Green protocol for synthesis of bis-indolylmethanes and bis-indolylglycoconjugates in the presence of iron(III) fluoride as a heterogeneous, reusable, and eco-friendly catalyst

Article abstract of DOI:10.1071/CH06127

An efficient method for the preparation of bis-indolylmethanes and bis-indolylglycoconjugates from carbonyl compounds with indoles in the presence of a catalytic amount of iron(iii) fluoride under solvent-free conditions is reported. The desired products

Full text of DOI:10.1071/CH06127

Communication
CSIRO PUBLISHING
www.publish.csiro.au/journals/ajc
Aust. J. Chem. 2006, 59, 837–840
Green Protocol for Synthesis of Bis-indolylmethanes and
Bis-indolylglycoconjugates in the Presence of Iron(iii) Fluoride
as a Heterogeneous, Reusable, and Eco-Friendly Catalyst
Vinod T. Kamble,A,B Babasaheb P. Bandgar, Satish B. Suryawanshi,
A
A
and Sudhir N. BavikarA
A
Organic Chemistry Research Laboratory, School of Chemical Sciences, Swami Ramanand Teerth
Marathwada University, Nanded 431606, India.
Corresponding author. Email: vtkd@rediffmail.com
B
An efficient method for the preparation of bis-indolylmethanes and bis-indolylglycoconjugates from carbonyl
compounds with indoles in the presence of a catalytic amount of iron(iii) fluoride under solvent-free conditions is
reported.The desired products were obtained in high yields with a simple and environmentally benign procedure.The
use of iron(iii) fluoride is feasible because of its stability, easy handling, easy recovery, reusability, and good activity.
Manuscript received: 19 April 2006.
Final version: 21 August 2006.
Indoles and their derivatives have applications in the field
Iron(iii) chloride has been used widely as a Lewis acid
[1]
[19,22]
of pharmaceuticals. Many bis-indolylmethanes have been
isolated from terrestrial and marine natural sources such as
catalyst in a variety of organic transformations;
how-
ever, the susceptibility of iron(iii) chloride to aqueous media
impedes its use for large-scale synthesis. On the other hand,
iron(iii) fluoride has emerged as a mild, non-toxic, inex-
pensive, and water-tolerant Lewis acid catalyst for various
[2]
parasitic bacteria, tunicates, and sponges, and some of
these exhibit biological activity. The acid-catalyzed reac-
tion of electron-rich heterocycles such as pyrroles and
indoles with para-dimethylaminobenzaldehyde is known as
the Ehrlich test.[ The analogous reaction of indoles with
other aromatic or aliphatic aldehydes and ketones pro-
duces azafulvenium salts. Azafulvenium salts can undergo
further addition with a second indole molecule to give bis-
[
23]
organic transformations.
There have been no reports
3]
on the use of iron(iii) fluoride for the synthesis of bis-
indolylmethanes and bis-indolylglycoconjugates from car-
bonyl compounds under solvent-free conditions. Moreover,
the catalytic applications of various reagents for the synthe-
sis of bis-indolylmethanes have been reported frequently, but
relatively few examples have been reported for the synthesis
[
4]
indolylmethanes. Early attempts involved the use of protic
acids and Lewis acids for the reaction of indoles or indolyl
Grignard reagents with aldehydes, ketones, α-ketoacids,
imines, iminium salts, or nitrones.[ However, many of these
procedures are associated with disadvantages like long reac-
[
24]
of bis-indolylglycoconjugates. Therefore, a more efficient
method to carry out this transformation is still highly sought.
5]
In continuation of our program to develop reactions
[
6a]
[6b]
[23]
tion time,
use of expensive Lewis acids,
preformed
in aqueous, solvent-free systems,
we report a simple,
reagents,[
6c–f]
or extremely low yields. In recent years, sev-
convenient, and efficient process for the synthesis of bis-
indolylmethanes and bis-indolylglycoconjugates 3a–3q from
carbonylcompounds1and 2, inwhichonlyacatalyticamount
of iron(iii) fluoride, a relatively environmentally acceptable
chemical, is required (Scheme 1).
