Acid-catalyzed reactions of 3-substituted-4,6-dimethoxyindoles with ketones

Article abstract of DOI:10.1071/CH10137

Activated 3-substituted-4,6-dimethoxyindoles undergo acid catalyzed condensation with acetone and acetophenones in the presence of hydrochloric acid to give pyrrolo[a]indoles. Mixed pyrrolo[a]indoles can similarly be formed using a 1:1 mixture of two indo

Full text of DOI:10.1071/CH10137

RESEARCH FRONT
Full Paper
CSIRO PUBLISHING
www.publish.csiro.au/journals/ajc
Aust. J. Chem. 2010, 63, 761–770
Acid-Catalyzed Reactions of 3-Substituted-
4,6-dimethoxyindoles with Ketones
Kasey Wood,A David StC. Black,A,B and Naresh KumarA,B
ASchool of Chemistry, The University of New South Wales, Sydney, NSW 2052, Australia.
BCorresponding authors. Email: d.black@unsw.edu.au; n.kumar@unsw.edu.au
Activated 3-substituted-4,6-dimethoxyindoles undergo acid catalyzed condensation with acetone and acetophenones in
the presence of hydrochloric acid to give pyrrolo[a]indoles. Mixed pyrrolo[a]indoles can similarly be formed using a 1:1
mixture of two indoles. The reaction was found to be sensitive to acidity, with a 3:2 spiro condensation product being
preferentially formed in the presence of p-toluenesulfonic acid.
Manuscript received: 22 March 2010.
Manuscript accepted: 21 April 2010.
Introduction
acid.[17,18] Similarly, Banerji and Mustafi have reported treat-
ment of skatole with acetone and boron trifluoride, to yield
pyrrolo[b]indole 7 and spiro dimer 8.[19]
In general, acid-catalyzed condensations of indoles with ace-
tone have been well studied, producing condensation products
in ratios of 2:1, 2:2, and 2:3, depending upon the reaction condi-
tions. Noland et al. have reported that the product ratios are
dependent upon the relative reactivity of the indole and the
acidity of the reaction mixture.[20]
Condensations of various indoles with acetone, in strongly
acidic conditions, rapidly give 1:1 condensation products
which can subsequently undergo cyclizative dimerization.[20]
For example, heating 2-methylindole under reflux with acetone
and ethanolic hydrochloric acid, produces tetrahydrocarbazole
5b in 82% yield.[21] Similar treatment of N-benzylindole pro-
duces a 3,3ꢀ-di-indolylmethane (9a) and a trace amount of the
N-substituted cyclopenta[b]indole spiro dimer (3b).[22,23]
Reducing the acidity can sufficiently slow the rate of con-
densation, thus allowing competing reactions to occur providing
access to alternate products.[20] Indole, in the presence of
acetone and boron trifluoride, forms pyrrolo[a]indole 10.[24] 2-
Methylindole, when heated under reflux, with acetone and acetic
acid, generates the 3,3ꢀ-di-indolylmethanes 9b in 78% yield.[21]
Steric hindrance and the electrophilicity of the attacking
carbonyl group, also plays a significant role in determining
the outcome of these reactions. The condensations of indoles
with acetophenones display significantly less product diver-
sity with indole, 1-methylindole and 2-methylindole both being
reported to give only 3,3ꢀ-di-indolylmethanes related to 9b
(Scheme 2).[20]
Yuehchukene 1 and isoborreverine 2[1] are natural bis-
indole alkaloids which possess related pyrrolo[a]indole and
pyrrolo[b]indole structures (Scheme 1). Yuehchukene 1, iso-
lated from the Murraya species,[2] has attracted considerable
attention[3–8] due to its potent anti-implantation activity in
rats.[9,10] Yuehchukene 1 has been characterized as a dimer of
β-(dehydroprenyl)indole 3 and synthetic studies have shown the
Diels–Alder reaction of diene 3 under acidic conditions produces
yuehchukene 1 in a single step.[11–16]
In a similar fashion, acid-catalyzed condensations of
indoles with acetone yield related pyrrolo[a]indole and
pyrrolo[b]indoles. In ethanolic hydrochloric acid, the parent
indole reacts with acetone to produce cyclopenta[b]indole 4,
as well as
a mixture of tetrahydrocarbazole 5a and
cyclopenta[b]indole spiro dimer 6a. Formation of the simplified
yuehchukene structure (4) has been optimized to afford 70%
yield, by heating the reactants under reflux in trifluoroacetic
NHMe
N
HN
H
H
HN
NH
NHMe
2
1
In contrast, 3-methylindole does not undergo acid-catalyzed
condensation with methyl ketones, diethyl ketones, or aceto-
phenones seemingly due to insufficient reactivity of the indole
towards these electrophiles.[21] An investigation into this reac-
tion when additional activation is supplied to the indole in
the form of 4,6-dimethoxy groups was therefore undertaken.
Additional indole activation has been shown to influence the
acid-catalyzed condensation of N-methyl-4,6-dimethoxyindole
N
H
3
Scheme 1.
© CSIRO 2010
10.1071/CH10137
0004-9425/10/050761

RESEARCH FRONT
762
K. Wood, D. StC. Black, and N. Kumar
R
N
NH
N
H
N
R
R
N
H
R
HN
5a R ꢀ H
5b R ꢀ Me
6a R ꢀ H
6b R ꢀ CH2Ph
4
N
N
NH
N
N
N
N
HN
R2
R1
R2
R1
R
9a R1 ꢀ CH2Ph, R2 ꢀ H
9b R1 ꢀ H, R2 ꢀ Me
10
8
7
Scheme 2.
OMe
with acetone, as a cyclopenta[b]indole related to 2 was obtained
in 84% yield in preference to a 3,3ꢀ-di-indolylmethane or spiro
dimer.[25]
R1
R2
MeO
HCl/alcohol
R1
N
OMe
O
R2
ꢁ
Results and Discussion
R2
R1
OMe
HN
N
H
MeO
4,6-Dimethoxy-3-methylindole 11a undergoes addition to ace-
tone in methanolic hydrochloric acid at room temperature to give
the pyrrolo[a]indole dimer 12a. Regioselectivity was found to
be specific for C(2), despite the additional activation of C(7)
by the dimethoxy system. Formation of 12a is consistent with
reports by Banerji and Mustafi on the parent 3-methylindole sys-
tem, though in this case it was obtained as a single product.[19]
Pyrrolo[a]indole dimer 12a has also been prepared in a similar
fashion through the acid catalyzed reaction of indole 11a with
mesityl oxide.[26]
11a R1 ꢀ Me
R2 ꢀ Me, Ph, 4-BrC6H4,
11b R1 ꢀ Ph
4-ClC6H4, 4-MeC6H4,
4-OMeC6H4, 4-FC6H4
11c R1 ꢀ 4-BrC6H4
11d R1 ꢀ 4-ClC6H4
MeO
12
11e R1 ꢀ 4-OMeC6H4
12
a
b
c
d
e
f
R1
R2
% Yield
92
67
52
60
69
75
63
73
14
6
Me
Me
Ph
Me
This reaction was found to be consistent across a range
of 3-subsituted indoles (Scheme 3). In general, 3-arylindoles
were found to be less reactive, with the reaction time at room
temperature increasing from 0.5 to 5 h, and poor yields of
pyrrolo[a]indoles 12b–e obtained. Yields were increased to
58–88% after reaction optimization by heating at reflux in
isopropanol for 3 h. Structural identification was performed, pre-
4-BrC6H4
4-ClC6H4
4-OMeC6H4
Me
Me
Me
Me
Ph
g
h
i
Me
4-MeC6H4
4-OMeC6H4
4-ClC6H4
4-BrC6H4
4-FC6H4
4-ClC6H4
4-MeC6H4
4-ClC6H4
4-OMeC6H4
4-BrC6H4
4-MeC6H4
4-ClC6H4
4-BrC6H4
4-MeC6H4
1
dominantly through H NMR spectroscopy, and an interesting
Me
downfield shift by ∼0.3 ppm of one methylene was noted upon
introduction of an aryl substituent. As evidenced in the X-ray
crystal structure of 12d, this downfield shift can be attributed to
one of the C(1) methylenes projecting towards the C(9) aromatic
ring (Fig. 1).
Me
j
Me
k
l
Me
18
17
6
4-OMeC6H4
4-OMeC6H4
4-ClC6H4
4-ClC6H4
4-ClC6H4
4-ClC6H4
4-BrC6H4
4-BrC6H4
4-BrC6H4
This heterocyclic system can also be accessed under basic
conditions. Yepuri et al. have reported that treatment of indoles
11b and 11e with acetone, in the presence of sodium hydride
and triflic anhydride, produces the corresponding pyrroloindoles
12b and 12e, respectively. The more active indole 11e, was also
found to produce a 20% yield of the spiropyrroloindole 14c.[27]
We have previously reported 3-methyl-4,6-dimethoxyindole
11a, in contrast to the parent skatole,[6] undergoes acid-catalyzed
condensation with activated p-substituted acetophenones, to
produce pyrrolo[a]indoles 12f–h.[25] Recently the parent 12f
system has been reported in literature, accessed via treatment
of skatole with phenylacetylene in the presence of a gold
catalyst.[28]
m
n
o
p
q
r
8
13
5
9
8
s
t
2
15
Scheme 3.

RESEARCH FRONT
Acid-Catalyzed Reactions of 3-Substituted-4,6-dimethoxyindoles
763
C(37)
O(3)
C(24)
C(23)
C(12)
O(4)
C(27)
O(3)
C(26)
C(35)
C(28)
C(29)
C(38)
C(36)
C(12)
C(22)
C(34)
C(31)
C(14)
C(19)
C(13)
C(16)
C(25)
C(24)
C(15)
C(18)
C(11)
C(30)
N(2)
C(33)
C(32)
C(23)
C(14)
N(2)
C(21)
C(10)
O(4)
C(10)
C(11)
C(9)
C(17)
C(12)
C(7)
N(1)
C(13)
C(16)
C(1)
C(2)
C(20)
C(9)
C(25)
C(17)
C(18)
C(3)
C(11)
C(8)
C(15)
C(1)
N(1)
C(22)
O(2)
C(20)
C(5)
C(19)
C(6)
C(4)
C(27)
O(1)
C(28)
C(26)
C(2)
C(8)
C(21)
C(7)
C(3)
C(29)
C(31)
C(4)
C(30)
C(11)
Fig. 1. ORTEP diagram of 12d.[29]
C(6)
O(2)
C(33)
C(5)
O(1)
We have now extended this reaction to deactivated aceto-
phenones to produce pyrrolo[a]indoles 12i–k. This reaction is
interesting because the formation of 3,3ꢀ-di-indolylmethanes in
the corresponding reactions of indole and 2-methylindole[20]
suggests that a 2,2ꢀ-diindolylmethane would be the anticipated
product.The methoxy indole activation therefore induced a rapid
condensation which tolerated increased steric hindrance.
