One-pot synthesis of β-diketimine ligands

Article abstract of DOI:10.1139/V10-109

Symmetric N,N'-dialkyl-2-amino-4-imino-pent-2-enes (nacnac^RH) can be prepared in high yields in a simple one-pot reaction from acetylacetone and 2 equiv. of amine. Optimized conditions require the azeotropic removal of water, use of a minimum amount of solvent, and of 1 equiv. of acid. Either para-toluenesulfonic acid, hydrochloric acid, or a mixture of both can be employed, with the latter being most advantageous. Symmetric nacnac^RH are thus obtained in higher than 95% purity and with 65% yield for R = Me and 80%-95% yields for R = n-Pr, i-Pr, i-Bu, Bn, Cy, and (+)-CH(Me)Ph.

Full text of DOI:10.1139/V10-109

1040
One-pot synthesis of b-diketimine ligands
Ibrahim El-Zoghbi, Aysha Ased, Paul O. Oguadinma, Ekou Tchirioua, and
Frank Schaper
Abstract: Symmetric N,N’-dialkyl-2-amino-4-imino-pent-2-enes (nacnacRH) can be prepared in high yields in a simple
one-pot reaction from acetylacetone and 2 equiv. of amine. Optimized conditions require the azeotropic removal of water,
use of a minimum amount of solvent, and of 1 equiv. of acid. Either para-toluenesulfonic acid, hydrochloric acid, or a
mixture of both can be employed, with the latter being most advantageous. Symmetric nacnacRH are thus obtained in
higher than 95% purity and with 65% yield for R = Me and 80%–95% yields for R = n-Pr, i-Pr, i-Bu, Bn, Cy, and (+)-
CH(Me)Ph.
Key words: diketimines, one-pot synthesis.
R
´
´
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´
´
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Resume : On peut preparer les N,N’-dialkyl-2-amino-4-iminopent-2-enes (nacnac H) avec des rendements eleves en reali-
´
´
´
´
´
´
´
sant la reaction monotope de l’acetylacetone avec deux equivalents d’amine. Les conditions optimisees necessitent l’elimi-
´
´
´
´
ˆ
nation azeotropique de l’eau, l’utilisation d’une quantite minimale de solvant et un equivalent d’acide qui peut etre l’acide
R
`
para-toluenesulfonique, l’acide chlorhydrique ou un melange des deux; ce dernier est le plus avantageux. Des nacnac H
´
ˆ
´
symetriques peuvent ainsi etre obtenus avec une purete de plus de 95 % et un rendement de 65 % lorsque R = Me et des
`
rendements allant de 80 a 95 % lorsque le groupe R = n-Pr, i-Pr, i-Bu, Bu, Cy et (+)-CH(Me)Ph.
´
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Mots-cles : dicetimines, synthese monotope.
Introduction
Scheme 1.
Preparation of b-diketimines (‘‘nacnac’’ ligands), based on
diimine analogues of acetylacetone, was described already in
1950,1 and their first metal complexes in 1968.2,3 They
played only a marginal role in coordination chemistry until
the introduction of nacnacdipp (dipp = 2,6-diisopropylphenyl)
as a spectator ligand in the late 1990s.4 Since then, b-
diketiminate ligands have become some of the most widely
used bidentate N-donor ligands in coordination chemistry.5
Interest in diketiminate ligands concentrated mostly on their
N-aryl derivatives, and N-alkyl substituted diketimines were
used only sparingly, mostly as low-molecular-weight ligands
for chemical vapour deposition and atomic layer deposition
applications.6 We recently started to investigate the coordi-
nation chemistry of diketiminate ligands with aliphatic N-
substituents.7–11 For these investigations, we required a sim-
ple, efficient, and economic access to these compounds.
