New method for the synthesis and the mechanism of formation of 1,2-di- and 1,2,3-trialkyldiaziridines

Article abstract of DOI:10.1007/s11172-006-0548-9

A new simple approach to the synthesis of 1,2-di-and 1,2,3- trialkyldiaziridines has been developed based on direct chlorination of a mixture of the corresponding aldehyde and an excess of primary aliphatic amine in water. The mechanism of this reaction is proposed and confirmed by quantum chemical calculations at the density functional theory level.

Full text of DOI:10.1007/s11172-006-0548-9

2056
Russian Chemical Bulletin, International Edition, Vol. 55, No. 11, pp. 2056—2060, November, 2006
New method for the synthesis and the mechanism of formation
of 1,2ꢀdiꢀ and 1,2,3ꢀtrialkyldiaziridines*
a
b†
a
aꢀ
V. V. Kuznetsov, V. B. Ovchinnikova, V. P. Ananikov, and N. N. Makhova
aN. D. Zelinsky Institute of Organic Chemistry, Russian Academy of Sciences,
4
7 Leninsky prosp., 119991 Moscow, Russian Federation.
Fax: +7 (495) 135 5328. Eꢀmail: mnn@ioc.ac.ru
b
Russian Scientific Center "Applied Chemistry,"
1
4 Dobrolyubova prosp., St. Petersburg, Russian Federation
A new simple approach to the synthesis of 1,2ꢀdiꢀ and 1,2,3ꢀtrialkyldiaziridines has been
developed based on direct chlorination of a mixture of the corresponding aldehyde and an
excess of primary aliphatic amine in water. The mechanism of this reaction is proposed and
confirmed by quantum chemical calculations at the density functional theory level.
Key words: 1,2ꢀdiꢀ and 1,2,3ꢀtrialkyldiaziridines, direct chlorination, aldehydes, primary
aliphatic amines, mechanism, quantum chemical calculations, B3LYP, PCM.
In recent years, we have concerned ourselves with the
development of optimal approaches to the synthesis of
and one mole of aldehyde. The required pH was achieved
by adding HCl or HBr (Scheme 1).
differently substituted diaziridines.1
a—c
These studies were
stimulated by the use of the resulting diaziridines in ring
expansion reactions with electrophilic reagents (ketenes,
isocyanates, or isothiocyanates), which led to the develꢀ
opment of new simple methods for the preparation of both
Scheme 1
2
a—e
known and previously unknown heterocyclic systems.
Diaziridines are among a few objects containing nitrogen
atoms configurationally stable under usual conditions and,
consequently, these compounds are used for studying the
X = Cl, Br
3
,4
stereochemistry of nitrogen. In addition, they are of
interest as psychotropic active compounds.5 Hence, a
search for new more efficient methods for the synthesis of
diaziridines remains an important problem. The simplest
methods for the synthesis of 1,2ꢀdiꢀ and 1,2,3ꢀtrialkylꢀ
diaziridines 1 and 2 are based on the reaction of carbonyl
compounds, primary aliphatic amines, and Nꢀhaloalkylꢀ
amines (aminating agents), which are prepared by the
reactions of hypohalites with the corresponding amines.
In the course of optimization of this method for the synꢀ
thesis of diaziridines 1 and 2 in an aqueous medium, it
was demonstrated that the maximum yield can be achieved
at particular pH (pHopt), which is shifted to less alkaline
values as the –I effect of the substituents in carbonyl
The aim of the present study was to further optimize
procedures for the synthesis of 1,2ꢀdiꢀ and 1,2,3ꢀtrialkylꢀ
diaziridines 1 and 2 by searching for new simpler apꢀ
proaches to the formation of pHopt without the use of
alkali metal hypohalites, which are unstable under stanꢀ
dard conditions.
—7
Earlier, it has been found1a,b that pH in the syntheꢀ
opt
1
2
sis of 1,2ꢀdiethyldiaziridine 1a (R = H, R = Et) and
1
1
,2ꢀdiethylꢀ3ꢀmethyldiaziridine 2a is 11.2—12.1 and
1.6—11.9, respectively. We expected that pHopt could be
efficiently achieved by passing the calculated amount of
gaseous chlorine through a mixture of a carbonyl comꢀ
pound and an excess of primary aliphatic amine. Initially,
we examined the synthesis of 1,2ꢀdiethyldiaziridine 1a
from formaldehyde and ethylamine. Formaldehyde and
ethylamine were mixed as 30% aqueous solutions at
1
a,b
compounds increases and pKBH
+
of amines decreases.
