An efficient 1,3-dipolar cycloaddition between aromatic selenoaldehydes and nitrile oxides or nitrile imines: an easy access to selenium-containing five-membered heterocyclic ring system

Article abstract of DOI:10.1016/j.tetlet.2007.01.153

1,3-Dipolar cycloaddition between aromatic selenoaldehydes, generated by thermal retro Diels-Alder reaction of anthracene cycloadducts, and nitrile oxides or nitrile imines proceeded efficiently to give the corresponding [3+2] cycloadducts as a single iso

Full text of DOI:10.1016/j.tetlet.2007.01.153

Tetrahedron Letters 48 (2007) 2303–2306
An efficient 1,3-dipolar cycloaddition between aromatic
selenoaldehydes and nitrile oxides or nitrile imines:
an easy access to selenium-containing five-membered
heterocyclic ring system
Masahito Segi,* Katsuhiko Tanno, Masumi Kojima, Mitsunori Honda and
Tadashi Nakajima
Division of Material Sciences, Graduate School of Natural Science and Technology, Kanazawa University, Kakuma-machi,
Kanazawa 920-1192, Japan
Received 10 January 2007; revised 26 January 2007; accepted 29 January 2007
Available online 1 February 2007
Abstract—1,3-Dipolar cycloaddition between aromatic selenoaldehydes, generated by thermal retro Diels–Alder reaction of anthra-
cene cycloadducts, and nitrile oxides or nitrile imines proceeded efficiently to give the corresponding [3+2] cycloadducts as a single
isomer in good yields, being 1,4,2-oxaselenazoles or 1,3,4-selenadiazoles, respectively.
Ó 2007 Elsevier Ltd. All rights reserved.
Selenocarbonyl compounds are very reactive selenium
O
Se
(Me2Al)2Se
analogues of carbonyl compounds and play an increas-
ingly important role in organic synthesis.1 Among them
selenoaldehydes and selenoketones have been well rec-
ognized to serve as significant 2p dienophiles in cycload-
dition reactions.2 In this context, cycloaddition of the
reactive selenoaldehydes is an important approach to
the preparations of selenium-containing heterocycles
which have been recently paid much attention because
of their interesting reactivities3 and their potential bio-
logical applications.4 In the course of our studies for
generation and reaction of reactive selenoaldehydes,5
we have developed an efficient method for the genera-
tion of selenoaldehydes under neutral conditions via
thermal retro Diels–Alder reaction of selenoaldehyde-
anthracene cycloadducts 1 that were easily synthesized
in good yields from the reaction of the corresponding
aldehydes with (Me2Al)2Se in the presence of anthracene
(Scheme 1).6 We have already reported the reactions of
selenoaldehydes with oxygen-functionalized conjugated
dienes,7 2-methoxyfuran,8 and 5-ethoxyoxazoles9 using
the above retro Diels–Alder protocol.
R
H
R
H
Δ
Se
R
R=Aryl, Alkyl
1
Scheme 1. Generation of selenoaldehydes.
On the other hand, 1,3-dipolar cycloaddition has been
considered to be the most useful method for the con-
struction of five-membered heterocyclic ring systems
containing one or more heteroatoms.10 Selenoaldehydes
serve as excellent dienophiles as mentioned above and
would also have a high potential as good dipolarophiles.
Indeed 1,3-dipolar cycloaddition between selenoaldehy-
des and a stable nitrile oxide (2,4,6-trimethylbenzonitrile
N-oxide) has been already reported.11 However, to our
knowledge, up to date there are no reports regarding
1,3-dipolar cycloaddition of other 1,3-dipoles with sele-
noaldehydes. We have carried out the reaction of seleno-
benzaldehyde, generated by our thermal retro Diels–
Alder reaction of 1 (R = Ph), with some popular 1,3-di-
poles such as nitrones, nitrile oxides, azomethine ylides,
and nitronates, but only reaction with nitrile oxides gave
the corresponding [3+2] cycloadducts of the selenoalde-
hyde in good yields as isolable compounds. This result
may indicate that efficient [3+2] cycloaddition reaction
Keywords: Selenoaldehyde; 1,3-Dipolar cycloaddition; Nitrile oxide;
Nitrile imine; Selenium-containing heterocycle.
