Synthesis and structural studies of symmetric and unsymmetric adamantylmethyleneazines

Article abstract of DOI:10.1002/(SICI)1099-1395(199906)12:6<455::AID-POC146>3.0.CO;2-3

The synthesis and spectroscopic properties (¹H, ¹³C and ¹⁵N NMR, in solution and in the solid state) of six new 1-adamantylmethlene azines are reported. The crystal and molecular structures of 1-adamantylcarbaldehyde azine and 1-adamantyl methyl ketone azine, which exist in the solid state in the E,E-configuration, were determined by x-ray analysis. The geometric characteristics of the azine central bridge and the preferred configuration with regard to it (E,E, E,Z, or Z,Z) were investigated by means of the crystallographic data retrieved from the Cambridge Structural Database and ab initio quantum chemical calculations. Copyright

Full text of DOI:10.1002/(SICI)1099-1395(199906)12:6<455::AID-POC146>3.0.CO;2-3

JOURNAL OF PHYSICAL ORGANIC CHEMISTRY
J. Phys. Org. Chem. 12, 455–469 (1999)
Synthesis and structural studies of symmetric and
unsymmetric adamantylmethyleneazines
1
1
1
2
Dionisia Sanz, Mar õ a Alejandra Ponce, † Rosa Mar õ a Claramunt, * Cristina Fern a ndez-Casta nÄ o,
2
3
Concepci o n Foces-Foces and Jos e Elguero
1
Departamento de Qu õ mica Org a nica y Biolog õ a, Facultad de Ciencias, UNED, Senda del Rey s/n, E-28040 Madrid, Spain
Departamento de Cristalograf õÂ a, Instituto de Qu õÂ mica F õÂ sica `Rocasolano,' CSIC, Serrano 119, E-28006 Madrid, Spain
Instituto de Qu õ mica M e dica, CSIC, Juan de la Cierva 3, E-28006 Madrid, Spain
2
3
Received 23 September 1998; revised 10 November 1998; accepted 11 November 1998
1
13
15
ABSTRACT: The synthesis and spectroscopic properties ( H, C and N NMR, in solution and in the solid state) of
six new 1-adamantylmethylene azines are reported. The crystal and molecular structures of 1-adamantylcarbaldehyde
azine and 1-adamantyl methyl ketone azine, which exist in the solid state in the E,E-configuration, were determined
by x-ray analysis. The geometric characteristics of the azine central bridge and the preferred configuration with regard
to it (E,E, E,Z or Z,Z) were investigated by means of the crystallographic data retrieved from the Cambridge Structural
Database and ab initio quantum chemical calculations. Copyright  1999 John Wiley & Sons, Ltd.
KEYWORDS: Adamantylmethyleneazines; x-ray structures; ab initio calculations; multinuclear magnetic resonance;
cross-polarization magic angle spinning NMR
INTRODUCTION
static effects and steric repulsion of the two endo
substituents, a reason why non-protonated azines undergo
criss-cross cycloaddition instead of [4 ‡ 2] cycloaddi-
Azines are 2,3-diazabutadiene derivatives that can also
be viewed as N—N-linked diimines. They have been
widely studied as a part of heterocyclic compounds and
recently are receiving increasing attention for their
3
tion. In azines, the gauche conformation is destabilized
1
,2
by alkyl substitution in favour of the s-trans form, which
is usually the only conformer detected by spectroscopic
3
–5
8
biological, chemical and physical properties.
On the
methods.
other hand, the adamantyl group has been successfully
used to stabilize certain functional groups, and the high
crystalline character of adamantyl compounds provides
an additional advantage in the product isolation proce-
EXPERIMENTAL
6
dure. Moreover, the pharmacodynamic effects of the
adamantyl group are closely related to its highly
lipophilic character and compact symmetrical architec-
ture. On these bases, the aim of our work has been the
General methods. Melting-points were determined on a
7
synthesis and stereochemical structural studies of the
symmetric and unsymmetric adamantylmethyleneazines
1–6 (Scheme 1).
The conformation of the N—N bond in these azines
can be s-cis, s-trans, both planar, or s-gauche and, for
unsymmetric azines, there are four possible configura-
tions, E,E, E,Z, Z,E and Z,Z (Scheme 2). The s-cis
conformation is obviously destabilized owing to strong
interactions of the vicinal electron lone pairs, electro-
*
Correspondence to: R. M. Claramunt, Departamento de Qu ´ı mica
Org a´ nica y Biolog ı´ a, Facultad de Ciencias, UNED, Senda del Rey s/n,
E-28040 Madrid, Spain.
†
On leave from the Departamento de Qu ´ı mica Org a´ nica, Facultad de
Ciencias Exactas y Naturales, Universidad de Buenos Aires, Buenos
Aires, Argentina.
Contract/grant sponsor: DGES; Contract/grant number: PB96-0001-
C01/C02/C03.
Scheme 1
Copyright  1999 John Wiley & Sons, Ltd.
CCC 0894–3230/99/060455–15 $17.50

