Synthesis of new substituted 2-(trimethylstannyl)indoles

Article abstract of DOI:10.1055/s-2008-1032162

Synthesis of the previously unreported 2-(trimethylstannyl)indole derivatives, 5-bromo-1-(tert-butoxycarbonyl)-2-(trimethylstannyl)-1H-indole, 6-bromo-1-(tert-butoxycarbonyl)-2-(trimethylstannyl)-1H-indole, 1-(tert-butoxycarbonyl)-2-(trimethylstannyl)-1H-indole-5-carbonitrile, 1-(tert-butoxycarbonyl)-2-(trimethylstannyl)-1H-indole-6-carbonitrile and 1-(tert-butoxycarbonyl)-2-(trimethylstannyl)-1H-pyrrolo[2,3-b] pyridine-6-carbonitrile, is described. Georg Thieme Verlag Stuttgart.

Full text of DOI:10.1055/s-2008-1032162

PAPER
707
Synthesis of New Substituted 2-(Trimethylstannyl)indoles
N
A
ew
S
ubstituted
2
r
-(Trimet
v
hylstannyl)in
i
doles nd Kumar, Martial Say, David W. Boykin*
Department of Chemistry, Georgia State University, Atlanta, GA 30303, USA
Fax +1(404)4135505; E-mail: dboykin@gsu.edu
Received 31 October 2007; revised 26 November 2007
Abstract: Synthesis of the previously unreported 2-(trimethylstan-
nyl)indole derivatives, 5-bromo-1-(tert-butoxycarbonyl)-2-(tri-
methylstannyl)-1H-indole, 6-bromo-1-(tert-butoxycarbonyl)-2-(tri-
methylstannyl)-1H-indole, 1-(tert-butoxycarbonyl)-2-(trimethyl-
stannyl)-1H-indole-5-carbonitrile, 1-(tert-butoxycarbonyl)-2-(tri-
a)
R
b)
R
SnMe3
R
N
N
N
H
Boc
Boc
methylstannyl)-1H-indole-6-carbonitrile
carbonyl)-2-(trimethylstannyl)-1H-pyrrolo[2,3-b]pyridine-6-carbo-
nitrile, is described.
and
1-(tert-butoxy-
1 R = 5-Br
2 R = 6-Br
9
R = 5-Br
5
R = 5-Br
6 R = 6-Br
7 R = 5-CN
8 R = 6-CN
10 R = 6-Br
11 R = 5-CN
12 R = 6-CN
3
4
R = 5-CN
R = 6-CN
Key words: 2-(trimethylstannyl)indoles, bromoindoles, cyanoin-
doles, lithiation
Scheme 1 Reagents and conditions: a) Boc O, DMAP, CH Cl ,
2
2
2
0
–5 °C; b) LDA, Me SnCl, THF, –20 °C to r.t.
3
The chemistry of indoles occupies a prominent place in
heterocyclic chemistry and continues to receive signifi-
cant attention from synthetic chemists. This ongoing in-
terest is due to the wide occurrence of the indole ring in
natural products, the common presence of this ring in syn-
thetic pharmaceuticals and the more recent use of the in-
dole unit in advanced materials. The indole alkaloids are
well known for their structural complexity and their useful
a)
N
N
H
Cl
N
NC
N
O
OMe
1
3
14
b)
1
biological activity. Synthetic indole analogues have fea-
c)
tured in numerous medicinal chemistry efforts, which
SnMe3
2
N
have led to useful therapeutics. Recently, the incorpora-
NC
N
N
NC
N
Boc
tion of indole units into advanced materials has led to in-
Boc
3
teresting photochromic properties. The 7-azaindoles are
also of much current interest for their potential as both ad-
16
1
5
4
5
vanced materials and as pharmaceuticals. Due to the im-
portance of indoles and 7-azaindoles in these various
fields, prodigious efforts have been devoted to developing
and expanding their synthetic methodology. The multi-
Scheme 2 Reagents and conditions: a) Zn(CN) , Pd(PPh ) , DMF,
2
3 4
1
–
75 °C; b) Boc O, DMAP, CH Cl , 0–5 °C; c) LDA, Me SnCl, THF,
2 2 2 3
20 °C to r.t.
