Efficient iminophosphorane-mediated preparation of benzofuro-[3,2-d] pyrimidin-4(3H)-ones and unexpected ring opening products

Article abstract of DOI:10.1002/hlca.200890090

The carbodiimides 4, obtained from aza-Wittig reactions of iminophosphorane 3 with aromatic isocyanates, reacted with secondary amines, phenols or alcohols in the presence of catalytic amounts of K₂CO₃ or sodium alkoxide to give 2-substituted benzofuro[3,2-d]pyrimidin-4(3H)-ones 6. However, when 2,2′-iminobis[ethanol] was used, the unexpected ring opening product 7 was formed instead of 6. Reaction of 4 with primary amines RNH₂ (R = Et, Pr, Bu, etc.) gave guanidine intermediates 8, which were further treated with EtONa to give only one regioisomer 9 via a base catalyzed cyclization. However, another regioisomer 11 was obtained when NH₃ or 'small' amines RNH₂ (R = Me, NH₂) were used in the absence of EtONa via a spontaneous cyclization of 8.

Full text of DOI:10.1002/hlca.200890090

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Helvetica Chimica Acta – Vol. 91 (2008)
Efficient Iminophosphorane-Mediated Preparation of Benzofuro-
[3,2-d]pyrimidin-4(3H)-ones and Unexpected Ring Opening Products
by Yang-Gen Hua)b), Ming-Guo Liua), and Ming-Wu Ding*a)
a) Key Laboratory of Pesticide & Chemical Biology of Ministry of Education, Central China Normal
University, Wuhan 430079, P. R. China (fax þ 86-27-67862041; e-mail: ding5229@yahoo.com.cn)
b) Department of Medicinal Chemistry, Yunyang Medical College, Shiyan 442000, P. R. China
The carbodiimides 4, obtained from aza-Wittig reactions of iminophosphorane 3 with aromatic
isocyanates, reacted with secondary amines, phenols or alcohols in the presence of catalytic amounts of
K2CO3 or sodium alkoxide to give 2-substituted benzofuro[3,2-d]pyrimidin-4(3H)-ones 6. However,
when 2,2’-iminobis[ethanol] was used, the unexpected ring opening product 7 was formed instead of 6.
Reaction of 4 with primary amines RNH2 (R ¼ Et, Pr, Bu, etc.) gave guanidine intermediates 8, which
were further treated with EtONa to give only one regioisomer 9 via a base catalyzed cyclization.
However, another regioisomer 11 was obtained when NH3 or ꢀsmallꢁ amines RNH2 (R ¼ Me, NH2) were
used in the absence of EtONa via a spontaneous cyclization of 8.
Introduction. – The derivatives of fused pyrimidinones have been the focus of great
interest over many years. This is probably due to the fact that many compounds
containing a fused pyrimidinone ring play a very important part in the biochemistry of
the living cell [1]. The recent development of physiologically highly potent purine
analogues with interesting antiviral, antiallergic, and especially with anticancer
activities have promoted a great current interest in facile and general routes to these
molecules in synthetically useful yields. Although some derivatives of benzofuropyr-
imidines have shown good analgesic, anti-inflammatory, antimicrobial, anticoccidial,
and blood sugar-lowering activities [2 – 5], there are only few reports on the synthesis of
benzofuro[3,2-d]pyrimidin-4(3H)-ones, which are of considerable interest as potential
biologically active compounds or pharmaceuticals. The methods described for the
preparation of some representative derivatives of this ring system involve the reaction
of 3-amino-2-(ethoxycarbonyl)benzofuran with orthoformate and an amine, the
rearrangement of benzofuro[3,2-d]oxazines by treatment with an amine, or the
cyclization of 3-amino-2-(aminocarbonyl)benzofuran with acyl chlorides [6 – 9].
However, 2-amino or 2-aryl(alkyl)oxy substituted benzofuro[3,2-d]pyrimidin-4(3H)-
ones were not easily accessible by currently existing routes.
The aza-Wittig reactions of iminophosphoranes have received increased attention in
view of their utility in the synthesis of N-heterocyclic compounds [10 – 16]. Annelation
of ring systems with N-heterocycles by means of an aza-Wittig reaction has been widely
utilized because of the availability of functionalized iminophosphoranes. Recently, we
have become interested in the synthesis of quinazolinones, thienopyrimidinones, and
imidazolinones via the aza-Wittig reaction of a- or b-(ethoxycarbonyl)iminophosphor-
ꢂ 2008 Verlag Helvetica Chimica Acta AG, Zürich

Helvetica Chimica Acta – Vol. 91 (2008)
863
anes with aromatic isocyanates and subsequent reaction with various nucleophiles
under mild conditions [17 – 21]. Here, we wish to report an efficient approach to
benzofuro[3,2-d]pyrimidin-4(3H)-ones and unexpected ring opening products.
Results and Discussion. – Ethyl 3-amino-1-benzofuran-2-carboxylate (1), easily
obtained by cyclization of 2-hydroxybenzonitrile (2), (with ethyl bromoacetate, under
basic conditions [22][23]), was converted to the iminophosphorane 3 via the reaction
with Ph3P, hexachloroethane and Et3N (Scheme 1).
Scheme 1
The iminophosphorane 3 reacted with aromatic isocyanates to give carbodiimides 4,
which were allowed to react with secondary amines to provide guanidine intermediates
5 (Y¼ R2N). In the presence of catalytic amounts of EtONa, the latter were easily
converted to 2-(dialkylamino)benzofuro[3,2-d]pyrimidin-4(3H)-ones 6 (Y¼ R2N) in
satisfactory yields at room temperature (Scheme 2). It is noteworthy that the yield of
isolated 6 was good even when Y was the bulky diisopropylamino group. The reaction
of carbodiimides 4 with phenols produced 2-(aryloxy)benzofuro[3,2-d]pyrimidin-
4(3H)-ones 6 (Y¼ ArO) in the presence of a catalytic amount of K2CO3 in good yields.
