Synthesis of thieno[3,2-e][1,2,4]triazolo[1,5-c]pyrimidin-5(6H)-ones via their [1,2,4]triazolo[4,3-c]pyrimidine compounds as new ring systems by Dimroth-type rearrangement

Article abstract of DOI:10.3987/COM-07-S(U)58

General and facile syntheses of thieno|3,2-e||1,2,4|triazolo|1,5-c|-pyrimidin-5(6H)-one (6a) and its 2-substituted derivatives (6b-j) produced by instantaneous isomerization of their |4,3-c| compounds (7a-j), which were prepared by condensation of 4-hydrazinothieno|2,3-d|pyrimidin-2(1/H)-one (10)with appropriate triethyl orthoesters or by oxidative cyclization of 4-(benzylidenehydrazino)thieno|2,3-d|pyrimidin-2(1H)-ones (11c-j), are described as novel ring systems and as a new class of potential xanthine oxidase inhibitors. The |1,5-c| isomers (6a-c) were further prepared by condensation of 3-amino-4-imino-2-oxo-1,2,3,4-tetrahydrothieno|2,3-d|pyrimidine (14) with appropriate triethyl orthoesters as a synthetic method for a reliable structure of the tricyclic ring systems.

Full text of DOI:10.3987/COM-07-S(U)58

HETEROCYCLES, Vol. 73, 2007
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HETEROCYCLES, Vol. 73, 2007, pp. 777 - 793. © The Japan Institute of Heterocyclic Chemistry
Received, 2nd August, 2007, Accepted, 5th September, 2007, Published online, 7th September, 2007. COM-07-S(U)58
SYNTHESIS OF THIENO[3,2-e][1,2,4]TRIAZOLO[1,5-c]PYRIMIDIN-
5(6H)-ONES VIA THEIR [1,2,4]TRIAZOLO[4,3-c]PYRIMIDINE
COMPOUNDS AS NEW RING SYSTEMS BY DIMROTH-TYPE
REARRANGEMENT
Tomohisa Nagamatsu,* Shoeb Ahmed, Abugafar M. L. Hossion, and Seiji
Ohno
Department of Drug Discovery and Development, Division of Pharmaceutical
Sciences, Graduate School of Medicine, Dentistry and Pharmaceutical Sciences,
Okayama University, 1-1-1, Tsushima-naka, Okayama 700-8530, Japan; e-mail:
nagamatsu@pheasant.pharm.okayama-u.ac.jp
Abstract – General and facile syntheses of thieno[3,2-e][1,2,4]triazolo[1,5-c]-
pyrimidin-5(6H)-one (6a) and its 2-substituted derivatives (6b–j) produced by
instantaneous isomerization of their [4,3-c] compounds (7a–j), which were
prepared by condensation of 4-hydrazinothieno[2,3-d]pyrimidin-2(1H)-one (10)
with appropriate triethyl orthoesters or by oxidative cyclization of
4-(benzylidenehydrazino)thieno[2,3-d]pyrimidin-2(1H)-ones
(11c–j),
are
described as novel ring systems and as a new class of potential xanthine oxidase
inhibitors. The [1,5-c] isomers (6a–c) were further prepared by condensation of
3-amino-4-imino-2-oxo-1,2,3,4-tetrahydrothieno[2,3-d]pyrimidine (14) with
appropriate triethyl orthoesters as a synthetic method for a reliable structure of
the tricyclic ring systems.
INTRODUCTION
In connection with ongoing work aimed at synthesis and biological evaluation of novel tricyclic fused
pyrimidine or purine systems,1–6 we have recently reported the potential xanthine oxidase (XO) inhibitory
activities of the angular type analogues such as 7β-D-ribofuranosyl-7H-[1,2,4]triazolo[3,4-i]purines (1),7
9H-[1,2,4]triazolo[3,4-i]purines (2),8 and 7H-pyrazolo[4,3-e]-1,2,4-triazolo[4,3-c]pyrimidines (3).9
Moreover, we have reported the reliable synthesis of thieno[2,3-e][1,2,4]triazolo[4,3-c]pyrimidin-5(6H)-
ones (4) and thieno[2,3-e][1,2,4]triazolo[1,5-c]pyrimidin-5(6H)-ones (5) as a new class of potential XO

