A convenient synthesis of linear pyridinoimidazo[1,2-a]pyridine and pyrroloimidazo[1,2-a]pyridine cores

Article abstract of DOI:10.1016/j.tetlet.2007.07.223

Two new imidazo[1,2-a]pyridine derivatives, pyridinoimidazo[1,2-a]pyridine (10) and pyrroloimidazo[1,2-a]pyridine (16), were synthesised from 2-amino-4-methyl-5-nitropyridine (1) by linear cyclisation, making use of dimethylformamide dimethylacetal (DMFDMA) as an agent of vinylamine functionalisation. This report describes first the formation of pyridine and pyrroloimidazopyridine from (1), and then the formation of pyridine-fused and pyrrolo-fused pyridine by the Friedl?nder method and reductive cyclisation followed by treatment of the resulting adduct with chloroacetaldehyde.

Full text of DOI:10.1016/j.tetlet.2007.07.223

Available online at www.sciencedirect.com
Tetrahedron Letters 48 (2007) 8392–8395
A convenient synthesis of linear pyridinoimidazo[1,2-a]pyridine
and pyrroloimidazo[1,2-a]pyridine cores
Mounir Andaloussi,* Emmanuel Moreau, Olivier Chavignon and Jean C. Teulade
Univ Clermont 1, UFR Pharmacie, Laboratoire de Chimie Organique, Clermont-Ferrand F-63001, France
Received 18 May 2007; revised 12 July 2007; accepted 16 July 2007
Available online 14 September 2007
Abstract—Two new imidazo[1,2-a]pyridine derivatives, pyridinoimidazo[1,2-a]pyridine (10) and pyrroloimidazo[1,2-a]pyridine (16),
were synthesised from 2-amino-4-methyl-5-nitropyridine (1) by linear cyclisation, making use of dimethylformamide dimethylacetal
(DMFDMA) as an agent of vinylamine functionalisation. This report describes first the formation of pyridine and pyrroloimidazo-
pyridine from (1), and then the formation of pyridine-fused and pyrrolo-fused pyridine by the Friedla¨nder method and reductive
cyclisation followed by treatment of the resulting adduct with chloroacetaldehyde.
Ó 2007 Elsevier Ltd. All rights reserved.
For several years, the imidazo[1,2-a]pyridine (IP) ring
has been known as a core structural unit of bioactive
molecules in synthetic and natural core (Zolpidem,
Saripidem).1 Thus, many structural modifications of this
scaffold have been intensively investigated with the aim
of developing novel therapeutic agents.2 A perusal of
the literature reveals, a large number of different
synthetic pathways using functionalisation of the imid-
azole3 or pyridine4 parts to create heterocyclic com-
pounds with potential therapeutic applications. In
contrast, the synthetic potential of the pyridine part
has long remained largely unexplored, not only because
of the problems with functionalisation, but also due to
the difficulty of finding commercial reagents to synthe-
sise new rings from this part. Recently we have shown
in our laboratory the possibility of reaching in angular
systems from monofunctionalisation of pyridine
sites.4b,c In these works,4b,c Chezal et al. reported that
during an intramolecular cyclisation the regiospecificity
was an angular annulation from C-8 to C-7 and from
C-5 to C-6 of IP (see (3) in Fig. 1 for numbering). This
regiospecificity can be explained by the higher electron
densities of the C-5 and C-8 sites, and by thermody-
namic stability of angular compounds. In view of all
the above reasons, heterocyclisation from C-6 and C-7
poses a significant challenge.
In this study, we decided to synthesise pyridine and pyr-
role rings from C-6 and C-7 of IP, because these two
kinds of heterocycles can be found as pharmacophores
in a wide variety of biologically active compounds, such
as antitumourals,5 antivirals6 and many other therapeu-
tic agents.7
Here, we report a new and efficient synthetic route for
the synthesis of linear pyridinoimidazopyridine and pyr-
roloimidazopyridine cores by the Friedla¨nder and
reductive cyclisation reactions. Our retrosynthetic anal-
ysis was based on three essential elements. Firstly, in
order to direct the reaction for the formation of a linear
system, we proposed a bifunctionalised system (in C-6
and C-7 of IP) as shown in the retrosynthetic scheme
(Fig. 1, first possibility). Secondly, the reaction of
DMFDMA with orthonitrated methyl pyridine (1)
allowed us access to vinylamine (compound (3) or (5))
followed by orthonitrated aldehyde synthons by action
of sodium periodate. This resulted in the formation of
the pyridine and pyrrole cores in a limited number
of steps8 (Fig. 1). Finally, the possibility of forming
the pyridine (A-ring) and pyrrole (C-ring) before forma-
tion of the imidazole part of IP gave us a second way to
obtain the linear pyridine and pyrroloimidazopyridine
scaffolds (Fig. 1, second possibility).