Diaziridines 1 and 2 containing identical substituents at
the nitrogen atoms were synthesized by the reaction of
NaOCl or NaOBr with a mixture of two moles of amine
1
5—20 °C, and then the calculated amount of chlorine
was bubbled through the reaction mixture at 0—5 °C. The
theoretically required EtNH : CH O : Cl molar ratio
*
Dedicated to Academician O. M. Nefedov on the occasion of
2
2
2
his 75th birthday.
Deceased.
(4 : 1 : 1) was used in first experiments. However, pHopt
was not achieved under these conditions. The use of stanꢀ
†
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 1978—1982, November, 2006.
066ꢀ5285/06/5511ꢀ2056 © 2006 Springer Science+Business Media, Inc.
1

Synthesis and mechanism of diaziridines formation
Russ.Chem.Bull., Int.Ed., Vol. 55, No. 11, November, 2006 2057
dard buffer solutions, such as a phosphate buffer (pH 9.13)
or a sodium tetraborate solution (borax, pH 9.7), instead
of water also did not provide the formation of pHopt. After
the addition of the reagents to the buffer solutions, pH of
the reaction mixture was close to the optimal value. Howꢀ
ever, pH was shifted to more acidic values as chlorine was
passed through the reaction mixture. The addition of one
Table 2. Yields and selected physicochemical characteristics of
diaziridines 1 and 2
Comꢀ
pound
Yielda
(%)
B.p./°C
(p/Torr)
B.p./°C
(p/Torr)b
96—97 (760)8
1
1
1c
1d
2
2
2
a
b
94/62
93/60
91/66
90/70
92/66
94/68
81/61
96—98 (760)
48—49 (760)
51—52 (15)
96—98 (10)
76—78 (760)
43—45 (20)
113—115 (10)
8,9
49 (760)
37.5—38.0 (11)1
c,8
8
mole of EtNH •HCl appeared to be more efficient. In
2
this case, pHopt was close to the required value in the
course of the reaction; however, it did shift to more acidic
values, which did not allow us to achieve the maximum
yield.
34—36 (0.015)
76—78 (760)
1
c,10
a
b
c
1
a,11
43—45 (20)
c
—
The necessary pHopt (11.7—11.5) in the final reaction
step was achieved only with the use of the molar ratio
EtNH : CH O : Cl = 10 : 1 : 1. Under these conditions,
a
Data from iodometric titration/the yield of the isolated product.
b Literature data.
c
The compound was not described in the literature.
2
2
2
the yield of diaziridine 1a was 94% (iodometric titration
of the reaction mixture, Table 1). A further variation of
the EtNH : CH O : Cl ratio (8 : 1 : 1, 12 : 1 : 1, or
Scheme 2
2
2
2
1
4 : 1 : 1) led to a decrease in the yield of diaziridine 1a
(
84, 87 and 77%, respectively).
Therefore, using the synthesis of 1,2ꢀdiethyldiaziridine
1
a as an example, we developed a new simple procedure
for the preparation of 1,2ꢀdialkyldiaziridines 1 based on
direct chlorination of a mixture of formaldehyde and priꢀ
mary aliphatic amine, which gave the final product in
virtually quantitative yield. These conditions appeared to
be suitable for the synthesis of other 1,2ꢀdialkyldiaziridines
Conditions: 1) 2 h at 0—5 °C; 2) 24 h at 20 °C.
R1
R2
Comꢀ
pound
1a
1b
H
H
H
H
Me
Et
Et
Me
Pr
Bu
Et
1
as well as of 1,2,3ꢀtrialkyldiaziridines 2. In the latter
1c
1d
2a
case, the reaction was carried out with both monoꢀ
aldehydes (acetaldehyde and propionaldehyde) and diꢀ
aldehydes (glutaraldehyde) (see Scheme 2). In all cases,
the yields of the final products estimated by iodometric
titration of the reaction mixture were higher than 90%.
After isolation, the yields of the products were 60—70%
because of losses during distillation of diaziridines, which
have low boiling points (Table 2).
