Indium triflate-catalyzed coupling of indoles with acyl phosphonates: Synthesis of bis(indolyl)methane phosphonates

Article abstract of DOI:10.1016/j.tet.2011.03.061

The coupling reaction of N-methylindole with alkyl and aryl phosphonate is described. The reaction works in the presence of 10 mol % of indium triflate and furnished bis(indolyl)methane phosphonates in good yield and high selectivity.

Full text of DOI:10.1016/j.tet.2011.03.061

Tetrahedron 67 (2011) 3355e3359
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Indium triflate-catalyzed coupling of indoles with acyl phosphonates:
synthesis of bis(indolyl)methane phosphonates
,
,
,
*
Teslima Dasbasi a b, Sidika Polat-Cakir a c, Meysun Abdullah b, Ayhan S. Demir a
a Department of Chemistry, Middle East Technical University, Inonu Bulvari, 06531 Ankara, Turkey
b Department of Chemistry, Nigde University, 51000 Nigde, Turkey
c Department of Chemistry, Nevsehir University, 50300 Nevsehir, Turkey
a r t i c l e i n f o
a b s t r a c t
Article history:
The coupling reaction of N-methylindole with alkyl and aryl phosphonate is described. The reaction
works in the presence of 10 mol % of indium triflate and furnished bis(indolyl)methane phosphonates in
good yield and high selectivity.
Received 25 January 2011
Received in revised form 1 March 2011
Accepted 21 March 2011
Available online 26 March 2011
Ó 2011 Elsevier Ltd. All rights reserved.
1. Introduction
triflate catalyzed addition of indole to carbonyl compounds, and
based on our previous studies carried out with acyl phosphonates,7
Bis(indolyl)methanes are an important class of heterocyclic
compounds with diverse pharmacological activities, such as fibro-
myalgia, chronic fatigue, and irritable bowel syndrome.1 They
promote beneficial estrogen metabolism2 and induce apoptosis in
human cancer cells.
we report an approach for the selective reaction of indole with acyl
phosphonates by using metal triflate to obtain bis(indolyl)phos-
phonates. To the best of our knowledge, the addition of indole to the
acyl phosphonates has not been reported so far.
The development of new methods for the synthesis of bis
(indolyl)methanes and their derivatives is of interest in view of their
versatile biological and pharmacological properties.1b,c Several
synthetic methods for the preparation of bis(indolyl)alkane de-
rivatives have been reported in the literature by the reaction of in-
doles with various carbonyl compounds in the presence of Lewis
acid3 and protic acid.4 Metal triflates, gallium(III) halide, and mo-
lecular iodine have also been used for the synthesis of bis(indolyl)
alkanes.5 We previously showed that the FriedeleCrafts reaction of
2. Results and discussion
In our first trial indole and benzoyl phosponate were reacted in
THF in the presence of a catalytic amount of indium triflate (10%).
After 6 h, no change was observed at room temperature and then the
mixture was heated under reflux for 3 h. According to TLC, several
spots were observed. GCeMS analysis of the reaction showed that
a trace amount of the bis(indolyl)methane phosphonate (3a) was
present in the reaction mixture, but no formation of a single addition
product was observed. The same procedure was applied to m-
chlorobenzoyl phosphonate and bis(indolyl)methane phosphonate
3b was isolated in 9% yield. Many attempts were made to obtain the
addition reaction in higher yield but without success (temperature,
equivalents, reaction sequence, etc.). It isknown inthe literaturethat
the amine can give various reactions including the cleavage of the
CeP bond of acyl phosphonates to form amides.8 Close inspection of
the reaction showed the decomposition of phosphonates. After this
result, we turned our attention to N-substituted indoles for avoiding
CeP bond cleavage. N-Methylindole 2 is used as a starting material
and the reaction with In(OTf)3 (10 mol %) was repeated at room
temperature. The purified product was obtained in 44% yield and
identified as bis(indolyl)methane phosphonate 3c as shown in
Scheme 1. No mono addition product was observed by monitoring
the reaction by TLC and GCeMS. Heating the reaction mixture at
reflux in THF (3e6 h) and the use of 2.2 equiv of 2 increased the yield
to 81% after purification (Scheme 1).
pyrrole derivatives with a,b-unsaturated compounds catalyzed by
metal triflates furnished a conjugate addition product.5d
Shortly thereafter, we published several papers in which acyl
phosphonates were used as an acceptor. The introduction of
a phosphonate moiety to a bis indole structure mayshowinteresting
biological activity and be used as precursors for the synthesis of
various interesting compound. Therefore, the development of
methods via the combination of two previous works for the syn-
thesis of bis(indolyl) phosphonate can be an interesting reaction
regarding the synthetic organic chemistry and biological aspects. As
we described recently, acyl phosphonates are readily available from
the corresponding carboxylic acids and can be used as both an
electrophile and an acylanion equivalent.6 In light of the metal
* Corresponding author. Fax: þ90 312 210 3200; e-mail address: asdemir@
metu.edu.tr (A.S. Demir).
