Functionalized heptahelicene bidentate ligands and chiral building blocks

Article abstract of DOI:10.1055/s-2005-872666

Syntheses of functionalized heptahelicenes 11-13 disubstituted at positions 3 and 16 by hydroxymethyl or bromomethyl functions are described as a new series of bidentate ligands or chiral building blocks. Those functions are flexible enough and properly p

Full text of DOI:10.1055/s-2005-872666

LETTER
2337
Functionalized Heptahelicene Bidentate Ligands and Chiral Building Blocks
Functionalized
H
epta
h
a
elicene Bid
r
entate
L
c
igands Gingras,*1 Christine Collet1
Chemical Laboratory of Organic and Inorganic Materials (CMOM), Faculty of Sciences, University of Nice-Sophia Antipolis,
28 Av. Valrose, 06700 Nice Cedex 2, France
Fax +33(4)92076578; E-mail: gingras@unice.fr
Received 12 June 2005
In spite of some efforts and modest results in asymmetric
Abstract: Syntheses of functionalized heptahelicenes 11–13 disub-
catalysis, numerous applications and improvements are
stituted at positions 3 and 16 by hydroxymethyl or bromomethyl
still sought in helicene chemistry. The heptahelicene se-
ries was particularly neglected, with only a few [7]carbo-
functions are described as a new series of bidentate ligands or chiral
building blocks. Those functions are flexible enough and properly
positioned for a possible chelate effect onto a metal center. Photo- helicenes synthesized, but none of them as bidentate
ligand.8 As a consequence, our objective was to disclose
cyclodehydrogenation, phase-transfer-catalyzed Wittig reaction,
and use of THP groups for increasing solubility and further func-
the first synthesis of functionalized heptahelicenes as bi-
tional group transformations were key elements in this synthetic
dentate ligands and to describe new helicoidal chiral inter-
route.
mediates. Several reasons guided us toward those targets:
a) in spite of early results as excellent chiral auxiliaries
Key words: arenes, chirality, helical structures, chelates, supramo-
lecular chemistry
two decades ago, heptahelicenes were not put forward
again in asymmetric synthesis until lately;9 b) high optical
rotation values ([a]D 25 +6200 for heptahelicene)10 would
The first carbohelicene, namely pentahelicene, was pre-
allow a better precision in evaluating enantio- and diaste-
pared in 1918.2 However, it took almost 20 and 30 years,
reopurities; c) good p-donor abilities helped in resolving
respectively, to report hexahelicene3 and heptahelicene4
hexahelicene with chiral TAPA3b; it was indicative that p-
(Figure 1). The first photocyclodehydrogenation reaction
stacking could serve as a key binding element for pre-as-
of stilbene-like derivatives leading to heptahelicene was
sembling aromatic substrates and catalysts prior to asym-
shown in 1967 but one of us also reported a non-photo-
metric reactions; d) because of distorded p-systems, the
chemical method in 1999.4b Helicenes are not only aes-
solubility of such compounds are usually better than their
thetic and intriguing helicoidal polyaromatics, often
polyaromatic linear analogues (e.g. pentacene); e) hepta-
studied in theoretical chemistry because of their distorted
helicenes could be used at relatively high temperatures
(<150 °C, DDH≠rac = 40.5 kcal/mol11) because of good ste-
reochemical stability, compared to some binaphthyl coun-
terparts; f) their helicoidal nature could serve as a large
chiral template for helicoidal recognition, chiral induction
and molecular assemblies in supramolecular chemistry
and advanced materials.
p-system, but they became the centerfold of newly ex-
panding research in the fields of asymmetric catalysis,5
advanced materials,6 molecular electronics (dendrimers,
conductors, polymers, liquid crystals, molecular mono-
layers and films, etc.), optics (OLED, chiroptical switch-
es, NLO, etc.) and supramolecular helicoidal chemistry.7
As shown in Scheme 1, a preliminary study in the synthe-
sis of functionalized heptahelicenes was achieved. After
molecular modeling experiments (MM2 calculations), it
appeared to us that a direct connection of a coordinating
heteroatom ligand (O, N, P, etc.) to the terminal benzene
rings, would not lead to a favorable geometry for a strong
chelate effect on a metal center. Previous experiments in
the hexahelicene series did not also lead to the best results
using this approach. The use of benzylic-type functions at
positions 3 and 16 would give enough degree of freedom
to help in the adjustment of the ligand onto a metal center,
as shown in Figure 2. Molecular mechanic calculations of
11 showed an approximative O–O distance of 3.9 Å,
which was indicative of a possible chelate arrangement on
a metal center. The closest distance between carbon atoms
of terminal phenyl rings was about 3.5 Å, indicating a dis-
torted and weak p-stacking.