*
Corresponding author. Tel.: +81 76 234 4787; fax: +81 76 234
4800; e-mail: segi@t.kanazawa-u.ac.jp
0040-4039/$ - see front matter Ó 2007 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2007.01.153

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M. Segi et al. / Tetrahedron Letters 48 (2007) 2303–2306
Table 1. 1,3-Dipolar cycloaddition between aromatic selenoaldehydes
and 2,4,6-trimethylbenzonitrile N-oxide
of selenoaldehydes can be achieved by using a linear-
type 1,3-dipole such as nitrile oxide. In this paper we de-
scribe an efficient 1,3-dipolar cycloaddition between aro-
matic selenoaldehydes and nitrile oxides or nitrile imines
as a linear-type 1,3-dipole to afford selenium-containing
five-membered ring products, 1,4,2-oxaselenazoles or
1,3,4-selenadiazoles, respectively.
C N
O
N
O
Se
Toluene
reflux, 30 min
Ar
Se
Ar
1
2
Most nitrile oxides are short-lived and reactive species,
and easily dimerize, rearrange, or polymerize.12 At first,
we used a stable aromatic nitrile oxide, 2,4,6-tri-
methylbenzonitrile N-oxide,13 easily prepared through
two steps from 2,4,6-trimethylbenzaldehyde. The toluene
solution of 1 (R = Ph) and the stable nitrile oxide was
heated at reflux for 30 min to give the desired [3+2] cyc-
loadduct (2a) as a single isomer in 85% yield (Eq. 1). The
structure of this adduct was supported by the analysis of
the NMR and mass spectra.14 In particular, regiochem-
istry of the cycloadduct was confirmed by the mass spec-
trum which showed a fragment peak at m/z 225 with an
isotope pattern involving one selenium atom, corre-
sponding to [MꢀPhCHO]+ as shown in Scheme 2. This
indicates that a carbon-oxygen bond exists in the
obtained cycloadduct, being 1,4,2-oxaselenazole.
Entry
Ar
Cycloadduct
Yield (%)a
1
2
3
4
5
Ph
2a
2b
2c
2d
2e
85
74
96
85
65
p-ClC6H4
1-Naphthyl
p-CF3C6H4
p-CH3C6H4
a Isolated yield.
Next we planned the reaction of selenoaldehydes with
unstable nitrile oxides which are in situ formed via dehy-
drochlorination of hydroximoyl chlorides with triethyl-
amine as a base.12 Generally, this dehydrochlorination
has to be carried out in the presence of the dipolaro-
phile, since the lifetime of the reactive nitrile oxide is
too short for isolation. However selenoaldehydes, being
a dipolarophile in this research, are also much more
reactive and very unstable. Accordingly, both seleno-
aldehyde and nitrile oxide must be efficiently in situ
generated in the reaction mixture simultaneously. After
several trials under some different conditions, we found
a following reaction procedure for an efficient 1,3-dipo-
lar cycloaddition. After 6 equiv of triethylamine was
added to a toluene solution involving 1 (R = Ar) and
3 equiv of aromatic hydroximoyl chloride at room tem-
perature, the reaction vessel was immediately placed for
30 min in an oil bath preheated at 110 °C. The results
are summarized in Table 2. In all cases, an efficient
1,3-dipolar cycloaddition proceeded to give the desired
[3+2] cycloadducts (3), 1,4,2-oxaselenazoles, as a single
regioisomer in good yields.15 They were very stable at
room temperature in the atmosphere. The regiochem-
istry of the obtained [3+2] cycloadducts was the same
as the case using 2,4,6-trimethylbenzonitrile N-oxide,
Se
Toluene
reflux, 30 min
Ph
H
Se
Ph
1 (R=Ph)
C N
O
N
O
Se
Yield = 85%
Ph
2a (R=Ph)
ð1Þ
Several anthracene cycloadducts with an aromatic sub-
stituent were similarly treated with 2,4,6-tri-
methylbenzonitrile N-oxide in toluene at reflux for
30 min to give the corresponding [3+2] cycloadducts
(2)14 as a single isomer in good yields. The results are
shown in Table 1. Mass spectra of all cycloadducts
showed a same fragment peak pattern at m/z 225 that
is corresponding to [MꢀArCHO]+, which indicates that
all obtained cycloadducts have 1,4,2-oxaselenazole skel-
eton. Anthracene cycloadducts having an aliphatic
group did not undergo retro Diels–Alder reaction at tol-
uene reflux temperature, but at over 150 °C, the genera-
tion of aliphatic selenoaldehydes was efficient. Thus, we
examined the reaction of 1 (R = n-Pr and CH2CH2Ph)
with the nitrile oxide at 160 °C in toluene, but no isola-
ble cycloadducts could be obtained from the reaction
mixture.