The most efficient and versatile preparation of 2-amino-4-
imino-pent-2-enes is condensation of acetylacetone with
amines. While condensation of the first amine proceeds
readily, the resulting enaminoketone has to be activated for
the second condensation.2,5 This might be achieved by trans-
formation into the ketal, and the ethylene glycol monoketal
has been used successfully as starting material for the
synthesis of nacnacBnH and some macrocyclic diketimines
(Scheme 1).12,13 Alternatively, in the case of aryl N-substituents,
reaction in ethanolic HCl yielded the desired dicondensation
product, probably by intermediate formation of the diethyox-
yketal.3 For the diketimines with N-alkyl substituents of in-
terest here, alkylation of the enaminoketone obtained after
the first condensation with Meerwein salt and subsequent re-
action with a second equivalent of amine is the most com-
monly employed method.2 In an isolated report, nacnacBnH,
1, has been obtained by refluxing the monocondensation
product acnacBnH, 1b, in methyl iodide.14 The mechanism
of this reaction (no second equivalent of amine was added)
remains unclear. Recently, Bradley et al. showed that Meer-
wein salt can be replaced by the less toxic and more eco-
nomic methyl sulfate as alkylating agent (Scheme 1).15 The
latter, to our knowledge, is the most efficient synthesis de-
scribed, and diketimines were obtained in yields of 46%–
87% starting from the enaminoketone intermediate after dis-
tillation. Diketimines with aliphatic substituents are thus ac-
cessible, but their synthesis still requires a two-step reaction,
often distillation of the obtained product for purification, ex-
Received 8 July 2010. Accepted 14 July 2010. Published on the NRC Research Press Web site at canjchem.nrc.ca on 5 October 2010.
1
´
´
´
´
I. El-Zoghbi, A. Ased, P.O. Oguadinma, E. Tchirioua, and F. Schaper. Departement de chimie, Universite de Montreal, Montreal,
QC H3C 3J7, Canada.
1Corresponding author (e-mail: Frank.Schaper@umontreal.ca).
Can. J. Chem. 88: 1040–1045 (2010)
doi:10.1139/V10-109
Published by NRC Research Press

El-Zoghbi et al.
1041
clusion of moisture, and the use of toxic alkylating reagents.
In the following, we describe a one-step preparation of these
compounds, which avoids these drawbacks.
Scheme 2.
Results and discussion
Initial explorations
We repeated the preparation of nacnacBnH, 1, described
by Dorman12 using either acetylacetone ethylene glycol
mono- or di-ketal as starting material. We found, however,
the reaction to give varying yields of diketimine product
and to be highly dependent on reaction conditions
(Scheme 2). If the reaction is carried out in diluted toluene
solution, only the monocondensation product 1b was ob-
tained. Reaction of acetylacetone with 2 equiv. benzylamine
in ethanolic HCl, following the procedure described by
Parks and Holm3 and Feldman et al.16 for N-aryl substituted
diketimines, also yielded only 1b. Direct condensation of
acetylacetone and benzylamine (no solvent, T > 100 8C, in
the presence of molecular sieves or thionyl chloride), under
microwave heating (neat or in toluene solution, without or
with addition of molecular sieves or acetyl chloride), or
under azeotropic removal of water (toluene solution, cata-
lytic quantities of para-toluenesulfonic acid, several days)
yielded either 1b or decomposition products and at best
traces (<10%) of the desired 1.
While aryl-substituted diketimines have been sometimes
obtained under typical ‘‘Dean–Stark conditions’’, i.e., cata-
lytic amounts of acid and azeotropic removal of water,
yields have been generally low-to-moderate. Budzelaar et
al. reported the synthesis of nacnacXylH, 2, (Xyl = 2,6-dime-
thylphenyl) in 75% yield in the presence of stoichiometric
amounts of acid. Applying this protocol, we had previously
obtained nacnacBnH,8 nacnacCyH,10 and nacnacCH(Me)PhH7 in
67%–82% yield. The initially obtained tosylate salt can be
neutralized using a variety of bases of which aqueous potas-
sium hydroxide proved to be the most convenient (aqueous
NaHCO3 failed in some cases to deprotonate the tosylate
salt). Azeotropic water removal is required and reaction of
BnNH2 (or i-BuNH2), acetylacetone, and 1 equiv. TsOH ei-
ther in toluene or without solvent only yielded the monocon-
densation product 1b.
pared to the stoichiometric reaction (Table 1), loss of the
low-boiling amine seems not to be responsible for the low
yields obtained.
Inspired by the decrease in yields in the reaction of acety-
lacetone ketal with amines on dilution, we found that con-
centration of the reaction mixture reduced drastically the
amounts of monocondensation product and impurities
formed (Table 2). Best results were obtained when the mini-
mum amount of toluene necessary to operate the Dean–Stark
apparatus was employed.
