Synthesis and structures of new 1,3,6,2-dioxazaborocanes containing substituents in the ocane fragment

Article abstract of DOI:10.1007/s11172-008-0259-5

New 1,3,6,2-dioxazaborocanes R¹N(CHR³CR ⁴R²O)(CHR⁶CHR⁵O)BX (1-11, X = Ph, 4-MeC₆H₄, Me; R¹ = Me, PhCH₂; R ², R³, R⁴, R⁵, R⁶ = H, Ph) were synthesized by the reactions of aryl- or methylboronic acids with dialkanolamines. The treatment of (Me₂NCH₂CH ₂O)₃B (15) with MeN(CH₂CH₂OH) (CH₂CPh₂OH) afforded 2-[2-(dime-thylamino)ethoxy]-1,3,6,2- dioxazaborocane (12). 2-Fluoro-1,3,6,2-dioxazaborocanes R¹N(CHR ³CHR²O)(CH₂CH₂O)BF (13: R ¹ = PhCH₂, R² = R³ = H; 14: R ¹ = Me, R² = R³ = Ph, threo) were synthesized by the reaction of bis(trimethylsilyl) ethers of the corresponding dialkanolamines with BF₃?Et₂O. The new borocanes can be used for the synthesis of the corre-sponding germanium derivatives PhCH ₂N(CH₂CH₂O)₂GeX₂ (16, X = OEt; 17, X = Cl), as exemplified by the reaction of compound 6. The structures of erythro-MeN(CH₂CH₂O)(CHPhCHPhO)BPh (3), threo-MeN(CH₂CH₂O)(CHPhCHPhO)BPh (4), erythro-MeN(CH ₂CH₂O)(CHPhCHPhO)B(4-MeC₆H₄) (8), and PhCH₂N(CH₂CH₂O)₂BF (13) were established by X-ray diffraction. The coordination polyhedra of the boron atoms in these complexes can be described as distorted tetrahedra. The boron-nitrogen distances (1.705(7)-1.723(3) A) provide unambiguous evidence for the presence of the B-N transannular interaction in these compounds. The structures of the resulting borocanes containing phenyl substituents at the carbon atoms of the ocane skeleton were studied by NMR spectroscopy and quantum chemical density functional theory calculations.

Full text of DOI:10.1007/s11172-008-0259-5

Russian Chemical Bulletin, International Edition, Vol. 57, No. 9, pp. 1920—1930, September, 2008
1920
Synthesis and structures of new 1,3,6,2ꢀdioxazaborocanes
containing substituents in the ocane fragment
E. Kh. Lermontova,a M. M. Huang,b S. S. Karlov,b M. V. Zabalov,c A. V. Churakov,a
B. Neumüller,d and G. S. Zaitsevab
aN. S. Kurnakov Institute of General and Inorganic Chemistry, Russian Academy of Sciences,
31 Leninsky prosp., 119991 Moscow, Russian Federation.
Fax: +7 (495) 954 1279
bDepartment of Chemistry, M. V. Lomonosov Moscow State University,
1 Leninskie Gory, 119992 Moscow, Russian Federation.
Fax: +7 (495) 932 8846. Eꢀmail: sergej@org.chem.msu.ru
cN. N. Semenov Institute of Chemical Physics, Russian Academy of Sciences,
4 ul. Kosygina, 119991 Moscow, Russian Federation.
Fax: +7 (495) 137 8247. Eꢀmail: zabalov@mail.ru
dDepartment of Chemistry, Philipps University of Marburg,
HansꢀMeerweinꢀStrasse, Dꢀ35032 Marburg/Lahn, Germany.*
Fax: +(49) 0642 1282 5653
New 1,3,6,2ꢀdioxazaborocanes R1N(CHR3CR4R2O)(CHR6CHR5O)BX (1—11, X = Ph,
4ꢀMeC6H4, Me; R1 = Me, PhCH2; R2, R3, R4, R5, R6 = H, Ph) were synthesized by
the reactions of arylꢀ or methylboronic acids with dialkanolamines. The treatment of
(Me2NCH2CH2O)3B (15) with MeN(CH2CH2OH)(CH2CPh2OH) afforded 2ꢀ[2ꢀ(dimeꢀ
thylamino)ethoxy]ꢀ1,3,6,2ꢀdioxazaborocane (12). 2ꢀFluoroꢀ1,3,6,2ꢀdioxazaborocanes
R1N(CHR3CHR2O)(CH2CH2O)BF (13: R1 = PhCH2, R2 = R3 = H; 14: R1 = Me, R2 = R3 = Ph,
threo) were synthesized by the reaction of bis(trimethylsilyl) ethers of the corresponding diꢀ
alkanolamines with BF3•Et2O. The new borocanes can be used for the synthesis of the correꢀ
sponding germanium derivatives PhCH2N(CH2CH2O)2GeX2 (16, X = OEt; 17, X = Cl),
as exemplified by the reaction of compound 6. The structures of erythroꢀ
MeN(CH2CH2O)(CHPhCHPhO)BPh (3), threoꢀMeN(CH2CH2O)(CHPhCHPhO)BPh (4),
erythroꢀMeN(CH2CH2O)(CHPhCHPhO)B(4ꢀMeC6H4) (8), and PhCH2N(CH2CH2O)2BF
(13) were established by Xꢀray diffraction. The coordination polyhedra of the boron atoms in
these complexes can be described as distorted tetrahedra. The boron—nitrogen distances
(1.705(7)—1.723(3) Å) provide unambiguous evidence for the presence of the B←N transannuꢀ
lar interaction in these compounds. The structures of the resulting borocanes containing phenyl
substituents at the carbon atoms of the ocane skeleton were studied by NMR spectroscopy and
quantum chemical density functional theory calculations.
Key words: 1,3,6,2ꢀdioxazaborocanes, dialkanolamines, transannular interaction, Xꢀray difꢀ
fraction study, B←N coordination bond.
1,3,6,2ꢀDioxazaborocanes (hereinafter, borocanes)
thesis. For example, the complex based on chiral 2,6ꢀpyriꢀ
dine (bis)methanol was shown to be a convenient catalyst
for the addition of diethylzinc at the carbonyl group.8 Vinylꢀ
substituted borocanes proved to be valuable intermediates
in cyclization reactions giving rise to biologically active
fiveꢀmembered heterocycles. The addition is enantioseꢀ
lective due to the configuration adopted by the asymmetric
carbon atoms in the borocane molecules.9,10 These comꢀ
pounds can also be used for the synthesis of various chiral
alcohols.11 It was shown12 that the configuration of the
C(OH) group in the product is substantially determined by
the structure of the diastereomer involved in the reaction.
and closely related cyclic boronic esters have a broad specꢀ
trum of cytotoxic activities,1 are used in antitumor theraꢀ
py,2 and exhibit antiviral,3,4 fungicidal, and antibacterial5
activities. In the organic synthesis, borocanes are used priꢀ
marily as intermediates for the isolation, purification, and
characterization of various boronic acids.6,7 Some boroꢀ
canes containing substituents at the carbon atoms of the
ocane moiety have found application in fine organic synꢀ
* Fachbereich Chemie, PhilippsꢀUniversität Marburg, Hansꢀ
MeerweinꢀStrasse, Dꢀ35032 Marburg/Lahn, Deutschland.
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1886—1896, September, 2008.
1066ꢀ5285/08/5709ꢀ1920 © 2008 Springer Science+Business Media, Inc.

Structures of new 1,3,6,2ꢀdioxazaborocanes
Russ.Chem.Bull., Int.Ed., Vol. 57, No. 9, September, 2008
1921
Scheme 1
An analysis of the published data showed that methods
for the synthesis of borocanes are well developed. In most
cases, these compounds were prepared by the reactions of
the corresponding boronic acids with dialkanolamines.13—17
Boronic acid esters can also be used as the starting comꢀ
pounds in these reactions.18—21 A method of choice for the
synthesis of 2ꢀfluoroborocanes is based on the reaction of
boron trifluoride etherate with bis(trimethylsilyl) ether of
diethanolamine.22
It should be noted that most of the hitherto synthesized
compounds have the simple RN(CH2CH2O)2B—X strucꢀ
ture, whereas data on the synthesis of derivatives containꢀ
ing various substituents at the carbon atoms of the ocane
skeleton are scarce. The exceptions are studies12,13,15,16
concerned with borocanes based on ephedrine or pseuꢀ
doephedrine derivatives. The structures of these comꢀ
pounds were studied in detail both in the solid state and in
solution. The mutual arrangement of the substituents at
the boron and nitrogen atoms and at the carbon atoms of
the ocane skeleton was determined.12,13,15 In addition,
the recent Xꢀray diffraction study23 of three chiral boroꢀ
canes based on (1R,1´R)ꢀ2,2´ꢀ(benzylimino)bis(1ꢀpheꢀ
nylethanol) and the study24 of iminodiacetic acid derivaꢀ
tives are worthy of note.
1: X = Ph, R1 = Me, R2 = Ph, R3 = R4 = R5 = R6 = H
2: X = Ph, R1 = Me, R2 = R4 = Ph, R3 = R5 = R6 = H
3*: X = Ph, R1 = Me, R2 = R3 = Ph, R4 = R5 = R6 = H
4**: X = Ph, R1 = Me, R2 = R3 = Ph, R4 = R5 = R6 = H
5*: X = Ph, R1 = Me, R2 = R3 = R5 = R6 = Ph, R4 = H
6: X = 4ꢀMeC6H4, R1 = PhCH2, R2 = R3 = R4 = R5 = R6 = H
7: X = 4ꢀMeC6H4, R1 = Me, R2 = R4 = Ph, R3 = R5 = R6 = H
8*: X = 4ꢀMeC6H4, R1 = Me, R2 = R3 = Ph, R4 = R5 = R6 = H
9**: X = 4ꢀMeC6H4, R1 = Me, R2 = R3 = Ph, R4 = R5 = R6 = H
10*: X = Me, R1 = Me, R2 = R3 = Ph, R4 = R5 = R6 = H
11**: X = Me, R1 = Me, R2 = R3 = Ph, R4 = R5 = R6 = H
* erythro. ** threo.
