Investigation of the interaction of 5-aryl-2,3-dihydro-2,3-furandiones with compounds containing C=N and C≡N bonds simultaneously

Article abstract of DOI:10.1007/s10593-005-0310-5

Aroylketenes, generated by the thermolysis of 5-aryl-2,3-dihydro-2,3- furandiones, react with S-methyl-N-cyano-N′-phenylisothiourea, N-cyano-N′,N′-dimethylformamidine, and N,N-bis(β-cyanoethyl) cyanamide with the formation of 6-aryl-2-[(methylthio)(phenyl

Full text of DOI:10.1007/s10593-005-0310-5

Chemistry of Heterocyclic Compounds, Vol. 41, No. 10, 2005
INVESTIGATION OF THE INTERACTION
OF 5-ARYL-2,3-DIHYDRO-2,3-FURANDIONES
WITH COMPOUNDS CONTAINING C=N
AND C≡N BONDS SIMULTANEOUSLY
D. D. Nekrasov and S. N. Shurov
Aroylketenes, generated by the thermolysis of 5-aryl-2,3-dihydro-2,3-furandiones, react with S-methyl-
N-cyano-N'-phenylisothiourea, N-cyano-N',N'-dimethylformamidine, and N,N-bis(β-cyanoethyl)-
cyanamide with the formation of 6-aryl-2-[(methylthio)(phenylamino)methylene]amino-, 6-aryl-2-
dimethylaminomethyleneamino-, and 6-aryl-2-[N,N-bis(β-cyanoethyl)amino]-4H-1,3-oxazin-4-ones
respectively. Modeling has been carried out of the interaction of benzoylketene with the indicated cyano
compounds by the SSP MO LCAO semiempirical method using the MNDO-PM3 approach. A mechanism
is proposed for the formation of substituted 4H-1,3-oxazin-4-ones.
Keywords: 5-aryl-2,3-dihydro-2,3-furandiones, aroylketenes, N,N-bis(β-cyanoethyl)cyanamide,
N-cyano-N',N'-dimethylformamidine, 2-substituted 6-aryl-4H-1,3-oxazin-4-ones, S-methyl-N-cyano-N'-
phenylisothiourea, cyano[di(methylthio)]imidocarbonate, SSP MO LCAO semiempirical method in
MNDO-PM3 approach, [4 + 2] cycloaddition.
It is known that thermolysis of 5-aryl-2,3-dihydro-2,3-furandiones (benzene, 80°C) is accompanied by
the elimination of carbon monoxide and leads to 3-aroyl-6-aryl-4-hydroxy-2H-pyran-2-ones [1]. The formation
of substituted pyrans in this reaction is explained by the dimerization of aroylketenes, the primary thermolysis
products. The fact of forming aroylketenes as a result of thermal decarbonylation of furandiones was reliably
confirmed in [2].
It was shown previously that aroylketenes generated in a similar way react with compounds containing a
C=N bond and an activated C≡N bond with the formation of [4 + 2] cycloaddition products, 6-substituted 3,4-
dihydro-2H-1,3-oxazin-4-ones [3-5] or 4H-1,3-oxazin-4-ones [6-8] respectively. Many of the 1,3-oxazines
obtained in this way display biological activity [9], which makes it expedient to study these reactions further.
In the presence of compounds with an unactivated cyano group (MeCN, PhCN) aroylketenes are
dimerized [7].
The interaction of 5-aryl-2,3-dihydro-2,3-furandiones with compounds containing C=N and C≡N bonds
simultaneously, and also activated and unactivated C≡N bonds is practically unstudied. It is known only that as a
result of the reaction of 5-aryl-2,3-dihydro-2,3-furandiones with methylenaminoacetonitrile, a compound
containing isolated C=N and C≡N bonds (toluene, 110°C, 1.5 h), the latter reacts as an azomethine by a [4 + 2]
cycloaddition reaction with the resulting aroylketenes. In the course of this reaction 6-aryl-3-cyanomethyl-3,4-
__________________________________________________________________________________________
Perm State University, Perm 614990, Russia; e-mail: cheminst@mpm.ru. Translated from Khimiya
Geterotsiklicheskikh Soedinenii, No. 10, pp. 1490-1501, October, 2005. Original article submitted May 7, 2003;
revision submitted December 10, 2004.
