A novel synthetic approach to diaminoacetylenes: Structural characterization and reactivity of aromatic and aliphatic ynediamines

Article abstract of DOI:10.1002/chem.201002211

Electron-rich diaminoalkynes with a variable substitution pattern can be conveniently prepared by lithiation of 2,2-dibromo-1,1-ethenediamines; the alkynes are formed by a Fritsch-Buttenberg-Wiechell rearrangement of intermediate LiBr-vinylidene species. The first two X-ray crystal structures of diaminoalkynes are presented, which show almost perpendicular orientations of the NC₃ planes.

Full text of DOI:10.1002/chem.201002211

DOI: 10.1002/chem.201002211
A Novel Synthetic Approach to Diaminoacetylenes: Structural
Characterization and Reactivity of Aromatic and Aliphatic Ynediamines
Alex R. Petrov, Constantin G. Daniliuc, Peter G. Jones, and Matthias Tamm*[a]
Acetylenes represent an important class of compounds
with a broad range of applications as versatile reagents, link-
ers, or ligands,[1] and numerous novel reactions involving, for
instance, cycloadditions,[2] cross-couplings,[3] and alkyne
metathesis[4] have been developed during the last few de-
cades. The reactivity and electronic properties of alkynes
are largely dictated by the nature of their substituents and
the degree of conjugation. Accordingly, heteroatom-func-
tionalized acetylenes have been shown to display a large va-
riety of different reactivity patterns,[5] with nitrogen-func-
tionalized systems such as electron-rich ynamines (1-amino-
alkynes) and ynamides (1-amidoalkynes) having found par-
ticularly widespread use in organic synthesis.[6,7] In contrast,
only a small number of bis(nitrogen-functionalized) acety-
Scheme 1. Preparative routes to alkynes.
ꢀ
lenes of the type R2NC CNR2 have been described in the
adapted to the preparation of diaminoalkynes with a varia-
ble substitution pattern. This approach is based on the
Fritsch–Buttenberg–Wiechell (FBW) rearrangement, which
was originally developed for the preparation of diarylacety-
lenes (tolanes) from 2,2-diaryl-1-chloroalkenes[14,15] and in-
volves the generation of halogen–metal–vinylidene species
followed by 1,2-migration and concomitant metal halide
elimination (Scheme 1b).[16] Notably, the FBW rearrange-
ment has recently evolved into a valuable synthetic method-
ology for the preparation of polyyne structures, which can
be accessed by treatment of 1,1-dibromo-2,2-dialkynyl-
literature, although the preparation of the first ynediamine,
1,2-bis(diethylamino)acetylene, from 1,1-dichloro-2-fluoro-
ethylene was reported in 1964 by Viehe and Reinstein.[8]
These highly reactive compounds were prepared by stepwise
addition of amines/amides to in situ prepared dihaloacety-
lenes or chloroaminoacetylenes, followed by elimination
(Scheme 1a).[9] However, these synthetic protocols are
rather tedious and involve the use of several equivalents of
lithium amides; these obstacles, together with the high reac-
tivity of diaminoalkynes, have hampered the widespread use
of these compounds in organic synthesis, although a number
of applications in organometallic chemistry have been re-
ported during the last two decades.[10]
AHCTUNGTRENNUNG
ethenes with n-butyllithium (nBuLi).[17] Developing a similar
protocol for the synthesis of diaminoalkynes required the
preparation of the corresponding 2,2-dibromo-1,1-ethenedi-
In searching for a new access to diaminocyclopropenyli-
denes[11,12] and their heavier analogues,[13] we became inter-
ested in developing a general synthetic approach that can be
ACHTUNGTRENaNUNG mines of type 2 (Scheme 2), which, to the best of our
knowledge, have not been described in the literature to
date, although a limited number of dichloro derivatives have
been reported that were obtained unexpectedly[18] or as by-
products.[19] a,a-Dibromoolefins are generally prepared
