6.52 mmol, 8.0 equiv) at 0 °C. The reac-
tion mixture was then allowed to slowly reach room temperature
while stirring and stirring was continued at the same tempera-
ture for an additional 21 h. The mixture was poured into ice and
extracted with diethyl ether (4 ꢀ 50 mL), then the combined
organic portions were washed with a 10% solution of CuSO4
(4 ꢀ 15 mL) and a saturated aqueous solution of KHCO3 (3 ꢀ
15 mL), dried over anhydrous Na2SO4, and evaporated in vacuo
to afford the diacetoxy derivative 3 (514 mg, 89%) as a viscous
1
oil. H NMR (500 MHz, CDCl3): 1.00-1.04 (42 H, m), 2.129
2,20-Ethyne-1,2-diylbis(5-chlorobenzaldehyde) (9). A Schlenk
flask was charged with triflate 8 (557 mg, 1.93 mmol), Pd(PPh3)2-
Cl2 (56.1 mg, 0.080 mmol, 4 mol %), and CuI (7.4 mg, 0.040
mmol, 2 mol %) and filled with acetylene. A mixture of Et3N
(2 mL) and THF (1 mL) was added and the flask was filled
with acetylene. The reaction mixture was stirred at 60 °C for 2 h.
The solvents were removed in vacuo and the crude product
was chromatographed on silica gel (hexane-dichloromethane
60:40) to provide dialdehyde 9 (243 mg, 83%) as a pale amor-
phous solid. Mp: 201 °C (acetone). 1H NMR (400 MHz,
CDCl3): 7.59 (2 H, dd, J = 8.4, 2.0), 7.64 (2 H, d, J = 8.4),
7.93 (2 H, d, J = 2.0), 10.51 (1 H, s). 13C NMR (101 MHz,
CDCl3): 91.6 (s), 123.2 (s), 128.4 (d), 133.9 (d), 134.8 (d), 136.3
(s), 137.2 (s), 189.5 (d). IR (CHCl3): 3067 vw, 2846 w, 2742 w,
1720 w, 1697 vs, 1592 w, 1586 w, 1554 vw, 1484 m, 1406 w, 1388
w, 1305 vw, 1278 w, 1246 m, 1186 s, 1114 w, 1079 w, 908 m, 900
w, 833 m, 703 vw, 658 w, 630 w cm-1. EI MS: 302 (Mþ•, 88), 274
(16), 267 (74), 246 (45), 239 (94), 210 (41), 176 (100), 160 (3), 150
(15), 105 (15), 98 (9), 87 (10), 74 (8). HR EI MS: calcd for
C16H8O2Cl2 301.9901, found 301.9907.
(3 H, s), 2.134 (3 H, s), 2.86 (2 H, dd, J = 17.2, 6.6), 2.89 (2 H, dd,
J = 17.1, 6.5), 3.08 (2 H, dd, J = 17.2, 5.2), 3.09 (2 H, dd, J =
17.2, 5.3), 6.40 (1 H, dd, J = 6.6, 5.2), 6.41 (1 H, dd, J = 6.5, 5.3),
7.28 (2 H, dd, J = 7.5, 1.3), 7.33 (2 H, dt, J = 7.5, 7.5, 1.3), 7.52
(2 H, dt, J = 7.5, 7.5, 1.3), 7.57 (2 H, dd, J = 7.5, 1.3). 13C NMR
(125 MHz, CDCl3): 11.2 (q), 18.5 (q), 21.0 (q), 26.67 (t), 26.77 (t),
71.89 (d), 71.97 (d), 83.11 (s), 83.17 (s), 92.7 (s), 103.33 (s), 103.36
(s), 120.94 (s), 120.96 (s), 126.1 (d), 126.2 (d), 127.84 (d), 127.86
(d), 128.60 (d), 128.62 (d), 132.6 (d), 140.5 (s), 140.6 (s), 169.7 (s).
IR (CCl4): 3070 w, 3022 w, 2958 s, 2944 s, 2925 m, 2891 m, 2866
s, 2177 m, 1750 s, 1603 vw, 1572 vw, 1493 w, 1464 m, 1453 w,
1428 w, 1383 w, 1372 m, 1289 w, 1234 s, 1216 s, 1102 w, 1030 m,
996 w, 937 w, 884 m, 678 m, 663 m, 644 w, 613 w cm-1. EI MS:
710 (Mþ•, 0.6), 667 (2), 607 (6), 565 (5), 477 (2), 413 (3), 349 (2),
307 (3), 215 (2), 173 (100), 115 (10), 73 (10), 59 (14), 43 (11). HR
EI MS: calcd for C44H62O4Si2 710.4187; found 710.4176.
Ethyne-1,2-diylbis(benzene-2,1-diylbut-1-yne-4,4-diyl) Diace-
tate (4). A Schlenk flask was charged with diacetoxy derivative
3 (490 mg, 0.689 mmol) and flushed with argon. THF (10 mL)
was added and the resulting solution was cooled to 0 °C. A
tetrabutylammonium fluoride solution (0.964 M in THF, 4.3
mL, 4.15 mmol, 6.0 equiv) was added. After stirring at 0 °C for
1.5 h, the solvent was removed in vacuo. The crude product was
chromatographed on silica gel (hexane-diethyl ether 80:20 to
60:40) to provide triyne 4 (147 mg, 54%) as an amorphous solid.
1H NMR (500 MHz, CDCl3): 1.99 (2 H, t, J = 2.6), 2.146 (3 H,
s), 2.151 (3 H, s), 2.85 (2 H, ddd, J = 17.0, 6.6, 2.6), 2.86 (2 H,
ddd, J = 17.0, 6.6, 2.6), 2.96 (2 H, ddd, J = 17.0, 5.5, 2.6), 2.97 (2
H, ddd, J = 17.0, 5.5, 2.6), 6.42 (1 H, t, J = 6.2), 6.43 (1 H, t, J =
6.2), 7.32 (2 H, dt, J = 7.5, 7.5, 1.4), 7.38 (2 H, dt, J = 7.5, 7.5,
1.3), 7.51 (2 H, ddd, J = 7.5, 1.3, 0.6), 7.60 (2 H, ddd, J = 7.5,
1.4, 0.6). 13C NMR (125 MHz, CDCl3): 21.0 (q), 25.56 (t), 25.6
(t), 70.8 (d), 71.50 (d), 71.54 (d), 79.4 (s), 91.95 (s), 91.97 (s),
121.09 (s), 121.14 (s), 125.89 (d), 125.92 (d), 128.0 (d), 128.74 (d),
128.75 (d), 132.60 (d), 132.63 (d), 140.5 (s), 169.8 (s). IR
(CHCl3): 3310 s, 3070 w, 3030 m, 2215 vw, 2125 w, 1743 vs,
1602 w, 1571 w, 1494 m, 1452 m, 1429 m, 1422 m, 1374 s, 1341 w,
1295 m, 1239 vs, 1163 w, 1103 w, 1049 s, 1032 s, 937 w, 820 w, 650
1,10-[Ethyne-1,2-diylbis(5-chlorobenzene-2,1-diyl)]bisbut-3-yn-
1-ol (10). A Schlenk flask was charged with gallium (50.6 mg,
0.730 mmol, 2.2 equiv), indium (3.8 mg, 0.030 mmol, 10 mol %),
THF (0.5 mL), and propargyl bromide (146 μL, 1.33 mmol, 80 w %
in toluene, 4.0 equiv) under argon and then vigorously stirred at
10 °C for 1 h. After complete consumption of gallium, a solution
of the dialdehyde 9 (100 mg, 0.330 mmol, 1.0 equiv) in THF
(3 mL) was slowly added and the reaction mixture was stirred at
room temperature for 1 h. The solvent was removed in vacuo
and the saturated aqueous solution of NaHCO3 (100 mL) was
added to the crude mixture. The product was extracted with
dichloromethane (3 ꢀ 200 mL) and the combined organic
portions were dried over anhydrous MgSO4. The solvent was
removed in vacuo and the crude product was chromatographed
on silica gel (hexane-ethyl acetate 70: 30) to provide a mixture
of the diastereoisomers of dialdehyde 10 (84.0 mg, 66%)
1
as a pale amorphous solid. H NMR (400 MHz, CDCl3): 2.14
(2 H, t, J = 2.4, one diastereoisomer), 2.15 (2 H, t, J = 2.4, one
6894 J. Org. Chem. Vol. 75, No. 20, 2010

Songis et al.