Table 2. 1,3-Dipolar cycloaddition between aromatic selenoaldehydes
and unstable nitrile oxides
X
C N OH
Cl
N
Et3N
O
X
Se
Toluene
reflux, 30 min
Ar
Se
Ar
3
+
X
C N OH
Cl
Et3N
X
C N
O
unstable
Entry
Ar
X
Cycloadduct
Yield (%)a
1
2
3
4
5
6
Ph
MeO
MeO
MeO
H
Cl
Cl
3a
3b
3c
3d
3e
3f
67
67
94
65
76
58
N
N
1-Naphthyl
p-CF3C6H4
p-CF3C6H4
Ph
O
O
Se
Se
Ph
Ph
not obtained
m/z 225
p-CF3C6H4
Scheme 2.
a Isolated yield.

M. Segi et al. / Tetrahedron Letters 48 (2007) 2303–2306
2305
that is, the mass spectra of the cycloadducts showed a
hydes, generated from 1 via thermal retro Diels–Alder
reaction, and nitrile oxides or nitrile imines proceeded
efficiently to afford the [3+2] cycloadducts, 1,4,2-oxasel-
enazoles or 1,3,4-selenadiazoles, respectively, in good
yields. This method offered a promising prospect for
building up selenium-containing five-membered hetero-
cyclic ring system. We are currently extending the scope
of 1,3-dipolar cycloaddition between selenoaldehydes
and other 1,3-dipoles. The results of our findings will
be reported in due course.
fragment peak corresponding to [MꢀArCHO]+.
The reaction of selenoaldehydes with unstable aliphatic
nitrile oxides did not give a satisfactory result, but the
use of a stable aliphatic nitrile oxide, 2,2,3-triphenylpro-
panenitrile N-oxide,16 resulted in the excellent result as
shown in Eq. 2. In this case, the [3+2] cycloadduct
was obtained in excellent yield as a single isomer with
the same regiochemical result as mentioned above.
Se
Acknowledgments
Toluene
reflux, 30 min
Ph
H
Se
Ph
This work was partially supported by a Grant-in-Aid
for Scientific Research from the Ministry of Education,
Science, Sports and Culture, Japan.
ð2Þ
PhCH2
Ph
C N
O
PhCH2
N
O
Ph
Ph
Ph
Se
References and notes
Yield = 91%
Ph
1. For reviews, see: (a) Paulmier, C. In Selenium Reagents
and Intermediates in Organic Synthesis; Baldwin, J. E., Ed.;
Pergamon Press: Oxford, UK, 1986; pp 58–83; (b) Guziec,
F. S., Jr. In Organoselenium Chemistry; Liotta, D., Ed.;
John Wiley & Sons: New York, 1987; pp 277–324; (c)
Guziec, F. S., Jr. In The Chemistry of Organic Selenium
and Tellurium Compounds; Patai, S., Ed.; John Wiley &
Sons: New York, 1987; Vol. 2, pp 215–273; (d) Segi, M.;
Nakajima, T. Yuki Gosei Kagaku Kyokaishi 1995, 53, 678–
686; (e) Murai, T.; Kato, S. In Topics in Current Chemistry
(Organoselenium Chemistry); Wirth, T., Ed.; Springer:
Berlin, 2000; Vol. 208, pp 177–199.
2. (a) Okazaki, R. Yuki Gosei Kagaku Kyokaishi 1988, 46,
1149–1163; (b) Tokitoh, N.; Okazaki, R. Pol. J. Chem.
1998, 72, 971–1000; (c) Guziec, L. J.; Guziec, F. S., Jr. In
Comprehensive Organic Functional Group Transformations
2; Katritzky, A. R., Taylor, R. J. K., Eds.; Elsevier:
Amsterdam, 2005; pp 397–417; For theoretical studies,
see: (d) Rohr, U.; Schatz, J.; Sauer, J. Eur. J. Org. Chem.
1998, 2875–2883; (e) Bachrach, S. M.; Jiang, S. J. Org.