pentahelicene
hexahelicene
heptahelicene
chelating
substituents
extended
π-stacking
functional or anchoring
substituent (solubilization
in H2O, solid support, etc.)
functionalized heptahelicene
Figure 1
Penta-, hexa- and heptahelicene. Strategic design of
heptahelicene bidentate ligands and building blocks.
As shown in the next paragraphs, short syntheses of 3,16-
and 3,9,16-substituted heptahelicenes are presented.
Starting from 2,6-naphthalene dicarboxylic acid (4), a
SYNLETT 2005, No. 15, pp 2337–2341
Advanced online publication: 07.09.2005
DOI: 10.1055/s-2005-872666; Art ID: G16205ST
© Georg Thieme Verlag Stuttgart · New York
1
9
.0
9
.2
0
0
5

2338
M. Gingras, C. Collet
LETTER
O
CO2R
a) BH3·THF (R = H, 77%)
THF, reflux
CH2OTHP
CH2OH
RO2C
or
TosOH cat., 25 °C
DMF–CH2Cl2
7
HOH2C
HOH2C
b) Red-Al (R = Me, 77%)
toluene, 25 °C
4 a) R = H
5 b) R = Me
6
48%
MnO2 , PhH
(possible recycling)
reflux
81%
CH2OTHP
OTHP
OTHP
PhH
I2, hν, 25 °C
Br
CH2Cl2/H2O
OTHP
H
O
8
NaOH, 25 °C
84%
O
OTHP
Br
Ph3P
Br
+
65%
9
10 racemic
Br
Br
PPh3
3
Scheme 1 Simple and efficient preparation of functionalized heptahelicene by photocyclodehydrogenation.
nucleophilic reaction. A double Wittig reaction generated
the bis(stilbene)-type derivative 914 in a 84% yield under
phase-transfer conditions in an aqueous mixture. The
‘bromine auxiliary’ strategy15 was used for a better regio-
selectivity and reactivity in the photocyclodehydro-
genation reaction, but more interestingly, it also allowed
anchoring groups for further chemical manipulations
(Figure 1, such as an attachment to a solid support for het-
erogeneous enantiocatalysis or for introducing solubiliz-
ing groups in aqueous conditions). Compound 9 showed a
Figure 2 MM2-calculated structure of 11.
reduction with BH3·THF (or generation in situ from greenish fluorescent aspect in solution. The use of THP
NaBH4 and BF3·OEt2) produced the corresponding 2,6- protecting groups helped in two ways: to improve solubil-
bis(hydroxymethyl) naphthalene (6)12 in a 77% yield on a ity of this intermediate before a double photocyclization
multiple gram scale. By analogy, 2,6-bis(carbomethoxy) and to prevent some adventitious side reactions. Concern-
naphthalene (5) was easily reduced to the same diol in a ing the key-step photochemical reaction, we used an ep-
82% yield (or 78% yield, 50 g scale) by using Red-Al® in oxide to trap the acid formed, and iodine to ensure the
toluene at room temperature for 30 minutes. A mono-se- oxidative aromatization.6m Doubly protected and bromi-
lective THP protection of the diol was achieved with di- nated heptahelicene 1016 was thus produced as a yellow
hydropyran (0.5 equiv). In order to dissolve the substrate, solid in a 65% yield.
a DMF–CH2Cl2 (3:2 v/v) solution was needed for better
homogeneity at 20 °C. In the best case, a yield of 48% of
Ph3P
Br
Br
7 was obtained along with unreacted diol 6 and di-THP
by-product. A trituration in chloroform allowed the isola-
tion of insoluble diol 6 after filtration. Mono- and di-THP
derivatives could easily be separated on silica gel
(CH2Cl2–EtOAc, 80:20). Acidic methanolysis of the di-
THP product provided diol 6 which could be combined to
the first crop and recycled toward a mono-protection.
