Facile synthesis of 6-aryl-1,3-dimethyl-5H-pyrimido-[4,5-b][1,4]diazepine-2,4(1H,3H)-diones

Article abstract of DOI:10.1135/cccc19990313

A facile procedure for the preparation of 6-aryl-1,3-dimethyl-5H-pyrimido[4,5-b][1,4]diazepine-2,4(1H,3H)-diones 8, 9 from 6-amino-5-arylideneamino-1,3-dimethyluracils 1, 2 and triethyl orthoacetate (3) in a two-step reaction via 6-aryl-8-ethoxy-6,7-dihydro-1,3-dimethyl-5H-pyrimido[4,5-b][1,4]diazepine-2,4(1H ,3H)-diones 6, 7 is described. Condensation of 1 with diethoxymethyl acetate (10) resulted in the formation of (1,3-dimethyl-2,6-(1H,3H)-dioxopurin-7-yl)(phenyl)methyl acetate (11) and a small amount of 1,3-dimethyl-6-phenyl-pyrazino[2,3-d]pyrimidine-2,4(1H,3H)-dione (12). The structures of 6 and 11 were unambiguously confirmed by single-crystal X-ray diffraction analysis.

Full text of DOI:10.1135/cccc19990313

Facile Synthesis
313
FACILE SYNTHESIS OF 6-ARYL-1,3-DIMETHYL-5H-PYRIMIDO-
[4,5-b][1,4]DIAZEPINE-2,4(1H,3H)-DIONES
1
Shahriyar TAGHAVI-MOGHADAM, Rüdiger STUMPF, Helmut FISCHER
and Wolfgang PFLEIDERER *
2,
Faculty of Chemistry, University of Constance, P.O. Box 5560, D-78434 Constance, Germany;
1
2
e-mail: hfischer@dgG.chemie.uni-konstanz.de, wolfgang.pfleiderer@uni-konstanz.de
Received Septem ber 4, 1998
Accepted Decem ber 12, 1998
In the memory of Dr Miroslav Protiva and in admiration of his contributions to heterocyclic
chemistry.
A facile procedure for th e preparation of 6-aryl-1,3-dim eth yl-5H-pyrim ido[4,5-b][1,4]diazepin e-
2,4(1H,3H)-dion es 8, 9 from 6-am in o-5-aryliden eam in o-1,3-dim eth yluracils 1, 2 an d trieth yl
orth oacetate (3) in
a two-step reaction via 6-aryl-8-eth oxy-6,7-dih ydro-1,3-dim eth yl-
5H-pyrim ido[4,5-b][1,4]diazepin e-2,4(1H,3H)-dion es 6, 7 is described. Con den sation of 1
with dieth oxym eth yl acetate (10) resulted in th e form ation of (1,3-dim eth yl-2,6-(1H,3H)-
dioxopurin -7-yl)(ph en yl)m eth yl acetate (11) an d a sm all am oun t of 1,3-dim eth yl-6-ph en yl-
pyrazin o[2,3-d]pyrim idin e-2,4(1H,3H)-dion e (12). Th e structures of 6 an d 11 were un am big-
uously con firm ed by sin gle-crystal X-ray diffraction an alysis.
Key w ord s: Orth oester con den sation ; Crystal structure; Purin es; Pyrim idin es; Pteridin es;
Pyrim ido[4,5-b][1,4]diazepin es.
Th e pyrim ido[4,5-b][1,4]diazepin e rin g system occurs rarely in n ature an d
h as n ot been studied very exten sively so far. Two types of th is n atural
h eterocyclic system h ave been discovered, both in Drosophila melanogaster.