Chem. 1999, 64, 8248–8355; (f) Liao, H.-Y.; Su, M.-D.;
Chu, S.-Y. Chem. Phys. 2000, 261, 275–287; (g) Orlova,
G.; Goddard, J. D. J. Org. Chem. 2001, 66, 4026–
4035.
Nitrile imines are also recognized as a linear-type 1,3-di-
pole and in situ generated via dehydrochlorination of
hydrazonoyl chlorides with triethylamine.12a We have
examined 1,3-dipolar cycloaddition between aromatic
selenoaldehydes and aromatic N-phenyl nitrile imines,
using a similar reaction procedure as the aforemen-
tioned 1,3-dipolar cycloaddition of nitrile oxides. The
expected [3+2] cycloadducts (4), 1,3,4-selenadiazoles,
were obtained as a single regioisomer in good yields
and identified by the analysis of the NMR and mass
spectra.17 The results are shown in Table 3. No signifi-
cant fragment peak corresponding to [MꢀArCHNPh]+
was observed in the mass spectra, but the signal corre-
sponding to the eliminated fragment ion, [ArCHNPh]+,
appeared clearly with over 50% relative intensity in all
cases. These selenium-containing five-membered hetero-
cycles were also stable at room temperature in the
atmosphere.
In conclusion, we have demonstrated that regioselective
1,3-dipolar cycloaddition between aromatic selenoalde-
3. (a) Renson, M. In The Chemistry of Organic Selenium and
Tellurium Compounds; Patai, S., Rappoport, Z., Eds.;
John Wiley & Sons: New York, 1986; Vol. 1, pp 399–516;
(b) Litvinov, V. P.; Dyachenko, V. D. Russ. Chem. Rev.
1997, 66, 923–951.
4. (a) Wendel, A. Selenium in Biology and Medicine;
Springer: Berlin, 1989; (b) Burk, R. F. Selenium in Biology
and Human Health; Springer: New York, 1994.
Table 3. 1,3-Dipolar cycloaddition between aromatic selenoaldehydes
and N-phenyl nitrile imines
X
C N NHPh
Cl
Ph
N
Et3N
N
X
5. (a) Segi, M.; Nakajima, T.; Suga, S.; Murai, S.; Ryu, I.;
Ogawa, A.; Sonoda, N. J. Am. Chem. Soc. 1988, 110,
1976–1978; (b) Segi, M.; Takahashi, M.; Nakajima, T.;
Suga, S.; Murai, S.; Sonoda, N. Tetrahedron Lett. 1988,
29, 6965–6968; (c) Segi, M.; Koyama, T.; Nakajima, T.;
Suga, S.; Murai, S.; Sonoda, N. Tetrahedron Lett. 1989,
30, 2095–2098; (d) Segi, M.; Kato, M.; Nakajima, T.
Tetrahedron Lett. 1991, 32, 7427–7430; (e) Li, G. M.; Segi,
M.; Nakajima, T. Tetrahedron Lett. 1992, 33, 3515–3518;
(f) Segi, M.; Takahashi, T.; Ichinose, H.; Li, G. M.;
Nakajima, T. Tetrahedron Lett. 1992, 33, 7865–7868; (g)
Li, G. M.; Niu, S.; Segi, M.; Zingaro, R. A.; Yamamoto,
H.; Watanabe, K.; Nakajima, T.; Hall, M. B. J. Org.
Chem. 1999, 64, 1565–1575.
Se
Toluene
reflux, 30 min
Ar
Se
Ar
4
+
X
C N NHPh
Cl
Et3N
X
C N NPh
unstable
Entry
Ar
X
Cycloadduct
Yield (%)a
1
2
3
4
5
Ph
H
H
H
NO2
NO2
4a
4b
4c
4d
4e
81
67
85
68
87
p-MeOC6H4
p-CF3C6H4
Ph
p-CF3C6H4
a Isolated yield.

2306
M. Segi et al. / Tetrahedron Letters 48 (2007) 2303–2306
6. Segi, M. Yuki Gosei Kagaku Kyokaishi 2003, 61, 661–669.
added in anthracene cycloadduct (1, 0.5 mmol), hydroxi-
moyl chloride (1.5 mmol), and toluene (15 mL) under an
argon atmosphere. This mixture was then stirred until all
of the solids dissolved at room temperature. Once a clear
solution was obtained, triethylamine (3.0 mmol) was
added to the reaction mixture, and the reaction vessel
was immediately placed into an oil bath preheated at
110 °C. After the heating at 110 °C for 30 min, the mixture
was allowed to cool to room temperature and evaporated
in vacuo. The resulting residue was purified by column
chromatography on silica gel with 40:1 hexane/ethyl
acetate to give the desired cycloadduct 3 as a single
isomer. Selected spectral data of [3+2] Cycloadducts 3.
