Unexpected regiospecific reactivity of a substituted phthalic anhydride

Article abstract of DOI:10.1016/j.tet.2006.11.090

Regioselective nucleophilic addition at C1 of anhydride 7 by a range of nucleophiles occurs to produce amide, ester and thioester derivatives 8-15 (60-99%). The increased electrophilic reactivity of the C1 carbonyl group of anhydride 7 is supported by a competition experiment with phthalic anhydride. Unexpected formation of lactams 18 and 19 from amides 12 and 13 was shown to proceed via the lactamols 16 and 17 and could be controlled by the reaction conditions. The solid-state structure of 19 is reported.

Full text of DOI:10.1016/j.tet.2006.11.090

Tetrahedron 63 (2007) 1395–1401
Unexpected regiospecific reactivity of a substituted
phthalic anhydride
a
Maria J. Petersson,a Camille Marchal,a,b Wendy A. Loughlin,c, Ian D. Jenkins,
*
c
Peter C. Healy and Ann Almesaker
a
˚
aEskitis Institute, Natural Product Discovery, Griffith University, Brisbane, QLD 4111, Australia
b
´
´
Magistere de Chimie, Ecole Normale Superieure, Paris 75055, France
cEskitis Institute, School of Science, Griffith University, Brisbane, QLD 4111, Australia
Received 12 September 2006; revised 10 November 2006; accepted 30 November 2006
Available online 19 December 2006
Abstract—Regioselective nucleophilic addition at C1 of anhydride 7 by a range of nucleophiles occurs to produce amide, ester and thioester
derivatives 8–15 (60–99%). The increased electrophilic reactivity of the C1 carbonyl group of anhydride 7 is supported by a competition
experiment with phthalic anhydride. Unexpected formation of lactams 18 and 19 from amides 12 and 13 was shown to proceed via the
lactamols 16 and 17 and could be controlled by the reaction conditions. The solid-state structure of 19 is reported.
Ó 2006 Published by Elsevier Ltd.
1. Introduction
to a rapid plug column upon work-up and then used imme-
diately in the next step. Diels–Alder cycloaddition of acetyl-
ene dicarboxylate in the presence of hydroquinone gave,
after work-up, a mixture of the diesters 4 and 5. The diester
5 was the exclusive product following a dehydrogenation
step using palladium on charcoal in acetic acid.
Phthalic anhydrides react with a range of nucleophiles, such
as alcohols,1–4 Grignard reagents,5,6 sugars7–9 and thienyl-
lithium10 to produce the carboxylic acid derivative arising
from anhydride opening. With hydroxylamine11 and other
amines12 they provide phthalimides, which can be used in
the synthesis of pharmaceutically interesting molecules,13–18
natural products,19,20 compounds that are chromophores,21
and compounds that have chiroptical,22 fluorescent23 or elec-
tron transfer properties.24,25 They are also useful as polymer-
supported reagents.26–28 There are very few phthalic
anhydrides with a gamma aliphatic ketone, and reactions
are restricted to ring opening of the anhydride via Friedel–
Crafts acylation29 or with an alcohol to form an ester
carboxylic acid.30–31 Herein, we report the unexpected
regiospecific ring opening of a phthalic anhydride with a
gamma aliphatic ketone, compound 7.
Alkaline hydrolysis of diester 5, followed by acidification
gave diacid 6, which was converted to anhydride 7 by
heating at 50–60 ꢀC with acetic anhydride. In summary, an-
hydride 7 was obtained in five steps and 27% overall yield
from cyclohexan-1,3-dione 1 (Scheme 1).
O
O
O
b
a
O
OEt
1
3
2
c
c,d
2. Results and discussion
O
CO2Me
CO2Me
O
CO2Me
CO2Me
Naphthofurantrione 7, a useful building block for the synthe-
sis of analogues of the natural product hyphodermin B,32
was prepared from cyclohexan-1,3-dione 1. Reaction of 1
with ethanol in the presence of hydrochloric acid gave keto-
enol 2. 1,4-Addition of vinyl magnesium bromide to 2 in
ether followed by a dilute acid quench gave ketodiene 3.
As ketodiene 3 decomposed upon standing, it was submitted
5
4
and 5
e
O
O
O
O
CO2H
O
f
CO2H
7
6
Scheme 1. Synthetic route for the preparation of anhydride 7. Reagents and
conditions: (a) ethanol, HCl, rt, 16 h, 96%; (b) vinyl magnesium bromide,
ether, rt, 16 h, 75%; (c) 1.5% hydroquinone, dimethyl acetylene dicarboxy-
late, toluene, reflux, 48 h; (d) Pd/C, acetic acid, reflux, 16 h, 41%; (e) 10%
NaOH, THF, rt, 4 h, 65%; (f) acetic anhydride, 50 ꢀC, 16 h, 98%.
Keywords: (3–8) Phthalic anhydride; Nucleophilic addition; Intramolecular
ring closure; Hydrobenzoindole.
* Corresponding author. Tel.: +61 7 3735 7567; fax: +61 7 3735 7656;
e-mail: w.loughlin@griffith.edu.au
0040–4020/$ - see front matter Ó 2006 Published by Elsevier Ltd.
doi:10.1016/j.tet.2006.11.090

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M. J. Petersson et al. / Tetrahedron 63 (2007) 1395–1401
Table 2. Product ratios from reaction of 7 and 20 with triethylamine
When anhydride 7 was treated with a range of nucleophiles,
the derivatives 8–15 were obtained (Scheme 2). In each case,
nucleophilic attack occurred exclusively at C1 of the anhy-
dride. Reactions with alcohols (methanol, isopropanol and
tert-butanol—Table 1, entries 1–4) were performed in the
presence of pyridine (1–5 equiv, Table 1, entries 1–4). In
the absence of pyridine, which can act as a nucleophilic
and/or base catalyst, the reaction was slow. Good yields of
esters 8 and 9 were obtained, except in the case of tert-
butanol, which gave the diacid 6, presumably via competi-
tive hydrolysis of 7 with adventitious water.