Reactions with other primary and secondary amines
showed that concentration of the solution in general im-
proved product yields and in most cases shortened reaction
times to less than one day (Table 3). The low isolated yields
for nacnacMeH are related to its high volatility and its high
sensitivity towards hydrolysis.15 Reactions with isopropyl
amine and isobutyl amine, however, did not show conver-
sions above 30% even under these conditions. Substituting
p-toluenesulfonic acid with sulfuric acid led to strongly de-
creased yields. The use of concentrated hydrochloric acid,
on the other hand, increased the yields to 85%–95% for R =
i-Pr and i-Bu, respectively. In addition, use of concentrated
HCl prevented the formation of impurities observed in reac-
tions with TsOH, and diketimines were obtained analytically
pure for R = i-Bu, i-Pr, and n-Pr without the need for further
purification. Diketimines with R = Bn or CH(Me)Ph were
obtained with >90% purity according to NMR (the main
contamination being the monocondensation product), which
is in most cases sufficient for their use in subsequent reac-
tions. Analytically pure compounds were obtained by
recrystallization from ethanol. For methylamine and cyclo-
hexylamine, yields were drastically reduced by replacing
para-toluenesulfonic acid with HCl. In both cases, the for-
mation of an insoluble precipitate even at reflux temperature
indicated that this might be related to the insolubility of the
respective ammonium chloride salt. Consequently, use of an
equimolar mixture of HCl/TsOH restored the yields ob-
served for TsOH in these two cases, but did not otherwise
affect reactions for other amines (Table 3).
Optimization of the reaction conditions
Attempts to widen the synthesis described above to dike-
timines with simple alkyl substituents such as Me, i-Pr, n-Pr,
and i-Bu yielded even after prolonged heating only mixtures
of bis- and mono-condensation products with less than 60%
of the desired diketimine according to NMR analysis. Use of
more than 1 equiv. of TsOH showed no or only detrimental
influence on product yields. While it has never been clari-
fied why reactions proceed differently when catalytic or sto-
ichiometric amounts of acid are used, we find it reasonable
to assume that alkylation of the intermediate enaminoketone
is replaced by its (reversible) protonation and that the latter
requires amounts of acid, which are equal or slightly higher
than those of the amine. In agreement with this putative
mechanism, presence of excess amine reduced the yield of
diketimine when not compensated with excess TsOH
(Table 1). Since the presence of excess amine and TsOH in
equimolar amounts did not increase the yield when com-
Non-symmetric diketimines
Synthesis of non-symmetrically substituted diketimines
with different substituents on N and N’ is a challenge and
Published by NRC Research Press

1042
Can. J. Chem. Vol. 88, 2010
Scheme 3.
Table 1. Influence of excess base in the preparation of nacnaci-BuH.
i-BuNH2/acacH
TsOH/acacH
Reaction time (h)
nacnaci-BuH (%)a
acnaci-BuH (%)a
2
3
3
3
1.1
1.1
1.5
2.2
24
24
20
18–54
60
5
15
60
30
70
30
30
1
aDetermined by H NMR from the crude product after basic workup.
Table 2. Influence of concentration in the preparation of
formed from the two species present in the highest concen-
trations, i.e., acnacXylH and either methylbenzylamine or
benzylamine. As was previously observed by others, separa-
tion of non-symmetrical substituted diketimines from their
symmetric counterparts is nearly impossible.18 Despite their
disproportionally high amount in the obtained product mix-
tures, 4 and 5 were not separated from the symmetric diketi-
mines 1–3 by recrystallization, sublimation, or column
chromatography (extensive hydrolysis in the latter case).
For 5, diketimine 1 could be separated by recrystallization
and 5 was obtained in 30% yield and 90% purity, still con-
taminated by 10% of 2.
nacnacnPrH.
[acacH]
(mol/L)
0.048
1.2
Reaction time nacnaci-BuH
acnaci-BuH
(%)a
18
Traces
Traces
(h)
68
68
16
(%)a
62
80
90
4.0
Note: acacH/n-PrNH2/TsOH = 1:2:1; toluene solution; azeotropic
removal of water.
aDetermined via H NMR from the crude product after washing with
1
aqueous KOH.
stepwise reaction using alkylating reagents such as Meer-
wein salt led to product mixtures.17,18 We thus explored if
non-symmetric diketimines can be obtained using the one-
pot procedure established above. Reactions of acetylacetone
with 1 equiv. 2,6-dimethylaniline and 1 equiv. of either (+)-
methylbenzylamine or benzylamine yielded product mix-
tures containing the non-symmetric diketimines 4 or 5 in
higher than statistical amounts, but always accompanied by
the two symmetric diketimines (Scheme 3).
