Liquid-crystalline properties of unsaturated piperazine-2,5-dione derivatives

Article abstract of DOI:10.1002/(SICI)1522-2675(19990908)82:9<1400::AID-HLCA1400>3.0.CO;2-0

The synthesis, characterization, and mesomorphic properties of a new type of liquid-crystalline compounds, (3Z,6Z)-3,6-bis(3,4- dialkoxybenzylidene)piperazine-2,5-diones are reported. These compounds were derived from unsaturated piperazine-2,5-dione as t

Full text of DOI:10.1002/(SICI)1522-2675(19990908)82:9<1400::AID-HLCA1400>3.0.CO;2-0

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Helvetica Chimica Acta ± Vol. 82 (1999)
Liquid-Crystalline Properties of Unsaturated Piperazine-2,5-dione
Derivatives
by Wen-Ren Li*, Kwo-Cheng Kao, Ying-Chih Yo, and Chung K. Lai*
Department of Chemistry, National Central University, Chung-Li, Taiwan, ROC
The synthesis, characterization, and mesomorphic properties of a new type of liquid-crystalline compounds,
(3Z,6Z)-3,6-bis(3,4-dialkoxybenzylidene)piperazine-2,5-diones are reported. These compounds were derived
from unsaturated piperazine-2,5-dione as the core group, and were prepared by condensation reactions of 1,4-
diacetylpiperazine-2,5-dione and 3,4-dialkoxybenzaldehydes. The products were characterized by 1H- and
13C-NMR spectroscopy, and elemental analysis, and the phase behavior of these compounds was characterized
and studied by differential scanning calorimetry (DSC) and polarization microscopy. The results indicate that
these rod-like compounds exhibit smectic C (Sc) phases. However, for the derivatives with two flexible alkoxy
side chains, highly ordered smectic G (SG) phases were also formed and confirmed by X-ray powder diffraction.
The liquid crystallinity of these molecules was attributed to the presence of intermolecular hydrogen bonds
involving the NH groups of the heterocyclic rings. The correlation of phase behavior and molecular shape is also
discussed.
1. Introduction. ± Organic structures that exhibit calamitic liquid-crystalline
properties often contain a long rigid core which consists of fused delocalized ring
systems [1]. In recent years, there has been considerable interest in materials based on
heterocyclic molecules [2], especially structures incorporating heterocyclic five-
membered rings such as thiophenes, pyrazoles, or isoxazoles, due to their diverse
structural features and remarkable mesomorphic properties. Structures incorporating
five-membered rings, however, are generally considered less suitable than six-
membered rings for the formation of mesogenic phases, since they tend to deviate
from linearity. Furthermore, the presence of lone-pair electrons in these heterocyclic
rings introduces a transverse dipole moment, often resulting in a change of dielectric
anisotropy [3]. It is well understood that mesomorphic behavior is determined and/or
controlled by a combination of many structural features, including molecular shape,
and rigidity, side-chain density, etc. Rod-shaped molecules with appropriate length/
width ratios often experience anisotropic intermolecular forces and thus generally
assemble to form smectic (S) or nematic (N) mesophases.
In this work, a new type of rod-like compounds (cf. 1 ± 3), in which the unsaturated
structure of piperazine-2,5-dione was used as part of the rigid core, were prepared
and their mesomorphic properties studied. All studies of piperazine-2,5-dione
(also termed cyclodipeptide) derivatives in the literature have exclusively focused
on the chemical and catalytic [4a], or biological [4b] activities; a study of the
role of piperazine-2,5-dione derivatives as the core group in molecular organization
has not yet appeared. A few interesting aspects deserve special attention: 1) H-bonding
by the NH groups, 2) stacking interactions due to weak p-p attractive forces
between the aromatic and heterocyclic rings, and 3) hydrophobic interactions of

