An imidazolidin-1-ol, nitrone and oxadiazinane ring-chain-ring tautomeric dynamic combinatorial library

Article abstract of DOI:10.1016/j.tetlet.2009.03.201

A dynamic combinatorial library (DCL) based on benzylidene exchange reactions between imidazolidin-1-ol, nitrone and oxadiazinane (INO) ring-chain-ring tautomers at room temperature is created. The probable mechanism of the reaction is discussed based on

Full text of DOI:10.1016/j.tetlet.2009.03.201

Tetrahedron Letters 50 (2009) 3008–3012
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Tetrahedron Letters
journal homepage: www.elsevier.com/locate/tetlet
An imidazolidin-1-ol, nitrone and oxadiazinane ring-chain-ring tautomeric
dynamic combinatorial library
*
Necdet Coßskun , Çag˘daßs Aksoy
Uludag˘ University, Department of Chemistry, 16059 Görükle-Bursa, Turkey
a r t i c l e i n f o
a b s t r a c t
Article history:
A dynamic combinatorial library (DCL) based on benzylidene exchange reactions between imidazolidin-
1-ol, nitrone and oxadiazinane (INO) ring-chain-ring tautomers at room temperature is created. The
probable mechanism of the reaction is discussed based on Hammett type correlation analyses. The equi-
libria in the DCL are defined as interconversion of INOAr-X to INOAr-Y as a result of reactions with the
Received 20 December 2008
Revised 18 March 2009
Accepted 27 March 2009
Available online 2 April 2009
corresponding aldehydes Y-ArCHO and X-ArCHO and are shown to depend on the
stituents and are described by a simple equation logKXY qrdif + logKXY(X = Y). The prediction of KXY for
any INOAr-X and INOAr-Y interconversion requires only the experimental values of and the known
constants of the substituents. The effect of Zn(II) and CF3SO3H on the DCL equilibria is also
r constants of the sub-
=
Keywords:
q
Ring-chain-ring tautomers
Dynamic combinatorial libraries
Linear free energy relationships
Benzylidene exchange reaction
Hammett
reported.
r
Ó 2009 Elsevier Ltd. All rights reserved.
Dynamic combinatorial chemistry1 (DCC) has added a new
dimension to the synthetic capability of combinatorial chemistry
exploiting reversible covalent chemistry to generate combinatorial
libraries that are under thermodynamic control. Since the library
members interconvert by equilibrium processes, any stabilization
of a given member of the library results in the thermodynamic
redistribution of the equilibrium to yield a new thermodynamic
equilibrium. Imines were first explored in a dynamic combinatorial
context in 1997 by Huc and Lehn,2 who described a virtual combi-
natorial library of imines the composition of which was influenced
by the presence of carbonic anhydrase as a ‘molecular trap’. Stabi-
lized imines, in the form of oximes and hydrazones,3 have since at-
tracted significant interest in DCC as they can provide kinetically
inert products without the need for subsequent reduction and
the attendant change in geometry and electronics. Eliseev and
co-workers have explored the use of O-aryl oximes to construct dy-
namic combinatorial libraries (DCLs).4 The relative degree of
amplification in the dynamic library will depend on the difference
in binding affinity of the library components to the template.5 The
identification of dynamic covalent bonds and the development of
catalysts which promote the fast exchange of covalent bonds are
crucial for furthering dynamic covalent chemistry.1b In this respect
creating DCLs based on scaffolds which could bind a compound to
give several products in equilibrium would be extremely impor-
tant for accessing richer DCLs than classical DCL scaffolds provide.
Recently, it was reported that nitrones are able to undergo dy-
namic exchange in non-polar solvents such as chloroform. By cou-
pling a nitrone-based replicator to a dynamic library based on
nitrone-imine exchange, it was demonstrated that a synthetic rep-
licator is able to exploit a network of reactions within a dynamic
library to amplify its own formation at the expense of other
species.6
Here we report on the benzylidene exchange reactions of imi-
dazolidin-1-ol, nitrone and oxadiazinane ring-chain-ring tauto-
meric mixtures (INOAr-X(Y))7 as
a
useful tool for the
construction of DCLs. The effect of substituents on the interconver-
sions of INOAr-X to INOAr-Y was investigated and correlations
with Hammett constants and their differences were performed to
elucidate the probable mechanism of the new benzylidene ex-
change reaction applied in the DCL formation.