4
56
D. SANZ ET AL.
Scheme 2
hot-stage microscope and are uncorrected. Analytical
thin-layer chromatography was performed on Merck
the traces of it remaining in the reaction mixture were
destroyed with ammonium chloride in an ice-bath to
prevent heating of the solution. The solution was then
extracted with diethyl ether or dichloromethane and the
solvent evaporated off.
60F254 silica gel with a layer thickness of 0.2 mm.
Combustion analyses were performed with a Perkin-
Elmer model 2400 CHN instrument. NMR spectra were
obtained on Bruker AC-200 and DRX-400 instruments.
Filtration over dry silica gel 60 (230–400 mesh) using
hexane separates the unreacted 1-bromoadamantane and
1
13
The H and C chemical shifts (ꢀ, ppm) are given
1
5
relative to external tetramethylsilane. N NMR spectra
are referred to nitromethane as external standard; no
high-R secondary products and elution with hexane–
f
ethyl acetate (75:25) affords pure 1-adamantylcarbalde-
9
corrections for bulk differences were applied. Solid-
hyde (7) (yields 50–75%), m.p. 160–162°C (lit. m.p.
1
3
14
15
state C cross-polarization magic angle spinning (CP/
MAS) NMR spectra were obtained with a Bruker AC200
spectrometer using the experimental conditions already
139–141°C and 195–197.3°C ), R = 0.52 in hexane-
f
�
1
diethyl ether (9:1). IR (KBr): ꢁ(C
ꢁ(C O) band shifts to a lower value, 1670 cm , when
=O) = 1720 cm . The
�
1
=
1
0
described.
the 1-adamantylcarbaldehyde (7) is not completely pure,
so the IR technique is a useful tool to determine its purity.
Compounds. 1-Bromoadamantane, 1-adamantyl methyl
ketone (9), (E)-cinnamaldehyde (11) and benzophenone
(
12) are commercial products. Benzophenone hydrazone
1-Adamantylcarbaldehyde azine (1). To a solution of
35 mg (1.1 mmol) of anhydrous hydrazine in 4 ml of
ethanol, 328.8 mg (2 mmol) of 1-adamantylcarbaldehyde
(13) was obtained from benzophenone and hydrazine,
1
1
according to the literature.
(7) in 10 ml of ethanol were added with external cooling.
1
-Adamantylcarbaldehyde (7). This compound was
The reaction mixture was stirred at 0°C for 30 min. Azine
1, m.p. 217–218°C (chloroform–propan-2-ol or hexane),
yield 90%, C H N (M 324.5). Analysis: calculated C
1
2
synthesized by the Bouveault reaction starting from
dry 1-bromoadamantane (1.07 g, 5.0 mmol), anhydrous
N,N'-dimethylformamide (5.2 mmol), 10.5 mmol of 25%
lithium dispersion in mineral oil or lithium wire (both
containing 1% sodium; with a lesser amount of Na, e.g.
22
32
2
r
81.43, H 9.95, N 8.63; found C 81.31, H 9.65, N 8.75%.
When using 2 ml of anhydrous hydrazine and 103 mg
(0.63 mmol) of 1-adamantylcarbaldehyde in 2 ml of
ethanol and after 1 h of reaction at room temperature,
the 1-adamantylcarbaldehyde hydrazone (8) was isolated,
containing a 9% of 1. Upon standing in the solid state for
24 h, the hydrazone 8 was completely converted into
azine 1.
1
3
0.05%, the reaction did not work) in 50 ml of anhydrous
THF under argon and external cooling with ultrasonic
radiation from a Virsonic 300 Model 175893 Cell
Disrupter (20 kHz), the reaction being completed at
room temperature in 5 min (lithium dispersion)–50 min
15
(lithium wire) (the reaction was followed by thin-layer
Labelled [ N ]-1-adamantylcarbaldehyde azine (1)
2
chromatography). The excess of lithium was filtered and
was similarly prepared from 1-adamantylcarbaldehyde
Copyright  1999 John Wiley & Sons, Ltd.
J. Phys. Org. Chem. 12, 455–469 (1999)

SYMMETRIC AND UNSYMMETRIC ADAMANTYLMETHYLENEAZINES
457
1
5
17
(
7) (27.4 mg, 0.167 mmol) and [ N ]hydrazine sulphate
were solved by direct methods (SIR92) and refined by
least-squares procedures on Fobs. All hydrogens atoms
were obtained from difference Fourier synthesis and
refined isotropically in the last cycles of the refinement.
2
in 5 ml of ethanol at room temperature for 18 h.
1
-Adamantyl methyl ketone azine (2). Refluxing, for
4
1
h, a solution of 1-adamantyl methyl ketone (9) (1.79 g,
0 mmol) and anhydrous hydrazine (0.33 g, 10.3 mmol)
The weighting schemes were established as to give no
2
trends in k!D Fl vs kF l and ksinꢂ/ꢃl.
0
in 40 ml of ethanol gave 1.53 g (yield 86%) of 1-
adamantyl methyl ketone azine (2), m.p. 206–208°C
The structure of 3 (Scheme 1) has not been determined
since it is pseudoisomorphous with that of 2 [same
symmetry and analogous cell parameters: a = 6.8895(4),
(
chloroform–propan-2-ol), C H N (M 338.5). Analy-
24 36 2 r
˚
sis: calculated C 81.74, H 10.31, N 7.95; found C 81.72,
H 9.97, N 7.92%.
By reacting 2 g (11.2 mmol) of 1-adamantyl methyl
ketone (9) in 12 ml of ethanol with 8 ml of anhydrous
hydrazine at room temperature for 18 h, 2.09 g (yield
b = 21.0538(29), c = 6.8299(6) A and b = 101.255(7)°].
The scattering factors were taken from the International
18
Tables for X-Ray Crystallography. The calculations
1
9
20
were carried out with the XTAL, PESOS and
21
PARST set of programs running on a DEC200 work-
station. The atomic coordinates of 1 and 2 have been
deposited (CSD 101729 and 101730, respectively).
9
7%) of 1-adamantyl methyl ketone hydrazone (10) were
formed, m.p. 74.5–76.5°C. Attempts to crystallize 10
from hexane yielded the azine 2 as the only product.
Theoretical calculations. The ab initio calculations,
Azine 3. Reaction of 1-adamantyl methyl ketone
hydrazone (10) (192.3 mg, 1 mmol) with 1-adamantyl-
carbaldehyde (7) (164.4 mg, 1 mmol) in 10 ml of ethanol
at room temperature for 1 h yielded azine 3, m.p. 132–
without any geometrical restrictions, were performed
using the Gaussian94 program.
22
1
33.5°C (chloroform–methanol) (yield 90%), C H N
r
RESULTS AND DISCUSSION
Chemistry
23 34 2
(M 338.5). Analysis: calculated C 81.60, H 10.12, N
8
.28; found C 81.20, H 10.19, N 8.08%.
Azines 4 and 5. These azines were obtained by refluxing
for 2 h in ethanol solution benzophenone hydrazone (13),
with stoichiometric amounts of 1-adamantylcarbalde-
hyde (7) and 1-adamantyl methyl ketone (9), respec-
tively. Azine 4: m.p 104–105°C (hexane), yield 90%,
C H N (M 342.5). Analysis: calculated C 84.17, H
The symmetrical azines 1 and 2 were prepared by
12
reacting 1-adamantylcarbaldehyde (7) and 1-adamantyl
methyl ketone (9) with hydrazine in ethanol solution,
according to Scheme 3. As will be discussed later, the
azines have an E,E-configuration, which is consistent
with the steric demands of the substituents at the azine-C
atoms.
2
4
26
2
r
7.65, N 8.18; found C 83.91, H 7.37, N 8.33%. Azine 5:
m.p 126–128°C (ethanol), yield 83%, C H N (M
Formation of hydrazones 8 and 10 was observed when
an excess of hydrazine was employed. 1-Adamantyl
methyl ketone hydrazone (10) is fairly stable, but 1-
adamantylcarboxaldehyde hydrazone (8) readily converts
into the azine 1 upon standing in the solid state after 24 h
and in ethanol solution after 20 min. In (CD ) SO at
2
5
28
2
r
356.5). Analysis: calculated C 84.22, H 7.92, N 7.86;
found C 83.88, H 8.21, N 7.84%.
Azine 6. To 1-adamantyl methyl ketone hydrazone (10)
(0.576 g, 3.0 mmol) in 25 ml of ethanol, 0.40 g
3
2
(3.03 mmol) in ethanol of (E)-cinnamaldehyde (11) were
373 K after 10 h and in CD OD at 323 K after 16 h there
3
added. The yellowish reaction mixture was stirred for 1 h
at room temperature, then the solvent was evaporated off
and the crude material was quickly chromatographed on
silica gel 60 (70–200 mesh) with chloroform as eluent.
R = 0.5, m.p 63.5–65.7°C, yield 75%, C H N (M
are mixtures of 1 and 8 in ratios of 60:40 and 80:20,
respectively. 1-Adamantylcarbaldehyde hydrazone (8)
does not change in CDCl solution in 1 week, but after 10
3
months in a refrigerator a mixture of 1 and 8 (66:34) is
obtained.
f
21 26
2
r
3
06.5). Analysis: calculated C 82.31, H 8.55, N 9.14;
We assume that the azine 1 is formed, in solution
during the synthesis or in the solid state, from two
molecules of hydrazone 8 by a classical addition–
elimination mechanism, addition of a hydrazone to
another hydrazone with elimination of hydrazine
found C 82.23, H 8.30, N 9.44%.
It must be noted that the unsymmetrical azine 6 readily
evolved to a mixture of 1-adamantyl methyl ketone azine
(2) and (E)-cinnamaldehyde azine.
3d
(
Scheme 4), but it remains to be explained why the
reaction is so fast in the solid state, even when the
hydrazone C N group is sterically hindered owing to the
Crystal structure determination of compounds 1 and 2.
Crystals of 1 and 2 were obtained from hexane and
chloroform–propan-2-ol, respectively. A summary of the
data collection and the refinement process is given in
Table 1. The temperature of the crystals was controlled
=
bulky adamantyl group.
In the case of the sterically hindered 1,1'-biadamantyl
ketone, all attempts to obtain the corresponding hydra-
zone and/or azine proved to be unsuccessful, e.g. by
1
6
using an Oxford Cryostream Cooler. The structures
Copyright  1999 John Wiley & Sons, Ltd.
J. Phys. Org. Chem. 12, 455–469 (1999)