Th ese studies sh ow th at th e 6-acetyl-2-am in o-7,8-dih ydro-9H-pyrim ido-
[4,5-b][1,4]diazepin -4(3H)-on e (6-acetyldih ydroh om opterin )1–4 fun ction s as
a biogen etic precursor of th e m ore com plex pen tacyclic red eye pigm en ts
kn own as drosopterin 5, aurodrosopterin 6 an d n eodrosopterin 7. Th e first
syn th esis of a pyrim ido[4,5-b][1,4]diazepin e based on con den sation of a
4,5-diam in opyrim idin e with eth yl acetoacetate was reported by Ch en g et
al.8 in 1965. A ph otoch em ical approach usin g 6-azido-1,3-dim eth yl uracil
was developed by Sen da9, but th e classical syn th etic route in volves con den -
sation s of 4,5-diam in opyrim idin es with 1,3-dicarbon yl com poun ds10 an alo-
gous to th e Gabriel–Isay pteridin e syn th esis11. Problem s regardin g th e
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314
Taghavi-Moghadam et al.:
regioselectivity arise in con den sation s with un sym m etrical 1,3-dicarbon yl
derivatives leadin g com m on ly to 6- an d 8-substituted isom eric m ixtures.
Un am biguous approach es were dem on strated by Aylin g et al.12 as well as by
Boyle4 applyin g a Polon ovski–Boon 11 type m eth od.
In th is paper, we would like to report a n ew approach to th e regio-
selective syn th esis of 6-aryl-1,3-dim eth ylpyrim ido[4,5-b][1,4]diazepin e-
2,4(1H,3H)-diones starting from simply accessible 6-amino-5-benzylidene-
am in opyrim idin es.
Durin g our studies of n ew variation s in th e pteridin e syn th esis13, we in -
vestigated th e possibility of con den sin g a on e-carbon un it with
a
6-am in o-5-aryliden eam in opyrim idin e to form th e correspon din g 6-aryl-
pteridin e derivative in a regioselective m an n er. Th is con den sation , term ed
accordin g to early fin din gs in Japan 15 th e Yon eda reaction 14, works espe-
cially well in th e 6-am in o-5-aryliden eam in o-1,3-dim eth yluracil series with
orth oesters an d am ide acetals, to give 6-aryl-1,3-dim eth ylpyrazin o-
[2,3-d]pyrim idin e-2,4(1H,3H)-dion es. An an alogous con den sation between
6-am ino-5-aryliden eam in o-1,3-dim eth yluracils (1) an d trieth yl orth oacetate
(2) described by Yon eda an d Higuch i15 proceeds in a sim ilar m an n er. Th e
first isolated reaction product was assign ed an open -ch ain 6-(1-eth oxy-
eth yliden eam in o)uracil structure 4 due to th e fact th at th e th erm al
cyclizations allegedly resulted in the form ation of 6-aryl-1,3,7-trim ethyl-
pyrazin o[2,3-d]pyrim idin e-2,4(1H,3H)-dion es. Un fortun ately, on ly m eltin g
poin ts an d elem en tal an alyses were reported wh ereas com m on an alytical
1
tools such as H NMR an d UV spectra clearly in dicated th at th e con stitu-
tion s of th e proposed in term ediates 4 an d th e en d products h ave to be re-
vised. Th eir spectroscopic properties are con sisten t with th e isom eric
8-eth oxy-6,7-d ih yd ro-1,3-d im eth yl-6-p h en yl-5H-p yrim id o[4,5-b][1 ,4 ]-
diazepin e-2,4(1H,3H)-dion e (6) structure, wh ich can be explain ed by th e pri-
m ary form ation of 5-arylm eth ylen am in o-6-(1-eth oxyeth yliden eam in o)uracil
(4), followed by tautom erization to th e en am in e form 5 an d subsequen t
cyclization to pyrim ido[4,5-b][1,4]diazepin es 6, 7 by en am in e addition
across th e n eigh bourin g im in e double bon d at position 5. Furth erm ore, sin -
gle crystal X-ray diffraction an alysis of com poun d 6 un am biguously con -
firm ed th e proposed n ew structure (Fig. 1, Sch em e 1).
Heatin g of th e pyrim ido[4,5-b][1,4]diazepin es 6, 7 to 220 °C for 1 h led to
elim in ation of EtOH an d form ation of stable h eteroarom atic
6-aryl-1,3-dim eth yl-5H-pyrim ido[4,5-b][1,4]diazepin es 8, 9. Th e structural
1
assign m en t of th ese com poun ds was based on NMR eviden ce. Th e H NMR
spectra of 8 an d 9 in DMSO-d6 sh owed th e presen ce of on e NH as a sin glet
sign al at 13.50–13.70 ppm wh ich was proved by a deuterium exch an ge ex-
Collect. Czech. Chem. Commun. (Vol. 64) (1999)

Facile Synthesis
315
perim en t. Th is clearly in dicates th at com poun ds 8 an d 9 exist in solution
in th e 5H an d n ot th e 9H tautom eric form an d also excludes th e
6-m eth ylen e tautom ers as stated by Fukush im a et al.16 for 6,8-disubstituted
pyrim ido[4,5-b][1,4]diazepin es.