Mono-protected diol 7 could be oxidized with activated
MnO2 in refluxing benzene for three hours. After filtration
on silica gel, the corresponding aldehyde 813 was pro-
duced on a gram scale as a sufficiently pure product (81%
yield) for a double Wittig reaction with reagent 3
(Scheme 2). The latter was easily prepared on a large
scale from a double benzylic bromination of 1-bromo-2,5-
dimethylbenzene with NBS,8m followed by triphe-
nylphosphine in refluxing DMF; the bis(triphenylphos-
phonium) salt 3 being smoothly produced by a double
Ph3P
NBS
DMF,
reflux
(PhCO2)2
CCl4, reflux
Br
Br
Br
Br
PPh3
Br
1
2
3
Scheme 2 Preparation of bisphosphonium salt 3.
Debromination of 10 was achieved by treatment with n-
BuLi in THF at –78 °C, followed by quenching with H2O.
It provided a protected C2-symmetric bifunctionalized
chiral building block 12. The choice and importance of
THP in ensuring an adequate solubilization at low temper-
ature played a major role in the polyarene anion formation
through a bromine–lithium exchange reaction.
Synlett 2005, No. 15, 2337–2341 © Thieme Stuttgart · New York

LETTER
Functionalized Heptahelicene Bidentate Ligands
2339
An acid-catalyzed ethanolic deprotection of 10 generated
9-bromo-3,16-bis(hydroxymethyl) heptahelicene 1117 in a
78% yield. This deprotection produced an interesting
functionalized diol, which could eventually be tested for
complexation with a metal center (Scheme 3).
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Br
12
THF, –78 °C
10
racemic
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Br
Br
Ph3PBr2
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CH2Cl2, 24 h,
80%
13
Br
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(i) Nuckolls, C.; Katz, T. J.; Katz, G.; Collings, P. J.;
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Scheme 3 Synthesis of functionalized heptahelicene chiral biden-
tate ligands and building blocks.
A straightforward functionalization through an activation
strategy leads us to convert both CH2O–THP groups into
benzylic bromide functions (CH2Br) as in 13. Triphe-
nylphosphine dibromide smoothly achieved that reaction
in a 80% yield, at room temperature for 24 hours. This
transformation set up possibilities for introducing various
metal-coordinating groups such as phosphine or amino
groups. Additionally, it also opened up new opportunities
for promoting C–C coupling reactions (Suzuki, Stille,
Neghishi, etc.) or carbon–heteroatom bond formations
(C–O, C–S, C–N, C–P, etc.). For instance, an Arbuzov re-
action with diphenylethoxyphosphine in refluxing tolu-
ene followed by a deoxygenative reduction with HSiCl3
might allow the formation of 3,16-bis(diphenylphosphi-
no) groups.
(j) Bender, T. P.; Qi, Y.; Gao, J. P.; Wang, Z. Y.
Macromolecules 1997, 30, 6001. (k) Fox, J. M.; Lin, D.;
Itagaki, Y.; Fujita, T. J. Org. Chem. 1998, 63, 2031. (l)Dai,
Y.; Katz, T. J. J. Org. Chem. 1997, 62, 1274. (m) Katz, T.
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E.; Robben, M. P.; Wuensch, M.; Ward, M. D. J. Am. Chem.
Soc. 1993, 115, 3182. (n) Gilbert, A. M.; Katz, T. J.; Geiger,
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1993, 115, 3199. (o) Katz, T. J.; Sudhakar, A.; Yang, B.;
Nowick, J. S. J. Macromol. Sci. Chem. A. 1989, 26, 309.
Molecular electronics, optics and switches: (p) Botek, E.;
Champagne, B.; Turki, M.; André, J.-M. J. Chem. Phys.
2004, 120, 2042. (q) Fox, J. M.; Katz, T. J.; Elshocht, S. V.;
Verbiest, T.; Kauranen, M.; Persoons, A.; Thongpanchang,
T.; Krauss, T.; Brus, L. J. Am. Chem. Soc. 1999, 121, 3453.