JOCArticle
diastereoisomer), 2.58-2.65 (2 H, m), 2.83-2.90 (2 H, m),
5.30-5.38 (2 H, m), 7.29 (2 H, dd, J = 8.4, 2.0), 7.44 (2 H, d,
J = 8.4), 7.63 (1 H, d, J = 2.0). 13C NMR (101 MHz, CDCl3): 28.4
(t), 28.5 (t), 69.9 (d), 70.0 (d), 71.5 (d), 71.6 (d), 80.1 (s), 80.3 (s), 91.8
(s), 91.9 (s), 118.5 (s), 126.00 (d), 126.02 (d), 128.0 (d), 133.45 (d),
133.47 (d), 135.4 (s), 145.6 (s). IR (CHCl3): 3600 m, 3307 vs, 3069
vw, 2927 m, 2855 m, 2121 vw, 1595 m, 1559w, 1489 s, 1467 m, 1407
m, 1307 w, 1270 m, 1180 m, 1117 m, 1092 vs, 1056 s, 902 m, 898 m,
825 s, 685 w, 642 s, 508 w cm-1. ESI MS: 381 ([M - H]-). HR ESI
MS: calcd for C22H15O2Cl2 381.0455, found 381.0452.
grown by slow evaporation from dichloromethane; C22H12Cl2,
Mr = 347.22, orthorhombic, Pbca (no. 61), a = 5.91540(10) A,
b = 20.1928(3) A, c = 26.1972(4) A, Z = 8, Dx = 1.474 Mg
m-3, colorless crystal of dimensions 0.4 ꢀ 0.1 ꢀ 0.03 mm3, an
absorption was neglected [μ = 0.41 mm-1; 45726 diffraction
collected (θmax = 27.5°), 3446 independent (Rint = 0.043) and
2786 observed (I > 2σ(I))]. 217 refined parameters, goodness of
fit 1.05, final R indices R[F2 > 2σ(F2)] = 0.035, wR(F2) = 0.099,
maximal/minimal residual electron density (ΔFmax = 0.23,
ΔFmin -0.34 e A-3). CCDC-784073 contains the supplemen-
3
Ethyne-1,2-diylbis[(5-chlorobenzene-2,1-diyl)but-1-yne-4,4-diyl]
Diacetate (11). To a solution of 10 (61.3 mg, 0.160 mmol) and
4-(dimethylamino)pyridine (2.3 mg, 0.020 mmol, 12 mol %) in
pyridine (0.25 mL) was added acetic anhydride (0.50 mL)
dropwise and the reaction mixture was stirred at room tempera-
ture for 1 h. The solvent was then removed in vacuo and the
crude product was chromatographed on silica gel (hexane-
ethyl acetate 70:30) to provide a mixture of two diastereoisomers
of diacetoxy derivative 11 (62.0 mg, 83%) as a white amorphous
solid. 1H NMR (400 MHz, CDCl3): 2.02 (2 H, t, J = 2.6), 2.16
(6 H, br s), 2.77-2.85 (2 H, m), 2.87-2.96 (2 H, m), 6.34 (2 H, t,
J = 6.0, one diastereoisomer), 6.37 (2 H, t, J = 6.0, one diaste-
tary crystallographic data for this compound. These data can be
obtained free of charge from Cambridge Crystallographic Data
Centre via www.ccdc.cam.ac.uk/data_reguest/cif or from the
Cambridge Crystallographic Data Centre, 12 Union Road,
Cambridge CB2 1EZ, UK; fax þ44(1223) 336033; e-mail deposit@
ccdc.cam.ac.uk.
3,12-Diphenylpentahelicene (14). A mixture of chloro helicene
13 (10.9 mg, 0.032 mmol), phenylboronic acid 19 (9.4 mg, 0.077
mmol, 2.4 equiv), Pd(MeCN)2Cl2 (2.0 mg, 0.008 mmol, 25 mol %),
tricyclohexyl phosphine (4.5 mg, 0.016 mmol, 50 mol %),
and TBAF (60.5 mg, 0.192 mmol, 6.0 equiv) was heated under
argon at 90 °C overnight. Water (5 mL) was added to the
mixture and the product was extracted with dichloromethane
(3 ꢀ 10 mL). The organic phase was dried over anhydrous
MgSO4 and the solvent was removed in vacuo. The crude
product was chromatographed on silica gel (hexane-ethyl
acetate 90:10) to provide the diphenyl derivative 14 (12 mg,
88%) as an amorphous white solid. Mp: 246-251 °C
(dichloromethane-diethyl ether). 1H NMR (400 MHz, CDCl3):
7.38-7.42 (2 H, m), 7.49-7.53 (4 H, m), 7.59 (2 H, dd, J = 8.8,
2.0), 7.79-7.82 (4 H, m), 7.89 (2 H, s), 7.92 (2 H, d, J = 8.6), 8.01
reoisomer), 7.29 (2 H, dd, J = 8.4, 2.6), 7.48-7.51 (4 H, m). 13
C
NMR (101 MHz, CDCl3): 21.0 (q), 25.50 (t), 25.53 (t), 70.80 (d),
70.85 (d), 71.2 (d), 78.69 (s), 78.73 (s), 91.7 (s), 119.3 (s), 126.36
(d), 126.38 (d), 128.4 (d), 133.62 (d), 133.64 (d), 135.06 (s), 135.08
(s), 142.3 (s), 169.6 (s). IR (CHCl3): 3309 m, 2927 w, 2855 w, 2125
vw, 1744 vs, 1595 w, 1559 vw, 1490 m, 1468 w, 1408 w, 1374 m,
1279 w, 1270 m, 1236 vs, 1182 w, 1116 w, 1046 m, 1032 m, 1091
m, 908 w, 826 m, 653 m, 641 m, 608 w, 508 w cm-1. EI MS: 466
(Mþ•, 21), 367 (9), 346 (87), 325 (91), 312 (100), 300 (33), 290
(85), 276 (97), 262 (97), 255 (80), 226 (95), 212 (13), 200 (5), 176
(16). HR EI MS: calcd for C26H20O4Cl2 466.0739, found
466.0755.