2b
Me
2c
Me
The new method for the synthesis of 1,2ꢀdiethylꢀ
diaziridine 1a was tested on a pilot apparatus at the Rusꢀ
sian Scientific Center "Applied Chemistry," which enꢀ
abled the optimization of the reaction conditions: the
temperature is 0—5 °C, the passing rate of chlorine is
Table 1. Dependence of pH of the reaction mixture and the yield
of 1,2ꢀdiethyldiaziridine 1a on the reaction conditions of direct
chlorination of a mixture of the starting compounds with gasꢀ
eous chlorine in water
–
1
5
2
—6 L h , the starting concentration of ethylamine is
0%, the concentration of the final product is 6.5—8%,
and the yield estimated by iodometric titration is 90—96%.
In addition to the formation of pHopt, the high yields of
diaziridines 1 and 2 prepared according to this method
are achieved due to the fact that carbonyl compounds are
not oxidized with chlorine in the presence of excess amine.
The new method has the following advantages over the
рНb
Yield of 1ac
Reagent
ratioa
(%)
A
B
C
D
4
4
1
: 1 : 1
: 1 : 1d
0 : 1 : 1
13.4
11.6 11.1
9.95
10.6
63
69
94
8
11.75 10.6 10.6
13.4
known method based on the use of NaOCl for this purꢀ
12.4 11.7 11.7—11.5
pose: 1) the step of the preparation of NaOCl, which
requires complex apparatus (particularly, under the conꢀ
ditions of industrial production), is excluded, 2) the conꢀ
centration of the final diaziridine in the reaction mixture
increases by a factor of two (6—8% instead of 3—4%),
which substantially simplifies the isolation, and 3) the
yield of the final diaziridine increases by ~30%.
a
b
The EtNH : CH O : Cl molar ratio.
pH of the reaction mixture before chlorination (A), after passꢀ
2
2
2
ing of 50% (B) and 100% of Cl (C), and after storage at 0—5 °C
2
for 1 h (D).
c
Iodometric titration.
An additive of EtNH •HCl (0.25 mol).
d
2

2058
Russ.Chem.Bull., Int.Ed., Vol. 55, No. 11, November, 2006
Kuznetsov et al.
Earlier,1a,b it has been hypothesized that the role of
Table 3. Relative energies and the free energy changes for
stationary points 1b, 3, 3´, and 4—7 calculated at the
PCMꢀB3LYP//6ꢀ31G* level
pH in the synthesis of diaziridines is to provide the most
favorable conditions for each particular aldehyde—amine
pair in protonation of the product of their reaction, viz.,
αꢀaminocarbinol 3, and its subsequent dehydration givꢀ
ing rise to carbeniumꢀiminium cation 4. Cation 4 reacts
with Nꢀhaloalkylamine to form intermediate 5, which is
transformed into final diaziridines 1 or 2 (Scheme 3,
Stationary
points
∆E
∆G
kcal mol–1
1
3
3
4
6
7
5
b
–30.04
0.00
–4.91
3.47
9.75
–6.14
–8.82
–35.67
0.00
path a) through the intramolecular S i reaction. (In
N
´
–3.66
–9.02
–4.34
–4.82
–8.06
Scheme 3, the possible pathways of the formation of
diaziridines 1 and 2 are exemplified by the synthesis of
,2ꢀdimethyldiaziridine 1b from formaldehyde, methylꢀ
1
amine, and Nꢀchloromethylamine. The latter can be preꢀ
pared either in advance or directly in the course of the
reaction by passing the required amount of chlorine
through a mixture of formaldehyde and methylamine.)
However, it is not improbable that carbeniumꢀiminium
cation 4 can be transformed into intermediate 5 accordꢀ
ing to alternative schemes, in particular, through the
formation of imine 6 followed by its reaction with
Nꢀchloromethylamine (Scheme 3, path b) or through
the formation of aminal 7 followed by its exchange chloꢀ
rination in the reaction with Nꢀchloromethylamine
viz., 1,2ꢀdimethyldiaziridine 1b, according to Scheme 3.
The quantum chemical calculations were carried out by
density functional theory (B3LYP) taking into account
the solvent effect with the use of the PCM model. The
calculated relative energies (∆E) and the free energy
changes (∆G) for stationary points 1b, 3, 3´, and 4—7 are
given in Table 3. Since the free energy change most fully
describes the nature of processes in the system, we chose
these parameters for the detailed discussion. The optiꢀ
mized molecular structures of the compounds under study
are shown in Fig. 1. The potential energy surface is preꢀ
sented in Fig. 2.
(
Scheme 3, path c).
