Reaction of N-methyl-5-tributylstannyl-4-fluoro-1H-pyrazole and its application to N-methyl-chromeno[2,3-d]pyrazol-9-one synthesis

Article abstract of DOI:10.1021/jo800431t

(Chemical Equation Presented) N-Methylation by sequential treatment of 5-tributylstannyl-4-fluoro-1H-pyrazole 1 with LDA and iodomethane regioselectively afforded the compound 2a in high yield. The addition reaction of 5-lithiated-4-fluoro-1H-pyrazole generated from 2a with a wide range of electrophiles allowed a facile introduction of different substituents at position 5 in good yields. The adduct 3d was efficiently converted to N-methyl-chromeno[2,3-d]pyrazol-9-one 9 in 3 steps.

Full text of DOI:10.1021/jo800431t

SCHEME 1. N-Methylation of 1
Reaction of
N-Methyl-5-tributylstannyl-4-fluoro-1H-pyrazole
and Its Application to
N-Methyl-chromeno[2,3-d]pyrazol-9-one Synthesis
Takeshi Hanamoto,*,† Eri Hashimoto,† Masayuki Miura,†
Hiroshi Furuno,‡ and Junji Inanaga‡
fluorinated pyrazoles bearing potential functional groups would
be promising for introducing more complex compounds in the
field of fine chemicals. As a part of our ongoing research on
incorporating fluorine into pyrazoles, we have recently reported
the synthesis and some cross-coupling reactions of 5-tributyl-
stannyl-4-fluoro-1H-pyrazole (1).4 Our next objective was to
synthesize and develop N-methylpyrazoles since these units are
widely encountered in agrochemicals and pharmaceuticals.5 We
herein report the facile preparation and reactions of N-meth-
ylpyrazole derivatives including an application to the synthesis
of N-methylchromeno[2,3-d]pyrazol-9-one (9).
Department of Chemistry and Applied Chemistry, Saga
UniVersity, Honjyo-machi 1, Saga 840-8502, Japan, and
Institute for Materials Chemistry and Engineering (IMCE),
Kyushu UniVersity, Hakozaki, Higashi-ku,
Fukuoka 812-8581, Japan
hanamoto@cc.saga-u.ac.jp
ReceiVed March 5, 2008
According to our previous procedure for the preparation of
N-methyl-5-tributylstannyl- 4-trifluoromethyl-1H-pyrazole, the
preliminary reaction of 1 with iodomethane was carried out by
using LDA under similar conditions.6 The reaction proceeded
smoothly providing the corresponding N-methylpyrazole deriva-
tive in 91% yield as a single regioisomer (Scheme 1). To confirm
the regiochemistry of 2a we attempted NOE experiments;
however, we could obtain no useful information. Although the
correct regioselectivity was not determined at this point, we
tentatively assigned this N-methylpyrazole to N-methyl-5-
tributylstannyl-4-fluoro-1H-pyrazole (2a) on the basis of our
previous results.6
It is well-accepted that transmetalation of tributylstannyl
compound with BuLi at low temperatures gives the correspond-
ing lithiated species in high yield.7 The transmetalation of 2a
was performed by addition of BuLi at -78 °C in THF to yield
the corresponding 5-lithiated-4-fluoro-1H-pyrazole. Then ben-
zaldehyde was added, and the mixture was gradually warmed
to room temperature while being stirred to yield the desired
product in 91% yield (Table 1, entry 1). Under similar
N-Methylation by sequential treatment of 5-tributylstannyl-
4-fluoro-1H-pyrazole 1 with LDA and iodomethane regi-
oselectively afforded the compound 2a in high yield. The
addition reaction of 5-lithiated-4-fluoro-1H-pyrazole gener-
ated from 2a with a wide range of electrophiles allowed a
facile introduction of different substituents at position 5 in
good yields. The adduct 3d was efficiently converted to
N-methyl-chromeno[2,3-d]pyrazol-9-one 9 in 3 steps.
The pyrazole skeleton is found widely not only in agrochemi-
cal compounds but also in pharmaceutically active compounds.1
On the other hand, it has been documented that the introduction
of fluorine in azaheterocycles may play an important role in
their biological activity.2 For example, Celecoxib having a
trifluoromethyl group on the pyrazole ring shows anti-inflam-
matory and analgetic activity.3 Accordingly, exploration of
(4) (a) Hanamoto, T.; Koga, Y.; Kido, E.; Kawanami, T.; Furuno, H.; Inanaga,
J. Chem. Commun. 2005, 2041. (b) Hanamoto, T.; Suetake, T.; Koga, Y.;
Kawanami, T.; Furuno, H.; Inanaga, J. Tetrahedron 2007, 63, 5062.
