Synthesis of hexahelicene and 1-methoxyhexahelicene via cycloisomerization of biphenylyl-naphthalene derivatives

Article abstract of DOI:10.1021/jo900077j

The new approach provides nonphotochemical syntheses of helicenes based on the easy, convergent, and modular assembly of key biphenylyl-naphthalenes and their platinum-catalyzed double cycloisomerization. This sequence of reactions provides a synthetic ro

Full text of DOI:10.1021/jo900077j

Synthesis of Hexahelicene and 1-Methoxyhexahelicene via
Cycloisomerization of Biphenylyl-Naphthalene Derivatives
,†
†
†
†
‡
ˇ
Jan Storch,* Jan Sy´kora, Jan Cerma´k, Jindˇrich Karban, Ivana C´ısarˇova´, and
Alesˇ Ru˚zˇicˇka§
Institute of Chemical Process Fundamentals, AS CR, RozVojoVá 135, CZ-16502 Prague 6, Czech Republic,
Center of Molecular and Crystal Structures, Faculty of Natural Science, Charles UniVersity, OVocny´ trh 5,
Praha 1, 116 36, Czech Republic, and Department of General and Inorganic Chemistry, Faculty of
Chemical Technology, UniVersity of Pardubice, Studentska´ 95,
532 10 Pardubice 2, Czech Republic
storchj@icpf.cas.cz
ReceiVed January 19, 2009
The new approach provides nonphotochemical syntheses of helicenes based on the easy, convergent,
and modular assembly of key biphenylyl-naphthalenes and their platinum-catalyzed double cycloisomer-
ization. This sequence of reactions provides a synthetic route to helicenes in two steps from simply
accessible building blocks. Furthermore, the method enables the introduction of substituents into the
hexahelicene skeleton. The strategy developed is exemplified by the synthesis of 6,10-dimethylhexahelicene
and 1-methoxy-6,10-dimethylhexahelicene.
Introduction
metric molecular recognition,5 liquid crystal molecules,6 and
even in molecular machinery.7 Their intriguing semiconductivity
and conductivity was foreseen depending on the radius and the
width of the helical aromatic ribbon.8 For a specific structure,
which is still far from any practical synthesis, even metallic
conductivity might be expected. Their ability to bind to specific
DNA structures has been demonstrated.9 Besides photocycliza-
tion reactions,10 new methodologies, including Diels-Alder
The helicenes were long considered academic curiosities
because of their twisted shape as a result of the steric repulsive
interaction between terminal aromatic rings.1 Their promising
optical2 and electronic3 properties have renewed a 50 year old
interest in helicene chemistry in the past decade. They are
considered potentially useful for asymmetric catalysis,4 asym-
† Institute of Chemical Process Fundamentals, AS CR.
(4) (a) Sato, I.; Yamashima, R.; Kadowaki, K.; Yamamoto, J.; Shibata, T.;
Soai, K. Angew Chem., Int. Ed. 2001, 40, 1096. (b) Dreher, S. D.; Katz, T. J.;
Lam, K. C.; Rheingold, A. L. J. Org. Chem. 2000, 65, 815. (c) Reetz, M. T.;
Sostmann, S. J. Organomet. Chem. 2000, 603, 105. (d) Okubo, H.; Yamaguchi,
M.; Kabuto, C. J. Org. Chem. 1998, 63, 9500. (e) Reetz, M. T.; Beutenmu¨ller,
E. W.; Goddard, R. Tetrahedron Lett. 1997, 38, 3211.
(5) (a) Reetz, M. T.; Sostmann, S. Tetrahedron 2001, 57, 2515. (b) Murguly,
E.; McDonald, R.; Branda, N. R. Org. Lett. 2000, 2, 3169–3172. (c) Weix, D. J.;
Dreher, S. D.; Katz, T. J. J. Am. Chem. Soc. 2000, 122, 10027. (d) Owens, L.;
Thilgen, C.; Diederich, F.; Knobler, C. B. HelV. Chim. Acta 1993, 76, 2757–
2774. (e) Yamamoto, K.; Ikeda, T.; Kitsuki, T.; Okamoto, Y.; Chikamatsu, H.;
Nakazaki, M. J. Chem. Soc., Perkin Trans. 1 1990, 271–276.