The electrophilic substitution reaction of indole with ben-
zaldehyde in the presence of 5 mol% iron(iii) fluoride at room
temperature afforded the corresponding bis-indolylmethane
within 10 min. Similarly, the scope of the reaction was
assessed using structurally diverse aldehydes and ketones
(Table 1). Aromatic (entries 1–10), aliphatic (entry 11),
α,β-unsaturated (entry 12), and alicyclic (entry 15) aldehy-
des reacted smoothly with indole to afford the corresponding
bis-indolylmethanes in high yields. In addition, the reaction is
[7]
[8]
eral efficient methods using InCl3, lanthanide triflates,
LiClO4,[ I2,
9]
[10]
NBS,
Dy(OTf)3,
[11]
KHSO4,
ZnCl4,
[12]
[16]
montmorillonite,
[13]
[14]
[15]
[17]
HY zeolite,
I2,
CeCl3·7H2O/
[19]
[
18]
NaI/SiO2,
iron(iii) salts in ionic liquids,
polyaniline
salts,[
20]
and ionic liquids
[21]
have been reported for the
synthesis of bis-indolylmethanes.
Although a number of different methods have been
reported for the preparation of bis-indolylmethanes, there
is still a need to search for better catalysts with regard to
their toxicity, handling, availability, economic viability, and
operational simplicity. In view of the recent trend in catalytic
process, investigations for new and less hazardous catalysts
have become a priority in synthetic organic chemistry.
©
CSIRO 2006
10.1071/CH06127
0004-9425/06/110837

8
38
V. T. Kamble et al.
R
O
C
FeF3 (5 mol%)
neat, r.t.
R1
ꢀ
R1
R
N
H
N
H
N
H
1
2
3a–3q
Scheme 1.
Table 1. FeF3-catalyzed synthesis of bis(indolyl)methanes
This result shows the strong catalytic ability of FeF in
3
comparison with FeCl3, FeBr3, and FeI3.
Entry
Aldehyde/Ketone
Product
Time
YieldA
[%]
In view of greener chemistry, efficient recovery and reuse
of the catalyst is highly desirable. In our process, the cata-
lyst was recovered and reused efficiently without activation.
The reusability of iron(iii) fluoride was examined by using
4-chlorobenzaldehyde as a model substrate, and the results
are described in the experimental procedure.
[
min]
1
2
3
4
5
6
7
8
9
C6H5CHO
4-ClC6H4CHO
3a
3b
3c
3d
3e
3f
3g
3h
3i
3j
3k
3l
3m
3n
3o
3p
3q
10
15
15
15
15
20
20
18
20
17
15
15
20
20
15
25
25
94
94
95
91
93
92
89
88
91
93
91
90
89
91
88
84
89
4-MeC6H4CHO
4-NO2C6H4CHO
4-MeOC6H4CHO
3,4-(MeO)2C6H3CHO
3,4-Cl2C6H3CHO
2-ClC6H4CHO
3,4-(EtO)2C6H3CHO
3,4-(OCH2O)2C6H3CHO
CH3(CH2)5CHO
C6H5CH=CHCHO
Thiophene-2-carboxaldehyde
Furfural
As compared with recently reported methods that required
[7–12]
[13]
large
and stoichiometric amounts of catalysts,
the
present procedure required less catalyst (5 mol%) for the
reaction to proceed cleanly. Although various methods have
been recently reported for this conversion, most require long
10
11
12
13
14
15
16
17
[7–9]
[8,15–18]
reaction times,
readily available and need to be prepared,
reagents are destroyed in the workup procedure and cannot be
expensive reagents
that are not
and some
[8,14–17]
Cyclohexanal
Cyclopentanone
Cyclohexanone
[
9–12]
recovered and reused.
In contrast, iron(iii) fluoride as a
mild, non-hygroscopic, inexpensive, eco-friendly, and com-
mercially available reagent that affords the desired products
in short reaction times and low catalyst loadings.
A
1
Yield of isolated pure product; products are characterized by IR,
H NMR, elemental analysis, and comparison with authentic samples.
To conclude, the present procedure clearly demonstrates
that conversion of aldehydes, ketones, and sugar aldehy-
des into bis-indolylmethanes and bis-indolylglycoconjugates
using iron(iii) fluoride as a mild, cheap, and commer-
cially available catalyst under solvent-free conditions is a
valid alternative to existing methods. It also offers several
advantages including high product yields products, cleaner
reactions, operational simplicity, and easy workup.
applicable to ketones such as cyclopentanone and cyclohex-
anone. The reaction of cyclohexanone with indole gave a bet-
teryieldthancyclopentanone, perhapsbecauseofthestability
of the six-membered ring compared with a five-membered
ring. Further, the present protocol was successfully applied
to heteroaromatic aldehydes (entries 13 and 14) to afford
the corresponding bis-indolylmethanes in high yields within
2
0 min. It is noteworthy that these substrates reacted with
Experimental
equal ease in short times to furnish the products in high yields
and without side reactions, which are normally encountered
under acidic conditions.