The cyclization can be completed smoothly under mild conditions, independent of the
substituents on the phenol. They can either be a halogen atom (Table 1, Entries 13 and
14) or typical electron-releasing groups (Entries 11, 12, and 15). The direct reaction of
carbodiimide 4 with ROH gave 2-(alkoxy)benzofuro[3,2-d]pyrimidin-4(3H)-ones 6
(Y¼ RO) in satisfactory yields in the presence of catalytic amounts of RONa. The
results are listed in Table 1.
Scheme 2
Unexpectedly, when 2,2’-iminobisethanol was used to react with carbodiimide 4, the
rearranged product 7 was obtained in the presence of catalytic amounts of EtONa
(Scheme 3). The structure of 7 was confirmed by spectroscopic data. The formation of
7 can be explained by an initial cyclization of a guanidine intermediate of type 5 to give
6s, which undergoes further ring cleavage to yield 7. Furthermore, a single crystal of 7a

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Helvetica Chimica Acta – Vol. 91 (2008)
Table 1. Synthesis of Compounds 6 and 7
Entry
Compound
Ar
Y
Yield [%]a)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
6a
6b
6c
6d
6e
6f
6g
6h
6i
6j
6k
6l
6m
6n
6o
6p
6q
6r
Ph
Ph
Ph
Ph
Ph
Ph
Et2N
Pr2N
86
82
87
76
85
82
75
73
83
83
87
90
81
89
88
82
78
84
88
82
piperidin-1-yl
(n-C5H11)2N
(i-Bu)2N
(Ph)MeN
(i-Pr)2N
4-ClꢀC6H4
4-ClꢀC6H4
4-MeꢀC6H4
3-MeꢀC6H4
Ph
Pr2N
Et2N
morpholin-1-yl
3-MeꢀC6H4O
4-MeOꢀC6H4O
4-ClꢀC6H4O
4-ClꢀC6H4O
4-MeSꢀC6H4O
EtO
MeO
EtO
(HOCH2CH2)2N
(HOCH2CH2)2N
Ph
Ph
4-MeꢀC6H4
3-MeꢀC6H4
Ph
4-ClꢀC6H4
4-MeꢀC6H4
Ph
7a
7b
4-MeꢀC6H4
a) Yields of isolated product based on iminophosphorane 3.
Scheme 3
was obtained from a CH2Cl2 soln., and an X-ray structure analysis verified the proposed
structure (Fig.).
It is interesting that the reaction of carbodiimide 4 with aliphatic primary amines
generates different products. The reaction of carbodiimide 4 with RNH2 (R ¼ Et, Pr,
Bu, etc.) gave guanidine intermediates 8, which in the presence of EtONa cyclized to
provide 2-(alkylamino)benzofuro[3,2-d]pyrimidin-4(3H)-ones 9 exclusively, i.e., one

Helvetica Chimica Acta – Vol. 91 (2008)
865
Figure. ORTEP Diagram of the crystal structure of compound 7a (50% thermal ellipsoids). Compound
7a has two unique molecules in the asymmetric unit of the monoclinic unit cell. One of the molecules is
numbered with atoms C1 – C20, O1, O2, O3, O4, O4’, N1, N2, and N3, while another molecule has atoms
C1a – C20a, O1a, O2a, O3a, O4a, O4a’, N1a, N2a, and N3a.
of the possible regioisomers (Scheme 4). The structure of 9 was deduced from their
1H-NMR data. For example, the 1H-NMR spectrum of 9c (R ¼ Bu) showed the signals
of the alkylamino-NH group at 4.10 ppm and NCH2 at 3.44 – 3.49 ppm as multiplets,
which strongly suggests the existence of an NHCH2CH2CH2Me group in 9c [24]. The
results are listed in Table 2. The exclusive formation of 9 can be rationalized in terms of
a base catalytic cyclization of the guanidine intermediate 8 to give 9 across the
arylamino group rather than the alkylamino one. This is probably due to the
preferential generation of a NꢀAr cycle than of the more acidic NHAr cycle under the
catalysis of EtONa.
It is deduced from Scheme 5 that if a primary amine such as 2-hydroxyethylamine is
used to react with carbodiimide 4, the ring-opening product 10 might be formed.
However, the normal product 9j was obtained, when 2-aminoethanol was utilized in the
Scheme 4

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Table 2. Synthesis of Compounds 9 or 11
Entry
Compound
Ar
R
Yield [%]a)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
9a
9b
9c
9d
9e
9f
9g
9h
9i
Ph
Ph
Ph
Ph
Et
n-Pr
n-Bu
i-Pr
i-Bu
i-Pr
cyclohexyl
t-Bu
CH2CH2OH
CH2CH2OH
H
Me
NH2
NH2
89
83
74
82
71
87
72
75
76
84
90
84
92
95
Ph
4-MeꢀC6H4
4-MeꢀC6H4
4-MeꢀC6H4
Ph
9j
4-MeꢀC6H5
11a
11b
11c
11d
Ph
Ph
Ph
4-MeꢀC6H4
a) Isolated yields based on iminophosphorane 3.
Scheme 5
presence of a catalytic amount of EtONa. The results show that the above described
rearrangement of 6 to 7 might be due to steric effects in 6 which facilitate the ring
opening.
On the other hand, the reaction of carbodiimides 4 with small amines, i.e., NH3,
MeNH2, or hydrazine, gave 2-(arylamino)benzofuro[3,2-d]pyrimidin-4(3H)-ones 11,
another possible regioisomer, as the only product in the absence of EtONa (Scheme 4).
It is deduced that the intermediate 8 is generated in a first step, which then cyclizes
quickly, and catalysis by EtONa is therefore not needed. The formation of 11 can be
explained in terms of a spontaneous cyclization of the guanidine intermediate 8 to give
11 directly for the slight sterically hindered and/or strong nucleophilic ammonia,
methylamino or hydrazine group, but not for the arylamines.
Conclusions. – We have developed an efficient synthesis of 2-substituted
benzofuro[3,2-d]pyrimidin-4(3H)-ones and previously not reported ring opening
products via aza-Wittig reactions. Due to the mild reaction conditions, good yields,
easily accessible starting material, and straightforward product isolation, the versatile
synthetic approach discussed here compares favorably with other existing methods.

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867
We gratefully acknowledge financial support of this work by theNational Basic Research Program of
China (No. 2007CB116302), the Key Project of Chinese Ministry of Education (No. 107082, 106116), the
National Natural Science Foundation of China (No. 20772041, 20672041) and the National Natural
Science Foundation of Hubei Province (No. 2006ABB016).
