On the synthesis of pyrazino[2,3-b]phenazine and 1H-imidazo[4,5-b]phenazine derivatives

Article abstract of DOI:10.1007/PL00010183

Several pyrazino[2,3-b]pnenazine derivatives were prepared by the reaction of 2,3-diaminophenazine with different 1,2-diketones. Nucleophilic substitution of 2,3-dibromomethylpyrazino[2,3-b]phenazine with propanol, morpholine, and potassium thiocyanate gave 2,3-bis-(propoxymethyl )-pyrazino[2,3-b]phenazine, 2,3-bis-(4-morpholinylmethyl)-pyrazino[2,3-b]phenazine, and 2,3-bis-(cyanosulfanylmethyl)-pyrazino[2,3-b]phenazine, 2-Aryl-1H-imidazo[4,5-b]phenazine derivatives were synthesized by a one-pot reaction of 2,3-diaminophenazine with different aromatic aldehydes or acids. Reaction of 2,3-diaminophenazine with acetic anhydride and formic acid afforded 1H-imidazo [4,5-b]phenazine and 2-methyl-1H-imidazo[4,5-b]phenazine. Chemical and spectroscopic evidences for the product structures of the new compounds arc presented.

Full text of DOI:10.1007/PL00010183

Monatshefte fuÈr Chemie 130, 1217±1225 (1999)
On the Synthesis of Pyrazino[2,3-b]phenazine
and 1H-Imidazo[4,5-b]phenazine Derivatives
Atef M. Amer1;Ã, Adel A. El-Bahnasawi1, Mohamed R. H. Mahran2,
and Mostafa Lapib1
1
Department of Chemistry, Faculty of Science, University of Zagazig, Egypt
2
National Research Centre, Dokki-Cairo, Egypt
Summary. Several pyrazino[2,3-b]phenazine derivatives were prepared by the reaction of 2,3-
diaminophenazine with different 1,2-diketones. Nucleophilic substitution of 2,3-dibromomethyl-
pyrazino[2,3-b]phenazine with propanol, morpholine, and potassium thiocyanate gave 2,3-bis-
(propoxymethyl)-pyrazino[2,3-b]phenazine, 2,3-bis-(4-morpholinylmethyl)-pyrazino[2,3-b]phena-
zine, and 2,3-bis-(cyanosulfanylmethyl)-pyrazino[2,3-b]phenazine. 2-Aryl-1H-imidazo[4,5-b]phe-
nazine derivatives were synthesized by a one-pot reaction of 2,3-diaminophenazine with different
aromatic aldehydes or acids. Reaction of 2,3-diaminophenazine with acetic anhydride and formic
acid afforded 1H-imidazo[4,5-b]phenazine and 2-methyl-1H-imidazo[4,5-b]phenazine. Chemical
and spectroscopic evidences for the product structures of the new compounds are presented.
Keywords. Diketone; Condensation; Substitution; Phenazine; Imidazole.
Zur Synthese von Pyrazino[2,3-b]phenazin- und 1H-Imidazo[4,5-b]phenazinderivaten
Zusammenfassung. Einige Pyrazino[2,3-b]phenazinderivate wurden durch Reaktion von 2,3-
Diaminophenazin mit verschiedenen 1,2-Diketonen dargestellt. Nucleophile Substitution von 2,3-
Dibrommethyl-pyrazino[2,3-b]phenazin mit Propanol, Morpholin und Kaliumthiocyanat ergab
2,3-Bis(propoxymethyl)-pyrazino[2,3-b]phenazin, 2,3-Bis-(4-morpholinylmethyl)-pyrazino[2,3-b]phe-
nazin und 2,3-Bis-(cyanosulfanylmethyl)-pyrazino[2,3-b]phenazin. 2-Aryl-1H-imidazo[4,5-b]phe-
nazinderivate wurden in einer Eintopfreaktion aus 2,3-Diaminophenazin mit verschiedenen
È
aromatischen Aldehyden oder Carbonsauren hergestellt. Reaktion von 2,3-Diaminophenazin mit
È
È
Essigsaureanhydrid oder Ameisensaure lieferte 1H-Imidazo[4,5-b]phenazin und 2-Methyl-1H-
imidazo[4,5-b]phenazin. Chemische und spektroskopische Nachweise fuÈr die Struktruren der neuen
Verbindungen werden mitgeteilt.