Scheme 2
The aims of the present study were to synthesize boroꢀ
canes containing phenyl substituents at the carbon atoms
of the ocane skeleton and groups of different nature at the
boron and nitrogen atoms and to establish the structures of
these compounds, in particular, to determine the strucꢀ
tures of possible diastereomers and examine the possibility
of using the resulting compounds in the synthesis of gerꢀ
mocanes.
Results and Discussion
We used several methods for the construction of the
ocane skeleton in the synthesis of the target borocanes 1—14.
Most of the compounds (1—11) were synthesized by
the reactions of methylꢀ or arylboronic acids with the corꢀ
responding dialkanolamines (Scheme 1).
Scheme 3
The reactions were carried out by refluxing mixtures of
the reagents in dioxane; the yields were 45—87%. Borocaꢀ
nes can also be synthesized by transalkoxylation (Scheme 2).
Compound 12 was prepared in quantitative yield.
All boronic acids used for the synthesis were commerꢀ
cial compounds. Alkoxide 15 (see Scheme 2) was syntheꢀ
sized in quantitative yield by the reaction of trimethyl boꢀ
rate with 2ꢀ(N,Nꢀdimethylamino)ethanol. Dialkanolꢀ
amines were prepared according to procedures described
earlier (see the Experimental section). The previously unꢀ
known 2,2´ꢀ(methylimino)bis(1,2ꢀdiphenylethanol) was
synthesized according to Scheme 3.
methylsilyl) ethers of the corresponding dialkanolamines
with BF3•Et2O (Scheme 4).
Compound 6 was tested as the starting compound for
the synthesis of dialkoxyꢀ and dihalogermocanes. It was
found that the reactions of borocane 6 with tetraethoxꢀ
ygermane in the presence of catalytic amounts of Al2(OEt)6
and with tetrachlorogermane in the presence of AlCl3 afꢀ
ford 2,2ꢀdiethoxyꢀ1,3,6,2ꢀdioxazagermocane (16) and
2,2ꢀchloroꢀ1,3,6,2ꢀdioxazagermocane (17), respectively,
in satisfactory yields (Scheme 5).
2ꢀFluoroꢀ1,3,6,2ꢀdioxazaborocanes 13 and 14 were
prepared in satisfactory yields by the reactions of bis(triꢀ

1922
Russ.Chem.Bull., Int.Ed., Vol. 57, No. 9, September, 2008
Lermontova et al.
Scheme 4
Evidently, the presence of at least one substituent at
the carbon atom (except for two identical substituents at
one atom) gives rise to three (or more, if there is more than
one substituent) asymmetric centers (C, B, and N atoms).
Theoretically, molecules containing one asymmetric carꢀ
bon atom in the ocane skeleton can exist as four diastereꢀ
omers (A—D), which differ in the mutual spatial arrangeꢀ
ment of the substituents. It should be noted that the relaꢀ
tive configurations of two substituents at different carbon
atoms in compounds 3—5, 8—11, and 14 (threoꢀ and/or
erythro isomers) are strictly fixed. For simplicity, in the
below discussion of the Xꢀray diffraction and NMR data
and the results of quantum chemical calculations, the subꢀ
stituent at the carbon atom bound to the nitrogen atom is
always situated above the plane of the figure (compounds
containing the substituent located beneath the plane are
enantiomers of one of the four structures A—D).
13: R1 = PhCH2, R2 = R3 = H; 14: R1 = Me, R2 = R3 = Ph (threo)
Scheme 5
X = OEt (16), Cl (17)
It should be noted that data on the existence of
the stereoisomers C and D, in which the substituents at the
boron and nitrogen atoms are oriented in the opposite
directions, are lacking in the literature. Actually, such isoꢀ
mers are energetically very unfavorable due to high steric
strain in the structures of this type.
The structures of borocanes 3, 4, 8, and 13 in the solid
phase were established by Xꢀray diffraction (Figs 1—4,
respectively). Principal geometric parameters of the boroꢀ
canes are given in Tables 1 and 2.
It seems reasonable to further examine the scope of this
reaction.
We found that all the borocanes synthesized in the
present study contain the fourꢀcoordinated boron atom as
a result of formation of the intramolecular B←N bond
(see below). It should be noted that the 1H NMR spectroꢀ
scopic data (the chemical shifts for the NMe and NCH2
groups in compounds 12 and 15 and the compounds
MeN(CH2CH2O)(CH2CPh2O)BX, where X = Ph (2) or
4ꢀMeC6H4 (7)) provide evidence that it is the ocane fragꢀ
ment of compound 12 in which the coordination bond
is present.
Table 1. Selected interatomic distances (d/Å) in compounds 3, 4,
8, and 13
The structures of the boron derivatives were studied by
1H, 11B, 13C, and 19F NMR specꢀ
troscopy and Xꢀray diffraction.
Bond
3*
4
8
13
(X = Ph)
(X = Ph) (X = pꢀTol) (X = F)
Special emphasis was given to the
estimation of the amounts of diasꢀ
tereomers of borocanes containing
substituents at the carbon atoms of
the ocane skeleton and the determination of the structures
of these diastereomers.
B—N 1.717(3) 1.710(3) 1.723(3) 1.717(2) 1.705(7)
B—O 1.456(3), 1.451(3), 1.443(3), 1.450(2), 1.427(8),
1.466(3) 1.469(3) 1.469(3) 1.462(2) 1.453(6)
B—X 1.609(3) 1.621(3) 1.603(3) 1.610(2) 1.376(7)
* Two independent molecules.

Structures of new 1,3,6,2ꢀdioxazaborocanes
Russ.Chem.Bull., Int.Ed., Vol. 57, No. 9, September, 2008
1923
Table 2. Selected bond angles (ω/deg) in compounds 3, 4, 8, and 13
Angle
3* (X = Ph)
118.6(2)
4 (X = Ph)
8 (X = pꢀTol)
13 (X = F)
N—B—X
N—B—O
117.4(2)
100.7(2),
100.8(1)
114.9(2)
110.8(2),
111.8(2)
108.6(2)—
114.2(2)
102.5(1)—
117.1(2)
115.9(2)
99.4(2),
99.9(2)
116.7(2)
111.6(2),
112.4(2)
111.0(2)—
114.1(2)
102.1(2)—
115.2(2)
115.8(1)
100.2(1),
100.8(1)
116.1(1)
111.0(1),
112.27(1)
109.7(1)—
113.4(1)
103.7(1)—
114.8(1)
111.2(5)
102.2(4),
102.9(4)
116.2(5)
110.7(5),
112.8(5)
112.4(4)—
113.6(4)
102.3(4)—
112.3(4)
99.7(1),
100.9(1)
116.3(2)
109.1(2),
111.9(2)
108.4(2)—
113.6(2)
102.1(1)—
116.8(2)
O—B—O
O—B—X
C—N—C
C—N—B
* Two independent molecules.
C(11)
C(12)
С(25)
С(24)
С(23)
O(11)
C(4)
C(3)
C(1)
С(1)
С(26)
С(14)
C(5)
С(21)
С(11)
С(27)
N(1)
B(1)
С(22A)
N
C(2)
С(22B)
С(7)
C(22)
C(13)
C(18)
С(12)
O(2)
C(6)
С(15)
С(16)
O(12) C(7)
С(6)
C(17)
C(21)
C(23)
B
С(13)
С(28)
С(2)
C(14)
O(1)
С(3)
С(18)
С(8)
C(15)
C(27)
С(17)
C(16)
С(5)
С(4)
C(28)
C(24)
C(25)
Fig. 3. Molecular structure of compound 8. The hydrogen atoms
of the disordered methyl group (at the C(8) atom) and the disordeꢀ
red methylene groups (at the C(21) and C(22) atoms) are omitted.
C(26)
Fig. 1. Molecular structure of compound 3 (one independent
molecule).
C(10)
C(9)
C(8)
C(11)
C(27)
C(28)
C(23)
C(26)
C(7)
C(25)
C(24)
C(6)
C(5)
C(2)
C(6)
C(17)
C(16)
C(18)
C(7)
O(2)
C(21)
C(13)
C(22)
C(1)
O(1)
C(4)
C(5)
F(1)
C(15)
C(2)
C(3)
N(1)
C(14)
B(1)
C(4)
N(1)
C(3)
B(1)
C(1)
C(12)
C(11)
O(1)
O(2)
Fig. 4. Molecular structure of compound 13.
Fig. 2. Molecular structure of compound 4.

1924
Russ.Chem.Bull., Int.Ed., Vol. 57, No. 9, September, 2008
Lermontova et al.
The coordination polyhedra of the boron and nitrogen
atoms in all compounds under consideration, as well as in
all borocanes studied earlier,13,14,19—23,25—35 can be deꢀ
scribed as slightly distorted tetrahedra, the smallest distorꢀ
tions being found in compound 13 (X = F). The B←N
bond lengths in borocanes, unlike those in derivatives of
hypervalent Group 14 elements (Si and Ge),36 are virtually
independent of the nature of the substituent at the boron
atom. Changes in the nature of the substituent X at the
boron atom in borocanes have a larger effect on the B—O
bond lengths rather than on the B←N bond lengths. The
replacement of the phenyl (3 and 4) or paraꢀtolyl (8) group
at the boron atom by the fluorine atom (13) leads to
a substantial shortening of the B—O bond.
