Transformations of S-substituted 5,7-dimethyl-4а,5а-diphenyl-3-thioxoperhydroimidazo[4,5-e]-1,2,4-triazin-2-ones under treatment of 1,2-benzoquinones and photochemical properties of reaction products

Article abstract of DOI:10.1016/j.tet.2018.03.056

For the first time 5,7-di-tert-butyl-1,3-dimethyl-3a,9a-diphenyl-3,3a-dihydro-1H-benzo[5,6][1,4]dioxino[2,3-d]imidazol-2(9aH)-one 13 and complex 9 of 4,6-di-tert-butyl-3-nitrobenzene-1,2-diol with 1,3-dimethyl-4,5-diphenyl-1H-imidazol-2(3H)-one 10a were p

Full text of DOI:10.1016/j.tet.2018.03.056

Accepted Manuscript
Transformations of S-substituted 5,7-dimethyl-4а,5а-diphenyl-3-
thioxoperhydroimidazo[4,5-e]-1,2,4-triazin-2-ones under treatment of 1,2-
benzoquinones and photochemical properties of reaction products
Angelina N. Kravchenko, Sergei V. Vasilevskii, Galina A. Gazieva, Vladimir V.
Baranov, Valery A. Barachevsky, Olga I. Kobeleva, Olga V. Venidiktova, Valentina A.
Karnoukhova
PII:
S0040-4020(18)30329-6
10.1016/j.tet.2018.03.056
TET 29396
DOI:
Reference:
To appear in: Tetrahedron
Received Date: 23 January 2018
Revised Date: 7 March 2018
Accepted Date: 26 March 2018
Please cite this article as: Kravchenko AN, Vasilevskii SV, Gazieva GA, Baranov VV, Barachevsky VA,
Kobeleva OI, Venidiktova OV, Karnoukhova VA, Transformations of S-substituted 5,7-dimethyl-4а,5а-
diphenyl-3-thioxoperhydroimidazo[4,5-e]-1,2,4-triazin-2-ones under treatment of 1,2-benzoquinones and
photochemical properties of reaction products, Tetrahedron (2018), doi: 10.1016/j.tet.2018.03.056.
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ACCEPTED MANUSCRIPT

ACCEPTED MANUSCRIPT
Transformations
of
S-substituted
5,7-dimethyl-4а,5а-diphenyl-3-
thioxoperhydroimidazo[4,5-e]-1,2,4-triazin-2-ones under treatment of 1,2-benzoquinones
and photochemical properties of reaction products
Angelina N. Kravchenko,*a Sergei V. Vasilevskii,a Galina A. Gazieva,a Vladimir V. Baranov,a
Valery A. Barachevsky,b Olga I. Kobeleva,b Olga V. Venidiktovab and Valentina A.
Karnoukhovac
aN. D. Zelinsky Institute of Organic Chemistry, Russian Academy of Sciences, Moscow, 119991
Russian Federation, Fax: +7 499 135 53 28; e-mail: kani@server.ioc.ac.ru
bPhotochemistry Center, FSIC “Crystallography and Photonics”, Russian Academy of
Sciences, Moscow, 119421, Russian Federation, Fax: +7 495 936 12 55; e-mail:
barva@photonics.ru
cA. N. Nesmeyanov Institute of Organoelement Compounds, Russian Academy of Sciences,
Moscow, 119991, Russian Federation, Fax: +7 499 135 55 08; e-mail: v_a_k_h_h@mail.ru
For the first time 5,7-di-tert-butyl-1,3-dimethyl-3a,9a-diphenyl-3,3a-dihydro-1H-
benzo[5,6][1,4]dioxino[2,3-d]imidazol-2(9aH)-one 13 and complex 9 of 4,6-di-tert-butyl-3-
nitrobenzene-1,2-diol with 1,3-dimethyl-4,5-diphenyl-1H-imidazol-2(3H)-one 10a were
prepared by the reactions of 3-alkylthio-5,7-dimethyl-4a,7a-diphenyl-4a,5,7,7a-tetrahydro-1H-
imidazo[4,5-e]-1,2,4-triazin-6(4H)-ones with 3,5-di-tert-butyl-1,2-benzoquinone 1 and 4,6-di-
tert-butyl-3-nitro-1,2-benzoquinone 2, respectively. Photochemical transformations of
compounds 9 and 10a as well as products of its photooxygenation involving singlet oxygen
under UV irradiation: urea 16, isomeric 1,3-dimethyl-4,5-diphenylimidazolidin-2-ones 17 and
17`, and compound 18 were studied by the spectral-kinetic method. Data on the absorption and
fluorescence properties of synthesized compounds and their photoproducts were obtained.
Keywords
1,2-benzoquinones, S-substituted 5,7-dimethyl-4а,5а-diphenyl-3-thioxoperhydroimidazo[4,5-e]-
1,2,4-triazin-2-ones; photochemical transformations; 5,7-di-tert-butyl-1,3-dimethyl-3a,9a-
diphenyl-3,3a-dihydro-1H-benzo[5,6][1,4]dioxino[2,3-d]imidazol-2(9aH)-one; 1,3-dimethyl-4,5-
diphenyl-1,3-dihydro-2Н-imidazol-2-one
Introduction
It is known that the reactivity of spatially hindered quinoid compounds is quite diverse and
depends on their structure. Reactions of sterically hindered 1,2-benzoquinones with heterocycles
containing a reactive methylene group at the ring or in a substituent do not stop at in nucleophilic
addition products as they are unstable and readily undergo various further reactions.1-3 For
example, we have recently found that 3,5-di-tert-butyl-1,2-benzoquinone (benzoquinone) 1 and
1