0040-4020/$ e see front matter Ó 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2011.03.061

3356
T. Dasbasi et al. / Tetrahedron 67 (2011) 3355e3359
In summary, we have described a simple, convenient, and effi-
O
P
OMe
OMe
O
cient protocol for the synthesis of bis(indolyl)methane phospho-
nates from N-methylindoles and acyl phosphonates using 10 mol %
of In(OTf)3 as a catalyst. This process offers several advantages, such
as good conversions, high selectivity, experimental simplicity, and
high catalytic activity, which makes it a useful and attractive
strategy for the preparation of bis(indolyl)methane phosphonates
in a single step operation.
In(OTf)3
OMe
OMe
P
O
+
THF
rt to
reflux
N
R
N
R
N
R
1
3
2
Scheme 1.
The formation reaction of 3c was repeated with various Lewis
acids and the formation of the product is monitored by TLC and
GCeMS. Among the Lewis acids that were tested, such as Bi(OTf)3,
Cu(OTf)2, InCl3, InBr3, InI3, YCl3, Y(OTf)3, Sc(OTf)3, and BiCl3, In(OTf)3
(10 mol %) was found to be the most effective for this conversion.
The scope and generality of this process are illustrated with
various phosphonates. The results are shown in Table 1. Aliphatic
and aromatic phosphonates underwent smooth coupling with N-
methylindole to afford the corresponding bis(indolyl)methane
phosphonates (Table 1). In the absence of a catalyst, no reaction was
observed and as a solvent, THF appeared to give the best results
among the other solvents used, i.e, toluene, diethylether.
3. Experimental
3.1. Materials and methods
All of the reactions that were sensitive to air or moisture was
conducted in flame-dried glassware under a dry Argon atmosphere.
THF was distilled over sodium and benzophenone. TLC was carried
out on aluminum sheets precoated with silica gel 60 F254 (Merck),
and the spots were visualized with UV light (
chromatography was conducted on silica gel 60 (40e63
spectra were recorded on a Bruker DPX 400. Chemical shifts are
l
¼254 nm). Column
m
m). NMR
reported in parts per million relative to CHCl3 (1H:
d
¼7.27), CDCl3
Table 1
Bisindolylphosphonate synthesized
Entry
Acyl phosphonates 1
Products 3
Time (h)
Yield (%)
O
1
6
>5
P(OMe)2
O
NH
P(OMe)2
HN
a
O
a
Cll
O
Cl
P(OMe)2
2
6
9
O
b
NH
P(OMe)2
HN
O
b
O
3
4
81
P(OMe)2
O
N
N
a
CH3
H3C
P(OMe)2
O
O
c
F
O
F
4
3
80
P(OMe)2
O
N
N
c
CH3
H3C
P(OMe)2
d
F
O
P(OMe)2
O
5
3
77
F
N
d
N
CH3
H3C
P(OMe)2
O
e

T. Dasbasi et al. / Tetrahedron 67 (2011) 3355e3359
3357
Table 1 (continued )
Entry
Acyl phosphonates 1
Products 3
Time (h)
Yield (%)
Cl
O
Cl
P(OMe)2
6
3
74
O
N
N
b
CH3
H3C
P(OMe)2
O
f
Cl
O
P(OMe)2
O
7
4
81
Cl
N
N
e
CH3
H3C
P(OMe)2
O
g
O
8
3
78
P(OMe)2
O
f
N
N
CH3
H3C
P(OMe)2
O
h
F
F
O
9
3
68
P(OMe)2
O
g
N
N
CH3
H3C
P(OMe)2
O
O
O
i
O
10
4
77
P(OMe)2
O
N
N
h
CH3
H3C
P(OMe)2
j
O
11
4
71
P(OMe)2
O
N
N
i
CH3
H3C
P(OMe)2
k
(
13C:
d
¼77.0 ppm) and CCl4 (13C:
d
¼96.4 ppm). Elemental analyses:
solution (3ꢁ10 mL). The combined organic phase was dried over
MgSO4, and then evaporated under reduced pressure. The crude
product was purified by flash column chromatography by using
EtOAcehexane (4:1).