Keywords: Friedla¨nder reaction; Reductive cyclisation; DMFDMA;
Pyridinoimidazo[1,2-a]pyridine; Pyrroloimidazo[1,2-a]pyridine.
*
Corresponding author at present address: Department of Bioorganic
Chemistry, Box 581, Biomedical Centre, Uppsala University, S-75123
Uppsala, Sweden. Tel.: +46 18 471 45 78; fax: +46 18 55 44 95;
e-mail: mounir@boc.uu.se
To verify the feasibility of this project, we chose to
investigate the synthesis of precursors (3) and (8)
0040-4039/$ - see front matter Ó 2007 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2007.07.223

M. Andaloussi et al. / Tetrahedron Letters 48 (2007) 8392–8395
8393
First possibility
8
7
R
H3C
O2N
N
N
NH2
2
Het
6
N
N
N
O2N
3
5
1
(10) : Het = Pyridine (from (8))
(16) : Het = Pyrrol (from (3))
(3) : R = CH=CH-N(CH3)2
(8) : R = CHO
Second possibility
R
NH2
NH2
N
Het
Het
N
N
N
O2N
(10) : Het = Pyridine (from (9))
(16) : Het = Pyrrol (from (11))
(9) : Het = Pyridine (from (6))
(11) : Het = Pyrrol (from (5))
(5) : R = CH=CH-N(CH3)2
(6) : R = CHO
Pyridine : A-ring
Pyrrol : C-ring
Figure 1. The two possible retrosynthetic pathways for the synthesis of pyridino and pyroloimidazopyridine cores.
(Scheme 1). Our initial route was based on the forma-
tion of (2) from 2-amino-4-methyl-5-nitropyridine (1)
according to the procedure of Tschitschibabin.9 How-
ever, our attempt at formation of the vinylogous enam-
ine (3) from compound (2) upon treatment with
DMFDMA in refluxing DMF was unsuccessful, and
use of Bredereck’s reagent (tert-butoxybisdimethylami-
nomethane) also failed to produce the desired enamine
(3). This result can be attributed to the non-delocalisa-
tion of p electrons of the pyridine ring in the IP scaffold,
which makes the removal of the methyl proton almost
impossible. The second route for the formation of
enamine (3) was the reaction of compound (1) with
DMFDMA according to the procedure of Filla et al.10
followed by acid hydrolysis to give amine (5) in a yield
of 71%. However, several attempts for the formation
of the imidazole ring from compound (5) with varying
solvents (e.g., EtOH, iPr-OH, n-butanol, DMF and
DME) failed to yield the desired compound (3). It seems
that either the vinylogous enamine on the C-7 position
of IP was unstable, or that the chain on the C-4 position
of compound (5) reduced the nucleophilicity of the
pyridino nitrogen and thus prevented formation of the
imidazole ring. Therefore, we concluded that the forma-
tion of vinylogous enamine function connected to the IP
scaffold in the C-7 position is not possible using this
strategy (Scheme 1).
Our strategy for the formation of the A-ring, consisted
of condensation of pyridine (6) with chloroacetaldehyde
in DMF; this gave the desired product (8) in a yield of
22%. An alternative strategy would be the treatment of
the same pyridine (6) with chloroacetaldehyde in reflux-
ing ethanol followed by acidic hydrolysis; this gave the
product (8) in a better yield of 39% (Scheme 1). For
the synthesis of compound (10), we chose the Friedla¨n-
der reaction for the construction of the A-ring. This
reaction is traditionally reported from the ortho amine
aldehyde compounds.3c In this work, we decided to
apply the same reaction but from the ortho nitrated
aldehyde compound under the McNaughton condi-
tions,11 which allowed us to obtain 7-methylimidazo-
[2,1-g][1,7]naphthyridine (10)12a in a yield of 43%
(Scheme 1).