Introduction
A number of phenazines have demonstrated a broad spectrum of signi®cant
biological properties [1±6], i.e. antibacterial [7], antifungicidal [8], antitumor [9],
antibiotic [10], antihypoxic, antileprosy, and anthelmintic activity [11]. They
inhibit metalloenzymes, and halosubstituted phenazines are useful as herbicides
Ã
Corresponding author

1218
A. M. Amer et al.
[12]. In recent years, semi- and photoconductivity has been reported for several aza
aromatic compounds [13±17]. In the course of a program on the synthesis of new
heterocyclic systems derived from phenazines for studying their utility as
pharmacological and photoconductive agents, we report the preparation of a
number of pyrazino[2,3-b]phenazines and imidazo[4,5-b]phenazines.
Results and Discussion
o-Diamino groups on aromatic rings have attracted considerable interest as
potential building blocks for many nitrogen containing heterocyclic systems. The
present work was focused on the synthesis of new series of fused phenazine
aystems. The condensation reaction of 2,3-diamino-phenazine (1) with appropriate
1,2-diketones (butane-2,3-dione, 1,4-dibromobutane-2,3-dione, benzil, phenanthre-
nequinone, acenaphthenequinone, and aceanthrenequinone) were carried out in the
presence of acetic acid under re¯ux to give the corresponding cyclic products 2±7
(Scheme 1). Compounds 3 could be also obtained in low yield from 2 and N-
bromosuccinimide. Similarly, the condensation of 1 with ninhydrin was carried out
in the same manner as the former reaction affording the hexacyclic compound 8.
Treatment of 1 with oxalyl chloride in boiling pyridine gave 9 (Scheme 2).
The 2,3-dibromomethyl derivative 3, however, was very unstable in the
presence of base or nucleophile. Addition of pyridine to 3 immediately gave a red
solution which turned dark brown within minutes. We ascribe the base sensitivity
Scheme 1

Synthesis of Condensed Phenazine Derivatives
1219
Scheme 2
of 3 to its benzylic methylene hydrogens which are activated by the electron
withdrawing effects of the pyrazine ring. Thus, the introduction of alkoxide side
chains into 3 was achieved by prolonged re¯uxing in the corresponding alcohol.
Among several alcohols tested, 1-propanol gave the cleanest product. Several by-
products were removed by chromatography, and 10 was obtained in moderate
yield. Continuing our efforts to substitute bromine in 3, it was found that 3 easily
reacted with morpholine and pyridine to give the dimorpholino compound 11. The
reaction of 3 with potassium thiocyanate afforded the corresponding cyanosulfa-
nylmethyl derivative 12 (Scheme 3).
Scheme 3
Several benzimidazol derivatives exhibit remarkable bioactivity and are
contained in commercially available pharmaceuticals [18, 19], e.g. benzimidazoles
in anti-tumor agents [20], whereas others show activity against fungi [21]. Thus it
was of interest to explore the scope of the above reactions by synthesizing the 1H-
imidazo[4,5-b]phenazine derivatives 14a±f from 1. It was found that these
compounds could be afforded by condensation of 1 with differently substituted
aromatic aldehydes (benzaldehyde, 4-chlorobenzaldehyde, 4-nitrobenzaldehyde, 4-
methoxybenzaldehyde, 4-ethyl benzaldehyde, and 5-isopropyl benzaldehyde) in
nitrobenzene or dimethylformamide at re¯ux (Scheme 4).