(r) Beljonne, D.; Kauranen, M.; Zhuai, Z.; Verbiest, T.;
Persoons, A.; Bredas, J. L. Polym. Prepr., Am. Chem. Soc.
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2001, 40, 3251. (u) Nuckolls, C.; Shao, R.; Jang, W.-G.;
Clark, N. A.; Walba, D. M.; Katz, T. J. Chem. Mater. 2002,
14, 773.
In summary, new functionalized heptahelicenes were pro-
duced in a synthetic sequence involving gram-scale prep-
aration of intermediates. They represent the first chiral
bidentate ligands in the heptahelicene series, after careful
positioning of coordinating substituents. Among the men-
tioned properties are possible p-stacking with aromatic
substrates, a large chiral template, use as a building block
for inducing chirality in supramolecular assemblies and
use in the preparation of new helicoidal colored materials.
Acknowledgment
The authors are indebted to the French Ministry of Research and ge-
nerous funding from FIRST program no 9613357 from the Ministry
of the Walloon Region (Belgium) for scientific training and techno-
logy in a collaboration with Lilly Research Center (Belgium). We
also acknowledge Dr. Carol Dallaire for helpful discussions.
(7) (a) Urbaño, A. Angew. Chem. Int. Ed. 2003, 42, 3986.
(b) Katz, T. J. Angew. Chem. Int. Ed. 2000, 39, 1921.
(c) Murguly, E.; McDonald, R.; Branda, N. R. Org. Lett.
2000, 2, 3169.
Synlett 2005, No. 15, 2337–2341 © Thieme Stuttgart · New York

2340
M. Gingras, C. Collet
LETTER
(8) Heptahelicenes, excluding heterohelicenes: (a) Carreño, M.
C.; González-López, M.; Urbano, A. Chem. Commun. 2005,
5, 611. (b) El Abed, R.; Ben Hassine, B.; Genêt, J.-P.;
Gorsane, M.; Marinetti, A. Eur. J. Org. Chem. 2004, 1517.
(c) Wang, D. Z.; Katz, T. J.; Golen, J.; Rheingold, A. L. J.
Org. Chem. 2004, 69, 7769. (d) Peña, D.; Cobas, A.; Pérez,
D.; Guitián, E.; Castedo, L. Org. Lett. 2003, 5, 1863.
(e) Paruch, K.; Vyklicky, L.; Wang, D. Z.; Katz, T. J.;
Incarvito, C.; Zakharov, L.; Rheingold, A. L. J. Org. Chem.
2003, 68, 8539. (f) Teplý, F.; Stará, I. G.; Starý, I.;
139.7 (C arom.), 192.0 (CHO). MS (EI, 70 eV): m/z
(%) = 270 (4.6) [M+], 186 (8.5) [M+ – C5H8O], 169 (100)
[M+ – OTHP], 141 (35) [M+ – CHO – OTHP]. Rf = 0.63
(TLC, SiO2, CH2Cl2–EtOAc, 95:5).
(14) Synthesis of Bis(stilbene) 9.
At 20 °C, aldehyde 8 (2.658 g, 9.84 mmol) was dissolved in
CH2Cl2 (50 mL), followed by addition of phosphonium salt
3 (4.266 g, 4.92 mmol) and an aq solution of 5 M KOH (50
mL). After vigorous stirring for 15 h, the organic layer was
separated and dried over anhyd MgSO4. After filtration and
evaporation of the solvent, the expected bis(stilbene) was
purified on a SiO2 flash chromatography column using
CH2Cl2–MeOH (98:2) as eluent. Bis(stilbene) (9) was
obtained as a solid (isomeric mixture, 2.85g. 4.13 mmol,
84% yield). 1H NMR (250 MHz, CDCl2CDCl2, isomeric
mixture): d = 1.40–2.00 (m, 12 H, CH2), 3.40–3.60 (m, 2 H,
CH2–O), 3.85–4.00 (m, 2 H, CH2–O), 4.50–4.75 (m, 4 H,
naphthyl-CH2, O–CH–O), 4.85–5.00 (m, 2 H,), 6.90–7.30
(m, 2 H, CH=CH), 7.40–8.00 (m, 16 H, H arom.), 8.26 (s, 1
H, H arom. CH=CBr). 13C NMR (62.9 MHz, CDCl2CDCl2,
isomeric mixture): d = 19.4 (CH2), 25.4 (CH2), 30.6 (CH2),
62.2 (CH2–O), 68.7 (CH2–O), 97.9 (O–CH–O), 123.0 (CH
arom.), 123.70–139.83 (multiple signals from an isomeric
mixture). MS (EI, 70 eV): m/z (%) = 690 (3.4) [M+ (81Br)],
688 (3.2) [M+ (79Br)], 606 (13) [M+ (81Br) – C5H8O], 604
(14) [M+ (79Br) – C5H8O], 522 (88) [M+ (81Br) – C10H16O2],
520 (100) [M+ (79Br) – C10H16O2]. HRMS (EI, 70 eV): m/z
(%) = 690.2193 [M+ (81Br), exp.; 690.2168 calcd], 688.2192
[M+ (79Br), exp.; 688.2188 calcd], 522.1004 [M+ (81Br) –
C10H16O2, exp.; 522.1017 calcd], 520.0999 [M+ (79Br) –
C10H16O2, exp.; 520.1038 calcd].
