PPh3-mediated reactions of diazoimides in water: a facile synthesis of fused triazine derivatives

Article abstract of DOI:10.1016/j.tetlet.2009.01.021

Triphenylphosphine-mediated reactions of diazoimides in water were carried out under mild conditions to afford several triazine derivatives in high yields. We have demonstrated an environment friendly methodology to synthesize triazine derivatives.

Full text of DOI:10.1016/j.tetlet.2009.01.021

Tetrahedron Letters 50 (2009) 1331–1334
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Tetrahedron Letters
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PPh3-mediated reactions of diazoimides in water: a facile synthesis
of fused triazine derivatives
*
Sengodagounder Muthusamy , Pandurangan Srinivasan
School of Chemistry, Bharathidasan University, Tiruchirappalli 620 024, India
a r t i c l e i n f o
a b s t r a c t
Article history:
Triphenylphosphine-mediated reactions of diazoimides in water were carried out under mild conditions
to afford several triazine derivatives in high yields. We have demonstrated an environment friendly
methodology to synthesize triazine derivatives.
Received 10 November 2008
Revised 2 January 2009
Accepted 9 January 2009
Available online 13 January 2009
Ó 2009 Elsevier Ltd. All rights reserved.
Keywords:
Aza-Wittig
Diazoimides
Triazine
Triphenylphosphine
Water
Water can participate in various organic reactions, such as
hydrolysis, hydration, hydrogen exchange, and free radical oxida-
tion chemistry.1 Unlike the previous decades, where the use of
water as a solvent had been restricted only to hydrolysis reactions,
chemists have started investigating the possibility of using water
as a solvent for other organic reactions, sometimes with surprising
and novel results.2 The importance of this green chemistry protocol
lies in the fact that organic solvents cannot be cheaper than water,
and are associated with risks such as flammable, explosive, and
carcinogenic.3a Organic solvents are major contributors of environ-
ment.3b The investigation of organic reactions in water may also
contribute to understanding basic mechanism of biological sys-
tems. 1,2,4-Triazines are a family of heterocycles that represent
an important class of pharmaceutically important scaffolds, and
their biological properties have been well studied.4a Examples
are 6-aza-20-oxyisocytidine (1), 6-aza-5-methyl-20-deoxyisocyti-
dine (2),4b 6-azauridine-50-monophosphate (6-AzaUMP)4c,d (3) (a
strong inhibitor of enzyme orotidine 50-monophosphate decarbox-
ylase), and tirapazamine (4)4e (a bioreductive as well as a substi-
tute to cis-platin in chemotherapy for cancer) (Fig. 1).
diazoimide 5a and an equimolar amount of triphenylphosphine as
the reactants in an aqueous medium, and allowed them to react
at room temperature. The reactants were initially insoluble in
water, gradually dissolved in the aqueous phase as the reaction
proceeded, and became homogenous at the end of the reaction.
The progress of the reaction was monitored by TLC, which showed
the gradual disappearance of the starting materials. The aqueous
phase was extracted using dichloromethane and concentrated.
O
N
O
N
CH3
N
N
N
N
H2N
HO
H2N
HO
HO
HO
1; 6-Aza--2'-deoxy-
2; 6-Aza-5-methyl-2'-
isocytidine
deoxyisocytidine
O
N
With the intention of carrying out an eco-friendly aqueous
phase reaction, we planned to employ diazoimides for this purpose.
In continuation of our ongoing research work5 centered on the
O
HN
N
N
N
O
O
O
O
exploitation of
a-diazocarbonyl compounds, we sought to report
N
O
NH2
P
O
the triphenylphosphine-mediated reactions of diazoimides in
water to synthesize triazines. Toward this, we have chosen cyclic
O
HO
OH
4; Tirapazamine
3; 6-Azauridine 5'-
monophosphate (6-AzaUMP)
* Corresponding author. Tel.: +91 431 2407053; fax: +91 431 2407045.
E-mail address: muthu@bdu.ac.in (S. Muthusamy).
Figure 1. Biologically important triazine derivatives.
0040-4039/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2009.01.021

1332
S. Muthusamy, P. Srinivasan / Tetrahedron Letters 50 (2009) 1331–1334
O
O
n
n
Water, rt
-Ph3PO
N2
N
O
R1
R1
NH2
PPh3
Water, rt
+
O
N
N
N
N
PPh3
+
N
R2
O
R2
-Ph3PO
N
O
O
8
9
R
R
5
6
Scheme 2. Reaction of diazocarbonyl compounds with PPh3.