4
58
D. SANZ ET AL.
Table 1. Crystal analysis parameters
1
2
Crystal data
Formula
C H N
C H N
24 36 2
2
2
32
2
Crystal habit
Crystal size (mm)
Symmetry
Colourless, plate
Colourless, prism
0.67 Â 0.30 Â 0.07
0.50 Â 0.33 Â 0.17
Monoclinic, P2 /c
Monoclinic, P2 /n
1
1
Unit cell determination:
Unit cell dimensions (A, °)
Least-squares fit from 66 reflections (ꢂ <45°)
Least-squares fit from 64 reflections (ꢂ <45°)
˚
a = 12.1439(8)
b = 6.8156(3)
c = 12.5173(7)
a = 90
b = 116.221(4)
ꢄ = 90
929.4(1), 2
1.160, 324.5, 356
5.05
a = 6.9996(3)
b = 20.7149(15)
c = 6.7400(3)
a = 90
b = 99.392(4)
ꢄ = 90
964.2(1), 2
1.214, 352.6, 388
5.24
3
˚
Packing: V (A ), Z
�
3
D (g cm ), M, F(000)
c
�
1
m (cm
)
Experimental data
Technique
Four-circle diffractometer, Philips PW1100, bisecting geometry; graphite oriented monochro-
wm iadt to hr ;= !1 /. 25 ꢂ° scans; detector apertures 1 Â 1°; 1 min per reflection; Cu Ka; ꢂmax = 65; scan
Number of reflections:
Independent
Observed [2s(I)criterion]
Standard reflections
Temperature (K)
Solution and refinement:
Solution
1575
1405
1642
1518
2 reflections every 90 min; no variation
200
200
Direct methods: Sir92
Refinement:
Least-squares on Fo
Full matrix
0.64(5)
4
Secondary extinction (Â10 )
0.27(4)
Parameters:
Number of variables
Degrees of freedom
Ratio of freedom
Final shift/error
H atoms
174
1231
8.08
0.0004
191
1327
7.95
0.004
From difference synthesis
2
Weighting scheme
Max. thermal value (A )
Final DF peaks (e A
Final R and Rw
Empirical so as to give no trends in k!D Fl vs kjF jl and ksinꢂ/ꢃl
obs
2
˚
U33[C13] = 0.051(1)
0.25
0.038, 0.045
U33[C3] = 0.0391(1)
0.24
�
3
˚
)
0.041, 0.051
Scheme 3
Copyright  1999 John Wiley & Sons, Ltd.
J. Phys. Org. Chem. 12, 455–469 (1999)

