a-DIAMINES ADDITION TO THIADIAZOLE DERIVATIVES
spectrum[19] and melting point (160.4–165.0 8C; Lit:163–
165 8C[20]; 162.5–163.5 8C[21,22]).
5,6-diphenyl-2,3-dihydropyrazine (4a) from 2a: 2a (239 mg
0.88 mmol) and EDA (112 mg, 1.86 mmol) were added to the
DMF solvent (0.53 ml) and left at r.t. for 22 days. The solvent was
vacuum rota-evaporated and the orange colored solid obtained
was extracted with cyclohexane (20 ml). The remaining solid was
dissolved in MeCN/benzene (1:1, 5 ml). The solution was cooled
to ꢀ5 8C and an oily, orange colored liquid separated. The
solution was evaporated to near dryness, and a yellow precipitate
was obtained. A similar solid was obtained by rota-evaporation
of the extracting cyclohexane solution to a ca. 1 ml final
volume. Both solids reunited were recrystalized from ethanol-
cyclohexane (1:3). The crystals (115 mg, 0.490 mmol, 56% yield)
were identified as 4a as above.
2,3-diphenylpyrazine: 4a (87 mg; 0.37 mmol) and EDA (24 mg;
0.40 mmol) were dissolved in DMF (1 ml) and left to stand at r.t. for
a month. The solvent was vacuum rota-evaporated at 40 8C. The
remaining crystalline solid (56 mg, 0.33 mmol) was filtered and
dried. It was identified as 2,3-diphenylpyrazine (yield: 89%) from
its IR spectrum.[23]
Phenanthro [9,10-b]-2,3-dihydropyrazine (4b): This compound
was identified by NMR spectroscopy in a solution of 1b (37.0 mg,
0.138 mmol) and EDA (10.0 mg, 0.166 mmol) in CDCl3 (0.7 ml)
freshly prepared. 4b dehydrogenates upon work-up yielding the
corresponding pyrazine, which was identified by its reported IR
spectrum.[24]
1H NMR (d, TMS) in CDCl3: 8.26–7.34 (multiplet, CArom—H, 8H),
[25]
3.74 (singlet, >CH2, 4H).
C NMR (d, TMS) same solution: 153.8 (—C N), 133.4–123.5
(six signals, CAr), 44.9 (heterocyclic sp3 C-atoms).
Figure 3. Ortep Diagram
of 4c showing the labeling of the non-H
13
—
—
atoms and their displacement ellipsoids at the 50% probability level. The
plot includes a crystallization water solvent molecule
Acenaphtho [5,6-b]-2,3-dihydropyrazine (4c): 1c (420 mg;
1.73 mmol) and EDA (134 mg; 2.23 mmol) were dissolved in
MeCN (15 ml). The dark brown precipitate obtained after a few
minutes at r.t. was filtered and washed with ethanol and dried at
reduced pressure at 25 8C (78 mg, solid A). The solvent was
evaporated from the remaining solution at reduced pressure at
r.t., and CHCl3 (20 ml) was added to the resulting residue. An
off-white solid remained undissolved and was identified by its IR
spectrum as sulfamide (125 mg, 1.30 mmol). The chloroformic
solution was decolorized with activated charcoal. Evaporation of
the CHCl3 solvent produced a dark orange solid (223 mg), which
was found to be identical (TLC, IR) to solid A. Both solids,
combined and recrystallized from ethanol/water (1:3) yielded
acenaphtho [5,6-b]-2,3-dihydropyrazine (180 mg; 0.873 mmol;
44%), mp 143.0–144.0 8C. The single crystal X-ray analysis
showed that the compound crystallyzed from ethanol/water
with one hydration water molecule (Fig. 3. The corresponding CIF
file is included as a supplementary material).
Reactions of 1,2,5-thiadiazole 1,1-dioxides (1)
Reactions with o-PDA
The reactions of 1a,b with o-PDA yielded the corresponding
2,3-diaryl substituted quinoxalines 3 (experimental Section) and
sulfamide. A typical series of CV scans is shown in Fig. 4 for the
reaction of 1a with o-PDA at a molar ratio [o-PDA]/[1a] ¼ 3. The
.
.
initially observed 1a/1a ꢀ and 1a ꢀ/1a2ꢀ reversible couples (E1/2
ca ꢀ0.86 and ꢀ1.40 V, Fig. 4, solid line) were replaced at the end
of the reaction by a peak at ca ꢀ2.0 V (Fig. 4, dotted line), which
corresponds to the cathodic reduction of 3a, as it is identical to
that obtained in the CV of a solution of a synthesized sample of 3a
measured in the same experimental conditions (i.e., including the
addition of sulfamide). The CV of pure 3a is changed by the
1H NMR (d, TMS) in DMSO-d6: 8.09–7.69 (multiplet, CArom—H,
Table 1. Summary of studied reactions
6H), 3.79 (singlet, >CH2, 4H).
13
—
C NMR (d, TMS) same solution: 158.0 (C N), 141.1–119.0 (six
—
Substrate
Nucleophile
Products
signals, CAr), 45.0 (heterocyclic sp3 C-atoms).
IR (BrK, cm–1): 3450 and 3350 (H2O), 3030 (CArom—H), 2920 and
1a, b
1a, b, c
o-PDA
EDA
Quinoxalines
—
2850 (CAliph—H), 1630 (—C N), 1580 (CArom—H), 1440–1405
—
(CArom—H).
Dihydropyrazines (1a, b, c) or
pyrazines (1a, b), according to
the reaction condition used.
3,4-disubstituted thiadiazolidine
1,1-dioxide, dihydropyrazine or
pyrazine depending on the
reaction condition used.
2a
EDA
RESULTS AND DISCUSSION
A summary of the reactions studied in this work is given in
Table 1.
Copyright ß 2008 John Wiley & Sons, Ltd.
J. Phys. Org. Chem. 2009, 22 163–169