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4,6-di-tert-butyl-3-nitro-1,2-benzoquinone
(nitrobenzoquinone)
2
react
with
imidazothiazolotriazine 3 in different ways (Scheme 1).1,2 Benzoquinone 1 is subjected to aldol-
crotonic condensation with compound 3 to give adduct 4, which rearranges to isomer 5 under the
reaction conditions.1 Similar transformations occur in the reaction of benzoquinone 1 with
(imidazotriazin-3-ylthio)acetic acid 6. However, in the reaction with nitrobenzoquinone 2,
nucleophilic 1,4-addition of the methylene-active group of compound 3 initiates a cascade
process resulted in an unusual polyheterocyclic compound 7.2
Scheme 1 Condensation of benzoquinone 1 and nitrobenzoquinone 2 with tricyclic structure 3.
In this work we have studied the reactions of 1,2-benzoquinones 1 and 2 with S-
substituted
5,7-dimethyl-4а,7а-diphenyl-3-thioxoperhydroimidazo[4,5-e]-1,2,4-triazin-2-ones
((imidazotriazin-3-ylthio)acetic acid 6 and 3-methylthioimidazotriazine 8) which lead to tricyclic
product containing annulated imidazolidine, dioxane and benzene moieties and complex 9
comprising 1,3-dimethyl-4,5-diphenyl-1,3-dihydro-2Н-imidazol-2-one (imidazolinone) and 4,6-
di-tert-butyl-3-nitrobenzene-1,2-diol. The photochemical transformations and absorption-
fluorescent properties of imidazolinone alone and in the complex 9, as well as compounds
synthesized from imidazolinone by photooxygenation involving singlet oxygen under UV
irradiation were investigated by a spectral-kinetic method for the first time.
Results and discussion
Synthesis
Since acid 6 has not been used in the interaction with nitrobenzoquinone 2 we studied this
reaction both under conditions of aldol-crotonic condensation of compound 3 with benzoquinone
2

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1 (60 °С, 5 h, AcOH)1 and under conditions of mentioned above polyheterocycle 7 formation (7
days at 20 °С, AcOH)2 (Table 1, entries 2 and 7, respectively). However, we obtained complex 9
consisting of known 1,3-dimethyl-4,5-diphenyl-1,3-dihydro-2Н-imidazol-2-one (imidazolinone)
10a4-7 and 4,6-di-tert-butyl-3-nitrobenzene-1,2-diol 118 instead of expected polycycle 7 or
analogues of compounds 4 and 5. The structure of cocrystal 9 was confirmed by X-ray single
crystal analysis (see X-Ray structural investigation).
Table 1 Synthesis of complex 9 and compound 13.
Entries
Reagents
T, °C
60
Reaction time
2 h
Product (Yield, %)
9 (38%)
1
2
6, 2
6, 2
60
5 h
9 (30%)
3
6, 2
70*
2 h*
9 (40%)
4
6, 2
70
5 h
9 (26%)
5
6, 2
20**
20
2 d**
9 (70%)
6
6, 2
5 d
9 (52%)
7
6, 2
20
7 d
9 (35%)
8
8, 2
8, 2
70*
20**
70*
20**
70*
2 h*
2 d**
2 h*
2 d**
2 h*
9 (74%)
9
9 (95%)
10
11
12
12, 2, BrCH2COOH
12, 2, BrCH2COOH
8, 1
9 (18%)
9 (32%)
13 (25%)
* - Conditions A: Solution of 2 (0.53 g, 2 mmol) and 6 (0.82 g , 2 mmol) in 10 mL of АсОН was
heated at 70 ºС and stirred for 2 h.
** - Conditions B: Solution of 2 (0.53 g, 2 mmol) and 8 (0.73 g, 2 mmol) in 10 ml of АсОН was
stirred at 20 ºС for 2 days.
3

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The yield of complex 9 was 30-35%. We varied conditions of the experiment: keeping
the reaction mixture for 2-5 h at 60 °С or 70 °С or for 2-7 days at 20 °С. However, the main
product of the reaction was only complex 9 the highest yields of which (40% and 70%) were
obtained upon keeping reagents 2 and 6 at 70 °С for 2 h (conditions А) and for 2 days at 20 °С
(conditions B), respectively.
Interesting, that nitrobenzoquinone 2 reacts with 3-methylthioimidazotriazine 8 in a
similar manner. Complex 9 is formed in 74% and 95% yields on keeping the reaction mixture
under conditions A and B, respectively. The presence of a substituent at the sulfur atom is a
prerequisite since imidazotriazine 12 does not react with nitrobenzoquinone 2. However,
complex 9 is formed in 18% (conditions A) and 32% yield (conditions B) under three-
component condensation conditions upon addition of bromoacetic acid as an alkylating reagent
to a mixture of compounds 12 and 2.
The study of the reaction of benzoquinone 1 with 3-methylthioimidazotriazine 8 (Scheme
2, conditions А) gave other result. 5,7-Di-tert-butyl-1,3-dimethyl-3a,9a-diphenyl-3,3a-dihydro-
1H-benzo[5,6][1,4]dioxino[2,3-d]imidazol-2(9aH)-one 13 was the main reaction product. The
13
structure of compound 13 was confirmed by 1Н and С NMR spectra and high resolution mass
spectra. We assumed that compound 13 could be the product of the hetero-Diels-Alder reaction
of imidazolinone 10a formed under reaction conditions and benzoquinone 1. However,
previously prepared imidazolinone 10a and benzoquinone 1 do not react under conditions А and
were isolated unchanged. Based on the results obtained we proposed the following path of the
formation of complex 9 and compound 13 depicted in Schemes 2 and 3, respectively.
Scheme 2 Pathway of complex 9 formation
Probably, redox reaction of nitrobenzoquinone 2 with methylthioimidazotriazine 8 leads
to 4,6-di-tert-butyl-3-nitrobenzene-1,2-diol 11 and 5,7-dimethyl-3-methylthio-4a,7a-diphenyl-
4