The preferred formation of the non-symmetric diketimine
can be rationalized by the trapping of the more reactive 2,6-
dimethylaniline in the monocondensation product, which di-
minishes its concentration in solution. Following reactions
between acnacXylH, 2b, with methylbenzylamine, and vice
versa of acnacCH(Me)PhH, 3b, with 2,6-dimethylaniline by
NMR showed that scrambling between the monocondensa-
tion products and free amines was observed already before
significant amounts of diketimine were obtained (Scheme 3).
In all cases, acnacXylH was obtained preferentially. In partic-
ular at the beginning of the reaction, diketimines were thus
Summary and conclusions
b-Diketimines with aliphatic substituents on nitrogen can
be obtained in simple one-pot condensation reactions be-
tween acetylacetone and primary or secondary amine, pro-
vided that water is removed azeotropically and that one
equivalent of acid is present. Under optimized reaction con-
ditions, we employed an equimolar mixture of hydrochloric
and para-toluenesulfonic acids, and the amount of solvent
was kept to the minimum required for water removal. Sym-
metric diketimines can thus be obtained very economically,
without the need of toxic alkylating reagents or moisture-
free conditions.
For non-symmetric diketimines, the fast scrambling be-
tween free amine and monocondensation products makes
the proposed protocol less efficient. Although they are ob-
tained in higher than statistic ratio, their separation from the
symmetric diketimines, invariably formed as side products,
was not possible and the synthetically more demanding
routes proposed by Park et al.18,19 are still more advanta-
geous.
Published by NRC Research Press

El-Zoghbi et al.
1043
Table 3. Yields in diketimine synthesis for different combinations of amines and acids (purity is given in parentheses).
R
n-Pr
Bn
CH(Me)Ph
i-Bu
i-Pr
TsOH (cacacH < 1 mol/L)
50% (EA)
TsOH
HCl
HCl/TsOH
Reaction time
72 h
24 h
5 d
18 h
24 h
72 h
18 h
80% (90%)
80% (>95%)
80% (90%)
30%
30% (>95%)
90% (>95%)
50% (95%)
90% (EA)
75% (>95%)
80% (90%)
95% (EA)
85% (EA)
0%
82% (EA)a
70% (EA)b
35% (EA)
80% (90%)
23% (90%)c
69% (EA)d
60% (50%)
1
95% (EA)
90% (90%)
65% (>95%)
Cy
Me
5%
Note: Purity was estimated by H NMR, EA indicates correct elemental analysis. Reaction conditions: acacH/RNH2/acid = 1:2:1; minimum amount of
toluene used with exception of the first column.
acacacH = 0.5 mol/L.8
bcacacH = 0.1 mol/L, 5 d.7
ccacacH = 0.2 mol/L, 3 d.9
dcacacH = 0.1 mol/L, 3 d.10
1
80%, 92% purity). H NMR (CDCl3, 400 MHz): d 11.89
Experimental section
(bs, 1H, NH), 7.20–7.35 (m, 10H, Ph), 4.68 (q, 2H, J =
7 Hz, CH(Me)Ph), 4.48 (s, 1H, CH(C=N)2), 1.82 (s, 6H,
Me(C=N)), 1.49 (d, 6H, J = 7 Hz CH(Me)Ph). Recrystalliza-
tion from a saturated ethanol solution at –20 8C gave the
following: Anal. calcd. for C21H26N2: C, 82.31; H, 8.55; N,
9.15. Found: C, 81.75; H, 8.52; N, 9.06.7,20
All chemicals were obtained from commercial suppliers
and used as received. Elemental analyses were performed at
´
´
´
the Laboratoire d’Analyse Elementaire (Universite de Mon-
´
treal). NMR spectra were recorded on a Bruker ARX
400 MHz spectrometer and referenced to residual solvent
(CHCl3: d 7.26).