It was of interest to compare the B←N bond lengths in
borocanes 3, 4, 8, and 13 with the corresponding bond
lengths in the already known boratranes N(CH2CH2O)3B
(1.676(7) Å)37 and threoꢀN(CH2CH2O)2(CHPhCHPhO)B
(1.684(4) and 1.687(4) Å).38 It was found that the B←N
bond in ocanes is longer (by 0.03—0.04 Å) than the correꢀ
sponding bond in atranes. An elongation of the B←N bond
is apparently attributed to steric requirements of aminoalꢀ
cohol ligands, which are more rigid in compounds with the
tricyclic atrane system compared to the bicyclic moiety of
the ocane skeleton.
the erythro configuration exist as diastereomers of the type A
(all three phenyl groups and one methyl group deviate in the
same direction from the plane of the —B—O—C—C—N—
ring). Complex 4, in which the phenyl groups have the
threo configuration, belongs to the type B (the NMe, BPh,
and OCPh substituents deviate in the same direction from
the plane of the —B—O—C—C—N— ring, whereas the
phenyl ring of the NCPh group lies on the opposite side).
According to the 11B NMR spectroscopic data, all boꢀ
rocanes under consideration contain the fourꢀcoordinated
boron atom (δ 9.5—14.5, br.s, in CDCl3). An analysis of
1
the H and 13C NMR spectra of the Cꢀsubstituted boroꢀ
canes synthesized in the present study, as well as of their
germanium analogs prepared in our earlier studies, showed
that all these compounds exist as a single diastereomer or a
mixture of two diastereomers (Table 3).
In most cases, the synthesis of ocanes gives rise to two
diastereomers, their relative amounts being only slightly
different. This is particularly typical of compounds conꢀ
taining the methyl group. On the contrary, the introducꢀ
tion of two bulky phenyl groups into the ocane skeleton
sometimes results in the formation (existence) of the comꢀ
pounds as a single diastereomer. The determination of the
structures of compounds containing one substituents at
the carbon atoms by NMR spectroscopy, even with the use
of the nuclear Overhauser effect, presents serious diffiꢀ
culties. Nevertheless, the assignment of the signals in the
spectra of derivatives of diphenylꢀcontaining dialkanolꢀ
In the crystal structures, compounds 3, 4, and 8 exist as
a single diastereomer. Borocanes 3 and 8 containing two
phenyl groups at the carbon atoms of the ocane skeleton in
Table 3. Ratios of diastereomers of Cꢀsubstituted borocanes and germocanes (X is one (for boron) or two
(for germanium) substituents at the heteroatom) produced in the synthesis of ocanes
Dialkanolamine
Single diastereomer
Two diastereomers
M
—
X
M
X
Ratio*
MeN(СH2СH2OH)(СH2СHPhOH)
—
Ge
Ge
B
Ge
Ge
B
B
B
B
Cl
Br
Ph
Cl
3 : 239
3 : 239
2 : 1 (1)
—**39
—**39
3 : 1 (11)
3 : 1 (4)
3 : 1 (9)
2 : 1 (14)
2 : 139 (10)
3 : 239 (3)
3 : 143 (8)
MeN(СH2СH2OH)(СHPhСH2OH)
—
—
Br
Me
Ph
4ꢀC6H4Me
threoꢀMeN(СH2СH2OH)(СHPhСHPhOH)
Ge
Br36
F
Cl
Br
F
erythroꢀMeN(СH2СH2OH)(СHPhСHPhOH)
B
B
B
Ge
—
Me
Ph
4ꢀC6H4Me
OEt37
—
Ge
Ge
Ge
MeN(СH2СH2OH)(СH2СHMeOH)
threoꢀMeN(СH2СH2OH)[СH(CH2)4СHOH]
erythroꢀMeN(СHPhСHPhOH)2
Ge
Ge
Ge
Ge
B
Cl
Br
Cl
Br
Ph
3 : 239
3 : 239
2 : 139
2 : 139
1 : 1 (5)
—
—
—
—
* The codes of the compounds synthesized in the present study are given in parentheses.
** It was impossible to determine the ratio of isomers in the mixture because of the low concentration of the compound
in solution.

Structures of new 1,3,6,2ꢀdioxazaborocanes
Russ.Chem.Bull., Int.Ed., Vol. 57, No. 9, September, 2008
1925
Table 4. 1H NMR spectroscopic data for borocanes and gerꢀ
mocanes (CDCl3, δ)
amines can be made due to the wellꢀknown shielding efꢀ
fect of the phenyl group on the protons of the the closely
spaced groups, resulting in the upfield shift of the signals
for the latter groups as they come in proximity to the pheꢀ
nyl group. The characteristics signals in the 1H NMR specꢀ
tra of these ocanes are given in Table 4. The assignment
was made based on the chemical shifts of the signals for
the MeN groups in these compounds. The formulas of the
possible diastereomers exemplified by the phenylboron deꢀ
rivatives are given below. The structures of the germanium
compounds are analogous because the second substituent
X at the germanium atom is in the trans position with
respect to the nitrogen atom and has no substantial effect
on the chemical shift of the MeN group. An analysis of
these structures clearly shows that the signal of the MeN
group in the diastereomers A shifts upfield compared to the
analogous signal in the spectra of the diastereomers B due
to the shielding effect of the phenyl group.
Ocane, M/X
δ(MeN)
Minor
Type
of the major isomer
Major
isomer
isomer
threoꢀMeN(CH2CH2OH)(CHPhCHPhOH) derivatives
11, B/Me
4, B/Ph
9, B/4ꢀC6H4Me
14, B/F
Ge/Br*36
2.62
2.26
2.27
2.67
2.63
2.24
1.93
1.94
2.32
—
B
B
B
B
B
erythroꢀMeN(CH2CH2OH)(CHPhCHPhOH) derivatives
10, B/Me
3, B/Ph
2.24
1.99
2.00
2.31
2.28
2.38
2.22
—
—
—
2.70
2.70
—
A
A
A
A
A
A
A
8, B/4ꢀC6H4Me
Ge/Cl36
Ge/Br36
Ge/F37
Ge/OEt37
—
* The data in DMSOꢀd6.
To confirm our conclusions, we optimized the geometꢀ
ric parameters of the possible diastereomers of two boron
derivatives and two germanium derivatives by quantum cheꢀ
mical methods. The energy differences between the pairs
of the isomers A and B estimated by the quantum chemical
method are given in Table 5. The calculations confirmed
that the diastereomer B is more favorable for the threo
derivatives; however, the energy difference is small and the
existence of both isomers would be expected. This concluꢀ
sion was confirmed by experimental data (except for threoꢀ
MeN(CH2CH2O)(CHPhCHPhO)GeBr2).39 The isomer A
is more favorable for the erythro derivatives of boron.
It should be noted that the energy difference between the
isomers A and B is rather large, i.e., only this isomer can be
formed. The energy difference between the isomers A and
Table 5. Energy differences (kcal mol–1) between the isomers A
and B (quantum chemical data, DFT/PBE)
It should be noted that the signal of the MeN group in
the derivatives containing the phenyl or paraꢀtolyl group at
the boron atom additionally shifts upfield due to shielding
by the aboveꢀmentioned closely spaced aromatic system.
This fact confirms the existence of isomers, in which
the substituents at the heteroatom and the nitrogen atom
are oriented in the same direction. Therefore, as can be
seen from Table 4, the type of the major isomer is deterꢀ
mined by the nature of substituents at the carbon atoms,
whereas the ratio of the diastereomers depends primarily
on the nature of the central atom; in the case of germaniꢀ
um (see Table 4), on the nature of the substituents at the
heteroatom.
Compound
Isoꢀ –ΔE*
mer**
erythroꢀMeN(СH2СH2O)(СHPhСHPhO)BF
erythroꢀMeN(СH2СH2O)(СHPhСHPhO)BPh (3)
erythroꢀMeN(СH2СH2O)(СHPhСHPhO)GeBr2
erythroꢀMeN(СH2СH2O)(СHPhСHPhO)GePh2
threoꢀMeN(СH2СH2O)(СHPhСHPhO)BF (14)
threoꢀMeN(СH2СH2O)(СHPhСHPhO)BPh (4)
threoꢀMeN(СH2СH2O)(СHPhСHPhO)GeBr2
threoꢀMeN(СH2СH2O)(СHPhСHPhO)GePh2
A
A
B
B
B
B
B
B
2.16
3.63
0.29
1.05
1.43
0.75
1.04
0.79
* The energy difference between the more stable and less staꢀ
ble isomers.
** The type of the more stable isomer.

1926
Russ.Chem.Bull., Int.Ed., Vol. 57, No. 9, September, 2008
Lermontova et al.
oxide (5.89 g, 0.03 mol) were placed in a thickꢀwalled flask with
a screw cap. The viscous suspension was stirred for 12 h. Then
the reaction mixture was heated in an oil bath at 60 °C for 107 h.
The precipitate was filtered off, washed with hexane (3×10 mL),
and dried in vacuo (1.5 Torr). erythroꢀ2,2´ꢀIminobis(1,2ꢀdipheꢀ
nylethanol) (a mixture of two diastereomers in a ratio of 5 : 4) was
obtained in a yield of 3.43 g (84%). Found (%): C, 82.40; H, 6.84;
N, 3.25. C28H27NO2. Calculated (%): C, 82.12; H, 6.65; N, 3.42.