Leco CHNS 932 analyzer.
3.2. General procedure for dimethyl bis(1-methyl-indol-3-yl)
(phenyl)methylphosphonate
3.2.1. Dimethyl bis(1-methyl-1H-indol-3-yl)(phenyl)methylphospho-
To a solution of 10 mol % of indium triflate in THF (5 mL) at room
temperature was added acyl phosphonate (1 mmol, 1 equiv) under
argon, and the reaction mixture was stirred for 5 min, and then 1-
methylindole (2.2 mmol, 288 mg, 2.2 equiv) was added. The re-
sultant reaction mixture was heated at 50 ꢀC for the time indicated
in Table 1 until the disappearance of acyl phosphonate was in-
dicated by TLC. The reaction mixture was cooled to room temper-
ature, diluted with ether and was washed with saturated NaHCO3
nate (3c). Orange needles, 371 mg (81%), mp 223-222 ꢀC; Rf: 0.43
(EtOAc); IR (KBr):
n
¼3518, 3052, 2953, 1600, 1530, 1480, 1374, 1208,
1070, 1048, 815, 750 cmꢂ1
;
1H NMR (400 MHz, CDCl3):
d
7.59 (d,
J¼7.5 Hz, 2H), 7.17e7.06 (m, 7H), 6.98 (t, J¼7.5 Hz, 2H), 6.85 (d, J¼2.3 Hz,
2H), 6.72 (t, J¼7.4 Hz, 2H), 3.62 (s, 6H, eNCH3), 3.37 (d, J¼10.5 Hz, 6H,
eOCH3); 13C NMR (100 MHz, CDCl3):
129.5 (d, JCeP¼7.0 Hz), 129.1 (d, JCeP¼6.2 Hz), 126.5, 126.2 (d,
JCeP¼6.6 Hz),125.6,122.1,120.1,117.6,113.2 (d, JCeP¼6.7 Hz), 107.7, 53.5
d
139.4 (d, JCeP¼4.4 Hz), 136.2,

3358
T. Dasbasi et al. / Tetrahedron 67 (2011) 3355e3359
(d, JCeP¼8.0 Hz, eOCH3), 52.3 (d, JCeP¼138.6 Hz, eCPO(OCH3)2), 31.6
(eNCH3). Anal. Calcd for C27H27N2O3P (458.18): C, 70.73; H, 5.94; N, 6.11.
Found: C, 70.52; H, 5.54; N, 5.88.
1247, 1058, 1025, 804, 754 cmꢂ1
;
1H NMR:
d
7.46 (dd, J¼8.3 and
1.7 Hz, 2H), 7.16e7.09 (m, 4H), 7.01e6.95 (m, 4H), 6.86 (d, J¼2.4 Hz,
2H), 6.73 (t, J¼7.4 Hz, 2H), 3.65 (s, 6H, eNCH3), 3.38 (d, J¼10.5 Hz, 6H,
eOCH3), 2.25 (s, eCH3); 13C NMR (100 MHz, CDCl3):
d 136.3
3.2.2. Dimethyl (3-fluorophenyl)bis(1-methyl-1H-indol-3-yl) meth-
ylphosphonate (3d). Violet solid, 381 mg (80%), mp 135e136 ꢀC; Rf:
(d, JCeP¼3.5 Hz), 136.2, 134.9 (d, JCeP¼3.5 Hz), 129.4 (d, JCeP¼6.8 Hz),
129.0 (d, JCeP¼6.2 Hz), 127.3, 126.2 (d, JCeP¼6.7 Hz), 122.2, 120.1,
117.6, 113.4 (d, JCeP¼6.5 Hz), 107.7, 52.3 (d, JCeP¼7.7 Hz, eOCH3), 50.9
(d, JCeP¼138.3 Hz, eCPO(OCH3)2), 31.7 (eNCH3), 28.6 (-CH3). Anal.
Calcd for C28H29N2O3P (472.19): C, 71.17; H, 6.19; N, 5.93. Found: C,
71.24; H, 5.94; N, 5.67.
