Use of the Pictet-Spengler reaction for the synthesis of 1,4-disubstituted-1,2,3,4-tetrahydro-β-carbolines and 1,4-disubstituted-β-carbolines: formation of γ-carbolines

Article abstract of DOI:10.1016/j.tet.2007.12.008

Microwave-assisted conjugate addition of indole on nitro-olefins furnished nitro compounds, which were reduced to tryptamines. Further, by using Pictet-Spengler condensation, new 1,4-disubstituted-1,2,3,4-tetrahydro-β-carbolines were synthesized in diaste

Full text of DOI:10.1016/j.tet.2007.12.008

Available online at www.sciencedirect.com
Tetrahedron 64 (2008) 1654e1662
www.elsevier.com/locate/tet
Use of the PicteteSpengler reaction for the synthesis of 1,4-disubstituted-
1,2,3,4-tetrahydro-b-carbolines and 1,4-disubstituted-b-carbolines:
formation of g-carbolines
a
a
b
Radhika S. Kusurkar a, , Nabil A.H. Alkobati , Anita S. Gokule , Vedavati G. Puranik
*
a Department of Chemistry, University of Pune, Pune 411007, Maharashtra, India
b Center for Materials and Characterization, National Chemical Laboratory, Pune 411008, Maharashtra, India
Received 19 December 2006; received in revised form 20 November 2007; accepted 6 December 2007
Available online 8 December 2007
Abstract
Microwave-assisted conjugate addition of indole on nitro-olefins furnished nitro compounds, which were reduced to tryptamines. Further, by
using PicteteSpengler condensation, new 1,4-disubstituted-1,2,3,4-tetrahydro-b-carbolines were synthesized in diastereoselective manner.
Dehydrogenation of the tetrahydro-b-carbolines produced new 1,4-disubstituted-b-carbolines. As a new observation, in some of the cases,
PicteteSpengler condensation and dehydrogenation gave two products, namely 1,4-disubstituted-b-carbolines and 1,4-disubstituted-g-carbo-
lines. A mechanism is proposed for this observation.
Ó 2007 Elsevier Ltd. All rights reserved.
Keywords: 1,4-Disubstituted-b-carboline; 1,4-Disubstituted-g-carboline; PicteteSpengler reaction; 1,4-Disubstituted-1,2,3,4-tetrahydro-b-carboline; 1,4-Disubsti-
tuted-1,2,3,4-tetrahydro-g-carboline
1. Introduction
have reported preliminary results about the conjugate addition
of indole on nitro-olefins using microwave technology.7 In con-
tinuation with those results we report herein further conversion
of the nitro compounds to new 1,4-disubstituted-tetrahydro-b-
carbolines and then to new b-carbolines. Surprisingly g-carbo-
lines are also obtained during the PicteteSpengler condensation
and dehydrogenation in some cases.
Tetrahydro-b-carbolines (THbCs) are potent neuroactive
alkaloids.1 THbCs as pharmacophores have exhibited a wide
range of pharmacological properties. They have been shown
to inhibit monoamine oxidase A and bind with nanomolar
affinity to serotonin receptors.2 THbCs also bind to GABA,
a receptor ion channel and modulate molecular mechanisms
controlling anxiety, convulsions, and sleep.3a,b b-Carbolines
exhibit many important biological activities like mutagenic
and co-mutagenic properties, significant anti-tumor and anti-
HIV activities, and inhibition of topoisomerase I.4aec
ThePicteteSpenglercondensationisthemostwidelyusedand
extensivelystudiedmethodforthesynthesisoftetrahydro-b-carb-
olines. Amongst the variously substituted THbCs, very few re-
ports are available typically for the 1,4-disubstituted THbCs,5aec
and also for 1,4-disubstituted-b-carbolines.6aed Recently, we
2. Results and discussions
Initially, indole was treated with methyl magnesium iodide
to get indolyl magnesium iodide, which on reaction with nitro-
styrene 1 at room temperature gave the expected Michael
addition product 12a in 71% yield in 5 min (Scheme 1). The
same product 12a was obtained in 80% yield when indole
and nitrostyrene 1 in dry benzene were heated at 120 ꢀC in
a sealed tube for 2 days. When the reactants were loaded on
silica gel and kept at room temperature for 1 or 2 h, the prod-
uct 12a was produced in quantitative yields. A microwave-as-
sisted reaction was also carried where indole and nitrostyrene
1 were loaded on silica gel (60e120 mesh) and then irradiated
* Corresponding author. Tel.: þ91 20 25601202; fax: þ91 20 25691728.
E-mail address: rsk@chem.unipune.ernet.in (R.S. Kusurkar).
0040-4020/$ - see front matter Ó 2007 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2007.12.008

R.S. Kusurkar et al. / Tetrahedron 64 (2008) 1654e1662
1655
Ar
Reactions of various other nitro-olefins (2e8) and indole un-
dermicrowaveirradiationfurnishedproducts(12be12h)ingood
yields (Scheme 1, Table 1). Alkylation of indole with a-methyl-
nitro-alkenes (9e11) using microwave irradiation produced the
corresponding Michael addition products (12ie12k) in good
yields (Scheme 1, Table 1). The H NMR spectra of 12ie12k
revealed the presence of diastereomers in the ratio of 2.3:1 for
12i, 1.1:1 for 12j and 1:1 for 12k.
R
NO2
M.W,Silica gel
800 W
Ar
+
NO2
R
N
H
N
H
1
12a: Ar = phenyl, R = H; 12b: Ar = 3,4-dimethoxyphenyl, R = H;
12c: Ar = 3,4-methylenedioxyphenyl, R = H; 12d: Ar = 2-furyl, R = H;
12e: Ar = p-nitrophenyl, R = H; 12f: Ar = 2-thienyl, R = H;
12g: Ar = p-methoxyphenyl, R = H; 12h: Ar = m-methoxyphenyl, R = H;
12i: Ar = 2-furyl, R = CH3, 12j: Ar = p-methoxyphenyl, R = CH3;
12k: Ar = p-nitrophenyl, R = CH3
After generalizing the conjugate addition of indole, the ni-
tro compound 12a was reduced using freshly prepared Raney
Nickel in methanol to obtain the substituted tryptamine 13a.
Treatment of amine 13a with benzaldehyde in the presence
of trimethylsilylchloride in dichloromethane furnished 1,4-di-
substituted-tetrahydro-b-carboline 14a. The product 14a was
a single diastereomer (probably trans isomer similar to the ear-
Scheme 1.
in a microwave oven (domestic Daewoo 616T) for 2 min to get
12a in 95% yield. From these results, it was concluded that the
microwave-assisted reaction was the most efficient method
with respect to time and yield.
