Unusual ring-chain tautomerism in bicyclo[4.2.0]octane derivatives

Article abstract of DOI:10.1016/j.tetlet.2011.04.013

A new type of ring-chain tautomerism, which consists of the reversible conversion of bicyclo[4.2.0]octane derivatives into trisubstituted enamines was found and studied by ¹H NMR spectroscopy. The starting materials were prepared by the stereos

Full text of DOI:10.1016/j.tetlet.2011.04.013

Tetrahedron Letters 52 (2011) 3029–3032
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Tetrahedron Letters
journal homepage: www.elsevier.com/locate/tetlet
Unusual ring-chain tautomerism in bicyclo[4.2.0]octane derivatives
Vladislav Yu. Korotaev a, Alexey Yu. Barkov a, Pavel A. Slepukhin b, Mikhail I. Kodess b,
Vyacheslav Ya. Sosnovskikh a,
⇑
a Department of Chemistry, Ural State University, pr. Lenina 51, 620083 Ekaterinburg, Russia
b Institute of Organic Synthesis, Ural Branch of the Russian Academy of Sciences, 620990 Ekaterinburg, Russia
a r t i c l e i n f o
a b s t r a c t
Article history:
A new type of ring-chain tautomerism, which consists of the reversible conversion of bicyclo[4.2.0]octane
derivatives into trisubstituted enamines was found and studied by 1H NMR spectroscopy. The starting
materials were prepared by the stereoselective reaction of (E)-3,3,3-trichloro-1-nitropropene with cyclo-
hexanone enamines.
Received 31 January 2011
Revised 23 March 2011
Accepted 1 April 2011
Available online 9 April 2011
Ó 2011 Elsevier Ltd. All rights reserved.
Keywords:
Cyclobutanes
Nitroalkenes
Enamines
Ring-chain tautomerism
1H NMR spectroscopy
Conjugated nitroolefins possess unique chemical reactivity in
both nucleophilic and cycloaddition reactions because of their
reactive double bond.1 As a result, partially fluorinated nitroal-
kenes have attracted attention as excellent building blocks for
the preparation of various RF-containing compounds.2 However,
to the best of our knowledge, very little information is available
on the reactivity of (E)-3,3,3-trichloro-1-nitropropene (1). There
have been only a few papers describing examples of the Diels–Al-
der reaction,3 1,3-dipolar cycloaddition,4 and Michael additions of
N- and O-nucleophiles.2e–g,5 Here we have examined the behaviour
of 1 in reactions with three cyclohexanone enamines, 2a–c with
the purpose of studying the structures and tautomeric properties
of the reaction products.
tautomeric equilibria of these compounds. Only one case of tauto-
meric equilibria between 1,2-oxazine N-oxides derived from amin-
ocycloalkenes and their corresponding trisubstituted enamines has
been reported.8 On the contrary, ring-opening of cyclobutane
derivatives to give nitroalkylated enamines is regarded as irrevers-
ible.9 This communication describes a new type of ring-chain tau-
tomerism in CCl3-containing bicyclo[4.2.0]octanes.
We have found that the reaction of CCl3-nitropropene 1 with
cyclohexanone enamines 2a–c in dry hexane for 15 min at 10–
15 °C, and for 0.5 h at room temperature results in the stereoselec-
tive formation of substituted bicyclo[4.2.0]octanes 3a–c, as the
products of kinetic control, in 61–76% yields.10 Notably, cyclobu-
tanes 3 contain four contiguous stereogenic centres, but only one
diastereomer could be observed by 1H NMR spectroscopy of the
crude products. The stereochemistry of 3b was confirmed unam-
biguously by X-ray crystal structure analysis (Fig. 1)11 and is con-
sistent with the literature data for related compounds.12 The
structures of 3a,c were firmly established by comparison of their
1H NMR spectra with those of 3b in C6D6, which showed signals
for the cyclobutane form only. The 1H NMR spectra of 3 exhibited
two downfield shifted signals assigned to H-7 (d 3.76–3.81,
dd, J = 9.8, 8.3 Hz) and H-8 (d 4.83–4.90, d, J = 8.3 Hz); the assign-
ment of all signals was achieved by using 2D HSQC and HMBC
experiments.