A straigh forward assign m en t of th e
pyrim ido[4,5-b][1,4]diazepin es structure could be ach ieved by 2D HMQC
NMR spectra from wh ich th e h eteron uclear couplin g of C–H n uclei in th e
diazepin e rin g can be depicted un am biguously (Fig. 2).
O
O
O
Me
Me
Me
N
CH
R
N
CH
R
N
N
CH
R
N
N
N
H C-C(OEt)
3
3
O
N
N
H
C
CH
O
N
NH
O
N
Me
4
C
CH
2
2
3
3
Me
OEt
Me
OEt
5
R
Ph
4-MeOPh
1
2
H
H
N
O
O
R
R
N
Me
Me
N
N
o
220
C
O
N
O
N
N
N
OEt
Me
Me
R
R
Ph
4-MeOPh
Ph
4-MeOPh
8
6
9
7
SCHEME 1
Addition ally, we h ave also been in terested in th e reaction of
6-am in o-5-ben zyliden eam in o-1,3-dim eth yluracil (1) with dieth oxym eth yl
acetate (10) as a m ore reactive reagen t for th e preparation of lum azin e de-
rivatives un der m ild reaction con dition s. Dieth oxym eth yl acetate (10) was
C64
C65
C63
C66
C62
C61
N4
C11
N1
C1
C6
C5
O2
C4
FIG. 1
C3
C2
O4
N2
ORTEP representation of 8-ethoxy-6,7-dihydro-
1,3-dim ethyl-6-phenyl-5H-pyrim ido[4,5-b][1,4]-
diazepin e-2,4(1H,3H)-dion e (6)
N3
C41
C21
C42
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316
Taghavi-Moghadam et al.:
already used by Mon tgom ery an d Tem ple13,14 for th e cyclization of
4,5-diam in opyrim idin es to purin es. Reaction of 6-am in o-5-ben zyliden e-
am in o-1,3-dim eth yluracil (1) with dieth oxym eth yl acetate (10) afforded a
m ixture givin g (1,3-dim eth yl-2,6(1H,3H)-dioxopurin -7-yl)(ph en yl)m eth yl
acetate (11) in 71% yield an d 1,3-dim eth yl-6-ph en ylpyrazin o[2,3-d]pyrim i-
din e-2,4(1H,3H)-dion e (12) as a by-product in 5% yield. Com poun d 11
could also be obtain ed in 73% isolated yield on treatm en t of 1 with an ex-
cess of a m ixture of trieth yl orth oform ate an d acetic an h ydride (Sch em e 2).
O
Me
N
CH Ph
N
O
N
NH
2
1
Me
AcOCH(OEt)
10
2
AcO
O
Ph
O
O
H
N
Me
Me
Me
N
Ph
N
N
N
N
+
N
N
O
N
O
N
O
N
N
Me
Me
Me
13
11
12
SCHEME 2
110
7
ppm
120
6b
6c
6d
ppm
130
140
8
FIG. 2
2D HMQC
NMR
spectrum
150
((DMSO-d6) of 1,3-dim eth yl-6-
ph en yl-5H-p yrim ido[4,5-b][1,4]-
diazepin e-2,4(1H,3H)-dion e (8)
8.0
7.5
7.0
6.5
ppm
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Facile Synthesis
317
Th e structure of th eoph yllin e derivative 11 was con firm ed by usual spec-
troscopic m eth ods (1H NMR, UV an d MS) an d elem en tal an alysis. Basic an d
acid h ydrolysis of 11 at room tem perature afforded th eoph yllin e (13) due
to th e sen sitive acylated h em iacetal structure of th e 7-substituen t. Addi-
tion ally, th e structure of com poun d 11 was again con firm ed by a sin gle-
crystal X-ray diffraction an alysis (Fig. 3).
Crystallograph ic data of com poun ds 6 an d 11 are sum m arized in Table I.