The 1H NMR spectra of 12f–k displayed a notable 0.6 ppm
downfield shift of the H(5) proton in comparison to the parent
compound 12a. This can be attributed to an aromatic ring cur-
rent effect, resulting from introduction of the C(3) phenyl. This
effect appeared to similarly extend to the C(6) methoxy, with a
characteristic downfield shift of one methoxy group by 0.4 ppm
also being observed.
Acid-catalyzed condensations of 3-arylindoles with p-
substituted acetophenones proved problematic. Only the most
activated indole 11e reacted at room temperature with 4-chloro-
acetophenone, giving a trace amount of the desired product after
24 h. A maximum 17% yield of 12k was obtained after reaction
optimization, by heating at reflux in methanolic hydrochloric
acid for 24 h. Similarly, a low yield of 12l was obtained under
these conditions.
The less activated indole 11d, showed only a trace amount
of product after heating at reflux with 4-chloroacetophenone
for 24 h. Reaction monitoring by thin-layer chromatography
indicated the slow formation of product over 48 h, followed
by subsequent degradation of all compounds before the reac-
tion reached completion. This degradation was attributed to the
extended exposure of the substrates to the harsh reaction condi-
tions, thus alternate acids were subsequently investigated. Boron
trifluoride, trifluoroacetic acid, and p-toluenesulfonic acid failed
to induce a reaction.
Conversely, a parallel degradation after 2–3 days was evi-
denced using a neat reaction of trifluoroacetic acid or sulfuric
acid. The best method of isolating and identifying the reaction
product was therefore to continue using the original reaction
conditions, deliberately quench the reaction mixture at 48 h and
purify to remove remaining starting materials.
C(32)
Fig. 2. ORTEP diagram of 13a.[29]
The bis-indole nature of these pyrrolo[a]indoles leads to the
interesting prospect of incorporating two different indoles into
the structure of the product. Formation of mixed indole dimers
could potentially be most readily achieved by the use of a 1:1
mixture of two indoles in the reaction. As such, indoles 11a
and 11c were heated at reflux with acetone and hydrochlo-
ric acid in isopropanol for 4 h. Interestingly, the precipitate
collected upon cooling was identified to be the single com-
pound 13a, which was obtained in a 59% yield. Furthermore,
no more soluble compounds were isolated from the reaction
solution.
1
The H NMR spectrum was characteristic for a pyrrolo[a]
indole, with a singlet at δ 2.44 and two doublets at δ 7.25
and 7.49, corresponding to the methyl and 4-bromophenyl pro-
tons respectively; thereby consistent with a mixed indole dimer.
This was further confirmed through high resolution mass spec-
trometry, with the obtained mass of 603.1826 congruent with
C33H35BrN2O4. NOE correlations indicated that the 3-methyl
substituted indole was bound to the new pyrrolidine ring, and
the 3-bromophenyl substituted indole was freely rotating, which
is consistent with the relative reactivity of the two indoles. The
structure was confirmed by X-ray crystallography (Fig. 2).
Two further combinations of indoles were subsequently
reacted with acetone to produce the mixed pyrrolo[a]indoles
13b–c as single compounds in 35 and 41% yields respectively
(Scheme 4). In both cases 1D and 2D NMR spectroscopy con-
firmed that the products were mixed dimers, with the more
reactive indole bound to the newly formed pyrrolidine ring.
The related mixed pyrrolo[a]indoles were not produced
when an acetophenone was employed, even though the steric
concerns were minimized through combination of 3-methyl-4,6-
dimethoxyindole 11a with a 3-arylindole.
In this manner indole 11d was reacted with a range of
p-substituted acetophenones to give the sterically hindered
pyrrolo[a]indoles 12n–q, in yields ranging from 6 to 13%. Sim-
ilarly, pyrrolo[a]indoles 12r–t were produced from indole 11c,
although the yields were unsurprisingly lower in response to the
increase in steric strain.
Mechanistically, there are several possible routes by which
methyl ketones condense with indoles.[17,18,20,21,25] In general,
however, vinyl indoles are implicated as an important reaction
intermediate which could be potentially trapped in the presence
of a dienophile, through a Diels–Alder reaction.

RESEARCH FRONT
764
K. Wood, D. StC. Black, and N. Kumar
OMe
congruent with the work reported by Banerji and Mustafi on the
parent 3-methylindole in the presence of boron trifluoride.[19]
Similarly, 3-arylindoles 11c and 11e were found to produce
spiro dimers 14b–c under these reaction conditions. Conversely,
the related reaction of 3-substituted indoles, with acetophenone
and p-toluenesulfonic acid, did not produce the corresponding
spiro adducts. This is not surprising as this 3:2 condensation
product probably requires the self condensation of the aceto-
phenones, a process which does not occur as readily as with
acetone.
MeO
OMe
OMe
R
N
Acetone
HCl
ꢁ
N
N
NH
MeO
MeO
H
H
R
11c–e
11a
MeO
OMe
13
13
a
R
% Yield
59
4-BrC6H4
4-ClC6H4
Conclusion
b
35
In contrast to the parent 3-methylindole, activated 3-substituted-
4,6-dimethoxyindoles undergo acid-catalyzed condensation
with acetone and acetophenones, in the presence of hydrochloric
acid, to give pyrrolo[a]indoles as a single product. Poorer yields
are obtained, however, as the steric hindrance is increased. Sim-
ilarly, mixed pyrrolo[a]indoles were successfully formed, with
the more active indole bound to the newly formed pyrrolidine
ring.
Furthermore, in agreement with literature reports, the nature
of the reaction product was found to be dependent upon the
acidity of the reaction mixture. A 2:2 condensation occurred in
the presence of a strong acid, compared with a 3:2 condensation
product being preferentially produced in the presence of a weak
acid. Notably, the 3:2 condensation occurred only with acetone,
presumably due to acetophenones not readily undergoing self
condensation.
c
4-OMeC6H4
41
Scheme 4.
R
N
Acetone
Toluenesulfonic acid
OMe
R
MeO
OMe
N
DCM
N
MeO
H
R
11a,c,e
OMe
14
14
R
% Yield
a
b
c
Me
18
20
15
4-BrC6H4
4-OMeC6H4
Experimental
General Method for Preparation of Pyrrolo[a]indoles
A mixture of the indole (1 equiv.) and ketone (1.5 equiv.) were
suspended in isopropanol (20 mL) and concentrated hydrochlo-
ric acid (1 mL) was subsequently added.The reaction was heated
under reflux for the specified duration, after which, the resulting
precipitate was collected and recrystallized from acetonitrile.
Scheme 5.
To this end, the acid-catalyzed reaction of 3-methyl-4,6-
dimethoxyindole with acetone in the presence of dimethyl
acetylenedicarboxylate was studied. Stirring the reactants at
room temperature for 2 h in methanolic hydrochloric acid
resulted in a white precipitate which was identified through
1H NMR spectroscopy as pyrrolo[a]indole 12a. In order to
increase the lifetime of the reaction intermediates the reaction
was repeated by heating the mixture in DCM, in the presence
6,8-Dimethoxy-3-(3-methyl-4,6-dimethoxyindole)-
1,1,3,9-tetramethyl Pyrrolo[a]indole 12a
This compound was prepared according to the general method
using indole 11a (0.503 g, 2.63 mmol) and acetone (0.2 mL,
2.72 mmol). The mixture was stirred at room temperature for
1/2 h to give 12a as a white solid (0.261 g, 42%), mp 203–
205◦C. δH 1.13 (s, 3H, CH3), 1.49 (s, 3H, CH3), 2.03 (s, 3H,
CH3), 2.45 (s, 3H, CH3), 2.48 (s, 3H, CH3), 2.61 (d, J 12.6 Hz,
1H, CH2), 2.86 (d, J 12.6 Hz, 1H, CH2), 3.68 (s, 3H, OCH3),
3.73 (s, 3H, OCH3), 3.86 (s, 3H, OCH3), 3.89 (s, 3H, OCH3),
6.12 (d, J 1.89 Hz, 1H, aryl), 6.19 (d, J 1.89 Hz, 1H, aryl), 6.20
(d, J 1.89 Hz, 1H, aryl), 6.25 (d, J 1.89 Hz, 1H, aryl), 7.29 (bs,
1H, NH). δC 10.0 (CH3), 11.6 (CH3), 27.3 (CH3), 28.3 (CH3),
28.5 (CH3), 37.4 (C), 55.0 (OCH3), 55.1 (OCH3), 55.4 (OCH3),
55.7 (OCH3), 60.9 (CH2), 61.6 (C), 86.5 (CH), 86.6 (CH), 91.2
(CH), 91.4 (CH), 100.6 (C), 105.1 (C), 114.2 (C), 117.6 (C),
131.8 (C), 135.0 (C), 135.1 (C), 144.7 (C), 155.1 (C), 155.4 (C),
156.2 (C), 156.7 (C). νmax (KBr)/cm−1 3448, 3383, 2959, 2928,
2837, 1623, 1591, 1572, 1510, 1455, 1374, 1301, 1455, 1245,
1210, 1151, 1132, 1035, 937, 807. UV-vis (MeOH): λmax 274
(ε 25700 cm−1 M−1), 227 (108200), 207 (67300). HRMS m/z
(ESI) C28H34N2O4 [M]+ requires 462.2519. Found: 462.2540.
1
of p-toluenesulfonic acid for 4 h. H NMR spectroscopy indi-
cated that the resultant solid obtained upon workup was neither
the targeted Diels–Alder adduct nor pyrrolo[a]indole 12a. The
C(2) and NH protons had disappeared but in contrast to the
pyrrolo[a]indole system, only two methyl groups originating
from acetone were present at δ 1.47 and 1.63. The 13C NMR
spectrum displayed characteristic signals for the indole scaffold,
as well as two CH3 groups at δ 28.1 and 29.3, a CH2 at δ 57.6
and a quaternary carbon at δ 37.2; which are characteristic of a
–CH2–C–(CH3)2 fragment. A final quaternary carbon at δ 78.8
was present, with HMBC correlations indicating it was attached
to the CH2. Finally, the NOESY experiment revealed the H(7)
proton had unusual correlations to both the CH2 group and the
methylene at δ 1.63.
