Self-Assembly of Trimesic Acid Analogues
2537±2547
1,3,5-Tribromo-2,4,6-tripropylbenzene (7c): With a procedure analogous to
that used for 7b, 6c (15 g, 90% pure by H NMR) was converted into 7c
113.2, 34.9, 31.5, 30.2, 22.1, 13.7; anal. calcd C24H33N3: C 79.29, H 9.15, N
11.56; found C 79.45, H 9.04, N 11.65.
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(22 g, 62%) as colorless needles: m.p. 111 ± 1138C (lit. m.p.[31] 112 ± 1138C);
1H NMR: d 3.03 (m, 2H, CH2-1'), 1.58 (m, 2H, CH2-2'), 1.04 (t, J 7.3 Hz,
3H, CH3); 13C NMR: d 141.3, 124.7, 41.1, 21.3, 14.2; anal. calcd C15H21Br3:
C 40.85, H 4.80, Br 54.35; found C 40.61, H 4.86, Br 54.53.
Trimethyl 2,4,6-triethylbenzene-1,3,5-tricarboxylate (9b): A mixture of 8b
(1 g, 4.2 mmol) and aqueous sulfuric acid (19 g, 80% w/w, water (4.5 mL),
and concentrated sulfuric acid (8 mL)) was heated at 150 ± 1608C for 5 h.
The resulting brown homogeneous reaction mixture was cooled to 80 ±
908C and finely ground sodium nitrite (2 g, 29 mmol) was added in portions
of about 0.2 g over 2 h with vigorous stirring during which time a tan
precipitate formed (Caution: foaming and gas evolution!). The heteroge-
neous mixture was allowed to stir for an additional hour, cooled to room
temperature, and poured into cold water (100 mL). The resulting brownish
solution was extracted with diethyl ether (150 mL). The organic layer was
separated, dried over magnesium sulfate, and concentrated at reduced
pressure to afford a tan solid (0.8 g). A solution of crude acid 4b (0.8 g,
ca. 2.7 mmol) in reagent grade THF (50 mL) was treated with an ethereal
solution of diazomethane (60 mL) at 08C: diazomethane was generated
from Diazaldꢂ (4.28 g, 20 mmol) and KOH (0.8 g, 14 mmol) as a solution in
diethyl ether (60 mL). Excess of diazomethane was quenched with glacial
acetic acid (5 mL) and the solvent was removed under reduced pressure.
The resulting brown oil was dissolved in CH2Cl2 (160 mL) and washed with
a saturated aqueous solution of sodium bicarbonate until the pH of the
aqueous layer was basic and no further gas evolution occurred. The organic
layer was dried with anhydrous magnesium sulfate and the solvent was
removed under reduced pressure. Flash chromatography over silica gel
(petroleum ether/CH2Cl2 1:3) followed by Kugelrohr distillation afforded
9b (0.5 g; 35% from 8b) as a thick colorless oil: 1H NMR: d 3.82 (s, 3H,
CO2CH3), 2.45 (q, J 7.5 Hz, 2H, CH2), 1.09 (t, J 7.5 Hz, 2H, CH3);
13C NMR: d 169.2, 138.6, 132.6, 51.8, 25.2, 15.3; anal. calcd C18H24O6: C
64.27, H 7.19; found C 64.36, H 7.31.
1,3,5-Tribromo-2,4,6-tributylbenzene (7d): With a procedure analogous to
that used for 7b, except that the 6d was added by syringe pump over 1 h, 6d
(10 g) was converted into a yellow solid which was subjected to a short-path
Kugelrohr distillation to afford 7d (17 g, 86%) as a white solid. The product
was recrystallized from 2-propanol to afford long white needles: m.p. 56 ±
588C; 1H NMR: d 3.07 (t, J 8.6 Hz, 2H, CH2-1'), 1.50 (m, 4H, CH2-2'),
1.39 (m, 2H, CH2-3'), 0.99 (t, J 6.9 Hz, 3H, CH3); 13C d 141.4, 124.6,
39.0, 30.0, 22.9, 13.9; anal. calcd C18H27Br3: C 44.74, H 5.63, Br 49.62; found
C 44.71, H 5.66, Br 49.58.
