Versatile synthesis of triptycene di- and tetracarboxylic acids

Article abstract of DOI:10.1055/s-2006-942385

A simple two-step synthesis of triptycene di- and tetracarboxylic acids is reported. Diels-Alder reaction between dimethylanthracenes and appropriate arynes, generated in situ from anthranilic or dimethylanthranilic acid, afforded di- or tetramethyltriptycenes in 41-69% yields. Subsequent oxidation of the methyl groups with potassium permanganate provided the corresponding triptycene carboxylic acids in 86-96% yields. Georg Thieme Verlag Stuttgart.

Full text of DOI:10.1055/s-2006-942385

PAPER
2039
Versatile Synthesis of Triptycene Di- and Tetracarboxylic Acids
Synthesis of
T
riptycen
a
e
Di- and
T
r
etracarb
k
A
cidséta Rybáčková, Martin Bělohradský, Petr Holý, Radek Pohl, Jiří Závada*
Institute of Organic Chemistry and Biochemistry, Academy of Sciences of the Czech Republic, Flemingovo nám. 2, 16610 Prague 6,
Czech Republic
Fax +42(2)20183560; E-mail: zavada@uochb.cas.cz
Received 20 January 2006; revised 17 February 2006
Table 1 Triptycenes 3a–f Prepared
Abstract: A simple two-step synthesis of triptycene di- and tetra-
carboxylic acids is reported. Diels–Alder reaction between dimeth-
Product
3a
R1
H
R2
Me
H
R3
H
R4
H
Yield (%)a
51b
ylanthracenes and appropriate arynes, generated in situ from
anthranilic or dimethylanthranilic acid, afforded di- or tetramethyl-
triptycenes in 41–69% yields. Subsequent oxidation of the methyl
groups with potassium permanganate provided the corresponding
triptycene carboxylic acids in 86–96% yields.
3b
Me
H
H
H
53b
3c
Me
H
Me
Me
H
H
69b
Key words: triptycenes, carboxylic acids, oxidations, Diels–Alder
reactions, arynes
3d
Me
H
H
61b
3e
Me
H
Me
Me
23,b 41c
52c
3f
Me
H
Unique geometric features of the triptycene skeleton ap-
peal to exploitation in molecular tectonics.1 Accordingly,
as a part of our interest in self-assembly of stereochemi-
cally biased carboxylic acids2,3 we turned our attention at
the corresponding triptycene derivatives and addressed
first the problem of synthetic methodology. Herein, we re-
port a simple two-step synthesis of triptycene di- and tet-
racarboxylic acids utilizing the easily accessible 2,6- and
2,7-dimethylanthracenes as the starting material.
a Isolated yield.
b Method A.
c Method B.
products 3a–f and their isolated yields (after chromatog-
raphy) are summarized in Table 1.
The following step is the oxidation of methyl groups in
3a–f, thus producing dicarboxylic acids 4a,b and tetracar-
boxylic acids 4c–f, respectively (Scheme 2). The oxida-
tion was achieved by the action of potassium
permanganate in pyridine–water mixture.
In the first step (Scheme 1), the dimethylanthracenes 1a,b
undergo a Diels–Alder reaction with aryne, generated in
situ from appropriate anthranilic acid 2a–c with isoamyl
nitrite. In most instances, the reaction could be carried out
conveniently in a mixture of 1,2-dichloroethane and THF
at reflux temperature (Method A). Occasionally, however,
the reaction mixture became heterogeneous and a lower
conversion resulted. To overcome this problem, THF was
replaced by diglyme as a co-solvent (Method B). The
All six carboxylic acids 4a–f were obtained in very good
yields (Table 2) and could be recrystallized from acetone–
n-heptane mixture. Despite prolonged drying at elevated
temperature under reduced pressure solvent molecules
tend to persist in the crystalline material.