Kollárovič, A.; Šaman, D.; Ruliček, L.; Fiedler, P. J. Am.
Chem. Soc. 2002, 124, 9175. (g) Paruch, K.; Katz, T. J.;
Incarvito, C.; Lam, K.-C.; Rhatigan, B.; Rheingold, A. L. J.
Org. Chem. 2000, 65, 7602. (h) Dreher, S.; Paruch, K.;
Katz, T. J. J. Org. Chem. 2000, 65, 806. (i) Fox, J. M.;
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63, 7456. (j) Howarth, J.; Finnegan, J. Synth. Commun.
1997, 27, 3663. (k) Liberko, C. A.; Miller, L. L.; Katz, T. J.;
Liu, L. J. Am. Chem. Soc. 1993, 115, 2478. (l) Yang, B.;
Liu, L.; Katz, T. J.; Liberko, C. A.; Miller, L. L. J. Am.
Chem. Soc. 1991, 113, 8993. (m) Sudharkar, A.; Katz, T. J.
Tetrahedron Lett. 1986, 27, 2231. (n) Van Meerssche, M.;
Declercq, J. P.; Soubrier-Payen, B. Bull. Soc. Chim. Belg.
1986, 95, 609. (o) Gorsane, M.; Defay, N.; Martin, R. H.
Bull. Soc. Chim. Belg. 1985, 94, 215. (p) Hewett
cyclization mentioned in: Martin, R. H. Angew. Chem., Int.
Ed. Engl. 1974, 13, 649. (q) Bernstein, W. J.; Calvin, M.;
Buchardt, O. J. Am. Chem. Soc. 1973, 95, 527. (r) Calvin,
M.; Buchardt, O. J. Am. Chem. Soc. 1972, 94, 494.
(9) Stoichiometric asymmetric reactions: (a) Ben Hassine, B.;
Gorsane, M.; Pecher, J.; Martin, R. H. Bull. Soc. Chim. Belg.
1987, 96, 801. (b) Hassine, B.; Gorsane, M.; Geerts-Evrard,
F.; Pecher, J.; Martin, R. H.; Castelet, D. Bull. Soc. Chim.
Belg. 1986, 95, 547. (c) Hassine, B.; Gorsane, M.; Pecher,
J.; Martin, R. H. Bull. Soc. Chim. Belg. 1986, 95, 557.
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Bull. Soc. Chim. Belg. 1985, 94, 597.
(15) (a) Ref. 8m. (b) Liu, L.; Katz, T. J. Tetrahedron Lett. 1991,
32, 6831.
(16) Photocyclodehydrogenation Procedure to 10.
In a photochemical reactor equipped with a water cooling
jacket and a stir bar, compound 9 (0.420 g, 0.609 mmol),
iodine (309 mg, 1.22 mmol) and 1,2-epoxybutane (8.0 mL)
were dissolved in high purity grade benzene (700 mL).