The product was therefore inferred to be the pyrrolo[a]indole
spiro dimer 14a (Scheme 5). This was supported through
high resolution mass spectrometry, with the obtained mass of
502.2826 consistent with C31H38N2O4. The structure is also

RESEARCH FRONT
Acid-Catalyzed Reactions of 3-Substituted-4,6-dimethoxyindoles
765
6,8-Dimethoxy-3-(3-phenyl-4,6-dimethoxyindole)-
1,1,3-trimethyl Pyrrolo[a]indole 12b
6,8-Dimethoxy-3-(3-(4-Methoxyphenyl)-4,6-
dimethoxyindole)-1,1,9-trimethyl Pyrrolo[a]indole 12e
This compound was prepared according to the general method
using indole 11b (0.499 g, 1.97 mmol) and acetone (0.29 mL,
3.94 mmol). The mixture was heated at reflux for 3 h to give 12b
as a white solid (0.387 g, 67%), mp 210–212◦C. δH 1.11 (s, 3H,
CH3), 1.19 (s, 3H, CH3), 1.76 (s, 3H, CH3), 2.38 (d, J 12.8 Hz,
1H, CH2), 2.82 (d, J 12.8 Hz, 1H, CH2), 3.56 (s, 3H, OCH3),
3.66 (s, 3H, OCH3), 3.73 (s, 3H, OCH3), 3.78 (s, 3H, OCH3),
6.14 (d, J 1.9 Hz, 1H, aryl), 6.23 (d, J 1.9 Hz, 1H, aryl), 6.31 (d,
J 1.9 Hz, 1H, aryl), 6.36 (d, J 1.9 Hz, 1H, aryl), 7.37 (m, 10H,
aryl), 7.81 (bs, 1H, NH).
This compound was prepared according to the general method
using indole 11e (0.546 g, 1.93 mmol) and acetone (0.29 mL,
3.86 mmol). The mixture was heated at for 3 h to give 12e as an
off-white solid (0.430 g, 69%), mp 250–251◦C. δH 1.12 (s, 3H,
CH3), 1.18 (s, 3H, CH3), 1.77 (s, 3H, CH3), 2.37 (d, J 12.8 Hz,
1H, CH2), 2.82 (d, J 12.8 Hz, 1H, CH2), 3.58 (s, 3H, OCH3),
3.67 (s, 3H, OCH3), 3.73 (s, 3H, OCH3), 3.77 (s, 3H, OCH3),
3.86 (s, 3H, OCH3), 3.87 (s, 3H, OCH3), 6.14 (d, J 1.9 Hz, 1H,
aryl), 6.22 (d, J 1.9 Hz, 1H, aryl), 6.30 (d, J 1.9 Hz, 1H, aryl),
6.35 (d, J 1.9 Hz, 1H, aryl), 6.88 (d, J 8.7 Hz, 2H, aryl), 6.91 (d, J
8.7 Hz, 2H, aryl), 7.34 (d, J 8.7 Hz, 4H, aryl), 7.78 (bs, 1H, NH).
3-(3-(4-Bromophenyl)-4,6-dimethoxyindole)-6,8-
dimethoxy-1,1,3-trimethyl Pyrrolo[a]indole 12c
6,8-Dimethoxy-1,9-dimethyl-3-(3-methyl-4,6-
This compound was prepared according to the general method
using indole 11c (0.517 g, 1.56 mmol) and acetone (0.17 mL,
2.34 mmol). The mixture was heated at reflux for 3 h to give
12c as a white solid (0.300 g, 52%), mp 170–172◦C. δH 1.14
(s, 3H, CH3), 1.16 (s, 3H, CH3), 1.77 (s, 3H, CH3), 2.39 (d, J
12.8 Hz, 1H, CH2), 2.79 (d, J 12.8 Hz, 1H, CH2), 3.58 (s, 3H,
OCH3), 3.67 (s, 3H, OCH3), 3.72 (s, 3H, OCH3), 3.78 (s, 3H,
OCH3), 6.14 (d, J 1.9 Hz, 1H, aryl), 6.22 (d, J 1.9 Hz, 1H, aryl),
6.25 (d, J 1.9 Hz, 1H, aryl), 6.35 (d, J 1.9 Hz, 1H, aryl), 7.29 (d,
J 8.3 Hz, 4H, aryl), 7.45 (d, J 8.3 Hz, 4H, aryl), 7.82 (bs, 1H,
NH). δC 27.9 (CH3), 29.0 (CH3), 30.1 (CH3), 38.2 (C), 54.9
(OCH3), 55.0 (OCH3), 55.5 (OCH3), 55.7 (OCH3), 61.6 (CH2),
61.9 (C), 86.4 (CH), 86.7 (CH), 91.8 (CH), 92.2 (CH), 107.1
(C), 111.7 (C), 113.6 (C), 116.4 (C), 119.8 (C), 120.5 (C), 129.9
(CH), 130.1 (CH), 130.2 (CH), 131.6 (C), 132.6 (CH), 134.8
(C), 134.9 (C), 135.4 (C), 135.9 (C), 145.8 (C), 154.6 (C), 154.8
(C), 156.7 (C), 157.4 (C). νmax (KBr)/cm−1 3441, 2957, 2935,
2835, 1623, 1591, 1498, 1483, 1452, 1389, 1375, 1347, 1308,
1248, 1207, 1147, 1069, 1048, 1012, 986, 940, 835, 809. UV-
vis (MeOH): λmax 275 nm (ε 107200 cm−1 M−1), 225 (123800),
207 (31700). HRMS m/z (ESI) C8H36Br2N2O4 [M]+ requires
742.1042. Found: 742.1081.
dimethoxyindole)-1,3-diphenyl Pyrrolo[a]indole 12f
This compound was prepared according to the general method
using indole 11a (0.508 g, 2.65 mmol) and acetophenone
(0.31 mL, 2.66 mmol). The mixture was stirred at room tem-
perature for 1/2 h to give 12f as a white solid (0.208 g, 27%),
mp 244–246◦C. δH 1.67 (s, 3H, CH3), 1.71 (s, 3H, CH3), 3.27
(s, 3H, OCH3), 3.49 (d, J 11.3 Hz, 1H, CH2), 3.55 (d, J 11.3 Hz,
1H, CH2), 3.66 (s, 3H, OCH3), 3.72 (s, 3H, OCH3), 3.79 (s, 3H,
OCH3), 5.38 (d, J 1.9 Hz, 1H, aryl), 6.05 (d, J 1.9 Hz, 1H, aryl),
6.08 (d, J 1.9 Hz, 1H, aryl), 6.24 (d, J 1.9 Hz, 1H, aryl), 6.97 (m,
3H, aryl), 7.08 (m, 5H, aryl), 7.18 (d, J 7.5 Hz, 2H, aryl), 9.88
(bs, 1H, NH). δC 11.2 (CH3), 11.6 (CH3), 27.9 (CH3), 45.9 (C),
55.0 (OCH3), 55.3 (OCH3), 55.4 (OCH3), 55.5 (OCH3), 63.9
(CH2), 67.5 (C), 86.9 (CH), 87.5 (CH), 90.7 (CH), 91.4 (CH),
101.5 (C), 108.9 (C), 113.4 (C), 116.7 (C), 126.0 (C), 126.5
(CH), 127.5 (CH), 128.2 (CH), 128.3 (CH), 130.8 (C), 133.6
(C), 136.9 (C), 141.9 (C), 142.5 (C), 146.6 (C), 155.1 (C), 155.8
(C), 156.7 (C). νmax (KBr)/cm−1 3447, 2927, 2834, 1624, 1597,
1510, 1493, 1448, 1296, 1244, 1208, 1150, 1031, 938, 804, 698.
UV-vis (MeOH): λmax 275 (ε 20800 cm−1 M−1), 226 (84000).
HRMS m/z (ESI) C8H38N2O4 [M]+ requires 586.2832. Found:
586.2860.
3-(3-(4-Chlorophenyl)-4,6-dimethoxyindole)-6,8-
dimethoxy-1,1,3-trimethyl Pyrrolo[a]indole 12d
6,8-Dimethoxy-1,9-dimethyl-1,3-(4-methylphenyl)-3-
(3-methyl-4,6-dimethoxyindole)-pyrrolo[a]indole 12g
This compound was prepared according to the general method
using indole 11d (0.554 g, 1.92 mmol) and acetone (0.29 mL,
3.84 mmol). The mixture was heated at reflux for 3 h to give 12d
as a white solid (0.381 g, 60%), mp 208–210◦C. δH 1.13 (s, 3H,
CH3), 1.16 (s, 3H, CH3), 1.77 (s, 3H, CH3), 2.39 (d, J 12.8 Hz,
1H, CH2), 2.79 (d, J 12.8 Hz, 1H, CH2), 3.57 (s, 3H, OCH3),
3.67 (s, 3H, OCH3), 3.72 (s, 3H, OCH3), 3.77 (s, 3H, OCH3),
6.14 (d, J 1.9 Hz, 1H, aryl), 6.22 (d, J 1.9 Hz, 1H, aryl), 6.25 (d,
J 1.9 Hz, 1H, aryl), 6.35 (d, J 1.9 Hz, 1H, aryl), 7.29 (d, J 8.6 Hz,
2H, aryl), 7.32 (d, J 8.6 Hz, 4H, aryl), 7.35 (d, J 8.6 Hz, 2H, aryl),
7.53 (bs, 1H, NH). δC 7.9 (CH3), 28.9 (CH3), 30.1 (CH3), 38.2
(C), 55.1 (OCH3), 55.1 (OCH3), 55.5 (CH3), 55.8 (CH3), 61.6
(CH2), 61.9 (C), 86.4 (CH), 86.8 (CH), 91.9 (CH), 92.2 (CH),
107.1 (C), 111.7 (C), 112.4 (C), 116.4 (C), 126.9 (CH), 127.2
(CH), 131.6 (C), 132.3 (CH), 134.3 (C), 134.9 (C), 135.4 (C),
135.4 (C), 145.8 (C), 154.6 (C), 154.8 (C), 156.6 (C), 157.4 (C).