Entry
Reactants (ratio)
Products (ratio in %)
7
20
Et2NH
7
11
20
21
1
2
3
1
2
10
1
2
10
2
1
1
0
26
40
47
24
8
0
45
51
53
5
1
The remarkable regioselectivity observed in the ring open-
ing of anhydride 7 suggested that the C1 carbonyl was
very electrophilic. This result was consistent with a model-
ling study carried out previously within our group on a
similar compound.32 To examine whether the gamma-ketone
had an inductive (activating) influence on the anhydride 7,
a competitive reaction was carried out by treating a mixture
of phthalic anhydride 20 and the gamma keto anhydride 7
with diethylamine. Initially, a 1:1 mixture of 7 and 20 was
treated with 2 equiv of diethylamine. As expected, this re-
sulted in aw1:1 ratio of 11 and 21 (Table 2, entry 1, Scheme
3). By contrast when anhydrides 7 and 20 were present in
excess relative to the diethylamine (Table 2, entries 2 and
3), 11 was formed as the major product with only minor
amounts of 21 being observed. This confirmed the activated
nature of the C1 carbonyl group in anhydride 7.
O
O
R
O
O
O
CO2H
O
solvent
nucleophile
7
8-15
H
12 R =
N
8 R =
9 R =
O
O
CH3
H
N
13 R =
10 R = O
14 R = N
O
N
11 R =
S
15 R =
Scheme 2. Synthetic route for the preparation of derivatives 8–15.
O
O
N
O
As expected, reactions with amines (benzylamine, aniline,
diethylamine and morpholine) were much faster and did
not require the presence of pyridine (Table 1, entries 5–9).
However, a polar solvent was required to fully dissolve the
starting anhydride 7. The slightly slower reaction in the
case of secondary amines (diethylamine, morpholine) was
attributed to steric factors. In these reactions, a minor precip-
itate was observed when complete formation of the product
had occurred. The precipitate was attributed to diacid 6
arising from the presence of traces of water. Although
aniline and benzylamine gave near quantitative yields of
12 and 13, respectively, isolation of these products by
column chromatography was complicated by the formation
of the corresponding ring closed products 16 and 17.
CO2H
O
20
21
HN(Et)2
O
O
N
O
O
O
CO2H
11
O
7
Scheme 3. Reaction of 7 and 20 with diethylamine.
During the synthesis of benzylamide 13, when anhydride 7
was treated with benzylamine in ethyl acetate for 1 h, unex-
pected formation of lactamol 17 occurred in 72% yield. The
structure of 17 was unambiguously assigned using gCOSY,
gHSQC and gHMBC NMR spectroscopy, with a diagnostic
correlation between the CH2 at d 4.93 ppm and C8a at d
87.0 ppm being observed in the gHMBC. The spectral data
1-Pentanethiol (Table 1, entry 10) reacted with anhydride 7
in the presence of pyridine in an analogous manner to give
the thiol ester 15.
Table 1. Derivatives of anhydride 7 shown in Scheme 2
Entry
Nucleophile
Solvent
Reaction conditions
Product
Yield (%)
1
2
3
4
5
6
7
8
9
10
Methanol
Pyridinea in methanol
Pyridinea in isopropanol
Pyridinec in isopropanol
Pyridinea in tert-butanol
CHCl3e
CHCl3
rt, 16 h, N2
rt, 16 h, N2
rt, 16 h, N2
rt, 16 h, N2
rt, 45 min, N2
rt, 15 min, N2
rt, 2 h, N2
rt, 16 h, N2
rt, 3 h, N2
rt, 16 h, N2
8
9
9
6
13
12
11
11
14
15
64
Isopropanol
Isopropanol
tert-Butanol
Benzylaminec
Anilinec
94b
60
99d
97b
99b
69
80
82
e
Diethylaminec
Diethylaminec
Morpholinec
1-Pentanethiola
Ethyl acetate
Ethyl acetate
Ethyl acetate
Pyridinea in dichloromethane
60
a
5.0 equiv.
Crude yield, >98% pure.
1.0 equiv.
NMR yield, >95% pure.
Chloroform was de-acidified by passing through K2CO3 prior to use.
b
c
d
e

M. J. Petersson et al. / Tetrahedron 63 (2007) 1395–1401
1397
for 17 were acquired in DMSO-d6. By contrast, it was noted
that upon standing for 3 h in CDCl3, 17 underwent total con-
version to lactam 19. A triplet at d 5.96 ppm in the 1H NMR
spectrum of 19 was diagnostic for formation of 19. In the
course of this work, 19 crystallised from toluene as pale
yellow plates suitable for single crystal X-ray structure
determination. In the structure of 19, formation of a strong
intramolecular O–H/O hydrogen bond between the carb-
oxy hydroxyl group and the C2 carbonyl oxygen results in
the co-planarity of the carboxylic acid group and the
‘lactam’ ring system (Fig. 1).
was obtained from anhydride 7 in de-acidified chloroform
after 15 min. A longer reaction time (45 min) resulted in
a mixture of amide 12 and lactamol 16 (84:16, respectively).