In order to expand the generality of the present pro-
tocol, we employed sugar aldehyde, 1,2-O-isopropylidene-
Melting points were measured by using a Buchi R-535 apparatus. IR
spectra were recorded on a Bomem MB FT-IR spectrometer. H NMR
spectra were recorded on aVarian Gemini-200 spectrometer. Mass spec-
tra were recorded on a VG Micromass-7000 H (70 eV). CHN analyses
were recorded on a Vario EL analyzer.
1
3
-O-methyl-α-d-xylo-pentadialdo-1,4-furanose (Scheme 2,
a).When indole was allowed to react with sugar-derived alde-
hyde a in the presence of 5 mol% iron(iii) fluoride at room
temperature, the corresponding bis-indolylglycoconjugate 4a
was obtained in good yield.
Further, we studied the catalytic ability of other iron
salts such as FeCl3, FeBr3 FeI3, Fe2(NO3)3·9H2O, and
Fe2(SO4)3·nH2O for the synthesis of bis-indolylmethanes.
Among these catalysts, FeF3 is more effective than other
catalysts. By using 5 mol% of FeCl3, FeBr3, and FeI3,
Fe2(NO3)3·9H2O, and Fe2(SO4)3·αH2O, benzaldehyde was
converted into the corresponding bis-indolylmethanes in 64,
Experimental Procedure
A mixture of indole (2 mmol), 4-chlorobenzaldehyde (1 mmol), and
iron(iii) fluoride (0.05 mmol) under solvent-free conditions was ground
in a mortar and pestle at room temperature for an appropriate time.After
completion of the reaction, as indicated by TLC, the reaction mixture
was quenched with water (10 mL), and the mixture was extracted with
ethyl acetate (2 × 10 mL). The combined organic layers were dried over
anhydrous Na2SO4 and solvent was removed under reduced pressure to
furnish a crude product that was further purified by column chromatog-
raphyonsilicagel(ethylacetate/hexane1/9).Theaqueouslayerwasthen
separated and evaporated under reduced pressure to afford the catalyst.
The recovered catalyst was then reused for the reaction of a fresh lot
of 4-chlorobenzaldehyde (1 mmol) with indole (2 mmol) to afford 90%
yield of the corresponding product after 20 min. The recovered cata-
lyst was reused for four consecutive reactions of 4-chlorobenzaldehyde
4
5, 42, 41, and 0% yield respectively when the reaction mix-
ture was ground under solvent-free conditions for 10 min.

Synthesis of Bis-indolylmethanes and -indolylglycoconjugates in the Presence of FeF3
839
R
H
FeF3 (5 mol%)
R
CHO
ꢀ
neat, r.t.
a
N
H
N
H
N
H
4a
O
OMe
R ꢁ
Product Time Yield
O
[
min]
[%]
O
4a
60
70
Scheme 2.
(
1 mmol) with indole (2 mmol), affording 88, 85, 82, and 80% yields of
Compound 3h
the corresponding products, respectively, in 25, 30, 35 and 40 min.
◦
Solid, mp73–74 C. (Found:(HR-MS):356.1070. Calc. forC23H17ClN2:
−
1
3
56.1080.) νmax (KBr)/cm
620, 3050, 3410 (NH). δH (CDCl3) 6.30 (s, 1H, Ar–CH), 6.70 (s, 2H),
1015, 1045, 1095, 1340, 1415, 1455,
Compound 3a
1
◦
7.05 (t, 2H, J 8.2), 7.10–7.20 (m, 6H), 7.35–7.41 (m, 4H), 7.97 (br s,
2H, NH).
Solid, mp 125–126 C. (Found: C 85.8, H 5.5, N 8.6%. Calc. for
−
1
C23H18N2 (322.14): C 85.7, H 5.6, N 8.7%.) νmax (KBr)/cm 750,
095, 1455, 1600, 1620, 3055, 3415 (NH). δH (CDCl3) 5.90 (s, 1H,
Ar–CH), 6.65 (s, 2H), 7.00 (t, 2H, J 7.0), 7.22 (m, 3H), 7.30 (m, 2H),
.35 (m, 6H), 7.95 (br s, 2H, NH).