It is well known6 that the first step of the reaction of nitroal-
kenes with enamines involves the diastereoselective formation of
a new C–C bond in the resulting dipolar intermediate, the fate of
which depends on the nature of the reactants, and it may lead to
different products. The most common is a tri- or tetrasubstituted
nitroalkylated enamine whose formation derives from abstraction
of a proton by the carbanion. Alternatively, the ambident nitronate
anion can react with the iminium carbon atom producing a cyclic
compound, which can be either a cyclobutane (more rarely) or a
1,2-oxazine N-oxide (more frequently), as a result of a formal
[2+2] or [4+2] cycloaddition reaction, respectively.7 Very little is
known concerning the nature of the substituents on the ring-chain
When the reaction of nitroalkene 1 with enamines 2a,b was
performed in chloroform at ꢀ20 °C for 3 h, trisubstituted syn-en-
amines 4a,b were obtained in 48–53% yields. These compounds
can also be prepared from bicyclo[4.2.0]octanes 3a,b in chloroform
in 50–53% yields. Irrespective of the preparation method, enamines
⇑
Corresponding author. Fax: +7 343 261 59 78.
E-mail addresses: vyacheslav.sosnovskikh@usu.ru, sosn1951@mail.ru (V.Ya.
Sosnovskikh).
0040-4039/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2011.04.013

3030
V. Yu. Korotaev et al. / Tetrahedron Letters 52 (2011) 3029–3032
followed by monitoring the reaction by 1H NMR spectroscopy at
25 °C. The proportions of the ring (3) and isomeric chain forms (4
and 5) in the tautomeric equilibria were determined by integration
of the well-separated H-7 and H-8 (ring) and H-1 and H-2 (chain)
proton signals in the 1H NMR spectra.
In the case of 3a, the ratio 3a:4a = 9:1 was recorded (2 min)
after dissolving the crystals in CDCl3. After 40 min, a 1:1 mixture
of 3a and 4a was present, while after 3 h an equilibrium ratio of
1:4.5 was observed which remained unchanged for 24 h. Moreover,
when the progress of the reaction was monitored by 1H NMR spec-
troscopy over several weeks, we observed the appearance of a third
product, indicating that under these conditions, compounds 3a and
4a irreversibly isomerize via dipolar intermediate A into the
tetrasubstituted enamine 5a (4% in seven days and 24% in 40 days).
The predominant amount of 4a in the final reaction mixture is
due to the higher thermodynamic stability of the open form in
comparison to cyclobutane 3a. The same tautomeric mixture
(4a:3a = 82:18 after 5 h) was obtained when the reaction was car-
ried out on the pure syn-enamine 4a (Scheme 1).
These results are of particular interest because reversible for-
mation of a cyclobutane system from an acyclic enamine has not
been described so far, and this is the first report of ring-chain tau-
tomerism in cyclobutane derivatives. The ring-opening reaction is
probably catalysed by traces of acid present in the deuterated chlo-
roform. As would be expected, the nature of the solvent affects the
state of this equilibrium. For instance, the equilibrium between
tautomers 3a and 4a was almost completely shifted towards acy-
clic form 4a immediately after dissolution of 3a in CD3OD.
Analogously, a 1:3.5 equilibrium mixture 3b ¡ 4b was ob-
served for the morpholino derivatives. In this case, ring-chain tau-
tomerism was complicated by the appearance of tetrasubstituted
enamine 5b, while cyclobutane 3b and trisubstituted enamine 4b
slowly disappeared during the course of the reaction. After 3 h at
25 °C, a third resonance signal for each proton from 5b appeared
(2%) and continued to grow until a ratio of 3b:4b:5b = 16:40:44
(24 h) was observed. The irreversible stage 3b ¡ 4b ? 5b, which
caused the total shift of the ring-chain equilibrium towards the tet-
rasubstituted enamine 5b, was complete within 48 h and gave 5b
as the sole reaction product. A similar equilibrium mixture was at-
tained from the pure enamine 4b, the conversion of which into 5b
was slower (for comparison, 4b:3b:5b = 71:23:6 after 24 h).
As for the cyclobutane 3c, there was a marked difference in its
propensity towards ring-opening. 1H NMR studies of 3c in CDCl3
indicated that this compound was less stable and underwent more
rapid ring-opening to give the tri- and tetrasubstituted enamines
4c and 5c. The 1H NMR spectrum of 3c in CDCl3, registered imme-
diately after the compound had been dissolved (2 min), indicated a
2:3 mixture of 3c and 4c, while after 0.5 h a 1:5 ratio was observed.