Amide 12 underwent ring closure in acetone (or ethyl
acetate) after 48 h to give lactamol 16. Recrystallisation of
16 from de-acidified ethyl acetate or acetone resulted in
the formation of a minor amount of lactam 18. Lactamol
16 was easily dehydrated to lactam 18 by treatment with
one drop of hydrochloric acid in chloroform (Scheme 4).
The apparent increased reactivity of aniline compared to
benzylamine towards the anhydride 7 can be attributed to
the higher basicity of benzylamine and its consequent pro-
tonation by the carboxylic acid moiety in the products.
Next, we sought to establish reaction conditions for the
controlled formation of 13, 17 and 19. We considered that
the carboxylic acid group in the product or solvent may
have catalysed the formation of 17 from 7 via 13, and resid-
ual acid in CDCl3 may have catalysed the dehydration of 17
to 19.
O
O
NHR
CO2H
O
O
O
O
a
7
12-13
Chloroform was de-acidified by passing it through a plug of
potassium carbonate. Treatment of anhydride 7 with benzyl-
amine in de-acidified chloroform for 45 min gave amide 13.
When a longer reaction time of 2 h was used, a mixture of 13
and 17 in a 89:11 ratio was obtained.
b
R
O
R
O
N
N
HO
CO2H
CO2H
c
Stirring amide 13 in de-acidified ethyl acetate for 48 h
directly gave lactamol 17. Dissociation of the carboxylic
acid proton of 13 will be influenced by the solvent.33 Forma-
tion of lactamol is presumably via activation of the ketone
group through protonation and subsequent attack by the
amide nitrogen. Lactamol 17 was surprisingly stable,
provided it was kept in the solid state. However, it was easily
dehydrated to lactam 19 by treatment with two drops of
hydrochloric acid in chloroform.
18-19
16-17
13, 17, 19 R =
12, 16, 18 R =
Scheme 4. Synthetic route for the preparation of 18 and 19. Reagents and
conditions: (a) benzylamine, chloroform (de-acidified), rt, 45 min, 13
97%; aniline, chloroform (de-acidified), rt, 15 min, 12 99%. (b) Ethyl
acetate (de-acidified), rt, 48 h, 17 99%; acetone, rt, 48 h, 16 96%. (c) Two
drops HCl, chloroform, rt, 4 h, 19 72%; one drop HCl, chloroform, rt,
16 h, 18 78%.
When aniline was reacted with anhydride 7, a similar reac-
tivity of the gamma-ketone in 7 was observed. Amide 12
In conclusion, the regioselective nucleophilic addition at C1
of anhydride 7 by a range of nucleophiles, to obtain amide,
ester and thioester derivatives 8–15 is reported. The in-
creased electrophilic reactivity of the C1 carbonyl group
of anhydride 7 is supported by a competition experiment
with phthalic anhydride. Unexpected formation of lactams
18 and 19 from amides 12 and 13 was observed. The
solid-state structure of 19 is reported. The unexpected
formation of lactams 18 and 19 was shown to proceed via
the lactamols 16 and 17 and could be controlled by the reac-
tion conditions. This potentially provides facile access to
such tricyclic systems present in bioactive natural products,
such as piperolactams34 and aristololactams.35
3. Experimental
3.1. General procedure
See Supplementary data.
3.1.1. 8-Oxo-5,6,7,8-tetrahydronaphthalene-1,2-dicarb-
oxylic acid (6). Sodium hydroxide (10% aqueous solution,
35 mL) was added to diester 536 (1.74 g, 6.65 mmol) in
tetrahydrofuran (15 mL), and the mixture stirred at room
temperature for 4 h. Tetrahydrofuran was removed under
Figure 1. ORTEP-3 drawing of lactam 19 (30% ellipsoidal probability).

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M. J. Petersson et al. / Tetrahedron 63 (2007) 1395–1401
reduced pressure, and the aqueous layer was washed with
hexane (100 mL) and ethyl acetate (100 mL). The aqueous
layer was acidified (pH 1) by the addition of concentrated
hydrochloric acid, and extracted with ethyl acetate
(4ꢁ100 mL). The combined organic layers were washed
with brine (100 mL), dried (MgSO4) and filtered. The
solvent was removed under reduced pressure to afford
a pale yellow solid. Recrystallisation (ethyl acetate) of the
solid gave compound 6 as an amorphous white solid
(1.01 g, 65%). Mp 222–223 ꢀC. IR (KBr) cmꢂ1: 1692. dH
(400 MHz, DMSO-d6): 2.03 (2H, tt, J 6.2, 12.4 Hz, H6),
2.63 (2H, t, J 6.4 Hz, H7), 3.02 (2H, t, J 5.8 Hz, H5), 7.49
(1H, d, J 8.4 Hz, H4), 8.00 (1H, d, J 8.0 Hz, H3), 12.95
(2H, br s, CO2H). dC (100 MHz, DMSO-d6): 22.1 (C6),
29.6 (C5), 39.6 (C7), 127.5 (C2), 129.2 (C8a), 129.5 (C4),
133.8 (C3), 136.4 (C1), 149.4 (C4a), 166.3 (CO2H), 169.2
(CO2H), 196.3 (C8). MS (ESI) m/z: 257 ([M+Na]+, 100%).
Anal. Calcd for C12H10O5: C, 61.54; H, 4.30. Found: C,
61.44; H, 4.47.
