[4 + 2] cycloaddition reaction of C-aryl ketenimines with PTAD as a synthetic equivalent of dinitrogen. Synthesis of triazolocinnolines and cinnolines

Article abstract of DOI:10.1021/jo900304a

C,C,N-Triaryl ketenimines and C-alkyl-C,N-diaryl ketenimines react with 2 equiv of PTAD to provide 1,2,4-triazolo[l,2-a]cinnolines with a pendant triazolidindione group by means of a Diels - Alder/ene sequence. The treatment of such adducts with potassium

Full text of DOI:10.1021/jo900304a

partner and the kind of substituents attached to their C and N
atoms, more often reacting with remarkable selectivity. Notably,
ketenimines can react as dienophiles, with either their NdC or
CdC bond getting involved in the cycloaddition process. In
addition, ketenimines have the ability to serve as the diene
partners, either as 2-azadienes [N-vinyl(aryl) ketenimines] or
as all-carbon dienes [C-vinyl(aryl) ketenimines].
[4 + 2] Cycloaddition Reaction of C-Aryl
Ketenimines with PTAD as a Synthetic
Equivalent of Dinitrogen. Synthesis of
Triazolocinnolines and Cinnolines
Mateo Alajarin,*,† Baltasar Bonillo,† Marta Marin-Luna,†
Angel Vidal,*,† and Raul-Angel Orenes‡
1,2,4-Triazoline-3,5-diones (TADs) are strong electron ac-
ceptors and known to be extremely reactive and synthetically
useful dienophiles5 and enophiles.6 Concerning the dienophilic
behavior of TADs, it is worth mentioning that these neutral
dienophiles have found application in efficient methods to
capture very unstable intermediates,7 for characterizing dienes,8
in the isolation of dienes from complex mixtures9 and for
temporarily protecting diene fragments.10
Departamento de Quimica Organica, Facultad de Quimica,
UniVersidad de Murcia, Campus de Espinardo,
30100 Murcia, Spain, and SerVicio UniVersitario de
Instrumentacion Cientifica, UniVersidad de Murcia, Campus
de Espinardo, 30100 Murcia, Spain
alajarin@um.es
ReceiVed February 12, 2009
The group of Battaglia has reported the periselective
Diels-Alder reaction of C-vinyl-N-(4-methylphenyl) keten-
imines with 4-phenyl-1,2,4-triazoline-3,5-dione (PTAD) which
gives rise to the monocycloadducts across the diene system
formed by the cumulative CdC bond and the adjacent vinyl
(3) For some recent examples, see: (a) Alajar´ın, M.; Ort´ın, M.-M.; Sa´nchez-
Andrada, P.; Vidal, A.; Bautista, D. Org. Lett. 2005, 7, 5281–5284. (b) Alajar´ın,
M.; Bonillo, B.; Ort´ın, M.-M.; Sa´nchez-Andrada, P.; Vidal, A. Org. Lett. 2006,
8, 5645–5648. (c) Alajar´ın, M.; Ort´ın, M.-M.; Sa´nchez-Andrada, P.; Vidal, A.
J. Org. Chem. 2006, 71, 8126–8139.
C,C,N-Triaryl ketenimines and C-alkyl-C,N-diaryl keten-
imines react with 2 equiv of PTAD to provide 1,2,4-
triazolo[1,2-a]cinnolines with a pendant triazolidindione
group by means of a Diels-Alder/ene sequence. The
treatment of such adducts with potassium hydroxide affords
3-aminocinnolines.
(4) For selected examples of [2 + 2] cycloadditions of ketenimines, see: (a)
Alajar´ın, M.; Molina, P.; Vidal, A. Tetrahedron Lett. 1996, 37, 8945–8948. (b)
Alajar´ın, M.; Vidal, A.; Tovar, F.; Arrieta, A.; Lecea, B.; Coss´ıo, F. P.