νmax (KBr)/cm−1 3441, 3376, 2958, 2931, 2837, 1707, 1624,
1596, 1497, 1487, 1452, 1376, 1346, 1308, 1249, 1207, 1148,
1088, 1048, 1030, 1016, 940, 808. UV-vis (MeOH): λmax 278 nm
(ε 32000 cm−1 M−1), 226 (125300), 200 (91300). HRMS m/z
(ESI) C8H36Cl2N2O4Na [M + Na]+ requires 677.1944. Found:
677.1951.
This compound was prepared according to the general
method using indole 11a (0.250 g, 1.31 mmol) and 4ꢀ-
methylacetophenone (0.52 mL, 3.89 mmol). The mixture was
stirred at room temperature for 21 h to give 12g as a white solid
(0.076 g, 19%), mp 266–268◦C. δH 1.68 (s, 3H, CH3), 2.07 (s,
3H, CH3), 2.12 (s, 3H, CH3), 2.33 (s, 3H, CH3), 2.34 (s, 3H,
CH3), 3.23 (d, J 12.8 Hz, 1H, CH2), 3.34 (OCH3), 3.71 (d, J
12.8 Hz, 1H, CH2), 3.73 (s, 3H, OCH3), 3.78 (s, 3H, OCH3),
3.89 (s, 3H, OCH3), 5.41 (d, J 1.9 Hz, 1H, aryl), 6.04 (s, 1H,
aryl), 6.11 (s, 1H, aryl), 6.14 (d, J 1.9 Hz, 1H, aryl), 6.84 (d, J
8.0 Hz, 2H, aryl), 7.06 (d, J 8.0 Hz, 2H, aryl), 7.12 (s, 4H, aryl),
7.19 (bs, 1H, NH). δC 10.7 (CH3), 12.1 (CH3), 20.6 (CH3), 20.9
(CH3), 27.4 (CH3), 45.8 (C), 54.9 (OCH3), 55.0 (OCH3), 55.1
(OCH3), 55.4 (OCH3), 64.3 (CH2), 67.3 (C), 86.2 (CH), 86.4
(CH), 91.1 (CH), 91.2 (CH), 102.6 (C), 108.6 (C), 114.0 (C),
116.9 (C), 125.6 (CH), 127.3 (CH), 128.4 (CH), 129.2 (CH),
130.1 (C), 132.9 (C), 135.2 (C), 135.4 (C), 137.4 (C), 138.8 (C),
142.0 (C), 143.0 (C), 155.1 (C), 155.2 (C), 156.0 (C), 156.6
(C). νmax (KBr)/cm−1 3455, 2989, 2927, 2829, 1623, 1590,
1511, 1453, 1296, 1242, 1208, 1150, 1061, 1038, 938, 805. UV-
vis (MeOH): λmax 276 nm (ε 18100 cm−1 M−1), 226 (75600).

RESEARCH FRONT
766
K. Wood, D. StC. Black, and N. Kumar
HRMS m/z (ESI) C40H42N2O4 [M + Na]+ requires 614.3145.
stirred at room temperature for 1 h to give 12j as an off-white
solid (0.054 g, 6%), mp 262–264◦C. δH 1.26 (s, 3H, CH3), 2.12
(s, 3H, CH3), 2.29 (s, 3H, CH3), 3.27 (d, J 12.8 Hz, 1H, CH2),
3.39 (s, 3H, OCH3), 3.53 (d, J 13.2 Hz, 1H, CH2), 3.74 (s, 3H,
OCH3), 3.88 (s, 6H, OCH3), 5.40 (d, J 1.89 Hz, 1H, aryl), 6.16
(d, J 1.89 Hz, 2H, aryl), 6.21 (d, J 1.89 Hz, 1H, aryl), 7.15 (d,
J 8.67 Hz, 2H, aryl), 7.28 (d, J 8.67 Hz, 2H, aryl), 7.37 (d, J
8.67 Hz, 2H, aryl), 7.41 (d, J 8.67 Hz, 2H, aryl) δC 10.6 (CH3),
12.6 (CH3), 25.2 (CH3), 45.4 (C), 55.1 (OCH3), 55.1 (OCH3),
55.2 (OCH3), 55.4 (OCH3), 65.3 (CH2), 67.1 (C), 85.8 (CH),
86.4(CH), 91.5(CH), 91.7(CH), 102.4(C), 108.4(C), 114.0(C),
117.3 (C), 120.2 (C), 121.9 (C), 128.1 (CH), 129.4 (CH), 130.5
(C), 131.4 (CH), 131.6 (CH), 132.4 (C), 135.6 (C), 140.1 (C),
142.9 (C), 145.7 (C), 155.3 (C), 155.5 (C), 156.5 (C), 157.1 (C).
νmax (KBr)/cm−1 3430, 2998, 2954, 2923, 2834, 1623, 1589,
1511, 1487, 1454, 1295, 1245, 1208, 1180, 1151, 1081, 1008,
Found: 614.3192.
6,8-Dimethoxy-1,9-dimethyl-1,3-(4-methoxyphenyl)-3-
(3-methyl-4,6-dimethoxyindole)-pyrrolo[a]indole 12h
This compound was prepared according to the general
method using indole 11a (0.501 g, 2.62 mmol) and 4ꢀ-
methoxyacetophenone (0.409 g, 2.72 mmol). The mixture was
stirred at room temperature for 6 h to give 12h as an off-white
solid (0.353 g, 42%). mp 250–252◦C. δH 1.44 (s, 3H, CH3),
2.10 (s, 3H, CH3), 2.35 (s, 3H, CH3), 3.34 (d, J 12.81 Hz, 1H,
CH2), 3.39 (s, 3H, OCH3), 3.49 (d, J 12.81 Hz, 1H, CH2), 3.72
(s, 3H, OCH3), 3.74 (s, 3H, OCH3), 3.80 (s, 3H, OCH3), 3.87
(s, 3H, OCH3), 3.89 (s, 3H, OCH3), 5.48 (d, J 1.89 Hz, 1H,
aryl), 6.15 (d, J 1.89 Hz, 1H, aryl), 6.17 (d, J 1.89 Hz, 1H,
aryl), 6.21 (d, J 1.89 Hz, 1H, aryl), 6.78 (d, J 9.03 Hz, 2H,
aryl), 6.84 (d, J 9.03 Hz, 2H, aryl), 7.23 (d, J 9.03 Hz, 2H, aryl),
7.34 (bs, 1H, NH), 7.36 (d, J 9.03Hz, 2H, aryl). δC 10.4 (CH3),
12.7 (CH3), 25.2 (CH3), 44.9 (C), 55.0 (OCH3), 55.1 (OCH3),
55.1 (OCH3) 55.2 (OCH3), 55.3 (OCH3), 55.4 (OCH3), 65.6
(CH2), 67.2 (C), 86.1 (CH), 86.5 (CH), 91.3 (CH), 91.5 (CH),
101.6 (C), 107.7 (C), 113.5 (CH), 113.6 (CH), 114.1 (C), 117.3
(C), 127.4 (CH), 129.0 (CH), 131.9 (C), 132.4 (C), 133.1 (C),
135.4 (C), 139.1 (C), 144.2 (C), 155.2 (C), 155.3 (C), 156.1 (C),
156.9 (C), 157.8 (C), 158.9 (C). νmax (KBr)/cm−1 3446, 2995,
2955, 2926, 2835, 1622, 1510, 1464, 1297, 1246, 1208, 1179,
1150, 1129, 1034, 937, 829, 805 cm−1. UV-vis (MeOH): λmax
933, 807. UV-vis (MeOH): λmax 270 nm (ε 28300 cm−1
M
−1),
226 (122400), 207 (87900). HRMS m/z (ESI) C8H36Br2N2O4
[M]+ requires 742.1042. Found: 744.1067.
6,8-Dimethoxy-1,9-dimethyl-1,3-(4-fluorophenyl)-3-
(3-methyl-4,6-dimethoxyindole)-pyrrolo[a]indole 12k
This compound was prepared according to the general
method using indole 11a (0.510 g, 2.66 mmol) and 4ꢀ-
fluroracetophenone (0.33 mL, 2.72 mmol). The mixture was
stirred at room temperature for 1/2 h to give 12k as a white solid
(0.142 g, 18%), mp 234–236◦C. δH 1.70 (s, 3H, CH3), 1.72 (s,
3H, CH3), 2.29 (s, 3H, CH3), 3.27 (s, 3H, OCH3), 3.50 (d, J
13.4 Hz, 1H, CH2), 3.62 (d, J 13.4 Hz, 1H, CH2), 3.66 (s, 3H,
OCH3), 3.72 (s, 3H, OCH3), 3.81 (s, 3H, OCH3), 5.38 (d, J
1.9 Hz, 1H, aryl), 6.05 (d, J 1.9 Hz, 1H, aryl), 6.10 (d, J 1.9 Hz,
1H, aryl), 6.40 (d, J 1.9 Hz, 1H, aryl), 6.85 (m, 6H, aryl), 7.09
(d, J 5.7 Hz, 1H, aryl), 1.11 (d, J 5.7 Hz, 1H, aryl), 9.96 (bs,
1H, NH). δC 11.2 (CH3), 11.5 (CH3), 28.5 (CH3), 45.6 (C), 55.0
(OCH3), 55.3 (OCH3), 55.4 (OCH3), 55.5 (OCH3), 62.9 (CH2),
66.9 (C), 86.7 (CH), 87.4 (CH), 90.7 (CH), 91.5 (CH), 101.9
(C), 109.3 (C), 113.4 (C), 114.5 (CH), 114.7 (CH), 114.8 (CH),
115.1 (CH), 116.5 (C), 128.5 (CH), 128.6 (CH), 129.4 (CH),
129.5 (CH), 130.0 (C), 133.5 (C), 136.9 (C), 138.0 (C), 141.6
(C), 142.4 (C), 155.1 (C), 155.2 (C), 156.0 (C), 156.8 (C). νmax
(KBr)/cm−1 3454, 3415, 2957, 2932, 2838, 1622, 1601, 1571,
1508, 1458, 1428, 1297, 1235, 1208, 1152, 1036, 938, 834, 809.
UV-vis (MeOH): λmax 272 (ε 33400 cm−1 M−1), 226 (126200),
204 (90000). HRMS m/z (ESI) C8H36F2N2O4 [M]+ requires
622.2643. Found: 622.2680.
274 nm (ε 42300 cm−1
M
−1), 228 (129100), 205 (91000). m/z
(ESI) [M + Na]+ 669.32, C40H42N2O6 requires C 74.28, H 6.55,
N 4.33. Found: C 74.51, H 6.51, N 4.46%.