3.1.4. 1-(Isopropoxycarbonyl)-8-oxo-5,6,7,8-tetrahydro-
naphthalene-2-carboxylic acid (9). Pyridine (16.5 mL,
0.19 mmol) was added to a suspension of anhydride 7
(42 mg, 0.19 mmol) in 2-propanol (5 mL), and the mixture
stirred under nitrogen at room temperature for 16 h. The
solvent was removed under reduced pressure and aqueous
hydrochloric acid (1 M, 5 mL) was added. The aqueous
layer was extracted with ethyl acetate (3ꢁ15 mL), and the
combined organic layers were washed with brine (25 mL),
dried (MgSO4) and filtered. The solvent was removed under
reduced pressure and the residue purified by silica column
chromatography (methanol/dichloromethane, gradient from
0:100 to 10:90; Rf¼0.4 (methanol/dichloromethane, 10:90))
followed by recrystallisation (ethyl acetate). Compound 9
was obtained as an amorphous white solid (32 mg, 60%).
Mp 183 ꢀC. IR (KBr) cmꢂ1: 3300–3600, 1732, 1701. dH
(400 MHz, acetone-d6): 1.32 (6H, d, J 6.0 Hz, CH3), 2.14
(2H, tt, J 6.3, 12.6 Hz, H6), 2.66 (2H, t, J 6.8 Hz, H7),
3.11 (2H, t, J 6 Hz, H5), 5.26 (1H, sept, J 6.3 Hz, CH),
7.53 (1H, d, J 8.0 Hz, H4), 8.13 (1H, d, J 7.6 Hz, H3),
11.49 (1H, br s, CO2H). dC (100 MHz, acetone-d6): 21.0
(2ꢁCH3), 22.5 (C6), 30.2 (C5), 39.3 (C7), 67.9 (OCH),
127.4 (C2), 130.0 (C4), 130.2 (C8a), 134.3 (C3), 137.0
(C1), 150.2 (C4a), 165.5 (CO2H), 167.4 (CO2i-Pr), 195.7
(C8). MS (ESI) m/z: 299 ([M+Na]+, 100%), 283 ([M+Li]+,
100%). Anal. Calcd for C15H16O5: C, 65.21; H, 5.84. Found:
C, 65.18; H, 5.83.
3.1.2. 7,8-Dihydro-6H-naphtho[1,2-c]furan-1,3,9-trione
(7). Dicarboxylic acid 6 (866 mg, 3.70 mmol) was sus-
pended in acetic anhydride (30 mL), and the mixture heated
under nitrogen at 50 ꢀC for 16 h. Co-evaporation of the
solvent with toluene under reduced pressure gave compound
7 as an amorphous white solid (785 mg, 98%). Mp 185 ꢀC.
IR (KBr) cmꢂ1: 1845, 1774, 1698. dH (200 MHz, CDCl3,):
2.25 (2H, tt, J 6.5, 13 Hz, H7), 2.84 (2H, t, J 6.7 Hz, H8),
3.15 (2H, t, J 6.1 Hz, H6), 7.81 (1H, d, J 7.8 Hz, H5), 8.06
(1H, d, J 7.6 Hz, H4). dC (100 MHz, CDCl3): 22.6 (C7),
30.8 (C6), 39.5 (C8), 128.1 (C4), 130.1 (C9b), 132.3
(C3a), 133.3 (C9a), 137.2 (C5), 153.9 (C5a), 159.2 (C1),
162.5 (C3), 194.3 (C9). MS (ESI) m/z: 239 ([M+Na]+,
100%), 223 ([M+Li]+, 100%). EIMS m/e: 216 (M, 18%),
188 (MꢂCO, 40%), 172 (MꢂCO2, 10%). HRMS calcd for
C12H8O4 [M]+: 216.0423. Found: 216.0418.
3.1.5. 1-[(N,N-Diethylamino)carbonyl]-8-oxo-5,6,7,8-
tetrahydronaphthalene-2-carboxylic acid (11). Di-
ethylamine (45 mL, 0.43 mmol) was added to a solution of
anhydride 7 (94 mg, 0.43 mmol) in ethyl acetate (4 mL), and
the mixture was stirred under nitrogen at room temperature
for 16 h. The solvent was removed under reduced pressure
and the residue recrystallised (ethyl acetate). Compound
11 was obtained as small yellow plates (99 mg, 80%). An
analytically pure sample of 11 was prepared by further
recrystallisation (ethyl acetate). Mp 172–174 ꢀC. IR (KBr)
cmꢂ1: 3300–3600, 1697, 1582. dH (400 MHz, acetone-d6):
0.94 (3H, t, J 7.2 Hz, CH3), 1.24 (3H, t, J 7.0 Hz, CH3),
2.08–2.15 (2H, m, H6), 2.56–2.9 (2H, m, H7), 3.01 (2H, q,
J 7.2 Hz, NCH2), 3.07–3.10 (2H, m, H5), 3.44–3.57 (2H,
m, NCH2), 7.45 (1H, dt, J 0.8, 8.0 Hz, H4), 8.06 (1H, d, J
8.0 Hz, H3), CO2H not observed. dC (100 MHz, acetone-
d6): 12.6 (CH3), 13.7 (CH3), 23.7 (C6), 31.6 (C5), 39.4
(NCH2), 40.9 (C7), 43.6 (NCH2), 129.2 (C2), 130.2 (C4),
131.3 (C8a), 135.6 (C3), 140.9 (C1), 151.0 (C4a), 167.4
(CO2H), 169.2 (C(O)N), 197.3 (C8). MS (ESI) m/z: 290
([M+H]+, 93%), 296 ([M+Li]+, 100%). Anal. Calcd for
C16H19NO4: C, 66.42; H, 6.62; N, 4.84. Found: C, 66.54;
H, 6.71; N, 4.58.