Helvetica Chimica Acta ± Vol. 82 (1999)
1401
aliphatic side chains. Structurally, the six-membered ring of piperazine-2,5-dione
derivatives can adopt either a flat conformation or a slightly puckered boat form
depending on substituents, and intermolecular H-bonding can give rise to the
formation of a relatively rigid molecular framework. The role of H-bonding by the
amide functional group of the piperazine-2,5-dione derivatives was probed with
compound 4e.
2. Results and Discussion. ± 2.1. Synthesis. The synthetic procedures for these
compounds are given in Scheme 1. The preparations of 4-alkoxybenzaldehydes, 3,4-
dialkoxybenzaldehydes, methyl 3,4,5-trialkoxybenzoates, and 3,4,5,-trialkoxybenzoic
acids were according to the literature [5]. The 3,4,5-trialkoxybenzaldehydes were
prepared by the reaction of 3,4,5-trialkoxybenzyl alcohols with pyridinium chloro-
chromate (PCC) in CH2Cl2 at room temperature. The C(3)H2 and C(6)H2 groups of
piperazine-2,5-dione are known to undergo facile condensation with aromatic
aldehydes to form symmetric dibenzylidene derivatives. The 3,6-bis(3,4-dialkoxyben-
zylidene)piperazine-2,5-diones were thus obtained by condensation of 1,4-diacetylpi-
perazine-2,5-dione with appropriate benzaldehydes in the presence of a base (e.g.,
Cs2CO3), and were isolated as light yellow needles.
The N-methylated compound 4e was prepared by substitution of 2e with MeI in
THF and NaH as base at room temperature (Scheme 2)
These derivatives were characterized by 1H- and 13C-NMR spectroscopy. The
NMR data revealed that these compounds are in the (all-Z)-configuration, and
that the vinylic proton is generally deshielded by ca. 0.65 ppm in the (Z)-isomer
compared to the (E)-isomer [6]. The 1H-NMR data of (3Z,6Z)-3,6-bis(4-dodecyloxy-
benzylidene)piperazine-2,5-dione (2e, n ˆ 10, where n corresponds to the number of
CH2 groups in the chain) in CDCl3 showed two characteristic peaks at 6.93 and
8.00 ppm, which were assigned to the olefinic methine and NH protons. The signal
of NH often appeared at higher magnetic field. In the IR spectrum the C
O
1
stretching bands occurred at 1670 ± 1690 cm and the N H stretching frequency at
1
3180 ± 3195 cm [7].
2.2. Mesomorphic Properties. The liquid crystalline behavior of these compounds
was studied by differential scanning calorimetry (DSC) and polarization microscopy.
The phase transitions for compounds 1 ± 3 are summarized in Table 1. The results
indicate that the phase of these compounds is quite sensitive to the number of flexible
alkoxy side chains.

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Helvetica Chimica Acta ± Vol. 82 (1999)
Scheme 1
a) RBr (1.0 ± 3.0 equiv.), K2CO3 (3.0 ± 7.0 equiv.), KI (cat.), at reflux in dry acetone 18 ± 72 h; 72 ± 96%. b)
LiAlH4 (1.1 equiv.), stirred at r.t. in dry THF 1 h, then refluxed 30 min; 77 ± 93%. c) PCC (1.1 equiv.), stirred in
dry CH2Cl2 8 h; 80 ± 91%. d) Ac2O (2.0m), stirred at 1308 12 h; 75 ± 82%. e) Cs2CO3 (2.1 equiv.), stirred in DMF/
toluene 1:1 at 808 7 h; 65 ± 72%.
2.2.1. Side-Chain Length. All (3Z,6Z)-3,6-bis(3,4-dialkoxybenzylidene)piperazine-
2,5-diones 2 exhibited a tilted structure in the enantiotropic smectic phase. For the
compounds 2 having shorter C-chains (e.g., 2a and b, n ˆ 3, 4, resp.), only the crystal-
to-isotropic transition was observed. However, an enantiotropic phase for compounds
with longer C-chains (2e ± g, n ˆ 6, 8, 10, 12, 14, resp.) was identified as smectic C based