Treatment of INOAr-X (X = H, R = p-MeOC6H4) in THF with an
equimolar amount of hydroxylamine hydrochloride8 dissolved in
MeOH at 25 °C for 4 h leads quantitatively to the corresponding
aldoxime and hydroxylaminoamine hydrochloride 3 (Scheme 1)
as confirmed by 1H NMR spectroscopy. A mixture of five aromatic
aldehydes was added to the in situ formed 3 and the resulting mix-
ture was left to equilibrate for 20 h.9 The 1H NMR analyses revealed
that compound 3 was fully consumed to give the corresponding
INOAr-X(Y) DCL. The concentrations of the aldehydes were moni-
tored by gas chromatography (Table 1). There are 25 inter IN-
OAr-X(Y) equilibria (Scheme 2) as depicted in Figure 1. Five of
the latter are between INOAr-X and Y-ArCHO where X = Y and
are non-productive.
The equilibrium constants KXY = [INOAr-Y][X-ArCHO]/[INOAr-
X][Y-ArCHO] for the equilibrium series A–E in the DCL were calcu-
lated and are presented in Table 2. A comparison of the equilibrium
series A–E clearly reveals the reactivity order of the aldehydes in
* Corresponding author. Tel.: +90 224 2941725.
E-mail address: coskun@uludag.edu.tr (N. Coßskun).
0040-4039/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2009.03.201

N. Coßskun, Ç. Aksoy / Tetrahedron Letters 50 (2009) 3008–3012
3009
Ph
Ph
Ph
NH2OH.HCl
-PhCHNOH
Reduction
(X)Y-ArCHO
N
N
R NH N O
R NH HN OH
.HCl
R
O
Ph
Ph
2a
1a (R = p-MeOC6H4)
3
INOArX(Y)
Ph
Ph
Ph
Imidazolidines 4
Nitrones 2
NH
O
N
N
NH
N
R
OH
R
O
N
R
Ar
4a-e
Ar
2a-e
Oxadiazinanes 5
Ar
5a-e
Scheme 1. Synthesis of an INO-based DCL
Table 1
Table 2
Concentrations of the aldehydes and INOAr-X(Y) in the DCL at 25 °C in THF–MeOH
Equilibrium (Eqm) series in INO-based DCLs and Hammett correlations
after equilibration
a
a
X
Y
KXY
logKXY
ry
rx À ry
2-5
X(Y)
[(Y)X-ArCHO]a (M)
STDEVb
[INOAr-X(Y)]c (M)
Eqm series A
a
b
c
d
e
H
p-Cl
p-MeO
p-NO2
m-NO2
0.0186
0.0170
0.0195
0.0096
0.0122
0.0006
0.0006
0.0001
0.0016
0.0013
0.0014
0.0030
0.0005
0.0105
0.0078
Kaa
Kab
Kac
Kad
Kae
H
H
H
H
H
H
p-Cl
p-MeO
p-NO2
m-NO2
1
0
0
0
2.34
0.34
14.61
8.49
0.37
À0.47
1.16
0.91
0.24
À0.28
0.81
À0.24
0.28
À0.81
À0.71
0.71
a
Eqm series B
The aldehyde concentrations were measured using GC–MS and are averages of
Kbb
Kba
Kbc
Kbd
Kbe
p-Cl
p-Cl
H
p-MeO
p-NO2
m-NO2
1
0
0.24
0
À0.28
0.81
0.71
0
two experiments. The integral areas were corrected using butylhydroxytoluene as
internal standard.
p-Cl
p-Cl
p-Cl
p-Cl
0.43
0.15
6.23
3.62
À0.37
À0.82
0.80
0.56
0.24
0.52
À0.57
À0.47
b
STDEV = standard deviation.
The INOAr-X(Y) tautomer contents were calculated as the difference of total
c
INO (0.2 mmol) and the content of the specific aldehyde. Starting concentrations of
the aldehydes and the library scaffold 3 are 0.02 M.