R3
R4
R4
R4
COOH
R4
R3
NH2
R1
R2
Me
R3
R3
2a–c
R1
R2
isoamyl nitrite
1,2-dichloroethane
THF (diglyme)
Me
1a,b
3a–f
R1, R2, R3, R4 = H or Me
Scheme 1
SYNTHESIS 2006, No. 12, pp 2039–2042
x
x.
x
x
.
2
0
0
6
Advanced online publication: 05.05.2006
DOI: 10.1055/s-2006-942385; Art ID: Z02206SS
© Georg Thieme Verlag Stuttgart · New York

2040
M. Rybáčková et al.
PAPER
R4
X4
R4
X4
R3
X3
1. KMnO4, pyridine/H2O
2. HCl/H2O
R3
X3
R1
R2
X1
X2
Me
COOH
3a–f
4a–f
R1, R2, R3, R4 = H or Me
X1, X2, X3, X4 = H or COOH
Scheme 2
Table 2 Triptycene Carboxylic Acids 4a–f Prepared
After cooling to r.t., the mixture from the respective method was
evaporated to dryness and chromatographed on silica gel using
CH2Cl2–n-hexane (5:95) as eluent. The following adducts were ob-
tained after crystallization from an EtOH–H2O mixture (Table 1).
Product X1
X2
X3
X4
Yield (%)a
4a
4b
4c
4d
4e
4f
H
CO2H
H
H
H
87
95
97
94
94
86
2,6-Dimethyltriptycene (3a)
Method A; white powder; yield: 175 mg (51%); mp 142–144 °C.
CO2H
H
H
H
CO2H
H
CO2H
CO2H
H
H
1H NMR (400 MHz, CDCl3): d = 2.23 (s, 6 H, CH3), 5.31 (s, 2 H,
H-9,10), 6.76 (ddq, J = 7.4, 1.8, 0.9 Hz, 2 H, H-3,7), 6.95 (m, 2 H,
H-14,15), 7.19 (d, J = 1.8 Hz, 2 H, H-1,5), 7.23 (d, J = 7.4 Hz, 2 H,
H-4,8), 7.33 (m, 2 H, H-13,16). These data are in accord with the
data in ref.9
13C NMR (100.6 MHz, CDCl3): d = 21.10 (CH3), 53.67 (CH-9,10),
123.22 (CH-4,8), 123.40 (CH-13,16), 124.45 (CH-1,5), 125.01
(CH-14,15), 125.34 (CH-3,7), 134.66 (C-2,6), 142.48 (C-4a,8a),
145.51 (C-11,12), 145.58 (C-9a,10a).
CO2H
H
H
CO2H
H
CO2H
CO2H
CO2H
H
a Isolated yield.
MS (EI, 70 EV): m/z (%) = 282 (85, [M+]), 267 (100), 252 (49), 126
(21).
Melting points were determined on a Kofler apparatus and are un-
corrected. NMR spectra were measured on Bruker Avance 400 (1H
at 400 MHz and 13C at 100.6 MHz) and Bruker Avance 500 (1H at
500 and 13C at 125.8 MHz) spectrometers. Chemical shifts (in ppm,
d scale) were referenced to TMS as an internal standard; coupling
constants (J) are given in Hz. Complete assignments of H-atoms
and carbons were attained by analysis of correlated heteronuclear
Anal. Calcd for C22H18: C, 93.57; H, 6.43. Found: C, 93.43; H, 6.40.
2,7-Dimethyltriptycene (3b)
Method A; white powder; yield: 180 mg (53%); mp 174–176 °C.
1H NMR (400 MHz, CDCl3): d = 2.23 (s, 6 H, CH3), 5.30 (s, 1 H,
H-9), 5.33 (s, 1 H, H-10), 6.77 (ddq, 2 H, J = 7.4, 1.5, 0.8 Hz, H-
3,6), 6.95 (m, 2 H, H-14,15), 7.20 (d, 2 H, J = 1.5 Hz, H-1,8), 7.23
(d, 2 H, J = 7.4 Hz, H-4,5), 7.34 (m, 2 H, H-13,16).