In the second part of our work, the formation of the A
and C rings was considered before accessing the imidaz-
ole part. 5-Aminopyrrolopyridine (11)13 was easily syn-
thesised from (5) under reductive conditions in the
presence of hydrazine monohydrate and Raney nickel
R2
R1
H3C
O2N
N
i
N
N
O2N
from 1 (95%)
1 : R1 = NH2, R2 = CH3
(100%)
2
ii
4 : R1 = N=CH-N(CH3)2, R2 = CH=CH-N(CH3)2
from 4 (71%)
ii, iii
X
x
iv
CH3
N
(22%)
(EtO)2HC
CH3
N
NH2
OHC
O2N
H3C
OHC
O2N
NH2
i
N
N
vii
N
i, vX, vi
viii
H3C
N
(44%)
N
8
N
3
O2N
N
(54%)
N
(73%)
O2N
O2N
5
6
7
ix
(43%)
N
N
N
C
A
N
N
N
H3C
H
10
16
Scheme 1. Reagents and conditions: (i) ClCH2CHO, EtOH, D; (ii) DMFDMA, DMF, D; (iii) Brederek’s reagent, DMF, D; (iv) HCl (3 N), D; (v)
ClCH2CHO, CH3CN, D; (vi) ClCH2CHO, DME, rt; (vii) NaIO4, THF, H2O, rt; (viii) HCl (10 N), CH3CN, H2O, D; (ix) acetone, SnCl2, ZnCl2, D; (x)
ClCH2CHO, DMF, D.

8394
M. Andaloussi et al. / Tetrahedron Letters 48 (2007) 8392–8395
NH2
R
N
O2N
5
R = CH=CH-N(CH3)2
R = CHO
ii
vi
(22%) from 5
(23%) from 6
(44%)
i
6
NH2
NH2
iii
N
N
N
12
N
N
N
(76%)
H3C
H3C
N
iv
9
H
11
OH
iv
(43%)
NH
R1
N
N
13: R1 = H, R2 = BOC
14: R1= BOC, R2= H
N
A
N
N
R2
10
13 (51%)+14 (10%) ratio 5/1
iii
from 12 (76%)
N
C
N
N
R
15
15 : R = BOC
16 : R = H
v
(48%)
Scheme 2. Reagents and conditions: (i) NaIO4, THF, H2O, rt; (ii) Raney Ni, NH2NH2 (8.6 equiv), THF, MeOH, 45–50 °C; (iii) ClCH2CHO, EtOH,
D; (iv) (BOC)2O, CH2Cl2, rt; (v) HCl (3 N), D; (vi) acetone, SnCl2, ZnCl2, EtOH, D.
as the catalyst. The condensation of compound (11) with
the chloroacetaldehyde resulted in the formation of the
unexpected product (12)12b (Scheme 2). The formation
of compound (12) can be explained by three factors:
(i) excesses of chloroacetaldehyde (3 equiv) necessary
for the Tchichibabin condensation, (ii) the nucleophilic
character of N-1 of pyrrole, resulting in the condensa-
tion product with chloroacetaldehyde and (iii) a higher
electron density at the C-5 position of IP. In addition,
a previous report from our laboratory describes the for-
mation of imidazopyridodiazepines from peri annula-
tion. The base of this work was a direct intramolecular
electrophilic attack of C-5 to vinylimine of the bicyclic
ring compound.14
the presence of DMFDMA and Bredereck’s reagents.
Furthermore, the synthesis described in this paper al-
lowed us to use known precursor (5), which permitted
in the synthesised new-fused systems in pyridine series,
which ultimately afforded a linear tricycle (10) and
(16). Further work is in progress to develop other hetro-
cycles (thiophene, furan, pyridazine and pyridinone)
from the C-6 and C-7 sites of IP using the same strategy,
and reports will follow in due course.
References and notes
1. Renard, S.; Olivier, A.; Granger, P.; Avenet, P.; Graham,
D.; Sevrin, M.; George, P.; Besnard, F. J. Biol. Chem.
1999, 274, 13370.
To circumvent this obstacle to the synthesis of our linear
tricyclic pyrroloimidazopyridine compound, we decided
to protect the N-1 group of 5-aminopyrrolo[2,3-c]pyri-
dine (11) with a BOC group. This yielded the formation
of two compounds, (13) and (14), in a ratio of 5:1 after
column chromatography. Thus, the desired compound
(16)12c was obtained by the building of an imidazole ring
followed by the removal of the BOC group. The overall
yield was 36% (Scheme 2).
2. (a) Zeng, F.; Southerland, J. A.; Voll, R. J.; Votaw, J. R.;
Williams, L.; Ciliax, B. J.; Levey, A. I.; Goodman, M. M.