0009-3122/05/4110-1245©2005 Springer Science+Business Media, Inc.
1245

dihydro-2H-1,3-oxazin-4-ones are obtained [6]. 2-(Cyanoimino)-1,3-dithiolane under analogous conditions
reacts with its own C≡N bond giving the corresponding 4H-1,3-oxazin-4-ones [7].
The aim of the present work is the investigation of the interaction of 5-aryl-2,3-dihydrofuran-2,3-diones
1 with S-methyl-N-cyano-N'-phenylisothioureas 3 (R2 = SMe, R3 = NHPh), N-cyano[di(methylthio)]-
imidocarbonate 4 R2 = R3 = SMe), N-cyano-N',N'-dimethylformamidine 5 (R2 = H, R3 = NMe2), containing the
N≡C–N=C fragment, and N,N-bis(β-cyanoethyl)cyanamide 6, having nonequivalent C≡N bonds, and also
modeling their reactions with aroylketenes using methods of quantum chemistry.
We established that as a result of briefly boiling equimolar amounts of compounds 1a,b and 3 in toluene
6-aryl-2-[(methylthio)(phenylamino)methylene]amino-4H-1,3-oxazin-4-ones 7a,b are formed. Melting points,
yields, and data of elemental analysis of the compounds synthesized are given in Table 1, and spectral
characteristics in Table 2.
The scheme of forming oxazines 7 includes thermal decarbonylation of furandiones 1 and a [4 + 2]
cycloaddition reaction of aroylketenes 2 at the C≡N bond of compound 3. Products of addition of aroylketenes at
the C=N bond of isourea 3, the substituted 3,4-dihydro-2H-1,3-oxazin-4-ones 8, were not detected in the
reaction mixture.
Boiling equimolar amounts of compounds 1 and 4 in toluene did not lead to the expected 6-aryl-2-
[di(methylthio)methylen]amino-4H-1,3-oxazin-4-one 10 nor to the alternative 3,4-dihydro-2H-1,3-oxazin-4-one
11. From the reaction mixture only dimers of aroylketenes 9, identified by comparison with known samples [1],
were isolated. The fact is that 2-(cyanoimino)-1,3-dithiolane, the electronic analog of compound 4, interacts with
furandione 1 under analogous conditions at the C≡N bond with the formation of [4 + 2] cycloadducts [7].
N-Cyanoamidine 5 reacts with ketenes 2, generated by thermolysis of furandiones 1, also at its C≡N
bond. The structure of the reaction products, 6-aryl-2-dimethylaminomethyleneamino-4H-1,3-oxazin-4-ones
12a,b, was established by X-ray structural analysis (XSA) [10]. As in the cases considered previously the
formation of substituted 3,4-dihydro-2H-1,3-oxazin-4-ones 13 was not observed.
Aroylketenes 2, generated by thermolysis of furandiones 1, add exclusively at the N–C≡N bond of
N,N-bis(β-cyanoethyl)cyanamide 6 with the formation of 6-aryl-2-[N,N-bis(β-cyanoethyl)amino]-4H-1,3-
oxazin-4-ones 14a-d. Other [4 + 2] cycloadducts (such as type 15) were not detected in the reaction mixture.
TABLE 1. Physicochemical Properties of Compounds 7, 12, and 14
Found, %
——————
Calculated, %
Com-
pound
Empirical
formula
mp, °С
Yield, %
С
Н
N
7а
С18H15N3O2S
C19H17N3O2S
C13H13N3O2
C14H15N3O2
C16H14N4O2
C17H16N4O2
C17H16N4O3
C16H13ClN4O2*
64.0
64.1
64.8
65.0
64.0
64.2
65.4
65.2
65.3
65.3
66.3
66.2
63.2
63.0
58.4
58.5
4.3
4.5
4.7
4.8
5.2
5.3
5.8
5.7
4.6
4.7
5.4
5.2
4.9
4.9
4.2
4.0
12.4
12.5
11.7
12.0
17.1
17.3
16.3
16.2
19.1
19.1
18.2
18.2
17.5
17.3
17.2
17.1
190-191
184-185
204-205
195-197
145-147
179-180
220-221
195-196
68
62
67
70
98
85
83
80
7b
12a
12b
14а
14b
14c
14d
_______
* Found, %: Cl 10.9; calculated, %: Cl 10.8.