6
tude of approaches to indole synthesis, as well as to 7-
7
azaindoles, have been carefully and extensively re- the multigram synthesis of four novel indoles and one
viewed. Much less attention has been given to the devel- such 7-azaindole which can be used as synthons for the
opment of functionally substituted indoles which could elaboration of larger indole-containing molecules.
serve as synthons for the incorporation of these indole
The synthesis used for the four bifunctional indoles is out-
systems into larger molecules which have useful photo-
lined in Scheme 1. The Boc-protected indoles 5–8 were
8
physical properties or lexitropsins which are capable of
prepared in high yields by employing a standard Boc-pro-
9
recognizing specific base pair sequences of DNA. The
tection protocol using di-tert-butyl dicarbonate (Boc O),
2
latter compounds are also being studied as potential ther-
14
4
-(dimethylamino)pyridine and dichloromethane. Lithi-
1
0
apeutic agents. We focused on trialkylstannyl-substitut-
ed indole synthons in order to take advantage, in
subsequent work, of the highly reliable palladium(0)-cat-
ation of the Boc-protected indoles 5–8 was readily
achieved with lithium diisopropylamide in tetrahydrofu-
ran at –20 °C. The use of lithium diisopropylamide is es-
pecially advantageous since lithiation of nitrile-
containing compounds with alkyllithium reagents often
requires the use of a very low temperature (–100 °C) to
1
1
alyzed Stille reaction. Several (trialkylstannyl)indole
1
2
synthons have been reported, however, only a limited
number bearing readily manipulatable functional groups
1
3
have been described in the literature. This report details
15
avoid addition to the cyano group. Subsequent reaction
of the lithioindole intermediates with trimethyltin chlo-
ride gave the bifunctional compounds 9–12 in good
yields. All of the 2-(trimethylstannyl)indoles are crystal-
SYNTHESIS 2008, No. 5, pp 0707–0710
x
x
.
x
x
.2
0
0
8
Advanced online publication: 08.02.2008
DOI: 10.1055/s-2008-1032162; Art ID: M08307SS
Georg Thieme Verlag Stuttgart · New York
©

7
08
A. Kumar et al.
PAPER
line solids which appear to have a reasonable shelf life (3 1-(tert-Butoxycarbonyl)-1H-indole-6-carbonitrile (8)
Yield: 87%; mp 122–123 °C.
months at room temperature).
1
H NMR (DMSO-d ): d = 1.65 (s, 9 H), 6.82 (d, J = 3.6 Hz, 1 H),
6
The synthesis employed in the preparation of the 2-(tri-
methylstannyl)-7-azaindole is shown in Scheme 2. In this
approach we used the previously reported 6-chloro-1-
7
.58 (d, J = 8.1 Hz, 1 H), 7.80 (d, J = 8.1 Hz, 1 H), 7.89 (d, J = 3.6
Hz, 1 H), 8.35 (s, 1 H).
1
3
C NMR (DMSO-d ): d = 28.26, 85.65, 106.76, 108.17, 119.42,
6
(
methoxycarbonyl)-7-azaindole (13) as the precursor for a
1
20.31, 123.01, 126.30, 130.48, 134.29, 134.42, 149.17.
new preparation of 6-cyano-7-azaindole (14) utilizing
palladium(0)-mediated cyanation with zinc cyanide.16
Anal. Calcd for C H N O : C, 69.40; H, 5.82; N, 11.56. Found: C,
14 14 2 2
6
9.22; H, 5.76; N, 11.42.
The subsequent steps of Boc protection, lithiation and fi-
nally stannylation are similar to that as outlined in
Scheme 1. This sequence yields 16 in reasonable yields.
1
-(tert-Butoxycarbonyl)-1H-pyrrolo[2,3-b]pyridine-6-carbo-
nitrile (15)
Yield: 90%; mp 118–119 °C.
In conclusion, we report the synthesis, in good yields, of
Boc-protected bromo- and cyano(trimethylstannyl)indole 1H NMR (DMSO-d
): d = 1.62 (s, 9 H), 6.84 (d, J = 3.6 Hz, 1 H),
.85 (d, J = 8.1 Hz, 1 H), 8.03 (d, J = 3.6 Hz, 1 H), 8.25 (d, J = 8.1
Hz, 1 H).