Bioorg. Med. Chem. Lett. 2006, 16, 3015; (b) Cai, D.; Byth,
K. F.; Shapiro, G. I. Cancer Res. 2006, 66, 435; (c) Engler,
T. A.; Malhotra, S.; Burkholder, T. P.; Henry, J. R.;
Mendel, D.; Porter, W. J.; Furness, K.; Diefenbacher, C.;
Marquart, A.; Reel, J. K.; Li, Y.; Clayton, J.; Cunning-
ham, B.; McLean, J.; O’Toole, J. C.; Brozinick, J.;
Hawkins, E.; Misener, E.; Briere, D.; Brier, R. A.;
Wagner, J. R.; Campbell, R. M.; Anderson, B. D.;
Vaughn, R.; Bennett, D. B.; Meier, T. I.; Cook, J. A.
Bioorg. Med. Chem. Lett. 2005, 15, 899; (d) Abadi, A. H.
Arch. Pharm. Pharm. Med. Chem. 2004, 337, 383; (e)
Engler, T. A.; Henry, J. R.; Malhotra, S.; Cunningham,
B.; Furness, K.; Brozinick, J.; Burkholder, T. P.; Clay, M.
P.; Clayton, J.; Diefenbacher, C.; Hawkins, E.; Iverson, P.
W.; Li, Y.; Lindstrom, T. D.; Marquart, A. L.; McLean,
J.; Mendel, D.; Misener, E.; Briere, D.; O’Toole, J. C.;
Porter, W. J.; Queener, S.; Reel, J. K.; Owens, R. A.;
Brier, R. A.; Eessalu, T. E.; Wagner, J. R.; Campbell, R.
M.; Vaughn, R. J. Med. Chem. 2004, 47, 3934; (f) Ismail,
M. A.; Brun, R.; Wenzler, T.; Tanious, F. A.; Wilson, W.
D.; Boykin, D. W. J. Med. Chem. 2004, 47, 3658; (g)
Next, the condensation of compound (6) with acetone
under the McNaughton conditions, allowed us to syn-
thesise aminopyridinopyridine (9). The reaction of the
latter with chloroacetaldehyde in the ethanol solution
at reflux yielded compound (10).12a
In summary, we have found a convenient route to syn-
thesise linear pyridinoimidazopyridine (10) and pyrrolo-
imidazopyridine (16) structures by bifunctionalisation of
the C-6 and C-7 sites of IP and the C-4 and C-5 sites of
the pyridine ring. We have also shown that the C-6
methyl group, ortho nitrated on C-7 is not reactive in

M. Andaloussi et al. / Tetrahedron Letters 48 (2007) 8392–8395
8395
Gudmundsson, K. S.; Johns, B. A. Org. Lett. 2003, 5,
1369; (h) Mavel, S.; Renou, J. L.; Galtier, C.; Allouchi, H.;
Snoeck, R.; Andrei, G.; De Clercq, E.; Balzarini, J.;
Gueiffier, A. Bioorg. Med. Chem. 2002, 10, 941; (i) Lima,
P. C.; Avery, M. A.; Tekwani, B. L.; Alves, H. M.;
Barreiro, E. J.; Fraga, C. A. M. Il Farmaco 2002, 57, 825.
3. (a) Shaabani, A.; Soleimani, E.; Maleki, A. Tetrahedron
Lett. 2006, 47, 3031; (b) Andaloussi, M.; Chezal, J. M.;
Moreau, E.; Lartigue, C.; El Laghdach, A.; Teulade, J. C.;
Chavignon, O. Heterocycles 2005, 65, 1071; (c) Desbois,
N.; Chezal, J. M.; Fauvelle, F.; Debouzy, J. C.; Lartigue,
C.; Gueiffier, A.; Blache, Y.; Moreau, E.; Madelmont, J.
C.; Chavignon, O.; Teulade, J. C. Heterocycles 2005, 65,
1121; (d) Chezal, J. M.; Moreau, E.; Chavignon, O.;
Lartique, C.; Blache, Y.; Teaulade, J. C. Tetrahedron 2003,
59, 5869; (e) Moreau, E.; Chezal, J. M.; Dechambre, C.;
Canitrot, D.; Blache, Y.; Lartigue, C.; Chavignon, O.;
Teulade, J. C. Heterocycles 2002, 57, 21; (f) Burkholder,
2898; (d) Mai, A.; Massa, S.; Cerbara, I.; Valente, S.;
Rango, R.; Bottoni, P.; Scatena, R.; Loidl, P.; Brosch, G.