SYMMETRIC AND UNSYMMETRIC ADAMANTYLMETHYLENEAZINES
459
Scheme 4
reflux with hydrazine in ethanol without an acid catalyst
or in acid conditions (hydrochloric or sulphuric acids) or
by microwave irradiation in open vessels or under
pressure.
present a crystallographic centre of symmetry relating the
two halves of the molecule, therefore only half a
molecule is in the asymmetric unit. The introduction of
a methyl group in 2 mainly affects the geometry around
the atom to which it is attached (Table 2 and Fig. 1): a
lengthening of the N1—C2 and C2—C4 bonds and a
narrowing of the N1—C2—C4 angle together with an
opening of the C2—C4—C5/C12 angles are observed.
The unsymmetric azines 3 (E,E) and 6 (E,E,E) were
prepared in quantitative yields from 1-adamantyl methyl
ketone hydrazone (10) and 1-adamantylcarbaldehyde (7)
or (E)-cinnamaldehyde (11), respectively. (Scheme 5).
To obtain azines 4 and 5, the starting material was the
benzophenone hydrazone 13, which in turn was formed
by refluxing in ethanol for 24 h a stoichiometric mixture
The N1
=C2 bond length presents a double bond
23
character, mainly in 1, in agreement with the standard
˚
Csp =N distance of 1.279 A and the N1—N1' length is
2
1
1
23
of benzophenone and hydrazine (Scheme 5).
greater than the tabulated value for the (C)(C,H)—N—
˚
N—(C)(C,H) of 1.401 A with planar N atoms. Azines 1
and 2 have an s-trans E,E-configuration and the
adamantyl group in an almost eclipsed disposition with
respect to the N1 atom (N1—C2—C4—C11 close to 0°).
They retain the same conformation at the expense of the
bond lengths and angular distortions mentioned above as
a clear effect of the methyl substituents to lessen the
X-ray crystallography
The molecular structures of 1-adamantylcarbaldehyde
azine (1) and 1-adamantyl methyl ketone azine (2) were
determined by x-ray analysis, proving that they exist in
the solid state in the E,E-configuration. Both compounds
steric interactions. A related effect is that one CH group
2
Scheme 5
Copyright  1999 John Wiley & Sons, Ltd.
J. Phys. Org. Chem. 12, 455–469 (1999)

4
60
D. SANZ ET AL.
a
Ê
Table 2. Experimental intra- and intermolecular geometric parameters (A, °)
1
2
1
2
N1—C2
1.264(2)
1.428(2)
—
1.496(2)
111.6(1)
123.7(1)
—
—
180.0(1)
—
� 179.5(1)
� 125.7(1)
117.1(2)
� 4.4(2)
1.280(2)
1.426(2)
1.504(2)
1.521(2)
C4—C5
C4—C11
C4—C12
kC—Cl
1.540(2)
1.531(2)
1.544(2)
1.531(1)
1.543(2)
1.541(2)
1.549(2)
1.533(1)
N1—N'
C2—C3
C2—C4
C2—N1—N1'
N1—C2—C4
N1—C2—C3
C4—C2—C3
C2—N1—N1'—C2'
N1'—N1—C2—C3
N1'—N1—C2—C4
N1—C2—C4—C5
N1—C2—C4—C12
N1—C2—C4—C11
112.9(1)
C2—C4—C11
C2—C4—C12
C2—C4—C5
kC—C—Cl
113.0(1)
112.0(1)
117.2(1)
124.1(1)
118.7(1)
180.0(1)
� 0.1(2)
108.7(1)
108.5(1)
109.5(1)
109.4(1)
110.3(1)
109.5(1)
179.3(1)
178.8(1)
� 178.1(1)
59.7(1)
C2—C4—C11—C10 � 179.7(1)
C2—C4—C12—C8
C2—C4—C5—C6
kC—C—C—Cl
177.2(1)
� 178.0(1)
59.9(1)
� 179.3(1)
� 126.0(1)
114.7(1)
� 5.2(2)
Interactions
D—H
D_A
H_A
D—H_A
1
2
: C13—H132_N1(x,y� 1,z)
: C13—H131_N1(x,y,z� 1)
1.03(2)
0.98(2)
3.680(2)
3.683(2)
2.89(2)
2.93(2)
134(2)
135(2)
a
o pk el r ar et ipo r ne ss ei nn t s1 t ah ne da 2v e rr ea sgp ee cv tai vl ue el yf.or the geometry of the adamantanyl group. Dashes stand for the (1� x, 1� y, 1� z) and (1� x,� y, 1� z) symmetry
of the adamantyl moiety is closer in 2 to the N1 nitrogen
lone pair, the C11_N1 distance in 2 being significantly
As expected, the four six-membered rings of the
conformationally rigid adamantyl groups adopt an
undistorted chair conformation following the Cremer
˚
shorter than in 1 [2.701(2) vs 2.821(2) A].
The central C N—N C fragment and the H3 or C3
substituents are in the same plane (w = 0.81 in 1 and 0.63
21
=
=
and Pople parameters.
2
In order to analyse the geometric characteristics of the
azine central unit, 51 molecules corresponding to 49
structures (neutral organic compounds without errors, R-
2
1
in 2 vs the tabulated value of 7.81 ), whereas the C4
˚
atom deviates by 0.012(1) and 0.018(1) A, respectively.
Figure 1. Molecular structures of compounds 1 and 2 showing the numbering system and the 30% displacement ellipsoids
Copyright  1999 John Wiley & Sons, Ltd. J. Phys. Org. Chem. 12, 455–469 (1999)

SYMMETRIC AND UNSYMMETRIC ADAMANTYLMETHYLENEAZINES
461
Figure 2. Histograms of (a) the CÐN and (b) the NÐN bond lengths and (c) the CÐNÐNÐC torsion angle corresponding to
the retrieved structures containing the azine central unit
factor<10% and with substituents at the end of the
E,Z-configuration although a polymorphic form of the
last one [(E,Z)-2-nitroacetophenone azine] exists in the
E,E-form (JULGUS), and the remaining structures
present a Z,Z-configuration. Figure 2(a)–(c) show the
histograms of the N—N and C—N distances and the
C—N—N—C torsion angle. The corresponding average
fragment, R to R = H, C, not belonging to a ring were
1
4
retrieved from the Cambridge Structural Database (CSD)
2
4
(
October 1997 release). It was found that 41 out of 49
structures present an E,E-configuration in coincidence
with azines 1 and 2, two (FEHBUP, JULHAZ) have an
Copyright  1999 John Wiley & Sons, Ltd.
J. Phys. Org. Chem. 12, 455–469 (1999)