(2 H, d, J = 8.6), 8.19 (2 H, d, J = 2.0), 8.64 (2 H, d, J = 8.8). 13
C
NMR (101 MHz, CDCl3): 123.7 (d), 125.6 (d), 126.8 (d), 127.0
(s), 127.23 (d), 127.26 (d), 127.5 (d), 127.8 (d), 128.9 (d), 129.5
(d), 130.0 (s), 132.4 (s), 133.1 (s), 138.7 (s), 140.6 (s). IR (CHCl3):
3052 m, 1621 w, 1600 m, 1578 w, 1556 w, 1493 m, 1486 m, 1446 m,
1435 w, 1384 w, 1322 w, 1169 w, 1143 w, 1102 w, 1077 w, 1042 w,
1024 w, 890 s, 854 m, 836 vs, 698 vs, 648 w, 581 m, 548 m, 521 w,
440 w. EI MS: 430 (Mþ•, 100), 413 (8), 387 (5), 352 (53), 350 (48),
339 (37), 276 (10), 176 (6). HR EI MS: calcd for C34H22
430.1722, found 430.1712. Crystallographic data: Single crystals
of 14 were grown by slow evaporation from the mixture of
dichloromethane-diethyl ether; C34H22, Mr = 430.52, mono-
clinic, C2/c (no. 15), a = 20.2803 (8) A, b = 9.1154(3) A, c =
3,12-Dichloro-5,6,9,10-tetrahydropentahelicene-5,10-diyl Diacetate
(12). A solution of triyne 11 (336 mg, 0.720 mmol), PPh3 (378 mg,
1.44 mmol, 2.0 equiv), and CpCo(CO)2 (95 μL, 0.720 mmol, 1.0
equiv) in decane (20 mL) was heated at 150 °C for 2 h under simul-
taneous irradiation with a halogen lamp. The solvent was then
removed in vacuo and the crude product was chromatographed on
silica gel (hexane-acetone 90:10) to provide a mixture of two dia-
stereoisomers of helicene diacetoxy derivative 12 (165 mg, 50%) as a
yellowish amorphous solid. 1H NMR (400 MHz, CDCl3): 1.95 (3 H,
s), 2.32 (3 H, s), 2.77-2.81 (1 H, m), 2.96-3.00 (1 H, m), 3.14-3.26
(2 H, m), 5.92 (1 H, s), 6.04-6.11 (1 H, m), 7.03-7.07 (2 H, m),
7.14-7.24 (4 H, m), 7.37 (1 H, s), 7.54 (1 H, s). IR (CHCl3): 3029 w,
3013 w, 2954 w, 2929 w, 2895 w, 2853 w, 2840 w, 1734 s, 1599 w, 1590
w, 1564 vw, 1488 w, 1482 w, 1407 w, 1347 m, 1242 vs, 1174 w, 1103 w,
1078 w, 1038 m, 833 m, 688 vw, 603 w, 525 w cm-1. ESI MS: 489
([M þ Na]þ). HR ESI MS: calcd for C26H20O4NaCl2 489.0636,
found 489.0637.
12.4619(5) A, β = 107.3695(18)°, Z = 4, Dx = 1.301 Mg m-3
,
colorless crystal of dimensions 0.4 ꢀ 0.3 ꢀ 0.3 mm3, an absorp-
tion was neglected [μ = 0.07 mm-1, 12781 diffraction collected
(θmax = 27.5°), 2509 independent (Rint = 0.031) and 2039
observed (I > 2σ(I))]. 154 parameters, goodness of fit 1.05, final
R indices R[F2 > 2σ(F2)] = 0.040, wR(F2) = 0.112, maximal/
minimal residual electron density (ΔFmax = 0.20, ΔFmin -0.17 e
3
A-3). CCDC-784074 contains the supplementary crystallo-
graphic data for this compound. These data can be obtained
free of charge from Cambridge Crystallographic Data Centre via
www.ccdc.cam.ac.uk/data_reguest/cif or from the Cambridge
Crystallographic Data Centre, 12 Union Road, Cambridge CB2
1EZ, UK; fax þ44(1223) 336033; e-mail deposit@ccdc.cam.ac.uk.
Representative Procedure for Solvent-Free Suzuki-Miyaura
Coupling: 4,40-Pentahelicene-3,12-diyldiphenol (15). A mixture
of chloro helicene 13 (103 mg, 0.300 mmol), 4-hydroxyphenyl-
boronic acid 20 (166 mg, 1.20 mmol, 4.0 equiv), Pd(MeCN)2Cl2
(32.1 mg, 0.120 mmol, 40 mol %), tricyclohexyl phosphine
(67.3 mg, 0.240 mmol, 80 mol %), and TBAF (947 mg, 3.01 mmol,
10.0 equiv) was heated under argon at 85 °C overnight. Water
(5 mL) was added to the mixture and the product was extracted
with dichloromethane (3 ꢀ 10 mL). The organic phase was dried
over anhydrous MgSO4 and the solvent was removed in
vacuo. The crude product was chromatographed on silica gel
3,12-Dichloropentahelicene (13). Helicene diacetate 12 (70.0
mg, 0.150 mmol) was dissolved in dichloromethane (2.0 mL)
and added to silica gel (8.0 g). The solvent was evaporated in
vacuo and the resulting solid was put under argon and stirred at
120 °C for 3 h. The silica gel with absorbed product was loaded
to the silica gel column and directly chromatographed (hexane)
to provide the desired product 13 (51.5 mg, 99%) as a crystalline
yellowish solid. Mp: 270 °C (dichloromethane). 1H NMR (400
MHz, CDCl3): 7.24 (2 H, dd, J = 9.0, 2.4), 7.84 (2 H, d, J = 8.4),
7.88 (2 H, s), 7.91 (2 H, d, J = 8.4), 7.93 (2 H, d, J = 2.4), 8.38
(2 H, d, J = 9.0). 13C NMR (101 MHz, CDCl3): 125.2 (d), 126.6
(s), 126.7 (d), 127.5 (d), 127.6 (d), 128.9 (s), 130.2 (d), 132.0 (s),
132.4 (s), 133.7 (s). IR (CHCl3): 3056 w, 1618 w, 1597 w, 1554 w,
1507 w, 1485 m, 1455 vw, 1434 m, 1384 vw, 1333 w, 1312 w, 1264 w
cm-1. EI MS: 346 (Mþ•, 35), 310 (49), 276 (100), 248 (2), 155 (8),
137 (19). HR EI MS: calcd for C22H12Cl2 346.0316, found
346.0305. Crystallographic data: Single crystals of 13 were
J. Org. Chem. Vol. 75, No. 20, 2010 6895

Songis et al.
JOCArticle
(hexane-acetone 70:30) to provide the diphenol 15 (134 mg,
98%) as an amorphous white solid. 1H NMR (400 MHz,
d6-DMSO): 6.91 (4 H, d, J = 8.4), 7.65 (2 H, dd, J = 8.8,
2.0), 7.73 (4 H, d, J = 8.4), 8.01 (2 H, s), 8.02 (2 H, d, J = 8.8),
8.11 (2 H, d, J = 8.8), 8.29 (2 H, d, J = 2.0), 8.42 (2 H, d, J =
8.8), 9.65 (2 H, s). 13C NMR (101 MHz, d6-DMSO): 115.7 (d),
122.7 (d), 123.9 (d), 125.8 (s), 126.5 (d), 127.0 (s), 127.8 (d),
128.42 (s), 128.42 (d), 129.9 (s), 131.8 (s), 132.8 (s), 137.7 (s),
157.3 (s). IR (CHCl3): 3433 vs, 1611 m, 1592 w, 1520 w, 1507 w,
1501 w, 1490 w, 1443 w, 1105 w, 1013 vw, 834 w, 821 w, 697 vw
cm-1. EI MS: 462 (Mþ•, 51), 368 (29), 355 (20), 337 (11), 313 (2),
276 (4), 186 (100), 157 (32), 128 (16). HR EI MS: calcd for
C34H22O2 462.1620, found 462.1603.
using dichloromethane, the crude reaction mixture was chro-
matographed on silica gel (hexane-acetone 70:30) providing the
compound 18 (238 mg, 50%) as an amorphous white solid. 1H
NMR (400 MHz, CDCl3): 1.21 (42 H, s), 7.54 (2 H, dd, J = 8.8,
1.6), 7.63 (2 H, d, J = 8.6), 7.73 (2 H, d, J = 8.6), 7.87 (2 H, s),
7.89 (2 H, d, J = 8.6), 7.97 (2 H, d, J = 8.6), 8.15 (2 H, d, J =
1.6), 8.59 (2 H, d, J = 8.8). 13C NMR (101 MHz, CDCl3): 11.4
(d), 18.7 (q), 91.6 (s), 107.0 (s), 122.7 (s), 123.4 (d), 125.6 (d),
126.91 (d), 126.94 (d), 127.4 (d), 127.8 (d), 129.6 (d), 130.2 (s),
132.53 (s), 132.59 (d), 133.0 (s), 137.9 (s), 140.4 (s). IR (CHCl3):
3602 w, 2959 s, 2892 m, 2866 vs, 2154 m, 1517 w, 1464 m, 1408 w,
1384 w, 1366 vw, 1321 w, 1184 vw, 1108 w, 1073 w, 1017 w, 997
w, 884 m, 704 m, 679 s, 660 s, 630 w cm-1. EI MS: 790 (Mþ•, 50),
740 (29), 534 (100), 491 (28), 463 (14), 491 (30), 463 (15), 449 (32),
435 (32), 421 (40), 276 (9), 218 (9), 210 (9). HR EI MS: calcd for
C56H62Si2 790.4390, found 790.4391.