Nitrogen gas was bubbled through the solution within 30
min while stirring vigorously for removing oxygen prior to
irradiation with a high-pressure mercury lamp for 3 h. When
the reaction was complete, excess of iodine was reduced
with a 15% aqueous solution of Na2S2O3 (20 mL). The
aqueous phase was separated and the organic layer dried
over MgSO4. After filtration and evaporation of solvent, the
crude was purified by flash chromatography on silica gel
with CH2Cl2–EtOAc (98:2) and then (95:5). Helicene 10 was
obtained as a yellow solid (0.270 g, 0.393 mmol, 65% yield).
1H NMR (250 MHz, CDCl2CDCl2): d = 1.40–2.00 (m, 12 H,
CH2), 3.50 (m, 2 H, CH2–O), 3.85 (m, 2 H, CH2–O), 4.36 (d,
J = 12.4 Hz, 2 H, naphthyl-CH2), 4.52 (m, 4 H, O–CH–O,
naphthyl-CH2), 6.39 (d, J = 7.0 Hz, 1 H, H arom.), 6.42 (d,
J = 7.7 Hz, 1 H, H arom.), 6.98 (d, J = 7.3 Hz, 2 H, H arom.),
7.22 (s, 1 H, H arom.), 7.24 (s, 1 H, H arom), 7.70 (d, J = 8.8
Hz, 1 H, H arom.), 7.74 (d, J = 8.8 Hz, 1 H, H arom.), 7.40–
7.50 (m, 2 H, H arom.), 7.87 (d, J = 8.0 Hz, 1 H, H arom.),
7.92 (d, J = 8.0 Hz, 1 H, H arom.), 7.99 (d, J = 8.8 Hz, 1 H,
H arom.), 8.32 (s, 1 H, H arom. CH=CBr), 8.42 (d, J = 8.4
Hz, 1 H, H arom.). 13C NMR (62.9 MHz, CDCl2CDCl2,
DEPT): d = 19.3 (CH2), 25.5 (CH2), 30.6 (CH2), 62.0
(CH2O), 67.7 (CH2O), 96.9 (OCHO), 121.1 (C arom.), 123.7
(CH arom.), 123.9 (CH arom.), 124.0 (CH arom.), 124.3
(CH arom.), 124.6 (C arom.), 125.2 (CH arom.), 125.3 (CH
arom.), 125.4 (CH arom.), 125.6 (CH arom.), 125.9 (CH
arom.), 126.9 (C arom.), 127.4 (CH arom.), 127.6 (C arom.),
127.9 (CH arom.), 128.3 (CH arom.), 128.4 (C arom.), 128.6
(C arom.), 129.9 (CH arom.), 130.2 (C arom.), 130.8 (C
(10) Meurer, K. P.; Vögtle, F. Top. Curr. Chem. 1985, 127, 32;
and references therein.
(11) Racemization of heptahelicene was evaluated: DDG≠ = 41.7
kcal/mol. (a) Martin, R. H.; Marchant, M.-J. Tetrahedron
1974, 30, 347. (b) Janke, R. H.; Haufe, G.; Wurthwein, E.-
U.; Borkent, J. H. J. Am. Chem. Soc. 1996, 118, 6031.
(12) Among several preparations: Vanderwerf, W. D. US Pat.
3,288,823, 1966; Chem. Abstr. 1966, 37699.
(13) For similar derivatives: (a) Ackerley, N.; Brewster, A. G.;
Brown, G. R.; Clarke, D. S.; Foubister, A. J.; Griffin, S. J.;
Hudson, J. A.; Smithers, M. J.; Whittamore, P. R. O. J. Med.
Chem. 1995, 38, 1608. (b) 6-Tetrahydropyranyloxy-
methyl-2-naphthalene Carboxaldehyde (8).