1H NMR, δ: 2.54 (br.s, 1 H, NH); 3.55 and 3.77 (both d, 1 H each,
NCH, J = 5.8 Hz); 4.59 and 4.84 (both d, 1 H each, OCH,
J = 5.8 Hz); 6.72—7.21 (m, 20 H, Ph).
erythroꢀ2,2´ꢀ(Methylimino)bis(1,2ꢀdiphenylethanol). A mixꢀ
ture of HN[CH(Ph)CH(Ph)OH]2 (1.3 g, 3 mmol) and a 30%
H2C=O solution (0.3 mL, 3 mmol) was placed in a threeꢀneck
flask equipped with a reflux condenser and a dropping funnel.
Then HCOOH (0.14 g, 3 mmol) was added dropwise to
the reaction mixture for 1 h. The reaction mixture was stirred at
75 °C for 5 h. Volatile components were removed in vacuo, the
residue was extracted with Et2O (30 mL), the ethereal extracts
were concentrated, water (50 mL) was added to the oily residue,
and the reaction mixture was vigorously stirred for one day.
The white solid precipitate was filtered off, and erythroꢀ2,2´ꢀ
(methylimino)bis(1,2ꢀdiphenylethanol) was obtained as a white
solid compound in a yield of 0.9 g (68%). The 1H and 13C NMR
spectra show signals of two diastereomers in a ratio of 5 : 4.
Found (%): C, 82.01; H, 7.07; N, 3.08. C29H29NO2. Calculatꢀ
ed (%): C, 82.24; H, 6.90; N, 3.31. 1H NMR, δ: 2.06 and
2.58 (both s, 3 H each, NMe); 3.57 and 3.95 (both d, 2 H each,
NCH, J = 5.8 Hz); 5.20 and 5.44 (both d, 2 H each, OCH,
J = 5.8 Hz); 7.00—7.04 and 7.11—7.25 (both m, 20 H, Ph).
13C NMR, δ: 35.26, 35.90 (NMe); 70.63, 71.40, 72.26, 72.43
(NCH, OCH); 126.30, 126.43, 127.33, 127.52, 127.55, 127.58,
127.62, 127.86, 127.96, 129.89, 129.95, 134.69, 135.42, 141.49,
141.57 (Ph).
Tris[2ꢀ(dimethylamino)ethyl] borate (15). A mixture of
B(OMe)3 (4.4 g, 0.04 mol) and HOCH2CH2NMe2 (11.33 g,
0.12 mol) was stirred at 50 °C. Volatile compounds were removed
under reduced pressure. Compound 15 was obtained as a yellow
oil in quantitative yield. This compound was used without addiꢀ
tional purification. 1H NMR, δ: 2.23 (s, 18 H, Me); 2.44 (t, 6 H,
NCH2); 3.76 (t, 6 H, OCH2). 13C NMR, δ: 45.79 (NMe); 60.46,
60.90 (NCH2, OCH2). 11B NMR, δ: 14.66.
erythroꢀ2,6ꢀDimethylꢀ4,5ꢀdiphenylꢀ1,3,6,2ꢀdioxazaborocane
(10). erythroꢀMeN(CHPhCHPhOH)(CH2CH2OH) (0.27 g,
1 mmol) was added to a solution of methylboronic acid (0.06 g,
1 mmol) in dioxane (10 mL). The reaction mixture was refluxed
for 5 h, the solvent and water were femoved in vacuo, and the
residue was recrystallized from toluene. Borocane 10 was obꢀ
tained as a white powder in a yield of 0.22 g (75%). Found (%):
C, 73.14; H, 6.92; N, 4.45. C18H22BNO2. Calculated (%):
C, 73.24; H, 7.51; N, 4.75. 1H NMR, δ: 0.08 (s, 3 H, BMe); 2.24
(s, 3 H, NMe); 3.15—3.18 and 3.46—3.53 (both m, 2 H, NCH2);
3.84—3.90 and 4.10—4.14 (both m, 2 H, OCH2); 4.18 (d, 1 H,
NCH, J = 4.5 Hz); 5.81 (d, 1 H, OCH, J = 4.5 Hz); 6.93—6.97,
7.04—7.12, and 7.20—7.00 (all m, 10 H, Ph). 13C NMR, δ:
0.97 (BMe); 43.33 (NMe); 60.82 (NCH2); 63.65 (OCH2);
75.99 (NCH); 79.68 (OCH); 126.03, 126.15, 127.50, 128.01,
128.62, 131.16, 133.12, 139.61 (Ph). 11B NMR, δ: 14.49 (br.s).
MS, m/z (Irel (%)): 295 [M]+ (8), 280 [M – Me]+ (22), 189
[M – PhCHO]+ (54), 174 [M – Me– PhCHO]+ (29).
B of erythroꢀMeN(CH2CH2O)(CHPhCHPhO)GeBr2 is
very small, which indicates that both diastereomers can
exist.
The conclusions about the structural types of the
C,Cꢀdiphenylꢀsubstituted ocanes synthesized in the preꢀ
sent study are indirectly confirmed by the Xꢀray diffracꢀ
tion data. The structures of all Cꢀsubstituted comꢀ
pounds (borocanes 3, 4, and 8 and germocane erythroꢀ
MeN(CH2CH2O)(CHPhCHPhO)GeBr2 (see Ref. 39))
determined by Xꢀray diffraction are identical to the strucꢀ
ture of isomer that is present in solution as either the major
or the only one isomer.
Experimental
The solvents were purified according to standard procedures
immediately before use. Diethyl ether and 1,4ꢀdioxane were kept
over potassium hydroxide and then refluxed and distilled over
sodium benzophenone ketyl; nꢀhexane and toluene were refluxed
and then distilled over sodium metal; acetonitrile was refluxed
and successively distilled over P4O10 and CaH2.
The 1H, 13C, and 19F NMR spectra were recorded in CDCl3
(unless otherwise stated) on Varian VXRꢀ400 or Bruker Avance
400 spectrometers (at 400, 100, and 376.4 MHz, respectively).
The 11B NMR spectra were measured on a Bruker DRXꢀ500
spectrometer (160 MHz). The residual protons of the deuterated
solvent were used as the internal standard; the chemical shifts are
given with respect to Me4Si (for 1H and 13C), CFCl3 (for 19F), or
BF3•Et2O (for 11B). The mass spectra were obtained using
a direct inlet system at an ionizing voltage of 70 eV on a Varian
CHꢀ7a mass spectrometer; all assignments were made taking
into account the masses of the most abundant isotopes. The eleꢀ
mental analysis was carried out in the Laboratory of Organic
Microanalysis of the Department of Chemistry of the M. V.
Lomonosov Moscow State University. Compounds 13 and 14
are hydrolytically very unstable, due to which it was difficult to
obtain satisfactory elemental analysis data for these compounds.
Boron trifluoride etherate was purified by distillation under
atmospheric pressure. transꢀStilbene and phenylboronic, paraꢀ
tolylboronic, and methylboronic acids (Aldrich) were used
without additional purification. NꢀBenzyldiethanolamine,40
2ꢀ[(2ꢀhydroxyethyl)(methyl)amino]ꢀ1ꢀphenylꢀ1ꢀethanol, and
2ꢀ[(2ꢀhydroxyethyl)(methyl)amino]ꢀ2ꢀphenylꢀ1ꢀethanol as a
mixture (20 : 1),41 2ꢀ[(2ꢀhydroxyethyl)(methyl)amino]ꢀ1,2ꢀ
threoꢀdiphenylethanol,39 2ꢀ[(2ꢀhydroxyethyl)(methyl)amino]ꢀ
1,2ꢀerythroꢀdiphenylethanol,36 2ꢀ[(2ꢀhydroxyethyl)(methyl)ꢀ
amino]ꢀ1,1ꢀdiphenylethanol,39 bis(trimethylsilyl) ether of
2ꢀ[(2ꢀhydroxyethyl)(methyl)amino]ꢀ1,2ꢀthreoꢀdiphenylethaꢀ
nol,39 and tetraethoxygermane42 were synthesized according to
known procedures. Bis(trimethylsilyl) ether of Nꢀbenzyldiethaꢀ
nolamine was prepared by the reaction of hexamethyldisilazane
with Nꢀbenzyldiethanolamine, b.p. 126—129 °C (0.3 Torr).
1H NMR, δ: 0.07 (s, 18 H, SiMe3); 2.67 (t, 4 H, NCH2, J = 7.6 Hz);
3.61 (t, 4 H, OCH2, J = 7.6 Hz); 3.69 (s, 4 H, PhCH2N);
7.18—7.32 (m, 5 H, Ph). 13C NMR, δ: 0.54 (SiMe3); 56.66
(NCH2); 60.07 (OCH2); 61.17 (PhCH2); 126.83, 128.13, 128.78,
139.83 (Ph).
erythroꢀ2,2´ꢀIminobis(1,2ꢀdiphenylethanol). A 2.0 M methaꢀ
nolic ammonia solution (5.5 mL, 0.01 mol) and transꢀstilbene
Compounds 1—9 and 11 were synthesized analogously.