(5) (a) Calle, M.; Calvo, M.; Gonza´lez-Ortega, A.; Gonza´lez-Nogal, A.
Tetrahedron 2006, 62, 611. (b) Cottineau, B.; Chenault, J.; Guillaumet, G.
Tetrahedron Lett. 2006, 47, 817. (c) Ivachtchenko, A. V.; Kravchenko, D. V.;
Zheludeva, V. I.; Pershin, D. G. J. Heterocycl. Chem. 2004, 41, 931. (d)
Cottineau, B.; Chenault, J. Synlett 2002, 769. (e) Smith, T. E.; Mourad, M. S.;
Velander, A. J. Heterocycles 2002, 57, 1211. (f) Katritzky, A. R.; Wang, M.;
Zhang, S.; Voronkov, M. V.; Steel, P. J. J. Org. Chem. 2001, 66, 6787. (g)
Azami, H.; Barrett, D.; Tanaka, A.; Sasaki, H.; Matsuda, K.; Sakurai, M.;
Terasawa, T.; Shirai, F.; Chiba, T.; Matsumoto, Y.; Tawara, S. Bioorg. Med.
Chem. 2001, 9, 961. (h) Calle, M.; Cuadrado, P.; Gonza´lez-Nogal, A. M.; Valero,
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Chem. Abstr. 2000, 133, 218748. (j) Chatani, N.; Fukuyama, T.; Tatamidani,
H.; Kakiuchi, F.; Murai, S. J. Org. Chem. 2000, 65, 4039. (k) Torrens, A.;
Castrillo, J. A.; Redondo, J. Synlett 1999, 765. (l) Hueso-Rodr´ıguez, J. A.;
Berrocal, J.; Gutie´rrez, B.; Farre´, A. J.; Frigola, J. Bioorg. Med. Chem. Lett.
1993, 3, 269. (m) Yamamoto, S.; Sato, T.; Morimoto, K.; Makino, K.
J. Heterocycl. Chem. 1991, 28, 1849. (n) Effenberger, F.; Krebs, A. J. Org.
Chem. 1984, 49, 4687.
* Author to whom correspondence should be addressed. Fax: 81-952-28-8548.
† Saga University.
‡ Kyushu University.
(1) Elguero, J. ComprehensiVe Heterocyclic Chemistry; Katritzky, A. R., Rees,
C. W., Scriven, E. F. V., Eds.; Pergamon: Oxford, UK, 1996; Vol. 5.
(2) (a) Mu¨ller, K.; Faeh, C.; Diederich, F. Science 2007, 317, 1881. (b) Be´gue´,
J.-P.; Bonnet-Delpon, D. J. Fluorine Chem. 2006, 127, 992. (c) Uneyama, K.
Organofluorine Chemistry; Blackwell Publishing: Oxforf, UK, 2006. (d)
Chambers, R. D. Fluorine in Organic Chemistry; Blackwell Publishing: Oxford,
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Organofluorine Compounds; Springer: Berlin, Germany, 2000. (g) Hudlicky,
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Monogragh No. 187; American Chemical Society: Washington, DC, 1995.
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Shen, J.; Yang, Y.; Jiang, H.; Chen, K. J. Med. Chem. 2002, 45, 4816. (b) Price,
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4736 J. Org. Chem. 2008, 73, 4736–4739
10.1021/jo800431t CCC: $40.75 2008 American Chemical Society
Published on Web 05/24/2008

TABLE 1. Reaction of 2a with Various Electrophilesa
a Aldehyde or ketone, 1.5 equiv. b Isolated yield. c The reaction was quenched at -78 °C.
conditions, the reaction of 2a with other aromatic aldehydes
bearing either an electron-donating or an electron-withdrawing
substituent on the aromatic ring proceeded to give the corre-
sponding adducts in high yields (entries 2-4). Cinnamaldehyde,
as an R,ꢀ-unsaturated aldehyde, proved to be a good electrophile
and delivered the 1,2-addition adduct. No conjugated addition
product was observed (entry 5). Linear and branched aliphatic
aldehydes successfully underwent addition reaction to give the
corresponding adducts in good yields (entries 6 and 7). Not only
2-undecanone as an aliphatic ketone but also acetophenone as
an aromatic ketone reacted satisfactorily (entries 8 and 9). In
addition to the above carbonyl compounds, S-phenyl benzeneth-
iosulfate gave the corresponding N-methyl-5-phenylthio-1H-
pyrazole in 80% yield (entry 10). These results are summarized
in Table 1.