This reaction proceeds via the initial formation of the corresponding Schiff
bases 13a±f which then undergo an oxidative cyclization step. The reaction

1220
A. M. Amer et al.
Scheme 4
conditions employed here are similar to those reported for the preparation of
related 2-arylbenzimidazoles [22]: the solvent acts also as an oxidant. Our efforts
to isolate the intermediate Schiff bases 13a±f were unsuccessful under a variety
of conditions. On the other hand, treatment of 1 with aromatic acids (4-
methoxybenzoic acid, 4-ethyl benzoic acid, and 4-isopropyl benzoic acid) in the
presence of POCl3 under re¯ux [23, 24] afforded the 2-aryl-1H-imidazo[4,5-
b]phenazines 14d±f (Scheme 4). Treatment of 2,3-diaminophenazine with two mol
of 3,4,5-trimethoxy benzoic acid in POCl3 under re¯ux gave 15. Also, 1 underwent
cyclization in formic acid and/or acetic anhydride at re¯ux temperature to yield
1H-imidazo[4,5-b]phenazines 16 and 17. The structure of all newly synthesized
compounds was con®rmed by their elemental and spectroscopic data.
Experimental
Melting points were measured on a Ko¯er hot stage microscope (Reichert, Vienna) and are
uncorrected. 1H and 13C NMR spectra were recorded on a Bruker DPX 200 spectrometer at 200 MHz
(1H) and 50 MHz (13C); chemical shifts are given in ꢀ relative to internal TMS at 295 K. IR spectra
are obtained on a Biorad FT-IR-45 instrument. All experiments were carried out with exclusion of
moisture. For all newly synthesized compounds satisfactory elemental analyses were obtained.
Pyrazino[2,3-b]phenazine derivatives 2±7; general procedure
A mixture of 1 mmol of 1,2-diketone and 0.21 g 1 (1 mmol) in 20 cm3 acetic acid was heated under
re¯ux for 5 h. The solid product obtained was ®ltered off and recrystallized from the given solvent to
yield the corresponding condensed products 2±7.

Synthesis of Condensed Phenazine Derivatives
1221
2,3-Dimethyl-pyrazino[2,3-b]phenazine (2; C16H12N4)
Prepared from butane-2,3-dione and 1; crystallization from DMF gave ®ne brown crystals (68%);
m.p.: >350ꢀC; IR (KBr): 3095, 1620, 1610±1480, 1450 cmꢁ1; 1H NMR (CDCl3): ꢀ ˆ 2.85 (s, 2CH3),
7.88 (m, 2Har), 8.10 (m, 2Har), 9.02 (s, 2Har) ppm.
2,3-Dibromomethyl-pyrazino[2,3-b]phenazine (3; C16H10Br2N2)
Prepared from 1,4-dibromobutane-2,3-dione and 1; crystallization from CHCl3 gave faint red
1
crystals (52%); m.p.: 225ꢀC; IR (KBr): 3098, 2923, 1622, 1612, 1480 cmꢁ1; H NMR (CDCl3):
ꢀ ˆ 5.03 (s, 2CH2), 7.90 (m, 2Har), 8.30 (m, 2Har), 9.15 (s, 2Har) ppm.
2,3-Diphenyl-pyrazino[2,3-b]phenazine (4; C26H16N4)
Prepared from benzil and 1; crystallization from DMF/H2O gave ®ne brown crystals (77%); m.p.:
220ꢀC; IR (KBr): 3108, 1620, 1610, 1580, 1522, 1482 cmꢁ1; 1H NMR (CDCl3): 7.41 (m, 6Har), 7.63
(m, 4Har), 7.91 (m, 2Har), 8.27 (m, 2Har), 9.23 (s. 2Har) ppm.