3.1.3. 1-(Methoxycarbonyl)-8-oxo-5,6,7,8-tetrahydro-
naphthalene-2-carboxylic acid (8). Pyridine (353 mL,
4.15 mmol) was added to a suspension of anhydride 7
(180 mg, 0.83 mmol) in methanol (20 mL), and the mixture
stirred under nitrogen at room temperature for 16 h. The
solvent was removed under reduced pressure and aqueous
hydrochloric acid (1 M, 10 mL) was added. The aqueous
layer was extracted with ethyl acetate (3ꢁ30 mL), and the
combined organic layers were washed with brine (50 mL),
dried (MgSO4) and filtered. The solvent was removed under
reduced pressure and the residue purified by silica column
chromatography (methanol/dichloromethane, gradient from
0:100 to 10:90; Rf¼0.6 (methanol/dichloromethane, 10:90))
followed by recrystallisation (ethyl acetate). Compound 8
was obtained as colourless plates (132 mg, 64%). Mp
176 ꢀC. IR (KBr) cmꢂ1: 3300–3600, 1714, 1697, 1264,
1236. dH (400 MHz, acetone-d6): 2.14 (1H, tt, J 6.4,
12.8 Hz, 2H, H6), 2.65 (2H, t, J 6.6 Hz, H7), 3.11 (2H, t,
J 6.2 Hz, H5), 3.83 (3H, s, OMe), 7.54 (1H, dt, J 0.9,
8.0 Hz, H4), 8.14 (1H, d, J 8.0 Hz, H3), CO2H proton not ob-
served. dC (100 MHz, acetone-d6): 22.5 (C6), 30.1 (C5),
39.2 (C7), 51.7 (OMe), 127.4 (C8a), 130.2 (C2), 130.3
(C4), 134.3 (C3), 136.4 (C1), 150.4 (C4a), 165.5 (CO2H),
168.6 (CO2Me), 195.9 (C8). MS (ESI) m/z: 271 ([M+Na]+,
100%), 255 ([M+Li]+, 100%). HRMS calcd for C13H12O5
[M]+: 248.0685. Found: 248.0688.
3.1.6. 1-[(N-Phenylamino)carbonyl]-8-oxo-5,6,7,8-tetra-
hydronaphthalene-2-carboxylic acid (12). Aniline (23 mL,
0.25 mmol) was added to a solution of anhydride 7 (54 mg,
0.25 mmol) in chloroform (3 mL, de-acidified with K2CO3)
and the reaction mixture stirred under nitrogen at room tem-
perature for 15 min. The reaction mixture was filtered and
the solvent removed under reduced pressure. Compound 12
was obtained as an amorphous brown solid (77 mg, 99%).
Mp 164–166 ꢀC. IR (KBr) cmꢂ1: 3200–3500, 2929, 1693,
1596. dH (400 MHz, DMSO-d6): 2.04 (2H, tt, J 6.4,
12.8 Hz, H6), 2.61 (2H, t, J 6.6 Hz, H7), 3.03 (2H, t, J

M. J. Petersson et al. / Tetrahedron 63 (2007) 1395–1401
1399
5.8 Hz, H5), 7.01 (1H, t, J 6.8 Hz, p-C6H5), 7.28 (2H, t, J
8.0 Hz, m-C6H5), 7.51 (1H, d, J 8.8 Hz, C4), 7.59 (2H, d, J
8.8 Hz, o-C6H5), 7.99 (1H, d, J 8.0 Hz, H3), 9.96 (1H, s,
NH), CO2H not observed. dC (100 MHz, acetone-d6): 23.3
(C6), 31.0 (C5), 40.3 (C7), 120.5 (o-C6H5), 123.6 (p-C6H5),
129.1 (C2), 129.3 (m-C6H5), 130.5 (C4), 131.5 (C8a), 134.8
(C3), 140.1 (C1), 141.2 (i-C6H5), 150.4 (C4a), 166.8
(C(O)N), 167.4 (CO2H), 196.8 (C8). MS (ESI) m/z: 310
([M+H]+, 58%), 316 ([M+Li]+, 100%). HRMS calcd for
C18H14NO4 [MꢂH]ꢂ: 308.0929. Found: 308.0928.
2.31 mmol) and pyridine (187 mL, 2.31 mmol) in dichloro-
methane (5 mL). The resulting reaction solution was stirred
under nitrogen at room temperature for 16 h. The solvent
was removed under reduced pressure and aqueous hydro-
chloric acid (1 M, 15 mL) was added. The aqueous layer
was extracted with ethyl acetate (3ꢁ30 mL), and the com-
bined organic layers were washed with brine (50 mL), dried
(MgSO4) and filtered. The solvent was removed under
reduced pressure and the residue purified by silica column
chromatography (ethyl acetate/dichloromethane, gradient
from 0:100 to 50:50) followed by high-pressure liquid chro-
matography (5 m HypersilÒ BDS C18 250ꢁ10 mm column;
tR 16 min; H2O/CH3CN with 0.2% TFA gradient: 60:40 for
20 min then 40:60 for 5 min). Compound 15 was obtained as
an amorphous white solid (32 mg, 60%). Mp 184–187 ꢀC.