Compound 3a: 1H NMR (400 MHz, CDCl3): d 3.83 (s,
3H), 6.90 (d, 2H), 7.32–7.39 (m, 3H), 7.52–7.56 (m, 2H),
7.54 (s, 1H), 7.59 (d, 2H); Mass (EI mode): m/z (relative
intensity) 51 (21.4), 77 (61.4), 90 (42.5), 103 (31.4), 105
(66.2), 106 (66.2), 133 (100), 213 (24.6), 319 (M+, 3.2);
HRMS calcd for C15H131NO2Se (M+) 319.0112; found
319.0109. Compound 3c: H NMR (400 MHz, CDCl3): d
3.84 (s, 3H), 6.91 (d, 2H), 7.57 (s, 1H), 7.59 (d, 2H), 7.63
(s, 4H); Mass (EI mode): m/z (relative intensity) 90 (32.0),
103 (22.2), 133 (100), 145 (64.9), 173 (73.0), 174 (53.9), 198
(22.0), 211 (21.9), 213 (44.7), 387 (M+, 8.6); HRMS calcd
for C16H12F3NO2Se (M+) 386.9985; found 386.9981.
Compound 3e: 1H NMR (400 MHz, CDCl3): d 7.37 (d,
2H), 7.44 (s, 1H), 7.45–7.55 (m, 5H), 7.58 (d, 2H); Mass
(EI mode): m/z (relative intensity) 77 (21.1), 105 (20.6),
137 (50.0), 176 (31.2), 215 (20.2), 217 (43.3), 246 (100), 248
(65.3), 323 (M+, 4.7); HRMS calcd for C14H10ClNOSe
(M+) 322.9616; found 322.9626.
7. (a) Segi, M.; Yamamoto, H.; Hori, T.; Nakajima, T.
Phosphorus, Sulfur Silicon Relat. Elem. 1998, 136–138,
599–602; (b) Tomoda, S.; Zhang, J.; Kaneno, D.; Segi, M.;
Zhou, A. Tetrahedron Lett. 2000, 41, 4597–4601.
8. Zhou, A.; Segi, M.; Nakajima, T. Tetrahedron Lett. 2003,
44, 1179–1182.
9. Segi, M.; Zhou, A.; Honda, M. Phosphorus, Sulfur, and
Silicon 2005, 180, 1045–1049.
10. Padwa, A.. In 1,3-Dipolar Cycloaddition Chemistry; John
Wiley & Sons: New York, 1984; Vols. 1 and 2.
11. (a) Meinke, P. T.; Krafft, G. A. Tetrahedron Lett. 1987, 28,
5121–5124; (b) Meinke, P. T.; Krafft, G. A. J. Am. Chem.
Soc. 1988, 110, 8671–8679; (c) Takeda, N.; Tokitoh, N.;
Okazaki, R. Angew. Chem. Int. Ed. Engl. 1996, 35, 660–
662; (d) Takeda, N.; Tokitoh, N.; Okazaki, R. Tetra-
hedron 1997, 53, 12167–12182.
12. (a) Caramella, P.; Grunanger, P. In Padwa, A., Ed.; 1,3-
Dipolar Cycloaddition Chemistry; John Wiley & Sons:
New York, 1984; Vol. 1, pp 291–392; (b) Torssell, K. B. G.
Nitrile Oxides, Nitrones, and Nitronates in Organic Syn-
thesis; VCH Publishers: New York, 1988; Chapter 2, pp
55–74.
13. Grundmann, C.; Richter, R. J. Org. Chem. 1968, 33, 476–
478.