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inhibitors.10 Allopurinol has been reported as a potential inhibitor of XO,11 which catalyzes the
conversion of hypoxanthine and xanthine to uric acid, and been used extensively for the clinical control of
uric acid production in gout and hyperuricemia.12 Although allopurinol is a medicine which toxicity is
comparatively rare, a life-threatening toxicity syndrome such as vasculitis, rash, eosinophilia, hepatitis,
progressive renal failure has been reported after its use.13 The XO inhibitory activities have been
discovered in some newly synthesized compounds and previously known compounds.14 However, the
clinically effective XO inhibitors for the treatment of hyperuricemia and gout have not been developed
yet since allopurinol was introduced for clinical use in 1963.12,15 Therefore, such tricyclic hetero analogs
(1–5) of allopurinol have aroused considerable recent interest for us. Recently, we have found the
[1,2,4]triazolo[4,3-c]pyrimidin-5(6H)-one ring system was easily isomerized into the corresponding
[1,2,4]triazolo[1,5-c]pyrimidin-5(6H)-one ring system.16 In this paper, we report a reliable and general
synthesis of 2-substituted thieno[3,2-e][1,2,4]triazolo[1,5-c]pyrimidin-5(6H)-ones (6) via 3-substituted
thieno[3,2-e][1,2,4]triazolo[4,3-c]pyrimidin-5(6H)-ones (7) by Dimroth-type rearrangement as novel ring
systems and a new class of the XO inhibitors.
RESULTS AND DISCUSSION
In the first place we tried to synthesize the key intermediate, 4-hydrazinothieno[2,3-d]pyrimidin-2(1H)-
one (10), which could be led through several processes from barbituric acid. The requisite starting
material, thieno[2,3-d]pyrimidin-2,4(1H,3H)-dione (8), was prepared according to a literature method.17
Treatment of 8 with Lawesson’s reagent in 1,4-dioxane under reflux afforded 2-oxo-4-thioxo-1,2,3,4-
tetrahydrothieno[2,3-d]pyrimidine (9) in 82% yield, which was identified by its physical data with a

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779
compound prepared by reaction of 2-aminothiophene-3-carbonitrile with carbonyl sulfide,18 as shown in
the sequential synthetic pathway of Scheme 2. Then, refluxing of 9 with excess hydrazine hydrate in
water afforded the desired 4-hydrazinothieno[2,3-d]pyrimidin-2(1H)-one (10) in 70% yield. The
compound (10) was anticipated as a versatile intermediate for the preparation of thieno[3,2-e][1,2,4]-
triazolo[4,3-c]pyrimidine ring system (7). However, the expected ring system (7) was isomerized
instantaneously to the thieno[3,2-e][1,2,4]triazolo[1,5-c]pyrimidine ring system (6) by Dimroth-type
rearrangement. Consequently, the hydrazinothienopyrimidine (10) was converted to the hydrazones
(11c–j) by reaction with an appropriate aldehyde in MeOH at room temperature in 72–90% yields (Tables