Chem.sEur. J. 1999, 5, 1106–1117. (c) Coss´ıo, F. P.; Arrieta, A.; Lecea, B.;
Alajar´ın, M.; Vidal, A.; Tovar, F. J. Org. Chem. 2000, 65, 3633–3643. (d)
Alajar´ın, M.; Vidal, A.; Tovar, F.; Ram´ırez de Arellano, M. C.; Coss´ıo, F. P.;
Arrieta, A.; Lecea, B. J. Org. Chem. 2000, 65, 7512–7515. (e) Alajar´; in, M.;
Vidal, A.; Tovar, F.; Ram´ırez de Arellano, M. C. Tetrahedron: Asymmetry 2004,
15, 489–494. (f) For selected examples of [4 + 2] cycloadditions of ketenimines,
see: Alajar´ın, M.; Vidal, A.; Tovar, F.; Conesa, C. Tetrahedron Lett. 1999, 40,
6127–6130. (g) Alajar´ın, M.; Vidal, A.; Tovar, F. Tetrahedron Lett. 2000, 41,
7029–7032. (h) Alajar´ın, M.; Vidal, A.; Ort´ın, M.-M.; Tovar, F. Synthesis 2002,
2393–2398. (i) Lee, K.-J.; Kim, D.-W.; Kim, B.-G. J. Heterocycl. Chem. 2003,
40, 363–367. (j) Martorell, A.; Inman, G.; Alper, H. J. Mol. Catal. A: Chem.
2003, 204-205, 91–96. (k) Alajar´ın, M.; Vidal, A.; Tovar, F.; Sa´nchez-Andrada,
P.; Bautista, D. Tetrahedron 2003, 59, 9913–9918. (l) Alajar´ın, M.; Vidal, A.;
Ort´ın, M.-M. Tetrahedron 2005, 61, 7613–7621. (m) Alajar´ın, M.; Bonillo, B.;
Sa´nchez-Andrada, P.; Vidal, A.; Bautista, D. J. Org. Chem. 2007, 72, 5863–
5866.
(5) For recent examples of using PTAD as dienophile, see: (a) Kobayashi,
S.; Furuya, T.; Otani, T.; Saito, T. Tetrahedron 2008, 64, 9705–9716. (b)
Su¨ennemann, H. W.; Banwell, M. G.; de Meijere, A. Chem.sEur. J. 2008, 14,
7236–7249. (c) Kobayashi, S.; Furuya, T.; Otani, T.; Saito, T. Tetrahedron Lett.
2008, 49, 4513–4515. (d) Alajar´ın, M.; Cabrera, J.; Pastor, A.; Sa´nchez-Andrada,
P.; Bautista, D. J. Org. Chem. 2008, 73, 963–973.
(6) For recent examples of using PTAD as enophile, see: (a) Acevedo, O.;
Squillacote, M. E. J. Org. Chem. 2008, 73, 912–922. (b) Basheer, A.; Rappoport,
Z. J. Org. Chem. 2008, 73, 184–190. (c) Vougioukalakis, G. C.; Roubelakis,
M. M.; Alberti, M. N.; Orfanopoulos, M. Chem.sEur. J. 2008, 14, 9697–9705.
(7) Anastassiou, A. G.; Yakali, E. J. Chem. Soc., Chem. Commun. 1972,
92–93.
Ketenimines, a group of organic nitrogen heterocumulenes
sharing a common 1-aza-1,2-propadiene system, have served
as useful substrates to create structural diversity and complexity
in the synthesis of nitrogen heterocycles. The basis of this
usefulness lies in the rich chemistry of ketenimines,1 which may
undergo the addition of nucleophiles and carbon-centered
radicals2 to their central carbon atom, and easily participate in
pericyclic events: cycloaddition reactions, 6π-electrocyclic ring
closures and sigmatropic rearrangements.3 Among these reac-
tions the [2 + 2] and [4 + 2] cycloaddition processes have
attracted the most attention.4 When participating in Diels-Alder
reactions, the role played by ketenimines depends on the reaction
† Facultad de Quimica.
‡ Servicio Universitario de Instrumentacion Cientifica.
(1) For reviews in the chemistry of ketenimines, see: (a) Krow, D. R. Angew.,
Chem. Int. Ed. Engl. 1971, 10, 435–449. (b) Gambaryan, N. P. Usp. Khim. 1976,
45, 1251–1268. (c) Dondoni, A. Heterocycles 1980, 14, 1547–1566. (d) Barker,
M. W.; McHenry, W. E. In The Chemistry of Ketenes, Allenes and Related
Compounds; Patai, S., Ed.; Wiley-Interscience: Chichester, UK, 1980; Part 2,
701. (e) Alajar´ın, M.; Vidal, A.; Tovar, F. Targets Heterocycl. Syst. 2000, 4,
293–326. (f) Perst, H. Sci. Synth. 2006, 23, 781–898.