Experimental Part
General. M.p. uncorrected. IR Spectra: PE-983 spectrometer as KBr pellets, in cmꢀ1. NMR Spectra:
in CDCl3 or (D6)DMSO on a Varian Mercury 400 spectrometer, in ppm (d) relative to TMS. MS:
Finnigan Trace MS spectrometer. Elemental analyses: Vario EL III elemental analyzer. The diffraction
data were collected on a Bruker SMART AXS CCD diffractometer, MoKa, 2q ¼ 1.86 – 27.508.
Ethyl 3-[(Triphenylphosphoranylidene)amino]-2-benzofurancarboxylate (3). To a mixture of ethyl
3-amino-1-benzofuran-2-carboxylate [22][23] (1; 1.64 g, 8 mmol), PPh3 (3.14 g, 12 mmol) and C2Cl6
(2.84 g, 12 mmol) in dry MeCN (40 ml), was added dropwise Et3N (2.42 g, 24 mmol) at r.t. The color of
the mixture quickly turned yellow. After stirring for 4 h, the solvent was removed under reduced pressure
and the residue was recrystallized from EtOH to give 3. White solid. Yield 3.27 g, 88%. M.p.: 172 – 1738.
1H-NMR (400 MHz, CDCl3): 1.23 (t, J ¼ 7.2, Me); 4.18 (q, J ¼ 7.2, CH2); 6.93 – 7.80 (m, 19 arom. H). IR
(KBr): 1755 (C¼O), 1599, 1212. MS: 465 (99, Mþ), 436 (31), 392 (100), 262 (37), 183 (80). Anal. calc.
for C29H24NO3P (465.48): C 74.83, H 5.20, N 3.01; found: C 74.96, H 5.25, N 2.79.
General Procedure for the Preparation of 2-(Dialkylamino)benzofuro[3,2-d]pyrimidin-4(3H)-ones
6a – 6j. To a soln. of 3 (0.93 g, 2 mmol) in dry CH2Cl2 (15 ml) was added arom. isocyanate (2 mmol) under
N2 at r.t. After the mixture was kept for 8 – 12 h at 0 – 58, the solvent was removed under reduced
pressure, and Et2O/petroleum ether (PE) (1:2, 20 ml) was added to precipitate Ph3PO. After filtration,
the solvent was removed to give carbodiimide 4, which was used directly without further purification. To
the soln. of 4 in CH2Cl2 (15 ml) was added dialkylamine (2 mmol), and allowed to stand for 0.5 – 6 h.
Then, the soln. was concentrated, and anh. EtOH (10 ml) with several drops of EtONa in EtOH was
added. The mixture was stirred for 1 – 6 h at r.t. The soln. was concentrated under reduced pressure, and
the residual was recrystallized to give 2-(dialkylamino)benzofuro[3,2-d]pyrimidin-4(3H)-ones 6a – 6j.
2-(Diethylamino)-3-phenylbenzofuro[3,2-d]pyrimidin-4(3H)-one (6a). White crystals, recrystal-
lized from EtOH. Yield 0.57 g, 86%. M.p. 170 – 1718. IR (KBr): 1695 (C¼O), 1529, 1346, 1074. 1H-NMR
(400 MHz, CDCl3): 0.85 (t, J ¼ 7.2, 2 Me); 3.13 (q, J ¼ 7.2, 2 CH2N); 7.34 – 8.04 (m, 9 arom. H). MS: 333 (7,
Mþ), 304 (38), 261 (35), 214 (18), 130 (65), 102 (100). Anal. calc. for C20H19N3O2 (333.38): C 72.05, H
5.74, N 12.60; found: C 72.27, H 5.87, N 12.54.
2-(Dipropylamino)-3-phenylbenzofuro[3,2-d]pyrimidin-4(3H)-one (6b). White crystals, recrystal-
lized from EtOH. Yield 0.59 g, 82%. M.p. 130 – 1318. IR (KBr): 1699 (C¼O), 1526, 1351, 1216. 1H-NMR
(400 MHz, CDCl3): 0.75 (t, J ¼ 7.2, 2 Me); 1.23 – 1.32 (m, 2 CH2); 3.02 (t, J ¼ 7.2, 2 CH2N); 7.33 – 8.04 (m, 9
arom. H). 13C-NMR (100 MHz, CDCl3): 11.1 (2 C); 20.4 (2 C); 53.0 (2 C); 112.5; 121.3; 122.8; 123.1;
128.1; 128.7 (2 C); 128.8 (2 C); 129.1; 134.7; 137.4; 142.9; 154.6; 156.5; 157.2. MS: 361 (3, Mþ), 318 (21),
261 (37), 214 (47), 130 (96), 102 (100). Anal. calc. for C22H23N3O2 (361.44): C 73.11, H 6.41, N 11.63;
found: C 73.04, H 6.32, N 11.87.
3-Phenyl-2-(piperidin-1-yl)benzofuro[3,2-d]pyrimidin-4(3H)-one (6c). White crystals, recrystal-
lized from EtOH/CH2Cl2 (v/v ¼ 1:1). Yield 0.60 g, 87%. M.p. 197 – 1988. IR (KBr): 1701 (C¼O), 1528,
1246, 1093. 1H-NMR (400 MHz, CDCl3): 1.22 – 1.45 (m, (CH2)3); 3.13 (t, J ¼ 5.2, 2 CH2N); 7.37 – 8.03 (m,
9 arom. H). MS: 345 (100, Mþ), 316 (40), 261 (40), 160 (82), 130 (40), 102 (96). Anal. calc. for
C21H19N3O2 (345.39): C 73.03, H 5.54, N 12.17; found: C 73.04, H 5.67, N 12.03.