1
lier report5), which was confirmed using H NMR, 13C NMR,
IR, DEPT, elemental analysis and mass spectra. Further
Table 1
Time and yields for Michael adducts 12ae12k
Entry
Electrophile
Product
Grignard reaction
Sealed tube reaction
Microwave reaction
Time (min)
Time
Yield (%)
Time (h)
48a
Yield (%)
Yield (%)
95
NO2
1
2
3
4
5
12a
12b
12c
12d
12e
5 min
71
73
73
60
35
80
53
60
85
65
2
10
10
2
NO2
MeO
20 h
72b
72b
48a
48b
80
89
86
84
MeO
O
NO2
20 h
O
NO2
5 min
5 min
5 min
O
NO2
10
O2N
MeO
6
7
12f
58
48a
82
2
93
92
NO2
S
NO2
12g
d
d
d
10
NO2
8
12h
d
d
d
d
10
94
OMe
O
NO2
CH3
9
12i
12j
d
d
d
d
d
d
d
d
20
1
96
87
NO2
CH3
10
MeO
O2N
NO2
CH3
11
12k
d
d
d
d
1
82
a
Heating at 120 ꢀC.
Heating at 140 ꢀC.
b

1656
R.S. Kusurkar et al. / Tetrahedron 64 (2008) 1654e1662
dehydrogenation by refluxing with Pd/C (5%) in xylene fur-
nished 1,4-disubstituted-b-carboline 15a. There is a report of
formation of two diastereomers in a similar PicteteSpengler
condensation using sulfuric acid in water.5a In contrast to
this, condensation using trimethylsilylchloride in dichlorome-
thane gave diastereoselectively only one product 14a.
After establishing the route from nitro compound 12a to
b-carboline 15a, all nitro compounds (12be12f and 12i) were
reduced with freshly prepared Raney Nickel in methanol to
amino compounds (13be13f and 13i). The nitro compound
12e gave reduction of aromatic nitro group (13l) initially. After
continuing the reaction for longer time, both the nitro groups
were reduced to get 13e.
Further, treatment of amino compounds (13be13f) with
benzaldehyde in the presence of trimethylsilylchloride in di-
chloromethane furnished new 1,4-disubstituted THbCs (14be
14f, Scheme 2). In this reaction, amines 13a and 13de13f
gave only one product in each reaction while the amines 13b
and 13c furnished two products. The products were separated
and characterized. On the basis of the spectral data, the products
were initially considered to be diastereomeric mixture of 14b
and 14c, respectively. Surprisingly during the PicteteSpengler
reaction with 13d, 1,4-disubstituted-b-carboline was also de-
tected in 10% yield along with THbC 14d. In all other similar
reactions, TLC indicated the presence of dehydrogenated prod-
uct in minor amount.
Figure 1. ORTEP diagram of the 15b molecule with 50% probability.
In the last step, refluxing THbCs (14be14d) with Pd/C in
xylene furnished 1,4-disubstituted-b-carbolines (15be15d).
Surprisingly, when the diastereomeric mixture of 14b was
dehydrogenated, two products were resulted, which was not
expected from the mixture of diastereomers of tetrahydro-
b-carbolines. Both of them were showing only aromatic pro-
NMR data that b-carboline showed C3eH (8.45), upfield
than that of g-carboline (8.56). Protons of two methoxyl
groups were resonating at different positions (4.01 and 3.91)
in the case of b-carboline, however, they showed a singlet
(3.96) in g-carboline. Surprisingly, in 13C NMR, b-carboline
showed only one singlet (56.0) for both the methoxyls while
g-carboline indicated two singlets (56.1 and 56.0).
The formation of two dehydrogenated products ruled out the
possibility of formation of two diastereomers of THbCs in the
previous reaction. From the mode of formation, the two prod-
ucts formed in the PicteteSpengler condensation were shown
1
tons and carbons in H NMR and 13C NMR, respectively.
The mass spectrum showed Mþ at 380 for both the com-
pounds. The spectral data was not sufficient to confirm the
structures of these compounds. Finally these products were
shown to be b-carboline 15b and g-carboline 17b by single
1
crystal X-ray analysis (Figs. 1 and 2). It was noted from H
Ar
Ar
Ar
R
R
R
(ii)
(i)
N
N
NH2
NO2
N
H
N
H
H
Ph
13
12
Ph
Ar
Ph
Ar
Ar
R
N
R
(iii)
NH
+
R
N
+
N
H
NH
N
H
N
H
R
N
H
14
Ar
Ph
Ph
16
15
17
12a, 13a, 14a, 15a: Ar = phenyl, R = H; 12b, 13b, 14b, 15b, 16b, 17b: Ar =3,4-dimethoxyphenyl, R = H; 12c, 13c, 14c,
15c, 16c, 17c: Ar = 3,4-methylenedioxyphenyl, R = H; 12d, 13d, 14d, 15d: Ar = 2-furyl, R = H; 12e, 13e, 14e:
Ar = p-aminophenyl, R = H; 12f, 13f, 14f: Ar = 2-thienyl, R = H; 12i, 13i: Ar = 2-furyl, R = methyl.
Scheme 2. Reagents and conditions: (i) Raney Nickel/MeOH; (ii) Si(CH3)3Cl, PhCHO, DCM, 88 h, 0e25 ꢀC; (iii) Pd/C (5%), xylene, reflux.

R.S. Kusurkar et al. / Tetrahedron 64 (2008) 1654e1662
1657
OMe
MeO
OMe
OMe
OMe
OMe
N H
1
+
+
N
N
N
N
H
N
H
H
H
H
H
Bond 1 migration.
OMe
MeO
N
H
2
H
+
H
N
N
+
N
H
N
H
N
H
H
OCH3
OCH3
OCH3
OCH3
Bond 2 migration.
Scheme 3.
Figure 2. ORTEP diagram of the 17b molecule with 50% probability.
and two g-carbolines. A successful use of microwave-assisted
reaction was demonstrated in one of the steps in the whole
sequence. Formation of all products as THbCs, THgCs, b-car-
boline, and g-carboline gave a strong evidence for a spiroindo-
lenium intermediate. The migration of both the bonds in the
spiro intermediate, giving regioisomers, was demonstrated
for the first time after confirmation by single crystal X-ray
analysis.
to be tetrahydro-b-carboline 14b and tetrahydro-g-carboline
16b. Dehydrogenation of 14c gave similar results (Table 2).