Scheme 1. Reaction of diazomides with triphenylphosphine.
in the formation of the above-mentioned hydrazone derivatives.
In order to understand the mechanism for the formation of tria-
zines 6 in an aqueous medium, we planned to perform similar
reactions on acyclic diazocarbonyl compounds. Thus, the treat-
ment of a representative diazo ketone 8a with PPh3 in water affor-
ded the corresponding hydrazones 9a in good yields (Scheme 2,
Table 2, entry a). This reaction was generalized with other diazo
ketones 8b–g and diazo esters 8h–k to furnish the corresponding
hydrazones 9b–k (Scheme 2, Table 2). A related report7 revealed
that the treatment of the diazocarbonyl compound with triphenyl-
phosphine in isopropyl ether and followed by water hydrolysis
provided the corresponding hydrazone derivatives. In order to ana-
The residue was purified by column chromatography to furnish the
interesting triazine derivative6 6a in 85% yield (Scheme 1,
Table 1, entry a) and triphenylphosphine oxide as the byproduct.
The structure of the product was confirmed by the characteris-
tic disappearance of a carbonyl group and by the appearance of
two imine quaternary carbons at d = 150.8, 149.2 in the 13C NMR
spectrum. The disappearance of the diazo group was also observed
in the IR spectrum. With this encouraging result in the aqueous
medium, we next explored the scope of the ring size and substitu-
ent in cyclic diazoimides. We also performed similar reactions on a
series of cyclic diazoimides 5b–h affording the corresponding
triazine derivatives 6b–h in excellent yields (Scheme 1, Table 1).
In all the above-mentioned reactions, product 6 has the closer Rf
value in TLC to triphenylphosphine oxide, which was formed as
the byproduct. Care must be taken during the chromatographic
isolation of the product. In order to analyze the feasibility of these
reactions in organic solvents, we have chosen anhydrous dichloro-
methane, diethyl ether, and methyl alcohol (Table 1). Thus, these
reactions were repeated in organic solvents to yield the corre-
sponding triazine derivatives 6 in comparatively lower yields. In
the above-mentioned experiments, we found that water is the
most efficient solvent for these reactions. The reaction time is
comparatively longer since the reactants are less soluble in water.
As an attempt to obtain a single crystal for a triazine, the prod-
ucts 6a and 6c were allowed to react with 2,4-dinitrophenylhydra-
zine to yield the corresponding yellow hydrazone derivatives 7a
and 7b in very good yields. The carbonyl group of 6 is involved
Table 2
Synthesis of hydrazones 9
Entry
R1
R2
Time (min)
Yielda (%) of 9
a
b
c
d
e
f
g
h
i
m-Cl–C6H4-
CH3–(CH2)14
2-Thienyl-
H
H
H
H
H
H
Me
OEt
OEt
OMe
OEt
60
65
50
50
40
20
80
45
50
60
70
85
93
95
95
89
93
90
90
92
95
94
-
Cyclohexyl-
o-CH3-C6H4–
m-CH3-C6H4-
Me
Me
Cyclohexyl-O-
OMe
OEt
j
k
a
Yields (unoptimized) refer to isolated pure compounds 9.
Table 1
Synthesis of triazine derivatives 6 in different solvents
Entry
n
R
Product
Solvent
Time (min)
Yielda (%) of 6
a
0
COMe
6a
6a
6a
6a
H2O
CH2Cl2
Et2O
90
30
45
35
85
77
70
85
MeOH
b
1
COMe
6b
6b
6b
6b
H2O
CH2Cl2
Et2O
120
40
50
85
75
72
80
MeOH
40
c
2
0
COMe
COOEt
6c
6c
6c
H2O
CH2Cl2
Et2O
120
40
48
85
74
63
d
6d
6d
6d
6d
H2O
CH2Cl2
Et2O
90
45
50
45
95
85
87
85
MeOH
e
f
1
2
0
2
COOEt
COOEt
COOMe
COOMe
6e
6e
H2O
CH2Cl2
120
55
95
90
6f
6f
H2O
CH2Cl2
2.0
50
95
85
g
h
a
6g
6g
H2O
CH2Cl2
60
40
90
80
6h
6h
H2O
CH2Cl2
55
48
92
86
Yields (unoptimized) refer to isolated pure compounds 6.