1
Compound 3i
◦
−1
max
(KBr)/cm 765, 1015, 1230, 1495, 1625,
7
Solid, mp 185–187 C. ν
2
7
2
7
990, 3100, 3420 (NH). δH (CDCl3) 1.35 (t, 3H, J 8.0), 1.42 (t, 3H, J
.0), 3.95 (q, 2H, J 7.0), 4.05 (q, 2H, J 7.0), 5.75 (s, 1H), 6.63 (d, 2H, J
.4), 6.75 (m, 2H), 6.80 (m, 1H), 6.95 (t, 2H, J 8.2), 7.05 (t, 2H, J 8.2),
Compound 3b
◦
Solid, mp75–77 C. (Found(HR-MS):356.1070. Calc. forC23H17ClN2:
+
.30 (m, 4H), 7.95 (br s, 2H, NH). m/z 410 (70%, M ), 266 (10), 248
−
1
3
(
2
56.1080.) νmax (KBr)/cm 1090, 1450, 1490, 3055, 3415 (NH). δH
CDCl3) 5.80 (s, 1H, Ar–CH), 6.65 (s, 2H), 7.05 (t, 2H, J 8.3), 7.15 (t,
H, J 7.9), 7.25–7.35 (m, 8H), 7.95 (br s, 2H, NH).
(
20), 215 (5), 160 (60), 135 (100), 121 (30), 91 (40), 69 (20).
Compound 3j
Solid, mp 96–98 C. νmax (KBr)/cm 765, 1075, 1210, 1490, 1615,
100, 3475 (NH). δH (CDCl3) 5.82 (s, 1H, CH), 5.90 (d, 2H), 6.65 (d,
◦
−1
Compound 3c
Solid, mp 94–96 C. (Found: C 85.4, H 5.9, N 8.0%. Calc. for C24H20N2
3
◦
2H, J 2.4), 6.72 (d, 1H, J 8.4), 6.85 (d, 2H, J 8.4), 7.05 (t, 2H, J 8.4),
7.20 (t, 2H, J 8.4), 7.25 (d, 2H, J 8.4), 7.35 (d, 2H, J 8.4), 7.95 (br s, 2H,
NH). m/z 366 (100%, M ), 245 (60), 204 (30), 57 (20), 43 (25).
−
1
(
349.45): C 85.7, H 6.0, N 8.3%.) νmax (KBr)/cm 775, 1055, 1220,
+
1515, 1610, 2930, 3040, 3415 (NH). δH (CDCl3) 2.35 (s, 3H, Ar–CH3),
5.85 (s, 1H, Ar–CH), 6.70 (s, 2H), 7.05 (t, 2H, J 7.2), 7.1 (d, 2H, J 7.6),
7.25–7.29 (m, 6H), 7.5 (d, J 7.6, 2H), 7.98 (br s, 2H, NH).
Compound 3k
◦
Solid, mp 67–69 C. (Found: C 83.5, H 8.2, N 8.1%. Calc. for C23H26N2
(
−
1
Compound 3d
Solid, mp 216–218 C. (Found: C 75.3, H 4.5, N 11.6%. Calc. for
330.47): C 83.4, H 7.9, N 8.5%.) νmax (KBr)/cm 790, 1095, 1335,
1450, 1620, 3055, 3410 (NH). δH (CDCl ) 0.85 (t, 3H, J 7.0), 1.25–1.35
(m, 8H), 2.20 (m, 2H), 4.60 (t, 1H, J 7.6), 7.00–7.05 (m, 4H), 7.15 (t,
H, J 8.0), 7.30 (d, 2H, J 8.0), 7.55 (d, 2H, J 7.2), 7.95 (br s, 2H, NH).
◦
3
−
1
C23H17N3O2 (367.40): C 75.2, H 4.7, N 11.4%.) νmax (KBr)/cm
340, 1455, 1510, 1595, 3050, 3420 (NH). δH (CDCl3) 5.98 (s, 1H,
Ar–CH), 6.70 (s, 2H), 7.00–7.05 (m, 3H), 7.35 (d, 3H, J 8.0), 7.40 (d,
H, J 8.2), 7.50 (d, 2H, J 8.8), 8.05 (br s, 2H, NH), 8.15 (d, 2H, J 8.8).