(2) (a) Alajar´ın, M.; Vidal, A.; Ort´ın, M.-M. Tetrahedron Lett. 2003, 44,
3027–3030. (b) Alajar´ın, M.; Vidal, A.; Ort´ın, M.-M. Org. Biomol. Chem. 2003,
1, 4282–4292. (c) Alajar´ın, M.; Vidal, A.; Ort´ın, M.-M.; Bautista, D. New
J. Chem. 2004, 28, 570–577. (d) Alajar´ın, M.; Vidal, A.; Ort´ın, M.-M.; Bautista,
D. Synlett 2004, 991–994.
(8) (a) Askani, R.; Chesick, J. P. Chem. Ber. 1973, 106, 8–19. (b) Imagawa,
T.; Sueda, N.; Kawanisi, M. J. Chem. Soc., Chem. Commun. 1972, 388. (c)
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95, 4420–4421.
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Kanedo, C.; Ishikawa, M.; DeLuca, H. F. J. Chem. Soc., Perkin Trans. 1 1979,
165–169. (b) Bosworth, N.; Emke, A.; Midgley, J. M.; Moore, C. J.; Whalley,
W. B.; Fergurson, G.; Marsh, W. C. J. Chem. Soc., Perkin Trans. 1 1977, 805–
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3558 J. Org. Chem. 2009, 74, 3558–3561
10.1021/jo900304a CCC: $40.75 2009 American Chemical Society
Published on Web 04/03/2009

TABLE 1. Triazolocinnolines 3
compd R1 R2
C6H5
SCHEME 1. Reaction of Ketenimines 1 with PTAD
Ar
yielda (%)
3a
3b
3c
3d
3e
3f
H
H
H
4-CH3-C6H4
71
64
72
80
67
66
66
70
51
50
C6H5
C6H5
2-[(CH3)2CH]-C6H4
3-CH3-C6H4
Cl 4-Cl-C6H4 3-CH3-C6H4
H
H
H
H
H
H
C6H5
C6H5
C6H5
C6H5
C6H5
CH3CH2
2-CH3-C6H4
4-CH3O-C6H4
4-[(CH3)2CH]-C6H4
2,6-(CH3)2-C6H3
2-[(4-CH3O-C6H4)2CH]-C6H4
4-[(CH3)2CH]-C6H4
3g
3h
3i
3j
a Isolated yield.
Next we submitted ketenimines 1b-j to reaction with 2 equiv
of PTAD obtaining the same type of double adducts, in moderate
to good isolated yields (50-80%) (Scheme 1, Table 1).
Due to the high reactivity of PTAD as dienophile and
enophile, some of its reported Diels-Alder reactions have been
shown to yield 1:1 diene/PTAD double adducts. These double
adducts resulted from either a two sequential [4 + 2] cycload-
dition processes12 or a Diels-Alder/ene sequence13 comparable
with that leading to compounds 3. In a few cases both types of
sequential processes occur simultaneously.14
In the present case, the first step of the periselective
conversion (1 + PTAD) f 3 is a [4 + 2] cycloaddition reaction,
where the ketenimine acts as all-carbon diene with participation
of its cumulative CdC bond and leads to the formation of the
monoadduct 2. Subsequently, this intermediate undergoes an
ene process with a second molecule of PTAD to give the
triazolocinnoline 3 (Scheme 1).
group.11 On the basis of this result and as a part of our research
activity on the chemistry of ketenimines, we planned to find
out if PTAD would be also reactive toward C,C,N-triaryl and
C-alkyl-C,N-diaryl ketenimines to produce similar Diels-Alder
reactions, but involving in such case an aryl CdC bond as part
of the diene component instead of a vinyl group. However, given
the diverse reactivity of ketenimines, we cannot discard either
their alternative behavior as 2-azadienes, by involving its CdN
bond and one conjugated CdC bond of the N-aryl substituent,
or their participation in ene reactions (as ene components) when
bearing and alkyl group at the terminal carbon atom.
Besides of testing the reactivity of C-aryl ketenimines as all-
carbon dienes versus PTAD one of our aims at the start of this
project was to be able of removing the OdCdN(Ph)dCdO
moiety of the presumed cycloadducts in order to use the
dienophile as a synthetic equivalent of molecular dinitrogen.