Alcohol 7 (2.221 g, 8.16 mmol) was dissolved in distilled
benzene (35 mL) at 20 °C and MnO2 (3.60 g, 50.7 mmol)
was added to the solution. The resulting black suspension
was refluxed for 3 h. After filtration on a short column of
silica gel and evaporation of solvent, compound 8 was
recovered as a solid (1.789 g, 6.62 mmol, 81% yield). 1H
NMR (250 MHz, CDCl3): d = 1.50–2.00 (6 H, m, CH2),
3.50–3.65 (1 H, m, CH2O), 3.90–4.05 (1 H, m, CH2O), 4.70
(1 H, d, J = 12.8 Hz, naphthyl-CH2O), 4.77 (1 H, app t,
J = 3.3 Hz, O–CH–O), 4.98 (1 H, d, J = 12.8 Hz, naphthyl-
CH2O), 7.58 (1 H, dd, J = 1.5 Hz, 8.4 Hz, H arom.), 7.85–
8.00 (4 H, m, H arom.), 8.31 (1 H, s, H arom.), 10.14 (1 H,
s, CHO). 13C NMR (62.9 MHz, CDCl3): d = 19.4 (CH2), 25.5
(CH2), 30.6 (CH2), 62.2 (CH2–O), 68.6 (CH2–O), 98.1 (O–
CH–O), 123.1 (CH arom.), 126.2 (CH arom.), 126.9 (CH
arom.), 129.0 (CH arom.), 129.6 (CH arom.), 130.7 (C
arom.), 132.1 (C arom.), 134.1 (CH arom.), 136.5 (C arom.),
Synlett 2005, No. 15, 2337–2341 © Thieme Stuttgart · New York

LETTER
Functionalized Heptahelicene Bidentate Ligands
2341
arom.), 131.4 (C arom.), 131.5 (C arom.), 131.9 (C arom.),
Hz, 2 H, CH), 6.86 (dd, J = 2.2 Hz, J = 8.8 Hz, 2 H, CH),
7.34 (2 H, app. s, CH arom.), 7.61 (1 H, d, J = 8.0 Hz, CH),
7.64 (d, 1 H, J = 8.0 Hz, CH), 7.84 (d, 1 H, J = 8.9 Hz, CH),
7.88 (d, 1 H, J = 9.1 Hz, CH), 8.10 (s, 2 H, CH arom.), 8.18
(d, 1 H, J = 8.4 Hz, CH), 8.35 (d, 1 H, J = 8.4 Hz, CH), 8.57
(s, 1 H, CH arom.). 13C NMR (62.9 MHz, DMSO-d6,
DEPT): d = 62.4 (CH2OH), 120.3 (C), 122.6 (CH), 123.1
(CH), 123.5 (CH), 124.1 (C), 124.6 (CH), 125.4 (CH arom.),
125.6 (CH), 125.7 (CH), 126.5 (C), 127.5 (C), 127.7 (C),
127.9 (CH), 128.4 (CH), 128.7 (CH), 128.8 (CH), 129.4 (C),
129.9 (CH), 130.5 (C), 130.6 (C), 131.6 (C), 131.7 (C),
139.5 (C), 139.6 (C). MS (EI, 70 eV): m/z (%) = 518 (66)
[M+ (81Br)], 516 (100) [M+ (79Br)], 374 (60) [M+ – HBr –
CH2OH –CH2OH], 187 (51) [C30H14++]. Rf = 0.05 (TLC,
SiO2, CH2Cl2–EtOAc, 4:1).
135.1 (C arom.). MS (EI, 70 eV): m/z (%) = 686 (45) [M+
(81Br)], 684 (43) [M+ (79Br)], 602 (41) [M+ (81Br) – C5H8O],
600(39) [M+ (79Br) – C5H8O], 520 (25) [M+ (81Br) –
2OTHP], 518 (30) [M+ (79Br) – 2OTHP]. Rf = 0.42 (TLC,
SiO2, CH2Cl2–EtOAc, 98:2).
(17) 9-Bromo-3,16-bis(hydroxymethyl)heptahelicene (11).
Compound 10 (83.2 mg, 0.121 mmol) was added to EtOH
(25 mL) as a suspension at 20 °C, followed by p-toluene-
sulfonic acid hydrate as catalyst (5.0 mg, 0.0026 mmol).
After vigorous stirring for 15 h, the solvent was evaporated
and crude diol 11 was purified by flash chromatography on
SiO2 with CH2Cl2–EtOAc (80:20) and then pure EtOAc as
eluent. Pure diol 11 was obtained (50.1 mg, 0.097 mmol,
80% yield). 1H NMR (250 MHz, DMSO-d6): d = 4.35 (4 H,
CH2OH), 5.10 (2 H, large, OH), 6.36 (dd, J = 1.1 Hz, J = 8.8
Synlett 2005, No. 15, 2337–2341 © Thieme Stuttgart · New York