1246

1247

1248

TABLE 2. Spectral Characteristics of Compounds 7, 12, and 14
IR spectrum,
Com-
pound
1Н NMR spectrum, δ, ppm (J, Hz)
ν, cm-1
7а
1640, 1670,
3060
2.5 (1Н, s, SCH3); 6.4 (1H, s, CH=C); 7.0-7.9 (10H, m, 2C6H5);
12.7 (1H, s, NH)
7b
1650, 1675,
3090
2.4 (1H, s, CH3); 2.5 (1H, s, SCH3); 6.4 (1H, s, CH=C); 7.0-7.8 (9H, m,
C6H4, C6H5); 12.8 (1H, s, NH)
12a
12b
1620-1660,
3060
3.06 (3H, s, CH3); 3.20 (3H, s, CH3); 6.5 (1H, s, CH=C);
7.35-7.95 (5H, m, С6H5); 8.68 (1H, s, N=CH)
1610-1630,
1670, 3060
2.29 (3H, s, CH3); 3.04 (3H, s, CH3); 3.18 (3H, s, CH3); 6.49 (1H, s,
CH=C); 7.28 (2Н, d, Jo = 8.3, Н-3 arom.); 7.73 (2Н, d, Jo = 8.3, Н-2
arom.); 8.66 (1H, s, N=CH)
14a
14b
1650-1670,
2280, 3090
1655, 2275,
3080
2.9 (2H, t, JHH = 6.8, CH2); 3.8 (2H, t, JHH = 6.8, CH2); 6.55 (1H, s,
CH=C); 7.4-7.8 (5H, m, C6H5)
2.3 (3H, s, CH3); 2.9 (2H, t, JHH = 6.8, CH2); 3.8 (2H, t, JHH = 6.8, CH2);
6.45 (1H, s, CH=C); 7.25 (2Н, d, Jo = 8.0, Н-3 arom.); 7.70 (2Н, d,
Jo = 8.0, Н-2 arom.)
14c
14d
1630-1660,
2267, 3080
2.9 (2H, t, JHH = 6.8, CH2); 3.8 (2H, t, JHH = 6.8, CH2); 3.85 (3H, s,
OCH3); 6.4 (1H, s, CH=C); 7.25 (2Н, d, Jo = 9.0, Н-3 arom.);
7.60 (2Н, d, Jo = 9.0, Н-2 arom.)
2.9 (2H, t, JHH = 6.8, CH2); 3.8 (2H, t, JHH = 6.8, CH2); 6.5 (1H, s,
CH=C); 7.25 (2Н, d, Jo = 9.0, Н-3 arom.); 7.70 (2Н, d, Jo = 9.0,
Н-2 arom.)
1655-1675,
2275, 3080
With the aim of explaining the results of this investigation and of data obtained previously [6, 7] we
have carried out calculations of the electronic structure of the molecules of cyano compounds 3-6, and also of
the above-mentioned methylenaminoacetonitrile 16 and 2-(cyanoimino)-1,3-dithiolane 17 by the semiempirical
SSP MO LCAO method using the MNDO-PM3 approach [11].
However the distribution of electron density in the molecules of the cyano compounds, as it turned out,
did not permit an explanation of their behavior in reactions with ketenes 2. Among the static reactivity indexes
of cyano compounds 3-6, 16, 17 (total and π-electron charges on nitrogen atoms and the populations of its AO) it
was not possible to find any index, analysis of which would permit arranging these cyano compounds in a series
of increasing (or decreasing) activity in relation to aroylketenes.
According to the calculation, the negative charge on the carbon atom of the cyano group is greater than
that on the nitrogen atom, which seems very unlikely in view of the electronegativity of these atoms. In cyano
compounds 3-5 it turned out that the sp2-hybridized nitrogen atom, according to the calculation, has more
electron excess than the sp-hybridized, although the aroylketene molecule attacks just the latter. The sizes of the
charges on atoms depends essentially on the approach used for the calculation. Thus the charges on the atoms of
the N≡C–N fragment of the compound 5 molecule, according to semiempirical calculations, in the various
approaches were: CNDO/2 [-0.212, +0.152, -0.199 arbitrary units (a. e.)], MNDO (-0.128, +0.002, -0.269 a. e.),
AM1(-0.084, -0.068, -0.212 a. e.), MNDO-PM3 (-0.099, -0.107, -0.050 a. e.).
