Reactions of donor-acceptor cyclopropanes or benzylidenemalonate with benzyl azide by generating gallium trichloride 1,2-zwitterionic complexes

Article abstract of DOI:10.1007/s11172-019-2584-2

The reactions of 1,2-zwitterionic complexes, generated from 2-arylcyclopropane-1,1-dicarboxylates (ACDC) or benzylidenemalonate and gallium trichloride, with benzyl azide proceeds as a formal [3+2] cycloaddition to form dihydro-1,2,3-triazoles. The latter, when the reaction mixture is treated with 10% aqueous HCl, undergo retrocyclization with elimination of diazomalonate. The reaction of ACDC, benzyl azide, and GaCl₃ with simultaneous mixing of the reagents leads to the interception of the 1,3-zwitterion, with this stage being accompanied by both the cyclization to substituted 1,2,3-triazinine and the elimination of a nitrogen molecule to form 3,4-dihydro-2H-1,2-oxazine structure, which after acid hydrolysis gives substituted 3-hydroxypyrrolidin-2-one.

Full text of DOI:10.1007/s11172-019-2584-2

Russian Chemical Bulletin, International Edition, Vol. 68, No. 8, pp. 1504—1509, August, 2019
1504
Reactions of donor-acceptor cyclopropanes
or benzylidenemalonate with benzyl azide by generating
gallium trichloride 1,2-zwitterionic complexes
I. A. Borisova, A. V. Tarasova, K. V. Potapov, R. A. Novikov, and Yu. V. Tomilov
N. D. Zelinsky Institute of Organic Chemistry, Russian Academy of Sciences,
47 Leninsky prosp., 119991 Moscow, Russian Federation.
E-mail: tom@ioc.ac.ru
The reactions of 1,2-zwitterionic complexes, generated from 2-arylcyclopropane-1,1-dicar-
boxylates (ACDC) or benzylidenemalonate and gallium trichloride, with benzyl azide proceeds
as a formal [3+2] cycloaddition to form dihydro-1,2,3-triazoles. The latter, when the reaction
mixture is treated with 10% aqueous HCl, undergo retrocyclization with elimination of di-
azomalonate. The reaction of ACDC, benzyl azide, and GaCl3 with simultaneous mixing of
the reagents leads to the interception of the 1,3-zwitterion, with this stage being accompanied
by both the cyclization to substituted 1,2,3-triazinine and the elimination of a nitrogen molecule
to form 3,4-dihydro-2H-1,2-oxazine structure, which after acid hydrolysis gives substituted
3-hydroxypyrrolidin-2-one.
Key words: donor-acceptor cyclopropanes, 1,2-zwitterionic complexes, gallium trichloride,
benzyl azide, N-heterocyclic compounds.
Scheme 1
The last decade is characterized by the intensive
development of donor-acceptor cyclopropane (DAC)
chemistry.1 New approaches to their synthesis are being
elaborated, new types of reactivity are being studied,
while DACs themselves are increasingly used in total
syntheses of natural compounds. One of the interesting
and important processes in DAC chemistry is the reaction
of the generated from them 1,3-zwitterions with various
substrates, which proceeds with the formation of six-
membered carbo- and heterocycles.2—6 A comparatively
recent paper7 was devoted to the formal [3+3] cycload-
dition of 2-arylcyclopropane-1,1-dicarboxylates (ACDC,
1) to azides in the presence of Lewis acids. The effect of
various Lewis acids (SnCl4, FeCl3, AlCl3 and TiCl4) on
the formation of substituted 1,2,3-triazinines 2 was stud-
ied (Scheme 1).