proved to be useful for the complete C-5-lithiation of
N-methyl-1H-pyrazole.5c,e,h,k–lm,8
On the basis of the successful syntheses of various N-methyl-
5-substituted-1H-pyrazoles shown in Table 1, we designed
procedures for further incorporation of substituents at position
3 of the N-methyl-4,5-disubstituted-1H-pyrazole ring. For this
purpose, we selected the product 3j, bearing no hydroxy group,
and examined the reaction conditions. The 3-lithiated species
was generated from 3j by treatment of BuLi at -78 °C in THF
followed by reaction with ethyl chloroformate to give the
corresponding 3,4,5-trisubstituted pyrazole in 52% yield
(Scheme 2).9
Finally, application of the product 3d (Table 1) to the
preparation of novel azaxanthones was planned.10 We hoped
that the corresponding tricyclic structure should be built up via
an intramolecular nucleophilic aromatic substitution using
Interestingly, the product 3g gave single crystals suitable for
X-ray crystallographic analysis. A crystal drawing of 3g is
shown in the Supporting Information. This X-ray analysis
revealed unambiguous proof of the regiochemistry of N-methyl-
5-alkylated-4-fluoro-1H-pyrazoles and definitely assigned the
structure of 2a as N-methyl-5-tributylstannyl-4-fluoro-1H-
pyrazole. Consequently, our findings and synthetic procedures
SCHEME 2. Reaction of 3j
J. Org. Chem. Vol. 73, No. 12, 2008 4737

SCHEME 3. Preparation of N-Methyl-chromeno[2,3-d]pyrazol-9-one 9
(10 mL) was added LDA-THF solution (3.11 mmol) by a double-
fluorine as a scaffold on the pyrazole ring. According to the
literature procedure, treatment of compound 5 with K2CO3 in
DMF at 50 °C resulted in decomposition.10c However, the vital
ring closure via the addition-elimination process of the 4-fluoro-
1H-pyrazole 8 bearing the keto-structure effectively took place
to produce the desired N-methyl-chromeno[2,3-d]pyrazol-9-one
(9) in 73% overall yield from 3d under similar reaction
conditions with Cs2CO3 (Scheme 3).11 To the best of our
knowledge, this is the first selective and high-yielding prepara-
tion of such compounds.10f,i
ended needle at -78 °C. At this temperature 0.21 mL (3.37 mmol)
of MeI was added to the mixture, and the reaction was allowed to
warm to room temperature with stirring overnight. The reaction
was quenched with water and hexane and extracted with hexane/
ether ) 3/1. The combined organic layer was dried over Na2SO4
and concentrated under reduced pressure. The residue was purified
by silica gel column chromatography (hexane/ethyl acetate/triethy-
lamine ) 150/50/1) to give the desired compound 2a as a colorless
oil (934.7 mg, 91%, >99:1): IR (neat) 2958, 2927, 2872, 2854,
1
1522, 1464, 1388, 1348, 1077, 977, 816 cm-1; H NMR (CDCl3,
In summary, we have developed a facile method for the
preparation of various N-methyl-4-fluoro-5-substituted-1H-
pyrazoles in high yield, and have illustrated the possibility of
construction of 3,4,5-trisubstituted pyrazoles. Furthermore, we
achieved the first selective and high-yielding preparation of
chromeno[2,3-d]pyrazol-9-one compound as a new class of
azaxanthones.
300 MHz) δ 0.90 (9H, t, J ) 7.2 Hz), 1.05-1.70 (18H, m), 3.82
(3H, s), 7.29 (1H, d, J ) 4.8 Hz); 13C NMR (CDCl3, 75 MHz) δ
10.1, 13.6, 27.1, 28.8, 41.6, 124.6 (d, J ) 17.4 Hz), 127.1 (d, J )
43.1 Hz), 158.1 (q, J ) 238.8 Hz); 19F NMR (CDCl3, 283 MHz)
δ -172.3 [dm, J ) 4.2 Hz, JF- Sn ) 25.3 Hz (7.6%), JF- Sn )
25.3 Hz (8.6%)]; GC-MS m/z 332 (2, M+ - Bu), 276 (21), 221
(51), 218 (100), 138 (37), 137 (31), 121 (44), 120 (62), 101 (36),
57 (25). Anal. Calcd for C16H31FN2Sn: C, 49.38; H, 8.03; N, 7.20.