Representative Procedure for Suzuki-Miyaura Coupling in
Solution: 4,40-Pentahelicene-3,12-diyldianiline (16). A mixture of
chloro helicene 13 (92.8 mg, 0.270 mmol), 4-aminophenylboron-
ic acid 21 (234 mg, 1.07 mmol, 4.0 equiv), Pd(OAc)2 (24.0 mg,
0.110 mmol, 40 mol %), 2-dicyclohexylphosphino-20-(N,N-
dimethylamino)biphenyl 24 (84.5 mg, 0.110 mmol, 80 mol %),
and cesium carbonate (783 mg, 2.40 mmol, 9.0 equiv) in a
mixture of dioxane-water (3:1, 4 mL) was heated under argon
at 85 °C overnight. After the removal of salt by filtration through a
paper filter using dichloromethane, the crude reaction mixture
was chromatographed on silica gel (hexane-ethyl acetate 70:30)
providing helicene dianiline 16 (88.5 mg, 72%) an amorphous
white solid. 1H NMR (400 MHz, CDCl3): 3.83 (4 H, br s), 6.82
(4 H, d, J = 8.4), 7.53 (2 H, dd, J = 8.8, 2.0), 7.62 (4 H, d, J =
8.4), 7.85 (2 H, s), 7.88 (2 H, d, J = 8.4), 7.95 (2 H, d, J = 8.4),
8.09 (2 H, d, J = 2.0), 8.59 (2 H, d, J = 8.8). 13C NMR (101
MHz, CDCl3): 115.5 (d), 123.2 (d), 124.2 (d), 126.6 (d), 126.97
(d), 127.02 (s), 127.6 (d), 128.1 (d), 129.4 (d), 130.9 (s), 132.2 (s),
133.1 (s), 138.6 (s), 146.1 (s). IR (CHCl3): 3486 w, 3455 w, 3401
w, 3376 w, 3051 w, 1620 vs, 1609 s, 1524 m, 1508 m, 1491 m, 1473
w, 1445 w, 1398 w, 1130 w, 1012 vw, 838 m, 822 m cm-1. EI MS:
460 (Mþ•, 100), 442 (10), 426 (3), 367 (56), 350 (18), 337 (12), 276
(5). HR EI MS: calcd for C34H24N2 460.1939, found 460.1923.
3,12-Bis(4-prop-1-yn-1-ylphenyl)pentahelicene (17). A mix-
ture of chloro helicene 13 (10.6 mg, 0.030 mmol), 4-prop-1-yn-
1-ylphenyl boronic acid 22 (19.5 mg, 0.122 mmol, 4.0 equiv),
Pd(OAc)2 (2.7 mg, 0.012 mmol, 40 mol %), 2-dicyclohexylphos-
phino-20-(N,N-dimethylamino)biphenyl 24 (9.5 mg, 0.024 mmol,
80 mol %), and cesium carbonate (49.5 mg, 0.152 mmol, 5.0 equiv)
in dioxane (0.5 mL) was heated under argon at 85 °C overnight.
After the removal of salt by filtration through a paper filter
using dichloromethane, the crude reaction mixture was chro-
matographed on silica gel (hexane-acetone 70:30) providing
diyne 17 (7.1 mg, 45%) as an amorphous white solid. 1H NMR
(400 MHz, CDCl3): 2.10 (6 H, s), 7.52 (4 H, d, J = 8.4), 7.56
(2 H, dd, J = 8.8, 2.0), 7.73 (4 H, d, J = 8.4), 7.89 (2 H, s), 7.91
(2 H, d, J = 8.4), 7.98 (2 H, d, J = 8.4), 8.17 (2 H, d, J = 2.0),
8.60 (2 H, d, J = 8.8). 13C NMR (101 MHz, CDCl3): 4.4 (q), 79.7
(s), 86.8 (s), 123.2 (s), 123.4 (d), 125.5 (d), 126.89 (d), 126.94 (d),
127.3 (d), 127.8 (d), 129.6 (d), 130.1 (s), 132.0 (d), 132.5 (s), 133.0
(s), 138.0 (s), 139.6 (s). IR (CHCl3): 3051 m, 2256 vw, 2220 vw,
1621 w, 1601 m, 1518 w, 1503 w, 1487 m, 1468 w, 1446 m, 1409 w,
1380 w, 1322 w, 1168 w, 1143 w, 1103 w, 1078 w, 1024 w, 890 s,
(4-Prop-1-yn-1-ylphenyl)boronic Acid (22). A Schlenk flask
containing a solution of 1-bromo-4-idophenyl (200 mg, 0.692
mmol), Pd(PPh3)2Cl2 (5.0 mg, 0.007 mmol, 1 mol %), and CuI
(2.7 mg, 0.014 mmol, 2 mol %) in pyridine (1 mL) was connected
with a bottle of prop-1-yne and the mixture was stirred at room
temperature for 2 h. After the evaporation of the solvent in
vacuo, salt was removed by precipitation using diethyl ether and
the crude mixture was chromatographed on silica gel (hexane) to
furnish the 1-bromo-4-prop-1-yn-1-ylbenzene23 (111 mg, 82%)
1
as colorless oil. H NMR (400 MHz, CDCl3) and 13C NMR
(101 MHz, CDCl3) spectra were in agreement with the published
data.23 IR (CHCl3): 3082 vw, 3056 vw, 2963 w, 2255 m, 2219 w,
1588 w, 1486 vs, 1466 m, 1395 s, 1378 w, 1297 vw, 1299 w, 1266 m,
1177 vw, 1112 w, 1071 vs, 1012 s, 971 m, 826 vs, 704 w, 636 w, 523 s,
485 m, 412 w cm-1. EI MS: 196 (Mþ• with 81Br, 10), 194 (Mþ•
with 79Br, 10), 167 (8), 147 (30), 115 (15), 75 (28), 73 (100). HR EI
MS: calcd for C9H779Br 193.9731, found 193.9738. To the
solution of 1-bromo-4-prop-1-yn-1-ylbenzene (0.8770 g, 4.50 mmol)
in THF (20 mL) at -78 °C under argon was carefully added a
butyllithium solution (1.6 M in hexanes, 3.7 mL, 5.85 mmol, 1.3
equiv) and the reaction was stirred at -78 °C for 20 min. The
mixture was transferred by a syringe into a cold solution of
triisopropyl borate (3.1 mL, 13.50 mmol, 3.0 equiv) at -78 °C,
and the reaction was stirred at the same temperature for 20 min
and 2 h at room temperature. After the evaporation of the
solvent in vacuo, the crude mixture was poured into aq HCl
(1 N, 20 mL) and stirred for 20 min. Then the water phase was
extracted with dichloromethane (3 ꢀ 20 mL). The organic phase
was dried over anhydrous MgSO4 and the solvent was removed
in vacuo. The flash chromatography on silica gel mixture
(hexane-acetone 70:30) of the crude mixture yielded boronic
acid 2216 (561 mg, 78%) as a white amorphous solid. 1H NMR
(400 MHz, CDCl3): 2.09 (3 H, s), 7.49 (2 H, d, J = 8.0), 8.09
(2 H, d, J = 8.0). 13C NMR (101 MHz, CDCl3): 4.4 (q), 79.98 (s),
88.4 (s), 128.4 (s), 131.0 (d), 135.4 (d). IR (CHCl3): 3212 vw, 3078
w, 3038 vw, 2254 w, 2217 vw, 1605 s, 1511 w, 1402 s, 1380 s, 1369
s, 1345 vs, 1309 s, 1298 m cm-1. ESI MS: 159 ([M - H]-). HR
ESI MS: calcd for C9H8O2B 159.0623, found 159.0620.