0.47 (EtOAc); IR (KBr):
n
¼3462, 2941, 1617, 1585, 1485, 1374, 1241,
1064, 1036, 804, 749 cmꢂ1
;
1H NMR (400 MHz, CDCl3):
d
7.51 (d,
J¼7.8 Hz, 1H), 7.46 (d, J¼11.3 Hz, 1H), 7.26e7.09 (m, 5H), 7.12
(t, J¼7.7 Hz, 2H), 7.00 (d, J¼2.2 Hz, 2H), 6.93 (d, J¼8.1 Hz, 1H), 6.86
(d, J¼7.7 Hz, 2H), 3.70 (s, 6H, eNCH3), 3.47 (d, J¼10.5 Hz, eOCH3);
13C NMR (100 MHz, CDCl3):
d
162.4 (d, JCeF¼244.0 Hz), 143.0 (dd,
3.2.7. Dimethyl (2-fluorophenyl)bis(1-methyl-1H-indol-3-yl) meth-
ylphosphonate (3i). Violet needles, 323.7 mg (68%), mp
JCeF¼6.6 and JCeP¼4.4 Hz), 137.3, 130.6 (d, JCeF¼6.7 Hz), 128.8 (d,
JCeP¼8.2 Hz), 127.0 (d, JCeP¼6.7 Hz), 125. 8 (dd, JCeF¼6.1 Hz and
JCeP¼2.6 Hz), 122.9, 121.2, 118.7, 117.2 (dd, JCeF¼23.3 Hz and
JCeP¼6.2 Hz), 113.7, 113.5 (d, JCeF¼6.4 Hz), 108.9, 53.5 (d,
JCeP¼7.7 Hz, eOCH3), 52.1 (d, JCeP¼139.9 Hz, eCPO(OCH3)2), 32.8
(eNCH3). Anal. Calcd for C27H26FN2O3P (476.17): C, 68.06; H, 5.50;
N, 5.88. Found: C, 68.42; H, 5.64; N, 5.68.
237e238 ꢀC; Rf: 0.37 (EtOAc); IR (KBr):
n
¼3355, 2916, 1617, 1463,
1340, 1259, 1053, 1035, 810, 757 cmꢂ1; 1H NMR (400 MHz, CDCl3):
d
7.67 ((br t), J¼7.4 Hz, 1H), 7.43 (d, J¼8.3 Hz, 2H), 7.25e7.27 (m, 3H),
7.16 (t, J¼7.4 Hz, 2H), 7.07 (t, J¼7.6 Hz, 1H), 6.98e6.91 (m, 5H), 3.69
(s, 6H, eNCH3), 3.44 (d, J¼10.6 Hz, 6H, eOCH3); 13C NMR (100 MHz,
CDCl3):
d
161.5 (dd, JCeF¼251.5 Hz and JCeP¼8.0 Hz), 137.3, 131.9 (dd,
JCeF¼5.9 Hz and JCeP¼3.2 Hz), 130.3 (d, JCeF¼7.4 Hz), 129.1
(d, JCeP¼8.5 Hz), 128.8 (d, JCeF¼10.8 Hz and JCeP¼3.4 Hz), 127.0
(d, JCeF¼10.8 Hz), 123.4 (d, JCeF¼2.9 Hz), 122.9, 121.1, 118.7, 116.4
(d, JCeF¼23.7Hz), 113.5 (d, JCeP¼7.0 Hz), 108.9, 53.5 (d, JCeP¼7.9 Hz,
eOCH3), 50.7 (JCeP¼142.5 Hz, eCPO(OCH3)2), 32.8 (eNCH3). Anal.
Calcd for C27H26FN2O3P (476.17): C, 68.06; H, 5.50; N, 5.88. Found:
C, 68.23; H, 5.29; N, 5.59.