2-(Dipentylamino)-3-phenylbenzofuro[3,2-d]pyrimidin-4(3H)-one (6d). White crystals, recrystal-
lized from EtOH. Yield 0.63 g, 76%. M.p. 105 – 1068. IR (KBr): 1692 (C¼O), 1628, 1417, 1115. 1H-NMR
(400 MHz, CDCl3): 0.86 (t, J ¼ 7.2, 2 Me); 1.08 – 1.27 (m, 3 CH2); 3.04 (t, J ¼ 7.6, 2 CH2N); 7.32 – 8.04 (m, 9
arom. H). MS: 417 (91, Mþ), 360 (89), 346 (100), 261 (87), 159 (21), 130 (69), 102 (88). Anal. calc. for
C26H31N3O2 (417.54): C 74.79, H 7.48, N 10.06; found: C 74.87, H 7.51, N 9.92.
2-(Diisobutylamino)-3-phenylbenzofuro[3,2-d]pyrimidin-4(3H)-one (6e). White crystals, recrystal-
lized from EtOH. Yield 0.66 g, 85%. M.p. 141 – 1428. IR (KBr): 1701 (C¼O), 1531, 1194. 1H-NMR

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Helvetica Chimica Acta – Vol. 91 (2008)
(400 MHz, CDCl3): 0.80 (d, J ¼ 6.8, 4 Me); 1.81 – 1.88 (m, 2 HꢀC); 2.90 (d, J ¼ 7.2, 2 CH2N); 7.35 – 8.04
(m, 9 H). MS: 389 (35, Mþ), 360 (27), 261 (38), 130 (100), 102 (79). Anal. calc. for C24H27N3O2 (389.49):
C 74.01, H 6.99, N 10.79; found: C 74.25, H 7.04, N 10.73.
2-[Methyl(phenyl)amino]-3-phenylbenzofuro[3,2-d]pyrimidin-4(3H)-one (6f). White crystals, re-
crystallized from EtOH. Yield 0.60 g, 82%. M.p. 191 – 1938. IR (KBr): 1706 (C¼O), 1528, 1352, 1085.
1H-NMR (400 MHz, CDCl3): 3.36 (s, MeN); 6.57 – 8.11 (m, 14 arom. H). MS: 367 (76, Mþ), 290 (20), 261
(44), 235 (52), 130 (62). 77 (100). Anal. calc. for C23H17N3O2 (367.40): C 75.19, H 4.66, N 11.44; found: C
75.22, H 4.52, N 11.68.
3-(4-Chlorophenyl)-2-(diisopropylamino)benzofuro[3,2-d]pyrimidin-4(3H)-one (6g). White crys-
tals, recrystallized from EtOH. Yield 0.59 g, 75%. M.p. 167 – 1698. IR (KBr): 1701 (C¼O), 1541, 1399,
1102. 1H-NMR (400 MHz, CDCl3): 1.14 (d, J ¼ 6.8, 4 Me); 3.49 – 3.56 (m, 2 CHN); 7.25 – 8.00 (m, 8 arom.
H). MS: 395 (19, Mþ), 352 (77), 295 (62), 185 (45), 130 (100). Anal. calc. for C22H22ClN3O2 (395.88): C
66.75, H 5.60, N 10.61; found: C 66.60, H 5.61, N 10.78.
3-(4-Chlorophenyl)-2-(dipropylamino)benzofuro[3,2-d]pyrimidin-4(3H)-one (6h). White crystals,
recrystallized from EtOH. Yield 0.58 g, 73%. M.p. 133 – 1348. IR (KBr): 1703 (C¼O), 1539, 1490, 1093.
1H-NMR (400 MHz, CDCl3): 0.77 (t, J ¼ 7.2, 2 Me); 1.29 – 1.35 (m, 2 CH2); 3.02 (t, J ¼ 7.2, 2 CH2N); 7.28 –
8.04 (m, 8 arom. H). MS: 395 (34, Mþ), 352 (67), 295 (68), 185 (45), 130 (100). Anal. calc. for
C22H22ClN3O2 (395.88): C 66.75, H 5.60, N 10.61; found: C 66.59, H 5.74, N 10.44.
2-(Diethylamino)-3-(4-methylphenyl)benzofuro[3,2-d]pyrimidin-4(3H)-one (6i). White crystals,
recrystallized from EtOH. Yield 0.58 g, 83%. M.p. 177 – 1788. IR (KBr): 1702 (C¼O), 1542, 1386,
1099. 1H-NMR (400 MHz, CDCl3): 0.86 (t, J ¼ 7.2, 2 Me); 2.42 (s, Me); 3.13 (q, J ¼ 7.2, 2 CH2N); 7.21 –
8.05 (m, 8 arom. H). 13C-NMR (100 MHz, CDCl3): 12.3 (2 C); 21.0; 45.2 (2 C); 112.6; 121.3; 122.9;
123.2; 128.4 (2 C); 129.1; 129.6 (2 C); 134.8; 134.9; 138.0; 142.8; 154.8; 156.5; 157.2. MS: 347 (75, Mþ), 318
(100), 275 (62), 214 (23), 130 (44), 102 (41). Anal. calc. for C21H21N3O2 (347.41): C 72.60, H 6.09, N 12.10;
found: C 72.76, H 6.31, N 12.07.
3-(3-Methylphenyl)-2-(morpholin-4-yl)benzofuro[3,2-d]pyrimidin-4(3H)-one (6j). White crystals,
recrystallized from EtOH/CH2Cl2 (v/v ¼ 1:1). Yield 0.60 g, 83%. M.p. 177 – 1788. IR (KBr): 1701
(C¼O), 1528, 1400, 1118. 1H-NMR (400 MHz, CDCl3): 2.43 (s, Me); 3.16 (t, J ¼ 4.8, 2 CH2N); 3.44 (t, J ¼
4.8, 2 CH2O); 7.19 – 8.02 (m, 8 arom. H). MS: 361 (69, Mþ), 316 (78), 304 (68), 214 (45), 130 (100). Anal.
calc. for C21H19N3O3 (361.42): C 69.79, H 5.30, N 11.63; found: C 69.84, H 5.53, N 11.47.
General Procedure for the Preparation of 2-(Aryloxy)benzofuro[3,2-d]pyrimidin-4(3H)-ones 6k –
6o. To the soln. of carbodiimide 4 (ca. 2 mmol) prepared above in MeCN (15 ml) was added K2CO3
(0.2 mmol) and ArOH (2 mmol) in anh. MeCN (10 ml). The mixture was stirred for 6 – 8 h at 50 – 608.