(6) Nuckolls, C.; Katz, T. J. J. Am. Chem. Soc. 1998, 120, 9541–9544.
(7) (a) Llunell, M.; Alemany, P.; Bofill, J. M. ChemPhysChem 2008, 9, 1117–
1119. (b) Kelly, T. R.; Cai, X.; Damkaci, F.; Panicker, S. B.; Tu, B.; Bushell,
S. M.; Cornella, I.; Piggott, M. J.; Salives, R.; Cavero, M.; Zhao, Y.; Jasmin, S.
J. Am. Chem. Soc. 2007, 129, 376–386.
(8) Treboux, G.; Lapstun, P.; Wu, Z. H.; Silverbrook, K. Chem. Phys. Lett.
1999, 301, 493.
‡ Charles University.
§ University of Pardubice.
(1) For reviews, see: (a) Rajca, A.; Miyasaka, M. Synthesis and Characteriza-
tion of Novel Chiral Conjugated Materials. Functional Organic Materials:
Syntheses and Strategies; Mueller, T. J. J., Bunz, U. H. F., Eds.; Wiley-VCH:
Weinheim, Germany, 2007; pp 543-577. (b) Urbano, A. Angew. Chem., Int.
Ed. 2003, 42, 3986–3989. (c) Katz, T. J. Angew. Chem., Int. Ed. 2000, 39, 1921–
1923.
(2) (a) Wigglesworth, T. J.; Sud, D.; Norsten, T. B.; Lekhi, V. S.; Branda,
N. R. J. Am. Chem. Soc. 2005, 127, 7272–7273. (b) Botek, E.; Champagne, B.;
Turki, M.; Andre´, J.-M. J. Chem. Phys. 2004, 120, 2042–2048. (c) Nuckolls,
C.; Katz, T. J.; Verbiest, T.; Van Elshocht, S.; Kuball, H.-G.; Kiesewalter, S.;
Lovinger, A. J.; Persoons, A. J. Am. Chem. Soc. 1998, 120, 8656–8660.
(3) (a) Furche, F.; Ahlrichs, R.; Wachsmann, C.; Weber, E.; Sobanski, A.;
Vo¨gtle, F.; Grimme, S. J. Am. Chem. Soc. 2000, 122, 1717–1724. (b) Treboux,
G.; Lapstun, P.; Wu, Z.; Silverbrook, K. Chem. Phys. Lett. 1999, 301, 493–497.
(c) Beljonne, D.; Shuai, Z.; Bre´das, J. L.; Kauranen, M.; Verbiest, T.; Persoons,
A. J. Chem. Phys. 1998, 108, 1301–1304.
3090 J. Org. Chem. 2009, 74, 3090–3093
10.1021/jo900077j CCC: $40.75 2009 American Chemical Society
Published on Web 03/16/2009

Synthesis of Hexahelicene and 1-Methoxyhexahelicene
SCHEME 1
SCHEME 2
SCHEME 3
manner. Boronic acids 3a and 3b were prepared from 2 by
lithiation and subsequent reaction with B(OMe)3. The synthesis
of the naphthalene building block (Scheme 2) starts from
naphthalene boronic acid, which was subjected to a Suzuki
reaction with bromophenol 2b under palladium/2-(2′,6′-
dimethoxybiphenyl)dicyclohexylphosphine L catalysis23 to give
hydroxy compound 4. Conversion to a lithium phenolate and
subsequent reaction with triflic anhydride gave triflate 5.
Construction of Hexahelicene. Having prepared the suitable
building blocks, we could approach assembling the hexahelicene
scaffold. Suzuki coupling of building blocks 5 and 3a or 3b
led to the biphenylyl-naphthalenes 6 or 7 (Scheme 3). Introduc-
tion of two chiral axes (naphthyl-phenyl and phenyl-phenyl
cycloadition,11 [2 + 2 + 2] cycloisomerization,12 carbenoid
coupling,13 radical tandem cyclization,14 domino Friedel-Crafts-
type cyclization,15 Pd-mediated techniques,16 and olefin me-
tathesis,17 have been developed.