Carrying out the reaction in the presence of TiCl4
provides the best results in terms of the synthesis of tri-
azinine derivatives 2 from ACDC and azides. The result-
ing triazinines upon heating undergo dediazotization to
form azetidines 3 in moderate yields. The latter, in turn,
can serve as convenient synthons in the design of bio-
logically active compounds.7 When azide anion acts as a
nucleophile, for example, with the use of sodium azide8
or trimethylsilyl azide9 and CF3CO2H, ACDC undergoes
nucleophilic ring opening to form the corresponding
azido diesters 4 (see Scheme 1). This type of reactions
accompanied by the three-membered ring opening at the
substituted 1,2-bond is a traditional process of the trans-
formation of ACDC treated with various nucleophilic
agents.8‒11
This work belongs to a series of publications5,12‒15
devoted to the study of the transformations of 1,2-zwit-
terionic intermediates generated from ACDC by treatment
with GaCl3. The generation of gallium 1,2-zwitterionic
complexes 5 (Scheme 2) allows one to carry out reactions
with various substrates, which were studied in the reactions
of interception of primary 1,3-zwitterionic intermediates,
but in other directions and with the formation of a differ-
ent composition of products. In this regard, it was interest-
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1504—1509, August, 2019.
1066-5285/19/6808-1504 © 2019 Springer Science+Business Media, Inc.

Addition of azide to zwitterion Ga-complex
Russ. Chem. Bull., Int. Ed., Vol. 68, No. 8, August, 2019
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Table 1. Yields of dihydrotriazole 6a and diazomalonate 7 in
the reaction of complex 5a, obtained by the reaction of 1a
with GaCl3, with benzyl azide depending on the reaction
conditions (solvent CH2Cl2, the reaction mixture was worked-
up with 10% aqueous HCl)
ing to study the reactivity of gallium complexes 5 in the
reactions with azides.
Scheme 2
Ratio
1а : BnN3
Reaction conditions
Product
yield (%)a
T/°C
t/min
6а
7
1 : 2
1 : 1
1 : 2
1 : 2
1 : 2
1 : 2
20
20
15
15
20
60
10
20
19b
16
36b
29
40
20b
20
39b
37
20
83c
–20
15
22
40
37
a The yields of dihydro-1,2,3-triazole 6a and diazomalonate
7 were calculated from the 1H NMR spectra with a weighed
sample of 1,4-dinitrobenzene as an internal standard.
b Isolated yield.
Results and Discussion
Using the simplest ACDC 1a as an example, we stud-
ied the reaction of 1,2-zwitterionic complex 5a with
benzyl azide under various conditions (Scheme 3, Table
1). In all cases, after the reaction mixtures were treated
with 8—10% aqueous HCl at room temperature, the ex-
pected [3+2] cycloaddition product, dihydro-1,2,3-tri-
azole 6a, was formed in only 15—23% yield, while di-
azomalonate 7 turned out to be the main reaction product
(see Table 1). It was logical to suppose that the appearance
of diazomalonate could be a consequence of the decom-
position of adduct 6a, which at a certain stage could un-
dergo partial retrocyclization16 to form diazomalonate 7
c In 1,2-dichloroethane.
and imine 8a (see Scheme 3). In fact, 1H NMR spectros-
copy showed the presence of phenylacetaldehyde as one
of the products of acid hydrolysis of imine 8a in the
worked-up reaction mixture.
We carried out additional experiments to confirm the
formation of diazomalonate 7 from dihydro-1,2,3-tri-
azole 6a. Thus, practically no changes were observed
when compound 6a (in CH2Cl2 at 20 °C) was treated
with 10% aqueous HCl or kept in contact with anhydrous
GaCl3. However, if a solution of dihydro-1,2,3-triazole
and GaCl3 in dichloromethane is treated with 10%
aqueous HCl, the appearance of diazomalonate 7 is
clearly detected by 1H NMR spectroscopy. Since it is
obvious that the decomposition of dihydro-1,2,3-triazole
occurs at the stage of the reaction mixture quenching,
the work-up should be carried out at a lowered tem-
perature and preceded by the decomposition of gallium
trichloride with methanol.
Scheme 3
Scheme 4
Ar = 4-ClC6H4 (b), 4-FC6H4 (c), 4-O2NC6H4 (d), 4-MeC6H4 (e)
Reagents and conditions: i. CH2Cl2, 0—5 °C, 15 min.

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Borisova et al.
Table 2. Yields of dihydrotriazoles 6a—e and diazomalonate
7 in the reaction of complexes 5, obtained by the reaction
of DAC 1a—e with GaCl3, with benzyl azide depending on
the work-up conditions of the reaction mixture
with methanol, while their yield sharply decreased with
the simultaneous appearance of diazomalonate 7 after
treatment of the reaction mixture with 10% aqueous HCl
(Scheme 4, Table 2).