In the benzoylketene 2a molecule the total/π-electron charges on atoms have the following values:
C(1)=O (-0.144/+0.303), C(1) (+0.417/+0.163), C(2) (-0.488/-0.382), C(3) (+0.426/+0.276). C(3)=O (-0.364/-0.391).
The total/π-electron bond orders are equal to: 2.119/0.592 [C(1)=O], 1.591/0.764 [C(1)=C(2)], 0.987/0.317
[C(2)–C(3)], 1.835/0.864 [C(3)=O]. (The calculated data published in [12] do not contain values for atomic charges
and bond orders)
Since the static indexes of reactivity of the cyano compounds were unable to explain the observed results
we localized the transition states of the [4 + 2] cycloaddition reactions of ketene 2a with cyano compounds 3-6
and the energies of activation were assessed (Ea) as the difference of the enthalpies of formation of the activated
complexes [∆Hf(AC)] and the initital reactants benzoylketene 2a and the cyano compound (CC) [∆Hf(2a)] –
[∆Hf(CC)].
1249

N
C
C
H2
N
CH2
16
1a
[2]
O
O
O
CH2CN
CH2CN
N
N
CH2
CH2
Ph
Ph
O
AK (18)
18
O
O
N
N
Ph
O
CH2N=CH2
Ph
O
CH2N=CH2
19
AK (19)
With the aim of clarifying the suitability of the MNDO-PM3 approach for solving this problem, we have
localized the transition states of the model reactions of ketene 2a with methyleneaminoacetonitrile 16 leading
respectively to 3-cyanomethyl-6-phenyl-3,4-dihydro-2H-1,3-oxazin-4-one 18 and 2-methyleneaminomethyl-6-
phenyl-4H-1,3-oxazin-4-one 19.
The correctness of the localization of the transition states is confirmed by one negative value of the
Hesse matrix. According to the calculation the activation barrier for the reaction forming oxazine 18
(56.0 kJ/mole) is less than for forming oxazine 19 (72.3 kJ/mol), which is not contrary to the experimental data
[6]. The calculated energy of activation for the reaction forming cycloadduct 20 (R2 + R3 = –SCH2CH2S–) from
ketene 2a and cyano compound 17 (73.3 kJ/mol) proved to be not only lower than that of the alternative
cycloadduct 21 (R2 + R3 = –SCH2CH2S–) (135.4 kJ/mol), but also lower than the energy of activation of the
dimerization reaction of ketene 2a (94.6 kJ/mol) [13], which explains the predominant formation of the
cycloadduct and not the dimer.
The calculated energies of activation of the reactions investigated in the present study are given in
Table 3.
As follows from the calculations, the values of Ea of all the reactions are less than the values of Ea for the
dimerization reaction of ketene 2a. This also indicates the preference to form cycloadducts 7, 10, 12, and 14. The
reasons for the passive nature of cyano compound 4 in the reaction with compound 2a prior to the end are not
clear, since the interaction of compound 2a and 17, characterized by a higher calculated energy of activation,
leads to the formation of a 1,3-oxazine.
The hypothesis was expressed previously that the interaction of aroylketenes with cyano compounds
leading to substituted 4H-1,3-oxazin-4-ones is a coordinated [4π + 2π] cycloaddition reaction [6]. The putting
into practice of such a mechanism requires the drawing together of the reactants in parallel planes [14] and the
formation of new bonds through the π-electron systems of the diene (aroylketene) and the dienophile (cyano
compound). However to localize the transition state in such an approach of reactants was unsuccessful. It turned
out that the activated complexes corresponding to the transition state of the reaction of ketene 2a with the
enumerated cyano compounds have a completely different geometry. Their main geometric parameters (bond
lengths and valence angles) are given in Table 4.