1,3,5-Tribromo-2,4,6-tripentylbenzene (7e): With a procedure analogous to
that used for 7b, 6e (10 g) was converted into a dark oil which was distilled
with a Kugelrohr apparatus. The resulting brownish oil was dissolved in a
mixture of light petroleum ether (50 mL) and CH2Cl2 (50 mL) and passed
through a short plug of silica gel. The solvent was evaporated and the
resulting colorless oil was heated in a Kugelrohr apparatus to 120 ± 1308C
to remove any volatiles to afford 7e (11.3 g, 61%) as a white waxy solid:
1
m.p. 40 ± 428C; H NMR: d 3.06 (m, 2H, CH2-1'), 1.55 (m, 2H, CH2-2'),
1.43 (m 4H, CH2-3', CH2-4'), 0.94 (t, J 6.9 Hz, 3H, CH3); 13C NMR: d
141.5, 124.6, 39.2, 32.0, 27.5, 22.3, 14.1.
1,3,5-Tricyano-2,4,6-triethylbenzene (8b): A mixture of 7b (14 g, 35 mmol)
and cuprous cyanide (19 g, 210 mmol) in reagent grade DMF (140 mL) was
refluxed for 50 h. The reaction mixture was cooled to room temperature,
poured into a solution of ferric chloride hydrate (50 g) in aqueous HCl
(400 mL, 10% w/w) and stirred at 808C for 30 min. The resulting dark
green mixture was extracted twice with CH2Cl2 (200 mL) and once with
benzene (200 mL). The combined organic fractions were dried over
magnesium sulfate and the solvent was removed under reduced pressure
to afford a dark green solid. Kugelrohr distillation followed by flash
chromatography (30% v/v petroleum ether/CH2Cl2) and recrystallization
from petroleum ether afforded 8b (1.8 g, 21%) as long white needles: m.p.
164 ± 1658C (lit. m.p.[32] 165 ± 1668C); 1H NMR: d 3.13 (q, J 7.6 Hz, 2H,
CH2), 1.36 (t, J 7.6 Hz, 3H, CH3); 13C NMR: d 156.6, 113.8, 112.7, 28.4,
14.4.
Trimethyl 2,4,6-tripropylbenzene-1,3,5-tricarboxylate (9c): With a proce-
dure analogous to that used for 9b, 8c (2.79 g, 10 mmol) was converted into
a crude product which was dissolved in 1:1 petroleum ether/CH2Cl2 and
passed through a short pad of silica gel, followed by a short-path Kugelrohr
distillation to afford 9c (1.57 g; 41% from 8c) as an oil, which later
crystallized as colorless thick needles: m.p. 37 ± 408C; 1H NMR: d 3.88 (s,
3H, OCH3), 2.43 (m, 2H, CH2-1'), 1.54 (m, 2H, CH2-2'), 0.90 (t, J 7.3 Hz,
3H, CH3); 13C NMR: d 169.5, 137.6, 133.0, 52.0, 34.7, 24.6, 14.6; anal. calcd
C21H30O6: C 66.64, H 8.00; found C 66.68, H 8.04.
Trimethyl 2,4,6-tributylbenzene-1,3,5-tricarboxylate (9d): With a proce-
dure analogous to that used for 9b, 8d (4.7 g) was converted into a crude
product which was purified by radial chromatography on 2 mm silica gel
coated plates (15% v/v petroleum ether/CH2Cl2), followed by a short-path
Kugelrohr distillation to afford 9d (0.62 g; 49% from 8d) as a colorless
viscous oil: b.p. 140 ± 1508C (Kugelrohr); 1H NMR: d 3.83 (s, 3H,
CO2CH3), 2.43 (t, J 5.7 Hz, 2H, CH2-1'), 1.46 (m, 2H, CH2-2'), 1.26 (m,
2H, CH2-3'), 0.83 (t, J 7.3 Hz, 3H, CH3); 13C NMR: d 169.3, 137.6, 132.7,
51.8, 33.2, 31.7, 22.9, 13.5; anal. calcd C24H36O6: C 68.54, H 8.63; found C
68.52, H 8.63. (Note: In scale-up experiments filtration of the ester as a
solution in 1:1 petroleum ether/CH2Cl2 through a pad of silica gel was
successfully used instead of radial chromatography.)