We carried out a similar process between benzyl azide
and benzylidenemalonate 9, which also can form a
1,2-zwitterionic complex with GaCl3 10 with somewhat
different structure (see Ref. 18). In this case, the [3+2]
cycloaddition proceeded more efficiently, giving the cor-
responding dihydrotriazole 11 in high yield (Scheme 5),
which, unlike 5-benzyl-substituted dihydrotriazoles 6a—e,
turned out to be a very stable compound and did not un-
dergo fragmentation to diazomalonate even when the
reaction mixture was treated with 10% aqueous HCl.
The methods for obtaining compounds of similar
structure directly from arylidenemalonates and aryl azides
described in the literature, despite the good yields of di-
hydrotriazoles, usually required prolonged reflux in a
suitable solvent (up to 30 days).19 The use of gallium tri-
chloride significantly accelerates the formation of dihydro-
1,2,3-triazole 11 (~ 10 min) and increases their yields.
Thus, the advantages of the developed process are the short
reaction time, the moderate temperature, and the simple
procedure for isolation of the target compound.
Entry
Starting
DAC
Work-up
Product
conditionsa
yield (%)b
6a—e
7
1
2
3
4
5
6
7
8
9
1a
1b
1c
1d
1e
1b
1c
1d
1e
A
A
A
A
A
B
B
B
B
53
54
56
59
57
16
12
4
—
—
—
—
—
36
38
72
40
11
a Work-up conditions: А, MeOH, 0 °C; B, 10% HCl, 20 °C,
10—15 min.
b
Reaction conditions: the ratio ACDC/GaCl3 = 1 : 1,
5—20 °C, 15—60 min,17 5/BnN3 = 1 : 2, 20 °C, 10—15 min.
In fact, the reaction between 1,2-zwitterionic inter-
mediate 5a and benzyl azide at 20 °C and the subsequent
treatment with methanol at 0 °C gives dihydro-1,2,3-
triazole 6a in up to 53% yield practically in the absence
of diazomalonate 7.
Next, we studied the reaction of benzyl azide with
1,2-zwitterionic complexes 5 (see Refs 12 and 13) obtained
from ACDC 1b—e containing both acceptor (Cl, F, NO2)
and donor (Me) substituents in the benzene ring. It turned
out that in this case, the formal [3+2] cycloaddition also
proceeded quite efficiently and the corresponding dihydro-
1,2,3-triazoles 6b—e were obtained in moderate yields
after the low-temperature work-up of the reaction mixture
As noted earlier,7 the reaction of ACDC with aryl
azides in the presence of Lewis acids, in particular, TiCl4,
leads to 1,2,3-triazinines 2 (see Scheme 1). We carried out
the reaction of ACDC 1a and benzyl azide in the presence
of GaCl3 by simultaneous mixing of the reactants, i.e.
when ACDC still mainly acts as a 1,3-zwitterion.
Unfortunately, the yield of triazinine 2a under these con-
ditions turned out to be only about 12% due to the paral-
lel processes of dimerization of ACDC 1a. However, after
the work-up of the reaction mixture, we isolated another
product, previously undescribed 3-hydroxypyrrolidin-2-
one 12 as approximately equal mixture of diastereomers
Scheme 5
Reagents and conditions: i. CH2Cl2, 10 min; ii. Ref. 19: 24—720 h, 25—100 °C, 50—67% yields.

Addition of azide to zwitterion Ga-complex
Russ. Chem. Bull., Int. Ed., Vol. 68, No. 8, August, 2019
1507
Scheme 6
Conditions: i. 1,2-dichloroethane, 83 °C, 1 h.
(Scheme 6). Most likely, the same intermediate 13 (as a
complex with GaCl3) is the source of the formation of
both triazinine 2a and pyrrolidinone 12. This intermediate
either cyclizes to triazinine 2a (path a) or loses a nitrogen
molecule, giving 3,4-dihydro-2H-1,2-oxazine 14 (path
b). The latter undergoes hydrolysis during the work-up of
the reaction mixture to pyrrolidinone 12, which is a mix-
ture of two diastereomers in approximately equal propor-
tions (see Scheme 6).
complex derived from benzylidenemalonate and GaCl3
gives a stable 5-phenyl-substituted triazoline in good yield,
which does not undergo fragmentation to diazomalonate.