In pursuit of our previous investigations in this field,18 we
describe an alternative approach to [6]helicene synthesis based
on a PtCl2-catalyzed double carbocyclization reaction of alky-
nylated biphenylyl-naphthalene derivatives. The potential of
platinum chloride and related salts to induce highly selective
skeletal rearrangements of polyunsaturated compounds was
recognized only recently.19 PtClx (x ) 2, 4) is able to catalyze
an amazingly broad spectrum of C-C bond formations that
allow one to convert enynes and related substrates into a myriad
of carbo- and heterocyclic products. A new pathway into highly
substituted phenanthrenes and related polycyclic arenes based
on the cycloisomerization process catalyzed by PtCl2 was
developed by Fu¨rstner.20 Our modular method for 1-substituted
and unsubstituted 6,10-dimethylhexahelicene synthesis is based
on assembling the target from functionalized building blocks
with a final atom economic transformation.
(11) (a) Carreno, M. C.; Enriquez, A.; Garcia-Cerrada, S.; Sanz-Cuesta, M. J.;
Urbano, A.; Maseras, F.; Nonell-Canals, A. Chem.sEur. J. 2008, 14, 603–620.
(b) Carren˜o, M. C.; Gonza´lez-Lo´pez, M.; Urbano, A. Chem. Commun. 2005,
611–613. (c) Carren˜o, M. C.; Garc´ıa-Cerrada, S.; Urbano, A. Chem.sEur. J.
2003, 9, 4118–4131. (d) del Mar Real, M.; Sestelo, J. P.; Sarandeses, L. A.
Tetrahedron Lett. 2002, 43, 9111–9114. (e) Carren˜o, M. C.; Garc´ıa-Cerrada, S.;
Urbano, A. J. Am. Chem. Soc. 2001, 123, 7929–7930. (f) Paruch, K.; Katz, T. J.;
Incarvito, C.; Lam, K. C.; Rhatigan, B.; Rheingold, A. L. J. Org. Chem. 2000,
65, 7602–7608. (g) Katz, T. J. Angew. Chem., Int. Ed. 2000, 39, 1921–1923. (h)
Katz, T. J.; Liu, L.; Willmore, N. D.; Fox, J. M.; Rheingold, A. L.; Shi, S.;
Nuckolls, C.; Rickman, B. H. J. Am. Chem. Soc. 1997, 119, 10054–10063.
(12) (a) Misek, J.; Teply, F.; Stara, I. G.; Tichy, M.; Saman, D.; Cisarova,
I.; Vojtisek, P.; Stary, I. Angew. Chem., Int. Ed. 2008, 47, 3188–319. (b)
Adriaenssens, L.; Severa, L.; Salova, T.; Cisarova, I.; Pohl, R.; Saman, D.; Rocha,
S. V.; Finney, N. S.; Pospisil, L.; Slavicek, P.; Teply, F. Chem.sEur. J. 2009,
15, 1072–1076. (c) Stara´, I. G.; Alexandrova´, Z.; Teply´, F.; Sehnal, P.; Stary´, I.;
ˇ
Saman, D.; Budeˇsˇ´ınsky´, M.; Cvacˇka, J. Org. Lett. 2005, 7, 2547–2550. (d) Stara´,
ˇ
I. G.; Stary´, I.; Kolla´rovicˇ, A.; Teply´, F.; Saman, D.; Fiedler, P. Collect. Czech.
Results and Discussion
Chem. Commun. 2003, 68, 917–930. (e) Teply´, F.; Stara´, I. G.; Stary´, I.;
ˇ
ˇ
Kolla´rovicˇ, A.; Saman, D.; Vyskocˇil, S.; Fiedler, P. J. Org. Chem. 2003, 68,
Synthesis of Building Blocks. 2-Bromo-1-iodo-3-methoxy-
benzene21 1c, whose methoxy group appears as a useful
functionality in a desired position at the [6]helicene scaffold,
and 1-bromo-2-iodobenzene 1a were reacted with propyne under
Sonogashira coupling conditions to obtain alkynylated products
2a and 2c (Scheme 1).