Phenanthraceno[10,20: 5,6]pyrazino[2,3-b]phenazine (5; C26H14N4)
Prepared from phenanthrenequinone and 1; crystallization from ethanol gave pink crystals (65%);
1
m.p.: 245ꢀC; IR (KBr): 3110, 1625, 1615, 1568, 1520, 1480 cmꢁ1; H NMR (CDCl3/DMSO-d6):
ꢀ ˆ 7.50 (m, 3Har), 7.62±7.84 (m, 3Har), 8.27 (m, 5Har), 8.55 (m, 3Har) ppm.
Acenaphtho[10,20:5,6]pyrazino[2,3-b]phenazine (6; C24H12N4)
Prepared from acenaphthenequinone (1 mmol) and 1; crystallization from ethanol gave pink crystals
(80%); m.p.: >350ꢀC; IR (KBr): 3103, 3046, 1630, 1620, 1599, 1585, 1480 cmꢁ1; 1H NMR (CDCl3/
DMSO-d6): ꢀ ˆ 7.88 (m, 4Har), 8.16 (m, 4Har), 8.42 (d, 2Har), 9.08 (s, 2Har) ppm.
Aceanthraceno[10,20: 5,6]pyrazino[2,3-b]phenazine (7; C28H14N4)
Prepared from aceanthrenequinone and 1; crystallization from DMF gave brown crystals (71%);
m.p.: >350ꢀC; IR (KBr): 3110, 3040, 1630, 1622, 1580, 1518, 1480 cmꢁ1; 1H NMR (CDCl3/DMSO-
d6): ꢀ ˆ 7.65 (m, 2Har), 7.81 (m, 3Har), 8.16 (m, 4Har), 8.45 (d, 1Har), 8.75 (s, 1Har), 9.08 (s, 2Har),
9.53 (d, 1Har) ppm.
Reaction of 2 with N-bromo succinimide: Formation 2,3-Dibromomethyl-pyrazino[2,3-b]phenazine
(3; C16H10Br2N2)
A suspension of 0.26 g 2 (1 mmol), 0.45 g N-bromo succinimide (2.5 mmol), and 0.1 g benzene
peroxide in 50 cm3 dry benzene was re¯uxed with stirring for 24 h. Then, 50 cm3 ether were added;
the organic phase was washed with 50 cm3 NaHCO3 conc. and water (three times) and dried over
anhydrous Na2SO4. After evaporation of the solvent the remaining crude product of dark red colour
was recrystallized twice from acetone and CHCl3 to yield 23% 3.
Indeno[1,2-b]pyrazino[5,6-b]phenazine (8; C21H10N4O)
A mixture of 0.21 g 1 (1 mmol), 0.18 g ninhydrin (1 mmol), 50 cm3 ethanol, and 3 drops of acetic
acid was re¯uxed for 3 h. After cooling, the formed solid was collected by suction and recrystallized
from dimethyl formamide as reddish brown crystals (43%).

1222
A. M. Amer et al.
1
M.p.: 355ꢀC; IR (KBr): 3110, 1680, 1622, 1618, 1567, 1518, 1489 cmꢁ1; H NMR (CDCl3):
ꢀ ˆ 7.77±7.95 (m, 4Har), 8.07±8.30 (m, 4Har), 9.13 (s, 1Har), 9.33 (s, 1Har) ppm.
2,3-Dihydroxy-pyrazino[2,3-b]phenazine (9; C14H8N4O2)
A mixture of 0.21 g 1 (1 mmol), 0.21 g oxalyl chloride (1.8 mmol), and 50 cm3 pyridine was re¯uxed
with stirring for 5 h. After cooling, the reaction mixture was poured into 35 cm3 H2O and 5 cm3 30%
HCl. The precipitated product was ®ltered, dried, and crystallized from ethanol to give dark red
crystals of 9 (38%).
M.p.: > 450ꢀC; IR (KBr): 3480 br, 1657, 1631, 1625, 1589, 1518, 1485 cmꢁ1; 1H NMR (DMSO-
d6) ꢀ ˆ 7.03 (s, 2Har), 7.74 (m, 2Har), 7.78 (br, 2H, 2NH), 8.02 (m, 2Har) ppm.