1,10-[Ethyne-1,2-diylbis(5-chlorobenzene-2,1-diyl)]bis[4-(trim-
ethylsilyl)but-3-yn-1-ol] (25). A Schlenk flask was charged with
gallium (101 mg, 1.45 mmol, 2.2 equiv), indium (8.0 mg, 0.070 mmol,
10 mol %), trimethylsilyl propargyl bromide (0.42 mL, 2.64 mmol,
4.0 equiv), and THF (1 mL) under argon. The reaction mixture was
then vigorously stirred at 10 °C for 1 h. After complete consumption
of gallium, a solution of dialdehyde 9 (200 mg, 0.660 mmol) in THF
(4 mL) was slowly added and the reaction mixture was stirred at
room temperature for 1 h. After removal of the solvent in vacuo, sat.
NaHCO3 (100 mL) was added to the crude reaction mixture, the
product was extracted with dichloromethane (3 ꢀ 200 mL) and the
854 m, 846 m, 836 vs, 824 m, 698 m, 582 m, 549 m, 415 w cm-1
.
EI MS: 506 (Mþ•, 100), 490 (6), 475 (3), 390 (25), 377 (28), 350
(2). HR EI MS: calcd for C40H26 506.2035, found 506.2033.
[Pentahelicene-3,12-diylbis(benzene-4,1-diylethyne-2,1-diyl)]-
bis[tris(1-methylethyl)silane] (18). A mixture of chloro helicene
13 (204 mg, 0.588 mmol), 4-tris(1-methylethyl)silane-acetylene
boronic acid 2315 (350 mg, 2.31 mmol, 4.0 equiv), Pd(OAc)2
(13.2 mg, 0.059 mmol, 10 mol %), 2-dicyclohexylphosphino-
20-(N,N-dimethylamino)biphenyl 24 (46.7 mg, 0.118 mmol, 20
mol %), and cesium carbonate (766 mg, 2.352 mmol, 4.0 equiv)
in dioxane (4 mL) was heated under argon at 80 °C overnight.
After the removal of salt by filtration through a paper filter
(23) An, D.-L.; Zhang, Z.; Orita, A.; Mineyama, H.; Otera, J. Synlett
2007, 1909.
6896 J. Org. Chem. Vol. 75, No. 20, 2010

Songis et al.
JOCArticle
organic phase was dried over anhydrous MgSO4. The solvent was
removed in vacuo and the crude product was chromatographed on
silica gel (hexane-ethyl acetate 70:30) providing a mixture of two
diastereosiomers of the hydroxy derivative 25 (176 mg, 50%) as a
(3,12-Dichloropentahelicen-7-yl)(trimethyl)silane (28). The com-
pound 27 (33.0 mg, 0.053 mmol) was dissolved in dichloromethane
and added to silica gel 60 (2 g). The solvent was evaporated in
vacuo and the resulting solid was put under argon and stirred at
120 °C for 5 h. The silica gel with absorbed product was loaded to
the silica gel column and directly chromatographed (hexane) to
provide the desired silylated pentahelicene 28 (14.9 mg, 67%) as a
colorless oil. 1H NMR (400 MHz, CDCl3): 0.56 (9 H, s), 7.20 (1 H,
dd, J = 8.8, 2.0), 7.22 (1 H, dd, J = 8.8, 2.0), 7.82-7.93 (5 H, m),
8.05 (1 H, s), 8.18 (1 H, d, J = 8.8), 8.26 (1 H, d, J =2.0), 8.29 (1H,
d, J = 2.0). 13C NMR (101 MHz, CDCl3): 0.4 (q), 125.1 (d), 125.3
(d), 125.9 (d), 126.3 (d), 126.5 (s), 126.7 (d), 127.1 (s), 127.4 (d),
127.6 (d), 128.8 (s), 129.3 (s), 130.3 (d), 130.8 (d), 131.3 (s), 131.9
(s), 132.0 (s), 132.9 (s), 133.8 (s), 135.2 (d), 135.6 (s), 137.5 (s). IR
(CHCl3): 3052 w, 2958 w, 2900 w, 1607 w, 1596 w, 1573 w, 1553 w,
1507 w, 1493 w, 1479 w, 1464 w, 1434 w, 1412 w, 1380 vw, 1255 m,
866 vs, 876 s, 841 s, 824 m, 812 m, 692 w, 631 w cm-1. TOF EI MS:
418 (Mþ•, 98), 403 (28), 383 (22), 353 (21), 348 (27), 310 (100), 289
(30), 275 (55), 167 (5), 73 (25). HR TOF EI MS: calcd for
C25H20Cl2Si 418.0711, found 418.0710.
4-tert-Butyl-2-formylphenyl Trifluoromethanesulfonate (30).
To a solution of alcohol 29 (235 mg, 1.32 mmol) and pyridine
(0.32 mL, 3.96 mmol, 3.0 equiv) in dichloromethane (6 mL) was
carefully added trifluoromethanesulfonic anhydride (0.24 mL,
1.45 mmol, 1.1 equiv) at 0 °C over 10 min. After 2.5 h of vigorous
stirring at room temperature, the solvent was removed in vacuo,
diethyl ether (5 mL) was added, and the precipitation was
filtered off. Flash chromatography of the crude mixture on
silica gel (dichloromethane) provided triflate 30 (369 mg,
90%) as a colorless oil. 1H NMR (400 MHz, CDCl3): 1.36
(9 H, s), 7.32 (1 H, d, J = 8.8), 7.72 (1 H, dd, J = 8.8, 2.8), 7.99
(1 H, d, J = 2.8), 10.27 (1H, s). 13C NMR (101 MHz, CDCl3):
31.1 (q), 35.1 (s), 118.7 (q, J = 322), 122.0 (d), 127.5 (d), 127.9
(s), 133.0 (d), 147.9 (s), 152.5 (s), 186.8 (d). IR (CHCl3): 3033 m,
2969 s, 2936 m, 2908 m, 2873 m, 2816 w, 2768 w, 1603 m, 1589 w,
1479 m, 1464 m, 1429 vs, 1400 s, 1367 m, 1249 vs, 1230 vs, 1176 s,
1118 s, 1077 s, 961 w, 929 m, 838 m, 573 w, 510 m cm-1. EI MS:
310 (Mþ•, 18), 295 (100), 231 (6), 203 (20), 175 (8), 134 (13),
105 (7). HR EI MS: calcd for C12H13F3O4S 310.0486, found
310.0486.
2,20-Ethyne-1,2-diylbis(5-tert-butylbenzaldehyde) (31). A
Schlenk flask was charged with triflate 30 (364 mg, 1.17 mmol),
Pd(PPh3)2Cl2 (34.0 mg, 0.050 mmol, 4 mol %), and CuI (5.0 mg,
0.025 mmol, 2 mol %) and filled with acetylene. A mixture of
Et3N (2 mL) and THF (1 mL) was added and reaction mix-
ture was stirred for 2 h at 60 °C. The solvents were removed in
vacuo and the crude product was chromatographed on silica gel
(hexane-acetone 90:10) to provide dialdehyde 31 (151 mg,
73%) as a pale amorphous solid. 1H NMR (400 MHz, CDCl3):
1.36 (18 H, s), 7.62 (2 H, d, J = 8.4), 7.65 (2 H, dd, J = 8.4, 2.0),
7.99 (2 H, d, J = 2.0), 10.61 (2 H, s). 13C NMR (101 MHz,
CDCl3): 31.0 (q), 35.1 (s), 91.3 (s), 123.1 (s), 124.6 (d), 131.2 (d),
133.3 (d), 135.8 (s), 153.0 (s), 191.5 (d). IR (CHCl3): 2968 m,
2933 w, 2909 w, 2870 w, 2845 w, 2749 w, 2208 vw, 1694 vs, 1602
m, 1550 w, 1502 w, 1477 w, 1465 w, 1412 vw, 1397 w, 1390 w,
1366 m, 1284 w, 1253 w, 1192 m, 1126 w, 1105 vw, 1094 vw, 933
w, 841 m, 638 w cm-1. ESI MS: 369 ([M þ Na]þ). HR ESI MS:
calcd for C24H26NaO2 369.1825, found 369.1827.