If the reaction of ACDC 1a and benzyl azide in the pres-
ence of GaCl3 is carried out by simultaneous mixing of
the reactants, in which the ACDC acts as a 1,3-zwitterion,
the process proceeds with both the preservation of all three
nitrogen atoms (cyclization to 1,2,3-triazinine) and the
elimination of a nitrogen molecule to form in the end
substituted 3-hydroxypyrrolidin-2-one.
In the 1H NMR spectrum, the signals of the cyclic
CH2 fragment of one of the isomers appear as a doublet
at δ 2.58, whereas in the other isomer they are far apart
(δ 2.18 and 2.90) and appear as a doublet of doublets with
a geminal spin-spin coupling constant of 13.9 Hz.
Compounds with pyrrolidinone structure can be con-
venient synthons in the design of biologically active sub-
stances. Despite the low yield of pyrrolidinone 12, the
presented synthesis method allows one to obtain it from
cyclopropane 1a and benzyl azide in one experimental
stage (the reaction conditions were not optimized).
In conclusion, using the model 2-arylcyclopropane-
1,1-dicarboxylates 1, we studied the reaction of gallium
trichloride 1,2-zwitterionic complexes with benzyl azide
as a 1,3-dipole, which leads to dihydro-1,2,3-triazoles.
The latter, during the work-up of the reaction mixture
with hydrochloric acid, undergo partial retrocyclization
to form diazomalonate and the corresponding benzyl
imines. At the same time, the use of the 1,2-zwitterionic
Experimental
1Н, 13С, and 15N NMR spectra were recorded on Bruker
AMX-III 400 (400.1, 100.6, and 40.5 MHz, respectively) and
Bruker Avance-III HD 300 spectrometers (300.1, 75.5, and
30.4 MHz, respectively) for solutions in CDCl3 containing 0.05%
of Me4Si as an internal standard. The assignment of signals and
the determination of the isomeric composition of the compounds
were carried out using homo- and heteronuclear 2D correlation
spectra 1H—1H COSY and NOESY, 1H—13C edited-HSQC and
HMBC, as well as 1H—15N HMBC. IR spectra were recorded
on a Bruker ALPHA-T instrument in a solution of CHCl3 in KBr
cells (d = 1.0 mm). Mass spectra (electron impact (EI), 70 eV)
were recorded on a Finnigan MAT INCOS-50 instrument. High-
resolution mass spectra (electrospray ionization (ESI)) were
recorded using a Bruker micro TOFII mass spectrometer. Thin
layer chromatography was performed on Merck Silica gel 60 F254
plates. Silica gel 60 (0.040—0.063 mm) from Merck was used for

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Borisova et al.
preparative chromatography. Anhydrous GaCl3 used in the work
was purchased from Aldrich handled in a dry argon atmosphere.
The starting cyclopropanes 1a—e,1 benzyl azide,20 and benzyl-
idenemalonate21 were synthesized according to the described
procedures. Solvents with a purity of at least 99.5% were used
without additional purification. Dichloromethane for the work
with GaCl3 was first dried over granulated KOH and then distilled
over P2O5 under dry argon.
Synthesis of substituted dimethyl 1,5-dihydro-4Н-1,2,3-
triazole-4,4-dicarboxylates 6а—e (general method). Gallium
chloride (89 mg, 0.5 mmol) was added to a solution of 2-arylcy-
clopropane-1,1-dicarboxylate 1 (0.5 mmol) in anhydrous dichlo-
romethane (1.5 mL) at 5 °C and the mixture was stirred at
5—25 °C for 10—75 min depending on the nature of the sub-
stituents in 1a—e.17 Then a solution of benzyl azide (133 mg,
1 mmol) in CH2Cl2 (1.5 mL) was added and the mixture was
stirred at 20 °C for 10—15 min. Then, the reaction mixture was
treated with methanol at 0 °C, the organic layer was separated
and dried with anhydrous MgSO4. The product was isolated by
column chromatography on SiO2, eluting first with benzene and
then with a mixture of benzene—EtOAc, 40 : 1. The yields of
dihydro-1,2,3-triazoles 6a—e are given in Table 2. When the
reaction mixture was quenched with 10% aqueous HCl, the
isolation procedure was similar, but in this case diazomalonate
was the main product.