The formation of two diastereomers of 14a in the reported5a
reaction using sulfuric acid in water was confirmed by the
dehydrogenation of the mixture of diastereomers using Pd/C
(5%), which resulted in the formation of only one product 15a.
The formation of two regioisomers 14b and 16b could be
explained as follows. The reported mechanism for the
PicteteSpengler condensation is through the five-membered
spiro intermediate,8 which would rearrange to six-membered
heterocyclic ring. There are two possibilities for this rear-
rangement. Migration of bond 1 would give 1,4-disubsti-
tuted-tetrahydro-b-carboline 14b, while bond 2 migration
would furnish the formation of 1,4-disubstituted-tetrahydro-
g-carboline 16b (Scheme 3). In the above two cases the migra-
tory aptitude of bond 2 would be increased due to electron
donating methoxy groups present on the phenyl ring, thus mi-
gration of both the bonds 1 and 2 would furnish b-carboline
and g-carboline, respectively. In all other cases probably there
would be a large difference in the migratory aptitudes resulting
in selective migration of bond 1 and formation of only THbCs.
This is the first report showing the migration of both the
bonds, furnishing tetrahydro b- and g-carbolines, which can
be explained only by involvement of a spiroindolenium
intermediate.
4. Experimental
4.1. General
Thin-layer chromatographic analysis was performed using
silica gel on glass plates and was detected under UV. All
recorded melting points are uncorrected. The 1H and 13C
NMR spectra were recorded as d values in CDCl3 (DMSO-
d6 when required) with reference to TMS as internal standard
on a Varian Mercury instrument (300 MHz for 1H and 75 MHz
for 13C). FTIR spectra were recorded on a PerkineElmer
1600. Mass spectra were recorded on a Shimadzu QP 5050.
Elemental analysis was recorded on Flash E.A. 1112 Thermo.
Table 2
Yields and ratios of 16/14 and 17/15
Compounds number
Total yield (%)
Ratio
3. Conclusions
16b/14b
17b/15b
16c/14c
17c/15c
40
81
49
70
1:4
1:4
Using PicteteSpengler condensation, five new 1,4-disubsti-
tuted THbCs and two THgCs were synthesized. Further
dehydrogenation gave four new 1,4-disubstituted b-carbolines
1:4.4
1:4.4

1658
R.S. Kusurkar et al. / Tetrahedron 64 (2008) 1654e1662
4.2. General procedure for reaction of nitro-olefins
with indole using microwave irradiation
(2H, m, ArH), 7.1 (1H, t, J¼7.4 Hz, ArH), 7.3 (1H, d,
J¼8.0 Hz, C7H of indole ring), 7.38 (1H, d, J¼8.0 Hz, C4H of
indole ring), 8.4 (1H, br s, exchangeable with D2O, NH); dC
(75 MHz, CDCl3þDMSO-d6) 42.5, 44.2, 99.2, 106.5, 106.8,
110.0, 113.9, 117.0, 117.2, 119.5, 119.8, 120.2, 125.1, 135.1,
144.4, 146.0; MS m/z 280 (Mþ), 278, 252, 250 (100%), 220,
204, 191, 115.
A
mixture of indole (0.0012 mol) and nitro-olefin
(0.001 mol) was loaded on silica gel (60e120 mesh) and irradi-
ated in a microwave oven. The completion of the reaction was
confirmed by TLC. The same silica gel was loaded on a silica-
gel column, and chromatographic separation using hexanee
ethyl acetate furnished the products (12ae12k).
4.3.4. 2-(2-Furyl)-2-(3-indolyl)-1-aminoethane11 (13d)
Blackish solid; yield 88.5%; mp 142e143 ꢀC; [Found: C,
74.40; H, 6.41; N, 12.80. C14H14N2O requires: C, 74.31; H,
6.24; N, 12.38%]; nmax (Nujol) 3356, 3292 cmꢁ1; dH
(300 MHz, CDCl3) 1.6 (2H, br s, exchangeable with D2O,
NH2), 3.26e3.42 (2H, m, C1H2), 4.33 (1H, t, J¼7.3 Hz,
C2H), 6.12 (1H, dd, J¼2.3, 0.9 Hz, furyl ring proton), 6.3
(1H, t, J¼2.3 Hz, furyl ring proton), 7.03e7.16 (2H, m, indole
ringþfuryl ring protons), 7.2 (1H, t, J¼7.9 Hz, indole ring
proton), 7.36 (2H, br d, J¼8.5 Hz, C2H and C7H of indole
ring), 7.57 (1H, d, J¼7.9 Hz, C4H indole ring), 8.18 (1H, br
s, exchangeable with D2O NH); dC (75 MHz, CDCl3) 40.9,
45.9, 106.3, 110.4, 111.6, 114.7, 119.4, 119.7, 122.3, 122.6,
126.7, 136.6, 141.5, 156.4; MS m/z 226 (Mþ), 196 (100%),
195, 167, 141, 139, 115.
4.3. Catalytic hydrogenation of 2-(aryl)-2-(3-indolyl)-1-
nitroethane (12ae12f and 12i)9
2-(Aryl)-2-(3-indolyl)-1-nitroethane (0.002 mol) in metha-
nol and Raney Nickel were treated with hydrogen at 70 psi
in Parr low pressure hydrogen apparatus for 2e48 h. The
catalyst was filtered off and the filtrate was concentrated by
vacuum distillation. Ether was added so that the products
(13ae13f and 13i) readily separated out.
4.3.1. 2-Phenyl-2-(3-indolyl)-1-aminoethane (13a)
Brown solid; yield 95%; mp 130 ꢀC (lit10 mp 131e132 ꢀC);
[Found: C, 81.80; H, 6.48; N, 11.71. C16H16N2 requires: C,
81.32; H, 6.82; N, 11.85%]; nmax (KBr) 3411, 3348,
3143 cmꢁ1; dH (300 MHz, CDCl3) 1.54 (2H, br s, exchangeable
with D2O, NH2), 3.30 (1H, dd, J¼7.0, 12.8 Hz, C1H), 3.44 (1H,
dd, J¼7.0, 12.8 Hz, C1H), 4.24 (1H, t, J¼7.0 Hz, C2H), 7.02
(2H, t, J¼7.0, indole ring protons), 7.12e7.22 (2H, m, ArH),
7.24e7.39 (5H, m, ArH), 7.46 (1H, d, J¼7.9 Hz, C4H of indole
ring), 8.31 (1H, br s, exchangeable with D2O, NH); dC (75 MHz,
CDCl3) 46.6, 47.1, 111.1, 117.2, 119.3, 122.1, 126.4, 126.9,
128.4, 136.4, 142.7; MS m/z 236 (Mþ), 206 (100%).