14. Selected spectral data of [3+2] Cycloadducts 2. Com-
pound 2a: 1H NMR (400 MHz, CDCl3): d 2.27 (s, 3H),
2.29 (s, 6H), 6.87 (s, 2H), 7.30–7.57 (m, 5H), 7.69 (s, 1H);
13C NMR (100 MHz, CDCl3): d 19.68, 21.10, 93.77,
125.17, 125.89, 128.53, 128.61, 128.95, 137.06, 139.33,
139.61, 153.99; 77Se NMR (76.2 MHz, CDCl3): d 617.72;
Mass (EI mode): m/z (relative intensity) 51 (11.9), 77
(37.9), 105 (36.5), 130 (89.3), 145 (100), 225 (51.6), 331
(M+, 0.7); HRMS calcd for [C10H11NOSe (M+ꢀPhCHO)]
225.0057; found 225.0058. Compound 2c; 1H NMR
(400 MHz, CDCl3): d 2.19 (s, 3H), 2.20 (s, 6H), 6.79 (s,
2H), 7.41–7.84 (m, 7H), 8.22 (s, 1H); 13C NMR (100 MHz,
CDCl3): d 19.73, 21.11, 91.24, 122.40, 123.33, 125.09,
125.40, 125.99, 126.57, 128.55, 128.72, 129.20, 129.35,
133.78, 134.73, 137.12, 139.64, 154.86; 77Se NMR
(76.2 MHz, CDCl3): d 615.61; Mass (EI mode): m/z
(relative intensity) 51 (14.3), 77 (28.1), 89 (27.5), 136
(81.3), 154 (100), 225 (27.7), 307 (16.1), 382 (M+, 25.4);
HRMS calcd for C21H210NOSe (M+) 382.0710; found
382.0712. Compound 2d: H NMR (400 MHz, CDCl3): d
2.25 (s, 3H), 2.27 (s, 6H), 6.87 (s, 2H), 765 (br s, 4H), 7.72
(s, 1H); 13C NMR (100 MHz, CDCl3): d 19.70, 21.13,
92.25, 124.62, 125.65, 125.70, 125.92, 128.66, 137.11,
139.92, 144.08, 153.69; 77Se NMR (76.2 MHz, CDCl3): d
622.33; Mass (EI mode): m/z (relative intensity) 63 (18.7),
77 (37.9), 136 (84.8), 146 (35.4), 154 (100), 173 (27.1), 225
(50.3), 400 (M+, 67.3); HRMS calcd for C18H17F3NOSe
(M+) 400.0427; found 400.0424.
16. Yao, C.-F.; Kao, K.-H.; Liu, J.-T.; Chu, C.-M.; Wang, Y.;
Chen, W.-C.; Lin, Y.-M.; Lin, W.-W.; Yan, M.-C.; Liu,
J.-Y.; Chuang, M.-C.; Shiue, J.-L. Tetrahedron 1998, 54,
791–822.
17. Selected spectral data of [3+2] Cycloadducts 4. Com-
1
pound 4a: H NMR (400 MHz, CDCl3): d 6.83–6.88 (m,
1H), 7.08 (s, 1H), 7.14–7.40 (m, 12H), 7.63–7.66 (m, 2H);
Mass (EI mode): m/z (relative intensity) 77 (69.2), 91
(82.1), 103 (28.3), 104 (100), 180 (54.2), 181 (51.2), 194
(34.4), 207 (43.2), 362 (22.2), 364 (M+, 44.2); HRMS calcd
for C20H16N2Se (M+) 364.0479; found 364.0481. Com-
1
pound 4c: H NMR (400 MHz, CDCl3): d 6.87–6.90 (m,
1H), 7.02–7.47 (m, 9H), 7.10 (s, 1H), 7.55 (d, 2H), 7.63 (d,
2H); Mass (EI mode): m/z (relative intensity) 77 (80.2), 91
(88.7), 103 (33.7), 104 (100), 172 (49.1), 173 (21.3), 194
(25.3), 248 (53.3), 249 (52.2), 275 (46.7), 430 (23.8), 432
(M+, 47.8); HRMS calcd for C21H15F3N2Se (M+)
432.0353; found 432.0350. Compound 4d: 1H NMR
(400 MHz, CDCl3): d 6.91–6.95 (m, 1H), 7.17–7.35 (m,
9H), 7.21 (s, 1H), 7.74 (d, 2H), 8.23 (d, 2H); Mass (EI
mode): m/z (relative intensity) 77 (66.2), 91 (67.9), 104
(100), 105 (30.5), 180 (67.8), 181 (51.5), 252 (37.1), 409
(M+, 35.1); HRMS calcd for C20H15N3O2Se (M+)
409.0330; found 409.0329.
15. Typical experimental procedure: To an oven dried 30 mL
round bottomed flask fitted with a reflux condenser were