Helvetica Chimica Acta ± Vol. 82 (1999)
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Scheme 2
Table 1. Phase Behavior of 1 ± 3. Transition temperatures [8] and enthalpies (in parenthesis, [kJ/mol])
determined by DSC at a scan rate of 10.08/min.
na)
10
12
14
3
Crystal Phasesb)
189:3ꢀ5:52†
195:3ꢀ2:49†
225:5ꢀ21:0†
*
*
)
*
1e
1f
1g
2a
2b
2c
2d
2e
2f
2g
K1
K1
K1
)
K2
K2
K2
SG
SG
SG
K
)
I
I
I
I
I
I
I
I
I
I
162:3ꢀ3:21†
199:2ꢀ5:54†
182:4ꢀ4:98†
226:0ꢀ1:04†
220:7ꢀ18:6†
243:2ꢀ24:3†
*
*
)
*
)
)
181:7ꢀ4:60†
131:1ꢀ8:61
207:7ꢀ1:04†
188:0ꢀ3:60†
239:5ꢀ23:0†
225:0ꢀ29:5†
*
128:6ꢀ7:45†
*
)
*
)
)
146:2ꢀ3:07†
221:3ꢀ28:1†
181:0ꢀ54:3†
*
)
169:7ꢀ38:3†
163:7ꢀ43:9†
*
4
K
)
144:6ꢀ38:4†
151:0ꢀ36:4†
132:1ꢀ3:72†
*
)
*
6
K
K
K
K
K
SC
SC
SC
SC
SC
)
130:0ꢀ1:74†
131:8ꢀ4:18†
145:8ꢀ35:0†
150:3ꢀ36:4†
*
)
*
8
)
125:3ꢀ2:54†
104:5ꢀ38:7†
145:7ꢀ35:4†
149:0ꢀ20:1†
*
)
*
137:3ꢀ19:5†
145:2ꢀ26:2†
10
12
14
)
75:8ꢀ28:9†
102:0ꢀ16:9†
*
)
*
)
76:7ꢀ17:4†
143:9ꢀ25:6†
141:8ꢀ30:2†
108:0ꢀ34:2†
*
)
*
)
88:6ꢀ39:6†
136:9ꢀ29:7†
40:3ꢀ2:06†
*
3e
10
K
)
I
39:5ꢀ1:18†
a) n ˆ the number of CH2 groups in the alkoxy chain. b) K, K1, K2 ˆ Crystal phases; SG ˆ smectic G phase, SC ˆ
smectic C phase; I ˆ isotropic.
on the observation of focal conic textures (see Fig.). Polarization microscopy of a thin
layer of sample pressed between two glass plates revealed the formation of a focal-conic
texture on very slow cooling from the isotropic. DSC Data showed that the transitions of
crystal-to-smectic were observed over a temperature range of 102.0 ± 132.18, with
transition enthalpies ranging from 3.72 ± 38.7 kJ/mol; the isotropic points were all in the
range of 151.0 ± 141.88, with enthalpies of 36.4 ± 20.1 kJ/mol. The temperature range of
the mesophase was 19.0 ± 43.28. The transition temperatures were slightly dependent on
the length of the side chains: increasing the C-number of the side chains slightly
lowered the clearing temperature. This trend is attributed to the larger dispersive forces
of the longer alkoxy chains. This smectic C phase was also confirmed by X-ray powder
diffraction. For example, compound 2d (n ˆ 8) at 1308 exhibited only a sharp reflection
at 44.53 Š in the small-angle region, indicating a diordered arrangement of layers. A
more diffuse peak at 4.58 Š, related to the alkoxy chains, was also observed.

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Helvetica Chimica Acta ± Vol. 82 (1999)
Figure. Optical textures observed by polarization microscopy for a) 1e (2108) and b) 2e (1258). Magnification
100 Â .