EXPERIMENTAL
Meltin g poin ts were m easured on a Gallen kam p apparatus an d are un corrected. UV/VIS
spectra were recorded on a Perkin –Elm er Lam bda 5 spectrom eter, λm ax in n m (log ε).
1H NMR spectra were m easured on Brucker AC 250 an d DRX 600 in strum en ts usin g TMS or
residual CHCl3 an d DMSO as in tern al stan dards. Ch em ical sh ifts are given in ppm (δ-scale)
an d couplin g con stan ts (J) in Hz. Flash ch rom atograph y (FC) was perform ed on silica gel
(Baker, 30–60 µm ) an d TLC on precoated silica gel TLC sh eets (Sch leich er an d Sch üll,
FS 1500 254).
8-Eth oxy-6,7-dih ydro-1,3-dim eth yl-6-ph en yl-5H-pyrim ido[4,5- b][1,4]diazepin e-
2,4(1H,3H)-dion e (6)
To a solution of 6-am in o-5-ben zyliden eam in o-1,3-dim eth yluracil19 (1; 1.3 g, 5.0 m m ol) in
dry DMF (10 m l), triethyl orthoacetate (2; 8.10 g, 50 m m ol) was added an d th e m ixture was
refluxed for 8 h . Th e solven t was evaporated un der reduced pressure an d th e residue crystal-
lized from EtOH (5 m l). Th e ligh t-yellow precipitate was collected, wash ed with Et2O, an d
dried to give 1.0 g (60%) of ch rom atograph ically pure m aterial, m .p. 187–189 °C (eth an ol). For
C17H20N4O3 (328.4) calculated: 62.18% C, 6.14% H, 17.06% N; foun d: 62.18% C, 6.29% H,
17.27% N. UV (MeOH): 222 (4.29), 345 (3.88). 1H NMR (CDCl3): 7.34 m , 5 H (arom . H);
5.13 m , 1 H (H-6); 4.30 q, 2 H, J = 7.2 (CH3CH2O); 4.21 s, 1 H (NH); 3.45 s, 3 H, (Me–N(1));
3.44 s, 3 H (Me–N(3)); 2.78 m , 1 H, (H-7); 2.62 m , 1 H, (H-7); 1.34 t, 3 H, J = 7.2 (CH3CH2O).
O12
C13
C12
C17
C18
O51
C5
C11
C14
C10
C15
O11
C6
C16
C41
N1
C1
N2
N4
C4
FIG. 3
C3
ORTEP represen tation of (1,3-dim eth yl-
2,6(1H,3H)-dioxopurin -7-yl)(ph en yl)m eth yl
acetate (11)
N3
O41
C31
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Taghavi-Moghadam et al.:
8-Eth oxy-6,7-dih ydro-6-(4-m eth oxyph en yl)-1,3-dim eth yl-5H-pyrim ido[4,5-b][1,4]-
diazepin e-2,4(1H,3H)-dion e (7)
To a solution of 6-am in o-5-(4-m eth oxyben zyliden eam in o-1,3-dim eth yluracil19 (2; 1.4 g,
4.86 m m ol) in dry DMF (10 m l), trieth yl orth oacetate (3; 8.10 g, 50 m m ol) was added
an d th e m ixture was refluxed for 8 h . Th e m ixture was evaporated to dryn ess in h igh vacuum
an d th e residu e was treated with Et2O (15 m l) to form crystals. Th e yellowish p owder
was collected, wash ed with Et2O, an d dried to give 1.37 g (83%) of ch rom atograph ically
pure m aterial. A part of of th e crude product (1.0 g ) was recrystallized from eth an ol (40 m l)
to give 0.82 g of yellowish crystals, m .p. 152–156 °C. For C18H22N4O4 (358.4) calculated:
60.32% C, 6.19% H, 15.63% N; foun d: 60.58% C, 6.03% H, 15.87% N. UV (MeOH): 221
(4.35), 346 (3.97). 1H NMR (CDCl3): 7.27 d, 2 H (H-3′, H-5′); 6.87 d, 2 H (H-2′,H-6′); 5.05 m ,
1 H (H-6); 4.30 q, 2 H, J = 7.1 (CH3CH2O); 4.15 s, 1 H (NH); 3.80 s, 3 H (MeO); 3.45 s, 3 H
(Me–N(1)); 3.43 s, 3 H (Me–N(3)); 2.78 m , 1 H (H-7); 2.62 m , 1 H (H-7); 1.34 t, 3 H, J = 7.1
(CH3CH2O).