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1 and 2). The hydrazones (11c–j) were cyclized oxidatively to the corresponding 2-arylthieno[3,2-e]-
[1,2,4]triazolo[1,5-c]pyrimidin-5(6H)-ones (6c–j) in 52–65% yields by heating with chloranil in acetic
acid (Method A). In case of oxidation for 11 using 70% HNO3, the drastic reactions took place and it
was difficult to isolate pure compounds from many by-products. Furthermore, the 2-unsubstituted,
2-methyl, and 2-phenyl derivatives (6a–c) were synthesized by treatment of the compound (10) with an
appropriate triethyl orthoester in DMF under refluxing in 68–95% yields (Method B).
We have recently reported that the fused heterocycles having the triazolo[4,3-c]pyrimidine ring system
with an oxo or a thioxo group at the 5-position easily undergo Dimorth-type rearrangement to yield their
triazolo[1,5-c] isomers.10,16 In order to determine to be either the [1,5-c] system (6) or the [4,3-c] system
(7) as the structure of products which were prepared by Methods A and B, we tried another reliable
synthetic route (Method C) starting from 2-oxo-4-thioxo-1,2,3,4-tetrahydrothieno[2,3-d]pyrimidine (9).
At first, treatment of 9 with CH3I in 2N NaOH solution gave the 4-(methylthio)thieno[2,3-d]pyrimidin-
2(1H)-one (12) in 56% yield. Then, reaction of 12 with 28% aqueous NH3 in steel sealed tube at 150 °C
afforded the 4-aminothieno[2,3-d]pyrimidin-2(1H)-one (13) in 67% yield. Thus, the second key
intermediate, 3-amino-4-imino-2-oxo-1,2,3,4-tetrahydrothieno[2,3-d]pyrimidine (14), was prepared in
39% yield by N-amination of reaction of 13 with excess hydroxylamine-O-sulfonic acid in 1N NaOH
solution at room temperature. Finally, heating 14 thus obtained with appropriate triethyl orthoesters
(Method C) gave the corresponding thieno[3,2-e][1,2,4]triazolo[1,5-c]pyrimidin-5(6H)-ones (6a–c),
which were identical to the compounds (6a–c) prepared by Methods A or B, respectively. Therefore, the
structure of the triazolo moiety for the tricyclic compounds (7) was assigned as not the triazolo[4,3-c]
system but the triazolo[1,5-c] system. All new compounds (6 and 10–14) exhibited satisfactory
1
elemental combustion analyses except for 14 and IR and H NMR spectral data consistent with the
structures indicated as shown in Tables 1-4 and experimental section.
Since the 1,2,4-triazolo[4,3-c]pyrimidine ring systems with an oxo or thiox group at the 5-position were
rapidly isomerized into their [1,5-c] isomers, it was difficult to isolate the compounds having the [4,3-c]
systems without isomerization.16
We have found recently that the 6-methyl derivatives of
1,2,4-triazolo[4,3-c]pyrimidin-5(6H)-ones, i.e. the methylated imide compounds, were quite stable.16
Therefore, in order to isolate the thieno[3,2-e][1,2,4]triazolo[4,3-c]pyrimidine ring system (7) without
isomerization, we tried to prepare the 6-alkylated derivatives of compound (7). As shown in Scheme 3
as the sequential pathway, methylation of 12 was carried out with MeI-NaH solution in the usual way to
get the 1-methyl-4-(methylthio)thieno[2,3-d]pyrimidin-2(1H)-one (15) in 75% yield. Then, treatment of
15 with 80% hydrazine hydrate in ethanol under reflux afforded the 4-hydrazino derivative (16) in 52%
yield. The subsequent treatment of 16 with benzaldehyde in DMF at room temperature yielded the
4-benzaldehydehydrazone (17) in 66% yield. The intramolecular cyclization of 17 thus obtained to the