ˇ
5193–5197. (f) Teply´, F.; Stara´, I. G.; Stary´, I.; Kolla´rovicˇ, A.; Saman, D.;
Rul´ısˇek, L.; Fiedler, P. J. Am. Chem. Soc. 2002, 124, 9175–9180. (g) Stara´,
ˇ
ˇ
I. G.; Stary´, I.; Kolla´rovicˇ, A.; Teply´, F.; Vyskocˇil, S.; Saman, D. Tetrahedron
Lett. 1999, 40, 1993.
(13) Gingras, M.; Dubois, F. Tetrahedron Lett. 1999, 40, 1309–1312.
(14) (a) Harrowven, D. C.; Guy, I. L.; Nanson, L. Angew. Chem., Int. Ed.
2006, 45, 2242–2245. (b) Harrowven, D. C.; Nunn, M. I. T.; Fenwick, D. R.
Tetrahedron Lett. 2002, 43, 7345–7347. (c) Harrowven, D. C.; Nunn, M. I. T.;
Fenwick, D. R. Tetrahedron Lett. 2002, 43, 3189–3191.
(15) Ichikawa, J.; Yokota, M.; Kudo, T.; Umezaki, S. Angew. Chem., Int.
Ed. 2008, 47, 4870–4873.
2-Bromo-3-iodophenol 1b prepared from 1c or according to
the literature procedure22 was converted into 2b in the same
(16) (a) Takenaka, N.; Sarangthem, R. S.; Captain, B. Angew Chem., Int.
Ed 2008, 47, 9708–9710. (b) Kamikawa, K.; Takemoto, I.; Takemoto, S.;
Matsuzaka, H. J. Org. Chem. 2007, 72, 7406–7408. (c) Caeiro, J.; Pen˜a, D.;
Dohas, A.; Pe´rez, D.; Guitia´n, E. AdV. Synth. Catal. 2006, 348, 2466. (d) Pen˜a,
D.; Dohas, A.; Pe´rez, D.; Guitia´n, E.; Castedo, L. Org. Lett. 2003, 5, 1863. (e)
Pen˜a, D.; Pe´rez, D.; Guitia´n, E.; Castedo, L. Org. Lett. 1999, 1, 1555.
(17) (a) Grandbois, A.; Collins, S. K. Chem.sEur. J. 2008, 14, 9323–9329.
(b) Collins, S. K.; Grandbois, A.; Vachon, M. P.; Cooˆte´, J. Angew. Chem., Int.
Ed. 2006, 45, 1–4.
(9) (a) Xu, Y.; Zhang, X. Y.; Sugiyama, H.; Umano, T.; Osuga, H.; Tanaka,
K. J. Am. Chem. Soc. 2004, 126, 6566–6567. (b) Honzawa, S.; Okubo, H.; Anzai,
S.; Yamaguchi, M.; Tsumoto, K.; Kumagai, I. Bioorg. Med. Chem. 2002, 10,
3213.
(10) (a) Rigamonti, C.; Ticozzelli, M. T.; Bossi, A.; Licandro, E.; Giannini,
C.; Maiorana, S. Heterocycles 2008, 76, 1439–1470. (b) Aloui, F.; El Abed, R.;
Marinetti, A.; Ben Hassine, B. Tetrahedron Lett. 2008, 49, 4092–4095. (c) Bossi,
A.; Maiorana, S.; Graiff, C.; Tiripicchio, A.; Licandro, E. Eur. J. Org. Chem.
2007, 4499–4509. (d) El Abed, R.; Aloui, F.; Genet, J.-P.; Ben Hassine, B.;
Marinetti, A. J. Organomet. Chem. 2007, 692, 1156–1160.
ˇ
(18) Storch, J.; Cermák, J.; Karban, J. Tetrahedron Lett. 2007, 48, 6814–
6816.
J. Org. Chem. Vol. 74, No. 8, 2009 3091

Storch et al.