Eqm series C
Kcc
Kca
Kcb
Kcd
Kce
p-MeO
p-MeO
H
p-Cl
p-NO2
m-NO2
1
0
À0.28
0
0.24
0.81
0.71
0
p-MeO
p-MeO
p-MeO
p-MeO
2.94
6.67
42.88
24.93
0.47
0.82
1.63
1.40
À0.28
À0.52
À1.09
À0.99
KXY
+
+
INOAr-X
Y-ArCHO
INOAr-Y
X-ArCHO
Eqm series D
Kdd
Kda
Kdb
Kdc
Kde
p-NO2
p-NO2
H
p-Cl
p-MeO
m-NO2
1
0
0.81
0
0.24
À0.28
0.71
0
Scheme 2. Benzylidene exchange equilibria.
p-NO2
p-NO2
p-NO2
p-NO2
0.068
0.16
0.023
0.58
À1.17
À0.79
À1.63
À0.24
0.81
0.57
1.09
0.10
a
Eqm series E
A
Kee
Kea
Keb
Kec
Ked
m-NO2
m-NO2
H
p-Cl
p-MeO
p-NO2
1
0
0.71
0
0.24
À0.28
0.81
0
e
b
m-NO2
m-NO2
m-NO2
m-NO2
0.12
0.28
0.04
1.72
À0.93
À0.56
À1.40
0.24
0.71
0.47
0.99
À0.10
E
B
A-E and a-e represent
INOAr-X and Y-ArCHO respectively
D
C
a
The substituent constants and their difference values.10,11
d
c
Figure 1. Possible benzylidene exchange equilibria in the INO-based DCL.
Table 3
Linear free energy relationships (LFERs) in INO-based DCLs. Equations from the
correlations with rY and rdif
the DCL to be p-NO2 > m-NO2 > p-Cl > p-H > p-MeO (Table 2). The
a
correlation equations for the equilibrium series A–E are given in
rY
rxÀry = rdif
Table 3. The correlations of logKXY with
stituents on the aldehyde) produced Hammett type equations
logKXY qrY + intercept, where the reaction constant, = 1.44, is
the same for all series. The intercepts from these correlations devi-
ate only by ca. 0.025 from the corresponding logKXY(Y = H)
The correlations of logKXY with rdif rY reveal that the
rY (the constant of the sub-
Eqm series A
Eqm series B
Eqm series C
Eqm series D
Eqm series E
General eqs
logKay = 1.436rY À 0.0257
logKby = 1.426rY À 0.39
logKay = À1.436rdif À 0.0257
logKby = À1.426rdif À 0.0478
=
q
logKcy = 1.436
r
Y + 0.4392
logKcy = À1.436rdif + 0.037
logKdy = 1.436rY À 1.19
logKdy = À1.436rdif À 0.0281
logKey = 1.436rY À 0.9546
logKey = À1.436
rdif + 0.0652
.
logKXY
=
qrY + logKXY(Y = H)
logKXY
=
qrdif
=
rX
À
a
The correlation coefficients from the correlations with
r
Y and rdif are ca. 0.995.
magnitudes of the equilibrium constants are linearly dependant
on the INOAr-X and INOAr-Y substituents and can be described
simply by the equation logKXY
constants are equal to those in the previous correlations but
have opposite sign. The average of the intercepts from the latter
= qrdif + logKXY(X = Y). The reaction
q
correlations is 0.00012.12 Representative graphs for the correla-
tions in equilibrium series C are given in Figure 2. Comparing

3010
N. Coßskun, Ç. Aksoy / Tetrahedron Letters 50 (2009) 3008–3012
To elucidate the effect of Zn(II) on the equilibria in the pre-
equilibrated DCL, ZnBr2 (equimolar amount with the library scaf-
fold) was added to the mixture which was then stirred for 20 h
at 25 °C (Table 4). The equilibrium constants KXY, defined as given
before, were calculated and the selective amplifications of the IN-
OAr-OMe equilibria were demonstrated for equilibria series A
and C (Table 5). Attempts to correlate logKXY with the Hammett
r
constants failed. The plots deviate from linearity with the great-
est deviation from linearity observed in the case of the OMe-
substituted library members.
A comparison of the parent equilibria with those in the pres-
ence of Zn(II) (exemplified for series A and C; the same conclusions
are true in the other series) reveal that the equilibria involving the
formation of INOAr-p-OMe are ca. nine times more shifted than IN-
OAr-p-NO2. Even more contrasting is the comparison of benzalde-
hyde and p-methoxybenzaldehyde involving equilibria where
about 20 times enhancement is seen for the latter. The reactivity
order of the aldehydes in the benzylidene exchange reaction be-
came p-NO2 > m-NO2 > p-Cl = p-MeO > p-H. In fact, the unsubsti-
tuted aldehyde-derived INO components were the more reactive
species in the DCL and the enhancement of the INOAr-p-OMe con-
centration is mainly due to the right-shifted INOAr-H MeO-ArCHO
equilibrium. The change of the reactivities of the latter two alde-
hydes is probably due to an increase of the negative inductive ef-
fect of the MeO group due to interactions with Zn(II).