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7,7a-dihydro-4aH-imidazo[4,5-e]-1,2,4-triazin-6(5H)-one (A). The latter undergoes opening of
the triazine ring to give imidazolinone 10a, methylthiocyanate and nitrogen molecule (Scheme
2).
Benzoquinone 1 is reduced into 3,5-di-tert-butylbenzene-1,2-diol B analogously to
nitrobenzoquinone 2. Apparently, pyrocatechol B as more nucleophilic agent than its
nitroanalogue 11 react with intermediate A to give the substitution product 13 (Scheme 3).
Scheme 3 Pathway of compound 13 formation
A synthesis of hitherto unreported methylthioimidazotriazine 8 was performed in 90%
yield by S-methylation of imidazotriazine 12 with methyl iodide under standard methylation
conditions (Scheme 4).9 Furthermore, the N-methylation product 14, in which the sulfur atom is
replaced by an oxygen atom, was isolated in 2% yield (Scheme 4). X-Ray single crystal
diffraction was used to confirm the structure of the hitherto unknown compound 14 (see X-Ray
structural investigation). It is interesting that imidazotriazine 15 do not undergo alkylation with
MeI in the same conditions. Only starting compound 15 is isolated from reaction mixture.
Scheme 4 Synthesis of methylimidazotriazines 8 and 14.
Spectral-kinetic and photochemical study
5

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We have found that solutions of complex 9 in CD3CN, CDCl3 and DMSO-d6 manifest
fluorescent properties. This phenomenon can be explained by the presence of compound 10a in
complex 9. Previously compound 10a was characterized only by the maximum of the absorption
band.6 To confirm that the fluorescent properties of complex 9 belong to imidazolinone 10a, we
were the first to study the photochemical transformations of complex 9 and imidazolinone 10a
(Fig.1-3, Table 1).
It has been found by the spectral-kinetic method that complex 9 in MeCN is characterized
by an absorption band with two maxima at 279 and 304 nm (Fig. 1, curve 1; Table 2) and a
fluorescence band with a maximum at 420 nm (Fig. 1, curve 5, Table 2), which belongs to this
particular compound, as follows from the match between the absorption and fluorescence
excitation spectra (Fig. 1, curve 6).
Fig 1 Absorption spectra (curves 1-4) (solid), fluorescence excitation spectra measured at a
wavelength of 428 nm (curves 6,8) (short dash) and fluorescence spectra with excitation with a
wavelength of 312 nm (curve 5) and 331 nm (curve 7) (dash dot dot) of complex 9 in MeCN
before irradiation (curves 1,5,6), in the beginning (curves 2,3) and after UV irradiation (curves
4,7,8). The working solution concentration is C = 4x10-5 М. The cell thickness is 10 mm. The
inset demonstrates a magnified part of the absorption spectra in the spectral region of 420-540
nm.
Table 2 Spectral, fluorescent and kinetic characteristics of the samples synthesized
Sample Solvent
λ0,
λ30,
nm (ΔD30) nm
λflu,
I0
,
I30
,
flu
λ30flu, nm
(I30sh,a.u.)
,
flu
М-1. cm-1
nm
a.u.
a.u.
MeCN 279
304
11175
11200
262(1.3),
330(0.3),
367(<0,1),
383(<0,1)
262(0,2),
322(<0,1),
336(0,1),
375(<0,1),
393(<0,1)
420
2500
1200 427(1280)
9
C6H14 316
2700
412
380
320
399(400),
421(360)
6

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MeCN
MeCN
304
13825
261(1,4),
330(0,2),
382(<0,1)
261(2,4)
330(0,5)
384(0,1)
258(0,3)
425
417
313
2750
2070
590
425
417
10a
18
261
330
384
258
72000
16900
3100
618
1895
Cмесь MeCN
17+17’
32
68
28
30
133
27
313
423
315
329(<0,1) 423
MeCN
257
425
-
315
17*
MeCN
MeCN
257
236
350
18975
-
-
313
0
23
0
22
0
313
0
17**
16
Note: λ0 and λ30 are the wavelengths of the absorption bands before and after irradiation for 30
min, respectively; ΔD30 is the optical density change at the absorption band maximum upon UV
irradiation for 30 min;  is the molar extinction coefficient at the absorption band maximum of
the original form; λflu and λ30flu are the wavelengths of the fluorescence band maxima before and
after UV irradiation for 30 min, respectively; I0flu, I30flu and I30sh are the fluorescence intensities at
the band maximum before and after UV irradiation for 30 min, without and with a shift of the
fluorescence band maximum, respectively.
* - the major isomer isolated from the (17 + 17`) mixture.
** - isomer 17 synthesized by the known procedure.10
Under UV irradiation, complex 9 undergoes irreversible photochemical transformations
that manifest themselves as changes in the absorption spectra (Fig. 1, curves 2-4) and
fluorescence spectra (Fig. 1, curve 7). The final photoproduct is characterized by a few
absorption bands located in the short-wave (at 262 and 330 nm) and long-wave (at 390 nm)
regions of the UV spectral range. In this case an intermediate short-living photoproduct 10`a
appears. It absorbs in the visible region of the spectrum with a maximum at 487 nm (Fig. 1,
inset; Table 3). It disappears during UV irradiation of the solution, as indicated by the photo-
induced spectral changes (Fig. 1, inset), as well as in the dark (Table 3). The nature of these
changes will be the subject of our further studies.
Table 3 Spectral-kinetic properties of the short-living photoinduced absorption band of samples
9 and 10a in acetonitrile.
Sample
λ, нм
Dmax
τ, с
487
480
0.011
0.017
60
80
9
10a
Note: λ is the wavelength of the absorption band maximum of the short-living photoproduct;
Dmax is the maximum optical density at the absorption band maximum of the short-living
photoproduct; τ is the life time of the short-living photoinduced absorption band.
Based on the data obtained by the Bieławski group11 during the studies of the
photochemical properties of compound 10b, we could assume a structure of short-living photo-
induced intermediate 10`a (Scheme 5). Analogous product 10’b obtained under UV irradiation
7

