Synthesis and Topochemistry of 2,5-Bisacrylate-Substituted 1,4-Benzoquinones
again refluxed for 24 h in 90 ml of n-propanol (abs.). After removal MgSO4. The solvent was removed and the oily residue was recrys-
FULL PAPER
of the solvent, the crude product was dissolved in 100 ml of ethyl
acetate and washed with 100 ml of water. The aqueous layer was
tallized from methanol to yield a white powder. It contained the
quinone bisketal 7a and 7f. To obtain the pure benzyl ester 7f it
extracted three times with 50 ml of ethyl acetate. The combined was necessary to repeat this procedure with the mixture of the es-
organic layers were washed with 100 ml of brine and dried with ters, using 3.0 g (28 mmol) of benzyl alcohol and 7.0 ml (11 mmol)
MgSO4. After concentration to dryness, the material was purified
of a solution of nBuLi. The mixture of the esters was dissolved in
by recrystallization from methanol to yield 2.0 g (87%) of the 10 ml of THF (abs.). After 2 h, 120 ml of water was added and the
colourless n-propyl ester 7c, m.p. 136Ϫ137°C (methanol). Ϫ MS organic material was extracted with 50 ml of ethyl acetate. This
(70 eV, EI); m/z (%): 424 (0.2) [Mϩ], 409 (0.4) [M Ϫ CH3ϩ], 393 solution was treated, as described, to yield 450 mg (21.1%) of the
(3.5) [M Ϫ CH3Oϩ], 333 (2.5) [C18H21O6ϩ], 280 (8.1) [C15H20O5ϩ], benzyl ester 7f, m.p. 156Ϫ157°C (methanol). Ϫ MS (70 eV, EI);
247 (3.5) [C14H15O4ϩ], 105 (90) [C5H12O2ϩHϩ], 75 (77) m/z (%): 520 (0.1) [Mϩ], 489 (0.6) [M Ϫ CH3Oϩ], 429 (0.4) [M Ϫ
[C3H7O2ϩ], 43 (100) [C3H7ϩ], 41 (52) [C3H5ϩ].
C7H7ϩ], 328 (6.4) [C19H20O5ϩ], 237 (3.3) [C12H13O5ϩ], 219 (4.6)
[C12H11O4ϩ], 105 (100) [C5H12O2 ϩ Hϩ], 92 (47) [C7H8ϩ], 91 (100)
[C7H7ϩ], 75 (100) [C3H7O2ϩ], 65 (29) [C5H5ϩ].
(E,E)-3,3,6,6-Tetramethoxy-1,4-bis(2-isopropoxycarbonyl-
ethenyl)cyclohexa-1,4-diene (7d): Compound 7a (2.5 g, 6.8 mmol)
was poured into a stirred solution of 150 mg of tetraethyl titanate
in 100 ml of 2-propanol (abs.) and refluxed for 66 h. After removal
of the solvent, the residue was again dissolved in a mixture of 150
mg of tetraethyl titanate with 100 ml of 2-propanol (abs.) and re-
fluxed for 92 h. The solution was concentrated to dryness, dissolved
in 50 ml of ethyl acetate, and washed with 100 ml of water. The
aqueous layer was extracted three times with 50 ml of ethyl acetate
The combined organic layers were washed with 50 ml of brine and
dried with MgSO4. After removal of the solvent, the crude material
was recrystallized from methanol to yield 2.1 g (73%) of the colour-
less isopropyl ester 7d, m.p. 198Ϫ199°C (methanol). Ϫ MS (70 eV,
EI); m/z (%): 424 (0.1) [Mϩ], 409 (0.2) [M Ϫ CH3ϩ], 393 (2.4) [M
Ϫ CH3Oϩ], 333 (1.8) [C18H21O6ϩ], 291 (2.2) [C16H19O5ϩ], 280 (10)
[C15H20O5ϩ], 261 (2.5) [C15H17O4ϩ], 247 (6.9) [C14H15O4ϩ], 105
All quinone bisketals 7aϪ7f have to be stored under an atmos-
phere of dry ammonia.
General Procedure for the Synthesis of the Quinones 1aϪ1f: To a
solution of the quinone bisketals, 1Ϫ3 drops of sulfuric acid (0.2
) were added (Table 3). All solutions turned yellow. After 16 h,
the quinones were precipitated and filtered off to yield yellow crys-
tals. These crystals were purified by recrystallization from acetone.
Table 3. Synthesis of the quinones 1aϪ1f
ketal
amount
solvent
acetone
quinone
amount yield
[g]
(74) [C5H12O2 ϩ Hϩ], 75 (68) [C3H7O2ϩ], 43 (100) [C3H7ϩ], 41 (30) 7a 0.5
[mmol]
1.36
[ml]
20
[g]
[%]
99
94
83
80
76
48
1a 0.37
[C3H5ϩ].
7b 0.1
7c 1.0
7d 1.0
7e 0.71
7f 0.25
0.25
3 (ϩ 3 ml of CH2Cl2) 1b 0.07
2.36
25
50
40
10
1c 0.65
1d 0.63
1e 0.43
1f 0.10
2.36
(E,E)-1,4-Bis(n-butoxycarbonylethenyl)-3,3,6,6-tetramethoxy-
1.47
cyclohexa-1,4-diene (7e): In a flame-dried vessel, 0.85 g (11.5 mmol)
of n-butanol was dissolved in 25 ml of THF (abs.) under nitrogen.