Helvetica Chimica Acta ± Vol. 82 (1999)
1405
2.2.2. Hydrogen Bonding. To probe the contribution of amide H-bonding to the
intermolecular forces in these layered structures, (3Z,6Z)-3,6-bis(3',4'-didodecyloxy-
benzylidene)-1,4-dimethylpiperazine-2,5-dione (4e) was prepared and studied. Sub-
stitution of the two amide H-atom of the piperazinedione ring by a tetrahedral Me
group decreases the intermolecular force between layers through disruption of the H-
bonding network and increased distance between layers. DSC Data indicated that the
mesomorphism was destroyed, and that this compound undergoes a crystal-to-isotropic
transition at 60.08.
2.2.3. Side-Chain Density. The dependence of mesophase formation on the numbers
of side chains (i.e., side-chain density) was also studied. Various (3Z,6Z)-3,6-bis(4-
alkoxybenzylidene)piperazine-2,5-diones (1e ± g, n ˆ 10, 12, and 14, resp.) and
(3Z,6Z)-3,6-bis(3, 4, 5-trialkoxybenzylidene)piperazine-2,5-diones (3e, n ˆ 10) were
also prepared and their properties investigated. An increase in the number of side
chains slightly altered the molecular shape from more rod-like in compounds 1 to more
lath-like in compounds 3. Compounds 1 exhibited similar tilted smectic phases which
were tentatively assigned as smectic G on the basis of observed mosaic textures (Fig.).
The clearing temperatures for compounds 1, ranging from 225.0 ± 243.28 in DSC
experiments, which were much higher than those for compounds 2, indicate a highly
ordered molecular arrangement. However, this mesophase of highly ordered structures
exhibited liquid-like behavior, and the isotropic-to-mesophase transition in cooling
cycles exhibited no supercooling. The X-ray powder data also confirmed this highly
ordered state. The diffraction pattern at 1508 for compound 1f (n ˆ 12) appeared at
40.46 Š, 20.87 Š, 15.33 Š, and 7.52 Š in the small-angle region, and at 4.81 Š, 4.57 Š,
4.42 Š, 4.25 Š, 3.83 Š, and 3.42 Š in the wide-angle region. Finally, the broader
compounds 3 formed only the crystalline phase.
3. Conclusions. ± The formation of liquid-crystalline phases directed by weak H-
bonding was demonstrated in derivatives of (3Z,6Z)-3,6-bis(3,4-dialkoxybenzylide-
ne)piperazine-2,5-diones. The overall molecular shapes for the piperazine-2,5-dione-
based derivatives are rod-like or lath-like depending on the number of flexible side
chains attached to the benzylidene ring. The relatively rigid structure of the piperazine-
2,5-dione as core group increased the interactive forces between the layers in the
smectic arrangement.
Experimental Part
General. All chemicals and solvents were reagent-grade from Aldrich Chemical Co. NMR-Spectra: Bruker
DRS-200; d in ppm and J in Hz. DSC Thermography was carried out on a Perkin-Elmer DSC-7 calibrated with a
pure In sample. All thermal phase behavior was determined with a scan rate of 10.08/min. Polarization
microscopy was carried out on Nikkon MICROPHOT-FXA with a Mettler FP90/FP82 HT hot-stage system.
Elemental analyses for C, H, and N were conducted on a Heraeus CHN-O rapid elemental analyzer and the
results are given in Table 2.
1,4-Diacetylpiperazine-2,5-dione. Piperazine-2,5-dione (1.05 g, 9.20 mmol) and Ac2O (4.60 ml) were stirred
at 1308 for 12 h. The soln. was concentrated under reduced pressure, and the solids were redissolved in 100 ml of
AcOEt. The soln. was extracted with NaHCO3 (5% soln.), dil. HCl (5%), and brine. The org. layer was dried
(Na2SO4) and concentrated to give brown solids. Pale yellow crystals were obtained after recrystallization from
AcOEt/hexane. Yield 86%. M.p. 151.68. 1H-NMR (CDCl3): 2.54 (s, 2 Me); 4.55 (s, 2 CH2). 13C-NMR (CDCl3):
26.65 (Me); 47.13 (C(1), C(4)); 165.82 (CO); 170.68 (C(2), C(5)).