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of the compound 10b solution in acetonitrile was characterized with absorption maximum at 476
nm.
Scheme 5 A known product 10’b obtained under UV irradiation of the compound 10b
(Bielawski group study) and proposed structure of the short-living photoinduced intermediate
10`a.
Similar photochemical transformations of complex 9 are also observed in C6H14. Unlike
the spectra in polar acetonitrile, both absorption spectra and the fluorescence spectra of the final
photoproduct manifest an electronic vibrational structure in non-polar hexane (Fig. 2).
Fig. 2 Absorption spectra (curves 1-4) (solid), fluorescence excitation spectra measured at a
wavelength of 412 nm (curve 6) and 421 nm (curve 8) (short dash), and fluorescence spectra
with excitation by light with a wavelength of 323 nm (curve 5) and 336 nm (curve 7) (dash dot
dot) of complex 9 in hexane before (curves 1,5,6), at the beginning (curves 2,3), and after UV
irradiation (curves 4,7,8). The working solution concentration is C = 4x10-5 М. The cell thickness
is 10 mm. The inset shows a magnified part of the absorption spectra.
Comparison of the photoinduced spectral changes of samples 9 (Fig. 1) and 10a (Fig. 3)
in MeCN indicate that the photochemical transformations of these compounds, including those
8

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with involvement of the short-living intermediate photoproduct that absorbs in the visible region,
are identical (Table 2).
Fig. 3 Absorption spectra (curves 1-4) of a solution of compound 10a in MeCN before (curve 1),
in the beginning (curves 2,3) and after UV irradiation (curve 4). The working solution
concentration is C = 2x10-4 М. The cell thickness is 2 mm. The inset shows a magnified part of
the absorption spectra.
The reversibility of the photoinduced transformations of compounds 10a and 10'a is
confirmed by the results of kinetic studies according to which the short-serving photoconductive
photoproduct 10'a undergoes reversible conversion to compound 10a both in the dark and under
the action of visible light (Fig ... S).
To establish the structure of products of irreversible photochemical transformations of
compound 10a we synthesized these products and studied their photochemical properties.
Previously H.M. Chawla and M. Pathak5 investigated dye sensitized photooxigenation of
imidazolidine-2-ones and showed that the oxidation of imidazolinone 10a with singlet oxygen
generated by UV irradiation in the presence of methylene blue gave 1,3-dibenzoyl-1,3-
dimethylurea 16 (Scheme 6). We found that not only urea 16 is a product of oxidation of
compound 10a with singlet oxygen generated from the oxygen in the air by UV irradiation. The
other products of this reaction are mesoform (4S,5R)-4,5-dihydroxy-1,3-dimethyl-4,5-
diphenylimidazolidin-2-one
17,10
racemic
(4R,5R)-4,5-dihydroxy-1,3-dimethyl-4,5-
diphenylimidazolidin-2-one 17`10 and 1,3-dimethyl-1H-phenanthro[9,10-d]imidazol-2(3H)-one
18. The formation of compounds 17, 17` and 18 under the action of singlet oxygen generated by
UV irradiation was not reported before. These processes do not occur without access of oxygen.
We noted that after UV irradiation of solution of compounds 10a for 12 h in NMR ampoules
(DMSO-d6 or CD3CN) the signal of 2 Me (6 H) is disappeared and the ratio of products 16-18
changed depending on the solvent used. The ratio of compounds 16 : 17+17` : 18 was
1
determined by integral intensity of signals of Me groups in H NMR spectra. In DMSO-d6 the
singlet of 2 Me (6 H) of urea 16 is located at 2.94 ppm; the singlet of 4 Me (12 H) of isomers 17
9

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and 17` is located at 2.61 ppm; the singlet of 2 Me (6 H) of hitherto unknown compound 18 is
located at 3.84 ppm. The ratio of compounds 17 : 17` was determined by integral intensity of
signals of Ph group protons. For compounds 17 and 17`, multiplets of Ph group protons are
located at 6.85-7.07 ppm (for 17) and 7.15-7.39 ppm (for 17`). Therefore, the ratio of compounds
16 : 17 : 17` : 18 is 1 : 4.2 : 6 : 6.8. In CD3CN the ratio of compounds 16 : 17 : 17` : 18 is 43 : 6 :
1 : 5. To prepare compounds 16,17+17` and 18, the oxidation of 1 g of compound 10 in DMSO
or MeCN was carried out. A mixture of isomeric diols 17 : 17` (5 : 2, 0.85 g, 72%) and
compound 18 (0.09 g, 9%) was obtained when using DMSO. Urea 16 (0.31 g, 55%) was
synthesized in MeCN.
Scheme 6 Photooxygenation of imidazolinone 10a
Apparently, the unexpected formation of compound 18 under the UV irradiation can be
explained by the formation of a short-living intermediate 10 `a, which is then oxidized by singlet
oxygen (Scheme 7).
Scheme 7 The proposed mechanism of the formation of compound 18.
Comparative absorption-fluorescent studies of samples 9 and 10a have shown that
compound 18 is the final photoproduct (Fig. 4, Table 1).
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Fig. 4 Absorption spectra (curves 1-3) (solid) and fluorescence spectra upon excitation with light
with a wavelength of 312 nm (curve 4), 310 nm (curve 5) and 331 nm (curve 6) (dash dot dot) of
compound 18 (curves 3,6) and of the photoproducts of samples 9 (curves 1,4) and 10a (curves
2,5) in MeCN.
In turn, the compound 18 undergoes irreversible transformations into a photoproduct
absorbing in the spectral field 400-450 nm (Fig. 5). This is evidenced by a decrease in the
intensity of the absorption and fluorescence bands of the compound 18 and the appearance of
absorption bands (Fig. 5, curves 5, 6) and fluorescence (Fig. 5, curves 7.8) of the photoproduct.
Fig. 5 Absorption spectra (curves 1,2,5,6), fluorescence spectra (3,4,7,8) upon excitation with
light with a wavelength 331 nm (3,4) and 429 nm (7,8) of compound 18 in MeCN before
irradiation (curves 1,3,5,7), upon an increase in exposure under UV light (curve 2,4,6,8). The
working solution concentration is C = 4x10-5 М. The cell thickness is 10 mm.
Photoinduced spectrum changes were also observed for the isomer mixture 17+17`(ratio
100 : 6.8) in MeCN (Fig. 6). The mixture of compounds 17+17` in MeCN is characterized by an
absorption spectrum with a maximum at 258 nm and a shoulder around 300-350 nm, as well as a
fluorescence spectrum with maxima at 320 and 422 nm. After UV irradiation, a new band with a
maximum at 335 nm appears in the absorption spectrum, while the intensity of the fluorescence
band increases. One can see from Fig. 6 that UV irradiation resulted not only in absorption
spectrum changes but also in photoinduced changes in the fluorescence excitation spectra and an
11