Found: C, 49.41; H, 7.97; N, 7.05.
117
119
Experimental Section
N-Methyl-5-[(phenyl)hydroxymethyl]-4-fluoro-1H-pyrazole (3a).
To a solution containing 351.7 mg (0.903 mmol) of pyrazole 2a in
THF (2 mL) was added BuLi (2.71 M in hexane solution, 0.37
mL, 1.00 mmol) by means of a syringe at -78 °C. At this
temperature 110 µL (1.08 mmol) of benzaldehyde was added to
the mixture, and the reaction was allowed to warm to room
temperature with stirring for 2 h. The reaction was quenched with
a saturated aqueous NaHCO3 solution and extracted with hexane/
ether ) 3/1. The extraction was repeated twice. The combined
organic layers were dried over Na2SO4 and concentrated under
reduced pressure. The residue was purified by silica gel column
chromatography (hexane/ethyl acetate/triethylamine ) 150/50/1)
to give the desired compound 3a as a white solid (170.2 mg, 91%):
mp 34.2-35.1 °C; IR (KBr) 3296, 1585, 1444, 1402, 1357, 1319,
N-Methyl-5-tributylstannyl-4-fluoro-1H-pyrazole (2a). To a
solution containing 971.0 mg (2.59 mmol) of pyrazole 14a in THF
(8) For the regiospecific C-5 lithiation of N-1 substituted pyrazoles, see:(a)
Hoffmann, M. G. Tetrahedron 1995, 51, 9511. (b) Subramanyam, C. Synth.
Commun. 1995, 25, 761. (c) Booker-Milburn, K. I. Synlett 1992, 327. (d)
Effenberger, F.; Roos, M.; Ahmad, R.; Krebs, A. Chem. Ber. 1991, 124, 1639.
(e) Heinisch, G.; Holzer, W.; Pock, S. J. Chem. Soc. Perkin. Trans. 1 1990,
1829.
(9) For some reports on 4-fluoro-3,5-disubstituted-pyrazole derivatives, see:
(a) Chanteau, F.; Plantier-Royon, R.; Portella, C. Synlett 2004, 512. (b) Katoch-
Rouse, T.; Pavlova, O. A.; Caulder, T.; Hoffman, A. F.; Mukhin, A. G.; Horti,
A. G. J. Med. Chem. 2003, 46, 642. (c) Sloop, J. C.; Bumgardner, C. L.; Loehle,
W. D. J. Fluorine Chem. 2002, 118, 135. (d) Bouillon, J.-P.; Didier, B.; Dondy,
B.; Doussot, P.; Plantier-Royon, R.; Portella, C. Eur. J. Org. Chem. 2001, 187.
(e) Dondy, B.; Doussot, P.; Portella, C. Tetrahedron Lett. 1994, 35, 409. (f)
Bumgardner, C.; Sloop, J. C. J. Fluorine Chem. 1992, 56, 141. (g) Ishihara, T.;
Okada, Y.; Kuroboshi, M.; Shinozaki, T.; Ando, T. Chem. Lett. 1988, 819.
(10) (a) Ghosh, T.; Bandyopadhyay, C. J. Heterocycl. Chem. 2006, 43, 1431.
(b) Atkinson, P.; Findlay, K. S.; Kielar, F.; Pal, R.; Parker, D.; Poole, R. A.;
Puschmann, H.; Richardson, S. L.; Stenson, P. A.; Thompson, A. L.; Yu, J.
Org. Biomol. Chem. 2006, 4, 1707. (c) Kristensen, J. L.; Vedsø, P.; Begtrup, M.