13C NMR (100.6 MHz, CDCl3): d = 21.20 (CH3), 53.27 (CH-10),
54.06 (CH-9), 123.20 (CH-4,5), 123.36, 123.44 (CH-13,16), 124.48
(CH-1,8), 124.98, 125.06 (CH-14,15), 125.39 (CH-3,6), 134.63 (C-
2,7), 142.70 (C-4a,10a), 145.29 (C-11 or C-12), 145.37 (C-8a,9a),
145.72 (C-11 or C-12).
1
1H, 13C-HSQC and H, 13C-HMBC spectra. Mass spectra were re-
corded on a ZAB-EQ (VG-Analytical) instrument.
The starting 2,6- and 2,7-dimethylanthracenes were prepared4 from
2,6- and 2,7-dimethylanthraquinones5,6 in 65 and 58% yield, respec-
tively. 3,6-Dimethylanthranilic acid7 and 4,5-dimethylanthranilic
acid8 were obtained according to literature procedures.
Methyl-Substituted Triptycenes 3a–f; General Procedure
Method A: To a refluxing solution of 2,6- or 2,7-dimethylanthracene
[1a (R1 = H, R2 = Me)] or 1b (R1 = Me, R2 = H; 250 mg, 1.2 mmol]
in a mixture of 1,2-dichloroethane (9 mL) and THF (3 mL) were si-
multaneously added a solution of anthranilic acid [2a (R3 = R4 = H);
500 mg, 3.6 mmol] or 3,6-dimethylanthranilic acid [2b (R3 = Me,
R4 = H); 400 mg, 2.4 mmol] in THF (2.5 mL) and a solution of
isoamyl nitrite (0.49 mL, 3.6 mmol) in 1,2-dichloroethane (2 mL)
during 4 h. The mixture was then refluxed for 3 h.
Method B: To a solution of 2,6- or 2,7-dimethylanthracene [1a (R1
= H, R2 = Me)] or 1b (R1 = Me, R2 = H]; 250 mg, 1.2 mmol] in a
mixture of 1,2-dichloroethane (15 mL) and diglyme (5 mL) heated
to 95 °C were simultaneously added a solution of 4,5-dimethylan-
thranilic acid [2c (R3 = H, R4 = Me); 600 mg, 3.6 mmol] in diglyme
(15 mL) and a solution of isoamyl nitrite (0.49 mL, 3.6 mmol) in
1,2-dichloroethane (15 mL) during 4 h. The mixture was then re-
fluxed for 3 h.
MS (EI, 70 eV): m/z (%) = 282 (100, [M+]), 267 (92), 252 (29), 126
(6).
Anal. Calcd for C22H18: C, 93.57; H, 6.43. Found: C, 93.29; H, 6.49.
1,4,6,14-Tetramethyltriptycene (3c)
Method A; white powder; yield: 260 mg (69%); mp 138–140 °C.
1H NMR (400 MHz, CDCl3): d = 2.23 (s, 6 H, CH3-6,14), 2.44 (s, 6
H, CH3-1,4), 5.54 (s, 2 H, H-9,10), 6.68 (s, 2 H, H-2,3), 6.76 (ddq,
J = 7.4, 1.6, 0.9 Hz, 2 H, H-7,15), 7.19 (d, J = 1.6 Hz, 2 H, H-5,13),
7.23 (d, J = 7.4 Hz, 2 H, H-8,16).
13C NMR (100.6 MHz, CDCl3): d = 18.37 (CH3-1,4), 21.09 (CH3-6,
14), 50.07 (CH-9,10), 123.22 (CH-8,16), 124.46 (CH-5,13), 125.27
(CH-7,15), 126.17 (CH-2,3), 129.12 (CH-1,4), 134.58 (C-6,14),
142.63 (C-8a,11), 143.44 (C-4a,9a), 145.77 (C-10a,12).