1,3-Dim eth yl-6-ph en yl-5H-pyrim ido[4,5-b][1,4]diazepin e-2,4(1H,3H)-dion e (8)
Com poun d 6 (100 m g, 0.30 m m ol) was h eated in an oil bath to 220 °C for 2 h . Th e origi-
n ally yellowish m elt was slowly con verted in to a yellow-brown ish solid. Th e residue was
TABLE I
Crystal data of com poun ds 6 an d 11
6
11
Em pirical form ula
Color; h abit
C17H20N4O3
C16H16N4O4
colorless n eedles
0.5 × 0.5 × 0.5
m on oclin ic
P21/n
colorless n eedles
0.3 × 0.3 × 0.3
orth orh om bic
Pbca
Crystal size, m m
Crystal system
Space group
Un it cell dim en sion s
a = 31.495(6) Å
b = 12.912(3) Å
c = 7.8150(10) Å
a = 12.012(4) Å
b = 8.257(3) Å
c = 16.525(4) Å
β = 110.11(2)°
1 539.1(9) Å3
4
Volum e
3 177.9(10) Å3
8
Z
Form ula weigh t
Den sity (calculated)
Absorption coefficien t
F(000)
328.21
328.33
1.373 g cm –3
0.090 m m –1
1 392
1.417 g cm –3
0.098 m m –1
688
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Facile Synthesis
319
recrystallized from a m ixture of DMF (4 m l) an d water (1 m l) to give 44 m g (51%) of colourless
solid 8, m .p. >300 °C. For C15H14N4O2 (282.3) calculated: 63.82% C, 5.00% H, 19.85% N; foun d:
63.61% C, 5.06% H, 19.83% N. UV (MeOH): 262 (4.14), 340 (4.51). 1H NMR (DMSO-d6):
13.61 s (NH); 7.64 d, 1 H, J = 16.4 (H-8); 7.62 m , 2 H (arom . H); 7.40 m , 3 H (arom . H); 7.03 d,
1 H, J = 16.4 (H-7); 3.47 s, 3 H (Me–N(1)); 3.25 s, 3 H (Me–N(3)).
1,3-Dim eth yl-6-(4-m eth oxyph en yl)-5H-pyrim ido[4,5-b][1,4]diazepin e-2,4(1H,3H)-dion e (9)
Com poun d 7 (100 m g, 0.28 m m ol) was h eated at 220 °C in an oil bath for 2 h . Th e result-
in g solid was recrystallized from DMF (4 m l) to give 42 m g (48%) of 9 as a yellowish crystal
powder, m .p. >300 °C. For C16H16N4O3 (312.3) calculated: 61.53% C, 5.16% H, 17.94% N;
foun d: 61.23% C, 5.38% H, 18.14% N. UV (MeOH): 269 (3.94), 340 (4.49). 1H NMR
(DMSO-d6): 13.47 s (NH); 7.60 d, 1 H, J = 16.4 (H-8); 7.56 m , 2 H (arom . H); 6.97 m , 3 H
(arom . H); 6.86 d, 12 H, J = 16.4 (H-7); 3.87 s, 3 H (MeO); 3.46 s, 3 H (Me–N(1)); 3.23 s, 3 H
(Me–N(3)).
(1,3-Dim eth yl-2,6(1H,3H)-dioxopurin -7-yl)(ph en yl)m eth yl Acetate (11)
Method A: A m ixture of 6-am in o-5-ben zyliden eam in o-1,3-dim eth yluracil19 (1; 0.3 g, 1.16
m m ol) an d dieth oxym eth yl acetate17 (10; 3 m l) was stirred for 20 m in at room tem perature
and then heated at 100 °C for 2 h. After evaporation, the residue was purified by FC (toluene–AcOEt
95 : 5 to 1 : 1) to give 16 m g (5%) of 12 as a yellowish p owd er, m .p . 258 °C (ref.20
)
an d 0.27 g (71%) of 11 as a colourless m aterial, m .p. 140–143 °C. For C16H16N4O4 (328.3)
calculated: 58.53% C, 4.91% H, 17.06% N; foun d: 58.57% C, 5.03% H, 16.63% N. UV
(MeOH): 275 (3.92). 1H NMR (DMSO-d6): 8.25 s, 1 H (CH–O); 8.10 s, 1 H (H-8); 7.45 m , 5 H
(arom . H); 3.41 s, 3 H (Me–N(1)); 3.20 s, 3 H (Me–N(3)); 2.19 s, 3 H (OAc).