Tetrahedron 2002, 58, 2397. (d) Tre´court, F.; Breton, G.; Bonnet, V.; Mongin,
F.; Marsais, F.; Que´guiner, G. Tetrahedron 2000, 56, 1349. (e) Rampa, A.; Bisi,
A.; Valenti, P.; Recanatini, M.; Cavalli, A.; Andrisano, V.; Cavrini, V.; Fin, L.;
Buriani, A.; Giusti, P. J. Med. Chem. 1998, 41, 3976. (f) Ghosh, C. K.; Sahana,
S.; Ghosh, C. Indian J. Chem. Sect. B. 1996, 35, 669. (g) Mongin, O.; Rocca,
P.; Thomas-dit-Dumont, L.; Tre´court, F.; Marsais, F.; Godard, A.; Que´guiner,
G. J. Chem. Soc., Perkin Trans. 1 1995, 2503. (h) Ghosh, C. K.; Bhattacharya,
K.; Ghosh, C. Tetrahedron 1994, 50, 4905. (i) Ghosh, C. K.; Bhattacharyya,
A.; Ghosh-Dastidar, P. P. Indian J. Chem. Sect. B. 1987, 26, 128. (j) Beelitz,
K.; Praefcke, K. Justus Liebigs Ann. Chem. 1979, 1081. (k) Sliwa, H.; Cordonnier,
G. J. Heterocycl. Chem. 1977, 14, 169. (l) Villani, F. J.; Magatti, C. V.
J. Heterocycl. Chem. 1975, 12, 1239. (m) Villani, F. J.; Hannon, J.; Wefer, E. A.;
Mann, T. A.; Morton, J. B. J. Org. Chem. 1975, 40, 1734.
1
1044, 835, 764, 720 cm-1; H NMR (CDCl3, 300 MHz) δ 2.34
(1H, d, J ) 4.4 Hz), 3.65 (3H, d, J ) 0.6 Hz), 6.11 (1H, d, J ) 4.4
Hz), 7.30-7.40 (5H, m); 13C NMR (CDCl3, 75 MHz) δ 38.5, 65.0,
124.6 (d, J ) 12.5 Hz), 125.7, 127.8, 128.5, 139.7, 147.0 (d, J )
246.6 Hz); 19F NMR (CDCl3, 283 MHz) δ -177.0 (d, J ) 4.9
Hz); GC-MS m/z 206 (16, M+), 205 (20), 127 (67), 115 (21), 109
(30), 105 (37), 99 (34), 77 (100), 51 (38). Anal. Calcd for
C11H11FN2O: C, 64.07; H, 5.38; N, 13.58. Found: C, 64.05; H, 5.40;
N, 13.50.
N-Methyl-5-[2′-(tert-butyldimethylsilyloxy)benzoyl]-4-fluoro-
1H-pyrazole (7). To a solution containing 211.0 mg (0.63 mmol)
of 3d in CH2Cl2 (3 mL) was added PCC (265.7 mg, 1.25 mmol) at
room temperature. The reaction mixture was stirred for 90 min and
diluted with ether. After the mixture was filtered through a short
Celite pad (ether as an eluent), the combined filtrate was concen-
trated in vacuo. The residue was purified by silica gel column
chromatography (hexane/ethyl acetate/triethylamine ) 200/20/1)
(11) The product yield was comparable when 8 was treated with K2CO3 under
similar conditions.
4738 J. Org. Chem. Vol. 73, No. 12, 2008

to give the desired compound 7 as a white solid (186.4 mg, 89%);
mp 48.7-50.6 °C; IR (KBr) 3120, 2858, 1651, 1600, 1557, 1487,
1301, 1106, 1011, 898, 841, 673 cm-1; 1H NMR (CDCl3, 300 MHz)
δ 0.12 (6H, s), 0.77 (9H, s), 4.14 (3H, s), 6.86 (1H, dd, J ) 6.1,
2.6 Hz), 7.04 (1H, t, J ) 7.5 Hz), 7.27 (1H, d, J ) 4.4 Hz), 7.36
(1H, d, J ) 1.7 Hz), 7.40 (1H, dt, J ) 7.7, 1.8 Hz); 13C NMR
(CDCl3, 75 MHz) δ -4.6, 17.9, 25.2, 40.9, 119.5, 121.2, 124.8 (d,
J ) 13.8 Hz), 126.8 (d, J ) 18.7 Hz), 129.5, 131.2 (d, J ) 1.2
Hz), 132.8, 150.8 (d, J ) 261.6 Hz), 153.8 (d, J ) 1.2 Hz), 184.1
(d, J ) 3.7 Hz); 19F NMR (CDCl3, 283 MHz) δ -162.3 (d, J )
3.7 Hz); GC-MS m/z 278 (23), 277 (100), 276 (18), 135 (4), 127
(4), 95 (5), 91 (5), 77 (23), 76 (5), 73 (13). Anal. Calcd for
C17H23FN2O2Si: C, 61.05; H, 6.93; N, 8.38. Found: C, 60.99; H,
6.92; N, 8.31.