4
62
D. SANZ ET AL.
˚ ˚
N=N [1.368(4) A], but the C—N distance [1.282(3) A]
is coincident with the average value of the histogram (a).
˚
The upper end of the N—N bond distances (1.448 A) is
due to 4,4'-dibromobenzalazine (BRBZAL), and its C—
˚
N distance (1.276 A) is close to the standard value of the
˚
Csp
2
=
=
N bond distance. The minimum value of 1.266 A in
N distribution is found in 4-trifluoromethoxy-
the C
benzalazine (LACGUR), for which the N—N bond
˚
distance (1.417 A) is in the upper end of its range. The
C—N—N—C histogram [Fig. 2(c)] shows a maximum at
180.0°, only 18 molecules have a torsion angle smaller
than 160.0° and five are in between the gauche and trans
conformations (range 166.2–169.4°). From the analysis
of the structures contributing to each part of the
histogram, we can conclude that all the aldazines are
trans and the cetazines can be either trans or gauche
(AACFAZ10 and SACFAZ10 are stereoisomers, both
E,E although the former presents a central torsion angle
of 180.0° and the latter 114.7°).
1-Adamantylcarbaldehyde azine (1) and 1-adamantyl
methyl ketone azine (2) show N—N distances in the
upper end of the histogram, reflecting a marked single
bond character. In 1, the C—N bond distance approaches
the minimum value of the distribution whereas in 2 it is
close to the average.
The molecules are grouped in layers, those of 2 being
disposed in a herringbone fashion (Fig. 3). Within each
layer, the molecules are related by a screw axis in 1,
whereas in 2 they are related by a translation along the a
direction. In both compounds, the adamantyl groups of
adjacent layers are facing to each other keeping
analogous C9_C7 distances between them [4.002(2)
25
˚
and 3.947(2) A in 1 and 2, respectively]. Only weak
C—H_N intermolecular interactions (Table 1) relate
molecules along the b and c directions. There are no
26
voids in the crystal structure and the total packing
coefficients amount to 0.66 and 0.69.
Ab initio calculations
Owing to the different configurational possibilities
present in azines, and also those observed in the
structures retrieved from the CSD, theoretical calcula-
Figure 3. Crystal packing of compounds 1 and 2 showing
the similar dispositions of the adamantyl groups in adjacent
layers
22
tions at the ab initio level were undertaken on some
simple compounds. Previous ab initio studies of azines
were limited to formaldazine (14); the potential hypersur-
face of this compound was calculated by Bachrach and
27
Liu at the MP2/6–31G*//HF/6–31G* level. Other
azines have been calculated using semi-empirical
8b,c
values with the standard deviation of the sample in
methods.
˚
parentheses are 1.403(15), 1.282(8) A and 162(24)°. 2,5-
We start with two ‘symmetrical’ azines devoided of
configurational isomerism, formaldazine (14) and acet-
one azine (15), and then we proceed with the study of the
E,E-, E,Z- and Z,Z-configurations of acetaldazine (16).
Moreover, taking into account the size of the adamantyl
8
b
Diacetyl-3,4-diazahexa-2,4-diene (FIFHUX) is located
in the lower end of the (a) and (c) histograms. This
molecule has a gauche conformation [C—N—N—
C = 102.7(2)°] and a partial double bond character in
Copyright  1999 John Wiley & Sons, Ltd.
J. Phys. Org. Chem. 12, 455–469 (1999)

SYMMETRIC AND UNSYMMETRIC ADAMANTYLMETHYLENEAZINES
463
Ê
Table 3. Calculated molecular geometry (A, °) by ab initio methods at the HF/6±31G* level (energy in hartree)
Compound:
R1 = R4:
R2 = R3:
14
H
H
15
CH3
CH3
16
CH3
H
17
C(CH3)3
H
E,E
E,Z
Z,Z
E,E
E,Z
Z,Z
N1—C2
1.253
1.395
1.253
112.3
112.3
118.4
118.4
—
—
180.0
—
—
—
—
1.262
1.390
1.262
114.0
114.0
117.6
117.6
180.0
180.0
180.0
—
—
—
—
—
—
1.255
1.394
1.255
112.7
112.7
121.4
121.4
180.0
180.0
180.0
—
—
—
—
—
—
1.256
1.393
1.258
112.2
115.1
121.5
129.4
180.0
0.0
180.0
—
—
—
—
1.258
1.391
1.258
114.6
114.6
129.5
129.5
0.0
0.0
180.0
—
—
—
—
1.255
1.395
1.255
112.7
112.7
123.4
123.4
180.0
180.0
180.0
� 0.1
1.256
1.394
1.258
111.8
116.4
123.9
131.9
180.0
0.0
180.0
0.1
121.2
� 121.0
61.5
1.259
1.390
1.259
115.6
115.6
131.9
131.9
0.0
0.0
180.0
61.5
� 61.5
180.0
61.5
N1—N1'
N1'—C2'
C2—N1—N1'
C2'—N1'—N1
N1—C2—C4/H4
N1'—C2'—C4'/H4'
C4—C2—N1—N1'
C4'—C2'—N1'—N1
C2—N1—N1'—C2'
C5—C4—C2—N1
C6—C4—C2—N1
C7—C4—C2—N1
C5'—C4'—C2'—N1'
C6'—C4'—C2'—N1'
C7'—C4'—C2'—N1'
121.0
� 121.1
0.1
—
—
—
—
—
—
121.2
� 120.9
� 61.5
� 61.5
180.0
180.0
a
E(RHF)
� 186.8860 � 343.0536 � 264.9756 � 264.9722 � 264.9688 � 499.1831 � 499.1740 � 499.1651
�
1
DE(kcal mol
)
—
—
0.0
2.1
4.3
0.0
5.7
11.3
a
� 1
1
hartree = 627.5095 kcal mol .
group, the geometry of the azine 17 with tert-butyl
groups at C2 was also optimized as a model for 1.
level are identical with ours for 14 in Tables 3 and 4).
Since MP2 and B3LYP calculations are of comparable
quality and owing to the computer time consumed by
MP2 calculations for the azines under study, only the HF
and B3LYP methods were applied to 15 and 17. Acetone
azine (15) has been thoroughly investigated in the
gaseous, liquid and crystalline states and it was
concluded that only one configuration exists in the
Concerning the geometry of the C=N—N=C frag-
ment, as the substituents change from hydrogen to tert-
butyl, the N1—C2—C/H bond angle increases. Formal-
dazine (14) has been examined in the gas phase by IR,
Raman spectroscopy and electron diffraction (ED)
28
techniques, suggesting a dominant trans conformation.
Its C N and N—N bond lengths [1.277(2) and
.418(3) A ] are longer than those calculated in the
29
=
different physical states. There is an experimental value
˚
˚
for acetaldazine (16) [d = 1.437(13)A] determined by
NN
1
30
˚
present study, and the C—N—N bond angle [111.4(2)°]
is smaller if the HF method is considered, but they agree
fairly well when methods that take into account electron
correlation effects are used (Table 4) (note that Bachrach
ED which is probably overestimated (1.41–1.42 A
would be more consistent with both calculations for 16
and experimental values for other azines in Table 4).
Concerning the stereochemistry of the C=N bonds in
2
7
30
and Liu geometries being calculated at the HF/6–31G*
azines, the ED data for acetaldazine (16) showed that
Copyright  1999 John Wiley & Sons, Ltd.
J. Phys. Org. Chem. 12, 455–469 (1999)