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increase in fluorescence intensity at 423 nm. The intensity of the second short-wave fluorescence
band remained invariable.
Fig. 6 Absorption spectra (curves 1,2) (solid), fluorescence excitation spectra measured at a
wavelength of 424 nm (curves 5,6) (short dash) and fluorescence spectra with excitation by light
with a wavelength of 258 nm (curve 3) and 261 nm (curve 4) (dash dot) for a mixture of
compounds 17+17` (ratio 100 : 6.8) in MeCN before (curves 1,3,5) and after UV irradiation
(curves 2,4,6). The working solution concentration is C = 4x10-4 М. The cell thickness is 10 mm.
The inset shows a magnified part of the absorption spectra.
Isomer 17 isolated from the mixture and synthesized by a reported procedure10 is
characterized by only one absorption band with a maximum at 258 nm and only one fluorescence
band at 315 nm (Fig. 7). The fluorescence excitation spectrum indicates that the observed
fluorescence is due only to the compound that absorbs at 258 nm, i.e., isomer 17 in the 17+17`
mixture is photochemically stable, since the absorption and fluorescence spectra remain almost
unchanged under UV irradiation. The photochemical transformations of this mixture are due to
the second component, 17`. However, the observed photochemical transformations with
photoinduced changes in the absorption and fluorescence spectra cannot be due to the formation
of a photoproduct with urea 17 structure (Table 1). Like in the case of compounds 9 and 10a,
insignificant changes were observed only in the visible spectral range (Fig. 7, inset).
Fig. 7 Absorption spectra (curves 1,2,3) (solid), fluorescence excitation spectra measured at a
wavelength of 315 nm (curves 6,7) (short dash), and fluorescence spectra with excitation with a
12

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wavelength of 258 nm (curves 4,5) (dash dot) of isolated compound 17 in MeCN before (curves
1,4,6) and in 30 min (curve 2) or 60 min (curves 3,5,7) of UV irradiation. The working solution
concentration is C = 4x10-4 М. The cell thickness is 10 mm.
X-Ray structural investigation
Molecules 14, 16 and cocrystal 9 were studied by X-ray diffraction. Experimental details and
crystallographic data are provided in Supporting Information.
The geometry of molecule 14 in crystal (Fig. 8) is very close to that in similar
imidazotriazines.12-14 The conformation of five-membered heterocyclic ring is close to an
envelope with deviation of atom C(1) by 0.176 Å, whereas the conformation of six-membered
ring is a distorted boat with atoms N(1) and N(3) deviating from the average plane C(1)-C(2)-
N(2)-C(3) by 0.345 and 0.590 Å, respectively. Nitrogen atoms N(1), N(2), N(3) and N(5) are
piramidalized with sum of CNN, CNC and CNH angles equal to 352.92, 357.18, 324.15 and
355.31°, respectively. The mutual disposition of the phenyl substituents is a cisoid one with the
torsion angle C(5)C(1)C(3)C(11) of 8.71(15)° that lead to a shortened intramolecular contact
C(5)···C(11) [2.858(2) Å]. Molecules of 14 in crystal are connected in centrosymmetric
homodimers via N(1)–H(1N)···O(1) bonds [N···O 2.8886(15) Å; NHO 172.5(18)°], which in
turn are assembled into infinite chains via N(3)–H(3N)···O(2) bonds [N···O 2.9100(16) Å; NHO
156.3(16)°].
Compound 16 crystallizes in C2/c space group, the molecule is symmetric with atoms
O(1) and C(1) located on a twofold axis. Atom N(1) is perfectly planar with sum of angles equal
to 360°. The torsion O(1)-C(1)···C(2)-O(2) equal to 78.66(16)° lead to a screwed conformation
of the central molecular fragment.
Crystal 9 was obtained by crystallization from glacial acetic acid. Despite the absence of
optical centers, the structure crystallizes in the chiral space group P212121. The structure 9
contains both molecules 10a and 11 in ratio 1:1 and is therefore an example of a binary
molecular complex, or a co-crystal in modern terminology. The molecules are connected with
each other via a bifurcated hydrogen bond of medium strength with slightly different distances
O(1)···O(2) and O(1)···O(3) [2.654(3) and 2.706(3) Å] and angles OHO close to 180° [179(4)º
and 173(4)º with atom H normalized to 0.993 Å] (Fig. 9). Geometry of the component 10a is
almost unaffected by cocrystallization, bond lengths and angles don’t actually differ from those
observed in the crystal of the pure compound (CSD refcode PEDLAN).7 The most significant
difference is the elongation of the C=O bond of the carbonyl group due to the formation of two
H-bonds (from 1.2358(16) to 1.259(3) Å). The NO2 group in 11 is rotated by 78.4° relative to the
plane of the cycle due to steric effects which is typical for ortho-substituted phenols, the
13

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distances between atom O(2) and atoms of NO2 group are shortened [2.588(3), 2.888(4) and
3.226(3) Å for N(3)···O(2), O(4)···O(2) and O(5)···O(2), respectively]. Intermolecular
interactions in co-crystal 9 other than H-bonds are non-directional and are represented by
numerous С–H···O, С–H···π and H···H contacts. Molecules form alternating layers in the
direction of the crystallographic c axis.
Fig. 8 General view of molecules 14 (left) and 16 (right) in crystal in thermal ellipsoid
representation (p=50%). Hydrogen atoms connected to carbon atoms are omitted for clarity.
Fig. 9 General view of cocrystal 9 in thermal ellipsoid representation (p=50%). Hydrogen atoms
connected to carbon atoms are omitted for clarity.
14