Synthesis 2006, No. 12, 2039–2042 © Thieme Stuttgart · New York

PAPER
Synthesis of Triptycene Di- and Tetracarboxylic Acids
2041
MS (EI, 70 eV): m/z (%) = 310 (85, [M+]), 295 (100), 280 (39), 265
Triptycene-2,6-dicarboxylic Acid (4a)
(6), 155 (5), 140 (11).
White powder; yield: 105 mg (87%); mp 333–335 °C.
Anal. Calcd for C24H22: C, 92.86; H, 7.14. Found: C, 92.77; H, 7.20.
1H NMR (400 MHz, DMSO-d6): d = 5.91 (s, 2 H, H-9,10), 7.04 (m,
2 H, H-14,15), 7.44 (m, 2 H, H-13,16), 7.57 (d, J = 7.7 Hz, 2 H, H-
4,8), 7.65 (dd, J = 7.7, 1.7 Hz, 2 H, H-3,7), 8.02 (d, J = 1.7 Hz, 2 H,
H-1,5), 12.83 (br s, 2 H, CO2H).
1,4,6,15-Tetramethyltriptycene (3d)
Method A; white powder; yield: 230 mg (61%); mp 220–222 °C.
1H NMR (400 MHz, CDCl3): d = 2.23 (s, 6 H, CH3-6,15), 2.44, 2.45
(2 s, 2 × 3 H, CH3-1,4), 5.53 (s, 1 H, H-9), 5.55 (s, 1 H, H-10), 6.68
(s, 2 H, H-2,3), 6.76 (ddq, 2 H, J = 7.4, 1.7, 0.8 Hz, H-7,14), 7.19
(d, 2 H, J = 1.7 Hz, H-5,16), 7.22 (d, 2 H, J = 7.4 Hz, H-8,13).
13C NMR (100.6 MHz, DMSO-d6): d = 52.58 (CH-9,10), 124.33
(CH-4,8), 124.47 (CH-13,16), 124.87 (CH-1,5), 125.86 (CH-
14,15), 127.56 (CH-3,7), 128.17 (C-2,6), 144.47 (C-11,12), 145.45
(C-9a,10a), 150.20 (C-4a,8a), 167.44 (C=O).
13C NMR (100.6 MHz, CDCl3): d = 18.37 (CH3-1,4), 21.09 (CH3-
6,15), 49.68 (CH-9), 50.46 (CH-10), 123.19 (CH-8,13), 124.50
(CH-5,16), 125.31 (CH-7,14), 126.15, 126.21 (CH-2,3), 129.08,
129.16 (C-1,4), 134.54 (C-6,15), 142.86 (C-8a,12), 143.22, 143.66
(C-4a,9a), 145.55 (C-10a,11).
MS (EI, 70 eV): m/z (%) = 342 (44, [M+]), 297 (18), 253 (32), 125
(5), 100 (8), 71 (19), 58 (37), 43 (100).
Anal. Calcd for C22H14O4·0.5CH3COCH3: C, 76.00; H, 4.61. Found:
C, 75.82; H, 4.57.
MS (EI, 70 eV): m/z (%) = 310 (86, [M+]), 295 (100), 280 (39), 265
Triptycene-2,7-dicarboxylic Acid (4b)
(7), 155 (8), 140 (20).
White powder; yield: 115 mg (95%); mp 208–210 °C.
Anal. Calcd for C24H22: C, 92.86; H, 7.14. Found: C, 92.85; H, 7.17.
1H NMR (400 MHz, DMSO-d6): d = 5.88 (s, 1 H, H-10), 5.94 (s, 1
H, H-9), 7.04 (m, 2 H, H-14,15), 7.49 (m, 2 H, H-13,16), 7.58 (d, 2
H, J = 7.7 Hz, H-4,5), 7.66 (dd, 2 H, J = 7.7, 1.6 Hz, H-3,6), 8.04
(d, 2 H, J = 1.6 Hz, H-1,8), 12.85 (br s, CO2H).