6
7
derivatives which can be used for the synthesis of larger
molecules involving more complex scaffolds.
1
3
C NMR (DMSO-d ): d = 28.3, 85.3, 105.8, 119.0, 124.1, 126.7,
6
1
26.8, 131.3, 131.9, 147.4, 147.7.
All commercial reagents were used without purification. Melting
points were determined on a Mel-Temp 3.0 melting point apparatus,
and are uncorrected. TLC analysis was carried out on silica gel 60
Anal. Calcd for C H N O : C, 64.18; H, 5.38; N, 17.27. Found: C,
13 13
3
2
6
4.05; H, 5.40; N, 17.26.
1
F254 precoated aluminum sheets using UV light for detection. H
and 13C NMR spectra were obtained on a Varian Unity 300 MHz
spectrometer using the indicated solvents and TMS as an internal
reference. Elemental analyses were performed by Atlantic Microlab
Inc., Norcross, GA, USA.
2-(Trimethylstannyl)indoles 9–12 and -7-azaindole 16
To a soln, cooled to –20 °C, of an indole or 7-azaindole derivative
(
0.15 mol) and Me SnCl (33.9 g, 0.17 mol) in THF (500 mL) was
3
slowly added 2.0 M LDA in heptane–tetrahydrofuran–ethylbenzene
90 mL, 0.18 mol) while keeping the temperature below –20 °C.
(
The reaction mixture was warmed to r.t. and left to stir for 6 h. TLC
analysis showed the presence of starting material for the 5-substitut-
ed indole derivatives, however, the reaction was complete for both
the 6-substituted indole derivatives and 1-(tert-butoxycarbonyl)-
Boc-Protected Indoles 5–8 and 7-Azaindole 15
DMAP (0.4 g, 3.27 mmol) was added in portions to a stirred mixture
of an indole or 7-azaindole derivative (0.24 mol) and Boc O (0.29
2
mol) in anhyd CH Cl (400 mL) at 0–5 °C. After 2 h, the reaction
2
2
1
H-pyrrolo[2,3-b]pyridine-6-carbonitrile (15). For those cases
mixture was quenched with ice water (50 mL). The organic layer
was separated and the aqueous layer was extracted with CH Cl (50
mL). The combined organic phase was washed with 0.5 M HCl soln
where starting material remained, another portion of Me SnCl
3
2
2
(
10.17 g, 0.051 mol) in THF (20 mL) and 2.0 M LDA in heptane–
tetrahydrofuran–ethylbenzene (27 mL, 0.054 mol) were added at
20 °C to the reaction mixture, which was stirred at r.t. for 24 h.
(
50 mL), brine (100 mL) and H O (200 mL), respectively, and dried
2
–
(
anhyd MgSO ). The solution was filtered, passed through a bed of
4
TLC analysis showed only traces of starting material. After quench-
silica gel (60 Å, 200 mm) and concentrated under reduced pressure;
the product was crystallized from cold EtOH–hexane (1:1).
ing the reaction with H O (30 mL), the solvent was removed under
2
reduced pressure and the residue was extracted with Et O (800 mL).
2
The organic phase was washed with 10% NaF soln (100 mL) and
H O (400 mL), dried (anhyd MgSO ) and concentrated.
5
-Bromo-1-(tert-butoxycarbonyl)-1H-indole (5)
1
7
Yield: 85%; mp 90–91 °C (Lit. 90–91 °C).
2
4
1
H NMR (DMSO-d ): d = 1.62 (s, 9 H), 6.67 (d, J = 3.6 Hz, 1 H),
6
5-Bromo-1-(tert-butoxycarbonyl)-2-(trimethylstannyl)-1H-in-
dole (9)
Yield: 80%; mp 57–58 °C.
7
8
.43 (d, J = 8.7 Hz, 1 H), 7.69 (d, J = 3.6 Hz, 1 H), 7.86 (s, 1 H),
.00 (d, J = 8.7 Hz, 1 H).