Structures of new 1,3,6,2ꢀdioxazaborocanes
Russ.Chem.Bull., Int.Ed., Vol. 57, No. 9, September, 2008
1927
6ꢀMethylꢀ2,4ꢀdiphenylꢀ1,3,6,2ꢀborocane (1). The reaction
of phenylboronic acid (0.37 g, 3 mmol) with a mixture of dialꢀ
shows signals of two diastereomers in a ratio of 3 : 1. 1H NMR of the
major isomer, δ: 2.26 (s, 3 H, NMe); 2.30—2.36 and 3.46—3.52
(both m, 1 H each, NCH2); 3.88 (d, 1 H, NCH, J = 10.5 Hz);
4.14—4.18 and 4.33—4.40 (both m, 1 H each, OCH2); 5.72 (d, 1 H,
OCH, J = 10.5 Hz); 7.16—7.49 and 7.84—7.86 (both m, 15 H,
Ph). 1H NMR of the minor isomer, δ: 1.93 (s, 3 H, NMe); 4.11
(d, 1 H, NCH, J = 10.5 Hz); 5.62 (d, 1 H, OCH, J = 10.5 Hz);
7.74 (m, 2 H, Hz). The proton signals of other groups overlap
with the signals of the major isomer. 13C NMR of the major
isomer, δ: 46.80 (NMe); 54.04 (NCH2); 63.02 (OCH2); 76.61
(NCH); 79.10 (OCH). 13C NMR of the minor isomer, δ: 42.25
(NMe); 58.26, 60.84 (NCH2, OCH2); 75.24 (NCH); 77.46
(OCH). 126.43, 126.62, 127.20, 127.25, 127.42, 127.45, 127.52,
127.55, 127.99, 128.70, 128.82, 129.58, 129.63, 130.54, 130.62,
130.83, 133.22, 133.27, 140.05 (Ph). Five signals for the aromatic
C atoms were not observed in the spectra due apparently to coꢀ
alescence of some signals. 11B NMR, δ: 13.05. MS, m/z (Irel (%)):
357 [M]+ (6), 280 [M – Ph]+ (100), 251 [M – PhCHO]+ (22),
179 [M – Ph – PhCHO]+ (43).
kanolamines
MeN(CH2CHPhOH)(CH2CH2OH)
and
MeN(CHPhCH2OH)(CH2CH2OH) (0.59 g, 3 mmol) afforded
borocane 1 as a white powder in a yield of 0.4 g (48%). Found (%):
C, 72.59; H, 7.34; N, 4.97. C17H20BNO2. Calculated (%):
C, 72.62; H, 7.17; N, 4.98. The 1H NMR spectrum shows signals
1
of two diastereomers in a ratio of 2 : 1. H NMR of the major
isomer, δ: 2.32 (s, 3 H, NMe); 4.13—4.20 (m, 2 H, OCH2);
1
5.35—5.39 (m, 1 H, OCH). H NMR of the minor isomer, δ:
2.38 (s, 3 H, MeN); 4.28—4.34 (m, 2 H, OCH2); 5.22—5.26 (dd,
1 H, OCH). 1H NMR (unresolved signals of a mixture of diasteꢀ
reomers), δ: 2.71—2.76, 2.83—2.96, 3.03—3.12, 3.16—3.20,
3.31—3.37, and 3.39—3.43 (all m, 4 H, NCH2); 7.25—7.32,
7.34—7.39, 7.50—7.53, 7.63—7.65, 7.72—7.74, and 8.23—8.25
(all m, 10 H, Ph). 13C NMR of the major isomer, δ: 48.76 (NMe);
60.89, 63.00, 68.66 (NCH2, OCH2); 74.37 (OCH), 125.66,
127.39, 127.67, 127.71, 128.51, 133.30, 135.60, 141.27 (Ph).
13C NMR of the minor isomer, δ: 46.82 (NMe); 61.01, 61.30,
65.68 (NCH2, OCH2); 73.97 (OCH); 125.92, 127.79, 127.95,
128.63, 132.68, 141.17 (Ph). Two signals for the aromatic C
atoms were not observed in the spectrum due apparently to coꢀ
alescence of some signals. 11B NMR, δ: 12.58. MS, m/z (Irel (%)):
281 [M]+ (2), 204 [M – Ph]+ (74), 175 [M – PhCHO]+ (100),
160 [M – CH2CHPhO]+ (23).
erythroꢀ6ꢀMethylꢀ2,4,5,7,8ꢀpentaphenylꢀ1,3,6,2ꢀdioxazaꢀ
borocane (5). The reaction of PhB(OH)2 (0.055 g, 0.45 mmol)
with erythroꢀMeN(CHPhCHPhOH)2 (0.19 g, 0.45 mmol) proꢀ
duced borocane as a white waxꢀlike compound in a yield of 0.19 g
(82%). Found (%): C, 81.60; H, 6.88; N, 3.28. C35H32BNO2.
Calculated (%): C, 82.52; H, 6.33; N, 2.75. The 1H NMR specꢀ
trum shows signals of two diastereomers in a ratio of 1 : 1. 1H NMR
of one diastereomer, δ: 2.26 (s, 3 H, NMe); 5.12 (d, 2 H, NCH,
J = 6.0 Hz); 6.55 (d, 2 H, OCH, J = 6.0 Hz); 6.98—7.50 (m, 25 H,
6ꢀMethylꢀ2,4,4ꢀtriphenylꢀ1,3,6,2ꢀdioxazaborocane (2). The
reaction of phenylboronic acid (0.054 g, 0.44 mmol) with
MeN(CH2CPh2OH)(CH2CH2OH) (0.12 g, 0.44 mmol) affordꢀ
ed borocane 2 as a white powder in a yield of 0.14 g (87%).
Found (%): C, 77.01; H, 6.60; N, 4.10. C23H24BNO2. Calculatꢀ
1
Ph). H NMR of another diastereomer, δ: 1.63 (s, 3 H, NMe);
4.16 and 4.60 (both d, 2 H, NCH, J = 5.5 Hz); 5.80 and 6.05
(both d, 2 H, OCH, J = 5.5 Hz). 1H NMR (unresolved signals of
a mixture of diastereomers), δ: 6.98—7.50 (m, 25 H, Ph). MS,
m/z (Irel (%)): 433 [M – Ph]+ (2), 390 [M – PhCHO – Me]+
(35), 299 [M – CHPhCHPhO – Me]+ (56).
1
ed (%): C, 77.33; H, 6.77; N, 3.92. H NMR, δ: 2.25 (s, 3 H,
NMe); 2.84—2.91 and 3.02—3.07 (both m, 1 H each, NCH2);
3.63—3.76 (m, 2 H, AB system, protons of the NCH2CPh2
group); 4.02—4.08 (m, 2 H, OCH2); 7.14—7.37 and 7.61—7.69
(both m, 15 H, Ph). 13C NMR, δ: 48.01 (NMe); 59.46 (NCH2);
61.38 (NCH2CPh2); 68.70 (OCH2); 82.01 (OCPh2); 125.22,
125.52, 126.67, 126.76, 127.29, 127.57, 128.24, 128.36, 133.68,
133.93, 147.97, 148.39 (Ph). 11B NMR, δ: 12.69. MS, m/z
(Irel (%)): 357 [M]+ (1), 280 [M – Ph]+ (100), 265 [M – Ph – Me]+
(5), 174 [M – Ph2CO]+ (47).
6ꢀBenzylꢀ2ꢀ(4ꢀmethylphenyl)ꢀ1,3,6,2ꢀdioxazaborocane (6).
The reaction of paraꢀtolylboronic acid (0.27 g, 2 mmol) with
PhCH2N(CH2CH2OH)2 (0.39 g, 2 mmol) afforded borocane 6
as a white powder in a yield of 0.46 g (78%). Found (%): C, 73.14;
H, 6.92; N, 4.45. C18H22BNO2. Calculated (%): C, 73.24;
1
H, 7.51; N, 4.75. H NMR, δ: 2.32 (s, 3 H, NMe); 2.79—2.85
erythroꢀ6ꢀMethylꢀ2,4,5ꢀtriphenylꢀ1,3,6,2ꢀdioxazaborocane
(3). The reaction of phenylboronic acid (0.144 g, 1 mmol) with
erythroꢀMeN(CHPhCHPhOH)(CH2CH2OH) (0.32 g, 1 mmol)
afforded borocane 3 as a white powder in a yield of 0.30 g (84%).
Found (%): C, 77.69; H, 6.64; N, 4.18. C23H24BNO2. Calculatꢀ
and 3.16—3.26 (both m, 4 H, NCH2); 3.38 (s, 2 H, PhCH2); 4.18
(t, 4 H, OCH2); 7.13—7.20, 7.33—7.35, and 7.60 (all m, 9 H,
1
Ph). H NMR (DMSOꢀd6, 87 °C), δ: 2.28 (s, 3 H, NMe); 3.01
(br.s, 4 H, NCH2); 3.34 (s, 2 H, PhCH2); 3.98 (t, 4 H, OCH2);
7.07, 7.35—7.39, 7.52 (d + m + d, 9 H, Ph). 13C NMR, δ: 21.37
(Me), 56.42 (NCH2), 62.89 (OCH2), 62.94 (PhCH2), 128.33,
128.84, 129.03, 130.73, 132.73, 133.46, 135.67, 137.26 (Ph).
11B NMR, δ: 12.94. MS, m/z (Irel (%)): 295 [M]+ (2), 204
[M – C6H4Me]+ (40), 174 [M – C6H4Me – CH2O]+ (4), 174
[M – Me– PhCHO]+ (29).
6ꢀMethylꢀ2ꢀ(4ꢀmethylphenyl)ꢀ4,4ꢀdiphenylꢀ1,3,6,2ꢀdioxaꢀ
zaborocane (7). A mixture of paraꢀtolylboronic acid (0.15 g,
1.1 mmol) and MeN(CH2CPh2OH)(CH2CH2OH) (0.3 g,
1.1 mmol) was refluxed in dioxane. After recrystallization from
acetonitrile, borocane 7 was obtained as a white powder in
a yield of 0.18 g (45%). Found (%): C, 77.36; H, 7.01; N, 3.59.
C24H26BNO2. Calculated (%): C, 77.64; H, 7.06; N, 3.77.