The oxidative hydrolysis of such moiety has been claimed by
Adam and De Lucchi to be a notably difficult reaction,15 in the
context of the synthesis of azoalkanes. However, Adam and
co-workers eventually succeeded in this task by sequential
treatment of the PTAD cycloadducts with KOH and CuCl2.16
We were pleased to find out that the simple treatment of
triazolocinnolines 3 with a methanolic KOH solution at room
temperature caused not only the desired hydrolysis of the urazole
fragment but also the removal of the pendant triazolidinedione
group with the concurrent oxidative aromatization of the
cinnoline ring system. This remarkable and unprecedented one-
pot reaction provided the corresponding 3-arylamino-4-substi-
tuted cinnolines 4 in excellent isolated yields (80-98%)
(Scheme 2, Table 2). We assume that the exocyclic imino
In this note we disclose that the reactions of C,C,N-triaryl
and C-alkyl-C,N-diaryl ketenimines with 2 equiv of PTAD
afford periselectively adducts resulting from a Diels-Alder/
ene sequence in which these heterocumulenes play the role of
all-carbon dienes.
Our investigations started by reacting C,C-diphenyl-N-(4-
methylphenyl)ketenimine 1a with PTAD. When a solution of
compound 1a in dichloromethane was treated, at room temper-
ature, with a stoichiometric amount of PTAD the reaction
seemed to be very fast as the deep pink color of PTAD
disappeared in a few seconds. However, the IR spectrum of a
small sample aliquot of the reaction mixture still showed the
strong absorption band near 2000 cm-1 associated with the
NdCdC grouping of the starting heterocumulene. Ketenimine
1a was totally consumed after the addition of a second
equivalent of PTAD, and a crystalline solid precipitated out from
the reaction medium.
The structure of the reaction product was determined to be
that of the Diels-Alder/ene double adduct 3a, showing a 1,2,4-
triazolo[1,2-a]cinnoline heterocyclic nucleus bearing a pendant
N-linked triazolidinone group (Scheme 1). An X-ray structure
determination of a monocrystal of 3a (see Supporting Informa-
tion) was crucial for its precise structural elucidation, also
showing that the exocyclic iminic CdN bond was (Z)-
configured. It seems clear that this configuration minimizes the
steric repulsion between the imine aryl and the phenyl and
triazoline rings attached to the C6 carbon atom of the triazolo-
cinnoline skeleton.
(12) Lai, Y.-C.; Mallakpour, S. E.; Butler, G. B. J. Org. Chem. 1985, 50,
4378–4381.
(13) (a) Mallakpouk, S. E.; Hajipour, A.-R.; Mahdavian, A.-R.; Khoee, S.
J. Appl. Polym. Sci. 2000, 76, 240–248. (b) Mallakpour, S. E.; Hajipour, A.-R.;
Roohipour-Fard, R. J. Appl. Polym. Sci. 2001, 79, 1716–1725. (c) Mallakpour,
S.; Hajipour, A.-R.; Vahabi, R. J. Appl. Polym. Sci. 2003, 89, 1942–1951.
(14) (a) Seguchi, K.; Tanaka, S. J. Chem. Soc., Chem. Commun. 1991, 89–
90. (b) Seguchi, K.; Tanaka, S. Bull. Chem. Soc. Jpn. 1991, 64, 3188–3190. (c)
Tanaka, S.; Seguchi, K.; Itoh, K.; Sera, A. J. Chem. Soc., Perkin Trans. 1 1994,
2335–2339. (d) Mallakpour, S. E.; Asghari, J. Polym. Int. 1996, 41, 43–52.
(15) Adam, W.; De Lucchi, O. Angew. Chem., Int. Ed. Engl. 1980, 19, 762–
779.
(16) (a) Adam, W.; De Lucchi, O.; Erden, I. Angew. Chem., Int. Ed. Engl.
1979, 18, 468–469. (b) Adam, W.; De Lucchi, O.; Erden, I. J. Am. Chem. Soc.
1980, 102, 4806–4809. (c) Adam, W.; De Lucchi, O.; Peters, K.; Peters, E. M.;
Von Schnering, H. G. J. Am. Chem. Soc. 1982, 104, 161–166.
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3296.