Scheme 3
In the calculations, we failed to find the stationary
point corresponding to the product of protonation of 3,
viz., cation 3´, because the geometry optimization led to
elimination of the water molecule giving rise to strucꢀ
ture 4. The estimated energy for 3´ presented in Table 3
and Fig. 2 was obtained by the geometry optimization
with the fixed C—O bond length of 1.4 Å. Since the
formation of cationoid species 4 is accompanied by a
–
1
substantial gain in energy (9.02 kcal mol ), dehydration
of compound 3 is presumably barrierless. The further
transformation of carbeniumꢀiminium cation 4 can proꢀ
ceed either directly through intermediate 5 (Scheme 3,
path a) or through intermediate imine 6 (path b) or, alterꢀ
natively, through gemꢀdiamine 7 (path c). As can be seen
from Table 3 and Fig. 2, the results of calculations conꢀ
firmed the mechanism of the transformation of carꢀ
beniumꢀiminium cation 4 into diaziridine 1b through inꢀ
termediate 5, which we have proposed earlier. It appeared
that the path a involving the direct reaction of cation 4
with Nꢀchloromethylamine is the energetically most faꢀ
vorable pathway of this transformation in an aqueous soꢀ
lution. The reaction can also proceed through the path b
or c, although these pathways are less probable because
the energies of possible intermediates 6 and 7 are higher
than that of intermediate 4 (see Fig. 2). The formation of
reaction product 1b is accompanied by a larger gain in
To reveal the optimal pathway of the transformation
of carbeniumꢀiminium ion 4 into diaziridines 1 and 2, we
performed quantum chemical calculations for the syntheꢀ
sis of the simplest representative of 1,2ꢀdialkyldiaziridines,
–
1
energy (35.67 kcal mol ), which provides the required
driving force for the transformation.

Synthesis and mechanism of diaziridines formation
Russ.Chem.Bull., Int.Ed., Vol. 55, No. 11, November, 2006 2059
C
C
N
C
N
C
N
N
O
O
C
C
C
C
3
3´
4
6
C
C
C
C
N
N
O
N
N
C
C
N
N
C
C
C
1
b
7
5
Fig. 1. Molecular structures of 1b, 3, 3´, 4—7, and those optimized at the B3LYP//6ꢀ31G* level.
∆
G/kcal mol–1
amine (3.0 mol) in water (100 mL) at 15—20 °C. Then the
reaction mixture was cooled to 0—5 °C, and gaseous chlorine
(0.33 mol) was bubbled through the resulting solution with
vigorous stirring at this temperature for 1 h (the amount of the
added chlorine was monitored based on the weight increase).
The reaction mixture was stirred at 0—5 °C for 2 h and kept at
room temperature for 24 h. Then the yield of the resulting
diaziridine was determined by iodometric titration, the reaction
mixture was saturated with KOH, the upper layer was separated,
and the unconsumed amine was distilled off. After titration, the
latter was used in the subsequent experiments, and the correꢀ
sponding diaziridine was twice distilled over solid K CO The
3
6
7
3
´
–
4.34
–4.82
0
4
5
–
3.66
–
8.06
–
9.02
1
b
–
35.67
Fig. 2. Potential energy surface calculated at the
PCMꢀB3LYP//6ꢀ31G* level.
2
3.
characteristics of the reaction products were identical to those
of the authentic structures described in the literature (see
Table 2).
Experimental
3
,3´ꢀPropylenebis(1,2ꢀdimethyldiaziridine) (2c). A 25% aqueꢀ
ous glutaraldehyde solution (56 mL, 0.14 mol) was added
dropwise to a 30% aqueous methylamine solution (360 mL,
2.8 mol) at 5—20 °C. Then the reaction was performed accordꢀ
ing to the general procedure for the synthesis of diaziridines 1
and 2, including distillation of methylamine. The yield of
diaziridine 2c determined by iodometric titration was 81%. Then
the reaction mixture was saturated with NaCl, extracted with
chloroform (4×100 mL), and dried with K CO . The solvent
The IR spectra were recorded on a URꢀ20 spectrometer in
thin films of the individual compounds. The H NMR spectra
1
were measured on a Bruker WMꢀ250 spectrometer (250 MHz).
13
The C NMR spectra were recorded on a Bruker AMꢀ300 specꢀ
trometer (75.5 MHz); the chemical shifts are given on the δ scale
relative to the signal of Me Si. Thinꢀlayer chromatography was
4
carried out on Silufol UVꢀ254 plates; spots were visualized using
iodine vapor and independently by spraying with a solution of
diphenylamine in acetone followed by heating of the plates.