J. Med. Chem. 2004, 47, 1098; (e) Galm, U.; Heller, S.;
Shapiro, S.; Page, M.; Li, S. M.; Heide, L. Antimicrob.
Agents Chemother. 2004, 48, 1307; (f) Biftu, T.; Feng, D.;
Ponpipom, M.; Girotra, N.; Liang, G. B.; Qian, X.;
Bugianesi, R.; Simeone, J.; Chang, L.; Gurnett, A.;
Liberator, P.; Dulski, P.; Leavitt, P. S.; Crumley, T.;
Misura, A.; Murphy, T.; Rattray, S.; Samaras, S.; Tamas,
T.; Mathew, J.; Brown, C.; Thompson, D.; Schmatz, D.;
Fisher, M.; Wyvratt, M. Bioorg. Med. Chem. Lett. 2005,
15, 3296.
8. (a) Son, J. K.; Son, J. K.; Jahng, Y. Heterocycles 2002, 62,
1109; (b) Edin, M.; Grivas, S. ARKIVOC 2001, 1, 144–
153.
9. Tschitschibabin, A. E. Ber. 1925, 58, 1704.
10. Filla, S. A.; Mathes, B. M.; Johnson, K. W.; Phebus, L.
A.; Cohen, M. L.; Nelson, D. L.; Zgombick, J. M.;
Erickson, J. A.; Schenck, K. W.; Wainscott, D. B.;
Branchek, T. A.; Schaus, J. M. J. Med. Chem. 2003, 46,
3060.
´
C.; Dolbier, W. R.; Medebielle, M.; Ait-Mohand, S.
Tetrahedron Lett. 2001, 42, 3077; (g) Jouanisson, A.;
Couquelet, J.; Teulade, J. C.; Chavignon, O.; Chabard, J.
L.; Dauphin, G. J. Heterocycl. Chem. 1996, 33, 1247; (h)
Jouanisson, A.; Chavignon, O.; Couquelet, J.; Teulade, J.
C.; Chabard, J. L.; Dauphin, G. Heterocycles 1995, 41, 21;
(i) Chavignon, O.; Teulade, J. C.; Roche, D.; Madesclaire,
M.; Blache, Y.; Gueiffier, A.; Chabard, J. L.; Dauphin, G.
J. Org. Chem. 1994, 59, 6413.
11. McNaughton, B. R.; Miller, B. L. Org. Lett. 2003, 5, 4257.
12. (a) 7-Methylimidazo[2,1-g][1,7]naphthyridine (10): mp
147–149 °C; m (KBr): 2924, 1610, 1527, 1376, 1259,
1
1105 cmÀ1; H NMR (CDCl3, 400 MHz) d: 2.67 (s, 3H),
7.16 (s, 1H), 7.23 (d, 1H, J = 8.5 Hz), 7.82 (d, 1H,
J = 8.5 Hz), 7.90 (s, 1H), 8.57 (s, 1H), 9.05 (s, 1H); 13C
NMR (CDCl3, 100 MHz) d: 45.8, 109.6, 121.4, 126.0,
132.1, 134.6, 135.2, 135.4, 140.4, 151.5, 155.7; MS m/z 183
(M+, 100), 155 (10), 129 (8), 102 (5), 77 (6), 63 (8), 51 (12);
Anal. Calcd for C11H9N3: C, 72.11; H, 4.95; N, 22.94.
Found: C, 72.25; H, 4.70; N, 22.64.; (b) 1,2-Dihydro-
2a,6,8a-triaza-cyclopenta[cd]-s-indacene-1-ol (12): mp
4. (a) Kiselyov, A. S. Tetrahedron Lett. 2006, 47, 2941; (b)
Chezal, J. M.; Moreau, E.; Chavignon, O.; Gaumet, V.;
´
Metin, J.; Blache, Y.; Diez, A.; Fradera, X.; Luque, J.;
Teulade, J. C. Tetrahedron 2002, 58, 295; (c) Chezal, J. M.;
Moreau, E.; Delmas, G.; Gueiffier, A.; Blache, Y.; Grassy,
G.; Lartigue, C.; Chavignon, O.; Teulade, J. C. J. Org.
Chem. 2001, 66, 6576.
184–186 °C; m (KBr): 3410, 1650, 1629, 1349, 1069 cmÀ1
;
5. (a) Berger, D.; Dutia, M.; Powell, D.; Wu, B.; Wissner, A.;
DeMorin, F.; Weber, J.; Boschelli, F. Bioorg. Med. Chem.
