Improved synthesis of 1,5-dinaphtho[38]crown-10

Article abstract of DOI:10.1016/j.tetlet.2009.12.060

We have devised a method of achieving the much-used macrocyclic polyether, 1,5-dinaphtho[38]crown-10, in three steps by a route that is more efficient and requires fewer purification procedures than those reported in the literature to date. The strategy c

Full text of DOI:10.1016/j.tetlet.2009.12.060

Tetrahedron Letters 51 (2010) 983–986
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Tetrahedron Letters
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Improved synthesis of 1,5-dinaphtho[38]crown-10
*
Carson J. Bruns, Subhadeep Basu, J. Fraser Stoddart
Northwestern University, Department of Chemistry, 2145 Sheridan Road, Evanston, IL 60208, USA
a r t i c l e i n f o
a b s t r a c t
Article history:
We have devised a method of achieving the much-used macrocyclic polyether, 1,5-dinaphtho[38]-
crown-10, in three steps by a route that is more efficient and requires fewer purification procedures than
those reported in the literature to date. The strategy can also be extended to the synthesis of asymmetric
crown-10 ether derivatives with one 1,5-dinaphtho ring system.
Received 26 October 2009
Revised 5 December 2009
Accepted 11 December 2009
Available online 16 December 2009
Ó 2009 Elsevier Ltd. All rights reserved.
Keywords:
Crown ethers
Macrocyclic polyethers
Mechanically interlocked molecules
Templates
Over 40 years ago, Pedersen’s groundbreaking discovery1 of the
crown ethers opened up an entirely new field of research called
host–guest chemistry by Cram2 and supramolecular chemistry by
Lehn.3 The observation that these crown ethers can act as ligands
for the complexation of metal (Groups Ia and IIa in particular)
and organic cations have inspired the investigation of a lot of
molecular recognition processes4 and self-assembly phenomena.5
DN38C10 were less than ideal for our purposes, we were prompted
to develop a new synthetic route for the preparation of this com-
pound, which is reported herein.
The three methods for the preparation of DN38C10 that are cur-
rently reported in the literature are characterized by the number of
steps detailed in Scheme 1. The first method reported9a in 1987 is a
four-step one (Method 1) involving the monobenzylation of 1,5-
dihydroxynaphthalene (DHNP) to afford 5-(benzyloxy)naphtha-
lene-1-ol (MBNP), followed by reaction with tetraethylene glycol
bistosylate (BTTEG) and a subsequent deprotection (catalytic
hydrogenolysis) before performing a ring closure with BTTEG. In
1998, Sanders and co-workers9b reported a protocol (Method 2)
which avoided the use of protecting groups by simply reacting
DHNP with a large excess of BTTEG to form 1,5-bis[2-[2-[2-(2-
hydroxyethoxy)ethoxy]ethoxy]ethoxy]naphthalene bis(4-methyl-
benzenesulfonate) (BTEEEEN) which was subjected to ring closure
with DHNP. In the same year, we reported9c a single-step approach
(Method 3) using cesium ions to template the formation of
DN38C10 directly from DHNP and BTTEG. Methods 2 and 3 both
had isolated yields of 16% representing a considerable improve-
ment over the original synthesis with its overall yield of 4%.
While we have verified that these overall yields hold to a first
approximation, this criterion is not the only one to take into con-
sideration in evaluating a synthetic strategy. Taking into consider-
ation other criteria, all three methods (Methods 1–3 in Scheme 1)
come with significant limitations. While Method 1 is tedious and
very low yielding, Methods 2 and 3 come at a price because of chal-
lenging purification steps. Method 2 requires the use of hot petro-
leum ether in order to achieve a reasonable chromatographic
separation of BTTEG from BTEEEEN in the first steps of the synthe-
sis. In our hands, BTEEEEN could not be isolated in yields in excess
of 40% without resorting to the inconvenience and danger of using
The ability of crown ethers containing fused (
p-electron rich) aro-
matic rings to act6 as receptors for
p-electron deficient substrates,
for example, Paraquat and Diquat, has led to the development of
templation7 as an efficient means to synthesize mechanically
interlocked molecules (MIMs) such as catenanes and rotaxanes.8
Of all the aromatic crown ethers employed as templates in the syn-
thesis of MIMs, 1,5-dinaphtho[38]crown-10 (DN38C10) is amongst
the most popular ones9 because of (i) the
p-electron-donating
characteristics10 of the 1,5-dioxynaphthalene (DNP) units and (ii)
the ability of these units in appropriate settings in catenanes to
support planar chirality.11
DN38C10 has already appeared as a compound in almost 100
different publications in the chemical literature. One reason it
has been employed in the synthesis of MIMs is its ability to act
as an efficient template for the assembly of a range of
p-electron
deficient cyclophanes,12 and at the same time, have its DNP units
express their dynamic chirality in the catenated products.11 The
DNP units can also participate in the functioning of bistable
MIMs13 as a recognition site. It is for all these reasons and more
that DN38C10 is going to remain a key synthon when it comes to
the chemistry of MIMs and other supramolecular precursors and
analogues. Since all the current methods for the synthesis of
* Corresponding author. Tel.: +1 847 491 3793; fax: +1 847 491 1009.
E-mail address: stoddart@northwestern.edu (J. Fraser Stoddart).
0040-4039/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2009.12.060