J. Org. Chem. Vol. 74, No. 9, 2009 3559

SCHEME 2. Preparation of Cinnolines 4
SCHEME 3. Reaction of Carbodiimides with PTAD
TABLE 2. 3-Aminocinnolines 4
compd R1 R2
C6H5
C6H5
Ar
yielda (%)
4a
4b
4c
4d
4e
4f
H
H
4-CH3-C6H4
2-[(CH3)2CH]-C6H4
91
89
91
97
98
95
98
93
80
Cl 4-Cl-C6H4 3-CH3-C6H4
of 3-arylamino-1,2,4-benzotriazines,21 compounds structurally
related with the anticancer agent tirapazamine.22
H
H
H
H
H
H
C6H5
C6H5
C6H5
C6H5
C6H5
CH3CH2
2-CH3-C6H4
4-CH3O-C6H4
4-[(CH3)2CH]-C6H4
2,6-(CH3)2-C6H3
2-[(4-CH3O-C6H4)2CH]-C6H4
4-[(CH3)2CH]-C6H4
In summary, C-aryl ketenimines participate as dienes in [4
+ 2] cycloaddition reactions with PTAD, which are followed
by in situ ene reactions of the primary cycloadducts with a
second equivalent of enophile. The Diels-Alder/ene double
adducts obtained are converted into 3-aminocinnolines in an
easy and efficient way. In this global sequence PTAD behaves
as a synthetic equivalent of molecular nitrogen reacting as
dienophile in a [4 + 2] cycloaddition with the starting
ketenimines. A diarylcarbodiimide displays a similar sequence,
lacking in the ene process, and leads to a 3-aminobenzotriazine.
4g
4h
4i
a Isolated yield.
function of 3 may cooperate with the external base in promoting
a ꢀ-elimination process along the NdN bond of the pendant
fragment, by stabilizing the negative charge originated at C-4
of the cinnoline nucleus. The PTAD resulting from such
elimination would probably become hydrolyzed in the reaction
medium.
Experimental Section
The structural determination of the previously unknown
3-aminocinnolines 4 was easily accomplished following their
analytical and spectral data. Cinnolines are known to show a
broad spectrum of pharmacological activities,17 the most
representative drug belonging to this class of compounds is
Cinoxacin.18 As far as we know, only a limited number of
3-aminocinnolines have been reported.19
Following the experiments with ketenimines we carried out
the treatment of N,N′-bis(4-methylphenyl)carbodiimide 5 with
PTAD. In this case, the starting carbodiimide 5 behaved as a
2-azadiene, by involving one of the cumulated NdC bonds.20
Then, only 1 equiv of the dienophile PTAD was added to 5,
providing the [1,2,4]triazolo[1,2-a][1,2,4]-benzotriazine 6 (93%
isolated yield), a new type of fused heterocyclic system (Scheme
3). No 1:2 diaddition products were formed, although this
transformation required an excess of PTAD for the total
consumption of the carbodiimide 5. By treatment of compound
6 with methanolic KOH at room temperature, it smoothly
converted into the 3-arylamino-1,2,4-benzotriazine 7 (59%
yield). Thus, this sequence opens a new route for the synthesis
Sample Procedure for the Preparation of Triazolo-
cinnolines 3. To a solution of the corresponding ketenimine 1 (1
mmol) in anhydrous dichloromethane (10 mL) was added solid
PTAD (0.35 g, 2 mmol) at once. The reaction mixture was stirred
at room temperature for 1 h. The precipitated solid was filtered
and air-dried.
Triazolocinnoline 3a (R ) H; Ar ) 4-CH3-C6H4): Yield 71%;
mp 267-268 °C (colorless prisms, dichloromethane); IR (Nujol)
3250 (w), 1778 (s), 1724 (vs), 1707 (vs), 1503 (s), 1492 (s), 1406
(vs), 1235 (s), 1150 (m), 835 (m), 763 (s), 744 (m), 713 (s), 638
(s) cm-1; 1H NMR (DMSO-d6; 300 MHz) δ 2.24 (s, 3 H), 7.09 (s,
4 H), 7.19-7.64 (m, 17 H), 7.91 (d, 1 H, J ) 7.5 Hz), 8.10 (d, 1
H, J ) 7.5 Hz), 9.84 (br s, 1 H); 13C NMR (DMSO-d6, 75 MHz)
δ 20.7, 71.5 (s), 118.6, 121.7, 126.2, 126.3, 126.5, 127.5 (s), 128.1,
128.2, 128.5 (s), 128.8, 129.0, 129.1, 129.2, 129.8, 130.1 (s), 131.5
(s), 134.4 (s), 134.5 (s), 135.6 (s), 143.1 (s), 143.7 (s), 144.2 (s),
153.3 (s), 155.3 (s); exact mass (EI) m/z calcd for C37H27N7O4 [M]+
633.2124, found 633.2132.