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Conclusion
The novel transformations of 3-alkylthio-5,7-dimethyl-4a,7a-diphenyl-4a,5,7,7a-tetrahydro-1H-
imidazo[4,5-e]-1,2,4-triazin-6(4H)-ones 6 and 8 under treatment of sterically hindered 1,2-
benzoquinones (3,5-di-tert-butyl-1,2-benzoquinone
1
and 4,6-di-tert-butyl-3-nitro-1,2-
benzoquinone 2) were studied and 5,7-di-tert-butyl-1,3-dimethyl-3a,9a-diphenyl-3,3a-dihydro-
1H-benzo[5,6][1,4]dioxino[2,3-d]imidazol-2(9aH)-one 13 and complex 9 of 4,6-di-tert-butyl-3-
nitrobenzene-1,2-diol with 1,3-dimethyl-4,5-diphenyl-1H-imidazol-2(3H)-one 10a were
prepared. Novel products of photooxygenation of imidazolinone 10a involving singlet oxygen
under UV irradiation, i.e. isomeric 1,3-dimethyl-4,5-diphenylimidazolidin-2-ones 17, 17`, and
compound 18, were found. Photochemical transformations of compounds 9,10a,16-18 were
investigated by the spectral-kinetic method for the first time. Data on the absorption and
fluorescence properties of synthesized compounds and their photoproducts were obtained. It was
also showed that compounds 17 and 17` exhibit different photochemical properties. Major
isomer 17 is photochemically stable while minor isomer 17’ is photochemically unstable
compound. Pathway for the formation of compounds 13 and 9 and for the photochemical
transformations of compound 10a involving singlet oxygen were proposed.
Experimental section
1
13
The H NMR and C NMR spectra were recorded on Bruker AM300 (300.13 MHz and 75.5
MHz, respectively) and Bruker DRX500 (500.13 MHz and 125.76 MHz, respectively)
spectrometers using DMSO-d6 as solvent. High resolution mass spectra (HRMS) were measured
on a Bruker micrOTOF II instrument using electrospray ionization (ESI).
The spectrophotometric and kinetic measurements were performed on spectrophotometer
«CARY 50bio» (Varian) in 2- or 10-mm thick quartz cells. Luminescent characteristics were
measured on the spectrofluorimeter «Cary Eclipse» (Varian) in 10-mm thick fluorimetric quartz
cell. The voltage on the fluorimeter photomultiplier was Е=600 V. The slit width of the
monochromator was 5 nm when spectra of fluorescence and fluorescence excitation were
measured. Photochemical transformations were carried out using xenon lamp included in an LC-
4 radiation unit (Hamamatsu) at a medium radiation power through colour glass filter UFS-1
(~51.2 W/m2 in the 235-400 nm range). Solutions of samples 9,10a,16-18 were prepared in
MeCN (99.8%, anhydrous, «Sigma-Aldrich») and C6H14 («Reakhim»). The solution
concentrations were С=4 x 10-5 М and С=2 х 10-4 М. The solutions were treated in an ultrasonic
bath «Sapphire» for 10 min.
The oxidation reactions were carried out by using UV lamp VL-6.C (254 nm). Progress
of the oxidation reaction (Scheme 4) was monitored using TLC sheets “Silufol UV254”. The
solvent system was CHCl3:MeCN – 5:1.
15

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Melting points were determined in open glass capillaries on a Gallenkamp (Sanyo)
melting point apparatus.
Starting compounds 1,2 were synthesized according to the known procedures.8,15 3,5-Di-
tert-butyl-1,2-benzoquinone 1 was prepared from pyrocatechol, tert- butyl alcohol and NaNO2.15
3-Nitro-4,6-di-tert-butyl-benzoquinone-1,2 2 was obtained under treatment of 2,4,6-tri-tert-
butylphenol with 60% nitric acid.8 (Imidazotriazin-3-ylthio)acetic acid 6 was prepared by the
reaction of bromoacetic acid with imidazotriazine 12 in ethanol.16 Syntheses of imidazotriazines
12 and 15 were carried out via an α-ureidoalkylation of thiosemicarbazide or semicarbazide with
1,3-dimethyl-4,5-dihydroxy-4,5-diphenylimidazolidin-2-one 17,12,13 obtained by the reaction of
benzil with 1,3-dimethylurea.10
Melting points and 1H NMR spectral data of compounds 1,15 2,8 6,16 10a,6 12,12 15,13 16,5 17 and
17+17`10 are consistent with literature values.
Compound (10): white solid; m.p. 186-189 °C (185-187 °C)6; 1H NMR (DMSO-d6), : 3.09 (s, 6
H, Me), 7.20 – 7.43 (s, 10 H, Ph).
Reactions of compounds 6, 8 and 12 with benzoquinones 1 and 2 were performed in
АсОН. Photooxygenation of imidazolinone 10a was carried out in DMSO and MeCN.
Synthesis
of
5,7-dimethyl-3-methylthio-4a,7a-diphenyl-4a,5,7,7a-tetrahydro-1H-
imidazo[4,5-e]-1,2,4-triazin-6(4H)-one (8) and 2,5,7-trimethyl-4a,7a-diphenyltetrahydro-
1H-imidazo[4,5-e]-1,2,4-triazine-3,6(2H,4H)-dione (14). Iodomethane (1 mL, 0.012 mol) was
added dropwise to a suspension of 5,7-dimethyl-4a,7a-diphenyl-3-thioxoperhydroimidazo[4,5-
e]-1,2,4-triazin-6-one (12) (2.1 g, 0.006 mol) and AcONa (0.5 g, 0.006 mol) in methanol (20
mL). Reaction mixture was stirred at 20 °С for 3 h. Suspension dissolved, then a new precipitate
was formed. The precipitate was filtered off, washed with methanol and dried to give compound
8. The filtrate obtained after isolation of compounds 8 was left at room temperature until the
crystals of the product 14 were precipitated. They were collected by filtration and dried in air.
1
Compound (8): Yield: 2 g, 91%; white solid; m.p. 252-254 °C (МеОН); H NMR (DMSO-d6,
300 MHz):  2.62 (s, 3Н, SМе), 2.64 (s, 6Н, NМе), 6.81, 6.84 (both s, 1Н, Ph), 7.12-7.17 (m,
8Н, Ph), 8.06, 10.34 (both br.s, 1Н, NH). 13C NMR (DMSO-d6, 75.5 MHz):  14.3 (SMe), 25.6,
26.2 (NMe), 83.6, 83.7 (Ph-C-C-Ph), 126.6, 127.7, 128.0, 128.67, 128.71 (CH(Ph)), 133.2, 133.9
(C(Ph)), 157.7, 158.3 (C=O, C=N). HRMS-ESI (m/z): calcd for C19H22N5OS [M+H]+: 368.1540,
found 368.1531.
1
Compound (14): Yield: 42 mg, 2%; colorless crystals; m.p. 274-276 °C (МеОН); H NMR
(DMSO-d6, 300 MHz):  2.57 (s, 3Н, NМе), 2.62 (s, 3Н, NМе), 2.97 (s, 3Н, NМе), 6.83 (s, 1Н,
HN-N), 7.01 (br. s, 10Н, 2Ph), 7.77 (s, 1Н, NH). 13C NMR (DMSO-d6, 75.5 MHz):  25.6, 26.2,
16