SCHEME 4
reversed phase chromatographic conditions, and their 1H NMR
spectra can be acquired via LC-NMR technique. The on-flow
LC-NMR experiment showed both isomers of 7 in an ap-
proximate ratio of 30:70 (7a/7b) in acetonitrile/deuterium oxide
solvent mixture (Figure S8, Supporting Information). Semi-
preparative HPLC led to isolation of pure compounds 7a and
7b. The full assignment was performed on the basis of classic
1D and 2D NMR experiments in CDCl3. The NOE experiment
on 7a revealed strong interaction between the methoxy group
and naphthyl ring B and weak interaction of propynyl group
and ring A. At the same time, only interactions between the
methoxy group and naphthyl ring A were found in 7b. The
results of NOE experiments indicate the opposite orientation
of the methoxy(propynyl)phenyl ring D around the phenyl-phenyl
bond in both isomers. The sharp signals of the methyl groups
indicate that no dynamic behavior takes place. The methox-
y(propynyl)phenyl group can stop even the rotation of the
(propynyl)phenyl group C around naphthyl-phenyl bond, and
thus the conformation is fixed in both isomers. Furthermore,
suitable single crystals were grown from the chloroform/
acetonitrile mixture, and both structures were proven by X-ray
crystallography (Figure 1).
FIGURE 1. ORTEP projection of the crystal structure 7a (top) and
7b (bottom).
bond) gives rise to four isomers of 6 and 7 (Scheme 3). Free
rotation in 6 around the phenyl-phenyl bond (ring C and D) at
ambient temperature makes it impossible to separate the two
diastereomers.
1
The H NMR spectra show broad signals of the aromatic
protons in rings C and D. On the other hand, presence of the
methoxy group in 7 hinders rotation at ambient temperature,
and two diastereomers 7a and 7b can be separated using
j
7a and 7b crystallize in the space group P1, thus the
(19) For a general review, see: (a) Me´ndez, M.; Echavarren, A. M. Eur. J.
Org. Chem. 2002, 15–28. (b) Lloyd-Jones, G. C. Org. Biomol. Chem. 2003, 1,
215–236. (c) Aubert, C.; Buisine, O.; Malacria, M. Chem. ReV. 2002, 102, 813–
834. (d) Me´ndez, M.; Mamane, V.; Fu¨rstner, A. Chemtracts 2003, 16, 397–425.
Pioneering studies, see: (e) Chatani, N.; Furukawa, N.; Sakurai, H.; Murai, S.
Organometallics 1996, 15, 901–903. (f) Blum, J.; Beer-Kraft, H.; Badrieh, Y.
J. Org. Chem. 1995, 60, 5567–5569.
(20) Mamane, V.; Hannen, P.; Fu¨rstner, A. Chem.sEur. J. 2004, 10, 4556–
4575.
(21) Ooi, T.; Takahashi, M.; Yamada, M.; Tayama, E.; Omoto, K.; Maruoka,
K. J. Am. Chem. Soc. 2004, 126, 1150.
crystals contain also the opposite enantiomers. To achieve
the desired cycloisomerization and, accordingly, to build up
the helix, biphenylyl-naphthalenes 6 and 7 were exposed to
PtCl2 (Scheme 4).
The desired double cycloisomerization took place following
a 6-endo pathway, and racemic unsubstituted and 1-substituted
6,10-dimethylhexahelicenes 8a and 8b were formed in good
yields. The enantiomers of 7a and 7b undergo double cycloi-
somerization, yielding hexahelicene 8b. Regardless of which
diastereomeric form of 7 (or a mixture of both) was taken into
the reaction, the same product (i.e., two enantiomeric forms of
(22) Sanz, R.; Castroviejo, M. P.; Ferna´ndez, Y.; Fan˜ana´s, F. J. J. Org. Chem.
2005, 70, 6548.
(23) Barder, T. E.; Walker, S. D.; Martinelli, J. R.; Buchwald, S. L. J. Am.
Chem. Soc. 2005, 127, 4685–4696.