There was no subsequent change in the percentage tautomerism
which remained unchanged for 3 h and only the content of the
thermodynamically more stable tetrasubstituted enamine 5c in-
creased (3% in 1 h and 14% in 3 h). It should be noted that only
decomposition products were detected in the 1H NMR spectrum
of 3c after standing in CDCl3 for 21 h.
Figure 1. X-ray crystal structure of 3b (ORTEP drawing, 50% probability level).
4a,b were always formed as one syn-diastereomer, the stereo-
chemistry of which was proved by X-ray diffraction after isolation
of 4b as a single crystal (Fig. 2).10,11 In the case of 3c, only tetrasub-
stituted enamine 5c was isolated under the same reaction condi-
tions, while 5b was prepared from 3b at room temperature in
two days. The conversion of the starting cyclobutanes 3b,c into
the tetrasubstituted enamines 5b,c was quantitative, and the con-
ditions were very mild. Only in one case, namely when the enam-
ine was N-cyclohexenylmorpholine (2b), were both tri- and
tetrasubstituted enamines 4b and 5b isolated in pure form.
Cyclobutanes 3 are sufficiently stable in the crystalline state and
can be stored in a freezer (ꢁ10 °C), without deterioration, for a long
time. However, in CDCl3 at room temperature, these compounds
exist as an equilibrium mixture of ring-chain tautomers 3 and 4.
Although the two isomers are stable in the solid state, upon dis-
solving either isomer in CDCl3, it begins to convert into the other,
and the process continues until an equilibrium mixture of 3 and
4 is reached. Opening of the cyclobutane ring 3 into trisubstituted
enamines 4 and the reverse process occur via betaine A, and were
The main information for the characterization of enamines 5a–c
was obtained from 1H NMR spectroscopy. The 1H NMR spectra of 5
showed no H-20 vinyl proton signal and no H-60 methine proton
signal, a result consistent with the tetrasubstituted enamine struc-
ture. The most downfield shifted signal assigned to the H-1
methine proton of the side chain appeared as a doublet of doublets
at d 5.9–6.0 with J = 10.5 and 3.0 Hz. The remarkable shift of this
signal compared with that of trisubstituted enamines (d 3.6–3.7)
can be explained by the influence of the double bond. Spectral
studies of tetrasubstituted enamines 5a–c in C6D6 and CDCl3
showed that these compounds were stable and did not exhibit
any tautomerism or isomerism.
Figure 2. X-ray crystal structure of 4b (ORTEP drawing, 50% probability level).

V. Yu. Korotaev et al. / Tetrahedron Letters 52 (2011) 3029–3032
3031
X
N
Cl3C
+
NO2
1
2a−c
C6H6
CHCl3
X
N
X
N
X
N
CCl3
CCl3 O
N
NO2
CCl3
1'
CDCl3
NO2
6'
8
7
1
6
2'
1'
1
2
O
6' 2'
CDCl3
H
A
3a−c
4a−c
X
CCl3
X
N
CCl3
N
O
O
1'
NO2
2'
N
X
6'
1
2
6
5a−c
X = NMe (a), O (b), CH2 (c)
Scheme 1.
It is important that while the reactions of enamines 2 with (E)-
3,3,3-trichloro-1-nitropropene (1) gave [2+2] cycloaddition ad-
ducts 3 (cyclic nitronate form 6 was not found, Scheme 1), their
reactions with (E)-1,1,1-trichloro-3-nitro-2-butene (7) under the
same conditions gave no [2+2] cycloadducts at all. The latter
reacted with 2 to give the [4+2] cycloaddition adducts, 3-methyl-
4-trichloromethyl-1,2-oxazine N-oxides 8, instead.13 This observa-
tion indicated that the reactions of nitrobutene 7 with enamines 2
took an entirely different course as compared with the reactions of
nitropropene 1. The failure of the [2+2] cycloaddition reaction with
7 possibly results from the methyl group, which hinders the ap-
proach of the carbanion to the iminium carbon atom. In this case,
steric interactions with the carbanionic centre become the decid-
ing factor and nucleophilic attack of the ambident nitronate anion,
which acts as an O-nucleophile, on the iminium carbon atom re-
sults in [4+2] heterocyclization to give 1,2-oxazine N-oxides 8 with
the Me group at the 3-position (Scheme 2).
In conclusion, we have shown, for the first time, that the reac-
tion of 3,3,3-trichloro-1-nitropropene with cyclohexanone enam-
ines affords bicyclo[4.2.0]octanes or linear enamines depending
on the reaction conditions. A new type of ring-chain tautomerism
consisting of the reversible transformation of cyclobutane deriva-
tives into trisubstituted enamines was found and studied by 1H
NMR spectroscopy. The ratios of the tautomeric forms involved
in the equilibria of these systems are not strongly influenced by
the nature of the amine. Further studies on the ring-chain and
ring-ring tautomeric equilibria of related compounds are now in
progress.