Dimethyl 1,5-dibenzyl-1,5-dihydro-4Н-1,2,3-triazole-4,4-
dicarboxylate (6а). The yield was 97.1 mg (53%), a colorless oil.
IR (solution in СHCl3), ν/cm–1: 1739 (C=O). 1H NMR (CDCl3),
δ: 2.70 (dd, 1 Н, CH2CH, J = 14.1 Hz, J = 9.3 Hz); 3.06 (dd,
1 Н, CH2CH, J = 14.1 Hz, J = 4.1 Hz); 3.78 and 3.85 (both s,
3 H each, 2 ОCH3); 4.01 and 5.08 (both d, 1 H each, CH2N,
2J = 15.4 Hz); 4.25 (dd, 1 Н, CH, J = 9.3 Hz, J = 4.1 Hz); 6.71
(dd, 2 Н, 2 СНAr, J = 7.4 Hz, J = 1.4 Hz); 7.18—7.36 (m, 8 H,
8 СНAr). 13C NMR (CDCl3), δ: 35.5 (CH2), 52.9 and 53.6
(2 OCH3), 53.1 (NCH2), 60.8 (C(5)), 92.7 (C(4)) 127.0 and
127.7 (2 p-CH), 128.1, 128.4, 128.6 and 129.1 (o-CH and m-CH
of two benzene rings), 134.1 and 136.7 (2 ipso-C), 165.6 and
166.6 (2 COO). HRMS: found: m/z 368.1615; C20H21N3О4;
calculated [М]: M + H, 368.1605.
J = 4.4 Hz); 6.76—6.84 (m, 2 Н, 2 СНAr); 6.97—7.09 (m, 3 H,
3 СНAr); 7.11—7.20 (m, 2 H, 2 СНAr); 7.21—7.31 (m, 2 H,
2 СНAr). 13C NMR (CDCl3), δ: 34.4 (CH2), 53.1 and 53.7
(2 OCH3), 53.2 (NCH2), 61.0 (C(5)), 92.7 (C(4)), 115.6 (d,
m-CH, 2JC,F = 21.5 Hz), 128.1 (o-CH, p-CH), 128.6 (m-CH),
3
130.0 and 134.2 (2 ipso-C), 130.7 (d, o-CH, JC,F = 8.1 Hz);
161.8 (d, CF, 1JC,F = 240 Hz), 165.6 and 166.5 (2 COO). HRMS:
found: m/z 386.1508; C20H20FN3О4; calculated [М]: M + H,
386.1511.
Dimethyl 1-benzyl-5-(4-nitrobenzyl)-1,5-dihydro-4Н-1,2,3-
triazole-4,4-dicarboxylate (6d). The yield was 121.6 mg (59%),
a colorless oil. IR (solution in СHCl3), ν/cm–1: 1738 (C=O),
1525 (NO2). 1H NMR (CDCl3), δ: 2.75 (dd, 1 Н, CH2CH,
J = 14.4 Hz, J = 9.1 Hz); 3.08 (dd, 1 Н, CH2CH, J = 14.4 Hz,
J = 4.2 Hz); 3.77 and 3.87 (both s, 3 H each, 2 ОCH3); 4.03 and
5.09 (both d, 1 H each, CH2N, 2J = 15.8 Hz); 4.31 (dd, 1 Н,
CH, J = 9.1 Hz, J = 4.2 Hz); 6.77—6.85 (m, 2 Н, 2 СНAr);
7.16—7.37 (m, 7 H, 7 СНAr). 13C NMR (CDCl3), δ: 34.7 (CH2),
53.0 and 53.8 (2 ОCH3), 53.3 (NCH2), 60.8 (C(5)), 92.8 (C(4)),
123.8 (m-CH), 127.8, 128.8 and 129.9 (CHAr) 128.3 (p-CH),
134.0 and 144.2 (2 ipso-C), 147.1 (CNO2), 165.5 and 166.4
(2 COO). HRMS: found: m/z 413.1436; C20H20N4О6; calcu-
lated [М]: M + H, 413.1456.