2,3-Bis-(propoxymethyl)-pyrazino[2,3-b]phenazine (10; C22H24N4O2)
A solution of 0.39 g 3 (1 mmol) in 20 cm3 1-propanol was heated under re¯ux for 25 h. The solvent
was removed under reduced pressure. The blue solid was chromatographed on silica with CH2Cl2 to
give a blue powder (55%).
1
M.p.: 140ꢀC; IR (KBr): 3110, 3046, 2930, 1632, 1618, 1585, 1488 cmꢁ1; H NMR (CDCl3):
ꢀ ˆ 0.95 (t, 2CH3), 1.66 (m, 2CH2), 3.47±3.88 (m, 4OCH2), 7.87 (m, 2Har), 8.28 (m, 2Har), 9.10 (d,
2Har) ppm.
2,3-Bis-(4-morphoinylmethyl)-pyrazino[2,3-b]phenazine (11; C26H30N6)
A mixture of 0.39 g 3 (1 mmol), 0.19 g morpholine (2.2 mmol), 0.17 g pyridine (2.2 mmol), and
20 cm3 acetone was stirred at room temperature for 30 min, ®ltered, and the ®lterate was evaporated
at 40ꢀC. Water was added to the dark residue, and undissolved material was ®ltered off. The green
solid was chromatographed on silica with CHCl3/MeOH (9:1) to give a green powder (32%).
M.p.: 87±89ꢀC; IR (KBr): 3103, 3046, 2986, 2915, 1632, 1615, 1580, 1520, 1486 cmꢁ1; 1H NMR
(CDCl3): ꢀ ˆ 2.50±2.63 (m, 8H, 2CH2-N-CH2), 3.72 (m, 8H, 2CH2-N-CH2), 4.09±4.24 (m, 2CH2),
7.78 (m, 2Har), 8.16 (m, 2Har), 8.45 (s, 2Har) ppm.
2,3-Bis-(cyanosulfanylmethyl)-pyrazino[2,3-b]phenazine (12; C18H10N6O2)
A solution of 0.20 g KSCN (2 mmol) in 5 cm3 acetone was added dropwise to a stirred solution of
0.39 g 3 (1 mmol) in 10 cm3 DMF at room temperature. The suspension was stirred for 30 min, the
solvent was evaporated, and 15 ml H2O were added to the solid residue. Water insoluble material was
®ltered off and washed with H2O to yield crude 12; recrystallization from DMF/H2O this gave
reddish crystals (72%).
M.p.: 233ꢀC; IR (KBr): 3100, 3025, 2985, 2160, 1632, 1618, 1580, 1488 cmꢁ1 1H NMR
;
(CDCl3): ꢀ ˆ 4.90 (s, 2CH2), 7.79 (m, 2Har), 8.25 (m, 2Har). 9.15 (s, 2Har) ppm.
Reaction of 2,3-diaminophenazine with aromatic aldehydes: Formation
of 2-aryl-1H-imidazo[4,5-b]phenazine derivatives 14a±f (general procedure)
To a stirred solution of 0.21 g 1 (1 mmol) in 10 cm3 nitrobenzene or DMF 1 mmol of the appropriate
arylaldehyde was added dropwise at room temperature. Stirring was continued for additional 30 min.
The reaction mixture was re¯uxed for 8 h and allowed to stand overnight at room temperature. The
resulting precipitate was collected, washed with ether, and recrystallized from the appropriate
solvent to yield 14a±f.

Synthesis of Condensed Phenazine Derivatives
1223
2-Phenyl-1H-imidazo[4,5-b]phenazine (14a; C19H12N4)
Prepared from 1 and benzaldehyde; crystallization from DMF gave dark red crystals (73%); m.p.:
358±360ꢀC as observed in Ref. [25]; IR (KBr): 3465 br, 3110, 3046, 1628, 1610, 1585, 1522,
1
1480 cmꢁ1; H NMR (DMSO-d6): ꢀ ˆ 6.92 (d, 2Har), 7.56±8.32 (m, 9Har), 13.40 (br, NH) ppm.