IR (KBr) cmꢂ1: 3300–3600, 1703, 1686, 1676. dH
(400 MHz, acetone-d6): 0.92 (3H, t, J 6.8 Hz, H50), 1.38–
1.46 (4H, m, H30, H40), 1.75 (2H, tt, J 7.4, 14.8 Hz, H20),
2.15 (2H, tt, J 6.4, 12.8 Hz, H6), 2.65 (2H, t, J 6.6 Hz,
H7), 3.04 (2H, t, J 7.2 Hz, H10), 3.12 (2H, t, J 6.2 Hz, H5),
7.58 (1H, d, J 8.4 Hz, H4), 8.09 (1H, d, J 8.0 Hz, H3),
CO2H not observed. dC (100 MHz, acetone-d6): 14.25
(C50), 22.90 (C40), 23.15 (C6), 29.35 (C20), 30.05 (C10),
30.88 (C5), 31.87 (C30), 40.10 (C7), 128.89 (C2), 131.15
(C8a), 131.48 (C4), 134.83 (C3), 142.24 (C1), 150.89
(C4a), 166.18 (CO2H), 193.31 (C(O)S), 195.99 (C8). MS
(ESI) m/z: 327 ([M+Li]+, 18%), 343 ([M+Na]+, 100%).
HRMS calcd for C17H20SO4Na [M+Na]+: 343.0975. Found:
343.0981.
3.1.7. 1-[(N-Benzylamino)carbonyl]-8-oxo-5,6,7,8-tetra-
hydronaphthalene-2-carboxylic acid (13). Benzylamine
(42 mL, 0.38 mmol) was added to a solution of anhydride 7
(82 mg, 0.38 mmol) in chloroform (3 mL, de-acidified
with K2CO3), and the reaction mixture stirred under nitrogen
at room temperature for 45 min. The reaction mixture was
filtered and the solvent removed under reduced pressure.
Compound 13 was obtained as an amorphous white solid
(119 mg, 97%). Mp 140–142 ꢀC. IR (KBr) cmꢂ1: 3200–
3600, 3257, 1713, 1692, 1646. dH (400 MHz, DMSO-d6):
2.02 (2H, tt, J 6.3, 12.6 Hz, H6), 2.60 (2H, t, J 6.6 Hz, H7),
2.99 (2H, t, J 5.8 Hz, H5), 4.39 (2H, d, J 5.6 Hz, NCH2),
7.20–7.23 (1H, m, p-C6H5), 7.30 (2H, t, J 7.2 Hz,
m-C6H5), 7.43 (1H, d, J 8.0 Hz, H4), 7.47 (2H, d, J
7.2 Hz, o-C6H5), 7.90 (1H, d, J 8.0 Hz, H3), 8.28 (1H, t, J
5.8 Hz, NH), 14.09 (1H, br s, CO2H). dC (100 MHz, ace-
tone-d6): 23.4 (C6), 31.1 (C5), 40.5 (C7), 44.5 (NCH2),
127.5 (p-C6H5), 128.9 (o-C6H5), 129.0 (m-C6H5), 129.8
(C2), 130.2 (C4), 131.8 (C8a), 134.6 (C3), 140.3 (C1),
140.6 (i-C6H5), 151.0 (C4a), 167.2 (CO2H), 169.2
(C(O)N), 196.8 (C8). MS (ESI) m/z: 324 ([M+H]+, 100%),
330 ([M+Li]+, 74%). Anal. Calcd for C19H17NO4: C,
70.58; H, 5.30; N, 4.33. Found: C, 70.96; H, 5.33; N, 4.06.
3.1.10. 1-Phenyl-8a-hydroxy-2-oxo-1,2,6,7,8,8a-hexa-
hydrobenzo[cd]indole-3-carboxylic acid (16). Phenyl-
amide 12 (26 mg, 0.08 mmol) was stirred under nitrogen
in acetone (5 mL) at room temperature for 48 h. The reaction
solution was filtered and the solvent removed. Compound 16
was obtained as an amorphous white solid (25 mg, 96%)
3.1.8. 1-[(N-Morpholino)carbonyl]-8-oxo-5,6,7,8-tetra-
hydronaphthalene-2-carboxylic acid (14). Morpholine
(16.6 mL, 0.19 mmol) was added to a solution of anhydride
7 (41 mg, 0.19 mmol) in ethyl acetate (3 mL). The mixture
was stirred under nitrogen at room temperature for 3 h and
the solvent removed under reduced pressure. The residue
was purified by silica column chromatography (acetone/
dichloromethane, gradient from 50:50 to 100:0; Rf¼0.1
(acetone)). Compound 14 was obtained as an amorphous
white solid (47 mg, 82%). Mp 202–206 ꢀC. IR (KBr)
cmꢂ1: 3300–3600, 1718, 1688, 1591. dH (400 MHz, ace-
tone-d6): 2.13 (2H, tt, J 6.5, 13.0 Hz, H6), 2.59–2.71 (2H,
m, H7), 2.96–3.05 (2H, m, NCH2), 3.07–3.11 (2H, m, H5),
3.50 (2H, t, J 5.0 Hz, OCH2), 3.57–3.80 (4H, m, OCH2,
NCH2), 7.48 (1H, dt, J 0.9, 8.0 Hz, H4), 8.08 (1H, d, J
8.0 Hz, H3), CO2H proton not observed. dC (100 MHz,
DMSO-d6): 22.1 (C6), 29.7 (C5), 39.2 (C7), 41.2 (NCH2),
46.0 (NCH2), 65.2 (OCH2), 65.3 (OCH2), 128.2 (C2),
129.4 (C8a), 129.4 (C4), 134.0 (C3), 137.5 (C1), 149.6
(C4a), 166.6 (C(O)N), 167.3 (CO2H), 197.8 (C8). MS
(ESI) m/z: 304 ([M+H]+, 100%), 326 ([M+Na]+, 36%),
310 ([M+Li]+, 100%). HRMS calcd for C16H16NO5
[M–H]ꢂ: 302.1034. Found: 302.1029.