Dimethyl 1-benzyl-5-(4-methylbenzyl)-1,5-dihydro-4Н-
1,2,3-triazole-4,4-dicarboxylate (6e). The yield was 151.9 mg
(57%), a colorless oil. IR (solution in СHCl3), ν/cm–1: 1740
(C=O). 1H NMR (CDCl3), δ: 2.37 (s, 3 Н, СН3); 2.65 (dd,
1 Н, CH2CH, J = 14.1 Hz, J = 9.4 Hz); 3.00 (dd, 1 Н, CH2CH,
J = 14.1 Hz, J = 4.1 Hz); 3.76 and 3.82 (both s, 3 H each,
2 ОCH3); 4.00 and 5.05 (both d, 1 H each, CH2N, 2J = 15.3 Hz);
4.22 (dd, 1 Н, CH, J = 9.4 Hz, J = 4.1 Hz); 6.71—6.75 (m, 2 Н,
2 СНAr); 7.07 and 7.13 (both br.d, 2 H each, С6Н4, 3J = 7.9 Hz);
7.18—7.25 (m, 3 Н, 3 СНAr). 13C NMR (CDCl3), δ: 21.1 (CH3),
34.9 (CH2), 53.0 and 53.6 (both OCH3), 53.1 (NCH2), 61.0
(C(5)), 92.7 (C(4)), 127.9 (p-CH), 128.3, 128.4, 129.2 and 129.4
(o-CH and m-CH of two benzene rings), 133.7, 134.4 and 136.8
(2 ipso-C and p-C), 165.7 and 166.6 (2 COO). HRMS: found:
m/z 382.1766; C21H23N3О4; calculated [М]: M + H, 382.1761.
Dimethyl 1-benzyl-5-phenyl-1,5-dihydro-4Н-1,2,3-triazole-
4,4-dicarboxylate (11). The reaction was carried out according
to the general procedure, starting from dimethyl benzylidene-
malonate 9 (0.11 g, 0.5 mmol) in CH2Cl2, sequentially adding
GaCl3 (88 mg, 0.5 mmol) and benzyl azide (133 mg, 1.0 mmol).
The reaction mixture was refluxed for 10 min, cooled, and
treated with 10% aqueous HCl to pH 3. The organic layer was
separated, the aqueous layer was extracted with CH2Cl2 (2×10 mL),
and the organic extracts were dried without anhydrous MgSO4.
The solvent was removed in vacuo, the product was isolated by
column chromatography on SiO2, eluting first with benzene, then
with benzene—EtOAc, 20: 1. Compound 11 (150 mg, 85%) was
obtained as a colorless oil. Its spectral characteristics agree with
the literature data.19
Dimethyl 1-benzyl-5-(4-chlorobenzyl)-1,5-dihydro-4Н-1,2,3-
triazole-4,4-dicarboxylate (6b). The yield was 108.5 mg (54%),
a colorless oil. IR (solution in СHCl3), ν/cm–1: 1740 (C=O).
1H NMR (CDCl3), δ: 2.71 (dd, 1 Н, CH2CH, J = 14.2 Hz,
J = 8.8 Hz); 3.00 (dd, 1 Н, CH2CH, J = 14.2 Hz, J = 4.5 Hz);
3.78 and 3.85 (both s, 3 H each, 2 ОCH3); 4.08 and 5.09 (both
2
d, 1 H each, CH2N, J = 15.5 Hz); 4.23 (dd, 1 Н, CH, J = 8.8
Hz, J = 4.5 Hz); 6.75—6.83 (m, 2 Н, 2 СНAr); 7.09 (d, 2 Н,
2 СНAr, J = 8.2 Hz); 7.21—7.34 (m, 5 H, 5 СНAr). 13C NMR
(CDCl3), δ: 34.5 (CH2), 53.1 and 53.7 (2 OCH3), 53.2 (NCH2),
60.9 (C(5)), 92.7 (C(4)), 128.0, 128.6, 128.8 and 130.5 (o-CH
and m-CH of two benzene rings), 128.1 (p-CH), 133.1, 134.2
and 135.2 (2 ipso-C and p-C), 165.6 and 166.6 (COO). HRMS:
found: m/z 402.1230; C20H20СlN3О4; calculated [М]: M + H,
402.1215.