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Helvetica Chimica Acta ± Vol. 82 (1999)
Table 2. Elemental-Analysis Data [%] for 1 ± 4 (calculated values in parentheses)
Compound
na)
C
H
1e
1f
1g
2b
2d
2e
2f
2g
3e
4e
10
12
14
4
76.24 (76.55)
77.42 (77.27)
77.69 (77.87)
73.09 (73.01)
75.91 (76.10)
77.11 (77.14)
77.69 (77.98)
78.77 (78.66)
77.28 (77.42)
77.19 (77.37)
10.00 (9.48)
9.19 (9.87)
10.18 (10.19)
9.02 (9.04)
10.33 (10.35)
10.71 (10.79)
11.15 (11.14)
11.30 (11.43)
11.52 (11.41)
10.95 (10.88)
8
10
12
14
10
10
a) n ˆ Number of CH2 groups in alkoxy chain.
4-Dodecyloxybenzaldehyde. Yield: 87%. White solid. M.p. 38.68. 1H-NMR (CDCl3): 0.85 (t, J ˆ 6.10, Me);
1.13 ± 1.47 (m, 9 CH2); 1.71 ± 1.85 (m, 2 CH2); 4.01 (t, J ˆ 6.40, CH2O); 6.96 (d, J ˆ 8.40, 2 arom. H); 7.79 (d, J ˆ
9.01, 2 arom. H); 9.85 (s, CHO). 13C-NMR (CDCl3): 14.07; 22.65; 25.93; 29.03; 29.31; 29.63; 31.89; 68.40;
114.72; 129.73; 131.94; 164.25; 190.73.
3,4-Didodecyloxybenzaldehyde. Yield: 83%. White crystals. M.p. 73.78. 1H-NMR (CDCl3): 0.79 (t, J ˆ 6.79,
2 Me); 1.18 ± 1.38 (m, 19 CH2); 1.68 ± 1.75 (m, 2 CH2); 3.97 (q, J ˆ 6.5, 2 CH2O); 6.78 (d, J ˆ 17.9, 1 arom. H);
7.33 (s, 1 arom. H); 7.37 (d, J ˆ 12.0, 1 arom. H); 9.73 (s, CHO). 13C-NMR (CDCl3): 14.01; 22.61; 25.92; 28.94;
29.02; 29.30; 29.55; 31.86; 69.04; 110.97 (C(6)); 111.72 (C(2)); 126.43 (C(5)); 129.85 (C(1)); 149.41 (C(4));
154.63 (C(3)); 190.72 (CO).
3,4,5-Tridodecyloxybenzyl Alcohol. Methyl 3,4,5-tridodecyloxybenzoate (10.0 g, 0.0145 mol) in 100 ml of
dry THF was added dropwise to a suspension of LiAlH4 (0.61 g, 0.0161 mol) in THF soln. at ice-bath temp. The
mixture was stirred at r.t. for 2 h, and then refluxed for 30 min. HCl (1.0m) was added to neutralize the soln., and
the soln. was extracted twice with CHCl3. The combined CHCl3 phases were evaporated to give pale yellow
solids. Recrystallization from acetone/MeOH gave white solids. Yield: 90%. 1H-NMR (CDCl3): 0.86 (t, 3 Me);
1.24 ± 1.80 (m, 30 CH2); 3.94 (t, 3CH2O); 4.55 (s, CH2OH); 6.52 (d, 2 arom. H). 13C-NMR (CDCl3): 14.10;
22.68; 26.13; 29.40; 29.49; 29.67; 29.78; 31.99; 32.01; 65.28; 68.88; 73.26; 114.97; 135.94; 137.67; 153.11.
3,4,5-Tridodecyloxybenzaldehyde. 3,4,5-Tridodecyloxybenzyl alcohol (5.00 g, 0.0075 mol) in dry CH2Cl2
(100 ml) was slowly added to a soln. of pyridinium chlorochromate (1.80 g, 0.0084 mmol) in CH2Cl2 (20 ml). The
soln. was stirred for 4 h., filtered through Celite, and the solvent was removed under reduced pressure. The
residue was purified by chromatography (silica gel; hexane/AcOEt, 5 :1). White solids were obtained after
recrystallization from CH2Cl2/MeOH. Yield: 75%. M.p. 49.88. 1H-NMR (CDCl3): 0.85 (t, J ˆ 6.38, 3 Me); 1.24 ±
1.49 (m, 27 CH2); 1.66-1.83 (m, 3 CH2); 4.02 (q, J ˆ 6.00, 3 CH2O); 7.05 (s, 2 arom. H); 9.80 (s, CHO).
13C-NMR (CDCl3): 14.08; 22.67; 26.04; 29.23; 29.35; 29.67; 30.32; 31.91; 69.21; 73.61; 107.82; 131.42; 143.81;
153.50; 191.26.
(3Z,6Z)-3,4-Bis(4-dodecyloxybenzylidene)piperazine-2,5-dione (1e). Yield: 72%. M.p. 225.58. IR (KBr):
1
3218, 2922, 2847, 1684, 1626, 1603, 1514, 1472, 1412, 1356, 1250, 1180, 796. H-NMR (CDCl3): 0.88 (t, J ˆ 6.13,
2 Me); 1.18 ± 1.38 (m, 18 CH2); 1.72 ± 1.83 (m, 2 CH2); 4.00 (t, J ˆ 6.50, 2 CH2O); 6.93 (s, 2 CHˆC); 6.95 (d, J ˆ
7.71, 4 arom. H); 7.31 (d, J ˆ 8.34, 4 arom. H); 8.00 (s, 2 NH). 13C-NMR (CDCl3): 13.88; 22.65; 26.09; 29.33;
29.66; 31.94; 68.57; 115.87; 116.32; 124.63; 125.32; 130.03; 157.32; 159.94. Anal. calc. for C42H62N2O4: C 76.55,
H 9.48, N 4.25; found: C 75.52, H 9.54, N 4.21.
(3Z,6Z)-3,6-Bis(3,4-didodecyloxybenzylidene)piperazine-2,5-dione (2e). 1,4-Diacetylpiperazine-2,5-dione
(0.70 mg, 3.51 mmol) and 3,4-didodecyloxybenzaldehyde (3.51 g, 3.51 mmol) were mixed in 25.0 ml of DMF/
toluene 1:1, CeCO3 (2.41 mg, 7.38 mmol) was added under N2, and the mixture was stirred at 808 for 7 h. The
soln. was concentrated to give yellow solids, which were washed with AcOEt several times until the filtrate was
completely colorless. Pale yellow solids were obtained after recrystalliztion from hot THF. Yield: 65%. M.p.
148.08. IR (neat): 3171, 2922, 2847, 1682, 1634, 1595, 1518, 1464, 1408, 1352, 1335, 1263, 1234, 1130, 1024, 783,
723. 1H-NMR (CDCl3): 0.86 (t, J ˆ 6.20, 4 Me); 1.24 ± 1.56 (m, 36 CH2); 1.77 ± 1.80 (m, 4 CH2); 3.99 (q, J ˆ 6.59,
4 CH2O); 6.84 (s, 2 CHˆC); 6.87 ± 6.98 (m, 6 arom. H); 8.13 (s, 2 NH). 13C-NMR (CDCl3): 13.92; 22.65; 26.13;