This mixture was vigorously stirred. A solution of n-BuLi in n-
hexane (1.6 , 7.5 ml, 12 mmol) was added in portions with a
syringe at Ϫ5°C. Methyl ester 7a (2.0 g, 5.4 mmol) was dissolved
in 90 ml of THF (abs.) and poured dropwise into the reaction mix-
ture. The temperature was kept at 0°C for 45 min and then the
cooling bath was removed. After 70 h, 1.0 g of n-butanol and 5 ml
of the BuLi solution were added and the stirring process was con-
tinued for 6 h. The reaction mixture was hydrolysed in 600 ml of
water. The aqueous layer was extracted with 200 ml of ethyl acetate.
The combined organic layers were washed with 100 ml of brine,
and dried with MgSO4. The solution was concentrated to dryness
and the residue was recrystallized from methanol to yield 1.2 g
(49%) of the n-butyl ester 7e, m.p. 128Ϫ129°C. Ϫ MS (70 eV, EI);
m/z (%): 452 (0.5) [Mϩ], 437 (0.9) [M Ϫ CH3ϩ], 421 (6.3) [M Ϫ
CH3Oϩ], 390 (3.0) [M Ϫ 2 ϫ CH3Oϩ], 347 (3.6) [C19H23O6ϩ], 294
(5.5) [C16H22O5ϩ], 105 (100) [C5H12O2 ϩ Hϩ], 75 (94) [C3H7O2ϩ],
57 (28) [C4H9ϩ], 41 (53) [C3H5ϩ].
0.48
Table 4a. 1H-NMR data of compounds 5, 6, 7aϪ7f; hydrogen
atoms: (a) methoxy; (b) ring; (c) vinyl (ring); (d) vinyl (ester); (e)
carboxylic acid of 8; (f)Ϫ(i) CH2 and CH3 groups of the ester
1H-NMR peaks (δ)
atom
5
6
7a
7b
7c
7d
7e
7f
(a)
(b)
(c)
(d)
(e)
3.87
7.37
7.81
6.68
3.86 3.19 3.20 3.20 3.18
7.01 6.35 6.36 6.36 6.34
7.93 6.62 6.62 6.63 6.57
6.53 7.23 7.23 7.23 7.18
3.18
6.34
6.61
7.20
Ϫ
3.19
6.36
6.68
7.26
Ϫ
12.1Ϫ12.7
Ϫ
Ϫ
Ϫ
Ϫ
Ϫ
(f)
Ϫ
Ϫ
Ϫ
Ϫ
Ϫ
4.26 3.77 4.23 4.13 5.07
4.15
1.65
1.39
0.93
Ϫ
5.22
Ϫ
Ϫ
(g)
(h)
(i)
1.34
Ϫ
Ϫ
Ϫ
Ϫ
Ϫ
1.31 1.70 1.26
Ϫ
Ϫ
Ϫ
0.97
Ϫ
Ϫ
Ϫ
Ϫ
Ϫ
Ϫ
arom.
Ϫ
Ϫ
7.33Ϫ7.42
Table 4b. 1H-NMR data of the quinones 1aϪ1f; assignment of the
hydrogen atoms as in Table 4a
(E,E)-1,4-Bis(benzyloxycarbonylethenyl)-3,3,6,6-tetramethoxy-
cyclohexa-1,4-diene (7f): A solution of 1.8 g (14 mmol) of benzyl
alcohol in 20 ml of THF (abs.) was poured into a flame-dried ves-
sel. A solution of n-BuLi in n-hexane (15%, 10.0 ml, 16 mmol) was
added dropwise with a syringe at Ϫ5°C. Compound 7a (1.5 g, 4.1
mmol) was dissolved in 100 ml of THF (abs.) and poured slowly
into the reaction mixture. The cooling bath was removed and the
contents of the vessel were stirred for a further 6.5 h. The solution
was hydrolysed in 500 ml of water. The organic material was ex-
tracted with 200 ml of ethyl acetate, the aqueous layer was stirred
with NaCl and the organic layer was isolated. The combined or-
ganic layers were washed with 100 ml of brine and dried with
1H-NMR peaks (δ)
atom
1a
1b
1c
1d
1e
1f
(b)
(c)
7.03
6.47
7.77
3.72
Ϫ
Ϫ
Ϫ
Ϫ
6.91
6.85
7.49
4.27
1.33
Ϫ
6.91
6.85
7.48
4.16
1.72
0.97
Ϫ
6.90
6.83
7.47
5.13
1.31
Ϫ
6.90
6.85
7.47
4.20
1.66
1.41
0.94
Ϫ
6.89
6.91
7.52
5.25
Ϫ
(d)
(f)
(g)
(h)
(i)
Ϫ
Ϫ
Ϫ
Ϫ
Ϫ
Ϫ
arom.
Ϫ
7.36Ϫ7.39
Eur. J. Org. Chem. 1998, 595Ϫ604
601