S. Muthusamy, P. Srinivasan / Tetrahedron Letters 50 (2009) 1331–1334
1333
Chapter 6.11, pp 507–573 (b) Seela, F.; He, Y. J. Org. Chem. 2003, 68, 367; (c)
Hay, M. P.; Gamage, S. A.; Kovacs, M. S.; Pruijn, F. B.; Anderson, R. F.; Patterson,
A. V.; Wilson, W. R.; Brown, J. M.; Denny, W. A. J. Med. Chem. 2003, 46, 169; (d)
Miller, B. G.; Snider, M. J.; Short, S. A.; Wolfenden, R. Biochemistry 2000, 39,
8113; (e) Seela, F.; Chittepu, P. J. Org. Chem. 2007, 72, 4358; (f) Limanto, J.;
Desmond, R. A.; Gauthier, D. R., Jr.; Devine, P. N.; Reamer, R. A.; Volante, R. P.
Org. Lett. 2003, 5, 2271.
n
n
PPh3
O
N
O
O
N
O
N
N
PPh3
N
O
O
N
R
5. (a) Muthusamy, S.; Gnanaprakasam, B. Tetrahedron Lett. 2008, 49, 475; (b)
Muthusamy, S.; Krishnamurthi, J. Tetrahedron Lett. 2007, 48, 6692; (c)
Muthusamy, S.; Krishnamurthi, J.; Suresh, E. Org. Lett. 2006, 8, 5101; (d)
Muthusamy, S.; Gnanaprakasam, B.; Suresh, E. Org. Lett. 2005, 7, 4577; (e)
Muthusamy, S.; Krishnamurthi, J.; Nethaji, M. Chem. Commun. 2005, 3862.
6. All new compounds gave satisfactory spectral data consistent with their
structures and selected spectral data are given below. General procedure for the
synthesis of triazine derivatives. (6): 3-Acetyl-7,8-dihydropyrrolo[2,1-c][1,2,4]-
triazin-4(6H)-one (6a): A 50 mL round bottomed flask was charged with the
diazoimide 5a (360 mg, 2 mmol) and PPh3 (524 mg, 2.2 mmol) in water, and
the reaction mixture was stirred well. The progress of the reaction mixture was
monitored by TLC. After the completion of the reaction, the reaction mixture
was extracted with dichloromethane. The solvent was removed under reduced
pressure. The crude reaction mixture was subjected to column
chromatography using silica gel (ethyl acetate/hexane 95:5, Rf = 0.6) to
furnish 304 mg of 3-acetyl-7,8-dihydropyrrolo[2,1-c][1,2,4]triazin-4(6H)-one
(6a) in 85% yield as a yellow thick oil. IR (film) 3521, 3440, 3058, 2985, 1727,
R
5
10; phosphazine
n
O
n
PPh3
N
O
N
N
N
O
N
-(Ph3P=O)
N
O
O
R
R
1680, 1568, 1471, 1413, 1364, 1281, 1162, 1040, 927, 733 cmꢀ1 1H NMR (200
;
6
11
MHz, CDCl3) 4.20 (2H, t, J = 7.2 Hz), 3.36 (2H, t, J = 8.0 Hz), 2.63 (3H, s, CH3),
2.40–2.32 (2H, m); 13C NMR (50.3 MHz, CDCl3) 195.6 (C@O), 163.2 (C@O),
150.8 (quat-C), 149.2 (quat-C), 47.5 (CH2), 31.3 (CH2), 27.8 (CH3), 18.3 (CH2).
HRMS (ESI) calcd for C8H9N3O2 (M+Na)+ 202.0592, found 202.0625.
Scheme 3. Proposed mechanism for the formation of triazine derivatives.
lyze the possibility of the formation of triazine 6 via the condensa-
tion of hydrazine with the amide carbonyl, the hydrazones 9g,h,j
were allowed to react with piperidin-2-one and 2-pyrrolidone in
water as well as dichloromethane. These reactions did not furnish
any condensed imine product, and the starting materials were
recovered.
The above-mentioned PPh3-mediated reactions proceeded with
water and also with other anhydrous organic solvents. The mech-
anism can be proposed for the formation of triazine derivatives
through the initial formation of the phosphazine8 10, which subse-
quently combines with the ring carbonyl group to furnish the
intermediate 11 (Scheme 3). The elimination of triphenylphos-
phine oxide would yield triazine 6. Generally, the reaction of azides
with PPh3 afforded imines via the aza-Wittig reaction.9 In the
above-mentioned reaction, the diazo functional group remains in-
tact in the presence of PPh3 without nitrogen extrusion. As the
above-mentioned reactions were performed under mild condi-
tions, we did not observe the probable O–H insertion10 with water
or ketene formation11 or decomposition.