1
with <5% of 18 present (cf. H NMR d 5.81). Mp 171–
173 ꢀC. IR (KBr) cmꢂ1: 3300–3600, 1701, 1618, 1589,
1451. H NMR (400 MHz, acetone-d6) d: 1.75–1.83 (1H,
1
m, H8), 2.07–2.12 (1H, m, H7), 2.30–2.44 (2H, m, H8,
H7), 2.86–2.94 (1H, m, H6), 3.12–3.22 (1H, m, H6), 5.90
(1H, d, J 2.4 Hz, OH), 7.46 (1H, dt, J 1.8, 7.5 Hz,
p-C6H5), 7.54 (2H, t, J 7.8 Hz, m-C6H5), 7.63–7.68 (3H,
m, H5, o-C6H5), 14.65 (1H, br s, CO2H). dC (100 MHz, ace-
tone-d6): 19.8 (C7), 25.6 (C6), 31.4 (C8), 90.6 (C8a), 127.8
(C3), 128.2 (C2a), 128.7 (o-C6H5), 129.4 (p-C6H5), 130.5
(m-C6H5), 134.0 (C5), 135.4 (C4), 136.4 (i-C6H5), 142.1
(C5a), 146.6 (C8b), 165.6 (CO2H), 170.9 (C2). MS (ESI)
m/z: 310 ([M+H]+, 100%), 332 ([M+Na]+, 100%), 316
([M+Li]+, 100%). HRMS calcd for C18H14NO4 [MꢂH]ꢂ:
308.0929. Found: 308.0918.
3.1.11. 1-Benzyl-8a-hydroxy-2-oxo-1,2,6,7,8,8a-hexa-
hydrobenzo[cd]indole-3-carboxylic acid (17). Benzyl-
amine (74 mL, 0.68 mmol) was added to a solution of
anhydride 7 (146 mg, 0.68 mmol) in ethyl acetate (5 mL),
and the reaction mixture stirred under nitrogen at room tem-
perature for 1 h. The solvent was removed under reduced
pressure and the residue recrystallised (ethyl acetate). Com-
pound 17 was obtained as an amorphous white solid
(159 mg, 72%). Mp 184 ꢀC. IR (KBr) cmꢂ1: 3300–3500,
1622, 1463, 1454. dH (400 MHz, DMSO-d6): 1.11–1.19
(1H, m, H8), 1.81–1.91 (1H, m, H7), 2.01–2.06 (1H, m,
3.1.9. 1-[(N-Thiopentyl)carbonyl]-8-oxo-5,6,7,8-tetra-
hydronaphthalene-2-carboxylic acid (15). A solution of
anhydride 7 (100 mg, 0.46 mmol) in dichloromethane
(2 mL) was added dropwise to pentane-1-thiol (286 mL,

1400
M. J. Petersson et al. / Tetrahedron 63 (2007) 1395–1401
H8), 2.10–2.21 (1H, m, H7), 2.69–2.77 (1H, m, H6), 2.98–
3.05 (1H, m, H6), 4.48 (1H, d, J 15.6 Hz, NCH2), 4.93
(1H, d, J 16.0 Hz, NCH2), 6.63 (1H, s, OH), 7.24–7.38
(5H, m, C6H5), 7.59 (1H, d, J 8.0 Hz, H5), 8.04 (1H, d, J
8.0 Hz, H4), 14.6 (1H, br s, CO2H). dC (100 MHz, DMSO-
d6): 18.0 (C7), 23.8 (C6), 30.2 (C8), 42.2 (NCH2), 87.0
(C8a), 125.3 (C3), 126.4 (C2a), 127.3 (o-C6H5), 127.7 (m-
or p-C6H5), 128.4 (m- or p-C6H5), 132.3 (C5), 132.9 (C4),
137.3 (i-C6H5), 140.2 (C5a), 145.2 (C8b), 164.7 (CO2H),
169.1 (C(O)N). MS (ESI) m/z: 324 ([M+H]+, 100%), 346
([M+Na]+, 89%), 330 ([M+Li]+, 100%). HRMS calcd for
C19H18NO4 [M+H]+: 324.1236. Found: 324.1230.
(p-C6H5), 130.16 (m-C6H5), 132.20 (C5), 135.05 (C8a),
135.10 (C4), 135.53 (C8b), 137.98 (i-C6H5), 138.97 (C5a),
165.58 (CO2H), 171.00 (C(O)N). MS (ESI) m/z: 306
([M+H]+, 36%), 328 ([M+Na]+, 89%), 312 ([M+Li]+,
100%). Anal. Calcd for C19H15NO3: C, 74.74; H, 4.95; N,
4.59. Found: C, 74.56; H, 4.82; N, 4.63.
3.2. Reactivity investigation—anhydride 7 versus
phthalic anhydride 20
Diethylamine ((i) 2 equiv, (ii) and (iii) 1 equiv) was added to
a solution of anhydride 7 ((i) 1 equiv, (ii) 2 equiv or (iii)
10 equiv) and phthalic anhydride 20 ((i) 1 equiv, (ii) 2 equiv
or (iii) 10 equiv) in ethyl acetate, and the mixture was stirred
under nitrogen at room temperature for 16 h. The crude
product mixtures were dried under high vacuum and the
1H NMR spectra obtained using acetone-d6 as solvent. Inte-
gration of the baseline-resolved peaks at d 1.02 ppm (CH3
for 2-(diethylcarbamoyl)benzoic acid 2137), 7.45 ppm (H4
for amide 11), 8.06 ppm (H4 for anhydride 7) and 8.05–
8.11 ppm (for the sum of H4–7 for phthalic anhydride 20
plus H4 for 7, plus H3 for 11, plus H2–6 for 21) was used
to calculate the percentage composition of these components
from the integral of the total crude mixture.