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3-phenylthieno[3,2-e][1,2,4]triazolo[4,3-c]pyrimidin-5(6H)-ones (7c) was accomplished by oxidation
using chloranil in acetic acid at reflux in 57% yield as shown in Tables 5 and 6. On the other hand,
heating the 4-hydrazino derivative (16) with appropriate triethyl orthoesters in DMF under reflux
afforded the corresponding thieno[3,2-e][1,2,4]triazolo[4,3-c]pyrimidin-5(6H)- ones (7a) and its 3-methyl
(7b) and 3-phenyl (7c) derivatives in 75–83% yields. All new compounds (7a–c and 15–17) exhibited
1
satisfactory elemental combustion analyses and IR, H-NMR, and UV spectral data consistent with the
structures indicated as shown in Tables 5-7 and experimental section. Especially, each isomer of the
1
[1,5-c]pyrimidines (6) and the [4,3-c]pyrimidines (7) was distinguishable by H-NMR and UV spectra.
1
In H-NMR [(CD3)2SO] spectra, the most prominent peak of the [1,5-c]pyrimidines (6a) was observed at
δ 8.43 as a singlet signal attributed to the proton at the 2-position, while the similar singlet signal
attributed to the proton at the 3-position of the [4,3-c]pyrimidines (7a) was observed at δ 9.26 in more
downfield. In a similar manner as above, the methyl protons observed at δ 2.44 as singlet signal for the
2-methyl derivative (6b) appeared in higher field than those observed at δ 2.77 for the 3-methyl derivative
(7b). It is noteworthy that the chemical shift of the proton or substituent at the 2-position for the
[1,5-c]pyrimidines (6) was observed in higher field in comparison with it at the 3-position for the
[4,3-c]pyrimidines (7). We have found the similar phenomenon in similar ring systems before.10,16 The

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UV spectrum of 6a in ethanol had maxima at 225, 271, and 280 nm, while those of 7a were at 244, 251,
and 273 nm. As a general rule, a bathochromic shift of the respective maximum absorption of 2–20 nm
was observed in each UV spectrum for the [1,5-c] compounds (6) compared to the corresponding [4,3-c]
isomers (7). Thus, compounds 6b (3-Me) and 6c (3-Ph) showed the maxima at 233, 272, and 280 nm
and the maxima at 241, 279, and 291 nm, respectively, whereas compounds 7b (3-Me) and 7c (3-Ph)
showed the maxima at 245, 253, and 274 nm and the maxima at 250, 277, and 285 nm, respectively.
BIOLOGICAL EVALUATION
Antitumor activity: The new compounds (6 and 11) prepared here were evaluated in vitro for the
growth inhibitory effect against CCRF-HSB2 (human T-cell acute lymphoblastoid leukemia) and KB

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783
(human oral epidermoid carcinoma) cells by the modified MTT [3-(3,4-dimethylthiazol-2-yl)-2,5-
diphenyltetrazolium bromide] assay19 for cellular growth and survival application method developed by
Mosmann.20 The results, i.e. IC50 (µg/mL) of each compound against the both cells, are summarized in
Table 8. Most compounds of 2-substituted thieno[3,2-e][1,2,4]triazolo[1,5-c]pyrimidin-5(6H)-ones (6a)
showed 50% inhibitory activity against CCRF-HSB-2 and KB cancer cells at the concentration ca. 15–40
µg/mL and ca. 12–57 µg/mL, respectively.
Xanthine oxidase inhibitory activity: The xanthine oxidase (XO) inhibitory activities of the
compounds (6a–j and 7a–c) against bovine milk xanthine oxidase in vitro were investigated significantly.

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Some of them (6a–j) showed more potential XO inhibitory activity than that of allopurinol. Further
investigations along this line are now in progress and the results of the inhibitory activities of the
compounds described in this paper will be reported elsewhere.
CONCLUSION

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785
We have established an efficient and reliable synthesis of thieno[3,2-e][1,2,4]triazolo[1,5-c]pyrimidin-
5(6H)-ones (6a) and its 2-substituted derivatives (6b–j) by instantaneous isomerization of their [4,3-c]
compounds (7a–j). The structures of some compounds (6a–c) were confirmed by synthesis from the
reaction of 3-amino-4-imino-2-oxo-1,2,3,4-tetrahydrothieno[2,3-d]pyrimidine (14) with appropriate
triethyl orthoesters. The isomer, 6-methylthieno[3,2-e][1,2,4]triazolo[4,3-c]pyrimidin-5(6H)-one (7a),
and its 2-substituted derivatives (7b,c) were prepared in a similar manner as above. Antitumor activities
for compounds (6) against CCRF-HSB-2 and KB cancer cells were evaluated in vitro and the most

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compounds showed moderate antitumor activities. The compounds (6a–j and 7a–c) were also examined
for the XO inhibitory activities against bovine milk xanthine oxidase in vitro and 6a–j were mostly found
better activities compared to allopurinol. However, the compounds (7a–c) were slightly less active than
that of allopurinol.
EXPERIMENTAL
Mps were determined using a Yanagimoto digital-micro-melting point apparatus MP 500D and were
uncorrected. IR spectra were recorded using a JASCO FT/ IR-200 spectrophotometer as Nujol mulls.