Synthesis of 1,2ꢀdialkylꢀ and 1,2,3ꢀtrialkyldiaziridines 1 and 2
by direct chlorination of a mixture of aldehyde and primary aliꢀ
phatic amine (general procedure). The corresponding aldehyde
2
3
was evaporated. The residue was twice distilled and the fraction
with b.p. 113—115 °C (10 Torr) was collected. The yield was
15.7 g (0.085 mol), 61%, nD20 1.4900. H NMR (CDCl ), δ:
1
3
1.59 (m, 6 H, (CH ) ); 2.32 (m, 14 H, 4 Me + 2 CHcycl).
2
3
13
1
C NMR (CDCl ), δ: 23.5 (t, CH —CH —CH , J = 115.6 Hz);
25.8 (t, CH —CH —CH , J = 128.1 Hz); 38.8 (d, Me—N,
2 2 2
3
2
2
2
1
(
0.3 mol) was added dropwise to a solution of primary aliphatic

2060
Russ.Chem.Bull., Int.Ed., Vol. 55, No. 11, November, 2006
Kuznetsov et al.
1
1
J = 134.8 Hz); 47.5 (d, Me—N, J = 134.8 Hz); 65.8 (d, CHcycl,
J = 169.9 Hz). IR, ν/cm–1: 792, 1080, 1120, 1288, 1396, 1460,
5. R. G. Kostyanovsky, G. V. Shustov, and O. L. Nabiev,
Khim.ꢀfarm. Zh., 1986, 20, 671 [Pharm. Chem. J., 1986, 20,
(Engl. Transl.)].
1
2
924, 2988. Found (%): C, 58.45; H, 11.05; N, 30.10. C H N .
9 20 4
Calculated (%): C, 58.66; H, 10.94; N, 30.40.
Quantum chemical calculations. The geometry optimization
and energy calculations were carried out with the use of the
6. L. I. Khmel´nitskii, N. N. Makhova, O. V. Lebedev, L. V.
Epishina, and L. I. Suvorova, Tez. dokl. II s"ezda formatsevtov
Latv. SSR, 1984 [Abstr. of Papers, II Meeting of Pharmacists
of Latv. SSR, Riga, 1984 (in Russian)].
7. A. A. Prokopov, L. I. Kotlova, and A. S. Berlyand,
Khim.ꢀfarm. Zh., 2005, 39, 8 [Pharm. Chem. J., 2005, 39,
(Engl. Transl.)].
8. R. Ohme, E. Schmitz, and P. Dolge, Chem. Ber., 1966,
99, 2104.
9. R. G. Kostyanovsky, V. A. Korneev, I. I. Chervin, V. N.
Voznesensky, Yu. V. Pusanovand, and P. Rademacher,
Mendeleev Commun., 1996, 106.
1
2—14
B3LYP hybrid functional
and the standard 6ꢀ31G* basis
1
5
set. The character of stationary points 1b, 3, 3´, and 4—7 was
controlled by calculating the eigenvectors of the matrix of secꢀ
ond derivatives of the energy (the absence of imaginary frequenꢀ
cies for intermediates). The thermodynamic functions were calꢀ
culated in terms of the harmonic oscillator—rigid rotator model.
The solvent effect was taken into account with the use of singleꢀ
point calculations in terms of the PCM model for modeling an
aqueous medium.6
—18
All calculations were carried out with
1
9
the use of the Gaussian 98 program package. The molecular
structures and vibrations were visualized with the use of the
MOLDEN graphics package.20
10. M. Komatsu, N. Nishikaze, M. Sakamoto, Y. Oshiro, and
T. Agawa, J. Org. Chem., 1974, 39, 3198.
11. B. Carbony, F. Tonnard, and R. Carrie, Bull. Soc. Chim. Fr.,
1
987, 525.
This study was financially supported by the Russian
Foundation for Basic Research (Project No. 04ꢀ03ꢀ
12. A. D. Becke, Phys. Rev. A, 1988, 38, 3098.
13. C. Lee, W. Yang, and R. G. Parr, Phys. Rev. B, 1988, 37, 785.
14. A. D. Becke, J. Chem. Phys., 1993, 98, 5648.
3
2799).
1
5. R. Ditchfield, W. J. Hehre, and J. A. Pople, J. Chem. Phys.,
971, 54, 724.