2,3,6,14-Tetramethyltriptycene (3e)
Method B; white powder; yield: 155 mg (41%); mp 155–157 °C.
1H NMR (400 MHz, CDCl3): d = 2.13 (s, 6 H, CH3-2,3), 2.22 (s, 6
H, CH3-6,14), 5.24 (s, 2 H, H-9,10), 6.74 (ddq, 2 H, J = 7.4, 1.5, 0.8
Hz, H-7,15), 7.14 (s, 2 H, H-1,4), 7.16 (d, 2 H, J = 1.5 Hz, H-5,13),
7.20 (d, 2 H, J = 7.4 Hz, H-8,16).
13C NMR (100.6 MHz, CDCl3): d = 19.45 (CH3-2,3), 21.08 (CH3-
6,14), 53.22 (CH-9,10), 123.06 (CH-1,4), 124.29 (CH-5,13),
124.87 (CH-8,16), 125.23 (CH-7,15), 132.72 (C-2,3), 134.53 (C-
6,14), 142.73 (C-8a,11), 143.15 (C-4a,9a), 145.83 (C-10a,12).
13C NMR (100.6 MHz, DMSO-d6): d = 52.16 (CH-9), 52.63 (CH-
10), 124.19 (CH-4,5, CH-13), 124.34 (CH-16), 124.60 (CH-1,8),
125.60, 125.73 (CH-14,15), 127.28 (CH-3,6), 128.07 (C-2,7),
143.92, 144.74 (C-11,12), 145.67 (C-8a,9a), 149.58 (C-4a,10a),
167.19 (C=O).
MS (EI, 70 eV): m/z (%) = 342 (86, [M+]), 297 (40), 253 (100), 125
(21), 100 (9), 71 (30), 57 (39), 43 (82).
Anal. Calcd for C22H14O4·0.5CH3COCH3: C, 76.00; H, 4.61. Found:
C, 76.26; H, 4.47.
MS (EI, 70 eV): m/z (%) = 310 (96, [M+]), 295 (100), 280 (35), 265
(5), 155 (7), 140 (10).
Triptycene-1,4,6,14-tetracarboxylic Acid (4c)
White powder; yield: 135 mg (97%); mp >360 °C.
Anal. Calcd for C24H22: C, 92.86; H, 7.14. Found: C, 92.83; H, 7.09.
2,3,6,15-Tetramethyltriptycene (3f)
Method B; white powder; yield: 195 mg (52%); mp 158–160 °C.
1H NMR (400 MHz, DMSO-d6): d = 6.95 (s, 2 H, H-9,10), 7.60 (s,
2 H, H-2,3), 7.63 (d, 2 H, J = 7.7 Hz, H-8,16), 7.70 (dd, 2 H, J = 7.7,
1.5 Hz, H-7,15), 8.01 (d, 2 H, J = 1.5 Hz, H-5,13), 13.20 (br s,
CO2H).
13C NMR (100.6 MHz, DMSO-d6): d = 49.37 (CH-9,10), 124.84
(CH-8,16), 125.12 (CH-5,13), 126.63 (CH-2,3), 127.80 (CH-7,15),
128.57 (C-6,14), 130.42 (C-1,4), 144.51 (C-10a,12), 146.45 (C-
4a,9a), 149.22 (C-8a,11), 167.09 (C=O, 6,14), 167.78 (C=O, 1,4).
1H NMR (400 MHz, CDCl3): d = 2.13 (2 s, 2 × 3 H, CH3-2,3), 2.22
(s, 6 H, CH3-6,15), 5.22 (s, 1 H, H-10), 5.25 (s, 1 H, H-9), 6.74 (ddq,
2 H, J = 7.4, 1.7, 0.8 Hz, H-7,14), 7.14 (d, 1 H, J = 2.0 Hz, H-1 or
4), 7.16 (d, 2 H, J = 1.7 Hz, H-5,16), 7.16 (d, 1 H, J = 2.0 Hz, H-1
or 4), 7.20 (d, 2 H, J = 7.4 Hz, H-8,13).