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Mass spectra were recorded at 70eV ionizing voltage with FAB ionization using a VG-70SE spectrometer
and glycerol as a matrix. 1H-NMR spectra were obtained using a Varian VXR 300 MHz spectrometer
with TMS as an internal standard. In all cases, chemical shifts are in ppm downfield to TMS. J values
are given in Hz. UV spectra were recorded in EtOH with a Hitachi U-2001 spectrophotometer.
Microanalyses were measured by a Yanako CHN Corder MT-5 apparatus. All reagents were of
commercial quality from freshly opened containers and were used without further purification. Reaction
progress was monitored by analytical thin layer chromatography (TLC) on pre-coated glass plates (silica
gel 70 FM Plate-Wako) using the solvent systems of A [AcOEt], B [AcOEt : EtOH (6:1)], C [AcOEt :
EtOH (4:1)], D [AcOEt : EtOH (1:1)], and E [EtOH] unless being cited in the table and products were
visualized by UV light. Column chromatography was accomplished on Daisogel IR-60 (63/ 210 µm,
Daiso Co.). The reaction temperatures are indicated as the temperature of the oil bath.

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2-Oxo-4-thioxo-1,2,3,4-tetrahydrothieno[2,3-d] pyrimidine (9)
A mixture of thieno[2,3-d]pyrimidin-2,4(1H,3H)-dione (8)17 (0.5 g, 2.97 mmol) and 2,4-bis(4-
methoxyphenyl)-1,3-dithia-2,4-diphosphetane-2,4-disulfide (Lawesson’s reagent 1.25 g, 2.97 mmol) in
1,4-dioxane (10 mL) was heated under reflux for 20 min. After the reaction was complete the solution
was evaporated in vacuo and the residue was triturated with AcOEt to give crystals, which were collected
by filtration and recrystallized from EtOH to afford the 4-thioxo derivative (9) (0.45 g, 82%) as pale
yellow powdery crystals, mp 303–305 °C (lit.18 mp 300 °C); Rf (B) 0.70; IR (Nujol) νmax/cm-1: 3160, 3080
(NH), 1700 (C=O); 1H-NMR [(CD3)2SO] δ: 7.12 (1H, d, J 5.6, 5-H), 7.26 (1H, d, J 5.6, 6-H), 12.49 (2H,
br s, 2 x NH); Anal. Calcd for C6H4N2OS2: C, 39.11; H, 2.19; N, 15.20, Found: C, 39.26; H, 2.38; N,
15.19; MS (FAB, glycerol matrix): m/z = 185 (MH+).
4-Hydrazinothieno[2,3-d]pyrimidin-2(1H)-one (10)
A mixture of the 4-thioxo derivative (9) (1.0 g, 5.43 mmol) and hydrazine monohydrate (0.8 g, 16 mmol)
in water (10 mL) was heated under reflux for 1.5 h. Upon cooling to rt after the reaction was complete,
the resulting precipitates were collected by filtration, washed with water and EtOH, and crystallized from
water to afford the hydrazine derivative (10) (0.69 g, 70%) as colorless powdery crystals, mp
238–241 °C; Rf (C) 0.30; IR (Nujol) νmax or δmax /cm-1: 3320 (νas, NH2), 3200 (νs, NH2), 3100, 3065 (ν,
NH), 1650 (ν, C=O), 1620 (δ, NH2); 1H-NMR [(CD3)2SO] δ: 5.83 (2H, br s, NH2), 6.96 (1H, d, J 5.4, 5-H),
7.13 (1H, d, J 5.4, 6-H), 9.65 (2H, br s, 2 x NH); Anal. Calcd for C6H6N4OS: C, 39.55; H, 3.32; N, 30.75,
Found: C, 39.41; H, 3.56; N, 30.48; MS (FAB, glycerol matrix): m/z = 183 (MH+).
General procedure for the preparation of 4-(benzylidenehydrazino)thieno[2,3-d]pyrimidin-2(1H)-
one (11c) and its 4-(4-substituted benzylidenehydrazino) derivatives (11d–j)
A mixture of the hydrazine derivative (10) (0.2 g, 1.1 mmol) and an appropriate arylaldehyde (1.31
mmol) in MeOH (20 mL) was stirred at rt for 8-10 h. After the reaction was complete, the precipitated
crystals were collected by filtration and washed with AcOEt, and recrystallized from a mixture of EtOH
and DMF to afford the corresponding hydrazones (11c–j) as shown in Tables 1 and 2.
General procedure for the preparation of thieno[3,2-e][1,2,4]triazolo[1,5-c]pyrimidin-5(6H)-one
(6a) and its 2-substitued derivatives (6b–j)