Acknowledgement
This work was financially supported by the Russian Foundation
for Basic Research (Grant 11-03-00126).
References and notes
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Kodess, M. I. Mendeleev Commun. 2010, 20, 17; (f) Korotaev, V. Yu.;
Sosnovskikh, V. Ya.; Kutyashev, I. B.; Barkov, A. Yu.; Matochkina, E. G.;
Kodess, M. I. Tetrahedron 2008, 64, 5055; (g) Korotaev, V. Yu.; Kutyashev, I. B.;
Sosnovskikh, V. Ya. Heteroat. Chem. 2005, 16, 492; (h) Aizikovich, A. Ya.;
Korotaev, V. Yu.; Kodess, M. I.; Barkov, A. Yu. Zh. Org. Khim. 1998, 34, 1149 [Russ.
J. Org. Chem. (Engl. Transl.) 1998, 34, 1093]; (i) Turconi, J.; Lebeau, L.; Paris, J.-M.;
Mioskowski, C. Tetrahedron Lett. 2006, 47, 121; (j) Korotaev, V. Yu.; Barkov, A.
Yu.; Kodess, M. I.; Kutyashev, I. B.; Slepukhin, P. A.; Zapevalov, A. Ya. Izv. Akad.
Nauk, Ser. Khim. 2009, 1827 (Russ. Chem. Bull., Int. Ed. 2009, 58, 1886); (k)
Molteni, M.; Consonni, R.; Giovenzana, T.; Malpezzi, L.; Zanda, M. J. Fluorine
Chem. 2006, 127, 901; (l) Molteni, M.; Belucci, M. C.; Bigotti, S.; Mazzini, S.;
Volonterio, A.; Zanda, M. Org. Biomol. Chem. 2009, 7, 2286.
CCl3
3. (a) Burkett, H.; Wright, W. J. Org. Chem. 1960, 25, 276; (b) Balthazor, T. M.;
Gaede, B.; Korte, D. E.; Shieh, H.-S. J. Org. Chem. 1984, 49, 4247.
4. (a) Baran´ ski, A. Pol. J. Chem. 1982, 56, 257; (b) Jasin´ ski, R.; Baran´ ski, A. Pol. J.
X
Me
Chem. 2006, 80, 1493.
N
N
Cl3C
Me
5. (a) Brower, F.; Burkett, H. J. Am. Chem. Soc. 1953, 75, 1082; (b) Burkett, H.;
Nelson, G.; Wright, W. J. Am. Chem. Soc. 1958, 80, 5812; (c) Thompson, I.;
Louloudes, S.; Fulmer, R.; Evans, F.; Burkett, H. J. Am. Chem. Soc. 1953, 75, 5006.
6. (a) Risaliti, A.; Forchiassin, M.; Valentin, E. Tetrahedron Lett. 1966, 6331; (b)
Risaliti, A.; Forchiassin, M.; Valentin, E. Tetrahedron 1968, 24, 1889; (c) Felluga,
F.; Nitti, P.; Pitacco, G.; Valentin, E. Tetrahedron 1989, 45, 2099; (d) Bradamante,
P.; Pitacco, G.; Risaliti, A.; Valentin, E. Tetrahedron Lett. 1982, 23, 2683; (e)
O
O
+
N
X
NO2
2
8
7
Scheme 2.

3032
V. Yu. Korotaev et al. / Tetrahedron Letters 52 (2011) 3029–3032
Benedetti, F.; Drioli, S.; Nitti, P.; Pitacco, G.; Valentin, E. ARKIVOC 2001, v, 140;
1H NMR (400 MHz, CDCl3) d 1.55–2.20 (m, 6H, 3CH2), 2.51 (dt, 2H, N(CHH)2,
J = 11.7, 5.0 Hz), 2.87 (br q, 1H, H-60, J = 3.5 Hz), 3.05 (dt, 2H, N(CHH)2, J = 11.7,
5.0 Hz), 3.70 (t, 5H, O(CH2)2, H-1, J = 4.5 Hz), 4.84 (dd, 1H, H-2a, J = 15.1,
4.7 Hz), 5.04 (dd, 1H, H-2b, J = 15.1, 5.5 Hz), 5.08 (t, 1H, H-20, J = 3.7 Hz); 13C
NMR (126 MHz, C6D6) d 17.1 (C-40), 24.1 (C-30), 30.5 (C-50), 34.5 (C-60), 50.6
(NCH2), 61.2 (C-1), 67.0 (OCH2), 75.6 (C-2), 103.0 (CCl3), 112.6 (C-20), 145.9 (C-
10). Anal. Calcd for C13H19Cl3N2O3: C, 43.66; H, 5.35; N, 7.83. Found: C, 43.64; H,
5.22; N, 7.79.