1250

TABLE 3. Enthalpies of Formation (∆Hf), Energies of Activation (Ea), Bond
Lengths (l, Å), Valence Angles (ω, deg) in the Activated Complexes (AC) of
the Reaction of Benzoylketene with Cyano Compounds 3-6
Parameter
АС (7)
АС (10)
АС (20)
АС (12)
АС (14)
304.4
21.3
230.9
65.2
289.0
73.3
176.9
42.9
385.6
61.1
∆Ηf, kJ/mol
Ea, kJ/mol
O(1)···C(2)
2.046
1.209
1.488
1.422
1.371
1.280
1.212
100.9
139.0
115.0
125.1
123.4
117.1
113.2
131.9
0.67
2.087
1.195
1.520
1.406
1.411
1.265
1.210
98.4
2.084
1.192
1.527
1.403
1.415
1.262
1.209
98.3
2.068
1.201
1.502
1.413
1.405
1.268
1.212
100.0
140.6
114.0
125.2
123.7
116.5
112.8
133.3
0.66
2.111
1.191
1.535
1.402
1.415
1.262
1.209
98.6
C(2)–N(3)
N(3)···C(4)
C(4)–C(5)
C(5)–C(6)
C(6)–O(1)
C(4)=O
O(1)···C(2)–N(3)
C(2)–N(3)···C(4)
N(3)···C(4)–C(5)
C(4)–C(5)–C(6)
C(5)–C(6)–O(1)
C(6)–O(1)···C(2)
N(3)···C(4)=O
C(5)–C(4)=O
∆lO(1)–C(2)
∆lС(2)=N(3)
∆lN(3)–C(4)
∆lC(4)–C(5)
∆lC(5)=C(6)
∆lC(6)–O(1)
∆lC(4)=O
142.5
112.9
125.7
123.8
116.7
112.4
134.8
0.66
142.8
112.3
125.9
123.8
116.7
112.4
134.4
0.66
141.7
113.3
126.3
123.4
116.8
111.3
135.4
0.64
1.09
1.09
1.10
1.09
1.10
0.97
0.95
0.94
0.96
0.94
1.03
1.05
1.05
1.04
1.05
0.99
0.96
0.96
0.96
0.96
1.08
1.09
1.10
1.10
1.10
1.00
1.00
1.00
1.00
1.00
As follows from the calculations, the activated complexes of the reactions of benzoylketene 2a with
cyano compounds 3-6 are practically planar. The dihedral angles have the following values.
θ О(1)–С(2)–N(3)–C(4) = 1.5±1.1°, θ C(2)–N(3)–C(4)–C(5) = 2.5±2.0°,
θ N(3)–С(4)–N(5)–C(6) = 1.2±1.2°, θ C(4)–С(5)–C(6)–O(1) = 0.6±0.1°,
θ C(5)–С(6)–O(1)–C(2) = 1.4±1.0°, θ C(6)–O(1)–C(2)–N(3) = 0.6±0.5°.
The interatomic distances O(1)···C(2) and N(3)···C(4) in the activated complexes were equal to 2.079±0.032
and 1.512±0.024 Å respectively, indicating the asynchronicity of forming the corresponding bonds, but within
the limits for a coordinated process. Attempts to find a zwitter ion intermediate of type 22 on the potential
energy surface of the reaction of ketene 2a with cyano compounds 3-6 proved to be in vain.
Probably at the stage of forming activated complexes the N(3)–C(4) bond is formed at an advanced time
while at the stage of converting them into reaction products the O(1)–C(2) bond is formed at an even higher rate.