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(1) Method A: a solution of an appropriate arylaldehyde hydrazone (11c–j) (0.6 mmol) with chloranil
(0.22 g, 0.9 mmol) in AcOH (20–30 mL) was refluxed for 15 min except for 11g, which was refluxed for
60 min. After the reaction was complete, the solvent was evaporated in vacuo to afford the solid. The
resulting solid was washed with EtOH–Et2O mixture and crystallized from an appropriate solvent to give
the corresponding thienotriazolopyrimidines (6c–j) as shown in Tables 3 and 4.
(2) Method B: a mixture of the hydrazino derivative (10) (0.2 g, 1.1 mmol) with an appropriate triethyl
orthoester (1.32 mmol) in DMF (4 mL) was refluxed for 30 min. After cooling, the precipitated crystals
were collected by filtration, washed with EtOH and recrystallized from EtOH to give the corresponding
thienotriazolopyrimidines (6a–c) as shown in Tables 3, 4 and 7.
(3) Method C: a mixture of 3-amino-4-imino-2-oxo-1,2,3,4-tetrahdrothieno[2,3-d]pyrimidine (14) (0.2 g,
1.1 mmol) with an appropriate triethyl orthoester (11 mmol) in AcOH (5 mL) was heated at 80 °C for
10–60 min. After cooling, the precipitated crystals were collected by filtration, washed with EtOH-H2O
mixture and recrystallized from EtOH to give the corresponding products (6a–c) as shown in Tables 3
and 4.
4-(Methylthio)thieno[2,3-d]pyrimidin-2(1H)-one (12)
To a cooling solution of the 4-thioxo derivative (9) (0.5 g, 2.71 mmol) in 2N NaOH solution (5 mL) at
5 °C was added MeI (1.15 g, 8.10 mmol) dropwise. The solution was vigorously shaken for 10 min to
afford precipitates. The precipitates were collected by filtration, dissolved in hot water and neutralized
with 10% HCl solution. The precipitated crystals thus obtained were collected by filtration and dried
under reduced pressure to yield the 4-methylthio derivative (12) (0.30 g, 56%) as colorless powdery
crystals (from EtOH), mp > 277 °C (decomp.); Rf (C) 0.65; IR (Nujol) νmax/cm-1: 3080 (NH), 1640 (C=O);
1H-NMR [(CD3)2SO] δ: 2.58 (3H, s, Me), 7.19 (1H, d, J 5.7, 5-H), 7.29 (1H, d, J 5.7, 6-H), 12.22 (1H, br
s, NH); Anal. Calcd for C7H6N2OS2 · 1/3H2O: C, 41.16; H, 3.29; N, 13.71, Found: C, 41.13; H, 3.00; N,
13.61; MS (FAB, glycerol matrix): m/z = 199 (MH+).
4-Aminothieno[2,3-d]pyrimidin-2(1H)-one (13)
A mixture of the 4-methylthio derivative (12) (1.0 g, 5.04 mmol) and 28% aqueous NH3 (50 mL) was
heated in a steel sealed tube at 150 °C (10 kg/cm2) pressure for 7 h. After the reaction was complete, the
precipitated crystals were collected by filtration, washed with EtOH and recrystallized from 70% aqueous
DMF to afford the 4-amino derivative (13) (0.56 g, 67%) as colorless powdery crystals, mp > 300 °C; Rf