1H NMR, δ: 2.26 and 2.29 (both s, 3 H each, 2 Me); 2.82—2.90
and 3.00—3.06 (both m, 1 H each, NCH2); 3.71—3.80 (m, 2 H,
AB system, NCH2C(Ph)2); 4.00—4.07 (m, 2 H, OCH2); 7.05—7.07
and 7.13—7.36 (both m, 10 H); 7.49—7.51 and 7.65—7.69
1
ed (%): C, 77.33; H, 6.77; N, 3.92. H NMR, δ: 1.99 (s, 3 H,
NMe); 2.22—2.31 and 3.23—3.31 (both m, 1 H each, NCH2);
4.25—4.43 (m, 2 H, OCH2); 4.45 (br.s, 1 H, NCH); 5.99 (br.s, 1 H,
OCH); 7.01—7.33 and 7.81—7.83 (both m, 15 H, Ph). 13C NMR,
δ: 45.16 (NMe); 63.13, 63.93 (NCH2, OCH2); 70.48 (NCH);
78.96 (OCH); 126.03, 126.17, 126.87, 127.28, 127.39, 127.58,
127.85, 128.51, 131.56, 132.58, 133.53, 140.18 (Ph). 11B NMR,
δ: 13.11. MS, m/z (Irel (%)): 357 [M]+ (13), 280 [M – Ph]+ (71),
251 [M – PhCHO]+ (73), 179 [M – Ph – PhCHO]+ (31), 146
[M – CHPhCHPhO]+ (29).
threoꢀ6ꢀMethylꢀ2,4,5ꢀtriphenylꢀ1,3,6,2ꢀdioxazaborocane
(4). The reaction of phenylboronic acid (0.34 g, 2.76 mmol) with
threoꢀMeN(CHPhCHPhOH)(CH2CH2OH) (0.75 g, 2.76 mmol)
gave borocane 4 as a white powder in a yield of 0.75 g (76%).
Found (%): C, 77.35; H, 6.49; N, 4.01. C23H24BNO2. Calculatꢀ
ed (%): C, 77.33; H, 6.77; N, 3.92. The 1H NMR spectrum

1928
Russ.Chem.Bull., Int.Ed., Vol. 57, No. 9, September, 2008
Lermontova et al.
(both m, 4 H, Ph). 13C NMR, δ: 21.35 (Me); 47.96 (NMe); 59.34
(NCH2); 61.30 (NCH2CPh2); 68.61 (OCH2); 81.86 (OCPh2);
125.23, 125.52, 126.61, 126.70, 128.09, 128.19, 128.32, 133.72,
136.92, 148.05, 148.47 (Ph). 11B NMR, δ: 12.73. MS, m/z
(Irel (%)): 371 [M]+ (11), 280 [M – C6H4Me]+ (58), 265
[M – C6H4Me – Me]+ (2), 188 [M – Ph2CO]+ (100).
erythroꢀ6ꢀMethylꢀ2ꢀ(4ꢀmethylphenyl)ꢀ4,5ꢀdiphenylꢀ1,3,6,2ꢀ
dioxazaborocane (8). The reaction of paraꢀtolylboronic acid (0.3 g,
2.2 mmol) with erythroꢀMeN(CHPhCHPhOH)(CH2CH2OH)
(0.6 g, 2.2 mmol) afforded borocane 8 as a white powder in
a yield of 0.52 g (63%). Found (%): C, 77.92; H, 6.98; N, 3.80.
C24H26BNO2. Calculated (%): C, 77.64; H, 7.06; N, 3.77.
1H NMR, δ: 2.00 and 2.33 (both s, 3 H each, 2 Me); 3.23—3.33
and 3.57—3.65 (both m, 1 H each, NCH2); 4.25—4.33 and
4.36—4.41 (both m, 1 H each, OCH2); 4.45 (br.s, 1 H, NCH);
5.99 (br.s, 1 H, OCH); 7.05—7.15, 7.26—7.32, and 7.66—7.73
(all m, 14 H, Ph). 13C NMR, δ: 21.35 (Me); 45.13 (NMe); 63.08
(NCH2); 63.87 (OCH2); 75.33 (NCH); 79.98 (OCH); 126.08,
126.24, 127.62, 127.78, 127.90, 128.18, 131.60, 133.57, 136.82,
140.15 (Ph). 11B NMR, δ: 13.00. MS, m/z (Irel (%)): 371 [M]+
(3), 280 [M – CH3Ph]+ (5), 265 [M – PhCHO]+ (12).
(unresolved signals of the mixture of two diastereomers), δ:
2.22—2.28 and 2.63—2.70 (both m, 1 H, NCH2); 3.88—3.93
(m, 1 H, OCH2, NCH); 7.12—7.18 and 7.26—7.39 (both m,
10 H, Ph). 13C NMR of the major isomer, δ: 1.03 (BMe); 45.00
(NMe); 53.61 (NCH2); 61.63 (OCH2); 76.53 (NCH); 78.86
(OCH); 126.56, 127.54, 128.11, 128.98, 129.75, 130.69, 140.83
(Ph). The signal for one quaternary C atom was not observed in
the spectrum. 13C NMR of the minor isomer, δ: 0.85 (BMe);
41.79 (NMe); 53.90 (NCH2); 60.08 (OCH2); 75.69 (NCH); 76.80
(OCH); 126.69, 127.61, 128.07, 128.89, 129.71, 130.85, 140.44
(Ph). The signal for one quaternary C atom was not observed in
the spectrum. 11B NMR, δ: 14.29. MS, m/z (Irel (%)): 295 [M]+
(4), 280 [M – Me]+ (90), 189 [M – PhCHO]+, (32) 174
[M – Me– PhCHO]+ (20).
N,NꢀDimethylꢀ2ꢀ[(6ꢀmethylꢀ4,4ꢀdiphenylꢀ1,3,6,2ꢀdioxazaꢀ
borocanꢀ2ꢀyl)oxy]ethaneamine (12). A solution of borate 15 (0.69 g,
2.5 mmol) and erythroꢀMeN(CHPhCHPhOH)(CH2CH2OH)
(0.68 g, 2.5 mmol) in toluene (15 mL) was stirred at ~20 °C for 24 h.
Volatile components were removed under reduced pressure, and
the residue was washed with Et2O (10 mL). Borocane 12 was
1
obtained as a white powder in quantitative yield. H NMR, δ:
threoꢀ6ꢀMethylꢀ2ꢀ(4ꢀmethylphenyl)ꢀ4,5ꢀdiphenylꢀ1,3,6,2ꢀdiꢀ
oxazaborocane (9). The reaction of paraꢀtolylboronic acid (0.15 g,
1.1 mmol) with threoꢀMeN(CHPhCHPhOH)(CH2CH2OH)
(0.3 g, 1.1 mmol) produced borocane 9 as a white powder in
a yield of 0.32 g (78%). Found (%): C, 78.02; H, 7.01; N, 3.63.
C24H26BNO2. Calculated (%): C, 77.64; H, 7.06; N, 3.77. The
1H and 13C NMR spectra show signals of two diastereomers in
2.19 (s, 6 H, NMe); 2.48 (t, 2 H, NCH2); 2.56 (s, 3 H, NMe);
2.80—2.96 (m, 2 H, NCH2); 3.55—3.86 (m, 6 H, NCH2, OCH2);
7.11—7.16, 7.23—7.27, and 7.54—7.57 (all m, 10 H, Ph).
13C NMR, δ: 45.52, 46.14 (NMe); 59.48, 59.99, 61.19, 61.51, 68.26
(NCH2, OCH2); 79.67 (OCH); 125.33, 125.51, 126.69, 128.12,
128.22, 147.46, 147.69 (Ph); one signal for the aromatic C atom
was not observed in the spectrum due apparently to coalescence
of some signals. 11B NMR, δ: 10.48. MS, m/z (Irel (%)): 297
[M – CH2CH2NMe2]+ (7), 114 [M – CPh2O – CH2CH2NMe2]+
(100).
1
a ratio of 3 : 1. H NMR of the major isomer, δ: 2.27 and 2.35
(both s, 3 H each, Me); 2.30—2.37 and 3.47—3.53 (both m, 1 H
each, NCH2); 3.87 (d, 1 H, NCH, J = 10.5 Hz); 4.13—4.18 and
4.35—4.38 (both m, 1 H each, OCH2); 5.72 (d, 1 H, OCH,
6ꢀBenzylꢀ2ꢀfluoroꢀ1,3,6,2ꢀdioxazaborocane (13). All operaꢀ
tions were carried out under argon. Boron trifluoride etherate
(0.7 g, 5 mmol) was added dropwise with stirring to a solution of
PhCH2N(CH2CH2OSiMe3)2 (1.69 g, 5 mmol) in toluene (15 mL).
The reaction mixture was refluxed for 45 h, the hot solution was
filtered, volatile components were removed in vacuo to 1/3 of the
initial volume, and the residue was cooled to –10 °C. The preꢀ
cipitate was filtered off. Borocane 13 was obtained as a white
1
J = 10.5 Hz). H NMR of the minor isomer, δ: 1.94 and 2.33
(both s, 3 H each, Me); 2.66—2.79 (m, 2 H, NCH2); 3.19—3.22
(m, 1 H, OCH2), 4.10 (d, 1 H, J = 10.5 Hz); 4.43—4.50 (m, 1 H,
OCH2); 5.60 (d, 1 H, OCH, J = 10.5 Hz); 7.13—7.24 and 7.36—7.48
(both m, 10 H, Ph); 7.62 and 7.72 (both m, 2 H each, C6H4).
13C NMR of the major isomer, δ: 21.41 (Me); 47.00 (NMe);
54.19 (NCH2); 63.18 (OCH2); 76.80 (NCH); 79.26 (OCH).
13C NMR of the minor isomer, δ: 21.39 (Me); 42.49 (NMe);
58.49 (NCH2); 61.00 (OCH2); 75.44 (NCH); 77.66 (OCH).