3.1.12. 1-Benzyl-8a-hydroxy-2-oxo-1,2,6,7,8,8a-hexa-
hydrobenzo[cd]indole-3-carboxylic acid (17). Amide 13
(6 mg, 0.019 mmol) was stirred under nitrogen in ethyl
acetate (1 mL, de-acidified) at room temperature for 48 h.
The reaction solution was filtered and the solvent removed.
Compound 17 was obtained as a white solid (5.95 mg, 99%).
3.1.13. 1-Phenyl-2-oxo-1,2,6,7-tetrahydrobenzo[cd]-
indole-3-carboxylic acid (18). Lactamol 16 (80 mg,
0.26 mmol) was stirred with one drop of hydrochloric acid
under nitrogen in chloroform (4 mL) at room temperature
for 16 h. The reaction solution was diluted with chloroform
(20 mL), washed with brine (20 mL), dried (MgSO4) and
filtered. The solvent was removed and the residue purified
by silica column chromatography (dichloromethane/ethyl
acetate, gradient from 100:0 to 0:100; Rf¼0.6 (dichloro-
methane/ethyl acetate, 90:10)). Compound 18 was obtained
as an amorphous white solid (59 mg, 78%) in approximately
95% purity. Mp 143–146 ꢀC. IR (KBr) cmꢂ1: 3300–3600,
1726, 1622. dH (400 MHz, acetone-d6): 2.88 (2H, dt, J 4.1,
8.0 Hz, H7), 3.20 (2H, t, J 7.6 Hz, H6), 5.82 (1H, t, J
4.4 Hz, H8), 7.50–7.53 (1H, m, C6H5), 7.58–7.64 (4H, m,
C6H5), 7.68 (1H, dd, J 7.2, 1.6 Hz, H5), 8.20 (1H, d, J
7.2 Hz, H4), CO2H not observed. dC (100 MHz, acetone-
d6): 24.27 (C7), 24.48 (C6), 110.08 (C8), 122.67 (C2a),
126.63 (C3), 127.69 (o- or m-C6H5), 129.22 (p-C6H5),
130.25 (o- or m-C6H5), 131.91 (C5), 134.70 (i-C6H5),
134.89 (C4), 135.01 (C8b), 135.43 (C8a), 138.64 (C5a),
164.84 (C(O)N), 169.79 (CO2H). MS (ESI) m/z: 292
([M+H]+, 100%), 298 ([M+Li]+, 89%). HRMS calcd for
C18H14NO3 [M+H]+: 292.0968. Found: 292.0972.
3.3. Crystal data for 19
Crystallised by slow evaporation from toluene. C19H15NO3
M¼305.3, monoclinic, space group P21/c,ꢀ a¼
˚
9.958(3), b¼18.917(7), c¼8.333(2) A, b¼107.36(2) , U¼
1498.2(8) A , Z¼4, Dc¼1.35g cmꢂ3, crystal size: 0.40ꢁ
3
˚
0.30ꢁ0.25 mm, 2976 reflections collected, 2627 unique
(Rint¼0.049), R¼0.049 [1778 reflections with I>2s(I)],
wR(F2)¼0.153 (all data). Crystallographic data for the struc-
tural analysis of 19 has been deposited with the Cambridge
Crystallographic Data Centre CCDC no. 608262.
Acknowledgements
Financial support for this work was provided by (1) Griffith
University, (2) Natural Product Discovery, Griffith Uni-
versity and (3) the Eskitis Institute for Cell and Molecular
Therapies, Griffith University.
3.1.14. 1-Benzyl-2-oxo-1,2,6,7-tetrahydrobenzo[cd]-
indole-3-carboxylic acid (19). Lactamol 17 (100 mg,
0.31 mmol) was stirred with two drops of hydrochloric
acid under nitrogen in chloroform (5 mL) at room tempera-
ture for 4 h. The reaction solution was diluted with chloro-
form (20 mL), washed with brine (20 mL), dried (MgSO4)
and filtered. The solvent was removed and the residue
recrystallised (ethyl acetate). Compound 19 was obtained
as small pale yellow plates (67 mg, 72%). An analytical
pure sample of 19 was prepared by further recrystallisation
(ethyl acetate). Mp 198–200 ꢀC. IR (KBr) cmꢂ1: 3200–
3600, 1716, 1616. dH (400 MHz, acetone-d6): 2.82 (2H, dt,
J 4.1, 8.0 Hz, H7), 3.11 (2H, t, J 8.2 Hz, H6), 5.11 (2H, s,
NCH2), 5.96 (1H, t, J 4.4 Hz, H8), 7.28–7.43 (5H, m,
C6H5), 7.60 (1H, d, J 7.6 Hz, H5), 8.13 (1H, d, J 7.6 Hz,
H4), 14.13 (1H, br s, CO2H). dC (100 MHz, acetone-d6):
24.80 (C7), 24.91 (C6), 45.21 (NCH2), 110.17 (C8),
123.39 (C2a), 127.21 (C3), 129.08 (o-C6H5), 129.14
Supplementary data
Supplementary data available: (a) general procedures and
experimental procedures for compounds 1, 3 and 5; (b) H
1
NMR spectra for compounds 7, 8, 12, 14, 16 and 17; (c)
X-ray crystallographic data collection, structure solution,
refinement of 19. Supplementary data associated with this
article can be found in the online version, at doi:10.1016/
j.tet.2006.11.090.
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