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(C) 0.60; IR (Nujol) νmax/cm-1: 3320 (νas, NH2), 3120 (νs, NH2), 3080 (ν NH), 1650 (ν, C=O), 1630 (δ,
1
NH2); H-NMR [(CD3)2SO] δ: 6.97 (1H, d, J 5.4, 5-H), 7.32 (1H, d, J 5.4, 6-H), 7.70 (2H, br s, NH2),
11.50 (2H, br s, 2 x NH); Anal. Calcd for C6H5N3OS · 1/4H2O: C, 41.97; H, 3.23; N, 24.47, Found: C,
42.24; H, 3.20; N, 24.35; MS (FAB, glycerol matrix): m/z = 168 (MH+).
3-Amino-4-imino-2-oxo-1,2,3,4-tetrahydrothieno[2,3-d]pyrimidine (14)
To a solution of 4-amino derivative (13) (0.3 g, 1.97 mmol) in 1N NaOH solution (9 mL) at rt was added
a solution of hydroxylamine-O-sulfonic acid (0.6 g, 5.31 mmol) in water (6 mL) dropwise. Then, the
solution was stirred at rt for 1.5 h to give the precipitates. The precipitates were collected by filtration
and washed with water to afford the 3-amino derivative (14) (0.13 g, 39%) as colorless powdery crystals,
mp 260 °C; Rf (D) 0.50; IR (Nujol) νmax/cm-1: 3400 (νas, NH2), 3320 (νs, NH2), 3170, 3080 (ν NH), 1665
1
(ν, C=O), 1620 (δ, NH2); H-NMR [(CD3)2SO] δ: 6.86 (1H, d, J 6.0, 5-H), 7.28 (1H, d, J 6.0, 6-H), 7.46
(2H, br s, NH2), 8.05 and 8.45 (each 1H, each br s, 2 x NH); MS (FAB, glycerol matrix): m/z = 183
(MH+). The product (14) was obtained as a single compound and was used for the following reactions
without further purification because it was difficult to purify since it was insoluble in usual solvents.
1-Methyl-4-(methylthio)thieno[2,3-d]pyrimidin-2(1H)-one (15)
To a solution of 4-(methylthio)thieno[2,3-d]pyrimidin-2(1H)-one (12) (0.25 g, 1.26 mmol) in dry DMF
(10 mL) were added 60% NaH (oil dispersion, 0.07 g, 1.75 mmol) and MeI (1.15 g, 8.10 mmol) and the
solution was heated 40 °C for 12 h. After the reaction was complete, the solution was evaporated in
vacuo. The residue was treated with water and the resulting crystals were collected by filtration, washed
with water and recrystallized from AcOEt to afford 1-methyl-4-(methylthio)thieno[2,3-d]pyrimidin-2-
(1H)one (15) (0.2 g, 75%) as colorless fine crystals, mp 257–258 °C; Rf (A) 0.38; IR (Nujol) νmax/cm- 1:
1
1640 (C=O); H-NMR (CDCl3) δ: 2.67 (3H, s, S-Me), 3.66 (3H, s, N-Me), 6.92 (1H, d, J 5.7, 5-H), 7.19
(1H, d, J 5.7, 6-H); Anal. Calcd for C8H8N2OS2: C, 45.26; H, 3.80; N, 13.20, Found: C, 45.29; H, 3.83; N,
13.11.
4-Hydrazino-1-methylthieno[2,3-d]pyrimidin-2(1H)-one (16)
A mixture of the 4-methylthio derivative (15) (0.25 g, 1.18 mmol) and 80% hydrazine monohydrate (0.07
g, 1.18 mmol) in EtOH was refluxed for 2.5–3 h. During the reaction was carrying out, the crystals