1
pale yellow oil. H NMR (400 MHz, CDCl3): 0.15 (18 H, s, one
diastereoisomer), 0.15 (18 H, s, one diastereoisomer), 2.60-2.68
(2 H, m), 2.83 (2 H, br s), 2.87-2.94 (2 H, m), 5.27-5.33 (2 H,
m), 7.22-7.26 (2 H, m), 7.40-4.43 (2 H, m), 7.61 (2 H, m). 13
C
NMR (101 MHz, CDCl3): -0.04 (q), 29.9 (t), 30.0 (t), 69.78 (d),
69.84 (d), 88.67 (s), 88.74 (s), 91.9 (s), 92.0 (s), 102.0 (s), 102.1 (s),
118.47 (s), 118.50 (s), 126.16 (d), 126.19 (d), 127.8 (d), 133.3 (d),
135.2 (s), 145.8 (s). IR (CHCl3): 3602 w, 2962 m, 2901 w, 2174 m,
1595 w, 1558 vw, 1488 m, 1408 w, 1308 vw, 1278 w, 1252 s, 1180
w, 1116 w, 1092 m, 1057 m, 908 m, 896 w, 846 vs, 825 m, 700 w,
651 w, 506 w cm-1. ESI MS: 525 ([M - H]-). HR ESI MS: calcd
for C28H31O2Cl2Si2 525.1245, found 525.1242.
Ethyne-1,2-diylbis[(5-chlorobenzene-2,1-diyl)-1-(trimethylsilyl)-
but-1-yne-4,4-diyl] Diacetate (26). To the solution of 25 (124 mg,
0.200 mmol) and 4-(dimethylamino)pyridine (2.4 mg, 0.020 mmol,
10 mol %) in pyridine (0.5 mL) was slowly added acetic anhydride
(1.0 mL, 11.0 mmol, 55 equiv) and the reaction mixture was stirred
at room temperature for 1 h. Solvent was then removed in vacuo
and the crude product was chromatographed on silica gel (hexane-
ethyl acetate 70:30) to provide a mixture of two diastereoisomers
of the diacetate 26 (0.126 mg, 87%) as yellowish oil. One dia-
stereoisomer of 26 was isolated in a pure form by precipitation in
hexane. Mixture of diastereoisomers of 26: 1H NMR (400 MHz,
CDCl3): 0.109 and 0.113 (18 H, 2 ꢀ s), 2.15 and 2.16 (6 H, 2 ꢀ s),
2.78-2.85 (2 H, m), 2.93-3.01 (2 H, m), 6.31-6.36 (2 H, m),
7.28 (2 H, dd, J = 8.4, 2.2), 7.47-7.51 (4 H, m). 13C NMR (101
MHz, CDCl3): -0.2 (q), 20.9 (q), 26.7 (t), 26.9 (t), 70.9 (d), 88.20
(s), 88.24 (s), 91.83 (s), 91.85 (s), 100.97 (s), 101.01 (s), 119.2 (s),
126.7 (d), 126.8 (d), 128.2 (d), 133.5 (d), 134.83 (s), 134.85 (s),
142.36 (s), 142.39 (s), 169.5 (s). IR (CHCl3): 2961 w, 2902 w,
2179 w, 1744 s, 1596 w, 1559 vw, 1491 w, 1421 w, 1408 w, 1374 m,
1250 s, 1238 vs, 1181 w, 1116 w, 1091 w, 1032 m, 900 w, 846 vs,
826 m, 701 w, 638 w, 606 vw cm-1. ESI MS: 1243 ([2M þ Na]þ),
633 ([M þ Na]þ). HR ESI MS: calcd for C32H36O4Cl2NaSi2
633.1421, found 633.1426. Pure diastereoisomer of 26: 1H NMR
(400 MHz, CDCl3): 0.11 (18 H, s), 2.15 (6 H, s), 2.82 (2 H, dd,
J = 17.2, 6.0), 2.97 (2 H, dd, J = 17.2, 6.0), 6.33 (2 H, t, J = 6.0),
7.28 (2 H, dd, J = 8.4, 2.2), 7.48 (2 H, d, J = 8.4), 7.50 (2 H, d,
J = 2.2). 13C NMR (101 MHz, CDCl3): -0.2 (q), 21.0 (q), 26.8
(t), 70.9 (d), 88.3 (s), 91.9 (s), 101.3 (s), 119.2 (s), 126.9 (d), 128.2
(d), 133.5 (d), 134.9 (s), 142.4 (s), 169.5 (s). IR (CHCl3): 2961 w,
2902 w, 2179 w, 1744 s, 1596 w, 1559 vw, 1491 w, 1421 w, 1408 w,
1374 m, 1250 s, 1238 vs, 1181 w, 1116 w, 1091 w, 1032 m, 900 w,
846 vs, 826 m, 701 w, 638 w, 606 vw cm-1. ESI MS: 633 ([M þ
Na]þ). HR ESI MS: calcd for C32H36O4Cl2NaSi2 633.1421,
found 633.1426.
3,12-Dichloro-7,8-bis(trimethylsilyl)-5,6,9,10-tetrahydropen-
tahelicene-5,10-diyl Diacetate (27). The solution of triyne 26
(35.0 mg, 0.066 mmol), PPh3 (31.3 mg, 0.133 mmol, 2.0 equiv),
and CpCo(CO)2 (8.7μL, 0.066 mmol, 1.0equiv) in decane (20 mL)
under agon was stirred at 150 °C for 2 h under simultaneous
irradiation with a halogen lamp. The solvent was then removed
in vacuo and the crude product was chromatographed on silica
gel (hexane) to provide a mixture of two diastereoisomers of
diacetate 27 (33.0mg, 94%) asa colorlessoil.1H NMR (400 MHz,
CDCl3): 0.41 (18 H, s), 1.95-2.34 (6 H, m), 2.63-2.84 (2 H, m),
3.40-3.80 (2 H, m), 6.00-6.20 (2 H, m), 6.94-7.02 (4 H, m),
7.34 (2 H, br s), 7.50 (2 H, br s). IR (CHCl3): 2960 m, 2902 w,
1736 vs, 1596 w, 1571 w, 1484 w, 1421 w, 1411 w, 1374 m, 1252
vs, 1237 vs, 1182 w, 1034 m, 846 vs, 697 w, 612 w cm-1. ESI MS:
1,10-[Ethyne-1,2-diylbis(5-tert-butylbenzene-2,1-diyl)]bisbut-
3-yn-1-ol (32). Purification by chromatography on silica gel
(hexane-acetone 90:10) provided two diastereoisomers of di-
hydroxy derivative 32 (98.5 mg, 30%) as oil containing some
traces of unknown impurities (for experimental details see the
preparation of 33). The degradation seems to occur during the
1243 ([2M þ Na]þ), 633 ([M þ Na]þ). TOF EI MS: 610 (Mþ•
,
purification on silica gel. H NMR (400 MHz, CDCl3): 1.34
1
15), 550 (25), 490 (68), 455 (17), 418 (63), 403 (20), 382 (41), 73
(100). HR TOF EI MS: calcd for C32H36O4Cl2Si2 610.1529,
found 610.1528.
(18 H, br s), 2.11 (2 H, br s), 2.63-2.69 (2 H, m), 2.86-2.93 (2 H,
m), 5.34-5.43 (2 H, m), 7.31-7.34 (2 H, m), 7.46-7.48 (2 H, m),
7.64-7.65 (2 H, m). 13C NMR (101 MHz, CDCl3): 28.5 (t), 28.6
J. Org. Chem. Vol. 75, No. 20, 2010 6897

Songis et al.