3092 J. Org. Chem. Vol. 74, No. 8, 2009

Synthesis of Hexahelicene and 1-Methoxyhexahelicene
129.2 (s), 129.1 (d), 128.7 (d), 128.4 (d), 126.4 (d), 126.0 (d), 125.6
(d), 125.2 (d), 120.9 (d), 92.0 (s), 77.5 (s), 4.3 (q); MS (EI) m/z
390 (80% M+), 257, 242, 226, 202. Anal. Calcd for C20H13F3O3S:
C, 61.53; H, 3.36. Found: C, 61.43; H, 3.49.
the helix; Scheme 4), was built. Thus, the final product always
contains a racemic mixture of the hexahelicenes. The X-ray
crystallography has revealed both enantiomers of 8b in the
crystal lattice (Figure S9, Supporting Information).
1-(2′-Methoxy-3,6′-di(propyn-1-yl)biphenyl-2-yl)naphtha-
lene (7): 3b (0.68 g, 3.6 mmol, 2 equiv) was used according to
general procedure. Purification by column chromatography on silica
gel 60 RP-C18 (acetonitrile/water, 70:30 to 80:20) gave 7 (0.24 g,
35%) as a white solid. 7a: 1H NMR (500 MHz, CDCl3) δ 7.70-7.67
(m, 2H), 7.64-7.61 (m, 1H), 7.57 (dd, J ) 1.3, 7.7 Hz, 1H), 7.42
(t, J ) 7.7 Hz, 1H), 7.36 (dd, J ) 1.3, 7.1 Hz, 1H), 7.34-7.25 (m,
4H), 6.87 (t, J ) 7.8 Hz, 1H), 6.68 (dd, J ) 0.9, 7.7 Hz, 1H), 6.53
(dd, J ) 0.8, 8.3 Hz, 1H), 3.62 (s, 3H), 1.85 (s, 3H), 1.51 (s, 3H);
13C NMR (125.69 MHz, CDCl3) δ 156.3 (s), 142.5 (s), 138.0 (s),
137.8 (s), 132.8 (s), 132.4 (s), 132.0 (s), 131.3 (d), 130.4 (d), 127.8
(d), 127.5 (d), 127.4 (d), 127.1 (d), 127.0 (d), 126.9 (d), 124.9 (d),
124.8 (s), 124.6 (s), 124.3 (d), 124.2 (d), 124.1 (d), 109.3 (d), 89.0
(s), 88.9 (s), 79.3 (s), 79.1 (s), 55.1 (q), 4.4 (q), 4.0 (q); MS (EI)
m/z 386 (100%, M+), 371, 356, 340, 313, 168, 156. Anal. Calcd
Experimental Section
For general procedure, see Supporting Information.
2-Bromo-1-methoxy-3-(propyn-1-yl)benzene (2c): 1c (6.3 g,
20 mmol) was used according to general procedure. Yield 4.3 g
(96%) of slightly yellow oil: H NMR (300 MHz, CDCl3) δ 7.17
1
(m, 1H), 7.05 (dd, J ) 1.4, 7.7 Hz, 1H), 6.80 (dd, J ) 1.4, 8.2 Hz,
1H), 2.11 (s, 3H), 3.87 (s, 3H); 13C NMR (75 MHz, CDCl3) δ 155.8
(s), 127.2 (d), 127.1 (s), 125.1 (d), 114.5, (s), 110.6 (d), 90.7 (s),
77.1 (s), 56.0 (q), 4.2 (q); MS (EI) m/z 224 (100% M+), 210, 182,
145, 130, 115, 102, 75. Anal. Calcd for C10H9BrO: C, 53.36; H,
4.03. Found: C, 53.25; H, 4.17.
2-Methoxy-6-(propyn-1-yl)phenylboronic acid (3b): 2c (11.55
g, 51.3 mmol) was used according to general procedure. Yield 8.0 g
(82%) of slightly yellow solid: 1H NMR (300 MHz, CDCl3) δ 7.14
(dd, J ) 0.7, 7.7 Hz, 1H), 6.92 (m, 1H), 5.33-4.58 (br s, 2H),
7.36 (m, 1H), 3.92 (s, 3H), 2.13 (s, 3H); 13C NMR (75 MHz, CDCl3)
δ 164.5 (s), 131.7 (d), 129.5 (s), 126.0 (d), 110.6 (d), 91.8 (s),
80.4 (s), 55.9 (q), 4.4 (q); MS (EI) m/z 146 (100%, M+ - BOOH),
131, 115, 103, 77. Anal. Calcd for C10H11BO3: C, 63.21; H, 5.84.