a
Ê
Table 4. Experimental and theoretical calculations at different levels for the E,E-isomers of azines: energies (E, hartree) and geometries (A,°)
Compound
R1
H
R2
H
Method
E
N—C
N—N
C—C
CNN
HCN/CCN
CNNC
b
HF/6–31G*
MP2/6–31G*
� 186.886
� 187.457
� 188.048
—
� 264.976
� 265.809
� 266.698
—
� 343.054
� 345.338
� 499.183
� 502.581
—
1.253
1.287
1.276
1.277(2)
1.255
1.290
1.279
1.277(3)
1.262
1.288
1.255
1.278
1.264(2)
1.263
1.280(2)
1.395
1.431
1.423
1.418(3)
1.394
1.425
1.417
1.437(13)
1.390
1.406
1.395
1.418
1.428(2)
1.390
1.426(2)
—
—
—
—
112.3
109.9
111.1
111.4(2)
112.7
110.5
111.6
110.4(9)
114.0
114.3
112.7
111.8
111.6(1)
114.4
112.9(1)
118.4
117.7
118.0
120.7(8)
121.4
120.3
121.1
121.4(10)
117.6
116.3
123.4
123.0
123.7(1)
118.0
117.2(1)
180.0
180.0
180.0
Not reported
180.0
180.0
180.0
Not reported
180.0
180.0
180.0
180.0
180.0(1)
179.3
180.0(1)
1
1
4
6
B3LYP/6–31G*
18
ED
HF/6–31G*
b
1.496
1.491
1.495
1.486(8)
1.504
1.506
1.511
1.511
1.496(2)
1.526
1.521(2)
Me
Me
H
MP2/6–31G*
B3LYP/6–31G*
20
ED
HF/6–31G*
b
1
5
7
Me
H
B3LYP/6–31G*
HF/6–31G*
t
b
1
Bu
B3LYP/6–31G*
XR (this work)
HF/6–31G*
1
2
Ad
Ad
H
Me
� 1038.710
XR (this work)
—
a
� 1
1
hartree = 627.5095 kcal mol
.
b
From Table 3.

