A high-yielding and convenient synthesis of rotaxane based on an ester forming capping methodology

Article abstract of DOI:10.1246/cl.2002.810

An efficient method for preparation of rotaxanes, involving hydrogen bonding guided self-assembly and diaryldiazoalkanes ester forming end-capping of pseudorotaxanes, is described. The end-capping reactions proceed under mild conditions and furnish the ex

Full text of DOI:10.1246/cl.2002.810

8
10
Chemistry Letters 2002
A High-Yielding and Convenient Synthesis of Rotaxane
Based On an Ester Forming Capping Methodology
ꢀ
y
Yuji Tokunaga, Suzuka Kakuchi, Koichiro Akasaka, Naoki Nishikawa, Youji Shimomura, Kimio Isa, and Toshihiro Seo
Department of Materials Science and Engineering, Faculty of Engineering, Fukui University, Bunkyo, Fukui 910-8507
y
Faculty of Education and Regional Studies, Fukui University, Bunkyo, Fukui 910-8507
(Received April 18, 2002; CL-020339)
An efficient method for preparation of rotaxanes, involving
hydrogen bonding guided self-assembly and diaryldiazoalkanes
ester forming end-capping of pseudorotaxanes, is described. The
end-capping reactions proceed under mild conditions and furnish
the expected rotaxanes in excellent yields.
Recently, the design and synthesis of rotaxanes has received
much attention because of the intriguing properties and unique
structures of these substances.1 An attractive synthetic approach
to the rotaxanes takes advantage of a self-assembly phenomena to
control formation of appropriate chemical bonds. A key
observation made in this area was that self-assembling pseudo-
rotaxanes are formed from secondary ammonium salts and crown
;2
Scheme 1.
4
f
1
ammonium salts. The H NMR spectrum of a 1 : 1 CDCl3/
À3
CD3CN solution, containing equimolar quantities (10 mol dm
)
of ammonium salt 3a and crown ether 4a, revealed the formation
of the expected pseudorotaxane (3.52, 4.54, 4.78, and 6.70 ppm,
Figure 1). The characteristic chemical shifts are consistent with
3
ethers. Subsequently, several techniques were developed for
rotaxane synthesis, which involved sequential threading and end-
4
capping of the pseudorotaxane skeleton. Numerous end-capping
methods have been investigated, including acylation of an
3
;5
those reported previously for similar complexes. The concen-
tration of each component in this mixture is readily determined
and these are used to calculate binding constants of
4
a
4b
4c
amine or alcohol function, 1,3-dipolar cycloaddition, Wittig
reaction, disulfide formation,4e and radical reaction. How-
4
d
4f
À3 À1
ꢁ
À3 À1 ꢁ
1
000 (mol dm
)
at 25 C and 2300 (mol dm
)
at 0 C.
These binding constants are in the range of those for association of
ever, in some cases the yields of these processes were
4
a,c,f
unacceptably low,
and in others the processes are restricted
3
dibenzylammonium salts with crown ethers. The agreement
to the synthesis of symmetric rotaxanes only.4e
between the chemical shifts and binding constants of pseudo-
rotaxanes, formed from ammonium salt 3a and from dibenzyl-
ammonium salts, shows that the carboxylic acid group does not
interfere with the hydrogen bonding interactions.
Recent investigations in our laboratories have led to the
development of an efficient and versatile method for the synthesis
of rotaxanes. Self-assembling pseudorotaxane formation is
controlled by weak intermolecular interactions between the
ammonium salt thread and crown ether. It is important that these
interactions be maintained under the conditions used for the
capping process. The new capping methodology, uncovered in
our studies, employs diaryldiazomethane esterification of a
terminal carboxylic acid residue in the ammonium salt thread of
a pseudorotaxane. The effectiveness of new technique is related to
the high yields, mild conditions and functional group compat-
ibility normally associated with diazoalkane esterification
reactions.
The synthesis of the requisite ammonium salts 3 used in this
procedure begins with condensation of primary benzylamines 1
and ester-aldehydes 2 to generate the corresponding imines
(
Scheme 1). Reduction of the imines, followed by ester hydrolysis
and salt formation then produces the ammonium salts 3, which
possess bulky aryl groups on one end and carboxylic acid groups
at the other.
NMR monitored titrations were performed to demonstrate
that pseudorotaxanes are formed by interaction of the ammonium
salts with crown ethers. These experiments showed that
complementary hydrogen bonding between the crown ether
oxygens and ammonium salt protons occurred effectively despite
the existence of more acidic carboxylic acid protons in the
1
Figure 1. H NMR spectra recorded in CDCl3/CD3CN
ꢁ
(1 : 1) at 25 C of a) 3a, b) 4a, and c) a 1 : 1 mixture of 3a
and 4a.
Diaryldiazomethane esterification of the pseudorotaxanes
provides a convenient route for rotaxane formation. Accordingly,
complexation of ammonium salts 3 with excess crown ethers 4
followed by reaction with diphenyldiazomethane gives the
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Copyright Ó 2002 The Chemical Society of Japan