2
1
Compound 3l
Semisolid. νmax (KBr)/cm 1 765, 990, 1050, 1475, 1595, 2960, 3110,
2
−
3
2
7
450 (NH). δH (CDCl3) 5.95 (s, 1H), 6.42 (d, 1H, J 16.0), 6.65 (d, 2H, J
.2), 7.05 (t, 2H, J 8.0), 7.15 (t, 2H, J 8.0), 7.30 (m, 4H), 7.40 (m, 3H),
Compound 3e
Solid, mp 187–188 C. (Found: C 81.7, H 5.8, N 8.0%. Calc. for
◦
.55 (m, 2H), 7.75 (d, 1H, J 16.0), 7.95 (br s, 2H, NH). m/z (EI) 346
−
1
C24H20N2O (352.43): C 81.8, H 5.7, N 8.0%.) νmax (KBr)/cm 1220,
240, 1455, 1505, 1610, 2930, 3415 (NH). δH (CDCl3) 3.75 (s, 3H,
CH3), 5.80 (s, 1H, Ar–CH), 6.65 (s, 2H), 6.80 (d, 2H, J 8.2), 7.05 (t,
H, J 7.2), 7.15 (t, 2H, J 7.2), 7.20 (s, 2H), 7.35–7.40 (m, 4H), 7.98 (br
+
(
20%, M ), 321 (100), 244 (80), 205 (30), 122 (15), 77 (10).
1
Compound 3m
Solid, mp 152–154 C. (Found: C 76.7, H 5.0, N 8.5%. Calc. for
2
◦
s, 2H, NH).
−1
C21H16N2S (328.10): C 76.8, H 4.9, N 8.5%.) νmax (KBr)/cm 1250,
1
6
455, 1710, 3410 (NH). δH (CDCl3) 6.15 (s, 1H, Ar–CH), 6.86 (s, 2H),
.90–7.47 (m, 1H), 7.95 (br s, 2H, NH).
Compound 3f
◦
−1
Solid, mp 197–199 C. νmax (KBr)/cm 765, 1005, 1235, 1495, 1620,
2
1
980, 3060, 3445 (NH). δH (CDCl3) 3.75 (s, 3H), 3.82 (s, 3H), 5.75 (s,
H), 6.72 (d, 2H, J 2.4), 6.80 (d, 2H, J 8.2), 6.85 (s, 1H), 6.90 (d, 2H,
Compound 3n
Solid, mp 113–115 C. νmax (KBr)/cm 665, 750, 790, 940, 1010, 1045,
◦
−1
J 8.2), 7.05 (t, 2H, J 8.0), 7.35 (t, 4H, J 8.2), 10.45 (br s, 2H, NH). m/z
3
1
1
5
095, 1145, 1160, 1215, 1248, 1345, 1410, 1450, 1505, 1555, 1610,
725, 2850, 2920, 3055, 3120, 3414, 3896. δH (CDCl3) 5.80 (s, 1H),
.95 (d, 1H, J 3.4), 6.22 (d, 1H, J 2.4), 6.75 (d, 1H, J 2.4), 6.95 (t, 2H),
+
82 (100%, M ), 265 (10), 245 (50), 69 (20).
+
Compound 3g
Solid, mp 153–154 C. νmax (KBr)/cm 775, 1015, 1250, 1475, 1610,
7.10 (t, 2H), 7.25–7.45 (m, 5H), 7.90 (br s, 2H, NH). m/z 312 (8%, M ),
◦
−1
137 (28), 105 (16), 91 (93), 43 (100).
2
6
975, 3050, 3450 (NH). δH (CDCl3) 5.83 (s, 1H), 6.75 (d, 2H, J 2.4),
Compound 3o
.87 (m, 1H), 6.95 (m, 2H), 6.92–7.02 (m, 4H), 7.2 (s, 1H), 7.25 (t, 2H,
+
◦
−1
J 8.2), 7.40 (s, 1H), 7.92 (br s, 2H, NH). m/z 390 (100%, M ), 392 (60,
Solid, mp 137–139 C. νmax (KBr)/cm 775, 1040, 1290, 1575, 1610,
2990, 3010, 3420 (NH). δH (CDCl3) 1.22 (m, 6H) 1.95 (m, 4H), 2.24
+
[
M+2] ), 274 (80), 245 (50), 204 (20), 176 (5), 117 (10).