1,3-(4-Chlorophenyl)-6,8-dimethoxy-1,9-dimethyl-3-
(3-methyl-4,6-dimethoxyindole)-pyrrolo[a]indole 12i
This compound was prepared according to the gen-
eral method using indole 11a (0.646 g, 3.38 mmol) and
4ꢀ-chloroacetophenone (0.55 mL, 4.24 mmol). The mixture was
stirred at room temperature for 1 h to give 12i as a white solid
(0.151 g, 14%), mp 260–262◦C. δH 1.73 (s, 3H, CH3), 1.99 (s,
3H, CH3), 2.29 (s, 3H, CH3), 3.29 (s, 3H, OCH3), 3.55 (d, J
12.8 Hz, 1H, CH2), 3.67 (s, 3H, OCH3), 3.73 (d, J 12.8 Hz, 1H,
CH2), 3.81 (s, 3H, OCH3), 3.88 (s, 3H, OCH3), 5.44 (d, J 1.9 Hz,
1H, aryl), 6.11 (d, J 1.9 Hz, 1H, aryl), 6.13 (d, J 1.9 Hz, 1H, aryl),
6.35 (d, J 1.9 Hz, 1H, aryl), 7.12 (d, J 9.0 Hz, 2H, aryl), 7.14 (d,
J 8.6 Hz, 2H, aryl), 7.18 (d, J 9.0 Hz, 2H, aryl), 7.24 (d, J 8.6 Hz,
2H, aryl), 8.98 (bs, 1H, NH). δC 10.2 (CH3), 11.1 (CH3), 26.8
(CH3), 45.5 (C), 54.2 (OCH3), 54.3 (OCH3), 54.4 (OCH3), 54.5
(OCH3), 63.6 (CH2), 66.9 (C), 86.3 (CH), 86.7 (CH), 90.7 (CH),
91.2 (CH), 102.3 (C), 109.2 (C), 113.9 (C), 116.8 (C), 127.7
(CH), 128.0 (CH), 128.2 (CH), 129.2 (CH), 129.7 (C), 131.0
(C), 132.6 (C), 133.3 (C), 136.6 (C), 140.5 (C), 141.3 (C), 145.3
(C), 155.2 (C), 155.3 (C), 156.5 (C), 157.2 (C). νmax (KBr)/cm−1
3446, 2945, 2932, 2836, 1623, 1593, 1570, 1511, 1491, 1455,
1436, 1296, 1246, 1208, 1151, 1095, 1037, 1012, 938, 823,
1,3-(4-Chlorophenyl)-6,8-dimethoxy-3-(3-(4-
methoxyphenyl)-4,6-dimethoxyindole)-1-methyl
Pyrrolo[a]indole 12l
This compound was prepared according to the general
method using indole 11e (0.253 g, 0.90 mmol) and 4ꢀ-
chloroacetopheonone (0.35 mL, 2.69 mmol). The mixture was
stirred at room temperature for 20 h to give 12l as a white solid
(0.040 g, 5%), mp 204–206◦C. δH 1.37 (CH3), 2.81 (d, J 12.8 Hz,
1H, CH2), 3.29 (d, J 12.8 Hz, 1H, CH2), 3.45 (s, 3H, OCH3), 3.54
(s, 3H, OCH3), 3.72 (s, 3H, OCH3), 3.74 (s, 3H, OCH3), 3.79
(s, 6H, OCH3), 5.53 (d, J 1.9 Hz, 1H, aryl), 6.11 (d, J 1.9 Hz,
1H, aryl), 6.23 (d, J 1.9 Hz, 1H, aryl), 6.29 (d, J 1.9 Hz, 1H,
aryl), 6.53 (d, J 8.7 Hz, 4H, aryl), 6.64 (d, J 9.0 Hz, 2H, aryl),
6.65 (d, J 9.0 Hz, 2H, aryl), 6.81 (d, J 8.7 Hz, 2H, aryl), 7.05
(d, J 8.7 Hz, 2H, aryl), 7.23 (d, J 8.7 Hz, 2H, aryl), 7.35 (d, J
8.7 Hz, 2H, aryl), 7.86 (bs, 1H, NH). δC 26.4 (CH3), 45.7 (C),
806. UV-vis (MeOH): λmax 272 nm (ε 31600 cm−1
M
−1), 226
(136200), 207 (98400). HRMS m/z (ESI) C8H36Cl2N2O4 [M]+
requires 654.2052. Found: 654.2088.
1,3-(4-Bromophenyl)-6,8-dimethoxy-1,9-dimethyl-3-
(3-methyl-4,6-dimethoxyindole)-pyrrolo[a]indole 12j
This compound was prepared according to the general
method using indole 11a (0.519 g, 2.71 mmol) and 4ꢀ-
bromoacetophenone (0.6511 g, 3.27 mmol). The mixture was

RESEARCH FRONT
Acid-Catalyzed Reactions of 3-Substituted-4,6-dimethoxyindoles
767
54.9 (OCH3), 54.9 (OCH3), 55.0 (OCH3), 55.1 (OCH3), 55.3
(OCH3), 55.4 (OCH3), 61.2 (CH2), 67.8 (C), 85.5 (CH), 86.0
(CH), 92.0 (CH), 92.4 (CH), 109.3 (C), 112.1 (CH), 112.2 (CH),
113.0(C), 115.3(C), 115.7(C), 127.0(C), 127.2(CH), 127.5(C),
127.7 (CH), 128.7 (CH), 129.3 (C), 129.5 (CH), 131.2 (C), 131.2
(CH), 132.9(C), 134.0(C), 135.7(C), 141.7(C), 143.1(C), 144.4
(C), 154.9 (C), 155.1 (C), 156.9 (C), 157.4 (C), 157.5 (C), 157.9
(C). νmax (KBr)/cm−1 3430, 2994, 2936, 2829, 1623, 1560,
1508, 1464, 1303, 1243, 1208, 1175, 1150, 1095, 1036, 1012,
818, 800. UV-vis (MeOH): λmax 277 nm (ε 29500 cm−1M−1),
226 (103600). HRMS m/z (ESI) C50H44Cl2N2O6 [M + Na]+
requires 838.2576. Found: 838.2605.
(ArCH), 132.2 (ArC), 132.9 (ArC), 133.1 (ArC), 133.9 (ArC),
134.3 (ArC), 135.6 (ArC), 141.2 (ArC), 143.4 (ArC), 143.9
(ArC), 154.7 (ArC), 155.0 (ArC), 157.2 (ArC), 157.7 (ArC).
νmax (KBr)/cm−1 3421, 3008, 2954, 2927, 2838, 1623, 1586,
1489, 1464, 1452, 1308, 1245, 1209, 1151, 1094, 1054, 1012,
831, 804. UV-vis (MeOH): λmax 277 nm (ε 19400 cm−1 M−1),
224 (76300), 201 (70900). HRMS m/z (ESI) C48H38Cl4N2O4Na
[M]+ requires 869.1478. Found: 869.1658.
3-(3-(4-Chlorophenyl)-4,6-dimethoxyindole)-6,8-
dimethoxy-1,3-(4-methoxyphenyl)-1-methyl
Pyrrolo[a]indole 12o
This compound was prepared according to the general
method using indole 11d (0.518 g, 1.80 mmol) and 4ꢀ-
methoxyacetopheonone (0.530 g, 3.53 mmol). The mixture was
heated at for 1 day to give 12o as a white solid (0.096 g, 13%),
mp 293–294◦C. δH 1.06 (s, 3H, CH3), 3.05 (d, J 12.8 Hz, 1H,
CH2), 3.29 (d, J 12.8 Hz, 1H, CH2), 3.39 (s, 3H, OCH3), 3.56
(s, 3H, OCH3), 3.65 (s, 3H, OCH3), 3.72 (s, 3H, OCH3), 3.76
(s, 3H, OCH3), 3.78 (s, 3H, OCH3), 5.64 (d, J 1.9 Hz, 1H, aryl),
6.13 (d, J 1.9 Hz, 1H, aryl), 6.20 (d, J 1.9 Hz, 1H, aryl), 6.33 (d,
J 1.9 Hz, 1H, aryl), 6.45 (d, J 8.7 Hz, 2H, aryl), 6.71 (d, J 8.7 Hz,
2H, aryl), 6.85 (d, J 8.7 Hz, 2H, aryl), 7.12 (m, 10H, aryl), 7.73
(bs, 1H, NH). δC 25.8 (CH3), 45.6 (C), 54.9 (CH3), 54.9 (CH3),
55.0 (CH3), 55.1 (CH3), 55.2 (CH3), 55.5 (CH3), 6.1 8 (CH2),
67.2 (C), 86.1 (CH), 86.2 (CH), 91.9 (CH), 92.4 (CH), 108.5
(C), 112.8 (CH), 113.4 (C), 113.6 (CH), 114.6 (C), 115.3 (C),
126.7 (CH), 126.9 (CH), 127.5 (CH), 128.7 (CH), 131.1 (C),
131.3 (C), 131.9 (CH), 133.1 (C), 133.5 (C), 133.7 (C), 134.4
(C), 135.0 (C), 138.7 (C), 143.3 (C), 154.8 (C), 154.9 (C), 156.7
(C), 157.3 (C), 157.7 (C), 158.9 (C). νmax (KBr)/cm−1 3443,
2993, 2932, 2836, 1621, 1581, 1151, 1463, 1438, 1375, 1345,
1307, 1248, 1209, 1181, 1150, 1134, 1089, 1035, 1015, 1000,
828, 815. UV-vis (MeOH): λmax 273 nm (ε 90700 cm−1 M−1),
225 (150300), 203 (142300). HRMS m/z (ESI) C50H44Cl2N2O6
[M]+ requires 838.2576. Found: 838.2403.