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deposited gradually. After ensuring complete consumption of the starting material (15), the mixture was
cooled at rt. The resulting crystals were collected by filtration, washed with EtOH-H2O mixture and
recrystallized from EtOH-DMF mixture to yield the hydrazino derivative (16) (0.12 g, 52%) as colorless
powdery crystals, mp > 300 °C; Rf (E) 0.12; IR (Nujol) νmax or νmax/cm- 1: 3260 (νas, NH2), 3200 (νs, NH2),
3100, 3080 (ν NH), 1685 (ν, C=O), 1620 (δ, NH2); 1H-NMR [(CD3)2SO] δ: 3.39 (3H, s, N-Me), 6.77 (2H,
br s, NH2), 7.11 (1H, d, J 5.4, 7-H), 7.32 (1H, d, J 5.4, 6-H), 10.03 (1H, br s, NH); Anal. Calcd for
C7H8N4OS · 5/9H2O: C, 40.77; H, 4.45; N, 27.17, Found: C, 41.03; H, 4.08; N, 26.82.
4-(Benzylidenehydrazino)-1-methylthieno[2,3-d]pyrimidin-2(1H)-one (17)
A mixture of the hydrazino derivative (16) (0.2 g, 1.02 mmol) and benzaldehyde (0.14 g, 1.32 mmol) in
DMF was stirred at rt for 12 h. After the reaction was complete, the precipitate was collected by
filtration and crystallized from EtOH to afford the blue powdery crystals of the 4-benzylidenehydrazino
derivative (17) (0.19 g, 66%), mp 210–212 °C; Rf (A) 0.27; IR (Nujol) νmax /cm- 1: 3280, 3120 (NH), 1690
1
(C=O); H-NMR [(CD3)2SO] δ: 3.40 (3H, s, N-Me), 7.22 (1H, d, J 5.4, 6-H), 7.26 (1H, d, J 5.4, 5-H),
7.41–7.43 (3H, m, Ar-m,pH), 8.01–8.04 (2H, m, Ar-oH), 8.44 (1H, s, N=CHAr), 10.57 (1H, br s, NH);
Anal. Calcd for C14H22N4OS: C, 59.14; H, 4.25; N, 19.70, Found: C, 58.94; H, 4.36; N, 19.64.
General procedure for the preparation of 6-methylthieno[3,2-e][1,2,4]triazolo[4,3-c]pyrimidin-
5(1H)-one (7a) and its 3-substituted derivative (7b,c)
(1) Method A: a solution of the benzaldehyde hydrazone (0.2 g, 0.71 mmol) (17) with choloranil (0.22 g,
0.9 mmol) in CH3CO2H (10 mL) was refluxed for 30 min. After the reaction was complete, water was
added to the solution and the crystals deposited immediately were collected by filtration. The product
was purified by column chromatography (eluent: AcOEt) to give the pure thienotriazolopyrimidine (7c)
as shown in Tables 5 and 6.
(2) Method B: a mixture of the hydrazino derivatives (16) (0.2 g, 1.02 mmol) with an appropriate triethyl
orthoester (2 mmol) in DMF (4 mL) was refluxed for 30 min. After the reaction was complete, small
amount of water was added to the solution and the solution was kept overnight. The needless fine
crystals deposited were collected by filtration, washed with H2O and recrystallized from EtOH to afford
the thienotriazolopyrimidine (7a–c) as shown in Tables 5, 6 and 7.

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ACKNOWLEDGEMENTS
The authors are indebted to the SC-NMR Laboratory of Okayama University for the NMR spectral
measurements.
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