1,3,5-Tricyano-2,4,6-tripropylbenzene (8c): With a procedure analogous to
that used for 8b, 7c (9.66 g) was converted into a yellow solid which was
recrystallized from petroleum ether to afford 8c (2.8 g) as long white
needles. The solvent from the mother liquor was removed under reduced
pressure and the resulting yellowish solid was chromatographed (petro-
leum ether/CH2Cl2 1:1). The product thus obtained was recrystallized from
petroleum ether to afford 8c (0.9 g) as long white needles. The solvent from
the mother liquor was removed under reduced pressure and the resulting
white solid was further purified by radial chromatography over 4 mm silica
gel coated plates (9% CH2Cl2/petroleum ether) to afford an additional
1.2 g of 8c as white needles (total yield: 4.9 g, 80%): m.p. 55 ± 578C;
1H NMR: d 3.08 (m, 2H, CH2-1'), 1.76 (m, 2H, CH2-2'), 1.07 (t, J 7.3 Hz,
3H, CH3); 13C NMR: d 154.9, 114.2, 113.5, 36.6, 23.9, 13.9; anal. calcd
C18H21N3: C 77.38, H 7.58, N 15.04; found C 77.22, H 7.55, N 15.05.
Trimethyl 2,4,6-tripentylbenzene-1,3,5-tricarboxylate (9e): A mixture of 8e
(1.5 g, 4 mmol) and aqueous sulfuric acid (30 mL, 80% w/w) was heated at
160 ± 1708C for 8 h (with reflux condensor attached!). Every 30 min water
(2 mL) was added through the condensor. (Caution!) The resulting brown
homogeneous reaction mixture was cooled to 80 ± 908C and methanesul-
fonic acid (5 mL) was added followed by nitrosyl tetrafluoroborate (2.1 g,
18 mmol) in portions of about 0.3 g with vigorous stirring. The addition was
complete, the reaction mixture was stirred for 30 min, cooled to room
temperature and poured into cold water (100 mL). The resulting creamy
solid was filtered, washed with water (200 mL), and air dried. A solution of
the crude acid in reagent grade THF (100 mL) was treated with diazo-
methane as described for 9b. Flash chromatography of the resulting brown
residue over silica gel (30% v/v CH2Cl2/petroleum ether to 50% CH2Cl2/
petroleum ether), followed by a short-path Kugelrohr distillation afforded
2,4,6-Tributyl-1,3,5-tricyanobenzene (8d): With a procedure analogous to
that used for 8b, 7d (7.2 g) was converted into a crude product which was
purified by flash chromatography (4% ethyl acetate/petroleum ether).
Mixed fractions were further purified by radial chromatography on a 4 mm
silica gel coated plates (petroleum ether). The combined product was
recrystallized from pentane to afford 8d (2.8 g, 58%) as long white needles:
m.p. 64 ± 668C; 1H NMR: d 3.09 (t, J 7.8 Hz, 2H, CH2-1'), 1.68 (m, 2H,
CH2-2'), 1.50 (m, 2H, CH2-3'), 0.98 (t, J 7.2 Hz, 3H, CH3); 13C NMR: d
155.3, 114.2, 113.3, 34.7, 32.5, 22.6, 13.5; anal. calcd C21H27N3: C 78.46, H
8.47, N 13.07; found C 78.42, H 8.45, N 13.09.
1,3,5-Tricyano-2,4,6-tripentylbenzene (8e): With a procedure analogous to
that used for 8b, 7e (10 g) was converted into a dark oil which was
chromatographed over silica gel (20% v/v CH2Cl2/light petroleum ether) to
afford, after Kugelrohr distillation and recrystallization from light petro-
leum ether (freezer), 8e (5.1 g, 74%) as long white needles: m.p. 41 ± 438C;
1H NMR: d 3.09 (m, 2H, CH2-1'), 1.71 (m, 2H, CH2-2'), 1.41 (m, 4H,
CH2-3', CH2-4'), 0.91 (t, J 7.3 Hz, 3H, CH3); 13C NMR: d 155.3, 114.2,
1
9e (0.79 g; 42% from 8e) as a colorless oil: b.p. 190 ± 2008C1 mm Hg
(Kugelrohr), 1H NMR: d 3.88 (s, 3H, OCH3), 2.45 (m, 2H, CH2-1'), 1.51
(m, 2H, CH2-2'), 1.27 (m 4H, CH2-3', CH2-4'), 0.87 (t, J 6.7 Hz, 3H, CH3);
13C NMR: d 169.3, 137.6, 132.7, 51.8, 32.0, 32.0, 30.8, 22.0, 13.7.
1,3,5-Tris(acetoxymethyl)-2,4,6-trimethylbenzene (11): A mixture of 10
(1.7 g, 4.3 mmol), anhydrous sodium acetate (2 g, 24 mmol), and glacial
Chem. Eur. J. 1999, 5, No. 9
ꢁ WILEY-VCH Verlag GmbH, D-69451 Weinheim, 1999
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2545