In summary, we have demonstrated highly efficient PPh3-med-
iated reactions of several diazoimides in water to afford the corre-
sponding fused bicyclic triazine derivatives. This protocol is an
easy and green procedure and could be an efficient methodology
for the synthesis of other heterocycles. Moreover, the facile envi-
ronmentally benign nature is the advantage of this method. The
scope of this chemistry to synthesize various heterocycles using
different trialkylphosphines is currently under progress in our
laboratory.
3-Acetyl-6,7,8,9-tetrahydropyrido[2,1-c][1,2,4]triazin-4-one (6b): A 50 mL round
bottomed flask was charged with the diazoimide 5b (385 mg, 2 mmol) and
PPh3 (524 mg, 2.2 mmol) in water as described in the general procedure (ethyl
acetate/hexane 90:10, Rf = 0.6) to furnish 345 mg of 3-acetyl-6,7,8,9-
tetrahydropyrido[2,1-c][1,2,4]triazin-4-one (6b) in 85% yield as
thick oil. IR (film) 3659, 3435, 3346, 3056, 2987, 2308, 1723, 1683, 1566,
1474, 1364, 1267, 1161, 1037, 965, 737 cmꢀ1 1H NMR (200 MHz, CDCl3) 4.23
a yellow
;
(2H, t, J = 7.3 Hz), 3.35 (2H, t, J = 8.0 Hz), 2.64 (3H, s, CH3), 2.43–2.22 (4H, m);
13C NMR (50.3 MHz, CDCl3) 195.7 (C@O), 163.0 (C@O), 151.1 (quat-C), 149.3
(quat-C), 42.6 (CH2), 32.4 (CH2), 27.6 (CH3), 18.3 (CH2), 17.9 (CH2). HRMS (ESI)
calcd for C9H11N3O2 (M+Na)+ 216.0749, found 216.0778.3-Acetyl-7,8,9,10-
tetrahydro[1,2,4]triazino[4,3-a]azepin-4(6H)-one (6c):
A
50 mL round
bottomed flask was charged with the diazoimide 5c (410 mg, 2 mmol) and
PPh3 (524 mg, 2.2 mmol) in water as described in the general procedure (ethyl
acetate/hexane 90:10, Rf = 0.6) to furnish 386 mg of 3-acetyl-7,8,9,10-
tetrahydro[1,2,4]triazino[4,3-a]azepin-4(6H)-one (6c) in 95% yield as
a
yellow thick oil. IR (film) 3668, 3432, 3018, 2982, 1720, 1679, 1567, 1470,
1402, 1261, 965, 739 cmꢀ1 1H NMR (200 MHz, CDCl3) 4.29 (2H, t, J = 5.0 Hz),
;
3.12 (2H, t, J = 5.6 Hz), 2.65 (3H, s, CH3), 1.87–1.78 (6H, m); 13C NMR (50.3 MHz,
CDCl3) 195.7 (C@O), 163.1 (C@O), 151.3 (quat-C), 149.5 (quat-C), 42.7 (CH2),
34.6 (CH2), 29.1 (CH2), 27.7 (CH3), 26.5 (CH2), 24.2 (CH2). HRMS (ESI) calcd for
C10H13N3O2 (M+Na)+ 230.0905, found 230.0875.Ethyl 4-oxo-4,6,7,8-
tetrahydropyrrolo[2,1-c][1,2,4]triazine-3-carboxylate (6d):
A 50 mL round
bottomed flask was charged with diazoimide 5d (450 mg, 2 mmol) and PPh3
(524 mg, 2.2 mmol) in water as described in the general procedure (ethyl
acetate/hexane 90:10, Rf = 0.6) to furnish 386 mg of ethyl 4-oxo-4,6,7,8-
tetrahydropyrrolo[2,1-c][1,2,4]triazine-3-carboxylate (6d) in 80% yield as a
yellow thick oil. IR (film) 3455, 2986, 1742, 1693, 1571, 1484, 1410, 1341,
1285, 1189, 1085, 755 cmꢀ1 1H NMR (200 MHz, CDCl3) 4.48–4.37 (2H,m), 4.20
;
(2H, t, J = 7.4 Hz), 3.32 (2H, t, J = 7.8 Hz), 2.40–2.25 (2H, m), 1.40 (3H, t, J = 7.0
Hz, CH3); 13C (50.3 MHz, CDCl3) 162.5 (C@O), 161.7 (C@O), 149.3 (quat-C),
148.8 (quat-C), 62.0 (CH2), 47.5 (CH2), 31.1 (CH2), 18.2 (CH2), 13.7 (CH3). HRMS
(ESI) calcd for C9H11N3O3 (M+Na)+ 232.0698, found 232.0689.