4.3.5. 2-(4-Aminophenyl)-2-(3-indolyl)-1-aminoethane
(13e)
Brown solid; yield 80%; mp 125e127 ꢀC; [Found: C, 76.34;
H, 6.77; N, 16.88. C16H17N3 requires: C, 76.46; H, 6.82; N,
16.72%]; nmax (KBr) 3645, 3570 cmꢁ1; dH (300 MHz,
CDCl3) 2.8 (4H, br s, exchangeable with D2O, 2ꢂNH2), 3.13
(1H, dd, J¼7.2, 12.4 Hz, C1H), 3.28 (1H, dd, J¼7.2, 12.4 Hz,
C1H), 4.07 (1H, t, J¼7.2 Hz, C2H), 6.54 (2H, d, J¼8.0 Hz,
ArH ortho to NH2), 6.88 (1H, t, J¼7.7 Hz, indole ring proton),
6.9e7.05 (4H, m, meta to NH2þindole ring protons), 7.3 (1H,
d, J¼8.0 Hz, C7H indole ring), 7.36 (1H, d, J¼7.7 Hz, C4H of
indole ring), 10.37 (1H, br s, exchangeable with D2O, NH); dC
(75 MHz, CDCl3þDMSO-d6) 44.7, 46.2, 110.1, 113.4, 115.9,
117.1, 117.7, 119.9, 120.1, 125.7, 127.3, 130.8, 135.3, 144.4;
MS m/z 251 (Mþ), 221 (100% MþꢁCH2NH2), 204, 192, 177.
4.3.2. 2-(3,4-Dimethoxyphenyl)-2-(3-indolyl)-1-amino-
ethane (13b)
White solid; yield 92%; mp 195 ꢀC; [Found: C, 72.48; H,
6.30; N, 9.92. C18H20N2O2 requires: C, 72.95; H, 6.80; N,
9.45%]; nmax (KBr) 3275 cmꢁ1 (broad); dH (300 MHz,
CDCl3) 1.88 (2H, br s, exchangeable with D2O, NH2), 3.25
(1H, m, C1H), 3.40 (1H, m, C1H), 3.8 (3H, s, OCH3), 3.85
(3H, s, OCH3), 4.20 (1H, t, J¼6.3 Hz, C2H), 6.72e6.9 (3H,
m, ArH), 6.94e7.08 (2H, m, ArH), 7.13 (1H, t, J¼7.4 Hz,
ArH), 7.30 (1H, d, J¼7.7 Hz, C7H of indole ring), 7.44 (1H,
d, J¼7.7 Hz, C4H of indole ring), 8.28 (1H, br s, exchangeable
with D2O, NH); dC (75 MHz, CD3OD) 42.3, 45.1, 56.5, 112.5,
112.9, 113.2, 114.9, 119.5, 120.0, 121.4, 122.8, 123.1, 127.5,
134.5, 138.4, 149.7, 151.0; MS m/z 296 (Mþ), 266 (100%),
265, 250, 234, 204, 178, 130, 76.
4.3.6. 2-(4-Aminophenyl)-2-(3-indolyl)-1-nitroethane (13l)
Orange solid; yield 10%; mp 138e140 ꢀC; [Found: C, 68.41;
H, 5.80; N, 15.38. C16H15N3O2 requires: C, 68.31; H, 5.37; N,
14.94%]; nmax (KBr) 3425, 3348, 3288, 1547, 1380 cmꢁ1; dH
(300 MHz, CDCl3) 3.57 (2H, br s, exchangeable with D2O,
NH2), 4.80 (1H, dd, J¼7.7, 11.3 Hz, C1H), 4.93e5.05 (2H,
m, C1HþC2H), 6.55 (2H, d, J¼7.4 Hz, ArH ortho to NH2),
6.89 (1H, s, C2H of indole ring), 7.03 (3H, m, meta to
NH2þindole ring proton), 7.13 (1H, t, J¼7.7 Hz, indole ring
proton), 7.26 (1H, d, J¼8.0 Hz, C7H of indole ring), 7.40
(1H, d, J¼7.7 Hz, C4H of indole ring), 8.03 (1H, br s, exchange-
able with D2O, NH); dC (75 MHz, CDCl3) 40.9, 79.8, 111.2,
114.7, 115.3, 118.9, 119.7, 121.4, 122.4, 126.0, 128.5, 128.8,
136.3, 145.5; MS m/z 281 (Mþ), 247, 234, 221 (100%), 204,
143, 130, 117.
4.3.3. 2-(3,4-Methylenedioxyphenyl)-2-(3-indolyl)-1-
aminoethane (13c)
White solid; yield 88%; mp 219 ꢀC; [Found: C, 72.96; H,
5.87; N, 10.30. C17H16N2O2 requires: C, 72.84; H, 5.75; N,
9.99%]; nmax (KBr) 3325 cmꢁ1 (broad); dH (300 MHz,
CDCl3) 3.0e3.4 (4H, 2ꢂbr m changes to 2ꢂm after D2O
exchange, C1H2þNH2), 4.2 (1H, br t, J¼6.6 Hz, C2H), 5.84,
5.86 (2H, 2ꢂbr s, OCH2O), 6.55e6.8 (3H, m, ArH), 6.9e7.02

R.S. Kusurkar et al. / Tetrahedron 64 (2008) 1654e1662
1659
4.3.7. 2-(2-Thienyl)-2-(3-indolyl)-1-aminoethane11 (13f)
143.0, 182.0; MS m/z 324 (Mþ), 295 (100%), 218; DEPT
showed the presence of one CH2 group and 11 CH groups,
CH3 group was absent.
Brown solid; yield 91%; mp 121 ꢀC; [Found: C, 69.50; H,
5.98; N, 12.02. C14H14N2S requires: C, 69.39; H, 5.82; N,
11.56%]; nmax (KBr) 3358, 3296, 3450 cmꢁ1; dH (300 MHz,
CDCl3) 1.5 (2H, br s, exchangeable with D2O, NH2), 3.28e3.5
(2H, m, C1H2), 4.52 (1H, t, J¼7.0 Hz, C2H), 6.94 (2H, d,
J¼3.5 Hz, thienyl ring protons), 7.1 (1H, t J¼7.9 Hz, indole
ring proton), 7.05e7.24 (3H, m, ArHþthienyl ring protons),
7.38 (1H, d, J¼7.9 Hz, C7H of indole ring), 7.55 (1H, d,
J¼7.9 Hz, C4H of indole ring), 8.11 (1H, br s, exchangeable
with D2O, NH); dC (75 MHz, CDCl3þDMSO-d6) 38.7, 39.0,
110.8, 115.0, 117.9, 118.0, 120.6, 121.4, 122.6, 123.4, 125.7,
135.8,146.7;MSm/z212(MþꢁCH2NH2),58, 44, 42(100%), 40.