984
C. J. Bruns et al. / Tetrahedron Letters 51 (2010) 983–986
O
O
O
O
O
O
O
O
O
OH
OH
O
O
BnBr
K2CO3
OTs
TsO
OTs
TsO
K2CO3
NaH
DMF
70 ºC / 12 h
DMF
RT / 18 h
Me2CO
Δ / 2 d
OH
OBn
OBn
OBn
63%
81%
21%
MBNP
BBNPTEG
DHNP
O
O
O
H2
Pd/C
OTs
TsO
Cs2CO3
CsOTs
80 ºC / 7 d
DMF
MeOH / CHCl3
70 ºC / 12 h
Method 2 / 1998
Method 3 / 1998
Method 1 / 1987
~100%
16%
OH
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
OTs
O
O
O
OH
K2CO3
OTs
TsO
NaH
THF
Δ / 5 d
Me2CO
Δ / 2 d
O
OTs
OH
OH
26%
30%
O
O
O
BHNPTEG
O
O
DN38C10
Scheme 1. Different methods employed to date in the synthesis of DN38C10.
BTEEEEN
hot petroleum ether as the eluant in accordance with the recom-
mendation in the literature.9b Method 3 also calls for a long reac-
tion time and an equally challenging separation of DN38C10
from higher and lower cyclic and acyclic oligomers using flash col-
umn chromatography (FCC) as well as the troublesome require-
ment to remove large volumes of N,N-dimethylformamide (DMF)
during the workup.
We now report (Scheme 2) another alternative method (Method
4) for the preparation of DN38C10. Not only does it offer an
improvement over all the other previous methods (Methods 1–3)
in terms of overall yield (28%), but it also offers the advantage of
being much easier to perform from start to finish than the other
three methods. It strikes a good balance between the painstaking
purification steps required in Methods 2 and 3, and the tedious
low-yielding steps that characterize Method 1. Each step in the
new synthesis will now be discussed critically.
O
Methods 1, 2, 3
Purification required
Method 4
O
O
OH
OH
TEG
No purification required
TsCl (xs)
NaOH
TsCl (xs TEG)
NaOH
THF / H2O
THF / H2O
96%
O
90%
O
O
O
O
O
OH
TsO
OTs
TsO
MTTEG
BTTEG
Scheme 3. Tosylation of TEG.
Firstly, the tosylation (Scheme 3) of tetraethylene glycol (TEG)—
a step which is ‘hidden’ in all four methods—works in favor of
Method 4. It is the only one to utilize tetraethylene glycol mono-
tosylate (MTTEG) in the glycolation of the dinaphthol, that is,
DHNP. Although the yields are comparable, the preparation14 of
MTTEG in high purity is less demanding than that of BTTEG15 sim-
ply because the production of pure BTTEG requires FCC in order to
separate the excess of tosyl chloride and/or MTTEG. By contrast,
the isolation of pure MTTEG using an excess of TEG proceeds with
an aqueous workup in 90% yield without the need for any further
purification.
O
O
O
O
O
OH
O
O
O
OH
O
OH
TsO
K2CO3 / LiBr
MeCN
Δ / 24 h
OH
OH
94%
O
DHNP
O
The first step in the new synthesis is the glycolation of DHNP
with exactly 2.0 equiv of MTTEG in MeCN containing sub-stoichi-
ometric amounts of LiBr. We have found that filtration of the crude
reaction mixture, followed by careful workup using a brine/10%
NaOH solution (3:1) affords (94% yield) BHEEEEN of sufficient pur-
ity to be employed in the next step and with an efficiency that has
already been reported in the literature.16
The second step in Method 4 is the tosylation of BHEEEEN in
THF/H2O with NaOH as base to give BTEEEEN. If 2.2 equiv of tosyl
chloride are used then this step can also be performed without
purification by chromatography to obtain a product that is suffi-
ciently pure to be able to continue on to the next step. Again we
followed the literature procedure reported16 for this reaction, the
only minor difference being that the product was filtered as a
solution in CH2Cl2 through a plug of silica. If a sample of high pur-
ity is required, then FCC on the crude product is a facile procedure
BHEEEEN
TsCl
NaOH
Method 4 / 2009
H2O / THF
0ºC
4 h
92%
RT
OH
O
O
O
O
O
O
O
O
O
O
OTs
O
O
OH
K2CO3
Me2CO
Δ / 70 h
OTs
O
33%
O
O
O
O
O
DN38C10
BTEEEEN
Scheme 2. New synthesis of DN38C10 in three steps.