JOCArticle
(t), 31.2 (q), 35.1 (s), 70.7 (d), 70.8 (d), 70.96 (d), 71.03 (d), 80.9
(s), 81.0 (s), 91.6 (s), 91.7 (s), 117.6 (s), 122.4 (d), 124.7 (d), 132.2
(d), 143.3 (s), 152.3 (s). IR (CHCl3): 3602 w, 3308 s, 2967 vs, 2933
m, 2908 m, 2870 m, 2210 vw, 2120 vw, 1606 w, 1505 m, 1477 w,
1464 w, 1419 w, 1396 w, 1365 m, 1261 m, 1185 w, 1128 w, 1105 w,
1083 w, 1054 m, 834 m, 643 m, 525 w cm-1. ESI MS: 449 ([M þ
Na]þ), 875 ([2M þ Na]þ). HR ESI MS: calcd for C30H34NaO2
449.2451, found 449.2454.
122.7 (d), 123.2 (d), 126.3 (d), 126.8 (d), 127.0 (s), 127.6 (d), 128.7
(d), 128.9 (s), 132.0 (s), 132.6 (s). IR (CHCl3): 3051 w, 2966 vs,
2932 m, 2907 m, 2869 m, 1621 w, 1606 w, 1513 w, 1496 w, 1478 w,
1464 w, 1444 w, 1394 w 1386 w, 1363 m, 888 m, 839 s cm-1. EI
MS: 390 (Mþ•, 26), 333 (11), 317 (6), 300 (11), 277 (100). HR EI
MS: calcd for C30H30 390.2348, found 390.2342.
2,20-Ethyne-1,2-diyldipyridine-3-carbaldehyde (37). A Schlenk
flask was charged with bromide 36 (300 mg, 1.61 mmol), Pd-
(PPh3)2Cl2 (45.0 mg, 0.060 mmol, 4 mol %), and CuI (6.0 mg,
0.030 mmol, 2 mol %) and filled with acetylene. A mixture of
Et3N (8 mL) and THF (2 mL) was added and the reaction
mixture was stirred at 50 °C for 2 h. The solvents were removed
in vacuo and the crude product was chromatographed on silica
gel (hexane-acetone 80:20) to provide dialdehyde 37 (143 mg,
75%) as a pale amorphous solid. 1H NMR (500 MHz, CDCl3):
7.53 (1 H, ddd, J = 7.9, 4.7, 0.9), 8.29 (1 H, dd, J = 7.9, 1.8), 8.90
(1 H, dd, J = 4.7, 1.8), 10.71 (1 H, d, J = 0.9). 13C NMR (125
MHz, CDCl3): 89.7 (s), 124.5 (d), 132.8 (s), 135.2 (d), 144.2 (s),
154.6 (d), 189.9 (d). IR (CHCl3): 3054 w, 2805 w, 2743 w, 2230
vw, 1701 vs, 1578 s, 1566 s, 1440 s, 1390 m cm-1. EI MS: 236
(Mþ•, 64), 208 (24), 179 (100), 153 (37), 126 (13), 99 (14), 87 (6),
75 (17), 69 (8), 62 (11), 55 (11), 51 (29), 41 (15). HR EI MS: calcd
for C14H8N2O2 236.0586, found 236.0581.
Ethyne-1,2-diylbis(pyridine-2,3-diylbut-1-yne-4,4-diyl) Diace-
tate (39). A solution of propargyl magnesiumbromide (freshly
prepared from magnesium turnings (83.0 mg, 3.41 mmol, 2.40
equiv) and propargyl bromide (441 mg, 3.71 mmol, 2.61 equiv)
in Et2O (15 mL)) was placed in a Schlenk flask under argon and
cooled to -78 °C. Dialdehyde 37 (336 mg, 1.42 mmol) in THF
(40 mL) was added dropwise to the solution of Grignard reagent
and the resulting mixture was stirred at -78 °C for 20 min to
provide 38. Then acetic anhydride (432 mg, 4.23 mmol, 2.98
equiv) was added and the mixture was stirred at room tempera-
ture for 1 h. After quenching the reaction with EtOH (5 mL),
ethyl acetate (50 mL) was added and the mixture was washed
with brine (3 ꢀ 20 mL) and dried over anhydrous MgSO4. The
solvents were removed in vacuo and the crude product was
chromatographed on silica gel (hexane-acetone 80:20) to pro-
vide the desired triyne 39 (200 mg, 35%) as a yellowish oil. 1H
NMR (500 MHz, CDCl3): 2.01 (2 H, t, J = 2.7), 2.15 (2 H, s),
2.93 (2 H, ddd, J = 17.1, 5.4, 2.7), 3.01 (2 H, ddd, J = 17.1, 5.7,
2.7), 6.40 (1 H, br t, J = 5.6), 6.43 (1 H, br t, J = 5.6), 7.35 (2 H,
ddd, J = 8.0, 4.8, 0.5), 7.88 (2 H, dd, J = 8.0, 1.7), 8.62 (2 H, br
dd, J = 4.8, 1.7). 13C NMR (125 MHz, CDCl3): 20.9 (q), 25.30
(t), 25.31 (t), 69.9 (d), 70.0 (d), 71.65 (d), 71.68 (d), 78.4 (s), 78.5
(s), 89.90 (s), 89.93 (s), 123.4 (d), 134.2 (d), 137.29 (s), 137.31 (s),
140.0 (s), 149.7 (d), 149.8 (d), 169.46 (s), 169.48 (s). IR (CHCl3):
3309 s, 3055 w, 2234 vw, 2124 w, 1746 vs, 1583 m, 1569 s, 1444 vs,
1420 m, 1373 s, 1341 w, 1236 vs, 1044 s, 1029 s, 651 s, 640 s, 604 w
cm-1. EI MS: 400 (Mþ•, 1), 357 (11), 341 (11), 319 (14), 297 (43),
281 (68), 269 (31), 259 (43), 247 (13), 231 (36), 209 (11), 181 (17),
149 (10), 128 (9), 112 (6), 97 (8), 71 (26), 57 (24), 43 (100). HR EI
MS: calcd for C24H20N2O4 400.1423, found 400.1427.
Ethyne-1,2-diylbis[(5-tert-butylbenzene-2,1-diyl)but-1-yne-4,4-diyl]
Diacetate (33). A Schlenk flask was charged with gallium (118 mg,
1.69 mmol, 2.2 equiv), indium (10.0 mg, 0.080 mmol, 10 mol %),
propargyl bromide (360 μL, 3.23 mmol, 3.0 equiv), and THF
(1 mL) under argon. The reaction mixture was then vigorously
stirred at 10 °C for 1 h. After complete consumption of gallium, a
solution of dialdehyde 31 (267 mg, 0.770 mmol) in hot THF (4 mL)
was slowly added and the reaction mixture was stirred at room
temperature for 1 h. After removal of the solvent in vacuo, sat.
NaHCO3 (100 mL) was added to the crude mixture and the
product was extracted with dichloromethane (3 ꢀ 200 mL). The
organic phase was dried over anhydrous MgSO4 and the solvent
was removed in vacuo affording the dihydroxy derivative 32. The
crude product was dissolved in pyridine (1 mL) and 4-(dimethyl-
amino)pyridine (20.8 mg, 0.170 mmol, 10 mol %) was added, then
acetic anhydride (2 mL, 22.0 mmol, 29 equiv) was carefully added
over 5 min. The mixture was left to react at room temperature for
30 min and then the solvent was removed in vacuo. Flash chro-
matography on silica gel (hexane-acetone 80:20) of the crude
mixture provided the desired diacetate 33 (311 mg, 79%) as an oil.