Although the correlations confirm the assumed benzylidene ex-
change mechanism which we have proposed, experiments involv-
ing the separate treatment of INOAr-H with equimolar amounts of
Y-ArCHO (Y = p-Cl, p-MeO, p-NO2, m-NO2) in the presence of equi-
molar amounts of F3CSO3H in THF at 25 °C undoubtedly confirmed
this assumption. The equilibrium constants are given in Table 6. A
comparison of the aldehyde starting concentration and after 20 h
reaction with INOAr-H in the presence of CF3SO3H at 25 °C in
THF is given in Figure 3.
Figure 2. Plot of logKXY in equilibrium series C versus rY (N) and rdif (j).
the KXY predicting power of the equations from correlations with
rY and rdif clearly reveals the advantages of the equation logK-
=
qrdif, where only three constants are required to calculate
XY
the corresponding KXY in the library for any aldehyde and INO
combination. However, the equations from the correlations with
rY require the experimental values of KXY(Y = H) which means that
these data cannot be used directly to predict the KXY when both
substituents are different from those included in the correlations
reported herein.
Thus the excellent correlations of the equilibrium series with
Hammett
r constants agree with the assumption that the main
equilibria in the DCL are of benzylidene exchange type between
the INOArs. The values of the reaction susceptibility constants
clearly implies that there should be a significant positive charge
formation in the rate limiting step of this exchange reaction
(Scheme 3, the formation of ammonium species A). The probable
mechanism of the latter reaction is depicted in Scheme 3. The
INO components able to undergo benzylidene exchange reactions
are nitrone NX and oxadiazinane OY (Scheme 3). The nucleophilic
attack of NX on the protonated aldehyde will lead to the formation
of intermediate A which is probably in equilibrium with B. The
cyclization of B produces the seven-membered oxadiazepine C,
the ring-opening of which can afford iminium salt D. Intermediate
D can cyclize to both cyclic components of the INO. We illustrate
the benzylidene exchange through the oxadiazinane ring deriva-
tive E. Proton migration in E probably gives intermediate F which
eliminates the protonated aldehyde X-Ar-CHO+-H to give the cor-
responding oxadiazinane OY.
Table 4
Concentrations of the aldehydes and INOAr-X(Y) in the DCL at 25 °C in THF–MeOH
(24:1) with Zn(II)
2–5
X(Y)
[(Y)X-ArCHO]a (M)
STDEVb
[INOAr-X(Y)]a (M)
a
b
c
d
e
H
p-Cl
p-MeO
p-NO2
m-NO2
0.0193
0.0160
0.0161
0.0090
0.0113
0.0016
0.0010
0.0013
0.0016
0.0012
0.0007
0.0040
0.0040
0.0110
0.0088
a
The concentrations of the aldehydes and INOAr-X(Y) were determined as
mentioned in the legend of Table 1.
b
STDEV = standard deviation.
Ph
O
Ph
N
OH
Ph
O
Ph
N
OH
H
N
N
N
Ar-X
Ar-X
Ar-Y
Ar-X
NH
N
R
O
H
N
O
O
O
R
R
H
H
Ar-X
R
H
Ar-Y
Ar-Y
Ar-Y
B
C
NX (R = p-MeOC6H4)
A
Ph Ar-X
Ph
Ph Ar-X
Ph
OH
OH
Ar-X
N
O
OH
N
N
O
OH
NH
O
H
N
N
N
N
H
O
R
R
R
H
R
-
Ar-Y
Ar-Y
Ar-Y
Ar-Y
X-Ar
E
D
F
OY
Scheme 3. Probable mechanism for the benzylidene exchange reactions in the INO-based DCL.

N. Coßskun, Ç. Aksoy / Tetrahedron Letters 50 (2009) 3008–3012
3011
Table 5
Equilibrium series in INO-based DCLs in the presence of the Zn(II) template
a
Eqm series A
X
Y
KXY À template
KXY
KXY À template/KXY
Kaa
Kab
Kac
Kad
Kae
H
H
H
H
H
H
p-Cl
p-MeO
p-NO2
m-NO2
1
1
2.34
0.34
14.61
8.49
1
6.89
6.76
33.70
21.44
2.95
19.96
2.31
2.53
Eqm series C
KXY/KXY À template
Kcc
Kca
Kcb
Kcd
Kce
p-MeO
p-MeO
p-MeO
p-MeO
p-MeO
p-MeO
H
p-Cl
p-NO2
m-NO2
1
1
1
0.147
0.984
4.97
3.16
2.94
6.67
42.88
24.93
20
6.78
8.62
7.89
a
KXY from the DCL without a template is included for comparison.