C. J. Bruns et al. / Tetrahedron Letters 51 (2010) 983–986
985
compared to the purification of the same compound after the first
Acknowledgment
step in Method 2. In this case, the impurities are much easier to
separate using FCC (SiO2, EtOAc/hexanes), which avoids the incon-
venience and danger of using a heated solvent as the eluant.
The final ring-closing step17 is similar to that of Method 2, the
only modifications being a slow addition of reactants by syringe
pump injection and the precipitation of the final product from
CH2Cl2/MeOH. We found that injecting BTEEEEN and DHNP over
the course of 48 h improved the yield by 7% in comparison with
the reported yield in the literature,9b affording DN38C10 in an
overall yield of 28%. In summary, we have found this three-step
method (Method 4) for the synthesis of DN38C10 to be the most
facile, practical, and high-yielding route to DN38C10. Method 4
exemplifies that subtle differences in synthetic protocol can corre-
spond to relatively large differences in overall yield and difficulty.
A comparison between the four methods is drawn in Table 1.
Method 4—the new proposed method—has an added advantage
that is only shared with Method 2: it is that constitutionally asym-
metric crown ethers can be prepared in a modular fashion from the
penultimate product, namely BTEEEEN. Indeed, it is surprising that
Method 4 has not been described already in the literature since it is
replete with examples12b,18 of other crown-10 ethers synthesized
from BTEEEEN. We have also assessed the use of Method 4 in the
preparation of asymmetric crown ethers by carrying out a ring-
closing reaction (Scheme 4) between methyl 3,5-dihydroxybenzo-
ate and BTEEEEN. We found that DN35C10-CO2Me is formed in 46%
yield, an 11% improvement over the literature reports.18d,19 This
crown ether could be modified to be employed in procedures to
immobilize, polymerize, and coordinate MIMs to metals.
This material is based upon work supported by the National Sci-
ence Foundation under CHE-0924620.
References and notes
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In conclusion, we have developed a straightforward three-step
procedure to make 1,5-dinaphtho[38]crown-10 which requires
purification only in the final step of the reaction sequence. The
purification-free route to BTEEEEN, combined with the slow injec-
tion ring-closure procedure gives the new method of synthesis a
unique advantage when it comes to preparing asymmetric
crown-10 ethers in better yields than those previously reported
in the literature. Given the status of 1,5-dinaphtho[38]crown-10
and its analogues, preparing them easier and faster means that
applications of MIMs can be brought into sharper focus.
11. (a) Tseng, H.-R.; Vignon, S. A.; Celestre, P. C.; Stoddart, J. F.; White, A. J. P.;
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Table 1
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Stoddart, J. F.; Venturi, M.; White, A. J. P.; Williams, D. J. J. Am. Chem. Soc. 1995,
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9591–9595; (d) Hamilton, D. G.; Sanders, J. K. M.; Davies, J. E.; Clegg, W.; Teat,
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5215.
Comparison between literature methods (Methods 1–3) and Method 4 by number of
steps, overall yield, FCC purifications, and reaction time
Method
Stepsa
Yieldb (%)
FCCc
Timed (days)
1
2
3
4
4
2
1
3
4
16
16
28
4
3
2
1
5
4
7
4
a
b
c
Number of steps from DHNP as starting material.
Total yield over the number of steps in column two (Steps).
Number of purifications by FCC including tosylation in Scheme 3.
Total reaction time (workups and purifications not considered).
d
HO
O
O
O
O
O
O
O
O
O
O
O
OTs
O
O
OMe
O
HO
O
K2CO3
Me2CO
Δ / 3 d
OMe
O
OTs
15. Ouchi, M.; Inoue, Y.; Liu, Y.; Nagamune, S.; Nakamura, S.; Wada, K.; Hakushi, T.
Bull. Chem. Soc. Jpn. 1990, 63, 1260–1262.
46%
O
O
O
O
16. Ashton, P. R.; Huff, J.; Menzer, S.; Parsons, I. W.; Preece, J. A.; Stoddart, J. F.;
Tolley, M. S.; White, A. J. P.; Williams, D. Chem.-Eur. J. 1996, 2, 31–44.
17. A typical ring-closing procedure is described. DHNP (160 mg, 1.0 mmol) and
BTEEEEN (820 mg, 1.0 mmol) were dissolved in Me2CO (40 mL) and injected
into a suspension of K2CO3 (7 g, 51 mmol) in Me2CO (200 mL) under reflux at a
DN35C10-CO2Me
functionalized asymmetric crown-10 ether from
BTEEEEN
Scheme 4. Synthesis of
a
BTEEEEN.