Chemistry Letters 2002
811
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expected rotaxanes 5 in high yields (Scheme 2 and Table 1). The
reactions were carried out in either CHCl3 or CH3CN/CHCl3
(
formation of pseudorotaxanes despite the existence of carboxylic
acid group in the latter substrates. In addition, the results
demonstrate that esterification of the acid by using diaryldia-
zoalkanes affords rotaxanes in excellent yields. Thus, it appears
that the conditions used for this end-capping reaction do not affect
the weak interactions responsible for pseudorotaxane formation.
The scope of the new technique for rotaxane synthesis is being
explored in our ongoing studies in this area.
1 : 1). Although heterogeneous solutions of the pseudorotaxanes
were achieved only when CHCl3 was used as a solvent, the
esterification reactions were high yielding in both solvent
systems.
References and Notes
1
V. Balzani, M. Gomez-Lopez, and J. F. Stoddart, Acc. Chem.
Res., 31, 405 (1998); J.-P. Sauvage, Acc. Chem. Res., 31, 611
(
2
1998); D. B. Amabilino and J. F. Stoddart, Chem. Rev., 95,
725 (1995); V. Balzani, A. Credi, F. M. Raymo, and J. F.
Stoddart, Angew. Chem., Int. Ed., 39, 3348(2000); G. A.
Breault, C. A. Hunter, and P. C. Mayers, Tetrahedron, 55, 5265
(
1999).
2
A. E. Kaifer, Acc. Chem. Res., 32, 62 (1999); C. P. Collier, E. W.
Wong, M. Belohradsky, F. M. Raymo, J. F. Stoddart, P. J.
Kuekes, R. S. Williams, and J. R. Heath, Science, 285, 391
(
1999); R. Ballardini, V. Balzani, A. Credi, M. T. Gandolfi, and
M. Venturi, Acc. Chem. Res., 34, 445 (2001); A. Harada, Acc.
Chem. Res., 34, 456 (2001); C. A. Schalley, K. Beizai, and F.
Vogtle, Acc. Chem. Res., 34, 465 (2001); J.-P. Collin, C.
Dietrich-Buchecker, P. Gavina, M. C. Jimenez-Molero, and
J.-P. Sauvage, Acc. Chem. Res., 34, 477 (2001).
3
4
P. R. Ashton, E. J. T. Chrystal, P. T. Glink, S. Menzer, C.
Schiavo, N. Spencer, J. F. Stoddart, P. A. Tasker, A. J. P. White,
and D. J. Williams, Chem. Eur. J., 2, 709 (1996).
a) A. G. Kolchinski, D. H. Busch, and N. W. Alcock, J. Chem.
Soc., Chem. Commun., 1995, 1289. b) H. Kawasaki, N. Kihara,
and T. Takata, Chem. Lett., 1999, 1015. c) P. R. Ashton, P. T.
Glink, J. F. Stoddart, P. A. Tasker, A. J. P. White, and D. J.
Williams, Chem. Eur. J., 2, 729 (1996). d) S. J. Rowan and J. F.
Stoddart, J. Am. Chem. Soc., 122, 164 (2000). e) A. G.
Kolchinski, N. W. Alcock, R. A. Roesner, and D. H. Busch,
Chem. Commun., 1998, 1437. f) T. Takata, H. Kawasaki, S.
Asai, Y. Furusho, and N. Kihara, Chem. Lett., 1999, 223.
P. R. Ashton, I. Baxter, M. C. T. Fyfe, F. M. Raymo, N. Spencer,
J. F. Stoddart, A. J. P. White, and D. J. Williams, J. Am. Chem.