nacnacn-PrH
General procedure for the synthesis of symmetric
diketimines
Acetylacetone (2.00 g, 20 mmol), HCl (12.1 mol/L,
1.65 mL, 20 mmol), and n-propylamine (2.36 g, 40 mmol)
in toluene (5 mL) gave a dark brown oil (3.3 g, 90%). H
NMR (CDCl3, 400 MHz): d 10.04 (bs, 1H, NH), 4.47 (s,
1H, CH(C=N)2), 3.17 (t, J = 9 Hz, 4H, NCH2), 1.87 (s, 6H,
Me(C=N)), 1.61 (m, 4H, CH2CH2CH3), 0.97 (t, J = 9 Hz,
6H, CH2CH3). Anal. calcd. for C11H22N2: C, 72.47; H,
12.16; N, 15.37. Found C, 72.41; H, 11.81; N, 15.39.15
Acetylacetone and 1 equiv. of the desired acid or acid
mixture (see Table 3) were combined in a minimum volume
of toluene, usually equal to the combined volumes of all re-
actants. The mixture was stirred for 10 min and 2 equiv. of
the desired amine were added to give a white suspension,
which was allowed to stir for approximately 20 min. The re-
action mixture was then refluxed for the required time
(Table 3) with azeotropic removal of water (Dean–Stark ap-
paratus). The brown precipitate formed after cooling to
room temperature and standing for 3–4 h was isolated by
decantation. Ether (50 mL) and aqueous KOH (11.2 g,
0.2 mol, 50 mL) were added and the mixture stirred for
15 min. The ether phase was separated, dried over Na2SO4,
and the solvent evaporated. Yields and purities of the ob-
1
nacnaci-PrH
Obtained from acetylacetone (2.00 g, 20 mmol), HCl
(12.1 mol/L, 1.65 mL, 20 mmol), and isopropylamine
(2.36 g, 40 mmol) in toluene (5 mL). To eliminate mono-
condensation product, the oil obtained after decantation of
toluene was treated with excess saturated aqueous NaHCO3
and ether (20 mL). Ether and water phases were decanted
from the remaining oil. Ether (50 mL) and aqueous KOH
(11.2 g, 0.2 mol, 50 mL) were added and the mixture
stirred. The ether phase was separated, dried over Na2SO4,
and evaporated to dryness to give a dark-red oil (3.4 g,
1
tained products, estimated from H NMR, are given in Ta-
ble 3. Characterization data and quantities are given below
for selected experiments.
nacnacBnH, 1
1
85%). H NMR (CDCl3, 400 MHz): d 11.43 (bs, 1H, NH),
Acetylacetone (2.00 g, 20 mmol), HCl (12.1 mol/L,
1.65 mL, 20 mmol), and benzylamine (4.28 g, 40 mmol) in
toluene (7 mL) gave a red brown solid (2.90 g, 75%, >95%
4.38 (s, 1H, CH(C=N)2), 3.06 (hept., J = 6 Hz, 2H,
CH(CH3)2), 1.89 (s, 6H, CH3(C=N)), 1.16 (d, J = 6 Hz,
12H, CH(CH3)2). Anal. calcd. for C11H22N2: C, 72.47; H,
12.16; N, 15.37. Found C, 72.06; H, 12.08; N, 15.15.2
1
purity). H NMR (CDCl3, 400 MHz): d 11.49 (bs, 1H, NH),
7.22–7.30 (m, 10H, Ph), 4.64 (s, 1H, CH(C=N)2), 4.46 (s,
4H, CH2), 1.95 (s, 6H, Me). Recrystallization from a satu-
rated ethanol solution at –20 8C gave the following: Anal.
calcd. for C21H26N2: C, 81.97; H, 7.97; N, 10.06. Found: C,
81.75; H, 8.19; N, 10.05.2,14,15
nacnaci-BuH
Acetylacetone (2.00 g, 20 mmol), HCl (12.1 mol/L,
1.65 mL, 20 mmol), and isobutylamine (2.92 g, 40 mmol)
in toluene (5 mL) gave a brown oil (4.3 g, 95%). H NMR
1
(CDCl3, 400 MHz): d 11.07 (bs, 1H, NH), 4.48 (s, 1H,
CH(C=N)2), 3.05 (d, J = 9 Hz, 4H, CH2), 1.88 (m, 2H,
CH(CH3)2), 1.86 (s, 6H, CH3(C=N)), 0.96 (d, J = 9 Hz,
12H, CH(CH3)2). Anal. calcd. for C13H26N2: C, 74.23; H,
12.46; N, 13.32. Found C, 74.06; H, 13.03; N, 12.99.15,21
nacnacCH(Me)PhH, 3
Acetylacetone (1.00 g, 10 mmol), HCl (12.1 mol/L,
0.82 mL, 10 mmol), and (+)-phenylethylamine (2.42 g,
20 mmol) in toluene (6 mL) gave a red brown oil (2.45 g,
Published by NRC Research Press

1044
Can. J. Chem. Vol. 88, 2010
nacnacCyH
their research internships to initial explorations of this sub-
ject.
