Synthetic study of tetramethyljulolidine - A key intermediate toward the synthesis of the red dopant DCJTB for OLED applications

Article abstract of DOI:10.1016/S0040-4039(02)02506-6

The formation and characterization of a novel chiral sulfonic acid derivative obtained during the synthesis of 1,1,7,7-tetramethyljulolidine (TMJ), a key intermediate towards the red dopant 4-(dicyanomethylene)-2-t-butyl-6-(1,1,7,7-tetramethyljulolidyl-9-

Full text of DOI:10.1016/S0040-4039(02)02506-6

TETRAHEDRON
LETTERS
Pergamon
Tetrahedron Letters 44 (2003) 145–147
Synthetic study of tetramethyljulolidine—a key intermediate
toward the synthesis of the red dopant DCJTB for OLED
applications
Banumathy Balaganesan, Shih-Wen Wen and Chin H. Chen*
Department of Applied Chemistry and Microelectronics and Information Systems Research Center,
National Chiao Tung University, Hsinchu, Taiwan, ROC 300
Received 14 May 2002; revised 24 October 2002; accepted 1 November 2002
Abstract—The formation and characterization of a novel chiral sulfonic acid derivative obtained during the synthesis of
1,1,7,7-tetramethyljulolidine (TMJ), a key intermediate towards the red dopant 4-(dicyanomethylene)-2-t-butyl-6-(1,1,7,7-tetra-
methyljulolidyl-9-enyl)-4H-pyran (DCJTB) used for organic electroluminescent devices, upon bis-annulation of N,N-bis(4-methyl-
2-butenyl)aniline is described. © 2002 Elsevier Science Ltd. All rights reserved.
Organic electroluminescent devices are of growing
interest in various display applications due to their high
luminous efficiency and capability of emitting many
colors throughout the visible spectrum. Commercial
interest in organic light emitting diode (OLED) tech-
nology has been the vital driving force in fueling the
recent research and development activities.1,2 4-
(Dicyanomethylene)-2-t-butyl-6-(1,1,7,7-tetramethyl-
julolidyl-9-enyl)-4H-pyran, (DCJTB) is one of the best
fluorescent dopants of choice for the red emitter of
tris(8-hydroxyquinolinato)aluminum hosted OLEDs
including Pioneer’s recently demonstrated passive
matrix full color prototype and Kodak/Sanyo’s 2.4-in
and 5.5-in low temperature poly silicon full color active
matrix OLED displays. The cost of manufacturing
DCJTB is prohibitively high owing to the synthetic
complications of one of the key intermediates, 1,1,7,7-
tetramethyljulolidine (TMJ), which can be prepared in
two steps from aniline and 1-chloro-3-methyl-2-butene
(Scheme 1). The low yield (ꢀ30%) obtained in the acid
catalyzed bis-annulation prompted us to reinvestigate
the reaction and analyze the products of the above
reaction.
bis-annulation in the presence of an acid catalyst to
form the key intermediate TMJ.
Different acid catalysts were employed to effect the
bis-annulation. The starting material was found to
remain unaffected in the presence of weak acids like
p-toluenesulfonic acid, methanesulfonic acid and acetic
acid. Strong acids such as aqueous perchloric acid,
trifluoroacetic acid and trifluoromethanesulfonic acid
led to the formation of TMJ in infinitesimal quantities
along with an inseparable polar mixture. In the pres-
ence of concentrated sulfuric acid at 0°C, TMJ was
obtained in 37% yield in addition to a major quantity
N,N-Bis(4-methyl-2-butenyl)aniline 1 was prepared by
the conventional N-alkylation of aniline with 2 equiv.
of 1-chloro-3-methyl-2-butene in the presence of K2CO3
at reflux. This compound was then subjected to a
* Corresponding author. Fax: (886) 03-575 0463; e-mail: fredchen@
eic.nctu.edu.tw
Scheme 1. Synthesis of DCJTB.
0040-4039/03/$ - see front matter © 2002 Elsevier Science Ltd. All rights reserved.
PII: S0040-4039(02)02506-6

