Molecules 2007, 12
1628
1
3
2
1
.14 (6H, d, J = 6.6 Hz), 5.55 (2H, q, J = 6.6 Hz); C-NMR (CDCl ) δ 21.55 (CH ), 40.12 (CH),
3
3
12.57 (CN), 131.35 (C-5, C-6), 157.10 (C-2, C-3); MS m/z (% rel. int.) 346 (1.5), 344 (M, 3.3), 342
7
9
81
(
1.6), 265 (49.8), 264 (7.8), 263 (50.8); Calc. for C H Br BrN : 343.9095. Found: 343.9090.
10 8 4
4
-Hydroxy-2,5-dimethyl-2,3-dihydrothiophen-3-one (4)
Compound 4 has been prepared by other workers from 2 and sodium sulfide nonahydrate in ethanol
6]. A solution of 2 (2.72 g, 10 mmol) in DCM (40 mL) was mixed with a solution of sodium sulfide
[
nonahydrate (3.6 g, 15 mmol) in water (20 mL) and the phase transfer catalyst methyl-
trioctylammonium chloride (“Aliquat”, 0.1 g). The mixture was stirred vigorously at ambient
temperature for 2 h. The reaction was monitored by TLC with chloroform on silica. The organic phase
was dried over magnesium sulfate, and the solvent was removed under reduced pressure to yield a
yellow semisolid, 1.1 g (76 %). Lit [6] m.p. 77–79 °C. Attempts to recrystallise the product were
1
unsuccessful, and compound 4 seemed slightly unstable even when kept in the dark at 5 °C. H-NMR
1
3
(CDCl
3
) δ 1.57 (3H, d, J = 7 Hz), 2.27 (3H, s), 3.69 (1H, q, J = 7 Hz), 6.20 (1H, broad s); C-NMR
(
CDCl ) δ 14.92, 16.99, 45.50, 141.37, 147.93, 197.98.
3
2
,3-Dicyano-5,7-bismethylthieno[3,4-b]pyrazine (5): Method A with trisodium thiophosphate
dodecahydrate
To a solution of 3 (0.52 g, 1.5 mmol) in methanol (15 mL) was added a suspension of trisodium
thiophosphate dodecahydrate (0.59 g, 15 mmol) in methanol (15 mL). The reaction mixture was heated
under reflux for 19 h, concentrated to about 5 mL and extracted with DCM (3 x 15 mL). The red DCM
extracts were chromatographed on silica eluting with DCM. The first red fractions were combined,
evaporated and the residue was filtered with diethyl ether to yield 0.02 g (8 %) of a crimson red
1
13
powder, m.p. 275 – 278 °C (dec.); H-NMR (CDCl
3 3 3
) δ 2.91 (6H, s); C-NMR (CDCl ) δ 11.94 (CH ),
1
14.02 (CN), 126.90, 134.18, 137.04; IR (KBr) < 2228 (CN), (1385, 1327, 1247, C=N or C=C), 1116
-1
(
(
C-S) cm ; UV-vis [CH
2
Cl
2
(,)] 340 (4 900), 484 (1 500) nm; MS m/z (% rel. int.) 216 (5.8), 215
S: 214.0313. Found 214.0311.
15.4), 214 (M, 100), 213 (74.8); Calc. for C10
6 4
H N
Method A with sodium sulfide
Finely ground 60 % sodium sulfide (0.10 g, 0.7 mmol) was dissolved in ethanol (20 mL). A
solution of compound 3 (0.21 g, 0.6 mmol) in ethanol (20 mL) was added dropwise during 30 min, and
the orange solution was stirred at ambient temperature for 48 h. The solvent was removed under
reduced pressure, and the residue was extracted with benzene (2 x 10 mL). Removal of the benzene
gave a glassy red residue (0.09 g) which was chromatographed on silica eluting with benzene. The
fractions with R (benzene) = 0.3 were combined to give 0.03 g of a red solid, which was recrystallized
f
from benzene to yield 0.02 g (15 %) of compound 5, m.p. 263–265 °C (dec.). The rest of the benzene
soluble material was eluted from the column with acetone and gave 0.06 g of a glassy solid, R
f
1
(CHCl
3
)
=
0, R
f
(benzene) = 0. This material decomposed slowly when kept in chloroform solution. H-NMR
(CDCl
3
) δ 1.3 – 2.0 and 2.6 – 2.9 (broad unresolved multiplets), 4.5 (weak, broad s). UV-vis (acetone)