6,8-Dimethoxy-3-(3-(4-methoxyphenyl)-4,6-
dimethoxyindole)-1-methyl-1,3-(4-methylphenyl)
Pyrrolo[a]indole 12m
This compound was prepared according to the general
method using indole 11e (0.516 g, 1.83 mmol) and 4ꢀ-
methoxyacetopheonone (0.28 mL, 2.30 mmol).The mixture was
heated at for 5 h to give 12m as a white solid (0.050 g, 6%), mp
232–234◦C. δH 1.37 (s, 3H, CH3), 2.12 (s, 3H, CH3), 2.37 (s, 3H,
CH3), 2.85 (d, J 12.8 Hz, 1H, CH2), 3.27 (d, J 12.8 Hz, 1H, CH2),
3.40 (s, 3H, OCH3), 3.51 (s, 3H, OCH3), 3.78 (s, 6H, OCH3),
5.55 (d, J 1.9 Hz, 1H, aryl), 6.07 (d, J 1.9 Hz, 1H, aryl), 6.20 (d,
J 1.9 Hz, 1H, aryl), 6.29 (d, J 1.9 Hz, 1H, aryl), 6.48 (d, J 8.2 Hz,
2H, aryl), 6.62 (d, J 8.2 Hz, 4H, aryl), 6.63 (d, J 8.7 Hz, 4H, aryl),
7.09 (d, J 8.7 Hz, 2H, aryl), 7.15 (d, J 8.7 Hz, 2H, aryl), 7.17 (d,
J 8.7 Hz, 2H, aryl), 7.87 (bs, 1H, NH). δC 20.6 (CH3), 20.9
(CH3), 26.2 (CH3), 45.9 (C), 54.9 (OCH3), 54.9 (OCH3), 55.0
(OCH3), 55.0 (OCH3), 55.1 (OCH3), 55.4 (OCH3), 61.3 (CH2),
68.1 (C), 85.8 (CH), 86.1 (CH), 91.8 (CH), 92.1 (CH), 108.7 (C),
111.9 (CH), 112.0 (CH), 113.3 (C), 114.6 (C), 115.6 (C), 126.2
(CH), 127.5 (C), 127.8 (CH), 127.9 (C), 128.0 (CH), 129.1 (CH),
130.4 (C), 131.6 (CH), 133.1 (C), 134.6 (C), 135.5 (C), 137.6
(C), 140.2 (C), 142.9 (C), 144.0 (C), 154.8 (C), 154.9 (C), 156.5
(C), 157.0 (C), 157.3 (C), 157.8 (C). νmax (KBr)/cm−1 3433,
2994, 2931, 2835, 1621, 1560, 1507, 1452, 1302, 1282, 1242,
1208, 1175, 1150, 1038, 831, 811. UV-vis (MeOH): λmax 281 nm
(ε 30800 cm−1 M−1), 227 (10100), 200 (110300). HRMS m/z
(ESI) C52H50N2O6Na [M + Na]+ requires 821.3567. Found:
821.3546.
1,3-(4-Bromophenyl)-3-(3-(4-chlorophenyl)-4,6-
dimethoxyindole)-6,8-dimethoxy-1-methyl
Pyrrolo[a]indole 12p
This compound was prepared according to the general
method using indole 11d (0.515 g, 1.79 mmol) and 4ꢀ-
bromoacetopheonone (1.408 g, 7.07 mmol). The mixture was
heated at for 2 days to give 12p as an off-white solid (0.040 g,
5%), mp 215–217◦C. δH 1.37 (s, 3H, CH3), 2.84 (d, J 13.5 Hz,
1H, CH2), 3.22 (d, J 13.5 Hz, 1H, CH2), 3.46 (s, 3H, OCH3),
3.54 (s, 3H, OCH3), 3.73 (s, 3H, OCH3), 3.79 (s, 3H, OCH3),
5.51 (d, J 1.9 Hz, 1H, ArH), 6.12 (d, J 1.9 Hz, 1H, ArH), 6.24
(d, J 1.9 Hz, 1H, ArH), 6.30 (d, J 1.9 Hz, 1H, ArH), 6.44
(d, J 8.3 Hz, 2H, ArH), 7.00 (d, J 8.6 Hz, 2H, ArH), 7.06 (m,
8H, ArH), 7.17 (d, J 8.6 Hz, 2H, ArH), 7.52 (d, J 8.3 Hz, 2H,
ArH), 7.86 (bs, 1H, NH). δC 26.2 (CH3), 45.8 (C), 54.9 (OCH3),
54.9 (OCH3), 55.3 (OCH3), 55.5 (OCH3), 61.5 (CH2), 67.9
(C), 85.5 (CH), 86.0 (CH), 92.2 (CH), 92.6 (CH), 108.6 (C),
112.7 (C), 114.6 (C), 115.2 (C), 119.7 (C), 122.5 (C), 126.8
(CH), 127.0 (CH), 127.9 (CH), 129.3 (C), 129.7 (CH), 130.4
(CH), 131.4 (C), 131.6 (CH), 131.9 (CH), 132.2 (C), 132.9 (C),
133.0 (C), 133.8 (C), 135.6 (C), 141.7 (C), 143.3 (C), 144.5 (C),
154.7 (C), 155.0 (C), 157.2 (C), 157.7 (C). νmax (KBr)/cm−1
3425, 2923, 2829, 1623, 1586, 1512, 1486, 1464, 1433, 1309,
1244, 1209, 1151, 1089, 1049, 1008, 821. UV-vis (MeOH): λmax
1,3-(4-Chlorophenyl)-3-(3-(4-chlorophenyl)-4,6-
dimethoxyindole)-6,8-dimethoxy-1-methyl
Pyrrolo[a]indole 12n
This compound was prepared according to the general
method using indole 11d (0.524 g, 1.82 mmol) and 4ꢀ-
chloroxyacetopheonone (0.46 mL, 3.54 mmol).The mixture was
heated at for 2 days to give 12n as an off-white solid (0.063 g,
8%), mp 215–217◦C. δH 1.37 (s, 3H, CH3), 2.85 (d, J 12.8 Hz,
1H CH2), 3.22 (d, J 12.8 Hz), 3.46 (s, 3H, OCH3), 3.53 (s, 3H,
OCH3), 3.73 (s, 3H, OCH3), 3.79 (s, 3H, OCH3), 5.52 (d, J
1.9 Hz, 1H, aryl), 6.12 (d, J 1.9 Hz, 1H, aryl), 6.24 (d, J 2.3 Hz,
1H, aryl), 6.30 (d, J 2.3 Hz, 1H, aryl), 6.50 (d, J 8.7 Hz, 2H, aryl),
6.85 (d, J 8.7 Hz, 2H, aryl), 7.06 (m, 8H, aryl), 7.23 (d, J 8.7 Hz,
2H, aryl), 7.37 (d, J 8.7 Hz, 2H, aryl), 7.87 (bs, 1H, NH). δC 26.3
(CH3), 45.7(C1), 54.9(OCH3), 54.9(OCH3), 55.3(OCH3), 55.5
(OCH3), 61.6 (CH2), 67.8 (C3), 85.5 (ArCH), 85.9 (ArCH), 92.2
(ArCH), 92.5 (ArCH), 108.6 (ArC), 114.5 (ArC), 115.2 (ArC),
126.8 (ArCH), 127.0 (ArCH), 127.4 (ArCH), 127.5 (ArCH),
128.9 (ArCH), 129.4 (ArCH), 131.4 (ArC), 131.6 (ArC), 131.6

RESEARCH FRONT
768
K. Wood, D. StC. Black, and N. Kumar
275 nm (ε 14600 cm−1 M−1), 224 (53600), 202 (56900). HRMS
m/z (ESI) C48H38Br2Cl2N2O4 [M]+ requires 934.0575. Found:
934.0584.
1,3-(4-Bromophenyl)-3-(3-(4-bromophenyl)-4,6-
dimethoxyindole)-6,8-dimethoxy-1-methyl
Pyrrolo[a]indole 12s
This compound was prepared according to the general
method using indole 11c (0.511 g, 1.54 mmol) and 4ꢀ-
bromoacetopheonone (1.24 mL, 6.23 mmol). The mixture was
heated at for 1 day to give 12s as an off-white solid (0.018 g,
2%), mp 227–229◦C. δH 1.37 (s, 3H, CH3), 2.85 (d, J 13.2 Hz,
1H, CH2), 3.20 (d, J 13.2 Hz, 1H, CH2), 3.45 (s, 3H, OCH3),
3.55 (s, 3H, OCH3), 3.73 (s, 3H, OCH3), 3.79 (s, 3H, OCH3),
5.50 (d, J 1.9 Hz, 1H, aryl), 6.12 (d, J 1.9 Hz, 1H, aryl), 6.24 (d,
J 1.9 Hz, 1H, aryl), 6.29 (d, J 1.9 Hz, 1H, aryl), 6.44 (d, J 8.7 Hz,
2H, aryl), 6.97 (d, J 8.7 Hz, 2HArH), 6.99 (d, J 8.7 Hz, 2H, aryl),
7.17 (d, J 8.7 Hz, 2H, aryl), 7.22 (d, J 8.7 Hz, 6H, aryl), 7.52 (d,
J 8.7 Hz, 2H, aryl), 7.86 (bs, 1H, NH). δC 26.2 (CH3), 45.8 (C),
54.9 (OCH3), 55.0 (OCH3), 55.3 (OCH3), 55.5 (OCH3), 61.5
(CH2), 67.9 (C), 85.5 (CH), 86.0 (CH), 92.2 (CH), 92.6 (CH),
108.6 (C), 114.5 (C), 115.2 (C), 119.6 (C), 119.7 (C), 120.4 (C),
122.5 (C), 127.9 (CH), 129.2 (C), 129.7 (CH), 129.8 (CH), 129.9
(CH), 130.4 (CH), 131.9 (CH), 132.0 (CH), 132.5 (C), 133.0 (C),
133.5 (C), 134.3 (C), 135.6 (C), 141.6 (C), 143.3 (C), 144.5 (C),
154.7 (C), 155.0 (C), 157.3 (C), 157.7 (C). νmax (KBr)/cm−1
3434, 2954, 2927, 2834, 1623, 1589, 1485, 1450, 1307, 1244,
1209, 1151, 1071, 1008, 813. UV-vis (MeOH): λmax 276 nm (ε
14900 cm−1 M−1), 225 (56300), 201 (83000). HRMS m/z (ESI)
C48H38Br4N2O4 [M]+ requires 1021.9565. Found: 1021.9536.