Lett. 2002, 12, 2761; (b) Staker, B. L.; Feese, M. D.;
Cushman, M.; Pommier, Y.; Zembower, D.; Stewart, L.;
Burgin, A. B. J. Med. Chem. 2005, 48, 2336; (c) Parrish, J.
P.; Kastrinsky, D. B.; Wolkenberg, S. E.; Igarashi, Y.;
Boger, D. L. J. Am. Chem. Soc. 2003, 125, 10971; (d)
Bolognese, A.; Correale, G.; Manfra, M.; Lavecchia, A.;
Mazzoni, O.; Novellino, E.; La Colla, P.; Sanna, G.;
Loddo, R. J. Med. Chem. 2004, 47, 849.
1H NMR (CDCl3, 400 MHz) d: 3.91 (m, 2H), 5.17 (t, 1H,
J = 6.5 Hz), 6.36 (d, 1H, J = 3 Hz), 7.44 (d, 1H, J = 3 Hz),
7.52 (s, 1H), 7.53 (s, 1H), 8.61 (s, 1H); 13C NMR (CDCl3,
100 MHz) d: 47.0, 67.1, 101.1, 102.4, 108.7, 122.3, 129.8,
131.7, 134.8, 135.7, 144.6; MS m/z 199 (M+, 13), 129 (22),
115 (11), 97 (27), 83 (37), 73 (55), 69 (65), 57 (100); Anal.
Calcd for C11H9N3O: C, 66.32; H, 4.55; N, 21.09; O, 8.03.
Found: C, 66.12; H, 4.81; N, 20.96; O, 8.17.; (c) 6H-
Imidazo[1,2-a]pyrrolo[3,2-d]pyridine (16): mp = 120–
121 °C; m (KBr): 2910, 1690, 1550, 1370, 1120 cmÀ1 1H
;
6. (a) Zhu, Z.; Lippa, B.; Drach, J. C.; Townsend, L. B. J.
Med. Chem. 2000, 43, 2430; (b) Rashad, A. E.; Mohamed,
M. S.; Zaki, M. E. A.; Fatahala, S. S. Arch. Pharm. Chem.
Life Sci. 2006, 339, 664; (c) Varaprasad, C. V. N. S.;
Ramasamy, K. S.; Girardet, J. L.; Gunic, E.; Lai, V.;
Zhong, W.; An, H.; Hong, Z. Bioorg. Chem. 2007, 35, 25.
7. (a) Vinosova, J.; Cermacova, K.; Tomeckova, A.; Ceck-
ova, M.; Jampilek, J.; Cermak, P.; Kunes, J.; Dolezal, M.;
Staud, F. Bioorg. Med. Chem. 2006, 14, 5850; (b) Marco-
Contelles, J.; Leon, R.; de los Rios, C.; Guglietta, A.;
Terencio, J.; Lopez, M. G.; Garcia, A. G.; Villaroya, M. J.
Med. Chem. 2006, 49, 7607; (c) Adamec, J.; Beckert, R.;
Weiß, D.; Klimesova, V.; Waisser, K.; Mo¨llmann, U.;
Kaustova, J.; Buchta, V. Bioorg. Med. Chem. 2007, 15,
NMR (CD3OD, 400 MHz) d: 6.47 (d, 1H, J = 3 Hz), 7.51
(d, 1H, J = 3 Hz), 7.70 (s, 1H), 7.80 (s, 1H), 8.10 (s, 1H),
8.51 (s, 1H); 13C NMR (CDCl3, 100 MHz) d: 101.8, 108.0,
131.6, 132.3, 137.2, 144.1, 144.9, 146.0, 155.8; MS m/z 157
(M+, 49), 129 (20), 118 (67), 57 (100); Anal. Calcd for
C9H7N3: C, 68.78; H, 4.49; N, 26.74. Found: C, 68.48; H,
4.62; N, 26.33.
13. Pineiro, J. L., Chambres, M. S.; Hobbs, S. C.; Matassa, V.
G.; Reeve, A. J.; Showell, G. A.; Street, L. J. E.U. Patent
9,532,196, 1995.
14. Dechambre, C.; Chezal, J. M.; Moreau, E.; Estour, F.;
Combourieu, B.; Grassay, G.; Gueiffier, A.; Enguehard,
C.; Gaumet, V.; Chavignon, O.; Teulade, J. C. Tetrahe-
dron Lett. 2002, 43, 9119.