Ethyl 4-oxo-6,7,8,9-tetrahydro-4H-pyrido[2,1-c][1,2,4]triazine-3-carboxylate (6e):
A 50 mL round bottomed flask was charged with the diazoimide 5e (480 mg, 2
mmol) and PPh3 (524 mg, 2.2 mmol) in water as described in the general
procedure (ethyl acetate/hexane 90:10 Rf = 0.6) to furnish 357 mg of ethyl 4-
oxo-6,7,8,9-tetrahydro-4H-pyrido[2,1-c][1,2,4]triazine-3-carboxylate (6e) in
80% yield as a yellow thick oil. IR (film) 3462, 2991, 1739, 1682, 1565, 1476,
Acknowledgments
1328, 1260, 1188, 1078, 757 cmꢀ1 1H NMR (200 MHz, CDCl3) 4.50–4.40 (2H,
;
m), 3.96 (2H, t, J = 5.8 Hz), 3.08 (2H, t, J = 6.4 Hz), 2.04–1.95 (4H,m), 1.41 (3H, t,
J = 7.2 Hz, CH3); 13C NMR (50.3 MHz, CDCl3) 162.2 (C@O), 158.1 (C@O), 150.4
(quat-C), 148.3 (quat-C), 62.2 (CH2), 42.3 (CH2), 28.7 (CH2), 21.0 (CH2), 18.0
(CH2), 13.9 (CH3). HRMS (ESI) calcd for C11H13N3O3 (M+Na)+ 246.0855, found
246.0895.
This research was supported by the Ministry of Environment
and Forests, New Delhi. P.S. thanks CSIR, New Delhi, for the award
of a research Fellowship.
Methyl 4-oxo-4,6,7,8-tetrahydropyrrolo[2,1-c][1,2,4]triazine-3-carboxylate (6g): A
50 mL round bottomed flask was charged with the diazoimide 5a (420 mg, 2
mmol) and PPh3 (524 mg, 2.2 mmol) in water as described in the general
procedure (ethyl acetate/hexane 90:10, Rf = 0.6) to furnish 312 mg of methyl 4-
oxo-4,6,7,8-tetrahydropyrrolo[2,1-c][1,2,4]triazine-3-carboxylate (6f) in 80%
yield as a yellow thick oil. IR (film) 3444, 2998, 1737, 1688, 1561, 1476, 1414,
References and notes
1. (a) Akiya, N.; Savage, P. E. Chem. Rev. 2002, 102, 2725; (b) Prat, L. R. Chem. Rev.
2002, 102, 2625.
2. (a) Dong, D.; Ouyang, Y.; Yu, H.; Liu, Q.; Liu, J.; Wang, M.; Jhu, J. J. Org. Chem.
2005, 70, 4535; (b) Jiang, Z.; Liang, Z.; Wu, X.; Lu, Y. Chem. Commun. 2006, 2801.
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Williamson, T. C. Green Chemical Syntheses and Processes; American Chemical
Society: Washington, DC, 2000.
1325, 1288, 1179, 1080, 756 cmꢀ1 1H NMR (200 MHz, CDCl3) 4.21 (2H, t, J = 7.2
;
Hz), 3.97 (3H, s, CH3), 3.34 (2H, t, J = 8.0 Hz), 2.41–2.26 (2H, m); 13C NMR (50.3
MHz, CDCl3) 162.7 (C@O), 162.2 (C@O), 149.4 (quat-C), 148.6 (quat-C), 52.9
(CH3), 47.7 (CH2), 31.2 (CH2), 18.4 (CH2). HRMS (ESI) calcd for C8H9N3O3
(M+Na)+ 218.0542, found 218.0527.