Helvetica Chimica Acta ± Vol. 82 (1999)
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26.35; 29.35; 29.45; 29.65; 31.95; 69.83; 70.10; 115.18; 115.42; 116.54; 121.45; 124.98; 125.98; 150.30; 150.57;
157.22. Anal. calc. for C66H110N2O6: C 77.14, H 10.79, N 2.73; found: C 77.11, H 10.71, N 3.37.
(3Z,6Z)-3,6-Bis(3,4,5-tridodecyloxybenzylidene)piperazine-2,5-dione (3e). Yield: 71%. M.p. 89.68. IR
(KBr): 3177, 2928, 2845, 1678, 1628, 1582, 1473, 1448, 1404, 1333, 1240, 1120, 721. 1H-NMR (CDCl3): 0.87 (t, J ˆ
6.35, 6 Me); 1.17 ± 1.46 (m, 54 CH2); 1.68 ± 1.86 (m, 6 CH2); 3.94 ± 4.02 (m, 6 CH2O); 6.64 (s, 4 arom. H); 6.90
(s, 2 CHˆC); 8.08 (s, 2 NH). 13C-NMR (CDCl3): 14.09; 22.68; 26.09; 29.37; 29.64; 30.32; 31.92; 69.39; 73.62;
106.92; 117.16; 125.08; 127.55; 139.06; 153.93; 156.95. Anal. calc. for C90H158N208: C 77.42, H 11.41, N 2.01;
found: C 76.28, H 11.52, N 1.90.
(3Z,6Z)-3,6-Bis(3,4-didodecyloxybenzylidene)-N,N-dimethylpiperazine-2,5-dione (4e). A mixture of 2e
(508 mg, mmol) and MeI (0.078 ml, mmol) was dissolved in THF (5.0 ml), 60% NaH (50.4 mg, mmol) was
added, and the mixture was stirred at r.t. for 8 h. The soln. was concentrated to dryness, and the solid was
redissolved in AcOEt (10 ml). The soln. was washed with HCl (5%). The org. layer was collected and dried.
Light yellow solids were obtained after recrystallization from hot THF. Yield: 83%. M.p. 60.08. IR (KBr): 2921,
2851, 1686, 1627, 1520, 1470, 1426, 1379, 1343, 1269, 1190, 1136, 1024, 810, 756, 716. 1H-NMR (CDCl3): 0.88
(t, J ˆ 6.17, 4 Me); 1.26 ± 1.57 (m, 36 CH2); 1.79 ± 1.82 (m, 4 CH2); 3.02 (s, 2 MeN); 3.99 (q, J ˆ 6.45, 4 CH2O);
6.82 ± 6.86 (m, 6 arom. H); 7.12 (s, 2 CH2ˆC). 13C-NMR (CDCl3): 14.10; 22.66; 26.01; 29.35; 29.62; 31.56; 31.90;
35.23; 69.00; 69.37; 112.68; 114.90; 121.97; 123.09; 125.76; 129.95; 148.62; 149.68; 162.81. Anal. calc. for
C68H114N2O6: C 77.37, H 10.88, N 2.65; found: C 77.11, H 10.71, N 2.62.
We thank the National Science Council of Taiwan, ROC (NSC-87-2113-M008-007, NSC-87-2113-M008-008)
for the generous support of this work.
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Received May 3, 1999