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35.3 (NMe), 83.4, 85.4 (Ph-C-C-Ph), 126.5, 127.4, 127.4, 127.5, 127.8 (CH(Ph)), 135.6, 137.1
(C(Ph)), 158.8, 160.2 (C=O). HRMS-ESI (m/z): calcd for C19H21N5OS [M+H]+: 368.1540, found
368.1533.
Synthesis of complex (9).
Method A: Solution of 2 (0.53 g, 2 mmol) and 6 (0.82 g , 2 mmol) in 10 mL of АсОН was
heated at 70 ºС and stirred for 2 h. Then reaction mixture was cooled to room temperature. The
precipitate 9 formed was filtered off, washed with АcOH and H2O and dried in air.
Method B: Solution of 2 (0.53 g, 2 mmol) and 8 (0.73 g, 2 mmol) in 10 ml of АсОН was stirred
at 20 ºС for 2 days. The precipitate 9 formed was filtered off, washed with АcOH and H2O (100
mL) and dried in air. Yield: 0.78 g, 74% (method 1), 1.01 g, 95% (method 2); white solid; m.p.
1
210-213° C (АсОН); H NMR (DMSO-d6, 300 MHz):  1.26 (s, 9Н, But(4)), 1.35 (s, 9Н,
But(6)), 3.10 (s, 6Н, NMe), 6.88 (s, 1Н, C(5)Н), 7.23-7.37 (m, 10Н, Ph), 8.72 (s, 1Н, OН(1)),
9.22 (s, 1Н, OH(2)). 13C NMR (DMSO-d6, 75.5 MHz):  28.6 (NMe), 29.3, 30.7 (Me(But)),
34.9, 35.0 (C(But)), 116.0, 120.5, 128.0, 128.6, 128.9, 129.5, 130.0, 137.8, 138.3, 141.4, 144.2
(C(Ar), C=C), 153.0 (C=O). IR (KBr), , cm-1: 3252 (OH), 2955, 1639 (C=O), 1605, 1577,
1527, 1493, 1478, 1403, 1371, 1307, 1237. Anal. calcd. for C31H37N3O5: C, 70.03; H, 7.01; N,
7.90; found: C, 70.12; H, 7.04; N, 7.85.
Synthesis
of
5,7-di-tert-butyl-1,3-dimethyl-3a,9a-diphenyl-3,3a-dihydro-1H-
benzo[5,6][1,4]dioxino[2,3-d]imidazol-2(9aH)-one (13). Solution of 1 (0.44 g, 2 mmol) and 8
(0.73 g, 2 mmol) in 10 ml of АсОН was heated at 70 ºС and stirred for 2 h. After cooling to
room temperature H2O (100 mL) was added. The precipitate formed was filtered off, washed
with H2O (100 mL) and dried in air. The precipitate was dissolved in a minimum amount of
CHCl3. The solution in chloroform was dried over anhydrous Na2SO4 for 4 h and passed through
a chromatographic column with SiO2 (eluent CHCl3). Colorless fraction (Rf = 0.6) was collected
and the solvent was removed in vacuo. Compound 13 was obtained.
1
Compound (13): Yield: 0.24 g, 25%; white solid, m.p. 239-241 °C; H NMR (CDCl3, 300
MHz):  1.34 (s, 9Н, But(5)), 1.44 (s, 9Н, But(7)), 2.78 (s, 3Н, MeN), 2.86 (s, 3Н, MeN), 6.96
13
(d, J = 2.3 Hz, 1H, CH), 7.03-7.15 (m, 11Н, 2Ph+CH). C NMR (CDCl3, 75.5 MHz):  25.9,
27.6 (NMe), 30.5, 31.5 (Me(But)), 34.6, 35.1 (C(But)), 96.0, 97.3 (Ph-C-C-Ph), 113.0, 118.2,
127.4, 127.7, 127.9, 128.4, 128.5, 135.41, 135.45, 137.5, 139.9, 141.4, 144.5 (C(Ar)), 159.2
(C=O). HRMS-ESI (m/z): calcd for C31H36N2O3Na [M+Na]+: 507.2624, found 507.2618.
Synthesis of N,N'-carbonylbis(N-methylbenzamide) (16). The solution of 1,3-dimethyl-4,5-
diphenyl-1H-imidazol-2(3H)-one 10a (0.50 g, 0.0019 mol) in MeCN (35 mL) was irradiated UV
for 12 h at 45°C. Then the reaction mixture was evaporated to solid and CHCl3 (10 mL) were
17