1
H NMR (DMSO-d ): d = 0.32 (s, 9 H), 1.67 (s, 9 H), 6.63 (s, 1 H),
6
-Bromo-1-(tert-butoxycarbonyl)-1H-indole (6)
6
1
7
7.28 (d, J = 9.0 Hz, 1 H), 7.59 (s, 1 H), 7.78 (d, J = 9.0 Hz, 1 H).
1
Yield: 86%; mp 102–103 °C (Lit. 102–103 °C).
3
1
C NMR (DMSO-d ): d = –6.80, 28.4, 84.8, 116.0, 116.8, 117.5,
H NMR (DMSO-d ): d = 1.61 (s, 9 H), 6.66 (d, J = 3.6 Hz, 1 H),
6
6
1
22.9, 126.5, 134.2, 136.4, 145.3, 152.1.
7
.36 (d, J = 8.1 Hz, 1 H), 7.54 (d, J = 8.1 Hz, 1 H), 7.62 (d, J = 3.6
Hz, 1 H), 8.22 (s, 1 H).
Anal. Calcd for C H BrNO Sn: C, 41.87; H, 4.83; N, 3.05. Found:
1
6
22
2
1
3
C, 42.09; H, 4.88; N, 3.08.
C NMR (CDCl ): d = 28.36, 84.40, 107.24, 118.15, 118.62,
3
1
22.15, 126.10, 126.54, 129.56, 136.16, 149.56.
6
-Bromo-1-(tert-butoxycarbonyl)-2-(trimethylstannyl)-1H-in-
dole (10)
1
-(tert-Butoxycarbonyl)-1H-indole-5-carbonitrile (7)
Yield: 75%; mp 124–125 °C (crystallized from EtOH–hexane, 1:9).
Yield: 88%; mp 128–129 °C.
1
1
H NMR (DMSO-d ): d = 0.29 (s, 9 H), 1.70 (s, 9 H), 6.78 (s, 1 H),
H NMR (CDCl ): d = 1.69 (s, 9 H), 6.61 (d, J = 3.6 Hz, 1 H), 7.52
6
3
7
.34 (d, J = 8.1 Hz, 1 H), 7.50 (d, J = 8.1 Hz, 1 H), 8.08 (s, 1 H).
(
d, J = 8.4 Hz, 1 H), 7.70 (d, J = 3.6 Hz, 1 H), 7.87 (s, 1 H), 8.24 (d,
1
3
J = 8.4 Hz, 1 H).
C NMR (DMSO-d ): d = –6.42, 28.2, 85.7, 117.3, 118.5, 118.6,
6
1
3
122.1, 125.8, 131.4, 138.3, 144.3, 151.8.
C NMR (CDCl ): d = 28.35, 85.17, 106.37, 107.18, 116.26,
3
1
20.00, 126.02, 127.57, 128.32, 130.77, 137.34, 149.30.
Anal. Calcd for C H BrNO Sn: C, 41.87; H, 4.83. Found: C,
1
6
22
2
4
2.04; H, 4.85.
Anal. Calcd for C H N O : C, 69.40; H, 5.82; N, 11.56. Found: C,
1
4
14
2
2
6
9.61; H, 5.89; N, 11.46.
Synthesis 2008, No. 5, 707–710 © Thieme Stuttgart · New York

PAPER
-(tert-Butoxycarbonyl)-2-(trimethylstannyl)-1H-indole-5-car-
New Substituted 2-(Trimethylstannyl)indoles
709
1
Acknowledgment
bonitrile (11)
This work was supported by NIH grants GM61587 and AI46365,
and by the Bill and Melinda Gates Foundation.
Yield: 75%; mp 136–137 °C (crystallized from EtOH–hexane, 1:4).
1
H NMR (DMSO-d ): d = 0.30 (s, 9 H), 1.67 (s, 9 H), 6.85 (s, 1 H),
6
7
.58 (d, J = 8.7 Hz, 1 H), 8.00 (s, 1 H), 8.03 (d, J = 8.7 Hz, 1 H).
1
3
References
C NMR (CDCl ): d = –7.23, 28.0, 85.3, 105.5, 115.9, 117.5, 119.9,
3
1
24.7, 126.4, 132.1, 139.1, 146.5, 151.4.
(
1) (a) Gul, W.; Haman, M. T. Life Sci. 2005, 78, 442.