Table 6
Benzylidene exchange reactions of INOAr-H (R = p-MeOC6H4) with Y-ArCHO
Y
[Y-ArCHO]a (M)
[H-ArCHO]a (M)
[INOAr-Y] (M)
[INOAr-H] (M)
KXY
H
p-Cl
p-MeO
p-NO2
m-NO2
1.00E+00
3.90EÀ02
4.50EÀ02
2.07E+00
1.00E+00
0.017
0.0033
0.0035
0.0118
0.0100
0.0033
0.0035
0.0118
0.0100
0.0167
0.0165
0.0082
0.0100
0.0165
0.0082
0.0100
a
The concentrations of the aldehydes (M) were measured using GC–MS. The integral areas were corrected using butylhydroxytoluene as internal standard.
The library constructed by addition of aldehydes Y-ArCHO
(Y = p-Cl, p-MeO, p-NO2 and m-NO2) to INOAr-H in the presence
of CF3SO3H revealed that under these conditions all the aldehydes
are more reactive than benzaldehyde (Table 7). The reactivity order
of the aldehydes in the latter DCL is p-NO2 > m-NO2 > p-MeO > p-
Cl > p-H. p-Methoxybenzaldehyde became more reactive than p-
chlorobenzaldehyde probably because of protonation of the meth-
oxy group by the strong acid.
Thus, the benzylidene exchange reactions of ring-chain-ring
tautomeric mixtures (INOAr-X(Y)) allow the construction of more
complete DCLs since the library members exist as multiple tautom-
ers, thus increasing the diversity of the system, and therefore
allowing for the greater possibility of different interactions with
a template. The discussions on the probable mechanism of the ben-
zylidene exchange reaction in the DCL were supported with Ham-
mett type correlation analyses. The correlations of logKXY with rdif
produced a more general and more useful equation for the predic-
tions of unknown KXY, namely logKXY
with rY alone.
= qrdif, than the correlations
Nitrone 1a was prepared in 50% yield according to a previously
reported procedure13 and converted to INOAr-H by reduction with
NaBH4 in THF at reflux.7 3,6-Diphenyl-5-p-methoxyphenyl-1,2,5-
oxadiazinane 5a: Yield 90%. Mp 150–150.3 °C. IR (KBr) mNH
3255 cmÀ1. The spectrum was obtained from the crystalline prod-
uct immediately upon dissolution in CDCl3. The solution consisted
of 2a (9%), 4a (12%) and 5a (78%). 1H NMR (400 MHz, CDCl3): d 3.75
(3H, s), 3.85–3.93 (1H, m), 4.04 (1H, br s), 4.51 (1H, dd, J = 12.0;
6.4 Hz), 5.61 (1H, s), 6.49 (2H, d, J = 9.2 Hz), 7.03 (2H, d,
J = 9.2 Hz), 7.25–7.38 (10H, m). Anal. Calcd for C22H22N2O2
(346.42) C, 76.28; H, 6.40; N, 8.09. Found: C, 76.32; H, 6.43; N, 8.15.
C-Phenyl-N-(1-phenyl-2-p-methoxyphenylaminoethyl) nitrone 2a:
The spectrum was obtained from an equilibrated tautomeric mix-
ture containing 2a (69%), 4a (18%) and 5a (12%). 1H NMR (400 MHz,
CDCl3): d 3.61 (1H, dd, J = 14.4; 4.0 Hz), 3.76 (3H, s), 4.04 (1H, br s),
4.30 (1H, dd, J = 14.4; 10.0 Hz), 5.20 (1H, dd, J = 10.0; 4.0), 6.62 (2H,
d, J = 9.2 Hz), 6.79 (2H, d, J = 9.2), 7.36–7.41 (7H, m), 7.57–7.59 (2H,
m), 8.19–8.22 (2H, m).