The 2py orbital of the C(1) atom of the benzoylketene 2a molecule and the 2s orbital of the nitrogen atom of the
cyano compound molecule participate in the formation of the N(3)–C(4) bond. This is confirmed by the
insignificant change in the C≡N bond length in the activated complexes compared with the isolated molecule of
compounds 3-6 (the increase is no more than 4%). The total order of the C(2)=N(3) bond in the activated
complexes is on average 86% of the total C≡N bond order in the cyano compound molecules. Participation in the
formation of the N(3)–C(4) bond by 2pz or 2py orbitals of the nitrogen atom would lead to a large increase in
length and a reduction of the order of the C=N bond in the cyano fragment of the activated complexes. The O(1)–
C(2) bond is formed by overlap of orbitals of one of the lone electron pairs of the oxygen atom and the
1251

TABLE 4. Total/π-Electron Charges of Atoms, Total/π-Electron Charges of
Bonds ∆p in the Activated Complexes (AC) in the Reaction of
Benzoylketene 2a with Cyano Compounds 3-6, 16
Parameter*
qO(1)
AC (7)
AC (10)
AC (20)
AC (12)
AC (14)
-0.565
-0.672
-0.517
-0.609
-0.497
-0.595
-0.541
-0.632
-0.531
-0.601
qC(2)
+0.217
+0.134
+0.149
+0.101
+0.138
+0.106
+0.196
+0.123
+0.071
+0.064
qN(3)
-0.020
+0.226
+0.037
-0.185
+0.057
-0.173
+0.009
-0.199
+0.074
-0.085
qC(4)
+0.444
+0.239
+0.448
+0.226
+0.448
+0.223
+0.447
+0.231
+0.440
+0.212
qC(5)
-0.558
-0.403
-0.586
-0.433
-0.587
-0.436
-0.582
-0.427
-0.589
-0.432
qC(6)
+0.401
+0.267
+0.414
+0.287
+0.420
+0.291
+0.412
+0.280
+0.429
+0.297
qC(4)=O
pO(1)···C(2)
pC(2)–N(3)
pN(3)···C(4)
pC(4)–C(5)
pC(5)–C(6)
pC(6)–O(1)
pC(4)=O
∆pO(1)–C(2)
∆pC(2)–N(2)
∆pN(3)–C(4)
∆pC(4)–C(5)
∆pC(5)–C(6)
∆pC(6)–O(1)
∆pC(4)=O
-0.346
-0.455
0.154
0.092
2.293
0.894
0.774
0.206
1.140
0.451
1.389
0.661
1.399
0.615
1.827
0.807
0.15
1.46
0.75
1.17
0.79
1.34
0.99
-0.346
-0.509
0.136
0.092
2.424
0.918
0.701
0.183
1.214
0.522
1.278
0.580
1.514
0.692
1.820
0.775
0.13
1.40
0.73
1.25
0.73
1.46
0.97
-0.350
-0.509
0.140
0.094
2.456
0.925
0.687
0.178
1.233
0.537
1.255
0.560
1.538
0.706
1.815
0.762
0.14
1.41
0.72
1.27
0.71
1.48
0.97
-0.355
-0.483
0.145
0.096
2.369
0.909
0.741
0.196
1.186
0.496
1.315
0.608
1.481
0.671
1.813
0.789
0.14
1.41
0.76
1.22
0.75
1.46
0.98
-0.342
-0.506
0.118
0.092
2.469
0.963
0.676
0.169
1.239
0.542
1.254
0.560
1.529
0.703
1.821
0.767
0.12
1.58
0.70
1.27
0.71
1.47
0.99
_______
* π-Electron charges on oxygen atoms were determined as the difference
between the calculated population of its 2pz-AO and 1.
2py-orbitals of the carbon atom, which is indicated by the value of the C(6)–O(1)···C(2) valence angle in the
activated complexes being equal to 116.8±0.3°. The change in the geometry of the dienophile fragment
compared with the isolated molecule is insignificant. Thus the C(1)–C(2) bond length in the 2a molecule [bond
C(4)–C(5) in the activated complex] is increased by 6.5±0.5%, the C(2)–C(3) bond becomes shorter by 4.5±1.5%,
and the C=O bond length is increased by 3 to 5%. The C(2)=C(1)=O valence angle undergoes the greatest change.
It is reduced from 179.1 to 133.7±1.8°. The valence angles C(1)=C(2)–C(3) and C(2)–C(3)=O are increased
insignificantly, by no more than 2.6°. The extent of bond formation in the activated complexes may be judged by
the value of ∆l, the ratio of bond length in the cycloadduct to the analogous bond length (interatomic distance) in
the activated complex (Table 3). As shown by the calculations, the O(1)···C(2) interatomic distance in
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the activated complexes is 64-67% of the lengths of the analogous bonds in the cycloadduct, but for N(3)···C(4) it
is 94-97%. The lengths of the remaining bonds also did not undergo significant changes, as follows from
comparison of the values of ∆l. In parallel with ∆l we calculated ∆p as the ratio of bond order in the activated
complex to the order of the analogous bond in the cycloadduct (Table 4). Analysis of these values, and also the
values of the atomic charges, shows that the distribution of electron density in the activated complexes differs
substantially from that in the cycloadducts. For example, ∆p for the O(1)–C(2) bond is on average14%, and ∆p for
the N(3)–C(4) bond is 73%.