SYMMETRIC AND UNSYMMETRIC ADAMANTYLMETHYLENEAZINES
Table 5. H NMR chemical shifts (ppm) and coupling constants (J, Hz) of azines 1±6 and hydrazones 8, 10 and 13
465
1
Compound
Solvent
CDCl3
R /R
R /R
2 4
1
3
a
1
7.53
1.63
1.81
2.02 (6H)
2.03 (6H)
2.03 (6H)
1.98 (3H)
1.69/1.75 (12H)
J = 12.6
1.69/1.74 (12H)
J = 12.0
1.65–1.80 (12H)
1.75 (12H)
1.82 (12H)
2
2
3
4
CDCl3
CDCl3
CDCl3
2
1.80 (6H)
1.76 (6H)
1.65 (6H)
2
b
7.10
J
7.41
1.65/1.72 (6H)
J = 12.2
2
C H = 7.61–7.63 (2H� o); 7.24–7.27 (2H� o); 7.33–7.41 (2H� p ‡ 4H� m)
6
5
CD OD
7.31
1.94 (3H)
1.65/1.72 (6H)
1.62 (6H)
3
2
J = 11.8
C H = 7.17–7.58(m)
6
5
5
6
CDCl3
CDCl3
1.82
1.97 (3H)
1.62/1.70 (6H)
1.64 (6H)
C H = 7.66–7.69 (2H� o); 7.19–7.21 (2H� o); 7.34–7.39 (2H� p ‡ 4H� m)
6
5
1.93
2.06 (3H)
1.71/1.77 (6H)
1.84 (6H)
2
J = 12.2
7
.96
C H = 7.50 (d, 2H, H� o); 7.36 (t, 2H, H� m); 7.31 (t, 1H, H� p)
6
5
3
3
3
3
J = 9.1
—HC
=CH— = 7.04 (dd, J = 16.0, J = 9.1), 6.94 (d, J = 16.0)
CD OD
1.90
2.05 (3H)
1.75/1.81 (6H)
1.86 (6H)
3
2
J = 12.5
7
.90
C H = 7.55 (d,2H, H� o); 7.38 (t,2H, H� m); 7.32 (t, 1H, H� p)
6
5
3
3
3
3
J = 9.0
—HC=CH— = 7.01 (dd, J = 16.0, J = 9.0), 7.10 (d, J = 16.0)
8
CDCl3
6.86
1.99 (br, 3H)
1.93 (br, 3H)
2.01 (br, 3H)
1.67/1.73 (6H)
1.66 (6H)
1.57 (6H)
1.72 (6H)
2
5
.0 (NH2)
J = 12.4
DMSO� d6
CDCl3
6.76
1.61/1.68 (6H)
2
5.79 (NH2)
J = 12.0
1
1
0
3
1.68
1.67/1.73 (6H)
2
4
.86 (NH2)
.44 (NH2)
J = 13.2
CDCl3
7.46–7.54 (m, 5H) 7.26–7.32 (m, 5H)
5
a 2
b
5
3
15
J( N) = ‡2.9, J( N) = � 6.0.
Not measurable.
the E,E-isomer prevails in the vapour phase in accor-
dance with the computed results in which the E,Z- and the
4), taking into account our previous comments about HF
calculations.
�
1
Z,Z-isomers are about 2.1 and 4.3 kcal mol , respec-
tively, less stable than the E,E-isomer (Table 3). The
effect is more marked with the bulkier tert-butyl group;
thus, in tert-butylcarbaldehyde azine (17), the relative
energies are 0.0 (E,E), 5.7 (E,Z) and 11.3 (Z,Z). Note that
the E,Z-isomer lies, in both cases, in the middle of the
E,E- and Z,Z-isomers, as if both halves were independent.
The difference between methyl and tert-butyl groups is
due essentially to the difference in steric effects of these
Multinuclear magnetic resonance
1
13
15
The H (Table 5), C (Table 6) and N (Table 7) NMR
spectra were recorded for azines 1–6 and hydrazones 8,
1
13
10 and 13. Assignment of the H and C NMR chemical
shifts was achieved by comparison with the data obtained
for the starting carbonyl compounds (Table 8) and by
32
groups (Taft’s E values are 0.00, � 1.24 and � 2.78, for
means of homonuclear and heteronuclear correlations.
The barriers to rotation about C N bonds in azines are
large enough to observe, by NMR at room temperature,
s
3
1
H, CH and t-C H , respectively). Therefore, for
=
3
4 9
R = 1-adamantyl and R = H (1) and for R = 1-adaman-
1
2
1
8a
tyl and R = CH (2), the observed predominance of E,E-
the different E/Z-isomers when they occur. The results
reported in Tables 5, 6 and 8 show the presence of only
one isomer in solution. An interesting feature is that, fo2r
the same C-substituents, the chemical shift of the sp
carbon atom is always higher for azines than for
hydrazones (between 6 and 16 ppm), a fact that can be
2
3
isomers is justified on these grounds (Table 2).
The tert-butyl groups in 17 show the same disposition
as that of the adamantyl group in 1 and 2 [N1—C2—
C4—C11 torsion angle: experimental value � 4.4(2),
�
5.2(2)°, calculated value � 0.1°). Finally we succeeded
3
3
in minimizing the E,E-configuration of 1-adamantyl
methyl ketone azine (2) at the HF/6–31G* level. The
theoretical distances and torsional angles are in reason-
ably good agreement with the experimental values (Table
used for identification.
15
The N NMR spectra of azines 1–6 present one
nitrogen of imine type C
� 33.9 ppm, except for the unsymmetrical azine 6 in
=
N in the range � 27.7 to
Copyright  1999 John Wiley & Sons, Ltd.
J. Phys. Org. Chem. 12, 455–469 (1999)

4
66
D. SANZ ET AL.
1
3
Table 6. C NMR chemical shifts (ppm) and coupling constants (J, H ) of azines 1±6 and hydrazones 8, 10 and 13
2
Compound
Solvent
CDCl3
R /R
R /R
4
C=N
1
3
2
a
1
—
36.7
39.6
J = 128.9
39.2
39.7
J = 128.4
39.2
39.8
J = 127.8
39.6
J = 127.8
39.4
27.9
J = 132.9
28.5
36.7
J = 126.0
36.5
36.9
J = 126.5
37.4
36.8
J = 127.2
36.7
J = 127.2
37.2
170.9
1
1
1
1
1
1
J = 157.6
CP/MAS
CDCl3
—
36.5
40.2
172.7
164.4
2
3
11.4
28.3
J = 133.7
28.5
1
1
J = 127.5
12.6
CP/MAS
CDCl3
41.0
40.0
174.2
171.2
11.9
28.2
J = 133.6
28.0
J = 133.6
28.4
1
1
1
1
1
1
1
J = 127.8
—
36.9
164.3
1
J = 156.3
CP/MAS
CDCl3
13.6
—
—
40.9
37.2
37.1
176.9
168.6
167.2
39.4
39.4
J = 128.5
28.4
37.2
36.6
J = 126.7
4
27.8
J = 131.4
1
1
1
1
J = 158.4
138.3
130.1
128.1
129.8
163.2
1
1
1
J = 162.0
J = 162.0
J = 160.6
3
3
J = J = 7.7
1
35.0
128.7
J = 160.1
40.6/39.6
127.4
J = 160.9
28.2/27.6
128.6
J = 160.1
37.6/37.0
1
1
1
CP/MAS
CDCl3
—
35.7
168.7/168.3
170.7/170.2
1
1
39.7
38.1/137.7
40.1
130.6, 129.6, 127.9, 125.4
5
6
13.1
39.4
28.2
J = 132.9
36.8
1
165.5
156.5
1
1
1
J = 127.5
J = 125.4
J = 124.1
138.2
128.9
J = 162.0
1
1
1
3
3
3
1
35.2
128.2
J = 160.2
1
3
3
3
CDCl3
12.4
40.3
36.0
39.6
J = 126.8
127.1
J = 159.6
173.5
157.7
1
1
J = 128.0
1
128.8
128.9
1
1
1
1
J = 160.6
J = 161.1
J = 160.6
3
3
3
3
J = 7.5
J = J = 7.4 J = 8.0
1
—
CH
=
CH—: 140.6 (C—C H , J = 155.3);
6
5
1
3
2
1
26.0 ( J = 158.6, J = 10.3, J = 3.8)
CP/MAS
12.4
39.7
37.7
39.7
127.0/128.3
28.2
128.3/129.6
37.0
130.6
171.5
156.2
1
—
CH=CH—: 140.2; 124.0
8
CDCl3
CDCl3
—
36.7
39.7
39.8
40.1
28.1
J = 130.4
28.2
J = 133.2
29.4
128.1
36.7
J = 126.0
36.7
J = 126.7
37.4
128.8
155.0
1
1
1
1
1
J = 129.4
39.5
J = 127.9
41.1
J = 152.0
1
0
8.9
J = 125.9
157.9
1
1
1
CP/MAS
CDCl3
8.8
—
154.7
149.1
1
3
138.4
129.3
1
1
1
J = 161.3
J = 160.2
J = 161.2
—
132.9
128.7
J = 160.5
126.4
J = 159.5
128.0
J = 160.3
1
1
1
a 1 15
2
15
J( N) = 3.6, J( N) = 3.6.
2
3
which the C
appears at � 16.6 ppm. Two nitrogen signals at around
60 ppm for the C
E)-hydrazones 8, 10 and 13 were observed.
=
N conjugated with the cinnamyl residue
J(N
=
=
C—H) = ‡ 2.9Hz and three bonds, J(N—
N
C—H) = � 6.0Hz, and N,C coupling through one
�
=
N and � 276 ppm for the NH in the
bond of 3.6 Hz and two bonds of also 3.6 Hz, calculated
by a complete analysis with the WINDAISY 3.0 program
2
3
4
(
(
15
1
34
A sample of [ N ]-1-adamantylcarbaldehyde azine
using a J(N,N) coupling constant of � 11.7Hz.
2
13
15
1) was synthesized and studied by multinuclear NMR
and the following characteristics typical of an E,E-isomer
were observed: N, H couplings through two bonds,
The C and N CP/MAS NMR of 1-adamantylcarb-
aldehyde azine (1) and 1-adamantyl methyl ketone azine
(2), which we have proved by x-ray analysis exist as E,E-
Copyright  1999 John Wiley & Sons, Ltd.
J. Phys. Org. Chem. 12, 455–469 (1999)