The soln. was concentrated, and the residue was recrystallized to give 6k – 6o.
2-(3-Methylphenoxy)-3-phenylbenzofuro[3,2-d]pyrimidin-4(3H)-one (6k). White crystals, recrystal-
lized from EtOH. Yield 0.64 g, 87%. M.p. 230 – 2328. IR (KBr): 1712 (C¼O), 1547, 1358, 1198. 1H-NMR
(400 MHz, CDCl3): 2.37 (s, Me); 6.97 – 7.90 (m, 13 arom. H). 13C-NMR (100 MHz, CDCl3): 21.2; 112.7;
118.2; 120.9; 121.6; 122.4; 123.5; 126.6; 128.0; 129.0; 129.1; 129.4; 129.8; 134.6; 135.5; 135.6; 139.7; 141.9;
149.6; 151.8; 153.4; 153.6; 157.2. MS: 368 (8, Mþ), 302 (63), 130 (23), 102 (23), 91 (27), 76 (100). Anal.
calc. for C23H16N2O3 (368.38): C 74.99, H 4.38, N 7.60; found: C 75.23, H 4.50, N 7.52.
2-(4-Methoxyphenoxy)-3-phenylbenzofuro[3,2-d]pyrimidin-4(3H)-one (6l). White crystals, recrys-
tallized from EtOH. Yield 0.69 g, 90%. M.p. 231 – 2328. IR (KBr): 1711 (C¼O), 1503, 1358, 1196.
1H-NMR (400 MHz, CDCl3): 3.84 (s, MeO); 6.91 – 7.90 (m, 13 arom. H). 13C-NMR (100 MHz, CDCl3):
55.4; 112.7; 114.2 (2 C); 121.6; 122.1 (2 C); 122.4; 123.5; 128.0 (2 C); 128.2; 129.1; 129.4 (2 C); 134.6;
135.5; 141.9; 145.3; 153.5; 153.7; 157.2 (2 C). MS: 384 (4, Mþ), 265 (51), 222 (46), 130 (100), 102 (93).
Anal. calc. for C23H16N2O4 (384.38): C 71.87, H 4.20, N 7.29; found: C 72.01, H 4.33, N 7.22.
2-(4-Chlorophenoxy)-3-phenylbenzofuro[3,2-d]pyrimidin-4(3H)-one (6m). White crystals, recrys-
tallized from EtOH. Yield 0.63 g, 81%. M.p. 224 – 2268. IR (KBr): 1717 (C¼O), 1543, 1359, 1202.
1H-NMR (400 MHz, CDCl3): 7.12 – 7.88 (m, 13 arom. H). MS: 388 (16, Mþ), 269 (38), 260 (34), 234 (27),
130 (62), 102 (100). Anal. calc. for C22H13ClN2O3 (388.80): C 67.96, H 3.37, N 7.21; found: C 68.01, H 3.43,
N 7.16.
2-(4-Chlorophenoxy)-3-(4-methylphenyl)benzofuro[3,2-d]pyrimidin-4(3H)-one (6n). White crys-
tals, recrystallized from EtOH. Yield 0.72 g, 89%. M.p. 220 – 2218. IR (KBr): 1710 (C¼O), 1541, 1348,

Helvetica Chimica Acta – Vol. 91 (2008)
869
1199. 1H-NMR (400 MHz, CDCl3): 2.44 (s, Me); 7.12 – 7.87 (m, 12 arom. H). MS: 402 (14, Mþ), 269 (43),
260 (27), 130 (63), 102 (100). Anal. calc. for C23H15ClN2O3 (402.83): C 68.58, H 3.75, N 6.95; found: C
68.63, H 3.82, N 6.78.
3-(3-Methylphenyl)-2-[4-(methylsulfanyl)phenoxy]benzofuro[3,2-d]pyrimidin-4(3H)-one (6o).
White crystals, recrystallized from EtOH. Yield 0.73 g, 88%. M.p. 222 – 2248. IR (KBr): 1709 (C¼O),
1
1545, 1359, 1202. H-NMR (400 MHz, CDCl3): 2.44 (s, Me); 2.50 (s, Me); 7.10 – 7.88 (m, 12 arom. H).
13C-NMR (100 MHz, CDCl3): 16.3; 21.4; 112.8; 121.6; 121.8 (2 C); 122.3; 123.5; 124.9; 127.5 (2 C); 128.4;
129.3; 129.5; 130.1; 134.4; 135.7; 135.8; 139.5; 141.7; 149.5; 153.4; 153.6; 157.2. MS: 414 (12, Mþ), 265 (47),
234 (29), 130 (52), 102 (100). Anal. calc. for C24H18N2O3S (414.48): C 69.55, H 4.38, N 6.76; found: C
69.24, H 4.56, N 6.70.
General Procedure for the Preparation of 2-(Alkoxy)benzofuro[3,2-d]pyrimidin-4(3H)-ones 6p – 6r.
To the soln. of 4 (ca. 2 mmol) prepared above in anh. ROH (8 ml) was added RONa (0.2 mmol, 10%
equiv) in ROH. The mixture was stirred for 4 – 6 h at r.t. The soln. was condensed, and the residue was
recrystallized to give 6p – 6r.
2-Ethoxy-3-phenylbenzofuro[3,2-d]pyrimidin-4(3H)-one (6p). White crystals, recrystallized from
MeOH. Yield 0.50 g, 82%. M.p. 148 – 1508. IR (KBr): 1700 (C¼O), 1541, 1342, 1198. 1H-NMR
(400 MHz, CDCl3): 1.26 (t, J ¼ 7.2, Me); 4.49 (q, J ¼ 7.2, CH2O); 7.28 – 8.02 (m, 9 arom. H). MS: 306 (100,
Mþ), 234 (23), 186 (84), 130 (34), 102 (98). Anal. calc. for C18H14N2O3 (306.32): C 70.58, H 4.61, N 9.15;
found: C 70.75, H 4.72, N 9.02.