(f) Felluga, F.; Nitti, P.; Pitacco, G.; Valentin, E. Tetrahedron 1989, 45, 5667; (g)
Asaro, F.; Pitacco, G.; Valentin, E. Tetrahedron 1987, 43, 3279; (i) Pitacco, G.;
Pizzioli, A.; Valentin, E. Synthesis 1996, 242.
7. (a) Brook, M. A.; Seebach, D. Can. J. Chem. 1987, 65, 836; (b) Seebach, D.;
Lyapkalo, I. M.; Dahinden, R. Helv. Chim. Acta 1999, 82, 1829; (c) Ioffe, S. L. In
Nitrile Oxides, Nitrones and Nitronates in Organic Synthesis: Novel Strategies in
Synthesis, 2nd ed.; Feuer, H.; Ed. John Wiley & Sons: Chichester, 2008, pp 435–
748.; (d) Smirnov, V. O.; Ioffe, S. L.; Tishkov, A. A.; Khomutova, Yu. A.; Nesterov,
I. D.; Antipin, M. Yu.; Smit, W. A.; Tartakovsky, V. A. J. Org. Chem. 2004, 69,
8485; (e) Klenov, M. S.; Lesiv, A. V.; Khomutova, Yu. A.; Nesterov, I. D.; Ioffe, S. L.
Synthesis 2004, 1159.
8. (a) Pitacco, G.; Valentin, E. Tetrahedron Lett. 1978, 2339; (b) Nitti, P.; Pitacco, G.;
Rinaldi, V.; Valentin, E. Croat. Chem. Acta 1986, 59, 165.
9. (a) Kuehne, M. E.; Foley, L. J. Org. Chem. 1965, 30, 4280; (b) Brannock, K. C.; Bell,
A.; Burpitt, R. D.; Kelly, C. A. J. Org. Chem. 1964, 29, 801; (c) Colonna, F. P.;
Valentin, E.; Pitacco, G.; Risaliti, A. Tetrahedron 1973, 29, 3011.
4-[2-(1,1,1-Trichloro-3-nitroprop-2-yl)cyclohex-1-enyl]morpholine (5b). Yield
100%, yellow oil; IR (KBr) 1646, 1558, 1378 cmꢁ1 1H NMR (400 MHz, C6D6) d
;
1.2–2.4 (m, 12H, 4CH2, N(CH2)2), 3.60–3.73 (m, 4H, O(CH2)2), 4.20 (t, 1H, H-2a,
J = 10.7 Hz), 4.41 (dd, 1H, H-2b, J = 11.0, 3.0 Hz), 5.93 (dd, 1H, H-1, J = 10.5,
3.0 Hz); 1H NMR (400 MHz, CDCl3) d 1.5–2.4 (m, 10H, 4CH2, NCH2), 2.6–2.7 (m,
2H, NCH2), 3.74 (br s, 4H, O(CH2)2), 4.76 (t, 1H, H-2a, J = 10.7 Hz), 4.98 (dd, 1 H,
H-2b, J = 10.8, 3.0 Hz), 5.93 (dd, 1H, H-1, J = 10.3, 3.0 Hz).