1
13
Table 8. H and C NMR chemical shifts (ppm) and coupling constants (J, Hz) of the starting carbonyl compounds
Compound
Solvent
CDCl3
CH /CHO
C1'
H2'/C2'
H3'/C3'
H4'/C4'
CO
Other
3
7
9.31 (s, 1H)
9.27 (s, 1H)
1.72 (6H)
1.73 (6H)
2.07 (br, 3H)
2.05 (br, 3H)
1.72 (6H)
—
—
—
—
CD OD
1.82/1.74 (6H)
3
2
J = 12.2
CDCl3
—
44.7
36.5
27.3
35.8
205.7
—
1
1
1
1
J = 127.2
J = 134.2
J = 128.8
J = 167.1
9
CDCl3
CDCl3
2.08 (s, 3H)
24.2
1.79 (br, 6H)
38.2
2.07 (br, 3H)
27.9
1.71 (6H)
36.5
—
213.9
—
—
46.4
46.7
1
1
1
1
J = 127.1
J = 128.7
J = 134.4
J = 128.0
CP/MAS
CDCl3
22.7
38.4
29.1
37.0
210.5
—
—
1
1
9.71 (d, 1H)
7.42–7.46 (m) 7.55–7.58 (m) 7.45(dd)
6.73 (dd, 1H)
7.48 (d, 1H)
3
3
J = 7.7
J = 16.0
CD OD
9.65 (d, 1H)
J = 7.8
7.48–7.41 (m) 7.71–7.62 (m) 7.48–7.41 (m)
—
6.77 (dd, 1H)
7.67 (d, 1H)
J = 15.0
3
3
3
CDCl3
CDCl3
—
133.8
137.6
128.9
128.3
131.1
193.5
128.34
152.6
1
1
1
1
1
1
J = 162.6
J = 159.9
J = 161.5
J = 172.5
J = 160.5
J = 152.7
3
3
3
3
3
J = J = 7.4
130.0
J = 9.0
J = J = 4.6
12
—
128.2
132.4
196.7
—

4
68
D. SANZ ET AL.
1
5
Table 7. N NMR chemical shifts (ppm) and coupling
constants (J, Hz) of azines 1±6 and hydrazones 8, 10 and 13
REFERENCES
1
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Compound
Solvent
N
N
2
1
CDCl3
CP/MAS
CDCl3
CP/MAS
CDCl3
� 27.7
� 20.8
� 33.9
� 31.9
� 31.4
ÆJ = 9.8
� 29.2
� 31.3
� 28.9
� 62.0
� 27.7
� 20.8
� 33.9
� 31.9
� 30.5
ÆJ = 4.5
� 27.9
� 28.4
� 16.6
� 275.1
2
3
3. (a) G. S. Chen, M. Anthamatten, C. L. Barnes and R. Glaser, J.
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4
5
6
8
CDCl3
CDCl3
CDCl3
CDCl3
4
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2
1 a
5. J. L. Serrano (Ed.), Metallomesogens: Synthesis, Properties and
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J = 3.3
J
1
0
3
CDCl3
� 66.0
ÆJ = 6.1
� 59.7
� 281.1
6
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058 (1974).
1
J = 73.3
� 273.8
3
1
CDCl3
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1
J = 77.9
a
Not observed.
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1
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isomers, show chemical shift values close to those
obtained in solution, meaning that the only isomer
detected in solution is the same as that found in solid
state. A close examination of the CP/MAS NMR data for
the remaining azines allows us to conclude that all of
them (1–6) exist in the E,E-configuration in the solid state
and in solution.
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1
1
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1
1
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CONCLUSIONS
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1
This work presents some novelties which can be
summarized as follows: (i) for the first time adamantyl-
methyleneazines have been synthesized; these azines can
be used as starting materials for preparing diazapenta-
(
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2
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1
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3
5
lenes (criss-cross cycloaddition reaction), 2-pyrazo-
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3
6
37
19. S. R. Hall, H. D. Flack and J. M. Stewart, Xtal 3.2. University of
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2
2
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3
8
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adamantyl residue, such as Ad–CO–Ad and Ad–NH–
3
9
COCH3, related to the plasticity of adamantane and its
4
0
13
15
derivatives; (iii) A set of novel C and N chemical
shifts, in solution and in the solid state, and also some
1
15
13
15
H– N and C– N coupling constants were described.
2
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2
Acknowledgements
2
We gratefully acknowledged the DGES of Spain (Project
No. PB96-0001-C01/C02/C03) for financial support.
M.A.P. thanks the Universidad Nacional de Educaci o´ n
a Distancia for financial assistance during her stay in
Spain.
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