3-(3-(4-Chlorophenyl)-4,6-dimethoxyindole)-6,8-
dimethoxy-1-methyl-1,3-(4-methylphenyl)
Pyrrolo[a]indole 12q
This compound was prepared according to the general
method using indole 11d (0.507 g, 1.76 mmol) and 4ꢀ-
methylacetopheonone (0.46 mL, 3.44 mmol). The mixture was
heated at for 2 days to give 12q as a white solid (0.067, 9%),
mp 306–308◦C. δH 1.06 (s, 3H, CH3), 2.13 (s, 3H, CH3), 2.28
(s, 3H, CH3), 3.08 (d, J 12.9 Hz, 1H, CH2), 3.31 (d, J 12.8 Hz,
1H, CH2), 3.37 (s, 3H, OCH3), 3.56 (s, 3H, CH3), 3.72 (s, 3H,
CH3), 3.77 (s, 3H, CH3), 5.62 (d, J 1.9 Hz, 1H, aryl), 6.13 (d, J
1.9 Hz, 1H, aryl), 6.20 (d, J 1.9 Hz, 1H, aryl), 6.32 (d, J 1.9 Hz,
1H, aryl), 6.71 (d, J 8.3 Hz, 2H, aryl), 6.82 (d, J 8.3 Hz, 2H,
aryl), 6.97 (d, J 8.3 Hz, 2H, aryl), 7.40 (m, 10H, aryl), 7.72 (bs,
1H, NH). δC 20.6 (CH3), 20.8 (CH3), 25.7 (CH3), 45.9 (C), 54.9
(OCH3), 54.9 (OCH3), 55.1 (OCH3), 55.4 (OCH3), 61.5 (CH2),
67.5 (C), 86.0 (CH), 86.1 (CH), 91.9 (CH), 92.4 (CH), 108.6
(C), 113.4 (C), 114.7 (C), 115.2 (C), 126.4 (CH), 126.7 (CH),
126.9 (CH), 127.4 (CH), 128.0 (CH), 128.8 (CH), 131.0 (C),
131.1 (CH), 131.1 (CH), 131.9 (C), 133.6 (C), 133.8 (C), 134.4
(C), 134.9 (C), 135.0 (C), 137.4 (C), 138.3 (C), 143.2 (C), 143.4
(C), 151.1 (C), 154.7 (C), 154.8 (C), 156.7 (C), 157.6 (C). νmax
(KBr)/cm−1 3444, 2996, 2932, 2837, 1622, 1585, 1512, 1498,
1452, 1436, 1378, 1345, 1308, 1247, 1209, 1151, 1089, 1048,
1016, 812. UV-vis (MeOH): λmax 272 nm (ε 70300 cm−1 M−1),
224 (165600), 205 (14900). HRMS m/z (ESI) C50H44N2O4Na
[M]+ requires 829.2576. Found: 829.2554.
3-(3-(4-Bromophenyl)-4,6-dimethoxyindole)-6,8-
dimethoxy-1-methyl-1,3-(4-methylphenyl)
Pyrrolo[a]indole 12t
This compound was prepared according to the gen-
eral method using indole 11c (0.503 g, 1.53 mmol) and
4ꢀ-methylacetopheonone (0.40 mL, 2.99 mmol). The mixture
was heated at for 3 days to give 12t as a white solid (0.100 g,
15%), mp 192–194◦C. δH 1.35 (s, 3H, CH3), 2.16 (s, 3H, CH3),
2.38 (s, 3H, CH3), 2.90 (d, J 13.2 Hz, 1H, CH2), 3.24 (d, J
13.2 Hz, 1H, CH2), 3.41 (s, 3H, OCH3), 2.51 (s, 3H, OCH3),
3.72 (s, 3H, OCH3), 3.78 (s, 3H, OCH3), 5.55 (d, J 1.9 Hz, 1H,
aryl), 6.09 (d, J 1.9 Hz, 1H, aryl), 6.22 (d, J 1.9 Hz, 1H, aryl),
6.30 (d, J 1.9 Hz, 1H, aryl), 6.43 (d, J 7.9 Hz, 2H, aryl), 6.69 (d, J
7.9 Hz, 2H, aryl), 7.00 (d, J 8.2 Hz, 2H, aryl), 7.17 (s, 8H, aryl),
7.18 (d, J 8.2 Hz, 2H, aryl), 7.87 (bs, 1H, NH). δC 20.7 (CH3),
21.0 (CH3), 26.1 (CH3), 45.9 (C), 54.9 (OCH3), 54.9 (OCH3),
55.2 (OCH3), 55.5 (OCH3), 61.8 (CH2), 68.1 (C), 85.8 (CH),
86.0 (CH), 91.9 (CH), 92.2 (CH), 108.6 (C), 112.6 (C), 114.5
(C), 115.2 (C), 119.6 (C), 120.4 (C), 127.5 (CH), 127.5 (CH),
128.9 (CH), 129.3 (CH), 129.4 (CH), 129.8 (CH), 129.9 (CH),
131.6 (C), 132.0 (CH), 132.4 (C), 133.0 (C), 133.6 (C), 134.3
(C), 134.4 (C), 135.6 (C), 141.1 (C), 143.4 (C), 143.9 (C), 154.7
(C), 155.0 (C), 157.2 (C), 157.7 (C). νmax (KBr)/cm−1 3449,
2993, 2933, 2836, 1623, 1587, 1560, 1512, 1497, 1482, 1452,
1436, 1345, 1309, 1245, 1209, 1150, 1071, 1012, 940, 811. UV-
vis (MeOH): λmax 281 nm (ε 37400 cm−1 M−1), 225 (135800),
201 (162500). HRMS m/z (ESI) C50H44Br2N2O4Na [M + Na]+
requires 917.1560. Found: 917.1539.
3-(3-(4-Bromophenyl)-4,6-dimethoxyindole)-1,3-
(4-chlorophenyl)-6,8-dimethoxy-1-methyl
Pyrrolo[a]indole 12r
This compound was prepared according to the general
method using indole 11c (0.528 g, 1.59 mmol) and 4ꢀ-
chloroacetopheonone (0.79 mL, 6.09 mmol). The mixture was
heated at for 2 days to give 12r as an off-white solid (0.062 g,
8%), mp 220–222◦C. δH 1.38 (s, 3H, CH3), 2.86 (d, J 12.8 Hz,
1H, CH2), 3.21 (d, J 12.8 Hz, 1H, CH2), 3.46 (s, 3H, OCH3), 3.54
(s, 3H, OCH3), 3.73 (s, 3H, OCH3), 3.79 (s, 3H, OCH3), 5.52 (d,
J 1.9 Hz, 1H, aryl), 6.12 (d, J 1.9 Hz, 1H, aryl), 6.24 (d, J 1.9 Hz,
1H, aryl), 6.30 (d, J 1.9 Hz, 1H, aryl), 6.51 (d, J 8.7 Hz, 4H,
aryl), 6.86 (d, J 8.3 Hz, 2H, aryl), 6.98 (d, J 8.7 Hz, 2H, aryl),
7.22 (d, J 8.3 Hz, 2H, aryl), 7.23 (d, J 8.7 Hz, 4H, aryl), 7.37
(d, J 8.7 Hz, 2H, aryl), 7.89 (bs, 1H, NH). δC 26.3 (CH3), 45.8
(C), 54.9 (OCH3), 54.9 (OCH3), 55.3 (OCH3), 55.4 (OCH3),
61.6 (CH2), 67.8 (C), 85.5 (CH), 85.9 (CH), 92.2 (CH), 92.5
(CH), 108.6 (C), 112.6 (C), 114.5 (C), 115.2 (C), 119.6 (C),
120.4 (C), 127.5 (CH), 127.6 (CH), 128.9 (CH), 129.3 (CH),
129.4 (CH), 129.8 (CH), 129.9 (CH), 131.6 (C), 132.0 (CH),
132.4 (C), 133.0 (C), 133.6 (C), 134.3 (C), 134.4 (C), 135.6
(C), 141.1 (C), 143.4 (C), 143.9 (C), 154.7 (C), 155.0 (C), 157.2
(C), 157.7 (C). νmax (KBr)/cm−1 3420, 2993, 2934, 2837, 1623,
1589, 1560, 1511, 1490, 1463, 1451, 1434, 1400, 1345, 1307,
1244, 1209, 1150, 1096, 1070, 1049, 1011, 831, 809. UV-vis
(MeOH): λmax 276 nm (ε 17900 cm−1 M−1), 225 (70200), 202
(67500). HRMS m/z (ESI) C48H38Br2Cl2N2O4Na [M + Na]+
requires 934.0575. Found: 934.0598.
General Method for Preparation of Mixed Dimers
The two selected indoles (1 equiv. each) were suspended in
isopropanol (10 mL) with acetone (1 mL) and concentrated
hydrochloric acid (1 mL) was added. The reaction was heated
at for 4 h and the resulting precipitate collected.

RESEARCH FRONT
Acid-Catalyzed Reactions of 3-Substituted-4,6-dimethoxyindoles
769
3-(3-(4-Bromophenyl)-4,6-dimethoxyindole)-
6,8-dimethoxy-1,1,3,9-tetramethyl Pyrrolo[a]indole 13a
(C), 158.1 (C). νmax (KBr)/cm−1 3438, 2956, 2834, 1624, 1589,
1572, 1501, 1453, 1301, 1275, 1241, 1208, 1149, 1132, 1037,
806 cm−1. UV-vis (MeOH): λmax 275 nm (ε 10400 cm−1 M−1),
227 (34200). HRMS m/z (ESI) C34H38N2O4 [M + H]+ requires
555.2853. Found: 555.2810.
This compound was prepared according to the general method
using indole 11a (0.255 g, 1.33 mmol) and indole 11c (0.432 g,
1.30 mmol) to give 13a as a white solid (0.471 g, 59%), mp 264–
266◦C. δH 1.25 (s, 3H, CH3), 1.41 (s, 3H, CH3), 1.64 (s, 3H,
CH3), 1.42 (d, J 13.2 Hz, 1H, CH2), 1.43 (s, 3H, CH3), 2.77 (d, J
13.2 Hz, 1H, CH2), 3.57 (s, 3H, OCH3), 3.68 (s, 3H, OCH3), 3.74
(s, 3H, OCH3), 3.89 (s, 3H, OCH3), 6.12 (d, J 1.9 Hz, 1H, aryl),
6.15 (d, J 1.9 Hz, 1H, aryl), 6.19 (d, J 1.9 Hz, 1H, aryl), 6.26 (d,
J 1.9 Hz, 1H, aryl), 7.25 (d, J 8.6 Hz, 2H, aryl), 7.49 (d, J 8.6 Hz,
2H, aryl), 7.67 (bs, 1H, NH). δC 10.5 (CH3), 28.1 (CH3), 29.2
(CH3), 29.3 (CH3), 37.9 (C), 55.5 (OCH3), 55.6 (OCH3), 55.9
(OCH3), 56.2 (OCH3), 62.3 (CH2), 62.3 (C), 86.9 (CH), 87.3
(CH), 91.6 (CH), 92.6 (CH), 101.3 (C), 111.8 (C), 114.1 (C),
118.4 (C), 120.9 (C), 130.7 (CH×4), 132.2 (C), 133.5 (C), 135.4
(C), 136.6 (C), 145.1 (C), 155.0 (C), 155.9 (C), 156.8 (C), 157.8
(C). νmax (KBr)/cm−1 3421, 2954, 2927, 2838, 1624, 1591,
1497, 1483, 1453, 1303, 1244, 1208, 1149, 1132, 1009, 933,
806. UV-vis (MeOH): λmax 274 nm (ε 17000 cm−1 M−1), 226
(77800). HRMS m/z (ESI) C33H35BrN2O4 [M + H]+ requires
603.1853. Found: 603.1826.
General Method for Preparation of Spiro Dimers
A mixture of the indole (1 equiv.), acetone (1 mL) and toluenesul-
fonic acid (1 equiv.) were dissolved in dichloromethane (10 mL)
and heated at for 4 h. The reaction was quenched with water
(40 mL) and extracted with dichloromethane (3 × 15 mL) before
being column chromatographed using hexane/DCM (70/30).