At the stage of forming the activated complexes a transfer occurs of from 0.450 elementary charge from
the molecule of cyano compound to the ketene molecule 2a in activated complex AC (14) to 0.503 elementary
charge in activated complex AC (7). As calculations showed, a large portion of the charge (-0.203 a. u.) is taken
by the ketenic oxygen atom and a lesser by the ketonic atom (-0.174 a. u.). The charge on the C(2) atom is
increased insignificantly (-0.092 a. u.), and the sp-hybridized nitrogen atom in all the activated complexes, with
the exception of AC (6), becomes electron-deficient.
According to the data of the calculations the energy of activation of the reaction forming oxazine 7
proved to be 63.1 kJ/mol less than for the hypothetical oxazine 8.
According to the calculation, the formation of oxazines 8 and 11 when carrying out the corresponding
processes may also occur in a coordinated manner. However the energy of activation of the reaction 2a + 3 → 7
is 63.1 kJ/mole less than the reaction 2a + 3 → 8a, and oxazine 8a is not formed. The difference in the energies
of activation of the reactions forming oxazines 14a and 15a is 15.8 kJ/mol.
According to the calculations, the formation of oxazine 13a from ketene 2a and cyanoamidine 5 must
proceed stepwise through zwitter ion 23.
O
CN
N
+
_
O
CH–NMe2
Ph
23
But the energy profile of this reaction lies higher in the ∆Hf scale than the profile of the coordinated
process of forming oxazine 12, and oxazine 13 is not formed. Quantum chemical modeling of the reaction of
benzoylketene 2a with cyano compounds 3, 5, 6, and 16 gives a qualitative agreement with experiment, but the
reaction of furandiones 1 with cyano compounds 4 and 17 deserves a deeper study.
EXPERIMENTAL
The IR spectra of the synthesized compounds were recorded on a UR 20 spectrometer in nujol. The
1H NMR spectra were obtained on a Tesla BS 487 (80 Hz) instrument in CDCl3, internal standard was HMDS
(δ 0.05 ppm). The progress of reactions and the purity of the compounds obtained were checked by TLC on
Silufol plates in the system benzene–ether, 3:2, visualization was with iodine vapor.
The quantum chemical calculations were carried out with the aid of the MOPAC 7.0 [15] set of
programs on a Pentium 200-MMX computer. Transition states were localized with the aid of the TS procedure
and were refined with the aid of the NLLSQ procedure.
6-Aryl-2-[(methylthio)(phenylamino)methylene]amino-4H-1,3-oxazin-4-ones 7a,b. A mixture of
furandione 1 (0.01 mol) and S-methyl-N-cyano-N'-phenylisothiourea 3 (0.01 mol) in anhydrous toluene
(15-20 ml) was boiled for 30 min. The reaction mixture was cooled to room temperature, the precipitated solid
filtered off, washed with ether, and recrystallized from toluene.
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Interaction of 5-Aryl-2,3-dihydro-2,3-furandiones with N-Cyano[di(methylthio)]imidocarbonate.
A mixture of furandione 1 (0.01 mol) and cyano compound 4 (0.01 mol) in toluene (20-25 ml) was boiled for
30 min. After cooling the reaction mixture to room temperature pyranone 9 was filtered off. The filtrate was
evaporated, the residue was recrystallized from hexane, and the initial cyano compound 4 was isolated.
6-Aryl-2-dimethylaminomethylenamino-4H-1,3-oxazin-4-ones 12a,b were obtained analogously to
compounds 7a,b from furandiones 1 and N-cyano-N',N'-dimethylformamidine (5).
6-Aryl-2-[N,N-bis(β-cyanoethyl)amino]-4H-1,3-oxazin-4-ones
14a-d.
N,N-Bis(β-cyanoethyl)-
cyanamide 6 (0.01 mol) was added to a solution of furandione 1 (0.01 mole) in anhydrous dioxan (20-25 ml),
and the mixture boiled for 1 h. The solid, precipitated on cooling the mixture to room temperature, was filtered
off, and recrystallized from ethanol.
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