11. X-Ray diffraction study of compounds 3b and 4b. Diffraction data were collected
at 130 K (3b) and 150 K (4b) on an Xcalibur
diffractometer (graphite-monochromated MoK
3
automatic single-crystal
radiation, -scans). The
10. 4-[(1R*,6S*,7S*,8R*)-8-nitro-7-(trichloromethyl)bicyclo[4.2.0]oct-1-yl]morpholine
(3b). Yield 72%, colourless crystals, mp 134–135 C (hexane–benzene, 1:2); IR
a
x
structures were solved by direct methods and refined by the full-matrix
least-squares method using the SHELX-97 programme package.14 The H atoms
were located geometrically using the riding model. Crystal data for 3b:
(KBr) 1540, 1458, 1357 cmꢁ1 1H NMR (500 MHz, C6D6) d 0.80–1.22 (m, 6H,
;
3CH2), 1.54–1.60 (m, 2H, CH2), 2.17–2.22 (m, 2H, N(CHH)2), 2.28 (ddt, 1H, H-6,
J = 9.8, 6.3, 1.7 Hz), 2.38–2.42 (m, 2H, N(CHH)2), 3.44 (ddd, 2H, O(CHH)2,
J = 10.8, 5.8, 3.3 Hz), 3.47 (ddd, 2H, O(CHH)2, J = 10.8, 5.8, 3.3 Hz), 3.76 (dd, 1H,
H-7, J = 9.8, 8.3 Hz), 4.83 (d, 1H, H-8, J = 8.3 Hz); 1H NMR (400 MHz, CDCl3) d
1.2–2.1 (m, 8H, 4CH2), 2.6–2.7 (m, 3H, N(CHH)2, H-6), 2.74–2.82 (m, 2H,
N(CHH)2), 3.68–3.75 (m, 4H, O(CH2)2), 3.87 (t, 1H, H-7, J = 9.1 Hz), 4.95 (d, 1H,
H-8, J = 8.4 Hz); 13C NMR (126 MHz, C6D6) d 20.5 (C-4), 21.0 (C-3), 22.3 (C-2),
24.3 (C-5), 36.5 (C-6), 47.1 (NCH2), 54.3 (C-7), 64.1 (C-1), 67.3 (OCH2), 83.7 (C-
8), 99.8 (CCl3). Anal. Calcd for C13H19Cl3N2O3: C, 43.66; H, 5.35; N, 7.83. Found:
C, 43.65; H, 5.51; N, 7.71.
C
13H19Cl3N2O3, M = 357.65, triclinic crystals, space group P-1, a = 8.5468(13),
b = 9.1515(13), c = 11.0677(14) Å,
a
q
= 89.894(11), b = 80.635(12),
c =
,
65.478(14)°, V = 775.01(19) Å3, Z = 2,
calcd = 1.533 g/cm3, = 0.602 mmꢁ1
l
F(000) = 372. Crystal data for 4b: C13H19Cl3N2O3, M = 357.65, triclinic crystals,
space group P-1, a = 8.8447(7), b = 9.0250(5), c = 11.8289(11) Å, = 72.800(8),
b = 74.919(7),
= 62.058(8) , V = 788.53(11) Å3, Z = 2, calcd = 1.506 g/cm3,
0.591 mmꢁ1
F(000) = 372. Crystallographic data for compounds 3b (CCDC
a
c
q
l =
,
deposition number 809202) and 4b (CCDC deposition number 809203) have
been deposited at the Cambridge Crystallographic Data Centre, 12 Union Road,
Cambridge CB2 1EZ, UK.
syn-4-[(1,1,1-Trichloro-3-nitroprop-2-yl)cyclohex-1-enyl]morpholine
(syn-4b).
Yield 50%, colourless crystals, mp 101–102 °C; IR (KBr) 1648, 1558,
12. (a) Brückner, S.; Pitacco, G.; Valentin, E. J. Chem. Soc., Perkin Trans. 2 1975, 1804;
(b) Calligaris, M.; Pitacco, G.; Valentin, E.; Zotti, E. J. Org. Chem. 1977, 42, 2720.
13. Korotaev, V. Yu.; Barkov, A. Yu.; Slepukhin, P. A.; Kodess, M. I.; Sosnovskikh, V.
Ya. Mendeleev Commun. 2011, 21, 112.
1383 cmꢁ1 1H NMR (500 MHz, C6D6) d 1.33–1.54 (m, 3H, H-40a, H-40b, H-
;
50a), 1.73 (m, 1H, H-30a), 1.83–1.90 (m, 2H, H-30b, H-50b), 2.06 (ddd, 2H,
N(CHH)2), J = 11.5, 5.8, 3.1 Hz), 2.53–2.60 (m, 3H, N(CHH)2, H-60), 3.32–3.42 (m,
4H, O(CH2)2), 3.62 (dt, 1H, H-1, J = 5.6, 4.4 Hz), 4.57 (dd, 1H, H-2a, J = 15.0,
4.4 Hz), 4.67 (dd, 1H, H-20, J = 4.1, 3.5 Hz), 4.82 (dd, 1H, H-2b, J = 15.0, 5.6 Hz);
14. Sheldrick, G. M. Acta Crystallogr., Sect. A 2008, 64, 112.