Methyl 1-benzyl-3-hydroxy-2-oxo-5-phenylpyrrolidine-3-
carboxylate (12). Gallium chloride (44.2 mg, 0.25 mmol) was
added to a solution of 2-phenylcyclopropane-1,1-dicarboxylate
1a (58.6 mg, 0.25 mmol) and benzyl azide (66.5 mg, 0.5 mmol)
in 1.2-dichloroethane (3 mL). The mixture was heated at 83 °C
for 1 h, cooled, and treated with 10% aqueous HCl to pH 3. The
organic layer was separated, the aqueous layer was extracted with
CH2Cl2 (2×10 mL), the organic extracts were dried with anhy-
drous MgSO4. The solvent was removed in vacuo. The residue
Dimethyl 1-benzyl-5-(4-fluorobenzyl)-1,5-dihydro-4Н-1,2,3-
triazole-4,4-dicarboxylate (6c). The yield was 108.0 mg (56%),
a colorless oil. IR (solution in СHCl3), ν/cm–1: 1738 (C=O).
1H NMR (CDCl3), δ: 2.71 (dd, 1 Н, CH2CH, J = 14.3 Hz,
J = 9.0 Hz); 3.02 (dd, 1 Н, CH2CH, J = 14.3 Hz, J = 4.4 Hz);
3.78 and 3.85 (both s, 3 Н each, 2 ОCH3); 4.06 and 5.10 (both d,
1 H each, CH2N, 2J = 15.5 Hz); 4.22 (dd, 1 Н, CH, J = 9.0 Hz,

Addition of azide to zwitterion Ga-complex
Russ. Chem. Bull., Int. Ed., Vol. 68, No. 8, August, 2019
1509
was separated by column chromatography on SiO2 (eluent:
benzene—EtOAc, 20 : 1). The isolated products were 1,2,3-tri-
azinine 2a (11.0 mg, 12%) with the spectral characteristics cor-
responding to those described in the literature7 and pyrrolidinone
12 (16.2 mg, 20%, a mixture of two diastereomers in a ratio
of ~ 1 : 1), a colorless oil. IR (solution in СHCl3), ν/cm-1: 1715
(NС=О), 1745 (C=O). 1H NMR (CDCl3), δ: 2.18 (dd, 1 Н,
Нa(4), 2J = 13.9 Hz, 3J = 7.3 Hz); 2.58 (d, 2 Н, Н2C(4), 3J =
= 7.5 Hz); 2.90 (dd, 1 Н, Нb(4), 2J = 13.9 Hz, 3J = 7.6 Hz); 3.54
and 3.56 (both d, 1 Н each, Нa (from NCH2), 2J = 15.0 Hz);
3.82 and 3.93 (both s, 3 H each, ОCH3); 4.00 (br.s, 2 Н, OH);
4.46 (dd, 1 Н, Н(5), 3J = 7.3 Hz, 3J = 7.6 Hz); 4.58 (t, 1 Н,
H(5), J = 7.5 Hz); 5.07 and 5.11 (both d, 1 Н each, Нb (from
NCH2), 2J = 15.0 Hz); 6.99—7.45 (m, 20 H, 2 Ph of two isomers).
13C NMR (CDCl3), δ: 40.6 and 40.7 (C(4)), 44.8 and 45.1
(NCH2), 53.3 and 53.6 (OCH3), 58.4 and 58.9 (C(5)), 78.1 and
78.5 (C(3)), 127.6 and 127.8 (p-C of two isomers), 128.4, 128.6,
128.7 and 129.1 (o- and m-C of two isomers), 135.1, 135.2, 138.8
and 139.0 (ipso- C of two isomers), 171.1 and 171.5 (NC=O),
172.10 and 172.13 (COO). HRMS: found: m/z 326.1374;
C19H19NО4; calculated [М]: M + H, 326.1384.
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This work was financially supported by the Russian
Foundation for Basic Research (Project No. 18-33-01000
(mol_а)).
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Received March 26, 2019;
in revised form May 17, 2019;
accepted May 21, 2019