3-(4-Chlorophenyl)-2-methoxybenzofuro[3,2-d]pyrimidin-4(3H)-one (6q). White crystals, recrystal-
lized from MeOH. Yield 0.51 g, 78%. M.p. 205 – 2078. IR (KBr): 1699 (C¼O), 1542, 1340, 1201. 1H-NMR
(400 MHz, CDCl3): 4.04 (s, Me); 7.22 – 8.03 (m, 8 arom. H). MS: 326 (91, Mþ), 295 (49), 268 (25), 186
(18), 159 (21), 130 (78), 124 (97), 102 (100). Anal. calc. for C17H11ClN2O3 (326.73): C 62.49, H 3.39, N
8.57; found: C 62.73, H 3.55, N 8.49.
2-Ethoxy-3-(4-methylphenyl)benzofuro[3,2-d]pyrimidin-4(3H)-one (6r). White crystals, recrystal-
lized from MeOH. Yield 0.51 g, 84%. M.p. 186 – 1888. IR (KBr): 1703 (C¼O), 1560, 1353, 1087. 1H-NMR
(400 MHz, CDCl3): 1.27 (t, J ¼ 7.2, Me); 2.43 (s, Me); 4.49 (q, J ¼ 7.2, CH2O); 7.22 – 8.03 (m, 8 arom. H).
13C-NMR (100 MHz, CDCl3): 13.8; 21.0; 65.0; 112.6; 121.1; 122.5; 123.3; 127.6 (2 C); 129.1; 129.7 (2 C);
131.9; 135.0; 138.6; 141.9; 153.7; 153.9; 157.0. MS: 320 (87, Mþ), 292 (55), 186 (100), 159 (88), 130 (35),
102 (60). Anal. calc. for C19H16N2O3 (320.34): C 71.24, H 5.03, N 8.74; found: C 71.30, H 5.22, N 8.49.
Preparation of 3-{[-3-(2-Hydroxyethyl)oxazolidin-2-ylidene]amino}-2-benzofurancarboxamides 7.
To the soln. of 4 prepared above in CH2Cl2 (15 ml) was added 2,2’-iminodiethanol (0.21 g, 2 mmol), and
the mixture was allowed to stand for 0.5 h. The soln. was condensed, and anh. EtOH (10 ml) with several
drops of EtONa in EtOH was added. The mixture was stirred for 1 – 6 h at r.t. The soln. was concentrated
under reduced pressure and the residue was recrystallized from CH2Cl2/PE to give 7.
3-{[(2E)-3-(2-Hydroxyethyl)oxazolidin-2-ylidene]amino}-N-phenyl-2-benzofurancarboxamide
(7a). White crystals, recrystallized from CH2Cl2/PE 1:1. Yield 0.64 g, 88%. M.p. 184 – 1868. IR (KBr):
3424, 1678 (C¼O), 1633, 1544, 1398, 1036. 1H-NMR (400 MHz, CDCl3): 3.74 (t, J ¼ 5.2, CH2N); 3.85 (t,
J ¼ 7.6, CH2N); 3.97 (t, J ¼ 5.2, CH2O); 4.47 (t, J ¼ 8.0, CH2O); 7.05 – 7.67 (m, 9 arom. H); 10.07 (s, NH).
MS: 365 (25, Mþ), 322 (35), 229 (77), 186 (69), 114 (100). Anal. calc. for C20H19N3O4 (365.38): C 65.74, H
5.24, N 11.50; found: C 65.87, H 5.41, N 11.46.
3-{[(2E)-3-(2-Hydroxyethyl)oxazolidin-2-ylidene]amino}-N-(4-methylphenyl)-2-benzofurancarbox-
amide (7b). White crystals, recrystallized from CH2Cl2/PE 1:1. Yield 0.62 g, 82%. M.p. 170 – 1718. IR
(KBr): 3354, 1680 (C¼O), 1628, 1547, 1410, 1253, 1036. 1H-NMR (400 MHz, CDCl3): 2.27 (s, Me); 3.41
(s, OH); 3.70 (t, J ¼ 5.2, CH2N); 3.81 (t, J ¼ 8.0, CH2N); 3.97 (t, J ¼ 5.2, CH2O); 4.46 (t, J ¼ 8.0, CH2O);
7.05 – 7.52 (m, 8 arom. H); 10.01 (s, NH). MS: 379 (34, Mþ), 322 (43), 229 (64), 186 (78), 114 (100). Anal.
calc. for C21H21N3O4 (379.41): C 66.48, H 5.58, N 11.08; found: C 66.33, H 5.60, N 11.13.
General Procedure for the Preparation of 2-(Alkylamino)benzofuro[3,2-d]pyrimidin-4(3H)-ones
(9). To the soln. of 4 prepared above in CH2Cl2 (15 ml) was added alkylamine (2 mmol), and the mixture
was allowed to stand for 0.5 – 4 h. The soln. was condensed, and anh. EtOH (10 ml) with several drops of
EtONa in EtOH was added. The mixture was stirred for 2 – 5 h at r.t. The soln. was concentrated under
reduced pressure and the residue was recrystallized to give 2-(alkylamino)benzofuro[3,2-d]pyrimidin-
4(3H)-ones 9.

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Helvetica Chimica Acta – Vol. 91 (2008)
2-(Ethylamino)-3-phenylbenzofuro[3,2-d]pyrimidin-4(3H)-one (9a). White crystals, recrystallized
from CH2Cl2/EtOH 2 :1. Yield 0.54 g, 89%. M.p. 197 – 1998. IR (KBr): 3362, 1703 (C¼O), 1534, 1353,
1091. 1H-NMR (400 MHz, CDCl3): 1.16 (t, J ¼ 7.2, Me); 3.48 – 3.55 (q, J ¼ 7.2, CH2N); 4.09 (s, NH); 7.33 –
8.04 (m, 9 arom. H). 13C-NMR (100 MHz, CDCl3): 14.6; 37.0; 112.6; 121.5; 123.0 (2 C); 128.8 (2 C);
129.1; 129.9; 130.6 (2 C); 133.1; 134.3; 144.5; 151.8; 153.7; 157.2. MS: 305 (45, Mþ), 275 (25), 260 (32), 160
(41), 130 (67), 102 (100). Anal. calc. for C18H15N3O2 (305.33): C 70.81, H 4.95, N 13.76; found: C 70.93, H
4.70, N 13.80.