4.4.2. 1-Phenyl-4-(3,4-dimethoxyphenyl)-1,2,3,4-
tetrahydro-b-carboline (14b)
Pale yellow solid; yield 32%; mp 190 ꢀC; [Found: C, 78.60;
H, 6.38; N, 7.70. C25H24N2O2 requires: C, 78.10; H, 6.29; N,
7.29%]; nmax (KBr) 3446 cmꢁ1 (broad); dH (300 MHz, CDCl3)
3.06 (1H, dd, J¼5.3, 12.8 Hz, C3H), 3.58 (1H, dd, J¼5.3,
12.8 Hz, C3H), 3.78 (3H, s, OCH3), 3.89 (3H, s, OCH3),
4.35 (1H, m, C4H), 4.66 (1H, br s, exchangeable with D2O,
NH), 5.39 (1H, br s, C1H), 6.75e6.90 (5H, m, ArH), 7.07
(1H, t, J¼5.9 Hz, ArH), 7.24 (1H, m, ArH), 7.37 (5H, br s,
ArH), 7.59 (1H, br s, exchangeable with D2O, NH of indole
ring); dC (75 MHz, CDCl3) 40.8, 52.1, 55.9, 57.7, 110.7,
111.1, 111.4, 112.6, 119.3, 120.0, 121.7, 128.7, 128.9,
134.3, 134.6, 135.9, 139.7, 147.6, 148.8; MS m/z 384 (Mþ),
355 (100%), 340, 278, 218, 178.
4.3.8. 1-Methyl-2-(2-furyl)-2-(3-indolyl)-1-aminoethane
(13i)
Blackish solid; yield 95%; mp 152e153 ꢀC; [Found: C,
75.29; H, 6.88; N, 11.76. C15H16N2O requires: C, 74.97; H,
6.71; N, 11.66%]; nmax (KBr) 3649, 3568 cmꢁ1; dH (300 MHz,
CDCl3) 1.15(3H, d, J¼2.8 Hz, CH3), 2.3(2H, br s, exchangeable
with D2O, NH2), 3.7 (1H, m, C1H), 4.18 (1H, d, J¼7.7 Hz, C2H),
6.13 (1H, br s, furyl ring proton), 6.27 (1H, br s, furyl ring
proton), 7.0e7.4 (5H, m, ArHþfuryl ring protons), 7.68 (1H,
d, J¼7.7 Hz, C4H indole ring), 8.44 (1H, br s, exchangeable
with D2O, NH); dC (75 MHz, CDCl3þDMSO-d6) 21.2, 45.1,
50.1, 105.9, 109.7, 111.2, 113.1, 118.8, 121.3, 122.8, 126.7,
136.0, 140.6, 156.0 (minor signals probably of other diastereo-
mer are also seen in the spectrum); MS m/z 196
(MþꢁCH3CHNO2), 167, 115.
4.4.3. 4-Phenyl-1-(3,4-dimethoxyphenyl)-1,2,3,4-
tetrahydro-g-carboline (16b)
White solid; yield 8%; mp 210 ꢀC; [Found: C, 78.55; H, 6.63;
N, 7.78. C25H24N2O2 requires: C, 78.10; H, 6.29; N, 7.29%];
nmax (KBr) 3346 cmꢁ1 (broad); dH (300 MHz, CDCl3þ
DMSO-d6) 2.59 (1H, br s, exchangeable with D2O, NH), 3.65e
3.78 (2H, m, C2H2), 3.82 (3H, s, OCH3), 3.87 (3H, s, OCH3),
4.69 (1H, br s, C1H), 5.64 (1H, s, C4H), 6.54 (1H, d, J¼
8.2 Hz, ArH), 6.74e6.84 (3H, m, ArH), 6.89 (1H, d, J¼8.2 Hz,
ArH), 7.0 (1H, t, J¼7.7 Hz, ArH), 7.29 (1H, d, J¼7.7 Hz, ArH),
7.36e7.42 (3H, m, ArH), 7.48e7.56 (2H, m, ArH), 10.21 (1H,
br s, exchangeable with D2O, NH of indole ring); dC (75 MHz,
CDCl3þDMSO-d6) 40.3, 50.3, 54.7, 56.5, 110.3, 110.6, 117.2,
117.9, 119.8, 124.2, 126.9, 126.9, 127.8, 133.3, 134.9, 142.0,
146.5, 147.5; Ms m/z 384 (Mþ), 355 (100%), 340, 278.
4.4. General procedure for synthesis of tetrahydro b- or g-
carboline from amino compounds (13ae13f)
To the solution of amino compounds (0.002 mol) in di-
chloromethane, benzaldehyde (0.0024 mol) was added, the so-
lution was cooled and trimethylsilylchloride (0.004 mol) was
added to it. The reaction mixture was stirred at 0 ꢀC for 1 h
and then at room temperature for 41 h. Trimethylsilylchloride
(0.004 mol) was added again and stirring was continued fur-
ther for 47 h. The reaction mixture was diluted with dichloro-
methane, washed with 10% NaOH and brine. The combined
organic layer was dried over sodium sulfate and concentrated.
The crude product obtained was chromatographed on silica gel
using pet-ether and ethyl acetate as an eluent yielding tetra-
hydro b- or g-carboline.