1
References
1
1
6. J. Tomasi and M. Persico, Chem. Rev., 1994, 94, 2027.
7. C. Amovilli, V. Barone, R. Cammi, E. Cances, M. Cossi,
B. Mennucci, and C. S. Pomelli, Adv. Quantum. Chem.,
1998, 32, 227.
1
. (a) V. V. Kuznetsov, N. N. Makhova, Yu. A. Strelenko, and
L. I. Khmel´nitskii, Izv. Akad. Nauk, Ser. Khim., 1991, 2861
Bull. Acad. Sci. USSR, Div. Chem. Sci., 1991, 40, 2496 (Engl.
[
18. C. J. Cramer and D. G. Truhlar, Chem. Rev., 1999, 99, 2161.
19. M. J. Frisch, G. W. Trucks, H. B. Schlegel, G. E. Scuseria,
M. A. Robb, J. R. Cheeseman, V. G. Zakrzewski, J. A.
Montgomery, R. E. Stratmann Jr., J. C. Burant, S. Dapprich,
J. M. Millam, A. D. Daniels, K. N. Kudin, M. C. Strain,
O. Farkas, J. Tomasi, V. Barone, M. Cossi, R. Cammi,
B. Mennucci, C. Pomelli, C. Adamo, S. Clifford,
J. Ochterski, G. A. Petersson, P. Y. Ayala, Q. Cui,
K. Morokuma, D. K. Malick, A. D. Rabuck,
K. Raghavachari, J. B. Foresman, J. Cioslowski, J. V. Ortiz,
B. B. Stefanov, G. Liu, A. Liashenko, P. Piskorz,
I. Komaromi, R. Gomperts, R. L. Martin, D. J. Fox,
T. Keith, M. A. AlꢀLaham, C. Y. Peng, A. Nanayakkara,
C. Gonzalez, M. Challacombe, P. M. W. Gill, B. Johnson,
W. Chen, M. W. Wong, J. L. Andres, C. Gonzalez,
M. HeadꢀGordon, E. S. Replogle, and J. A. Pople,
Gaussian 98, Gaussian: Pittsburgh, PA, 1998.
Transl.)]; (b) V. V. Kuznetsov, N. N. Makhova, and L. I.
Khmel´nitskii, Izv. Akad. Nauk, Ser. Khim., 1997, 1410 [Russ.
Chem. Bull., 1997, 46, 1354 (Engl. Transl.)]; (c) V. V.
Kuznetsov, N. N. Makhova, D. E. Dmitriev, and V. V.
Seregin, Mendeleev Commun., 2005, 116.
. (a) A. V. Shevtsov, V. Yu. Petukhova, Yu. A. Strelenko,
K. A. Lyssenko, I. V. Fedyanin, and N. N. Makhova,
Mendeleev Commun., 2003, 221; (b) A. V. Shevtsov, V. Yu.
Petukhova, Yu. A. Strelenko, and N. N. Makhova, Mendeleev
Commun., 2005, 29; (c) A. V. Shevtsov, V. Yu. Petukhova,
Yu. A. Strelenko, K. A. Lyssenko, N. N. Makhova, and V. A.
Tartakovskii, Izv. Akad. Nauk, Ser. Khim., 2005, 997 [Russ.
Chem. Bull., Int. Ed., 2005, 54, 1021]; (d) A. V. Shevtsov,
V. V. Kuznetsov, A. A. Kislukhin, V. Yu. Petukhova, Yu. A.
Strelenko, and N. N. Makhova, J. Het. Chem., 2006, 43,
2
8
81; (e) A. V. Shevtsov, V. V. Kuznetsov, S. I. Molotov,
K. A. Lyssenko, and N. N. Makhova, Izv. Akad. Nauk, Ser.
Khim., 2006, 534 [Russ. Chem. Bull., Int. Ed., 2006, 55, 554].
. A. Mannschreck, R. Radeglia, E. Grundemann, and
R. Ohme, Chem. Ber., 1967, 100, 1778.
. G. V. Shustov, A. B. Zolotoi, N. L. Zaichenko, O. A.
Dyachenko, L. O. Atovmyan, and R. G. Kostyanovsky,
Tetrahedron, 1984, 40, 2151.
20. G. Schaftenaar and J. H. Noordik, J. Comput.ꢀAided Mol.
Des., 2000, 14, 123.
3
4
Received September 15, 2006;
in revised form October 2, 2006