3-Phenyl-2-(propylamino)benzofuro[3,2-d]pyrimidin-4(3H)-one (9b). White crystals, recrystallized
from CH2Cl2/EtOH 1:1. Yield 0.53 g, 83%. M.p. 160 – 1628. IR (KBr): 3353, 1699 (C¼O), 1540, 1342,
1112. 1H-NMR (400 MHz, CDCl3): 0.86 (t, J ¼ 7.2, Me); 1.50 – 1.60 (m, CH2); 3.42 – 3.47 (m, CH2N); 4.12
(s, NH); 7.34 – 8.05 (m, 9 arom. H). MS: 319 (29, Mþ), 277 (38), 260 (28), 160 (36), 130 (65), 102 (100).
Anal. calc. for C19H17N3O2 (319.36): C 71.46, H 5.37, N 13.16; found: C 71.43, H 5.26, N 13.28.
2-(Butylamino)-3-phenylbenzofuro[3,2-d]pyrimidin-4(3H)-one (9c). White crystals, recrystallized
from CH2Cl2/EtOH 1:1. Yield 0.49 g, 74%. M.p. 163 – 1648. IR (KBr): 3342, 1701 (C¼O), 1542, 1340,
1
1110. H-NMR (400 MHz, CDCl3): 0.91 (t, J ¼ 7.2, Me); 1.26 – 1.52 (m, 2 CH2); 3.44 – 3.49 (m, CH2N);
4.10 (s, NH); 7.32 – 8.03 (m, 9 arom. H). MS: 333 (18, Mþ), 289 (43), 261 (46), 160 (27), 130 (61), 102
(100). Anal. calc. for C20H19N3O2 (333.38): C 72.05, H 5.74, N 12.60; found: C 72.11, H 5.82, N 12.38.
3-Phenyl-2-(isopropylamino)benzofuro[3,2-d]pyrimidin-4(3H)-one (9d). White crystals, recrystal-
lized from CH2Cl2/EtOH 1:1. Yield 0.52 g, 82%. M.p. 192 – 1948. IR (KBr): 3332, 1702 (C¼O), 1544,
1
1346, 1118. H-NMR (400 MHz, CDCl3): 1.16 (d, J ¼ 6.4, 2 Me); 3.88 (d, J ¼ 7.2, NH); 4.32 – 4.38 (m,
CHN); 7.32 – 8.02 (m, 9 arom. H). MS: 319 (100, Mþ), 304 (33), 261 (69), 160 (27), 130 (49), 102 (87).
Anal. calc. for C19H17N3O2 (319.36): C 71.46, H 5.37, N 13.16; found: C 71.25, H 5.11, N 13.22.
2-(Isobutylamino)-3-phenylbenzofuro[3,2-d]pyrimidin-4(3H)-one (9e). White crystals, recrystal-
lized from CH2Cl2/EtOH 1:1. Yield 0.47 g, 71%. M.p. 152 – 1548. IR (KBr): 3328, 1698 (C¼O), 1543,
1341, 1116. 1H-NMR (400 MHz, CDCl3): (d, J ¼ 6.8, 2 Me); 1.82 – 1.86 (m, CH); 3.28 – 3.32 (m, CH2N);
4.15 (s, NH); 7.34 – 8.04 (m, 9 arom. H). MS: 333 (80, Mþ), 290 (56), 261 (61), 160 (49), 130 (51), 102
(100). Anal. calc. for C20H19N3O2 (333.38): C 72.05, H 5.74, N 12.60; found: C 72.17, H 5.77, N 12.57.
3-(4-Methylphenyl)-2-(isopropylamino)benzofuro[3,2-d]pyrimidin-4(3H)-one (9f). White crystals,
recrystallized from CH2Cl2/EtOH 2 :1. Yield 0.58 g, 87%. M.p. 200 – 2028. IR (KBr): 3336, 1699 (C¼O),
1540, 1340, 1115. 1H-NMR (400 MHz, CDCl3): 1.08 (d, J ¼ 6.4, 2 Me); 2.37 (s, Me); 3.87 (d, J ¼ 7.2, NH);
4.24 – 4.29 (m, CHN); 7.10 – 7.94 (m, 8 arom. H). MS: 333 (43, Mþ), 301 (33), 261 (56), 160 (54), 130 (61),
102 (100). Anal. calc. for C20H19N3O2 (333.38): C 72.05, H 5.74, N 12.60; found: C 72.01, H 5.86, N 12.73.
2-(Cyclohexylamino)-3-(4-methylphenyl)benzofuro[3,2-d]pyrimidin-4(3H)-one (9g). White crys-
tals, recrystallized from CH2Cl2/EtOH 2 :1. Yield 0.54 g, 72%. M.p. 209 – 2118. IR (KBr): 3342, 1695
(C¼O), 1541, 1213, 1091. 1H-NMR (400 MHz, CDCl3): 1.06 – 2.00 (m, (CH2)5); 2.46 (s, Me); 4.00 – 4.08
(m, NH, CHN); 7.19 – 8.04 (m, 8 arom. H). 13C-NMR (100 MHz, CDCl3): 21.1; 24.4 (2 C); 25.3; 32.5
(2 C); 50.2; 112.4; 121.4; 122.8; 123.0; 128.2 (2 C); 128.9; 131.2 (2 C); 131.5; 132.9; 140.0; 144.4; 151.2;
153.8; 157.0. MS: 373 (75, Mþ), 261 (71), 159 (87), 130 (75), 102 (100). Anal. calc. for C23H23N3O2
(373.45): C 73.97, H 6.21, N 11.25; found: C 74.21, H 6.24, N 11.15.
2-(tert-Butylamino)-3-(4-methylphenyl)benzofuro[3,2-d]pyrimidin-4(3H)-one (9h). White crystals,
recrystallized from CH2Cl2/EtOH 2 :1. Yield 0.52 g, 75%. M.p. 205 – 2078. IR (KBr): 3378, 1704 (C¼O),
1542, 1214, 1091. 1H-NMR (400 MHz, CDCl3): 1.43 (s, 3 Me); 2.45(s, Me); 4.08 (s, NH); 7.18 – 8.01 (m, 8
arom. H). MS: 347 (38, Mþ), 331 (53), 261 (68), 159 (87), 130 (64), 102 (100). Anal. calc. for C21H21N3O2
(347.41): C 72.60, H 6.09, N 12.10; found: C 72.64, H 6.22, N 12.01.