N-Methyl-5-(2′-hydroxybenzoyl)-4-fluoro-1H-pyrazole (8). To
a solution containing 94.2 mg (0.28 mmol) of 7 in DMF (2 mL)
was added CsF (78.1 mg, 0.74 mmol) at room temperature. After
stirring for 15 min, the reaction mixture was quenched with aqueous
NH4Cl solution, then extracted with hexane/ether ) 3/1. Additional
extraction was repeated twice. The combined organic solution was
dried over Na2SO4 and concentrated in vacuo. The residue was
purified by silica gel column chromatography (hexane/ethyl acetate/
triethylamine ) 150/30/1) to give the desired compound 8 as a
white solid (55.0 mg, 89%): mp 86.1-87.2 °C; IR (KBr) 3003,
2882, 1651, 1574, 1557, 1417, 1394, 1010, 818, 777 cm-1; 1H NMR
(CDCl3, 300 MHz) δ 4.04 (3H, d, J ) 0.7 Hz), 6.90-7.00 (1H,
m), 7.06 (1H, dd, J ) 8.4, 0.9 Hz), 7.41 (1H, d, J ) 4.6 Hz), 7.56
(1H, ddd, J ) 8.6, 7.2, 1.5 Hz), 7.67 (1H, ddd, J ) 7.8, 6.0, 1.7
Hz), 11.61 (1H, s); 13C NMR (CDCl3, 75 MHz) δ 40.1, 118.2,
119.4, 125.1 (d, J ) 14.3 Hz), 132.3, 132.4, 137.4, 148.4 (d, J )
259.1 Hz), 163.0, 188.2 (d, J ) 3.7 Hz); 19F NMR (CDCl3, 283
MHz) δ -162.5 (t, J ) 5.2 Hz); GC-MS m/z 221 (M+ + 1, 1),
220 (M+, 17), 219 (2), 127 (3), 121 (33), 120 (100), 99 (3), 92
(35), 76 (2), 65 (27). Anal. Calcd for C11H9FN2O2: C, 60.00; H,
4.12; N, 12.72. Found: C, 60.09; H, 4.16; N, 12.71.
N-Methylchromeno[2,3-d]pyrazol-9-one (9). To a solution
containing 15.1 mg (0.07 mmol) of 8 in DMF (0.5 mL) was added
Cs2CO3 (31.2 mg, 0.09 mmol) at 25 °C. The mixture was heated
to 50 °C, then stirred for 2 h. The reaction was quenched with aq
NH4Cl solution and extracted with hexane/ether ) 3/1. Additional
extraction was repeated twice. The combined organic layers were
dried over Na2SO4 and concentrated under reduced pressure. The
residue was purified by silica gel column chromatography (hexane/
ethyl acetate/triethylamine ) 150/30/1) to give the desired com-
pound 9 as a white solid (12.6 mg, 92%): mp 166.4-168.2 °C; IR
(KBr) 3107, 2923, 1668, 1524, 1435, 1333, 1092, 913, 793, 660
1
cm-1; H NMR (CDCl3, 300 MHz) δ 4.36 (3H, s), 7.41 (1H, t, J
) 7.5 Hz), 7.53 (1H, dd, J ) 8.5, 0.5 Hz), 7.69 (1H, s), 7.72 (1H,
ddd, J ) 8.6, 7.0, 1.6 Hz), 8.37 (1H, dd, J ) 8.0, 1.7 Hz); 13C
NMR (CDCl3, 75 MHz) δ 39.2, 112.9, 118.3, 123.9, 124.8, 126.5,
134.1, 146.5, 156.3, 169.1; GC-MS m/z 200 (M+, 70), 199 (100),
171 (4), 146 (6), 121 (5), 116 (3), 104 (37), 89 (15), 76 (61), 68
(4), 63 (10), 50 (24). Anal. Calcd for C11H8N2O2: C, 66.00; H,
4.03; N, 13.99. Found: C, 65.98; H, 4.09; N, 13.94.
Acknowledgement.. We greatly thank F-Tech Co. Ltd for a
gift of 1,1-difluoroethylene and Professor M. Jelokhani-Niaraki
at Wilfrid Laurier University for his crucial reading of this
manuscript.
Supporting Information Available: Characterization of new
compounds 3b-j, preparation of compound 4, NMR spectra
for all new compounds, ORTEP drawing of 3g, and crystal data
for 3g. This material is available free of charge via the Internet
at http://pubs.acs.org.
JO800431T
J. Org. Chem. Vol. 73, No. 12, 2008 4739