126.67, 126.82, 127.69, 128.18, 128.24, 128.29, 128.89, 129.02,
129.77, 130.58, 130.85, 131.04, 133.48, 133.53, 135.69, 137.09,
140.36 (Ph). Seven signals for the aromatic C atoms were
not observed in the spectrum due apparently to coalescence
of some signals. 11B NMR, δ: 13.12. MS, m/z (Irel (%)): 371 [M]+
(4), 280 [M – CH3Ph]+ (18), 265 [M – PhCHO]+ (17), 179
[M – CH3Ph – PhCHO]+ (19).
threoꢀ2,6ꢀDimethylꢀ4,5ꢀdiphenylꢀ1,3,6,2ꢀdioxazaborocane
(11). The reaction of methylboronic acid (0.044 g, 0.74 mmol)
with threoꢀMeN(CHPhCHPhOH)(CH2CH2OH) (0.2 g,
0.74 mmol) afforded borocane 11 as a white powder in a yield of
0.12 g (55%). Found (%): C, 73.56; H, 7.62; N, 4.65. C18H22BNO2.
Calculated (%): C, 73.24; H, 7.51; N, 4.75. The 1H and 13C NMR
spectra show signals of two diastereomers in a ratio of 3 : 1. 1H NMR
of the major isomer, δ: 0.13 (s, 3 H, BMe); 2.62 (s, 3 H, NMe);
3.44—3.51 (m, 1 H, NCH2); 3.81 (d, 1 H, NCH, J = 10.5 Hz);
4.13—4.18 (m, 1 H, OCH2); 5.51 (d, 1 H, OCH, J = 10.5 Hz).
1H NMR of the minor isomer, δ: 0.06 (s, 3 H, BMe); 2.24 (s, 3 H,
NMe); 3.18—3.21 (m, 1 H, NCH2); 4.03—4.07 and 4.26—4.32
(both m, 2 H, OCH2); 5.23 (d, 1 H, OCH, J = 10.0 Hz). 1H NMR
1
powder in a yield of 0.17 g (15%). H NMR, δ: 2.78—2.84 and
3.29—3.36 (both m, 2 H each, NCH2); 3.88—4.00 (m, 4 H,
OCH2); 4.02 (s, 2 H, CH2Ph); 7.33—7.43 (m, 5 H, Ph). 1H NMR
(DMSOꢀd6, 87 °C), δ: 3.49—3.57 (m, 4 H, NCH2); 3.72 (br.s,
4 H, OCH2); 3.96 (s, 2 H, CH2Ph); 7.37—7.41 and 7.54—7.56
(both m, 5 H, Ph). 13C NMR, δ: 56.22 (NCH2); 58.97, 59.04
(OCH2); 60.28 (CH2Ph); 129.17, 129.47, 129.17 (Ph). 19F NMR,
δ: –158.33. 11B NMR, δ: 9.37. MS, m/z (Irel (%)): 223 [M]+ (10).
threoꢀ2ꢀFluoroꢀ6ꢀmethylꢀ4,5ꢀdiphenylꢀ1,3,6,2ꢀdioxazaboroꢀ
cane (14). The synthesis was carried out as described above startꢀ
ing from threoꢀMeN(CHPhCHPhOSiMe3)(CH2CH2OSiMe3)
(0.68 g, 1.6 mmol) and BF3•Et2O (0.23 g, 1.6 mmol). Borocane
14 was obtained as a white powder in a yield of 0.14 g (29%). The
1H and 13C NMR spectra show signals of two diastereomers in
a ratio of 2 : 1. 1H NMR, δ: 2.32 and 2.67 (both s, 3 H each, NMe);
2.20—2.26, 2.75—2.85, 3.20—3.24, 3.51—3.61, and 3.98—4.17
(all m, 4 H, NCH2, OCH2); 3.88 and 4.00 (both d, 1 H, NCH,
J = 10.0 Hz); 5.44 and 5.45 (both d, 1 H, OCH, J = 10.5 Hz);
7.33—7.43 (m, 5 H, Ph). 13C NMR of the major isomer, δ: 42.57
(NMe); 53.51 (NCH2); 60.56 (OCH2); 75.28 (NCH); 78.69
(OCH). 13C NMR of the minor isomer, δ: 39.97 (NMe); 58.96
(NCH2); 59.72 (OCH2); 75.68 (NCH); 76.92 (OCH). 126.38,

Structures of new 1,3,6,2ꢀdioxazaborocanes
Russ.Chem.Bull., Int.Ed., Vol. 57, No. 9, September, 2008
1929
126.58, 127.46, 127.79, 127.87, 128.10, 128.22, 129.09, 129.15,
130.08, 130.14, 130.52, 130.83, 139.63, 139.93 (Ph). One signal
for the aromatic C atom was not observed in the spectrum due
apparently to coalescence of some signals. 19F NMR, δ: –157.27.
11B NMR, δ: 8.84.
6ꢀBenzylꢀ2,2ꢀdiethoxyꢀ1,3,6,2ꢀdioxazagermocane (16). Gerꢀ
manium ethoxide (0.25 g, 0.75 mmol) and AlCl3 (∼0.01 g) were
added to a solution of borocane 6 (0.22 g, 0.75 mmol) in toluene
(15 mL). The reaction mixture was refluxed for 6 h, volatile
components were removed in vacuo, and the solid residue was
washed with diethyl ether and dried in vacuo. Compound 16 was
obtained as a white solid substance in a yield of 0.17 g (63%). The
1H and 13C NMR spectra are identical to those published in the
literature.43
(NCH2Ph); 58.64 (OCH2), 129.14, 129.44, 131.01, 131.27
(C arom.).
Xꢀray diffraction study. The crystallographic characteristics
and the Xꢀray data collection and refinement statistics for comꢀ
pounds 3, 4, 8, and 13 are given in Table 6. The Xꢀray diffraction
data for compounds 3, 4, and 8 were collected on an automated
SMART APEX diffractometer; for compound 13, on a STOE
IPDS II diffractometer (MoꢀKα radiation, λ = 0.71073 Å). The
structures were solved by direct methods (SHELXꢀ86).44 All nonꢀ
hydrogen atoms were refined anisotropically by the fullꢀmatrix
leastꢀsquares method based on F2 (SHELXLꢀ97).45 In the strucꢀ
tures of 3 and 4, all hydrogen atoms were located in difference
Fourier maps and refined isotropically. In the structure of 8, all
hydrogen atoms (except for the hydrogens of the disordered meꢀ
thyl and methylene groups) were also located in difference Fouꢀ
rier maps and refined isotropically. In the structure of 13, all
hydrogen atoms were positioned geometrically and refined using
a riding model. In the structure of 8, the methylene group at the
C(22) atom is disordered over two envelope positions of the fiveꢀ
membered ring with an occupancy ratio of 0.63/0.37; the hydroꢀ
gen atoms of the methyl group at the C(8) atom are rotationally
disordered with an occupancy ratio of 0.60/0.40.
6ꢀBenzylꢀ2,2ꢀdichloroꢀ1,3,6,2ꢀdioxazagermocane (17). Gerꢀ
manium tetrachloride (0.33 g, 1.5 mmol) and AlCl3 (∼0.01 g)
were added to a solution of borocane 6 (0.45 g, 1.5 mmol) in
toluene (15 mL). The reaction mixture was refluxed for 6 h, the
hot solution was filtered, and volatile components were removed
in vacuo. The solid residue was washed with diethyl ether and
dried in vacuo. Compound 17 was obtained as a paleꢀbrown powꢀ
der in a yield of 0.2 g (40%). Found (%): C, 39.35; H, 4.50;
N, 4.28. C11H15Cl2GeNO2. Calculated (%): C, 39.23; H, 4.49;
Quantum chemical calculations. The calculations were carꢀ
ried out by the density functional theory (DFT) method with the
use of the nonempirical generalized gradient approximation, the
PBE functional46,47 and the TZ2P basis set using the PRIRODA
program.48,49 The geometry optimization was performed for all
1
N, 4.16. H NMR, δ: 2.71—2.77 and 3.01—3.07 (both m, 4 H,
2 NCH2); 3.97—4.03 and 4.08—4.14 (both m, 4 H, 2 OCH2);
4.00 (s, 2 H, CH2Ph); 7.13—7.16, 7.21—7.23, 7.41—7.42 (all m,
5 H, H arom.). 13C NMR (CDCl3), δ: 49.18 (NCH2); 57.29
Table 6. Crystallographic characteristics and the Xꢀray data collection and refinement statistics for compounds 3, 4, 8, and 13
Parameter
3
4
8
13
Molecular formula
М
Crystal dimensions/mm
Crystal system
Space group
a/Å
b/Å
c/Å
C23H24BNO2
357.24
0.20×0.20×0.10
Triclinic
Pꢀ1
10.5161(11)
11.0230(11)
16.9209(17)
92.035(2)
90.844(2)
99.318(2)
1933.9(3)
4
C23H24BNO2
357.24
0.30×0.05×0.05
Orthorhombic
Pna21
10.8716(13)
18.748(2)
9.1986(11)
90
C24H26BNO2
371.27
0.30×0.26×0.26
Monoclinic
P21/c
11.3647(5)
10.2607(4)
17.5091(7)
90
91.0550(10)
90
C11H15BFNO2
223.05
0.17×0.14×0.09
Orthorhombic
Pbca
12.058(4)
10.925(2)
16.534(6)
90
90
90
2178(1)
8
1.360
α/deg
β/deg
90
90
1874.9(4)
4
1.266
γ/deg
3
V/Å
2041.39(15)
4
Z
dcalc/g cm–3
1.227
0.077
1.208
0.075
μ/mm–1
0.079
0.102
F(000)
760
760
792
944
Temperature/K
θꢀScan range/deg
Number of measured reflections
umber of independent
120(2)
1.20—28.00
12994
120(2)
2.17—28.00
11482
120(2)
1.79—28.00
13460
173(2)
2.46—26.04
14215
9160
2400
4923
2067
reflections (Rint
)
(0.0255)
6520
679
0.0585
0.1302
(0.0447)
2099
340
0.0386
0.0899
1.048
(0.0320)
3716
341
0.0464
0.1136
(0.3445)
606
146
0.0676
0.1120
0.796
Number of reflections with I ≥ 2σ(I)
Number of refinement parameters
R1 [I ≥ 2σ(I)]
wR2 (based on all reflections)
Goodnessꢀofꢀfit on F2
1.061
1.038
Residual electron density
/e Å–3, max/min
0.274/–0.215
0.202/–0.164
0.267/–0.209
0.166/–0.188

1930
Russ.Chem.Bull., Int.Ed., Vol. 57, No. 9, September, 2008
Lermontova et al.
stable compounds. The type of stationary points was confirmed
by the vibrational frequency analysis. The zeroꢀpoint vibrational
energy correction was not applied. It has been previously estabꢀ
lished that this correction in calculations of the compounds unꢀ
der consideration is very small and has virtually no effect on
the relative changes in the energy of the systems.