146
B. Balaganesan et al. / Tetrahedron Letters 44 (2003) 145–147
of an insoluble material. To enhance the yield of TMJ,
the temperature of the reaction was raised to about
30°C, but this led to a further decrease in the yield of
TMJ (34%) accompanied by a proportionate increase in
the formation of the insoluble by-product (Table 1).
Moreover, in both cases, conc. sulfuric acid was used in
large excess (about three v/w equivalents), which led to
a voluminous precipitation during the basic work-up of
the reaction, which in turn made the process of filtra-
tion more tedious. Hence, we decided to use a combina-
tion of acids to avoid these complications.
Various proportions of methanesulfonic acid and sulfu-
ric acid were prepared (v/v equivalents—1:1, 2:1, 4:1) to
catalyze the formation of TMJ. A decrease in the
concentration of sulfuric acid resulted in a drastic
decrease in the yield of TMJ (Table 1). However, the
insoluble by-product 2 was obtained predominantly
Figure 1. ORTEP diagram for compound 2. For the sake of
clarity, H atoms are not labeled.
(59%) when
a
1:1 mixture of methanesulfonic
acid:sulfuric acid was used, which provoked our interest
in characterizing and studying its formation.
The mass spectra of compound 2 showed peaks at m/e
309 (M+) and at 229 (M+−SO3H+1), indicating that
product 2 must bear a –SO3H group in its skeleton. The
1
unsymmetrical nature of the H NMR spectrum sug-
gested that the compound might have undergone an
unexpected rearrangement during the acid-catalyzed
bis-annulation. The 13C NMR showed signals for three
quaternary, four methine, five methylene and two
methyl carbons. A methylene at 116.88 ppm indicated
the presence of an exocyclic double bond whose pro-
tons resonated at 5.28 and 4.94 ppm as singlets. Based
on a detailed analysis of both one and two C–C dimen-
sional NMR spectra (1H–1H COSY, 1H–13C HET-
COR), the structure was found to be consistent with
structure 2 (Fig. 1).3 It was further unequivocally con-
firmed by a single crystal X-ray diffraction study.4
Scheme 2.
product, a novel chiral sulfonic acid derivative 2
obtained during the synthesis of TMJ, a key intermedi-
ate towards the red dopant DCJTB for organic electro-
luminescent devices upon bis-annulation of N,N-bis(4-
methyl-2-butenyl)aniline 1. It was also found that 2 is a
water-soluble compound and hence can be eliminated
easily to furnish highly pure TMJ.
A plausible mechanism for the formation of 2-(4%,4%-
dimethyl-1%-phenyl-3%-piperidyl)-2-propene-1-sulfonic
acid 2 is presented in Scheme 2.
The mechanism is likely to involve an acid-catalyzed
intramolecular alkylation of the double bond by the
first-formed carbonium ion to form the intermediate 3.
Further the exocyclic double bond of 3 undergoes
sulfonation in the presence of sulfuric acid to form the
sulfonic acid 2.
Acknowledgements
We wish to thank the National Science Council, Tai-
wan, Republic of China for providing a post-doctoral
fellowship for B.B. The authors gratefully acknowledge
the help of L. W. Kelts of Eastman Kodak Company,
Rochester, New York for providing the 500 MHz
To summarize, we have characterized and proposed a
plausible mechanism for the formation of the by-
Table 1. Yields of TMJ and 2 obtained by catalysis using various proportions of sulfuric acid and methane sulfonic acid
Entry
Acid/solvent
Temperature (°C)
Time (h)
Yield of TMJ (%)
Yield of 2 (%)
1
2
3
4
5
Conc. H2SO4
Conc. H2SO4
H2SO4:CH3SO3H (1:1)
H2SO4:CH3SO3H (1:2)
H2SO4:CH3SO3H (1:4)
0
0.5
3
1
3
3
37
34
16
10
B5
20
22
59
22
–
0–30
0
0–30
0–30