Found: C, 63.11; H, 5.53.
2-(Naphthalen-1-yl)-3-(propyn-1-yl)phenol (4): The Schlenk
tube was charged with Pd2(dba)3 ·CHCl3 (612 mg, 0.59 mmol, 3
mol %), 2-dicyclohexylphosphino-2′,6′-dimethoxybiphenyl (485
mg, 1.18 mmol, 6 mol %), anhydrous K3PO4 (12.55 g, 59.1 mmol,
3 equiv), and naphthaleneboronic acid (8.45 g, 49.1 mmol, 2.5
equiv). The Schlenk tube was then evacuated and backfilled with
argon (this sequence was repeated three times). Dry toluene (170
mL) was added, and the resulting mixture was stirred at room
temperature for ∼2 min. Then 2c (4.13 g, 19.6 mmol) was added,
and the reaction mixture was heated at 90 °C with stirring for 20 h.
The reaction mixture was then allowed to cool to room temperature,
diluted with diethyl ether (50 mL), filtered through a thin pad of
silica gel (eluting with diethyl ether), and concentrated under
reduced pressure. The crude material obtained was purified by flash
chromatography on silica gel (hexane/ethyl acetate, 3:1) to provide
1
for C29H22O: C, 90.12; H, 5.74. Found: C, 90.28; H, 5.80. 7b: H
NMR (500 MHz, CDCl3) δ 7.80-7.76 (m, 1H), 7.75-7.71 (m,
1H), 7.62-7.59 (m, 1H), 7.55 (dd, J ) 1.5, 7.6 Hz, 1H), 7.41 (t,
J ) 7.7 Hz, 1H), 7.38-7.34 (m, 3H), 7.20-7.16 (m, 1H), 7.14
(dd, J ) 1.3, 7.1 Hz, 1H), 6.96-6.90 (m, 2H), 6.26 (dd, J ) 1.9,
7.4 Hz, 1H), 2.77 (s, 3H), 1.90 (s, 3H), 1.45 (s, 3H); 13C NMR
(125.69 MHz, CDCl3) δ 156.0 (s), 142.5 (s), 138.0 (s), 137.8 (s),
132.9 (s), 132.6 (s), 132.0 (s), 131.0 (d), 130.7 (d), 127.8 (d), 127.6
(d), 127.4 (d), 127.1 (d), 126.9 (d), 126.8 (d), 125.4 (s), 124.7 (d),
124.6 (s), 124.5 (d), 124.4 (d), 123.8 (d), 109.2 (d), 89.4 (s), 89.1
(s), 79.5 (s), 79.2 (s), 54.4 (q), 4.4 (q), 4.0 (q); MS (EI) m/z 386
(100%, M+), 371, 356, 340, 313, 168, 156. Anal. Calcd for C29H22O:
C, 90.12; H, 5.74. Found: C, 90.26; H, 5.82.
1-Methoxy-6,10-dimethylhexahelicene (8b): 7 (0.5 g, 1.3 mmol)
was used according to general procedure. Purification by column
chromatography on silica gel (hexane/chloroform, 3:1) gave 0.38 g
1
(76%) of 8b as a colorless oil: H NMR (500 MHz, CDCl3) δ 8.17
(d, J ) 8.3 Hz, 1H), 8.14 (d, J ) 8.8 Hz, 1H), 8.02 (d, J ) 8.3 Hz,
1H), 7.90 (d, J ) 8.8 Hz, 1H), 7.84 (s, 1H), 7.76 (d, J ) 7.9 Hz, 1H),
7.72 (s, 1H), 7.42 (d, J ) 7.9 Hz, 1H), 7.17 (t, J ) 7.8 Hz, 1H), 7.11
(t, J ) 7.6 Hz, 1H), 7.06 (d, J ) 8.5 Hz, 1H), 6.51 (t, J ) 8.2 Hz,
1H), 6.03 (d, J ) 7.8 Hz, 1H), 2.93 (s, 3H), 2.91 (s, 3H), 2.58 (s, 3H);
13C NMR (125.69 MHz, CDCl3) δ 154.9 (s), 133.2 (s), 132.6 (s), 132.4
(s), 131.4 (s), 131.3 (s), 131.2 (s), 130.9 (s), 128.4 (s), 128.3 (s), 127.4
(d), 127.0 (d), 126.6 (d), 126.3 (d), 126.2 (d), 126.2 (d), 126.1 (d),
124.9 (s), 124.4 (s), 123.2 (d), 122.2 (d), 122.1 (d), 121.2 (s), 119.2
(d), 104.5 (d), 89.8 (d), 53.7 (q), 20.2 (q), 20.0 (q); MS (EI) m/z 386
(100%, M+), 369, 356, 178, 156. Anal. Calcd for C29H22O: C, 90.12;
H, 5.74. Found: C, 90.20; H, 5.82.