1H NMR (400 MHz, CDCl3): 1.34 (18 H, s), 1.99 (2 H, t, J = 2.7),
2.15 (6 H, s), 2.79-2.87 (2 H, m), 2.93-3.01 (2 H, m), 6.41-6.44
(2 H, m), 7.32-7.34 (2 H, m), 7.50-7.54 (4 H, m). 13C NMR (101
MHz, CDCl3): 21.0 (q), 25.5 (t), 31.1 (q), 34.9 (s), 70.7 (d), 71.77
(d), 71.79 (d), 79.7 (s), 91.42 (s), 91.45 (s), 118.3 (s), 118.4 (s), 123.2
(d), 125.0(d), 132.3 (d), 139.80 (s), 139.83 (s), 151.79 (s), 151.82 (s),
169.7 (s). IR (CHCl3): 3309 m, 2967 m, 2933 w, 2908 w, 2870 w,
2124 vw, 1741 s, 1608 w, 1507 w, 1478 w, 1463 w, 1422 w, 1395 w,
1374 m, 1368 m, 1240 vs, 1191 w, 1128 w, 1103 w, 1078 w, 1044 m,
1031 m, 834 w, 647 m, 606 w, 523 vw cm-1. ESI MS: 533 ([M þ
Na]þ). HR ESI MS: calcd for C34H38NaO4 533.2662, found
533.2666.
3,12-Di-tert-butyl-5,6,9,10-tetrahydropentahelicene-5,10-diyl
Diacetate (34). A solution of 33 (132 mg, 0.259 mmol), triphe-
nylphosphine (136 mg, 0.517 mmol, 2.0 equiv), and CpCo(CO)2
(35 μL, 259 mmol, 1.0 equiv) in decane (7 mL) under argon was
heated at 150 °C for 3 h under simultaneous irradiation with a
halogen lamp. The solvent was then removed in vacuo and the
crude product was chromatographed on silica gel (hexane-
acetone 90:10) to provide two diastereoisomers of helicene
1
diacetate 34 (72.1 mg, 55%) as a yellowish oil. H NMR (400
MHz, CDCl3): 1.34 (18 H, s), 1.95-2.33 (6 H, m), 2.97-3.25
(4 H, m), 5.99 (2 H, m), 7.01 (4 H, m), 7.31-7.48 (4 H, m). IR
(CHCl3): 2966 m, 2933 w, 2906 w, 2870 w, 1739 m, 1726 s, 1611
w, 1595 vw, 1501 w, 1478 w, 1465 w, 1425 w, 1412 w, 1395 w,
1373 m, 1366 m, 1248 vs, 1240 s, 1182 w, 1123 vw, 1102 vw, 1077
5,6,9,10-Tetrahydrobenzo[1,2-h:4,3-h0]diquinoline-5,10-diyl Dia-
cetate (40). A solution of triyne 39 (150 mg, 0.380 mmol), PPh3
(39.0 mg, 0.150 mmol, 40 mol %), and CpCo(CO)2 (10 μL, 0.080
mmol, 20 mol %) in decane (7 mL) under argon was heated at
150 °C for 3 h under simultaneous irradiation with a halogen
lamp. After removal of solvent, the flash chromatography of the
crude mixture on silica gel (hexane-acetone 70:30) afforded
helicene diacetate 40 (114 mg, 76%) as an amorphous yellowish
solid. 1H NMR (500 MHz, CDCl3): 2.14 (1 H, s), 2.18 (1 H, s),
2.98-3.10 (1 H, m), 3.16 (1 H, dd, J = 15.1, 4.9), 3.19 (1 H, dd,
J = 15.1, 4.9), 6.15 (1 H, br s), 6.17 (1 H, br dd, J = 8.8, 4.9), 7.13
(2 H, dd, J = 7.6, 4.7), 7.26 (2 H, s), 7.73 (1 H, ddd, J = 7.6, 1.7,
0.9), 7.75 (1 H, br dd, J = 7.6, 1.7), 8.24 (1 H, ddd, J = 4.7, 1.8,
0.5), 8.25 (1 H, br dd, J = 4.7, 1.7). 13C NMR (125 MHz,
CDCl3): 21.28 (q), 21.32 (q), 34.7 (t), 34.8 (t), 69.66 (d), 69.73 (d),
w, 1035 w, 1023 m, 842 w, 693 vw, 610 w, 527 vw, 457 vw cm-1
.
EI MS: 510 (Mþ•, 9), 450 (3), 390 (90), 375 (14), 333 (36), 277
(100), 263 (10), 180 (5), 152 (7), 57 (28). HR EI MS: calcd for
C34H38O4 510.2770, found 510.2769.
3,12-Di-tert-butylpentahelicene (35). To the solution of heli-
cene diacetate 34 (72.1 mg, 0.140 mmol) in dichloromethane was
added silica gel (7 g). The solvent was evaporated in vacuo, then
the solid was put under argon and stirred at 120 °C for 5 h. The
silica gel with absorbed product was loaded to the silica gel
column and directly chromatographed (hexane) providing the
desired pentahelicene 35 (49.5 mg, 90%) as a yellowish oil. 1H
NMR (400 MHz, CDCl3): 1.48 (18 H, s), 7.38 (2 H, dd, J = 9.0,
2.4), 7.83 (2 H, s), 7.85 (2 H, d, J = 9.0), 7.90-7.92 (4 H, m), 8.53
(2 H, d, J = 9.0). 13C NMR (101 MHz, CDCl3): 31.4 (q), 34.8 (s),
6898 J. Org. Chem. Vol. 75, No. 20, 2010

Songis et al.
JOCArticle
122.0 (d), 129.0 (d), 130.1 (s), 133.0 (s), 133.2 (d), 135.05 (s),
135.09 (s), 147.7 (d), 148.0 (d), 152.8 (s), 153.1 (s), 170.7 (s), 170.8
(s). IR (CHCl3): 3060 w, 1732 s, 1587 w, 1571 m, 1461 m, 1435 m,
1374 s, 1241 vs, 1035 s, 614 w cm-1. EI MS: 400 (Mþ•, 17), 297
(6), 280 (100), 269 (13), 252 (17), 178 (23), 161 (12), 140 (27), 97
(9), 81 (12), 69 (32), 57 (29), 41 (36). HR EI MS: calcd for
C24H20N2O4 400.1423, found 400.1426.
Benzo[1,2-h:4,3-h0]diquinoline (1,14-Diaza[5]helicene) (41).
Helicene diacetate 40 (90.0 mg, 0.225 mmol) was dissolved in
dichloromethane (10 mL) and trifluoromethanesulfonic acid
coated silica gel (10 wt % of trifluoromethanesulfonic acid on
silica gel, 5.5 g) was added. The solvent was evaporated in vacuo,
and the resulting solid was put under argon and stirred at 120 °C
for 2 h. The silica gel with absorbed product was loaded to the
silica gel column and directly chromatographed (hexane-
acetone-triethylamine 80:20:1) to provide the desired diaza-
pentahelicene 41 (42.1 mg, 67%) as an amorphous yellowish
solid.2a,21 Mp (toluene), 1H NMR (400 MHz, CDCl3), 13C
NMR (101 MHz, CDCl3), IR (CHCl3 or CCl4), and EI MS spec-
tra were in agreement with the published data.2a
Acknowledgment. This research was supported by the Eu-
ropean Commission under Grant No. FP6-015847, by the Grant
Agency of the AS CR under Grant No. IAA400550916, by the
Ministry of Education, Youth and Sports of the Czech Republic
under Project No. MSM0021620857, by the Center for Bio-
molecules and Complex Molecular Systems (supported by
the Ministry of Education, Youth and Sports of the Czech
Republic) under Project No. LC512 (O.S., I.G.S., and I.S.),
and by the Institute of Organic Chemistry and Biochemistry,
Academy of Sciences of the Czech Republic (this work is part
of Research Project Z4 055 0506).
Supporting Information Available: Crystallographic data
for 13 and 14, copies of 1H NMR and 13C NMR spectra for the
compound 22 and the new compounds 2-5, 9-18, 25-28,
30-35, 37, 39, 40 (for 3, 5, 12, 27, and 34 only 1H NMR spectra),
and CIF files for 13 and 14. This material is available free of
charge via the Internet at http://pubs.acs.org.
J. Org. Chem. Vol. 75, No. 20, 2010 6899