P. K. Bhowmik et al. / Tetrahedron Letters 48 (2007) 5383–5387
5387
shown in Figure S7 in the supplementary material. The
reaction for the synthesis of compound 2 was repeated
once for a long period of 48 h. Its yield improved
significantly giving 3.3 g (46%) of the desired product at
the expense of monoaldehyde.
award from Research Corporation for the support of
this research.
Supplementary data
The procedure for the synthesis of compound 3 was
followed identically (24 h) to that for compound 2 up to
the neutralization step. After air-drying, it was purified by
column chromatography over silica gel eluting in CHCl3.
On evaporation of CHCl3 yielded compound 3, which was
then recrystallized from CHCl3/acetone to produce 2.0 g
(28%) of light yellow powder. 1H NMR (400 MHz,
CDCl3) d (ppm) 8.60 (d, J = 6.4 Hz, 4H), 7.44 (s, 1H),
7.40 (d, J = 6.0 Hz, 4H), 7.26–7.70 (m, 3H), 7.32 (d,
J = 16.4 Hz, 2H), 7.06 (d, J = 16.4 Hz, 2H); 13C NMR
(100 MHz, CDCl3) d (ppm) 150.29, 144.78, 136.96, 133.01,
129.59, 127.47, 126.88, 125.92, 121.14; Anal. Calcd
(found) for C20H16N2 (284.36): C, 84.48 (84.09); H, 5.67
(6.03); N, 9.85 (9.97).
1
The H and 13NMR spectra of 1, 2, and 5 (Figs. S1–
S3), their photoluminescence spectra in solid state,
CHCl3, THF, and DMSO (Figs. S4–S6), and DSC
thermograms of a monoaldehyde (Fig. S7) are provided
as supplementary data. Supplementary data associated
with this article can be found, in the online version, at
References and notes
1. Attias, A.-J.; Cavalli, C.; Bloch, B.; Guillou, N.; Noe¨l, C.
Chem. Mater. 1999, 11, 2068.
The reaction setup for compound 4 was identical to the
described procedure (vide supra). The reaction was carried
out for a period of 48 h. Upon cooling, the reaction
mixture was treated with 100 mL of 6 M aqueous HCl.
When the solution was neutralized with 3 M aqueous
NaOH a sticky material was formed. It was allowed to
settle down and the solution was decanted. It was washed
with fresh distilled water. The material was dried in a
vacuum oven. It was eluted in CHCl3 through a column
chromatography on silica gel. The solvent was evaporated.
The resulting material was lighter in color but still had a
sticky appearance. After drying it was dissolved in
methanol and was treated with aqueous NaHSO3 to
remove any residual aldehydes. Subsequently, the com-
pound was recrystallized for methanol/water mixture to
yield 2.8 g (39%) of off-white powder. 1H NMR
(400 MHz, CDCl3) d (ppm) 8.62 (d, J = 7.6 Hz, 2H),
7.66–7.80 (m, 4H), 7.43 (s, 1H), 7.41 (d, J = 8.4 Hz, 2H),
7.26–7.70 (m, 3H), 7.21 (d, J = 16 Hz, 2H), 7.15–7.19 (m,
2H); 13C NMR (100 MHz, CDCl3) d (ppm) 155.64,
149.80, 137.29, 136.92, 132.76, 129.35, 128.46, 127.30,
126.00, 122.47, 122.41; Anal. Calcd (found) for C20H16N2
(284.36): C, 84.48 (84.45); H, 5.67 (6.00); N, 9.85 (10.02).
The procedure for compound 5 was followed in an
identical manner (24 h) to that for compound 2 up to
the neutralization step. After air-drying, the crude product
was recrystallized from toluene twice resulting 1.5 g of the
desired compound, which was eluted in CH2Cl2 through a
column chromatography on silica gel. The solvent was
evaporated to yield 0.4 g (6%) of bright yellow powder.
Anal. Calcd (found) for C32H26N4 (466.59): C, 82.38
(81.99); H, 5.62 (6.01); N, 12.01 (12.17).
2. Ko, C.-W.; Lin, H.-C. Thin Solid Films 2000, 363, 81.
3. Lin, H.-C.; Sheu, H.-Y.; Chang, C.-L.; Tsai, C. J. Mater.
Chem. 2001, 11, 2958.
4. Lu, X.; He, C.; Terrell, C. D.; Griffin, A. C. Macromol.
Chem. Phys. 2002, 203, 85.
5. Lin, H.-C.; Tsai, C.-M.; Huang, G.-H.; Tao, Y.-T.
Macromolecules 2006, 39, 557.
6. General procedure for Knoevenagel condensation reaction
for compound 1: 3.4 g (25.3 mmol) of terephthalaldehyde
and 4.8 g (53.2 mmol) of c-picoline was heated to reflux
for 24 h in 3 mL of acetic acid and 5 mL of acetic
anhydride at 135 ꢁC. The reaction mixture was cooled
down to rt. It was placed in 100 mL of aqueous 6 M HCl.
The resulting precipitate was collected and subsequently
washed repeatedly with copious water. The filtrate was
neutralized with 3 M NaOH. Upon air-drying, crude
product 1 of 5.4 g was collected and then recrystallized
from CHCl3/acetone to yield 4.1 g (57%) of orange
powder. Anal. Calcd (found) for C20H16N2 (284.36): C,
84.48 (84.09); H, 5.67 (6.02); N, 9.85 (9.96).
The reaction for compound 2 was set up using similar
procedure (24 h) and on an identical scale for compound
1. After completion of the reaction period, the reaction
mixture was cooled down to rt. It was placed in 100 mL of
aqueous 6 M HCl. The solution was neutralized with the
slow addition of aqueous 3 M NaOH resulting in a
precipitate that was washed with a large volume of water.
Upon air-drying, 5.7 g of crude product 2 was collected
and then recrystallized from CHCl3/acetone to yield 2.0 g
(28%) of golden-yellow crystals. Anal. Calcd (found) for
C20H16N2 (284.36): C, 84.48 (83.85); H, 5.67 (5.88); N,
9.85 (9.78). The collected mother liquor from recrystalli-
zation flask was run through a column chromatography
over silica gel. Upon evaporation of solvents, 2.8 g (58%)
of bright yellow powder was collected, characterized and
identified to be 2-(4-formylstyryl)pyridine-a monoalde-
hyde byproduct. 1H NMR (400 MHz, CDCl3) d (ppm)
10.01 (s, 1H), 8.64 (d, J = 7.2 Hz, 1H), 7.88 (d, J = 8.4 Hz,
2H), 7.72 (d, J = 8.4 Hz, 2H), 7.60–7.71 (m, 2H), 7.41 (d,
J = 7.6 Hz, 1H), 7.29 (d, J = 16.4 Hz, 1H), 7.20–7.26 (m,
1H); 13C NMR (100 MHz, CDCl3) d (ppm) 191.83,
154.92, 149.98, 142.86, 137.04, 136.05, 131.63, 131.20,
130.44, 127.76, 123.06, 123.02; Anal. Calcd (found) for
C14H11NO (209.25): C, 80.36 (79.99); H, 5.30 (5.70); N,
6.69 (6.98). It had a Tm at 83 ꢁC (DH = 4.2 kcal/mol) in
the first heating cycle; and its DSC thermograms are
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