Soc., 120, 2297 (1998).
Scheme 2.
Table 1. Esterfication of pseudorotaxane
a
Run Axis Crown Ether
Solvent
Product Yield/%
1
2
3
4
5
6
7
8
9
3a
3a
3b
3b
3a
3a
3b
3b
3a
3a
4a
4a
4a
4a
4b
4b
4b
4b
4a
4a
CHCl3-MeCN (1 : 1)
5a
5a
5b
5b
5c
5c
5d
5d
5e
87 (62)
81
b
CHCl3
5
6
7
CHCl3-MeCN (1 : 1)
97 (83)
97
b
CHCl3
4b: P. R. Ashton, I. Baxter, S. J. Cantrill, M. C. T. Fyfe, P. T.
Glink, J. F. Stoddart, A. J. P. White, and D. J. Williams, Angew.
Chem., Int. Ed., 37, 1294 (1998).
CHCl3-MeCN (1 : 1)
81 (79)
91
CHCl3b
CHCl3-MeCN (1 : 1)
CHCl3b
91 (67)
92
(78)
The typical synthesis procedure: Ammonium salt 3a (59.8mg,
0
.135 mmol) and crown ether 4b (128.8 mg, 0.270 mmol) were
dissolved in a mixture of CHCl3 (13.5 ml) and CH3CN
13.5 ml). Diphenyldiazomethane (31.4 mg, 0.162 mmol) was
CHCl3-MeCN (1 : 1)
1
0
CH2Cl2-MeCN (1 : 1) 5f
45 (38)
(
1
13
added to the reaction mixture under ice-bath, and the reaction
ꢁ
All new compounds were identified by H and C NMR, MS, and
a
1
mixture was stored in refrigerator (at 4 C) for 2d. After removal
of solvent, the residue was washed with toluene and ethyl
IR spectra. Determind by H-NMR spectra of crude products. ( ):
b
isolated yield. Heterogeneous.
1
acetate to provide 5c (120 mg, 79%) as a white solid. H NMR
(
500 MHz, CDCl3) ꢀ1.23 (s, 9H), 3.48–3.70 (m, 8H), 3.70–3.95
To demonstrate the versatility of this method, 9-diazo-9H-
fluorene was used in place of diphenyldiazomethane for the
esterification process. Reaction with excess amount of this
reagent proceeds to furnish the corresponding rotaxane 5e in high
yield (Scheme 2, run 9 Table 1). In a similar manner, by using 9-
anthryldiazomethane, carboxyl groups in the pseudorotaxane can
be efficiently transformed to 9-methylanthryl ester 5f (run 10
Table 1).
(
m, 8H), 3.95–4.22 (m, 8H), 4.55–4.62 (m, 2H), 4.77–4.85 (m,
2
7
1
5
7
1
1
H), 6.56–6.87 (m, 7H), 7.05 (s, 1H), 7.28–7.34 (m, 2H), 7.35–
.47 (m, 10H), 7.63–7.73 (br, 2H), 7.79–7.82 (m, 2H), 9.65 (s,
H). C NMR (100 MHz, CDCl3) ꢀ 22.61, 31.15, 31.55, 34.63,
1.87, 52.48, 67.70, 67.93, 68.33, 70.00, 70.03, 70.23, 70.58,
0.80, 70.87, 77.20, 77.62, 109.85, 111.80, 112.06, 121.64,
25.74, 127.20, 128.04, 128.08, 128.23, 128.59, 128.66, 129.01,
1
3
29.69, 130.18, 130.57, 136.69, 140.02, 140.06, 146.64, 147.94,
À1
In conclusion, the observations made in this effort show that
complementary hydrogen bonding interactions between diben-
zo[24]crown-8and secondary ammonium salts results in efficient
152.73, 152.79, 164.51, 190.68. Ir ꢁmax (KBr) cm : 2940,
1720, 1700, 1460, 1690, 560. mp 112–115 C. HRMS Found:
m=z ¼ 941:4773 (M-PF6 ). Calcd for C57H66NO11: 941.4714.
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