4.4.4. 1-Phenyl-4-(3,4-methylenedioxyphenyl)-1,2,3,4-
tetrahydro-b-carboline (14c)
Pale yellow solid; yield 40%; mp 189 ꢀC; [Found: C, 77.99;
H, 5.67; N, 7.30. C24H20N2O2 requires: C, 78.24; H, 5.47; N,
7.6%]; nmax (Nujol) 3387, 3346 cmꢁ1; dH (300 MHz, CDCl3)
1.9 (1H, br s, exchangeable with D2O, NH), 3.0 (1H, dd,
J¼5.2, 12.6 Hz, C3H), 3.52 (1H, dd, J¼5.2, 12.6 Hz, C3H),
4.32 (1H, br t, J¼5.2 Hz, C4H), 5.30 (1H, br s, C1H), 5.93
(2H, br s, OCH2O), 6.7 (1H, s, ArH), 6.54e6.57 (2H, m,
ArH), 6.94 (2H, m, ArH), 7.03e7.14 (1H, m, ArH), 7.21e
7.27 (1H, d, J¼8.2 Hz, ArH), 7.36 (5H, br m, ArH), 7.55 (1H,
s, exchangeable with D2O, NH of indole ring); dC (75 MHz,
CDCl3) 41.2, 52.7, 58.0, 100.8, 108.1, 108.6, 110.7, 112.5,
119.3, 119.8, 121.3, 121.5, 126.6, 128.3, 128.5, 128.8, 135.7,
135.9, 137.1, 141.4, 146.1, 147.6; MS m/z 277 (MþꢁC7H7,
100%), 118 (MþꢁC8H8N), 89, 76.
4.4.1. 1,4-Diphenyl-1,2,3,4-tetrahydro-b-carboline (14a)
Yellow solid; yield 48.5%; mp 189 ꢀC; [Found: C, 84.93; H,
6.38; N, 8.28. C23H20N2 requires: C, 85.15; H, 6.21; N, 8.63%];
nmax (KBr) 3406, 3686 cmꢁ1; dH (300 MHz, CDCl3) 1.87 (1H,
br s, exchangeable with D2O, NH), 3.02 (1H, dd, J¼7.2,
12.7 Hz, C3H), 3.53 (1H, dd, J¼7.2, 12.7 Hz, C3H), 4.37 (1H,
br t, J¼7.2 Hz, C4H), 5.25 (1H, s, C1H), 6.83 (2H, m, ArH),
7.04 (1H, t, J¼7.7 Hz, ArH), 7.12e7.40 (11H, m, ArH), 7.64
(1H, br s, exchangeable with D2O, NH of indole ring); dC
(75 MHz, CDCl3) 41.7, 52.9, 58.2, 110.7, 112.5, 119.3, 119.8,
121.5, 126.5, 126.7, 128.4, 128.5, 128.9, 135.8, 135.9, 141.4,
4.4.5. 4-Phenyl-1-(3,4-methylenedioxyphenyl)-1,2,3,4-
tetrahydro-g-carboline (16c)
Pale yellow solid; yield 9%; mp 195 ꢀC; [Found: C, 78.52; H,
5.57; N, 7.91. C24H20N2O2 requires: C, 78.24; H, 5.47; N,

1660
R.S. Kusurkar et al. / Tetrahedron 64 (2008) 1654e1662
7.6%]; nmax (KBr) 3446 cmꢁ1 (broad); dH (300 MHz, CDCl3)
1.61 (1H, br s, exchangeable with D2O, NH), 3.22 (1H, br d,
J¼12.9 Hz, C2H), 3.48 (1H, dd, J¼5.0, 12.9 Hz, C2H), 4.23
(1H, br s, C1H), 5.22 (1H, br s, C4H), 5.93 (2H, br s,
OCH2O), 6.70e6.90 (4H, m, ArH), 7.0 (1H, t, J¼7.3 Hz,
ArH), 7.1e7.22 (3H, m, ArH), 7.33e7.50 (4H, br s, ArH),
7.65 (1H, br s, exchangeable with D2O, NH of indole ring);
dC (75 MHz, CDCl3) 39.2, 51.5, 57.9, 100.8, 108.1, 108.7,
110.8, 112.0, 119.1, 119.5, 121.3, 121.9, 126.9, 128.3, 128.5,
128.9, 135.6, 136.0, 138.1, 141.2, 146.1, 147.7; Ms m/z 368
(Mþ) (339, 100%), 309, 307, 278, 262, 204.
4.5. General procedure for dehydrogenation of THbCs or
THgCs
A mixture of THbCs or THgCs (0.10 g), 5% Pd/C (50 mg),
and dry xylene (5 ml) was refluxed for 1e4 h. The reaction
mixture was cooled and ethyl acetate (10 ml) was added to
it. The catalyst was filtered off through Celite and the filtrate
was concentrated by vacuum distillation. The crude product
obtained was chromatographed on neutral alumina using pet-
ether and ethyl acetate as an eluent yielding b- and g-carboline
(15ae15d and 17b, 17c).
4.4.6. 4-(2-Furyl)-1-phenyl-1,2,3,4-tetrahydro-b-
carboline (14d)
4.5.1. 1,4-Diphenyl-b-carboline (15a)
Yellow solid; yield 81%; mp 125 ꢀC; [Found: C, 86.32; H,
5.35; N, 8.32. C23H16N2 requires: C, 86.22; H, 5.03; N,
8.74%]; nmax (KBr) 3427 cmꢁ1; dH (300 MHz, CDCl3) 7.0e
7.1 (1H, m, Ph), 7.40e7.61 (8H, m, ArH), 7.66 (3H, br d,
J¼7.4 Hz, ArH), 7.94 (2H, d, J¼8.0 Hz, ArH), 8.4 (1H, s,
C3H), 9.0 (1H, br s, exchangeable with D2O, NH); dC
(75 MHz, CDCl3) 111.4, 119.8, 121.4, 123.4, 127.2, 128.1,
128.2, 128.6, 128.7, 129.1, 129.3, 130.9, 133.2, 137.5, 137.9,
139.4, 140.5, 141.6; MS m/z 320 (Mþ 100%), 291, 242, 241,
216, 215.
Pale yellow solid; yield 49.3%; mp 150 ꢀC; [Found: C, 79.98;
H, 5.64; N, 8.83. C21H18N2O requires: C, 80.23; H, 5.77; N,
8.91%]; nmax (KBr) 3400 cmꢁ1 (broad); dH (300 MHz, CDCl3)
1.25 (1H, br s, exchangeable with D2O, NH), 3.25 (1H, dd,
J¼5.0, 12.7 Hz, C3H), 3.48 (1H, dd, J¼5.0, 12.7 Hz, C3H), 4.42
(1H, t, J¼5.0 Hz, C4H), 5.20 (1H, br s, C1H), 6.06 (1H, d,
J¼3.0 Hz, furyl ring proton), 6.3 (1H, dd, J¼1.9, 3.0 Hz, furyl
ring proton), 6.94e7.04 (1H, m, ArH), 7.1 (2H, distorted dt,
J¼3.6, 8.0 Hz, ArHþfuryl ring protons), 7.2e7.48 (7H, m,
ArH), 7.61 (1H, br s, exchangeable with D2O, NH of indole
ring); dC (75 MHz, CDCl3) 34.4, 47.5, 57.2, 106.6, 110.1, 110.4,
110.8, 119.0, 119.4, 121.7, 126.5, 128.1, 128.5, 128.7, 135.0,
135.7, 141.3, 156.1; Ms m/z 314 (Mþ) (285, 100%), 268, 256.