13C NMR (100.6 MHz, CDCl3): d = 19.45 (CH3-2,3), 21.08 (CH3-
6,15), 52.83 (CH-9), 53.61 (CH-10), 123.03 (CH-5,16), 124.33
(CH-8,13), 124.85, 124.90 (CH-1,4), 125.27 (CH-7,14), 132.68,
132.77 (C-2,3), 134.49 (C-6,15), 142.92 (C-4a or C-9a), 142.96 (C-
8a,12), 143.38 (C-4a or C-9a), 145.62 (C-10a,11).
MS (EI, 70 eV): m/z (%) = 430 (2, [M+]), 368 (8), 340 (5), 297 (4),
250 (8), 236 (10), 125 (11), 97 (42), 83 (53), 69 (81), 55 (100), 43
(98), 36 (77).
Anal. Calcd for C24H14O8·H2O: C, 64.29; H, 3.60. Found: C, 64.34;
H, 3.22.
MS (EI, 70 eV): m/z (%) = 310 (99, [M+]), 295 (100), 280 (33), 265
(5), 155 (8), 140 (13).
Triptycene-1,4,6,15-tetracarboxylic Acid (4d)
White powder; yield: 130 mg (94%); mp >360 °C.
Anal. Calcd for C24H22: C, 92.86; H, 7.14. Found: C, 92.65; H, 7.08.
Triptycene Carboxylic Acids 4a–f; General Procedure
1H NMR (500 MHz, DMSO-d6): d = 6.94 (s, 1 H, H-10), 6.95 (s, 1
H, H-9), 7.60 (s, 2 H, H-2,3), 7.61 (d, 2 H, J = 7.7 Hz, H-8,13), 7.69
(dd, 2 H, J = 7.7, 1.6 Hz, H-7,14), 8.03 (d, 2 H, J = 1.6 Hz, H-5,16),
13.20 (br s, 4 H, CO2H).
13C NMR (125.8 MHz, DMSO-d6): d = 49.22 (CH-10), 49.48 (CH-
9), 124.78 (CH-8,13), 125.12 (CH-5,16), 126.60 (CH-2,3), 127.73
(CH-7,14), 128.58 (C-6,15), 130.31, 130.38 (C-1,4), 144.88 (C-
10a,11), 146.11, 146.79 (C-4a,9a), 148.78 (C-8a,12), 167.07 (C=O,
6,15), 167.68, 167.75 (C=O, 1,4).
To a refluxing solution of methyltriptycenes 3a–f (100 mg) in a
mixture of pyridine (5 mL) and H2O (3 mL), was added KMnO4 (9
equiv per each CH3 group) portionwise over 24 h. After cooling to
r.t., the precipitated MnO2 was filtered off and washed with 1% aq
solution of KOH (15 mL). The filtrate was concentrated on a rotary
evaporator to approximately one third of its original volume and
then acidified to pH 1 with 3 M HCl. The precipitated products were
collected by filtration and dried under vacuum at 60 °C. Analytical
samples were further recrystallized from acetone–n-heptane mix-
ture and dried repeatedly in vacuo (Table 2).
MS (EI, 70 eV): m/z (%) = 430 (4, [M+]), 368 (6), 342 (3), 297 (4),
253 (6), 236 (6), 125 (8), 97 (26), 83 (34), 69 (59), 55 (64), 43 (64),
36 (100).
Synthesis 2006, No. 12, 2039–2042 © Thieme Stuttgart · New York

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M. Rybáčková et al.
PAPER
Anal. Calcd for C24H14O8·0.5H2O: C, 65.60; H, 3.44. Found: C,
65.48; H, 3.33.
Anal. Calcd for C24H14O8·0.5CH3COCH3: C, 66.39; H, 4.13. Found:
C, 66.27; H, 3.99.