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H, 5.47.
1
7
22
2
2
1
-(tert-Butoxycarbonyl)-2 -(trimethylstannyl)-1H-indole-6-car-
bonitrile (12)
Yield: 74%; mp 119–120 °C (crystallized from EtOH–hexane, 1:4).
1
H NMR (DMSO-d ): d = 0.33 (s, 9 H), 1.70 (s, 9 H), 6.88 (s, 1 H),
6
7
.50 (d, J = 8.1 Hz, 1 H), 7.70 (d, J = 8.1 Hz, 1 H), 8.19 (s, 1 H).
1179. (c) Palomer, A.; Cabre, F.; Pascual, J.; Campos, J.;
1
3
C NMR (DMSO-d ): d = –6.38, 28.3, 86.5, 106.3, 118.6, 119.6,
6
Trujillo, M. A.; Entrena, A.; Gallo, M. A.; Garcia, L.;
Mauleon, D.; Espinosa, A. J. Med. Chem. 2002, 45, 1402.
1
20.5, 121.9, 126.0, 135.7, 136.7, 148.7, 151.7.
(
d) Cui, J. J.; Araldi, G.-L.; Reiner, J. E.; Reddy, K. M.;
Anal. Calcd for C H N O Sn: C, 50.41; H, 5.47. Found: C, 50.43;
1
7
22
2
2
Kemp, S. J.; Ho, J. Z.; Siev, D. V.; Mamedova, L.; Gibson,
T. S.; Gaudette, J. A.; Minami, N. K.; Anderson, S. M.;
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K.; Rai, R.; She, M.; Shrader, W.; Sprengeler, P. A.; Trapp,
S.; Wang, J.; Young, W. B.; Mackman, R. L. J. Med. Chem.
2001, 44, 2753.
H, 5.49.
1
-(tert-Butoxycarbonyl)-2-(trimethylstannyl)-1H-pyrrolo[2,3-
b]pyridine-6-carbonitrile (16)
Yield: 75%; mp 123–124 °C (crystallized from hexane).
1
H NMR (DMSO-d ): d = 0.34 (s, 9 H), 1.66 (s, 9 H), 6.93 (s, 1 H),
6
7
.82 (d, J = 8.1 Hz, 1 H), 8.17 (d, J = 8.1 Hz, 1 H).
1
3
C NMR (DMSO-d ): d = –7.19, 27.4, 84.7, 115.2, 118.4, 122.9,
6
1
25.1, 126.6, 129.0, 148.7, 149.6, 150.4.
(3) (a) Yagi, K.; Irie, M. Bull. Chem. Soc. Jpn. 2003, 76, 1625.
(
b) Giordano, L.; Vermeij, R. J.; Jares-Erijman, E. A.
Anal. Calcd for C H N O Sn: C, 47.32; H, 5.21; N, 10.38. Found:
C, 47.57; H, 5.34; N, 10.25.
16
21
3
2
ARKIVOC 2005, (xii), 268.
(
4) (a) Wang, S. Coord. Chem. Rev. 2001, 215, 79. (b) Cheng,
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G.-R.; Chou, P.-T. J. Phys. Chem. A 2003, 107, 1459.
6
-Chloro-1-(methoxycarbonyl)-1H-pyrrolo[2,3-b]pyridine (13)
ClCO Me (17.75 g, 0.18 mol) was added to a soln of 7-azaindole N-
2
oxide18 (10 g, 0.075 mol) and HMDS (12.08 g, 0.075 mol) in THF
(5) (a) O’Neill, D. J.; Shen, L.; Prouty, C.; Conway, B. R.;
Westover, L.; Xu, J. Z.; Zhang, H.-C.; Maryanoff, B. R.;
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M.; Patel, D. N.; Gupta, A. A.; Sharma, A.; Tom, R.;
Bandyopadhya, D.; Modi, H.; Patel, P. R. Bioorg. Med.
Chem. 2007, 15, 6782.
(
750 mL) dropwise at 0 °C. After stirring for 2 h at r.t., the solvent
was removed and the residue was extracted with EtOAc (500 mL).