4.5.2. 1-Phenyl-4-(3,4-dimethoxyphenyl)-b-carboline (15b)
Pale yellow solid; yield 65.4%; mp 199 ꢀC; [Found: C,
78.57; H, 5.50; N, 7.60. C25H20N2O2 requires: C, 78.93; H,
5.30; N, 7.36%]; nmax (KBr) 3325 cmꢁ1; dH (300 MHz,
CDCl3) 3.91 (3H, s, OCH3), 4.01 (3H, s, OCH3), 7.09 (2H,
m, ArH), 7.18e7.28 (2H, m, ArH), 7.44e7.54 (3H, m,
ArH), 7.6 (2H, t, J¼7.1 Hz, ArH), 7.77 (1H, d, J¼8.0 Hz,
C5H of indole ring), 7.97 (2H, d, J¼7.2 Hz, ArH), 8.45 (1H,
s, C3H), 8.65 (1H, br s, exchangeable with D2O, NH); dC
(75 MHz, CDCl3) 56.0, 111.3, 111.5, 112.4, 120.0, 121.5,
123.6, 128.1, 128.4, 128.9, 129.2, 129.9, 130.9, 133.2,
139.0, 140.7, 148.8; MS m/z 380 (Mþ 100%), 363.
4.4.7. 1-Phenyl-4-(4-aminophenyl)-1,2,3,4-tetrahydro-b-
carboline (14e)
Brown solid; yield 20%; mp 175 ꢀC; [Found: C, 81.47; H,
6.50; N, 12.02. C23H21N3 requires: C, 81.38; H, 6.24; N,
12.38%]; nmax (KBr) 3421, 3336, 3174 cmꢁ1; dH (300 MHz,
CDCl3) 3.0 (1H, t, J¼10.5 Hz, C3H), 3.50 (3H, m, with D2O
changes to dd, C3HþNH2), 4.36 (1H, m, C4H), 5.30 (2H, d,
with D2O changes to s, NHþC1H), 6.65 (2H, d, J¼7.6 Hz,
ArH), 6.95 (2H, br s, ArH), 7.0e7.20 (3H, m, ArH), 7.38
(6H, br s, ArH), 7.52 (1H, br s, exchangeable with D2O, NH
of indole ring); dC (75 MHz, CDCl3) 40.8, 58.1, 58.2, 110.7,
113.0, 115.3, 119.1, 120.0, 121.4, 126.8, 128.3, 128.6, 128.9,
129.2, 133.1, 135.7, 135.9, 141.5, 144.6; MS m/z 310
(MþꢁCH2NH), 233 (MþꢁPhCH2NH), 116 (MþꢁC6H6).
4.5.3. 4-Phenyl-1-(3,4-dimethoxyphenyl)-g-carboline (17b)
Pale yellow solid; yield 16.2%; mp 205 ꢀC; [Found: C,
78.79; H, 5.51; N, 7.39. C25H20N2O2 requires: C, 78.93; H,
5.30; N, 7.36%]; nmax (KBr) 3329 cmꢁ1; dH (300 MHz,
CDCl3) 3.96 (6H, s, 2ꢂOCH3), 7.06 (1H, d, J¼8.3 Hz, ArH),
7.13 (1H, br t, J¼9.9 Hz, ArH), 7.19 (1H, d, J¼1.9 Hz,
ArH), 7.24e7.32 (2H, m, ArHþCDCl3), 7.38e7.49 (2H, m,
ArH), 7.53e7.64 (3H, m, ArH), 7.76 (1H, d, J¼8.0 Hz, C5H
of indole ring), 7.86 (2H, dd, J¼8.0, 1.7 Hz, ArH), 8.56 (1H,
s, C2H), 8.84 (1H, br s, exchangeable with D2O, NH); dC
(75 MHz, CDCl3) 56.0, 56.1, 111.0, 111.6, 111.7, 117.1,
119.4, 120.5, 120.7, 121.8, 122.5, 126.8, 128.0, 128.4, 128.8,
128.9, 139.5, 140.0, 142.7, 142.9, 148.9, 149.5, 153.2; MS m/z
380 (Mþ 100%), 363, 319, 305, 243, 190, 77.
4.4.8. 4-(2-Thienyl)-1-phenyl-1,2,3,4-tetrahydro-b-
carboline (14f)
Brown solid; yield 42.9%; mp 190 ꢀC; [Found: C, 76.12; H,
5.69; N, 8.64. C21H18N2S requires: C, 76.33; H, 5.49; N,
8.48%]; nmax (Nujol) 3321, 3392 cmꢁ1; dH (300 MHz,
CDCl3) 1.9 (1H, br s, exchangeable with D2O, NH), 3.13 (1H,
dd, J¼7.4, 12.9 Hz, C3H), 3.56 (1H, dd, J¼7.4, 12.9 Hz,
C3H), 4.66 (1H, t, J¼7.4 Hz, C4H), 5.25 (1H, br s, C1 H),
6.95e7.01 (3H, m, thienyl protons), 7.05e7.14 (2H, m, ArH),
7.15e7.24 (2H, m, ArH), 7.27e7.40 (5H, m, ArH), 7.74 (1H,
br s, exchangeable with D2O, NH of indole ring); dC
(75 MHz, CDCl3) 34.8, 49.8, 55.8, 110.4, 110.7, 117.7, 117.8,
120.1, 122.6, 123.6, 125.4, 125.5, 126.8, 127.5, 127.7, 134.1,
135.3, 141.2, 147.1; MS m/z 301 (MþꢁCH2NH).