Sample Procedure for the Preparation of 3-Amino-
cinnolines 4. KOH (0.56 g, 10 mmol) was dissolved in methanol
(15 mL) and the corresponding triazolocinnoline 3 (1 mmol) was
(20) (a) Molina, P.; Alajar´ın, M.; Vidal, A. J. Chem. Soc., Chem. Commun.
1990, 1277–1279. (b) Molina, P.; Alajar´ın, M.; Vidal, A.; Sa´nchez-Andrada, P.
J. Org. Chem. 1992, 57, 929–939. (c) Saito, T.; Ohkubo, T.; Murayama, K.;
Kuboki, H.; Motoki, S. Chem. Lett. 1993, 1127–1130.
(21) For reviews concerning 1,2,4-triazines and their benzo derivatives, see:
(a) Neunhoeffer, H. In 1,2,4-Triazines and their Benzo DeriVatiVes; Boulton,
A. J., Ed.; Comprehensive Heterocyclic Chemistry II; Elsevier: Oxford, 1996;
Vol. 6, pp 507-573; 1177-1307. (b) Lindsley, C. W.; Layton, M. E. Sci. Synth.
2004, 17, 357–447.
(17) For reviews in the synthesis of cinnolines, see: (a) Haider, N.; Holzer,
W. Sci. Synth. 2004, 16, 251–313. (b) Vinogradova, O. V.; Balova, I. A. Chem.
Heterocycl. Compd. 2008, 44, 501–522. (c) For a review dealing with the
bioactivity of cinnolines, see: Lewgowd, W.; Stanczak, A. Arch. Pharm. 2007,
340, 65–80.
(18) (a) Scavone, J. M.; Gleckman, R. A.; Fraser, D. G. Pharmacotherapy
1982, 2, 266–271. (b) Sisca, T. S.; Heel, R. C.; Romankiewicz, J. A. Drugs
1983, 25, 544–569.
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1984, 49, 289–295. (b) Scobie, M.; Tennant, G. J. Chem. Soc., Chem. Commun.
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3560 J. Org. Chem. Vol. 74, No. 9, 2009

added. The reaction mixture was stirred at room temperature for
36 h. The solvent was removed to dryness under reduced pressure,
and the solid residue was triturated with water. The precipitated
yellow solid was filtered and dried.
Acknowledgment. This work was supported by the Minis-
terio de Educacio´n y Ciencia of Spain and FEDER (Project No.
CTQ2008-05827/BQU), and Fundacio´n Se´neca-CARM (Project
No. 08661/PI/08). B.B. also thanks Fundacio´n Se´neca-CARM
for a fellowship.
3-(4-Methylphenyl)amino-4-phenylcinnoline 4a: Yield 91%;
mp 200 °C (yellow prisms, diethylether); IR (Nujol) 3404 (s), 1610
(vs), 1570 (vs), 1534 (vs), 1493 (vs), 1334 (s), 1177 (m), 1121
(m), 1102 (m), 1089 (s), 1065 (w), 1015 (w), 870 (m), 837 (s),
780 (s) cm-1; 1H NMR (CDCl3; 400 MHz) δ 2.31 (s, 3 H), 6.23 (s,
1 H), 7.11 (d, 2 H, J ) 7.2 Hz), 7.33-7.35 (m, 1 H), 7.43-7.50
(m, 6 H), 7.57-7.63 (m, 3 H), 8.36 (d, 1 H, J ) 8.0 Hz); 13C
NMR (CDCl3, 100 MHz) δ 20.8, 117.9 (s), 119.6, 123.7, 126.5,
126.9 (s), 129.3, 129.4, 129.9, 130.0, 130.9, 131.7 (s), 131.8 (s),
137.9 (s), 147.5 (s), 151.5 (s); exact mass (ESI) m/z calcd for
C21H18N3 [M + H]+ 312.1495, found 312.1493.
Supporting Information Available: Experimental details for
the synthesis of compounds 6 and 7; spectral data (NMR, IR,
MS) for compounds 3b-j, 4b-i, 6 and 7; CIF file of 3a. This
material is available free of charge via the Internet at
http://pubs.acs.org.
JO900304A
J. Org. Chem. Vol. 74, No. 9, 2009 3561