8
40
V. T. Kamble et al.
(
7
m, 1H), 4.40 (m, 1H), 6.96 (d, 2H, J 2.4), 7.05 (m, 2H), 7.10 (m, 2H),
(d) H. Singh, K. Singh, Tetrahedron 1988, 44, 5897.
doi:10.1016/S0040-4020(01)81447-2
(e) J.-N. Denis, H. Mauger, Y. Vallee, Tetrahedron Lett. 1997, 38,
.25 (d, 2H, J 8.2), 7.45 (d, 2H, J 8.0), 7.95 (br s, 2H, NH). m/z 328
+
(
30%, M ), 246 (80), 130 (25), 84 (60), 57 (90), 41 (100).
8
515. doi:10.1016/S0040-4039(97)10302-1
Compound 3p
(f) H. Chalaye-Mauger, J.-N. Denis, M.-T. Averbuch-Pouchot,
Y. Vallee, Tetrahedron 2000, 56, 791. doi:10.1016/S0040-
4020(99)01051-0
◦
Solid, mp 73–74 C. (Found: C 84.0, H 6.7, N 9.3%. Calc. for C21H20N2:
−
1
C 84.0, H 6.7, N 9.3%.) νmax (KBr)/cm 775, 1010, 1490, 1585, 1610,
965, 3430 (NH). δH (CDCl3) 1.72 (m, 4H), 2.40 (m, 4H), 6.70 (t, 2H,
J 8.2), 6.95 (m, 4H), 7.25 (d, 2H, J 8.2), 7.42 (d, 2H, J 8.0), 7.98 (br s,
H, NH).
[
[
[
7] G. Babu, N. Sridhar, P. T. Perumal, Synth. Commun. 2000, 30,
2
1
609.
8] D. Chen, L. Yu, P. G. Wang, Tetrahedron Lett. 1996, 37, 4467.
doi:10.1016/0040-4039(96)00958-6
9] J. S.Yadav, B.V. S. Reddy, Ch.V. S. R. Murthy, G. Mahesh Kumar,
Ch. Madan, Synthesis 2001, 783. doi:10.1055/S-2001-12777
[10] B. P. Bandgar, K. A. Shaikh, Tetrahedron Lett. 2003, 44, 1959.
doi:10.1016/S0040-4039(03)00032-7
[11] H. Koshima, W. Matsuaka, J. Heterocycl. Chem. 2002, 39, 1089.
[12] R. Nagarajan, P. T. Perumal, Chem. Lett. (Jpn.) 2004, 33, 288.
doi:10.1246/CL.2004.288
2
Compound 3q
Solid, mp 119–120 C. (Found: C 84.1, H 7.1, N 9.0%. Calc. for
◦
−
1
C22H22N2: C 84.1, H 7.1, N 9.9%.) νmax (KBr)/cm 785, 1015, 1235,
1
2
480, 1580, 1620, 2950, 3030, 3450 (NH). δH (CDCl3) 1.82 (m, 6H),
.50 (m, 4H), 6.80 (t, 2H, J 8.2), 7.05 (m, 4H), 7.24 (d, 2H, J 8.0), 7. 55
(
d, 2H, J 8.0), 7.98 (br s, 2H, NH).
[
13] (a) M. Chakrabarty, S. Sarkar, Tetrahedron Lett. 2002, 43, 1351.
Compound 4a
Solid, mp 102–103 C. (Found: C 71.8, H 6.3%. Calc. for C25H26N2O4:
doi:10.1016/S0040-4039(01)02380-2
(b) M. Chakrabarty, N. Ghosh, R. Basak,Y. Harigaya,Tetrahedron
◦
Lett. 2002, 43, 4075. doi:10.1016/S0040-4039(02)00682-2
14] A. V. Reddy, K. Ravinder, V. L. N. Reddy, T. V. Goud,
V. Ravikant, Y. Venkateswarlu, Synth. Commun. 2003, 33, 3687.
doi:10.1081/SCC-120025177
−
1
C 71.8, H 6.3%.) νmax (KBr)/cm 1010, 1075, 1160, 1305, 1510, 1710,
[
1725, 2935, 2990, 3390 (NH). δH (CDCl3) 1.22 (s, 3H), 1.60 (s, 3H),
3.10 (s, 3H), 3.30 (d, 1H, J 4.2), 4.50 (d, 1H, J 5.2), 4.98 (t, 2H, J 17.2),
5.80 (d, 1H, J 5.2), 6.75–7.22 (m, 8H), 7.33–7.50 (m, 1H), 7.65 (d, 1H,
[
[
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