B. Balaganesan et al. / Tetrahedron Letters 44 (2003) 145–147
147
NMR spectroscopic data and the Department of Crys-
tallography, National Tsing-Hua University, Taiwan
for single crystal X-ray diffractional analyses.
49.26 (CH, C-2%), 50.32 (CH2, C-2%), 61.89 (CH2, C-1),
116.18 (2CH’s, C-2%%, C-6%%), 116.88 (CH2, C-3), 118.96
(CH, C-4%%), 129.32 (2CH’s, C-3%%, C-5%%), 142.60 (C-2),
151.11 (C-1%%).
4. Compound 2 was crystallized from acetonitrile:water. 2-
(4,4-Dimethyl-1-phenyl-3-piperidyl)-2-propene-1-sulfonic
acid 2 was found to be a dl-pair as seen from the X-ray
diffractional pattern.
References
1. Chen, C. H.; Tang, C. W.; Shi, J.; Klubek, K. P. Macro-
mol. Symp. 1997, 125, 49–58.
2. Chen, C. H.; Tang, C. W. In Chemistry of Functional
Dyes; Yoshida, Z.; Shirota, Y., Eds.; Mita Press: Tokyo,
Japan, 1993; Vol. 2, pp. 536–543.
Crystal data for compound 2[F1]: C32H58N2O13S2, M=
742.92 (dl-pair), monoclinic, space group P2(1)/c at a
,
temperature 294(2) K and wavelength=0.71073 A, a=
,
,
20.7836(18) A, h=90°, b=9.7131(9) A, i=117.156(2)°,
3. Typical experimental procedure: To a mixture of methane-
sulfonic acid and sulfuric acid (1:1 v/v equivalents, 5 mL),
N,N-bis(4-methyl-2-butenyl)aniline (1, 2.5 g, 11 mmol)
was added at 0°C and the mixture stirred for 1 h. After
complete disappearance of the starting material (moni-
tored by TLC), the reaction mixture was poured onto ice
and extracted using dichloromethane (3×300 mL). The
organic layer was washed with saturated NaHCO3 solu-
tion and water, dried over anh. MgSO4 and the solvent
was evaporated to dryness to yield TMJ (4 g, 16%).
During basification of the aqueous layer of the reaction
mixture using saturated NH4OH solution, compound 2
crystallized as needles (2.0 g, 59%; mp 56–58°C). Spectral
3
,
,
c=21.9556(19) A, k=90°, U=3943.7(6) A , Z=4, Dc=
1.251 mg/m3; absorption coefficient=0.196 mm−1
,
F(000)=1600, crystal size=1.10×0.15×0.10 mm3; q range
for data collection=1.10–28.28°, index ranges −235h5
26, −125k512, −285l524, reflections collected=22 977,
independent reflections=8752 [Rint=0.0728], completeness
to q=28.28° is 89.6%, absorption correction=empirical,
max. and min. transmission=0.8960 and 0.4552, refine-
ment method=full-matrix least-squares on F2, data/
restraints/parameters=8752/0/442, goodness-of-fit on
F2=1.124, final R indices [I>2|(I)] R1=0.0761, wR2=
0.2203; R indices (all data) R1=0.1260, wR2=0.2533,
largest difference peak and hole=0.582 and −0.597. Crys-
tallographic data (excluding structure factors) for the
structure in this paper have been deposited with the Cam-
bridge Crystallographic Data Centre as supplementary
publication number CCDC 181958. Copies of the data can
be obtained, free of charge, on application to CCDC, 12
Union Road, Cambridge CB2 1EZ, UK [fax: +44(0)-1223-
336033 or e-mail: deposit@ccdc.cam.ac.uk].
1
characteristics of 2: H NMR (CDCl3, 500MHz) l 0.86 (s,
3H), 0.95 (s, 3H), 1.43 (m, 1H), 1.66 (dt, J=13.5, 2.5 Hz,
1H), 2.55 (dd, J=12.0, 4.5 Hz, 1H), 2.85 (m, 2H), 3.35
(dd, J=12.5, 3.0 Hz, 1H), 3.45 (dd, J=12.5, 3.0 Hz, 1H),
3.55 (q, J=13.25 Hz, 2H), 4.94 (s, 1H), 5.28 (s, 1H), 6.82
(t, J=8.0 Hz, 1H), 6.95 (d, J=7.8 Hz, 2H), 7.22 (t, J=8.0
Hz, 2H). 13C NMR (CDCl3, 125 MHz) l 19.74, 30.66
(2Me’s), 32.70 (C-4%), 40.08 (CH2, C-5%), 45.44 (CH2, C-6%),