4. (a) Neunhoeffer, H.. In Comprehensive Heterocyclic Chemistry II; Katrizky, A. R.,
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3-[(1E)-N-(2,4-Dinitrophenyl)ethane-hydrazonoyl]-7,8,9,10-tetrahydro[1,2,4]-

1334
S. Muthusamy, P. Srinivasan / Tetrahedron Letters 50 (2009) 1331–1334
triazino[4,3-a]azepin-4(6H)-one (7c): 3-Acetyl-7,8,9,10-tetrahydro[1,2,4]-
triazino[4,3-a]azepin-4(6H)-one (6c) (2 mmol) in methanol was stirred well
(CH), 128.2 (CH), 123.1 (CH). HRMS (ESI) calcd for C8H7ClN2O (M+Na)+
205.0144, found 205.0112.
to get a clear solution. To this mixture, 2,4-dinitrophenylhydrazine was added
and stirred well for 1 h. The obtained yellow solid was filtered off to furnish
735 mg of 3-[(1E)-N-(2,4-dinitrophenyl)ethanehydrazonoyl]-7,8,9,10-tetrahydro-
[1,2,4]triazino[4,3-a]azepin-4(6H)-one (7c) in 95% yield as a yellow solid; mp
136–137 °C. IR (KBr) 3362, 3313, 3179, 3106, 2922, 2855, 1682, 1614, 1590,
2-Hydrazonomalonic acid diethyl ester (9b): Diazo ketone 8a (370 mg, 2 mmol)
was treated with PPh3 (524 mg, 2.2 mmol) as described in the general
procedure to afford 9b (ethyl acetate/hexane 55:45, Rf = 0.6) in 94% yield as a
colorless solid; mp 110–111 °C. IR (KBr) 3328, 3187, 2991, 2939, 2906, 1690,
1671, 1581, 1499, 1369, 1336, 1253, 1194, 1017, 807, 785, 480 cmꢀ1 1H NMR
;
1533, 1506, 1461, 1330, 1310, 1270, 1138, 1059, 968, 739 cmꢀ1
;
1H NMR (200
(200 MHz, CDCl3) 9.79 (2H, s, NH2), 4.37–4.25 (4H, m), 1.39–1.31 (6H, m); 13C
NMR (50.3 MHz, CDCl3) 163.2 (C@O), 162.4 (C@O), 120.5 (quat-C), 60.7 (CH2),
60.6 (CH2), 14.0 (CH3), 13.8 (CH3). HRMS (ESI) calcd for C7H12N2O4 (M+Na)+
211.0695, found 211.0673.
MHz, CDCl3) 11.39 (1H, br s, NH), 9.16 (1H, d, J = 2.6 Hz), 8.31 (1H, dd, J1 = 2.6
Hz, J2 = 29.2 Hz), 8.22 (1H, d, J = 9.6 Hz), 4.35 (2H, t, J = 4.6 Hz), 3.14 (2H, t,
J = 2.8 Hz), 2.53 (3H, s, CH3), 1.91–1.72 (6H, m); 13C NMR (50.3 MHz, CDCl3)
160.8 (C@O), 151.9 (quat-C), 150.4 (quat-C), 148.3 (quat-C), 144.7 (quat-C),
139.2 (quat-C), 130.4 (quat-C), 130.2 (Arom-CH), 123.0 (Arom-CH), 117.7 (Arom-
CH), 43.1 (CH2), 34.8 (CH2), 29.5 (CH2), 27.0 (CH3), 24.8 (CH2), 12.7 (CH2). HRMS
(ESI) calcd for C16H17N7O5 (M+Na)+ 410.1189, found 410.1167.
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73, 3928.
1-(3-Chlorophenyl)-hydrazonoethanone (9a): Diazo ketone 8a (360 mg, 2 mmol)
was treated with PPh3 (524 mg, 2.2 mmol) as described in the general
procedure to afford 9a (ethyl acetate/hexane 55:45, Rf = 0.6) in 78% yield as a
yellow solid; mp 105–107 °C. IR (KBr) 3362, 3179, 1586, 1557, 1482, 1089,
1006, 796, 563 cmꢀ1 1H NMR (200 MHz, CDCl3) 9.87 (2H, s, NH2), 7.99–7.85
;
(2H, m, arom-H), 7.56–7.27 (2H, m, arom-H), 5.61 (1H, s, CH); 13C NMR (50.3
MHz, CDCl3) 192.1 (C@O), 137.4 (quat-C), 131.2 (quat-C), 129.3 (CH), 129.0