1,1ꢀ-Dihydro-1,1,1ꢀ,1ꢀ,9,9ꢀ-hexamethyl-6,6ꢀ,8,8ꢀ-
tetramethoxy-3,3ꢀ-spirobi[cyclopent[a]indole] 14a
This compound was prepared according to the general method
using indole 11a (0.249 g, 1.30 mmol) to give 14a as an off-
white solid (0.118 g, 18%), mp 274–276◦C. δH 1.47 (s, 6H,
CH3), 1.63 (s, 6H, CH3), 2.45 (s, 6H, CH3), 2.59 (d, J 13.2 Hz,
2H, CH2), 3.07 (d, J 13.2 Hz, 2H, CH2), 3.49 (s, 6H, OCH3),
3.82 (s, 6H, OCH3), 5.50 (d, J 1.89 Hz, 2H, H7, H7ꢀ), 6.05 (d, J
1.89 Hz, 2H, H5, H5ꢀ). δC 10.1 (CH3), 28.1 (CH3), 29.3 (CH3),
37.2 (C), 54.9 (OCH3), 55.2 (OCH3), 57.7 (CH2), 78.8 (C), 85.9
(C), 91.3 (C), 100.7 (C), 117.9 (C), 130.9 (C), 142.7 (C), 155.0
(C), 156.0 (C). νmax (KBr)/cm−1 3450, 2959, 2860, 2842, 1623,
1572, 1499, 1453, 1388, 1361, 1315, 1297, 1247, 1215, 1150,
1124, 1063, 1035, 938, 807. UV-vis (MeOH): λmax 274 nm (ε
12000 cm−1 M−1), 228 (44500). HRMS m/z (ESI) C31H38N2O4
[M + H]+ requires 503.2904. Found: 503.2864.
3-(3-(4-Chlorophenyl)-4,6-dimethoxyindole)-6,8-
dimethoxy-1,1,3,9-tetramethyl Pyrrolo[a]indole 13b
This compound was prepared according to the general method
using indole 11a (0.257 g, 1.34 mmol) and indole 11d (0.389 g,
1.21 mmol) to give 13b as a off-white solid (0.238 g, 35%), mp
261–263◦C. δH 1.26 (s, 3H, CH3), 1.43 (s, 3H, CH3), 1.65 (s, 3H,
CH3), 2.42 (d, J 13.1 Hz, 1H, CH2), 2.44 (s, 3H, CH3), 2.78 (d,
J 13.1 Hz, 1H, CH2), 3.57 (s, 3H, OCH3), 3.74 (s, 3H, OCH3),
3.76 (s, 3H, OCH3), 3.90 (s, 3H, OCH3), 6.13 (d, J 1.9 Hz, 1H,
aryl), 6.16 (d, J 1.9 Hz, 1H, aryl), 6.20 (d, J 1.9 Hz, 1H, aryl), 6.27
(d, J 1.9 Hz, 1H, aryl), 7.34 (m, 4H, aryl), 7.66 (bs, 1H, NH). δC
10.0 (CH3), 27.6 (CH3), 28.7 (CH3), 28.8 (CH3), 37.4 (C), 55.0
(OCH3), 55.1 (OCH3), 55.5 (OCH3), 55.8 (OCH3), 61.7 (C),
61.8 (CH2), 86.4 (CH), 86.8 (CH), 91.1 (CH), 92.1 (CH), 100.8
(C), 111.3 (C), 113.7 (C), 117.8 (C), 127.2 (CH), 131.7 (C),
132.2 (C), 134.8 (C), 135.7 (C), 136.1 (C), 144.6 (C), 154.5 (C),
155.4 (C), 156.3 (C), 157.2 (C). νmax (KBr)/cm−1 3424, 2963,
2935, 2829, 1624, 1590, 1571, 1509, 1486, 1453, 1345, 1303,
1244, 1208, 1149, 1129, 1088, 1018, 806. UV-vis (MeOH): λmax
275 nm (ε 15300 cm−1 M−1), 226 (70400). HRMS m/z (ESI)
C33H35ClN2O4 [M + H]+ requires 559.2358. Found: 559.2312.
9,9ꢀ-Di(4-bromophenyl)-1,1ꢀ-dihydro-6,6ꢀ,8,8ꢀ-
tetramethoxy-1,1,1ꢀ,1ꢀ-tetramethyl-3,3ꢀ-
spirobi[cyclopent[a]indole] 14b
This compound was prepared according to the general method
using indole 11a (0.402 g, 1.21 mmol) to give 14b as a white
solid (0.188 g, 20%), mp 303–305◦C. δH 1.41 (s, 6H, CH3),
1.52 (s, 6H, CH3), 2.75 (d, J 13.56 Hz, 2H, CH2), 3.25 (d, J
13.56 Hz, 2H, CH2), 3.51 (s, 6H, OCH3), 3.60 (s, 6H, OCH3),
5.45 (d, J 1.89 Hz, 2H, H5, H5ꢀ), 6.07 (d, J 1.89 Hz, 2H, H7,
H7ꢀ), 7.31 (d, J 8.28 Hz, 4H, aryl), 7.48 (d, J 8.28 Hz, 4H,
aryl). δC 28.1 (CH3), 31.3 (CH3), 38.3 (C), 54.9 (OCH3), 55.1
(OCH3), 57.8 (CH2), 78.9 (C), 85.1 (CH), 92.4 (CH), 107.3
(C), 116.0 (C), 119.9 (C), 130.1 (CH), 130.7 (C), 132.5 (CH),
134.8 (C), 143.7 (C), 154.6 (C), 156.6 (C). νmax (KBr)/cm−1
2958, 2927, 2834, 1708, 1617, 1565, 1500, 1465, 1374, 1317,
1246, 1207, 1147, 1089, 1051, 1011, 947, 834, 808 cm−1. UV-
vis (MeOH): λmax 281 nm (ε 16600 cm−1 M−1), 229 (43900).
HRMSm/z (ESI)C41H40Br2N2O4 [M + H]+ requires783.1433.
Found: 783.1458.
6,8-Dimethoxy-3-(3-(4-methoxyphenyl)-4,6-
dimethoxyindole)-1,1,3,9-tetramethyl Pyrrolo[a]indole 13c
This compound was prepared according to the general method
using indole 11a (0.158 g, 0.82 mmol) and indole 11e (0.226 g,
0.80 mmol) to give 13c as a white solid (0.186 g, 41%) mp 268–
270◦C. δH 1.26 (s, 3H, CH3), 1.42 (s, 3H, CH3), 1.65 (s, 3H,
OCH3), 2.44 (d, J 13.2 Hz, 1H, CH2), 2.44 (s, 3H, CH3), 2.82 (d,
J 13.2 Hz, 1H, CH2), 3.57 (s, 3H, OCH3), 3.69 (s, 3H, OCH3),
3.75 (s, 3H, OCH3), 3.88 (s, 3H, OCH3), 3.89 (s, 3H, OCH3),
6.11 (d, J 1.9 Hz, 1H, aryl), 6.19 (bs, 2H, aryl), 6.26 (d, J 1.9 Hz,
1H, aryl), 6.92 (d, J 9.0 Hz, 2H, aryl), 7.31 (d, J 9.0 Hz, 2H,
aryl), 7.60 (bs, 1H, NH). δC 10.0 (CH3), 27.6 (CH3), 28.6 (CH3),
28.7 (CH3), 37.4 (C), 55.0 (OCH3), 55.1 (OCH3), 55.2 (OCH3),
55.4 (OCH3), 55.8 (OCH3), 61.2 (CH2), 62.0 (C), 86.4 (CH),
86.8 (CH), 91.1 (CH), 92.0 (CH), 100.6 (C), 112.1 (C), 112.5
(CH×4), 114.1 (C), 117.7 (C), 129.7 (C), 131.7 (C), 134.8 (C),
136.1 (C), 144.8 (C), 154.7 (C), 155.3 (C), 156.2 (C), 157.0
1,1ꢀ-Dihydro-9,9ꢀ-di(4-methoxyphenyl)-6,6ꢀ,8,8ꢀ-
tetramethoxy-1,1,1ꢀ,1ꢀ-tetramethyl-3,3ꢀ-
spirobi[cyclopent[a]indole] 14c
This compound was prepared according to the general method
using indole 11e (0.405 g, 1.43 mmol) to give 14c as an off-white
solid (0.151 g, 15%), mp 280–282◦C. δH 1.40 (s, 6H, CH3), 1.51
(s, 6H, CH3), 2.75 (d, J 13.2 Hz, 2H, CH2), 3.25 (d, J 13.2 Hz,
2H, CH2), 3.51 (s, 6H, OCH3), 3.59 (s, 6H, OCH3), 3.87 (s, 6H,
OCH3), 5.46 (d, J 2.3 Hz, 2H, H5, H5ꢀ), 6.06 (d, J 2.3 Hz, 2H,
H7, H7ꢀ), 6.90 (d, J 8.6 Hz, 4H, aryl), 7.35 (d, J 8.6 Hz, 4H, aryl).

RESEARCH FRONT
770
K. Wood, D. StC. Black, and N. Kumar
Acknowledgements
We thank the University of New South Wales and the Australian Research
Council for financial support.
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