Acetylacetone (2.00 g, 20 mmol), HCl (12.1 mol/L,
0.82 mL, 10 mmol), p-toluenesulfonic acid monohydrate
(2.00 g, 11 mmol), and cyclohexylamine (3.98 g, 40 mmol)
in toluene (15 mL) gave a colorless oil that crystallizes into
References
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1
colorless crystals upon standing for 2–3 h (4.75 g, 90%). H
NMR (CDCl3, 400 MHz): d 11.72 (bs, 1H, NH), 4.44 (s, 1H,
CH(C=N)2), 3.32–3.35 (m, 2H, Cy CH), 1.90 (s, 6H,
Me(C=N)), 1.80–1.35 (m, 20H, Cy). Anal. calcd. for
C13H26N2: C, 77.80; H, 11.52; N, 10.64. Found C, 77.44; H,
11.57; N, 10.67.22
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nacnacMe
H
Acetylacetone (3.00 g, 30 mmol), HCl (12.1 mol/L,
1.24 mL, 15 mmol), p-toluenesulfonic acid monohydrate
(2.99 g, 16 mmol), and methylamine (40%, 4.65 g,
0.06 mol) in toluene (6 mL). The aqueous phase was re-
extracted with ether (3 Â 300 mL), and the combined
organic phases were dried over Na2SO4 and evaporated to
dryness. The dark-yellow oil obtained solidifies to an orange
precipitate that darkens upon standing to room temperature
1
(2.5 g, 65%). H NMR (CDCl3, 400 MHz): d 10.04 (bs, 1H,
NH), 5.2 (s, 1H, CH(C=N)2), 2.99 (s, 6H, NMe), 1.86 (s,
6H, CH3(C=N)). 13C{1H} NMR (CDCl3, 400 MHz): d 162.1
(C=N), 93.9 (CH(C=N)2), 33.3 (Me), 19.0 (CH3(C=N)). Ele-
mental analysis data were unsatisfactory due to easy decom-
position.2,15
nacnacXyl,Bn
H
Acetylacetone (3.00 g, 30 mmol), HCl (12.1 mol/L, 2.5 mL,
30 mmol), and 2,6-dimethylaniline (3.63 g, 30 mmol) in tol-
uene (12 mL) were refluxed for approximately 2 h. To the
obtained yellow suspension, benzylamine (3.27 g, 30 mmol)
was added and allowed to reflux for 3 days under azeotropic
removal of water in a Dean–Stark apparatus. After cooling
to room temperature and decantation of toluene, the brown
oil obtained was treated with ether (50 mL) and aqueous
KOH (16.8 g, 0.3 mol, 50 mL). The ether phase was sepa-
rated and evaporated to dryness. The obtained red-brown oil
was dissolved in a minimum amount of ethanol and kept
at –20 8C for several days. Crystals of nacnacBnH formed
were removed by filtration, and the remaining ethanol solu-
tion was evaporated to dryness to yield a brown oil (2.62 g,
30%, in 90% purity containing 10% of 2). Further recrystal-
lizations in MeOH or in EtOH as well as sublimation still
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1
yielded product mixtures. H NMR (CDCl3, 400 MHz): d
11.18 (bs, 1H, NH), 7.22–7.30 (m, 8H, Ph), 4.45 (s, 1H,
CH(C=N)2), 4.43 (s, 2H, CH2), 2.07 (s, 6H, Ar Me), 1.90
(s, 3H, Me(C=N)), 1.63 (s, 3H, Me(C=N)). 13C{1H} NMR
(CDCl3, 400 MHz): d 160.1 (C=N), 140.1 (C=N), 128.4,
128.3, 127.6, 127.5, 127.2, 127.0, 126.7, 126.3 (all Ph),
93.9 (CH(C=N)2), 46.5 (CH2), 21.2 (Me(C=N)), 19.1
(Me(C=N)), 18.3 (Me2Ph). EI-HR-MS (m/z): calcd. for
C20H25N2 [M + H]+: 293.2012; found: 293.2013.5
¨
¨
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Acknowledgements
Financial support from the Natural Sciences and Engi-
neering Research Council of Canada (NSERC) and the Uni-
´
´
versite de Montreal is gratefully acknowledged. Boris Vabre,
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´
Marie Teillard, and Sebastian Guiollard contributed during
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El-Zoghbi et al.
1045
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