The extract was washed with sat. aq NaHCO (100 mL) and H O
3
2
(
200 mL), and dried (anhyd Na CO ). The crude product was chro-
2 3
matographed over silica gel (EtOAc–hexane, 1:9) to give 13; yield:
1
9
9
.2 g (62%); mp 120–121 °C (Lit. 118–119 °C).
1
H NMR (DMSO-d ): d = 3.99 (s, 3 H), 6.77 (d, J = 4.0 Hz, 1 H),
6
7
.40 (d, J = 8.0 Hz, 1 H), 7.85 (d, J = 4.0 Hz, 1 H), 8.11 (d, J = 8.0
Hz, 1 H).
(
6) (a) Humphrey, G. R.; Kuethe, J. T. Chem. Rev. 2006, 106,
2875. (b) Gribble, G. W. J. Chem. Soc., Perkin Trans. 1
2000, 1045. (c) Gilchrist, T. L. J. Chem. Soc., Perkin Trans.
1
3
C NMR (DMSO-d ): d = 54.40, 105.40, 119.12, 121.71, 127.43,
6
1
32.63, 144.96, 145.67, 149.50.
1
1999, 2849. (d) Sundberg, R. J. Indoles; Academic Press:
1H-Pyrrolo[2,3-b]pyridine-6-carbonitrile (14)
San Diego, CA, 1996.
A mixture of 6-chloro-1-(methoxycarbonyl)-1H-pyrrolo[2,3-b]py-
ridine (13; 1 g, 4.8 mmol), Zn(CN)2 (0.91 g, 7.7 mmol) and
Pd(PPh ) (3 mol%) in DMF (15 mL) was heated at 175 °C (bath
(7) Popowycz, F.; Routier, S.; Joseph, B.; Merour, J.-Y.
Tetrahedron 2007, 63, 1031.
(8) Gogrichiani, E. O.; Katsadze, E. A.; Gavtadze, N. G.;
Samsoniya, Sh.; Durr, H. Chem. Heterocycl. Compd. (Engl.
Transl.) 2004, 40, 1271.
3
4
temperature) in a pressure vessel for 24 h. After cooling, the reac-
tion mixture was partitioned between sat. NaHCO soln (40 mL)
3
and EtOAc (200 mL). The organic solution was washed with brine
(9) (a) Bando, T.; Sasaki, S.; Minoshima, M.; Dohno, C.;
Shinohara, K.-I.; Narita, A.; Sugiyama, H. Bioconjugate
Chem. 2006, 17, 715. (b) Reddy, B. S.; Sharma, S. K.;
Lown, J. W. Curr. Med. Chem. 2001, 8, 475. (c) Chang, A.
Y.; Dervan, P. B. J. Am. Chem. Soc. 2000, 122, 4856.
(
30 mL), dried (anhyd Na CO ) and concentrated. The crude prod-
2 3
uct was purified by column chromatography (silica gel, EtOAc–
hexane, 1:4) to give 14; yield: 280 mg (41%); mp 186–187 °C
(
Lit.20 175–177 °C).
(
5
d) White, J. M.; Clark, C. I. Acta Crystallogr., Sect. C 1998,
4, 1304.
1
H NMR (DMSO-d ): d = 6.63 (d, J = 3.2 Hz, 1 H), 7.61 (d, J = 8.0
6
Hz, 1 H), 7.84 (d, J = 3.2 Hz, 1 H), 8.17 (d, J = 8.0 Hz, 1 H).
(
10) (a) Khalaf, A. I.; Ebrahimabadi, A. H.; Drummond, A. J.;
Anthony, N. G.; Mackay, S. P.; Suckling, C. J.; Waigh, R. D.
Org. Biomol. Chem. 2004, 2, 3119. (b) Burli, R. W.;
1
3
C NMR (DMSO-d ): d = 100.8, 119.0, 119.9, 122.4, 123.7, 129.1,
6
1
31.2, 147.9.
McMinn, D.; Kaizerman, J. A.; Hu, W.; Ge, Y.; Pack, Q.;
Anal. Calcd for C H N : C, 67.12; H, 3.52; N, 29.35. Found: C,
8
5
3
6
7.04; H, 3.53; N, 29.34.
Synthesis 2008, No. 5, 707–710 © Thieme Stuttgart · New York

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A. Kumar et al.
PAPER
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