Method B: 6-Am in o-5-ben zyliden eam in o-1,3-dim eth yluracil19 (1; 1.0 g, 3.87 m m ol) was
added to a m ixture of trieth yl orth oform ate (3.5 m l, 21 m m ol) an d acetic an h ydride (2 m l,
21 m m ol) an d h eated, first at 100 °C for 1 h followed by refluxin g overn igh t. After coolin g
to room tem perature, th e m ixture was evaporated to dryn ess an d th e residue crystallized
from eth an ol (5 m l) to give 0.92 g (73%) of 11, m .p. 141–143 °C. Th e product was
ch rom atograph ically an d spectroscopically iden tical with th e substan ce from m eth od A.
Th eoph yllin e (13)
Method A: A suspen sion of com poun d 11 (0.5 g, 1.52 m m ol) in a saturated solution of h y-
drogen ch loride in m eth an ol (15 m l) was stirred at room tem perature overn igh t. Th e m ix-
ture was evaporated, th e residue suspen ded in water (5 m l) an d eth an ol (1 m l) an d th en
n eutralized by 1 M aqueous am m on ia. Th e resultin g precipitate was collected, wash ed with
water, an d dried in a vacuum desiccator over ph osph orus pen toxide to yield 0.21 (78%) of
13 as a colourless m aterial, m .p. 270 °C. Th e product was iden tical in all respects with an
auth en tic sam ple.
Method B: A suspen sion of com poun d 11 (0.5 g, 1.52 m m ol) in a saturated solution of
m eth an olic am m on ia (15 m l) an d was stirred overn igh t. Th e suspen sion was evaporated, th e
residue treated with water (5 m l) an d eth an ol (1 m l) an d th en n eutralized by 2 M h ydroch lo-
ric acid. Th e precipitate was collected, wash ed with water an d dried at 100 °C to yield 0.19
(70%) of 13 as a colourless crystallin e powder, m .p. 270 °C.
Collect. Czech. Chem. Commun. (Vol. 64) (1999)

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Taghavi-Moghadam et al.:
X-Ray Structure An alyses of 6 an d 11
Crystal data an d param eters of th e data collection are com piled in Table I. Sin gle crystals
were grown from CHCl3–pen tan e (com poun d 6), or from MeOH–Et2O (com poun d 11) an d
m oun ted in
a glass capillary. All crystal data were collected on a Siem en s R3m /V
diffractom eter (Wyckoff scan , scan ran ge 4° < 2θ < 54°, scan speed variable, 2.0 to 29.3°
m in –1 in ω) with a graph ite m on och rom ator (MoKα, λ = 0.71073). Th e structures were
solved by direct m eth ods usin g th e Siem en s SHELXTL PLUS program package. Th e position s
of th e h ydrogen atom s were calculated by assum in g ideal geom etry (dC–H = 0.96 Å) an d th eir
coordin ates were refin ed, togeth er with th e attach ed carbon atom s, as a “ridin g m odel”. Th e
position s of all oth er atom s were refin ed an isotropically by full-m atrix least-squares tech -
n iques. Crystallograph ic data for th e structures reported in th is paper h ave been deposited
with th e Cam bridge Crystallograph ic Data Cen tre as supplem en tary publication n um bers
CCDC-115863 (6) an d CCDC-115864 (11). Copies of th e data can be obtain ed free of ch arge
on application to CCDC, e-m ail: deposit@ccdc.ca.ac.uk.
We thank Dr A. Geyer for the NMR spectroscopic studies and the interpretation of the spectra. We
are also grateful to the Analytical Laboratory of the Department of Chemistry, University of Con-
stance, for elemental analyses.
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