3.2.3. Dimethyl (4-fluorophenyl)bis(1-methyl-1H-indol-3-yl)methyl-
phosphonate (3e). Violet solid, 366.5 mg (77%), mp 216e217 ꢀC; Rf:
0.40 (EtOAc); IR (KBr):
n
¼3369, 3046, 2959, 1613, 1508, 1474, 1380,
1247, 1053, 1025, 815, 754 cmꢂ1
;
1H NMR (400 MHz, CDCl3):
d
7.71e7.67 (m, 2H), 7.26 (s, 2H), 7.16 (d, J¼8.4 Hz, 2H), 7.12 (dd, J¼8.0
and 1.0 Hz, 2H), 6.98 (d, J¼2.4 Hz, 2H), 6.95 (t, J¼8.9 Hz, 2H), 6.87
(t, J¼8.0 Hz, 2H), 3.73 (s, 6H, eNCH3), 3.48 (d, J¼10.5 Hz, 6H, eOCH3);
13C NMR (100 MHz, CDCl3):
d
161.6 (d, JCeF¼245.9 Hz), 137.3, 136.2,
3.2.8. Dimethyl 1,1- bis(1-methyl-1H-indol-3-yl) ethylphosphonate
(3j). Orange solid, 305 mg (77%), mp140e141 ꢀC; Rf: 0.20 (EtOAc);
131.8 (t, JCeF¼7.0 Hz), 130.6 (d, JCeP¼6.7 Hz), 127.0 (d, JCeP¼6.8 Hz),
121.2, 118.7, 114.4 (d, JCeF¼6.7 Hz), 114.0 (d, JCeP¼6.5 Hz), 109.0, 53.5
(d, JCeP¼7.9 Hz, eOCH3), 51.6 (d, JCeP¼139.5 Hz, eCPO(OCH3)2), 32.8
(eNCH3). Anal. Calcd for C27H26FN2O3P (476.17): C, 68.06; H, 5.50; N,
5.88. Found: C, 68.22; H, 5.66; N, 5.59.
IR (KBr):
(400 MHz, CDCl3):
n
¼2925, 1470, 1380, 1264, 1107, 1031, 811 cmꢂ1
;
1H NMR
d
7.15 (d, J¼2.2 Hz, 2H) 7.11 ((br t), J¼7.3 Hz, 4H),
7.00 (t, J¼7.9 Hz, 2H), 6.70 (t, J¼7.7 Hz, 2H), 3.63 (s, 6H, eNCH3), 3.46
(d, J¼10.5 Hz, 6H, eOCH3), 2.11 (d, J¼16.5 Hz, 3H, eCH3), 13C NMR
(100 MHz, CDCl3):
d
137.1, 128.0 (d, JCeP¼6.3 Hz), 126.8 (d,
3.2.4. Dimethyl (3-chlorophenyl)bis(1-methyl-1H-indol-3-yl) methyl-
phosphonate (3f). White needles, 271 mg (74%), mp 212e213 ꢀC; Rf:
JCeP¼8.7 Hz), 121.5, 120.9, 118.4, 114.5 (d, JCeP¼5.3 Hz), 108.8, 53.2
(d, JCeP¼7.7 Hz, eOCH3), 40.8 (d, JCeP¼141.9 Hz, eCPO(OCH3)2), 32.6
(eNCH3) 25.4 (d, JCeP¼198.9 Hz, eCH3). Anal. Calcd for C22H25N2O3P
(396.16): C, 66.66; H, 6.36; N, 7.07. Found: C, 66.23; H, 6.27; N, 7.28.
0.45 (EtOAc); IR (KBr):
n
¼3413, 3052, 2941, 1596, 1535, 1474, 1375,
1247, 1053, 1025, 820, 754 cmꢂ1; 1H NMR (400 MHz, CDCl3);
d
7.64
(dd, J¼3.7 and 1.7 Hz, 1H), 7.48 (ddd, J¼7.6, 4.3, and 1.7 Hz, 1H),
7.17e7.07 (m, 6H), 7.03 (t, J¼8.1 Hz, 2H), 6.85 (d, J¼2.4 Hz, 2H), 6.78
(t, J¼8.1 Hz, 2H), 3.67 (s, 6H, eNCH3), 3.41 (d, J¼10.5 Hz, 6H, eOCH3);
3.2.9. Dimethyl 1,1-bis(1-methyl-1H-indol-3-yl) propylphosphonate
(3k). Yellow needles, 291 mg (71%), mp 96e97 ꢀC; Rf: 0.25
13C NMR (100 MHz, CDCl3):
d
142.3 (d, JCeP¼4.4 Hz), 137.3, 133.6 (d,
EtOAcehexane (4:1); IR (KBr):
n
¼2941, 1474, 1336, 1236, 1058, 1042,
JCeP¼1.7 Hz), 130.7 (d, JCeP¼6.7 Hz), 130.1 (d, JCeP¼5.9 Hz), 128.8,
128.4 (d, JCeP¼6.3 Hz), 127.1, 127.0, 123.0, 121.3, 118.8, 113.5 (d,
JCeP¼6.6 Hz), 109.0, 53.6 (d, JCeP¼7.9 Hz, eOCH3), 52.2 (d,
JCeP¼139.5 Hz, eCPO(OCH3)2), 32.9 (eNCH3). Anal. Calcd for
C27H26ClN2O3P (492.14): C, 65.79; H, 5.320; N, 5.68. Found: C, 65.65;
H, 5.46; N, 5.72.