1
4.0 g (79%) of 4 as a slightly yellow oil: H NMR (300 MHz,
CDCl3) δ 7.96-7.89 (m, 2H), 7.64-7.39 (m, 5H), 7.28 (m, 1H),
7.16 (dd, J ) 1.2, 7.7 Hz, 1H), 7.00 (dd, J ) 1.2, 8.1 Hz, 1H),
4.72 (s, 1H), 1.57 (s, 3H); 13C NMR (75 MHz, CDCl3) δ 153.3 (s),
134.3 (s), 133.9 (s), 132.2 (s), 132.0 (s), 129.1 (d), 129.0 (d), 128.9
(d), 128.4 (d), 128.3 (d), 126.6 (d), 126.3 (d), 125.7 (d), 125.6 (d),
124.7 (d), 115.0 (d), 89.1 (s), 78.5 (s), 4.1 (q); MS (EI) m/z 258
(100%, M+), 241, 231, 226, 213, 202, 189, 119, 113, 106, 101.
Anal. Calcd for C19H14O: C, 88.34; H, 5.46. Found: C, 88.22; H,
5.61.
Acknowledgment. The synthetic part and the purchase/
service of the X-ray diffractometers in Prague and Pardubice
were supported by the Ministry of Education, Youth and Sport
of the Czech Republic (Grant Nos. LC06070, MSM0021620857,
and VZ0021627501, respectively). The LC-NMR experiments
were supported by the Czech Science Foundation (Grant No.
203/06/0738). All the financial support is gratefully acknowledged.
2-(Naphthalen-1-yl)-3-(propyn-1-yl)phenyl trifluoromethane-
sulfonate (5): n-Butyllithium (2.5 M in hexanes, 6.8 mL, 17.0
mmol, 1.1 equiv) was added dropwise to phenol 4 (4.0 g, 15.5
mmol) in THF (80 mL) under an atmosphere of argon, and the
mixture was stirred at -78 °C for 10 min. Triflic anhydride (6.0
mL, 35.7 mmol, 2.3 equiv) was added dropwise, and the reaction
mixture was stirred at -78 °C for 20 min. To prevent decomposition
of the product, triethylamine (3.2 mL, 23.0 mmol, 1.5 equiv) was
added, and the reaction mixture was allowed to reach rt. The
solvents were removed in vacuo, and the residue was chromato-
graphed on silica gel (hexane/acetone, 4:1) to obtain triflate 5 (4.5
Supporting Information Available: Experimental proce-
dures and spectroscopic details for compounds 1b, 2a, 2b, 3a,
1
6, 8a; and a copy of H NMR spectra for all compounds; and
X-ray diffraction data for 7a, 7b, and 8b. This material is
available free of charge via the Internet at http://pubs.acs.org.
1
g, 75%) as an oil: H NMR (300 MHz, CDCl3) δ 7.95-7.88 (m,
2H), 7.61-7.34 (m, 8H), 1.59 (s, 3H); 13C NMR (75 MHz, CDCl3)
δ 148.0 (s), 136.4 (s), 133.6 (s), 132.4 (d), 131.9 (s), 131.8 (s),
JO900077J
J. Org. Chem. Vol. 74, No. 8, 2009 3093