4.5.4. 1-Phenyl-4-(3,4-methylenedioxyphenyl)-b-
carboline (15c)
Pale yellow solid; yield 57%; mp 155 ꢀC; [Found: C, 79.34;
H, 4.62; N, 7.44. C24H16N2O2 requires: C, 79.11; H, 4.43; N,
7.69%]; nmax (KBr) 3304 cmꢁ1; dH (300 MHz, CDCl3) 6.1

R.S. Kusurkar et al. / Tetrahedron 64 (2008) 1654e1662
1661
(2H, br s, OCH2O), 7.0 (1H, d, J¼8.5 Hz, ArH), 7.06e7.2 (3H,
m, ArH), 7.44e7.52 (3H, m, ArH), 7.58 (2H, t, J¼7.2 Hz, ArH),
7.8 (1H, d, J¼8.3 Hz, C5H of indole ring), 7.98 (2H, d,
J¼8.3 Hz, ArH), 8.40 (1H, s, C3H), 8.74 (1H, br s, exchangeable
with D2O, NH); dC (75 MHz, CDCl3) 101.2, 108.5, 109.7, 111.4,
119.8, 121.4, 122.8, 123.5, 127.2, 128.05, 128.1, 128.7, 129.1,
130.6, 131.3, 133.2, 138.0, 139.5, 140.5, 141.5, 147.5, 147.7;
MS m/z 364 (Mþ 100%), 335, 181, 153.
effects using SAINT and SADABS programs. SHELX-97
(ShelxTL)12 was used for structure solution and full matrix
least squares refinement on F2. The regiochemistry of all the
molecules was confirmed by single crystal X-ray analysis
like difference in the pattern of H-bonding (Supplementary
data).
5.1.1. Crystal data for 15b (C25H20N2O2)
M¼380.43, yellow colored crystal, grown from a mixture
of ethanol and water, approximate size 0.32ꢂ0.25ꢂ0.04 mm,
multiscan data acquisition. Total scans¼5, total frames¼3030,
exposure/frame¼15.0 s/frame, q range¼2.06e25.00ꢀ, com-
pleteness to q of 25.0ꢀ is 100%. Monoclinic, space group
4.5.5. 4-Phenyl-1-(3,4-methylenedioxyphenyl)-g-
carboline (17c)
Pale yellow solid; yield 13%; mp 234 ꢀC; [Found: C, 79.20;
H, 4.02; N, 7.52. C24H16N2O2 requires: C, 79.11; H, 4.43; N,
7.69%]; nmax (KBr) 3420 cmꢁ1; dH (300 MHz, CDCl3) 5.9
(2H, s, OCH2O), 6.90 (1H, d, J¼7.7 Hz, ArH), 7.02e7.20
(3H, m, ArH), 7.45 (1H, t, J¼7.7, Hz, indole ring proton),
7.5e7.67 (4H, m, ArH), 7.72 (1H, d, J¼7.9 Hz, C5H of indole
ring), 7.85 (2H, br s, ArH), 8.40 (1H, s, C2H), 9.9 (1H, br s,
exchangeable with D2O, NH); dc (75 MHz, CDCl3þDMSO-
d6) 99.9, 107.6, 107.7, 110.6, 115.6, 118.0, 118.4, 119.6,
120.3, 120.9, 125.1, 127.0, 127.3, 127.5, 127.9, 138.7,
139.2, 141.0, 141.2, 145.9, 146.6, 151.2; MS m/z 364 (Mþ
100%), 363, 333, 167, 152.
˚
P21/n, a¼10.7329(4), b¼16.7366(7), c¼17.2684(7) A,
3
b¼101.608(1) , V¼3038.5(2) A, Z¼4, Dc¼1.517 mg mꢁ3
,
ꢀ
˚
m(Mo Ka)¼0.770 mmꢁ1, 31,910 reflections measured, 5356
unique [I>2s(I)], R value¼0.0320, wR2¼0.0803.
5.1.2. Crystal data for 17b (C25H20N2O2)
M¼380.43, yellow colored crystal, grown from a mixture
of ethanol and water, approximate size 0.32ꢂ0.25ꢂ0.04 mm,
multiscan data acquisition. Total scans¼5, total frames¼3030,
exposure/frame¼15.0 s/frame, q range¼2.06e25.00ꢀ, com-
pleteness to q of 25.0ꢀ is 100%. Monoclinic, space group
4.5.6. 4-(2-Furyl)-1-phenyl-b-carboline (15d)
˚
P21/n, a¼10.7329(4), b¼16.7366(7), c¼17.2684(7)ꢁA3,
Orange solid; yield 60%; mp 115 ꢀC; [Found: C, 81.70; H,
4.90; N, 9.52. C21H14N2O requires: C, 81.27; H, 4.55; N,
9.03%]; nmax (KBr) 3435 cmꢁ1; dH (300 MHz, CDCl3) 6.67
(1H, d, J¼1.2 Hz, furyl ring proton), 6.87 (1H, d, J¼3.0 Hz,
furyl ring proton), 7.18e7.3 (1H, m, ArH), 7.4e7.62 (5H, m,
ArH), 7.75 (1H, br s, furyl ring proton), 7.90 (2H, d,
J¼8.0 Hz, ArH), 8.3 (1H, d, J¼8.0 Hz, C5H of indole ring),
8.7 (1H, s, C3H), 8.9 (1H, br s, exchangeable with D2O, NH);
dC (75 MHz, CDCl3) 109.0, 111.3, 111.8, 119.8, 120.1,
121.2, 124.3, 128.1, 128.4, 128.8, 129.1, 133.4, 137.8, 138.5,
140.6, 142.1, 142.7, 151.4; MS m/z 310 (Mþ 100%) 243,
203, 155, 141.
3
ꢀ
˚
b¼101.608(1) , V¼3038.5(2) A , Z¼4, Dc¼1.517 mg m
,
m(Mo Ka)¼0.770 mmꢁ1, 31,910 reflections measured, 5356
unique [I>2s(I)], R value¼0.0320, wR2¼0.0803.
Acknowledgements
We are grateful to Prof. M. S. Wadia for helpful discussion,
A. P. Gadgil for IR spectra and elemental analysis, J.P. Chaud-
hari for NMR spectra, and V. S. Shinde and D. S. Shishupal for
mass spectra.
Supplementary data
5. Crystallography
Supplementary data associated with this article can be
found in the online version, at doi:10.1016/j.tet.2007.12.008.
X-ray data for 15b and 17b have been deposited at the
Cambridge Crystallographic Data Centre, deposition numbers
CCDC 630523 and CCDC 630524. Copies of the data can be
obtained free of charge on application to CCDC, 12 Union
Road, Cambridge CB2 1EZ, UK (fax: þ44 1223 336 033;
e-mail: deposit@ccdc.cam.ac.uk).
References and notes
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5.1. Crystal data
The X-ray data of the two compounds were collected at room
temperature on a SMARTAPEX CCD single crystal X-ray dif-
fractometer with omegaand phi scan mode and different number
of scans and exposure times for different crystals using l (Mo
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˚
Ka)¼0.71073 A radiation, at T¼293(2) K with Oscillation/
frame ꢁ0.3ꢀ, maximum detector swing angle¼ꢁ30.0ꢀ, beam
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