Triptycene-2,3,6,14-tetracarboxylic Acid (4e)
White powder; yield: 130 mg (94%); mp 250–252 °C.
Acknowledgment
1H NMR (400 MHz, DMSO-d6): d = 6.09 (s, 2 H, H-9,10), 7.61 (d,
2 H, J = 7.7 Hz, H-8,16), 7.69 (dd, 2 H, J = 7.7, 1.6 Hz, H-7,15),
7.80 (s, 2 H, H-1,4), 8.06 (d, 2 H, J = 1.6 Hz, H-5,13), 12.97 (br s,
CO2H).
This work was carried out under the research project Z4 055 0506.
The financial support provided by the Grant Agency of the Czech
Republic (Grant No. 203/03/0087) is gratefully acknowledged.
13C NMR (100.6 MHz, DMSO-d6): d = 51.93 (CH-9,10), 124.17
(CH-1,4), 124.48 (CH-8,16), 125.01 (CH-5,13), 127.67 (CH-7,15),
128.37 (C-6,14), 130.64 (C-2,3), 144.39 (C-10a,12), 147.12 (C-
4a,9a), 149.03 (C-8a,11), 167.09 (C=O, 6,14), 168.51 (C=O, 2,3).
MS (EI, 70 eV): m/z (%) = 412 (90, [M+ – H2O]), 368 (20), 340
(14), 323 (22), 296 (16), 279 (18), 250 (39), 125 (26), 97 (41), 83
(51), 69 (100), 55 (97), 43 (96).
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Chem. 2002, 114, 179.
(4) Hinshaw, J. C. Org. Prep. Proced. Int. 1972, 4, 211.
(5) Gready, J. E.; Hata, K.; Sternhell, S.; Tansey, Ch. W. Aust.
J. Chem. 1990, 43, 593.
(6) House, H. O.; Holt, J. T.; VanDerveer, D. J. Org. Chem.
1993, 58, 7516.
Anal. Calcd for C24H14O8·0.5CH3COCH3: C, 66.39; H, 4.13. Found:
C, 66.63; H, 4.31.
Triptycene-2,3,6,15-tetracarboxylic Acid (4f)
White powder; yield: 120 mg (86%); mp 255–257 °C.
1H NMR (500 MHz, DMSO-d6): d = 6.06 (s, 1 H, H-9), 6.11 (s, 1
H, H-10), 7.61 (d, 2 H, J = 7.8 Hz, H-8,13), 7.68 (dd, 2 H, J = 7.8,
1.6 Hz, H-7,14), 7.84 (s, 1 H, H-4), 7.85 (s, 1 H, H-1), 8.05 (d, 2 H,
J = 1.6 Hz, H-5,16), 13.00 (br s, 4 H, CO2H).
13C NMR (125.8 MHz, DMSO-d6): d = 51.73 (CH-10), 52.14 (CH-
9), 124.51 (CH-1,4,8,13), 124.89 (CH-5,16), 127.58 (CH-7,14),
128.42 (C-6,15), 130.82, 130.90 (C-2,3), 144.79 (C-4a,11), 146.63
(C-9a), 147.40 (10a), 148.67 (C-8a,12), 167.07 (C=O, 6,15), 168.42
(C=O, 2,3).
(7) Wilcox, C. F. Jr.; Farley, E. N. J. Am. Chem. Soc. 1984, 106,
7195.
(8) Baker, B. R.; Schaub, R. E.; Joseph, J. P.; McEvoy, F. J.;
Williams, J. H. J. Org. Chem. 1952, 17, 149.
(9) Klanderman, B. H.; Criswell, T. R. J. Org. Chem. 1969, 34,
3426.
MS (EI, 70 eV): m/z (%) = 342 (100, [M+ – 2CO2]), 297 (53), 253
(99), 176 (6), 125 (14), 69 (8), 55 (8), 43 (8), 36 (9).
Synthesis 2006, No. 12, 2039–2042 © Thieme Stuttgart · New York