23. M. M. Olmstead, J. C. Fettinger, S. Gamsey, J. W. Clary,
B. Singaram, Acta Crystallogr., 2006, C62, o333.
24. T. Mancilla, L. S. ZamudioꢀRivera, H. I. Beltrán, R. Santilꢀ
lan, N. Farfán, ARKIVOC, 2005, 366.
25. C. Bresner, S. Aldridge, I. A. Fallis, C. Jones, L. L. Ooi,
Angew. Chem., Int. Ed. Engl., 2005, 44, 3606.
26. S. J. Rettig, J. Trotter, Can. J. Chem., 1975, 53, 1393.
27. R. A. Howie, O. C. Musgrave, J. L. Wardell, Main Group
Met. Chem., 1997, 20, 723.
We thank J. A. K. Howard (UK) for allowing us to
perform Xꢀray diffraction studies.
28. S. M. S. V. DoidgeꢀHarrison, O. C. Musgrave, J. L. Wardell,
J. Chem. Crystallogr., 1998, 28, 361.
29. S. J. Sopkovaꢀde Oliveira, A. Bouillon, J. C. Lancelot,
S. Rault, Acta Crystallogr., Sect. C, 2004, 60, o582.
30. T. Mancilla, H. Hopfl, G. Bravo, L. Carrillo, Main Group
Met. Chem., 1997, 20, 31.
This study was financially supported by the Russian
Foundation for Basic Research (Project No. 06ꢀ03ꢀ33032a).
References
31. A. N. Thadani, R. A. Batey, A. J. Lough, D. V. Smil, Acta
Crystallogr., Sect. E, 2002, 58, o238.
1. R. Csuk, H. Honig, H. Weidmann, H. K. Zimmermann,
Arch. Pharm., 1984, 317, 336.
32. H. Hoepfl, N. Farfan, J. Organomet. Chem., 1997, 547, 71.
33. N. Farfan, H. Hoepfl, V. Barba, E. M. Ochoa, R. Santillan,
E. Gomez, A. Gutierrez, J. Organomet. Chem., 1999, 581, 70.
34. Z. Taira, K. Osaki, Inorg. Nucl. Chem. Lett., 1971, 7, 509.
35. M. A. PazꢀSandoval, C. FernandezꢀVincent, G. Uribe,
R. Contreras, Polyhedron, 1988, 7, 679.
36. A. A. Selina, S. S. Karlov, G. S. Zaitseva, Khim. Geterotsikl.
Soedin., 2006, 1777 [Chem. Heterocycl. Compd., 2006
(Engl. Transl.)].
37. A. A. Korlyukov, K. A. Lyssenko, M. Y. Antipin, V. N. Kirin,
E. A. Chernyshev, S. P. Knyazev, Inorg. Chem., 2002,
41, 5043.
38. S. S. Karlov, A. A. Selina, E. S. Chernyshova, Yu. F.
Oprunenko, A. A. Merkulov, V. A. Tafeenko, A. V. Churakov,
J. A. K. Howard, G. S. Zaitseva, Inorg. Chim. Acta, 2007,
360, 563.
39. E. Kh. Lermontova, A. A. Selina, S. S. Karlov, A. V.
Churakov, J. A. K. Howard, Yu. F. Oprunenko, M. Yu. Anꢀ
tipin, J. Sundermeyer, G. S. Zaitseva, J. Organomet. Chem.,
2006, 691, 5722.
40. A. Sonoda, N. Takagi, K. Ooi, T. Hirotsu, Bull. Chem. Soc.
Jpn, 1998, 71, 161.
41. S. S. Karlov, E. Kh. Lermontova, M. V. Zabalov, A. A. Seliꢀ
na, A. V. Churakov, J. A. K. Howard, M. Yu. Antipin, G. S.
Zaitseva, Inorg. Chem., 2005, 44, 4879.
42. O. H. Jonson, H. E. Fritz, J. Am. Chem. Soc., 1953, 75, 718.
43. E. Kh. Lermontova, A. V. Churakov, M. M. Huang, Yu. F.
Oprunenko, S. S. Karlov, G. S. Zaitseva, Zh. Neorg.
Khim., 2009, No. 2 [Russ. J. Inorg. Chem., 2009, No. 2
(Engl. Transl.)].
2. C. A. Perks, A. J. Mill, G. Constantine, K. G. Harrison,
J. A. B. Gibson, Br. J. Radiol., 1988, 61, 1115.
3. A. Jabbour, D. Steinberg, V. M. Dembitsky, A. Moussaieff,
B. Zaks, M. Srebnik, J. Med. Chem., 2004, 47, 2409.
4. A. Jabbour, M. Srebnik, B. Zaks, V. Dembitsky, D. Steinꢀ
berg, Int. J. Antimicrob. Agents, 2005, 26, 491.
5. A. M. Irving, C. M. Vogels, L. G. Nikolcheva, J. P. Edwards,
X.ꢀF. He, M. G. Hamilton, M. O. Baerlocher, F. J. Baerloꢀ
cher, A. Decken, S. A. Westcott, New J. Chem., 2003, 27, 1419.
6. V. Martichonok, J. B. Jones, J. Am. Chem. Soc., 1996,
118, 950.
7. H. C. Brown, A. K. Gupta, J. V. N. V. Prasad, Bull. Chem.
Soc. Jpn, 1988, 61, 93.
8. H. C. Brown, G. M. Chen, P. V. Ramachandran, Chirality,
1997, 9, 506.
9. C. D. Davies, S. P. Marsden, E. S. E. Stokes, Tetrahedron
Lett., 1998, 39, 8513.
10. C. D. Davies, S. P. Marsden, E. S. E. Stokes, Tetrahedron
Lett., 2000, 41, 4229.
11. C. N. Farthing, S. P. Marsden, Tetrahedron Lett., 2000,
41, 4235.
12. J. Mortier, M. Vaultier, B. Plunian, L. Toupet, Heterocycles,
1999, 50, 703.
13. N. Farfan, T. Mancilla, D. Castillo, G. Uribe, L. Carrillo,
P. JosephꢀNathan, R. Contreras, J. Organomet. Chem., 1990,
381, 1.
14. N. Farfan, P. JosephꢀNathan, L. M. Chiquete, R. Contreras,
J. Organomet. Chem., 1988, 348, 149.
15. T. Mancilla, R. Contreras, J. Organomet. Chem., 1987,
321, 191.
44. G. M. Sheldrick, Acta Crystallogr. Sect. A, 1990, 46A, 467.
45. G. M. Sheldrick, SHELXLꢀ97. Program for the Refinement of
Crystal Structures, University of Göttingen, Götinngen, Gerꢀ
many, 1997.
16. N. Farfan, R. Contreras, Heterocycles, 1985, 23, 2989.
17. B. Abarca, R. Ballesteros, F. Blanco, A. Bouillon, V. Collot,
J. R. Dominguez, J. C. Lancelot, S. Rault, Tetrahedron, 2004,
60, 4887.
46. J. P. Perdew, K. Burke, M. Ernzerhoff, Phys. Rev. Lett.,
1996, 77, 3865.
18. P. B. Hodgson, F. H. Salingue, Tetrahedron Lett., 2004,
45, 685.
47. M. Ernzerhoff, G. E. Scuseria, J. Chem. Phys., 1999,
110, 5029.
19. A. N. Thadani, R. A. Batey, A. J. Lough, Acta Crystallogr.,
Sect. E, 2001, 57, o762.
48. D. N. Laikov, Chem. Phys. Lett., 1997, 281, 151.
49. D. N. Laikov, Yu. A. Ustynyuk, Izv. Akad. Nauk, Ser. Khim.,
2005, 804 [Russ. Chem. Bull., Int. Ed., 2005, 54, 820].
20. A. N. Thadani, R. A. Batey, A. J. Lough, Acta Crystallogr.,
Sect. E, 2001, 57, o1010.
21. G. Laus, A. G. Müller, H. Schottenberger, K. Wurst, M. R.
Buchmeiser, K.ꢀH. Ongania, Monatsh. Chem., 2006, 137, 69.
22. S. Aldridge, R. J. Calder, D. L. Coombs, C. Jones, J. W.
Steed, S. Coles, M. B. Hursthouse, New J. Chem., 2002, 26, 677.
Received February 20, 2008;
in revised form June 26, 2008