Preparation of INOAr-X(Y) DCL: To
a solution of INO-ArH
(0.2 mmol, 0.0693 g) in THF (4.8 mL), NH2OHÁHCl (0.2 mmol,
0.0135 g) dissolved in MeOH (0.2 mL) was added and the reaction
mixture was stirred at 25 °C for 4 h. Completion of the reaction was
confirmed by 1H NMR. A solution of aromatic aldehydes Y-ArCHO
was prepared by dissolving 0.8 mmol of each aldehyde in 20 mL
of THF. The same solution was used to obtain calibration curves
Table 7
Concentrations of the aldehydes and INOAr-X(Y) in the DCL at 25 °C in THF with
CF3SO3H
2–5
X(Y)
[(Y)X-ArCHO]a (M)
STDEVb
[INOAr-X(Y)]a (M)
a
b
c
d
e
H
p-Cl
p-MeO
p-NO2
m-NO2
0.0212
0.017
0.0162
0.0122
0.0133
0.0016
0.0010
0.0013
0.0016
0.0012
À0.0012
0.003
0.0038
0.0078
0.0067
a
The concentrations of the aldehydes and INOAr-X(Y) were determined as
Figure 3. Comparison of the benzylidene exchange reactions of INOAr-H with Y-
ArCHO; ( ) and ( ) denote the concentrations of the aldehydes before and after
treatment with INO-Ar-H and CF3SO3H, respectively.
mentioned in the legend of Table 1.
b
STDEV = standard deviation.

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N. Coßskun, Ç. Aksoy / Tetrahedron Letters 50 (2009) 3008–3012
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for the chromatographic analyses as well as for the syntheses of
DCL. The concentrations used for the calibration curves were
0.04, 0.02 and 0.01 M. Five millilitres from the 0.04 M solution of
aldehydes were added to the in situ formed aminohydroxylamine
3 and the library was left to equilibrate for 20 h at 25 °C. The alde-
hyde content of the DCL was analyzed by GC–MS. ZnBr2 (0.2 mmol,
0.0450 g) was added to the equilibrated DCLs which were then stir-
red at 25 °C for 20 h.
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4076–4078; (b) Sadownik, J. W.; Philp, D. Angew. Chem., Int. Ed. 2008, 47, 9965–
9970.
Aldehyde exchange reactions of INOAr-H with Y-ArCHO in the pres-
ence of CF3SO3H : To
a solution of the aromatic aldehyde
7. Coßskun, N.; Asutay, O. Tetrahedron Lett 2007, 48, 5151–5155.
8. Coßskun, N.; Parlar, A. Synth. Commun. 2005, 35, 2445–2451.
9. In a separate experiment, the ratio of the aldehydes in the DCL were measured
from the integral areas of the corresponding aldehyde proton signals in the 1H
NMR spectra of the mixture at different times. After 15 hours, the values did
not deviate significantly and thus we assumed that the exchange reactions in
the library had reached an equilibrium.
(0.02 mmol) in 1 mL of THF, INOAr-H (0.02 mmol, 0.0069 g) was
added. CF3SO3H (0.02 mmol, 0.003 g) was added and the reaction
mixture was stirred at 25 °C for 20 h. The amounts of the aldehydes
were determined by GC–MS. The concentrations used for the cali-
bration curves were 0.02, 0.01 and 0.005 M.
10. (a) Jaffe, H. H. Chem. Rev. 1953, 53, 191–261; (b) Hansch, C.; Leo, A.; Taft, R. W.
Chem. Rev. 1991, 91, 165–195.
11. March, J. Advanced Organic Chemistry Reactions Mechanism and Structure, 3rd
ed.; John Wiley and Sons, 1985. p 244.
Acknowledgement
Uludag˘ University Scientific Projects Commission is gratefully
acknowledged for the financial support.
12. The correlations with rsum = rX + rY produced the equations logKXY =
qrsum + intercept where the intercept are ca. 2logKXY(Y = H). The predicting
power of the latter is not higher than the equations from the correlations
with rY
.
References and notes
13. (a) Cosßkun, N.; Sümengen, D. Synth. Commun. 1993, 23, 1699–1706; (b) Coßskun,
N.; Asutay, O. Chim. Acta Turc. 1997, 25, 69–71; (c) Cosßkun, N.; Asutay, O. Chim.
Acta Turc. 1999, 27, 17–23.
1. (a) Lehn, J. M. Chem. Eur. J. 1999, 5, 2455–2463; (b) Rowan, S. J.; Cantrill, S.
J.; Cousins, G. R. L.; Sanders, J. K. M.; Stoddart, J. F. Angew. Chem., Int. Ed.