820 cmꢂ1; 1H NMR (400 MHz, CDCl3):
d
7.17 (d, J¼2.3 Hz, 2H), 7.11
(d, J¼8.1 Hz, 2H), 6.96e6.90 (m, 4H), 6.62 (t, J¼7.5 Hz, 2H), 3.72
(s, +eNCH3, 6H), 3.42 (d, J¼10.4 Hz, 6H, eOCH3), 2.64 (qd, J¼7.3 and
J¼18.6 Hz, 1H), 0.79 (t, J¼7.3 Hz, 3H, eCH3); 13C NMR (100 MHz,
CDCl3):
d
137.0, 129.2 (d, JCeP¼6.1 Hz), 127.6 (d, JCeP¼8.9 Hz), 122.0,
121.1, 118.6,112.7 (d, JCeP¼6.4 Hz), 53.1 (d, JCeP¼7.8 Hz, eOCH3), 46.1
(d, JCeP¼138.7 Hz, eCPO(OCH3)2), 32.9 (eNCH3), 29.7 (d,
JCeP¼2.0 Hz, -CH2CH3), 10.1 (d, JCeP¼5.1 Hz, eCH2CH3). Anal. Calcd
for C23H27N2O3P (410.18): C, 67.30; H, 6.63; N, 6.83. Found: C, 69.11;
H, 6.48; N, 6.92.
3.2.5. Dimethyl (4-chlorophenyl)bis(1-methyl-1H-indol-3-yl) methyl-
phosphonate (3g). Orange solid, 398.6 mg (81%), mp 233e234 ꢀC; Rf:
0.25 EtOAcehexane (4:1); IR (KBr):
n
¼3460, 2959, 1613, 1590, 1490,
1
1375, 1264, 1060, 1036, 810, 750 cmꢂ1; H NMR (400 MHz, CDCl3):
d
7.59 (dd, J¼8.7 and 1.8 Hz, 2H), 7.20e7.09 (m, 6H), 7.05 (t, 2H,
Acknowledgements
J¼7.5 Hz), 6.90 (d, 2H, J¼2.4 Hz), 6.79 (t, 2H, J¼7.5 Hz), 3.65 (s, 6H,
eNCH3), 3.40 (d, J¼10.5 Hz, 6H, eOCH3), 13C NMR (100 MHz, CDCl3):
We gratefully acknowledge the Scientific and Technological
Research Council of Turkey (TUBITAK), the Turkish Academy of
Sciences (TUBA), and the Middle East Technical University (METU).
d
139.2 (d, JCeP¼4.4 Hz), 137.4, 132.6, 131.6 (d, JCꢂP¼6.3 Hz), 130.7 (d,
JCeP¼6.8 Hz), 127.8, 127.4 (d, JCeP¼6.8 Hz), 123.0, 122.3, 118.8, 113.0
(d, JCeP¼6.8 Hz), 107.0, 53.6 (d, JCeP¼7.8 Hz, eOCH3), 51.9 (d,
JCeP¼139.9 Hz, eCPO(OCH3)2), 32.9 (eNCH3). Anal. Calcd for
C27H26ClN2O3P (492.14): C, 65.79; H, 5.32; N, 5.68. Found: C, 65.84;
H, 5.44; N, 5.45.
Supplementary data
Supplementary data associated with this article can be found in
online version at doi:10.1016/j.tet.2011.03.061. These data include
MOL files and InChIKeys of the most important compounds de-
scribed in this article.
3.2.6. Dimethyl (4-methylphenyl)bis(1-methyl-1H-indol-3-yl)methyl-
phosphonate (3h). Yellow solid, 368 mg (78%), mp 228e229 ꢀC; Rf:
0.25 EtOAcehexane (4:1); IR (KBr):
n¼3496, 2959, 1617, 1480, 1380,

T. Dasbasi et al. / Tetrahedron 67 (2011) 3355e3359
3359
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