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C. J. Bruns et al. / Tetrahedron Letters 51 (2010) 983–986
rate of 0.8 ml/h and the reaction proceeded for 70 h. The reaction mixture was
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N.; Spencer, N.; Quick, A.; Stoddart, J. F.; Tolley, M. S.; White, A. J. P.; Williams,
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cooled to ambient temperature, filtered, and washed with CHCl3 (50 mL). The
solvent was evaporated from the filtrate and the residue was partitioned
between H2O (100 mL) and CHCl3 (100 mL). The organic layer was separated
and the aqueous layer was extracted with CHCl3 (2 Â 75 mL). The organic
extracts were combined and the solvent was evaporated to afford a brown oil,
which was purified by FCC (SiO2, Et2O/CHCl3/MeOH 69:30:1). All fractions
containing the product were concentrated and precipitated from CH2Cl2/MeOH
(1:6) to afford DN38C10 as a white powder. (210 mg, 33%) 1H NMR (500 MHz,
CDCl3, 298 K): d 7.79 (d, 4H, J = 8 Hz), 7.19 (t, 4H, J = 8 Hz), 6.50 (d, 4H, J = 8 Hz),
4.06 (m, 8H), 3.93 (m, 8H), 3.78 (m, 8H), 3.75 (m, 8H); 13C NMR (125 MHz,
CDCl3, 298 K): d 154.1, 126.6, 125.0, 114.4, 105.4, 70.9, 69.7, 67.7; HRMS (APPI-
TOF-MS): m/z calcd for C36H45O10 [M+H]+: 637.3007; found: 637.3012.
19. The compound was purified by FCC (SiO2, EtOAc) and the 1H NMR spectrum
was in agreement with that published in: Menzer, S.; White, A. J. P.; Williams,
ˇ
´
18. (a) Neumann, B.; Joachimi, D.; Tschierske, C. Adv. Mater. 1997, 9, 241–244; (b)
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