2-(4-Chlorophenyl)-1H-imidazo[4,5-b]phenazine (14b; C19H12ClN4)
Prepared from 1 and 4-chloro-benzaldehyde; crystallization from DMF/H2O gave dark brown
crystals (65%); m.p.: >360ꢀC; IR (KBr): 3469 br, 3110, 3046, 1627, 1618, 1585, 1485 cmꢁ1
;
1H NMR (DMSO-d6): ꢀ ˆ 6.92 (d, 2Har), 7.57 (m, 3Har), 7.89 (m, 3Har), 8.29 (d, 2Har), 13.40
(br, NH) ppm.
2-(4-Nitrophenyl)-1H-imidazo[4,5-b]phenazine (14c; C19H11N5O2)
Prepared from 1 and 4-nitro-benzaldehyde; crystallization from DMF/H2O gave dark brown crystals
1
(70%); m.p.: >360ꢀC; IR (KBr): 3460, 3100, 3046, 1630, 1610, 1585, 1522, 1486 cmꢁ1; H NMR
(DMSO-d6): ꢀ ˆ 6.92 (d, 2Har), 7.58±8.55 (m, 8Har), 13.60 (br, NH) ppm.
2-(4-Methoxyphenyl)-1H-imidazo[4,5-b]phenazine (14d; C20H14N4O)
Prepared from 1 and 4-methoxy-benzaldehyde; crystallization from ethanol gave red crystals (82%);
1
m.p.: 360ꢀC; IR (KBr): 3465, 3100, 3046, 2986, 1628, 1618, 1585, 1480 cmꢁ1; H NMR (CDCl3):
ꢀ ˆ 3.50 (s, OCH3), 7.76 (d, 1Har), 7.93 (m, 3Har), 8.07 (d, 1Har), 8.29 (m, 3Har), 9.13 (s, 1Har), 9.33
1
(s, 1Har) ppm; H NMR (DMSO-d6): ꢀ ˆ 3.91 (s, OCH3), 7.10 (d, 2Har), 7.90 (m, 2Har), 8.25 (m,
3Har), 8.40±8.48 (m, 3Har), 13.30 (br, NH) ppm; 13C NMR (DMSO-d6/D2O) ꢀ ˆ 65.00 (OCH3),
124.50, 130.00, 135.80, 138.00, 138.95, 139.48, 151.50, 153.20, 171.50, 172.79 (aryl) ppm.
2-(4-Ethylphenyl)-1H-imidazo[4,5-b]phenazine (14e; C21H16N4)
Prepared from 1 and 4-ethyl-benzaldehyde; crystallization from DMF gave reddish brown crystals
(60%); m.p.: >360ꢀC; IR (KBr): 3460, 3100, 3046, 2986, 2918, 1630, 1585, 1522, 1480, 1378 cmꢁ1
;
1H NMR (DMSO-d6): ꢀ ˆ 1.18 (t, 3H, CH3), 2.70 (q, 2H, CH2), 7.19 (d, 2Har), 7.84 (m, 3Har), 8.19
(m, 2Har), 8.27±8.37 (m, 3Har) ppm.
2-(4-Isopropylphenyl)-1H-imidazo[4,5-b]phenazine (14f; C23H20N4)
Prepared from 1 and 4-isopropyl-benzaldehyde; crystallization from DMF gave ®ne brown crystals
(78%); m.p.: >360ꢀC; IR (KBr): 3460 br, 3100, 3046, 2986, 1632, 1618, 1585, 1522, 1485 cmꢁ1
;
1H NMR (DMSO-d6): ꢀ ˆ 1.49 (s, 2CH3), 2.90 (m, 1H, CH-), 7.45 (m, 5Har), 7.77 (m, 5Har) ppm.