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added to the reaction mixture. Formed precipitate of 17 : 17` (100 : 6.8; 0.05 g) was filtered off.
The filtrate was evaporated and crude product 16 was purified by column chromatography
1
CHCl3:MeCN – 5:1. Yield: 0.31 g, 55 %; colorless crystals; m.p. 149-150 °C (149 °C)5; H
NMR (DMSO-d6, 300 MHz):  2.94 (s, 6H, Me), 7.38 (d, J = 7.4 Hz, 2H, Ph), 7.50 (t, J = 7.5
Hz, 2H, Ph), 7.60 (t, J = 7.3 Hz, 2H, Ph).
Synthesis of 4,5-dihydroxy-1,3-dimethyl-4,5-diphenylimidazolidin-2-ones (17+17`) and 1,3-
dimethyl-1H-phenanthro[9,10-d]imidazol-2(3H)-one (18). The suspension of 1,3-dimethyl-
4,5-diphenyl-1H-imidazol-2(3H)-one 10a (1.00 g, 0.00379 mol) in DMSO (15 mL) was
irradiated UV for 12 h at 45°C. Then the H2O (30 mL) and CHCl3 (20 mL) were added to the
reaction mixture. Formed precipitate (0.85 g) of (17+17`) was filtered off. The organic layer was
separated from filtrate and evaporated to beige solid. Compound 18 was separated from beige
solid by column chromatography CHCl3:MeCN – 5:1.
1
Sample 17+17`. Yield: 0.85 g, 72 % (17 : 17` - 5 : 2); white solid; H NMR (DMSO-d6, 300
MHz):  2.60 (s, 12H, Me(17+17`)), 5.97 (s, 2H, OH(17`)), 6.56 (s, 2H, OH(17)), 6.85 – 6.96
(m, 4H, Ph(17)),6.98 – 7.07 (m, 6H, Ph(17)),7.15 – 7.24 (m, 4H, Ph(17`)),7.29 – 7.38 (m, 6H,
Ph(17`)).
Compound 18. Yield: 0.09 g, 9 %; yellow needles; m.p. 248-250 °C, 1H NMR (DMSO-d6, 500
MHz):  3.84 (s, 6H, Me), 7.59 (t, J = 7.5 Hz, 2H, CH), 7.67 (t, J = 7.5 Hz, 2H, CH), 8.43 (d, J =
8.3 Hz, 2H, CH), 8.88 (d, J = 8.3 Hz, 2H, CH). 13C NMR (DMSO-d6, 125 MHz):  31.33,
120.28, 120.77, 121.53, 124.01, 124.44, 126.97, 127.05, 154.94. IC 1685 (C=O). HRMS-ESI
(m/z): calcd for C17H14N2ONa [M + Na]+: 285.0998, found: 285.0999.
X-ray diffraction analysis. Data collection for sample 16 was performed on a Bruker
APEX DUO diffractometer, equipped with Apex II CCD detector, and for samples 9 and 14 on a
Bruker SMART 1000 diffractometer, equipped with Bruker SMART 1000 CCD detector (both
operating with graphite-monochromated MoKα radiation, λ=0.71073 Å). Frames were integrated
using the Bruker SAINT software package17 by a narrow-frame algorithm. A semiempirical
absorption correction was applied with the SADABS18 program using the intensity data of
equivalent reflections. The structures were solved with direct methods and refined by the full-
matrix least-squares technique against F2hkl in anisotropic approximation with SHELX19 software
package. Hydrogen atoms of NH groups in 14 and OH groups in 9 were found from difference
Fourier synthesis and refined isotropically. All other hydrogen atoms were placed in calculated
positions and refined in riding model with Uiso(H) = 1.5Ueq(Cm) and 1.2Ueq(Ci), where Ueq(Cm)
and Ueq(Ci) are respectively the equivalent thermal parameters of the methyl carbon and other
18

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carbon atoms to which corresponding H atoms are bonded. Detailed crystallographic information
is given in Table 3. Crystallographic data have been deposited to the Cambridge
Crystallographic Data Centre, CCDC numbers 1574578-1574580; copies of the data can be
obtained free of charge via http://www.ccdc.cam.ac.uk/data_request/cif.
Table 3 Crystallographic data for crystals 9, 14 and 16.
9
C31H37N3O5
531.63
100
14
C19H21N5O2
351.41
100
16
C17H16N2O3
296.32
120
Empirical formula
Formula weight
T, K
Crystal system
Orthorhombic
P212121
4 / 1
Monoclinic
P21/c
Monoclinic
C2/c
Space group
Z / Z'
4 / 1
4 / 0.5
a, Å
9.860(2)
10.524(2)
26.911(5)
90
16.4618(16)
6.9012(7)
15.7448(16)
90
13.9890(15)
7.3378(8)
16.1193(18)
90
b, Å
c, Å
α, °
β, °
90
105.334(2)
90
115.478(2)
90
90
, °
V, Å3
dcalc, g cm-3
2792.5(10)
1.265
1725.0(3)
1.353
1493.7(3)
1.318
μ, cm-1
0.86
0.92
0.92
F(000)
1136
744
624
2θmax, °
60
60
61
Refls collected
Independent refls [Rint]
Observed refls [I>2σ(I)]
R1
31880
15669
9931
7985 [0.0383]
5692
4959 [0.0279]
3647
2292 [0.0431]
1708
0.0570
0.1430
0.949
0.0503
0.1243
1.035
0.0466
0.1211
1.035
wR2
Goodness-of-fit on F2
Residual density, e Å-3 (dmin/dmax
)
-0.205/0.415
-0.276/0.389
-0.190/0.361
Acknowledgment
The authors would like to thank Dr. Yu.V. Nelyubina (INEOS RAS) for technical assistance.
19

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X-ray diffraction data were collected at the Center for molecular composition studies of
INEOS RAS. High resolution mass spectra were recorded in the Department of Structural
Studies of N.D. Zelinsky Institute of Organic Chemistry, Moscow.
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21