2-[(2-Hydroxyethyl)amino]-3-phenylbenzofuro[3,2-d]pyrimidin-4(3H)-one (9i). White crystals,
recrystallized from EtOH. Yield 0.49 g, 76%. M.p. 224 – 2268. IR (KBr): 3410, 1705 (C¼O), 1544,
1
1342, 1117. H-NMR (400 MHz, CDCl3): 3.58 – 3.62 (m, CH2N); 3.78 (t, J ¼ 4.8, CH2O); 4.18 (s, OH);
4.72 (t, J ¼ 4.8, NH); 7.32 – 7.96 (m, 9 arom. H). MS: 321 (10, Mþ), 302 (68), 260 (18), 130 (65), 102 (100).
Anal. calc. for C18H15N3O3 (321.33): C 67.28, H 4.71, N 13.08; found: C 67.15, H 4.78, N 13.27.
2-[(2-Hydroxyethyl)amino]-3-(4-methylphenyl)benzofuro[3,2-d]pyrimidin-4(3H)-one (9j). White
crystals, recrystallized from EtOH. Yield 0.56 g, 84%. M.p. 210 – 2118. IR (KBr): 3410, 1701 (C¼O),
1540, 1342, 1114. 1H-NMR (400 MHz, CDCl3): 2.43 (s, Me); 3.59 – 3.63 (m, CH2N); 3.80 (t, J ¼ 4.8,
CH2O); 4.28 (s, OH); 4.77 (t, J ¼ 4.8, NH); 7.20 – 7.97 (m, 8 arom. H). MS: 335 (16, Mþ), 320 (38), 260

Helvetica Chimica Acta – Vol. 91 (2008)
871
(44), 130 (52), 102 (100). Anal. calc. for C19H17N3O3 (335.66): C 68.05, H 5.11, N 12.53; found: C 68.11, H
5.26, N 12.35.
General Procedure for the Preparation of 2-(Arylamino)benzofuro[3,2-d]pyrimidin-4(3H)-ones 11.
To the soln. of 4 prepared above in CH2Cl2 (15 ml) was added ammonia hydrate (0.08 g, 2 mmol, 80%),
methylamine hydrate (0.19 g, 2 mmol, 33%) or hydrazine (0.21 g, 2 mmol) in MeCN (5 ml). The mixture
was stirred for 0.5 – 1 h at r.t. The soln. was concentrated under reduced pressure and the residue was
recrystallized to give 11.
2-(Phenylamino)benzofuro[3,2-d]pyrimidin-4(3H)-one (11a). White crystals, recrystallized from
CH2Cl2/EtOH 3 :1. Yield 0.50 g, 90%. M.p. > 3008. IR (KBr): 3337, 3171, 1700 (C¼O), 1560, 1400, 1211.
1H-NMR (400 MHz, (D6)DMSO): 7.06 – 8.01 (m, 9 arom. H); 8.82 (s, NH); 11.19 (s, NH). MS: 277 (21,
Mþ), 184 (23), 130 (31), 102 (48), 76 (100). Anal. calc. for C16H11N3O2 (277.28): C 69.31, H 4.00, N 15.15;
found: C 69.24, H 3.81, N 15.19.
3-Methyl-2-(phenylamino)benzofuro[3,2-d]pyrimidin-4(3H)-one (11b). White crystals, recrystal-
lized from CH2Cl2/EtOH 3 :1. Yield 0.49 g, 84%. M.p. 269 – 2708. IR (KBr): 3330, 1702 (C¼O), 1520,
1400, 1211. 1H-NMR (400 MHz, CDCl3): 3.73 (s, Me); 6.58 (s, NH); 7.19 – 7.98 (m, 9 arom. H). MS: 291
(100, Mþ), 265 (23), 130 (54), 102 (48). Anal. calc. for C17H13N3O2 (291.30): C 70.09, H 4.50, N 14.42;
found: C 70.15, H 4.63, N 14.45.
3-Amino-2-(phenylamino)benzofuro[3,2-d]pyrimidin-4(3H)-one (11c). White crystals, recrystal-
lized from CH2Cl2/EtOH 3 :1. Yield 0.54 g, 92%. M.p. 263 – 2658. IR (KBr): 3320, 1701 (C¼O), 1542,
1
1402, 1199. H-NMR (400 MHz, (D6)DMSO): 5.85 (s, NH2); 7.09 – 8.00 (m, 9 arom. H); 9.45 (s, NH).
MS: 292 (21, Mþ), 184 (23), 130 (31), 102 (48), 76 (100). Anal. calc. for C16H12N4O2 (292.29): C 65.75, H
4.14, N 19.17; found: C 65.58, H 4.24, N 19.15.
3-Amino-2-[(4-methylphenyl)amino]benzofuro[3,2-d]pyrimidin-4(3H)-one (11d). White crystals,
recrystallized from CH2Cl2/EtOH 3 :1. Yield 0.58 g, 95%. M.p. 292 – 2948. IR (KBr): 3327, 1702 (C¼O),
1
1544, 1401, 1200, 742. H-NMR (400 MHz, (D6)DMSO): 2.31 (s, Me); 5.82 (s, NH2); 7.18 – 7.98 (m, 8
arom. H); 9.35 (s, NH). MS: 306 (100, Mþ), 288 (76), 201 (35), 130 (29). Anal. calc. for C17H14N4O2
(306.32): C 66.66, H 4.61, N 18.29; found: C 66.47, H 4.75, N 18.26.
X-Ray Structure of 7a1). The crystal data of 7a are as follows: formula C20H19N3O4; Mr 365.38;
crystal system: monoclinic; space group: P2(1)/c; unit cell dimensions: a ¼ 13.9052(18) Š, b ¼
10.0674(14) Š, c ¼ 13.5305(18) Š, b ¼ 111.119(2)8, V ¼ 1766.9(4) Š3 ; Z ¼ 4; d ¼ 1.374 Mg/
m3; m(MoKa) ¼ 0.097 mmꢀ1
.
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Helvetica Chimica Acta – Vol. 91 (2008)
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Received November 14, 2007