Reaction of 1 with aromatic acids: Formation of 2-aryl-1H-imidazo[4,5-b]phenazine
derivatives 14d-f (general procedure)
A ®nely powdered mixture of 0.21 g 1 (1 mmol) and 1 mmol of the appropriate aromatic acid was
added in portions to 20 cm3 POCl3 under stirring. This mixture was heated at re¯ux for 4 h; after
cooling, the excess of POCl3 was removed in vacuo. 100 cm3 ice/H2O was added to the residue,
followed by aqu. NH3 until pH 11. The mixture was extracted with CHCl3, and the combined
extracts were dried and evaporated to dryness. The crude product was recrystallized from DMF to
give 14d±f (20±25%).

1224
A. M. Amer et al.
2,3-Bis-(3,4,5-trimethoxybenzamido)-phenazine (15; C32H30N4O8)
A ®nely powdered mixture of 0.21 g 1 (1 mmol) and 0.42 g, 3,4,5-trimethoxybenzoic acid (2 mmol)
was added in portions to 40 cm3 POCl3 with stirring. This mixture was heated at re¯ux for 6 h and the
excess of POCl3 was removed in vacuo. 100 ml ice/H2O was added to the residue followed by aqu.
NH3 until pH 8. The precipitated product was ®ltered, dried, and crystallized from ethanol to give 15
(48%).
M.p.: 155ꢀC; IR (KBr): 3350, 3078, 2974, 1686, 1628, 1558, 1507, 1490, 1458, 1433,
1389 cmꢁ1; 1H NMR (CDCl3): ꢀ ˆ 3.88 (s, 4OCH3), 3.95 (s, 2OCH3), 7.21 (s, 4Har), 7.75 (m, 2Har),
8.07 (m, 2Har), 8.42 (s, 2Har), 9.45 (br, 2NH) ppm. 13C NMR (CDCl3): ꢀ ˆ 65.71 (4OCH3), 70.55
(2OCH3), 114.45, 137.49, 138.99, 140.00, 140.13, 143.97, 150.72, 152.83, 162.78 (aryl), 176.19
(2C=O) ppm.
1H-Imidazo[4,5-b]phenazine (16; C13H8N4)
A suspension of 0.21 g 1 (1 mmol) in 20 cm3 HCOOH was re¯uxed for 10 h in the presence of 0.50 g
CH3COONa. The greyish crystalline material which separated upon cooling was washed with 25 cm3
H2O, dried under reduced pressure, and recrystallized from DMF/H2O to give greyish ®ne crystals
(62%).
M.p.: 303ꢀC; IR (KBr): 3350, 3078, 1632, 1620, 1558, 1507, 1483 cmꢁ1; 1H NMR (DMSO-d6):
ꢀ ˆ 7.87 (m, 2Har), 8.22 (m, 2Har), 8.38 (m, 2Har), 8.50 (s, 1Har) ppm.
2-Methyl-1H-imidazo[4,5-b]phenazine (17; C14H10N4)
A suspension of 0.21 g 1 (1 mmol) in 12 cm3 acetic anhydride was heated at re¯ux for 30 min to give
a dark yellow solution. After cooling in ice, the product was ®ltered off and recrystallized from
acetic acid to give yellow crystals (78%).
M.p.: 320ꢀC; IR (KBr): 3365, 3077, 2972, 1630, 1615, 1560, 1531, 1485, 1450, 1390 cmꢁ1
;
1H NMR (DMSO-d6): ꢀ ˆ 2.66 (s, CH3), 7.86 (m, 2Har), 8.20±8.33 (m, 4Har), 12.80 (br, NH) ppm.
Acknowledgements
È
È
A. M. A. thanks his colleagues at the Institut fur Chemie, Johannes Kepler Universitat Linz, for their
kind assistance during a fellowship sponsored by the Austrian Academic Exchange Service, Vienna,
Austria.
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Synthesis of Condensed Phenazine Derivatives
1225
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Received December 29, 1998. Accepted February 2, 1999