from aldehydes or ketones by a dibromoolefination protocol
by using Ph3P/CBr4;[20] however, the low reactivity of the
corresponding N,N,N’,N’-tetrasubstituted ureas precludes
the application of this method for the preparation of com-
pounds 2.
[a] Dr. A. R. Petrov, Dr. C. G. Daniliuc, Prof. Dr. P. G. Jones,
Prof. Dr. M. Tamm
Institut fꢀr Anorganische und Analytische Chemie
Technische Universitꢁt Braunschweig
Hagenring 30, 38106 Braunschweig (Germany)
Fax : (+49)531-391-5309
E-mail: m.tamm@tu-bs.de
Alternatively, we studied the bromination of 1,1-ethenedi-
amines (or ketene aminals) 1 and started our investigation
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/chem.201002211.
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COMMUNICATION
The bromination of 1b–1d proceeded cleanly under the
same conditions as described for 1a (vide supra), and the di-
bromoketene aminals 2b–2d were isolated as yellow solids
in satisfactory yield (67–85%). Upon treatment with one
equivalent of nBuLi at 08C in toluene (2a) or hexane (2b–
2d), all dibromides 2 underwent the FBW rearrangement to
form the diaminoalkynes 3a–3d in 77–90% yield as color-
less oils (3b, 3d) or crystalline solids (3a, 3c), respectively
(Scheme 2). All ynediamines were characterized by NMR
spectroscopy, mass spectrometry, and elemental analysis. In
the 13C{1H} NMR spectra, the resonances for the acetylenic
carbon resonances are found between d=72 and 78 ppm,
which falls in the normal range expected for alkynes.
Scheme 2. Synthesis of a,a-dibromoketene aminals 2 and diaminoalkynes
3.
with the diamine (PhMeN)2C=CH2 (1a), which can be pre-
pared on a large scale by a two-step procedure starting from
N-methylaniline.[21] Addition of two equivalents of bromine
to a solution of 1a in CH2Cl2 at 08C in the presence of an
excess of Et3N cleanly afforded the dibromide 2a as a pale
yellow crystalline solid in 73% yield (Scheme 2). The molec-
ular structure of 2a was determined by X-ray diffraction
analysis (Figure 1);[22] the asymmetric unit contains one half
Surprisingly, there are no reports available on X-ray crys-
tal structure determinations of diaminoalkynes, although a
perpendicular conformation was theoretically predicted for
[24,25]
ꢀ
diaminoacetylene, H2NC CNH2.
Single crystals of 3a
and 3c were obtained from a hexane (3a) or tetramethylsi-
lane solution (3c) at À308C, and the resulting molecular
structures are shown in Figure 2 and Figure 3, respective-
Figure 1. ORTEP diagram of 2a with thermal displacement parameters
Figure 2. ORTEP diagram of 3a with thermal displacement parameters
À
drawn at 50% probability. Selected bond lengths [ꢃ] and angles [8]: C1
À
drawn at 50% probability. Selected bond lengths [ꢃ] and angles [8]: C1
À
À
C2 1.338(6), C1 Br 1.887(2), C2 N 1.394(3); C2-C1-Br 123.12(11), C1-
C2-N 121.8(2), N-C2-Nꢄ 116.4(4), Br-C1-Brꢄ 113.8(2).
À
À
C2 1.1992(12), C1 N1 1.3461(11), C2 N2 1.3442(10); C1-C2-N2
174.10(9), C2-C1-N1 176.28(9).
of the molecule, which displays crystallographic C2 symme-
À
try about an axis passing through the C1 C2 double bond.
At 1.338(6) ꢃ, this bond length is virtually identical to those
determined for the dichloroketene aminals 2-(dichloro-
methylene)-1,3-dimesitylimidazoline (1.337(6) ꢃ) and 2-(di-
chloromethylene)-4,5-dichloro-1,3-dimesitylimidazole
(1.353(4) ꢃ).[19] The C C double bond in 2a is significantly
À
twisted and exhibits an interplanar angle of 17.68 between
the CN2 and CBr2 planes. The nitrogen atoms are in a slight-
ly distorted trigonal-planar environment (sum of angels at
N=359.38); the two NC3 planes deviate strongly from a co-
Figure 3. ORTEP diagram of 3c with thermal displacement parameters
drawn at 50% probability. Selected bond lengths [ꢃ] and angles [8] for
À
À
À
À
C1 C2 1.206(2), C1 N1 1.357(2), C2 N2 1.359(2); C1-C2-N2 177.87(14),
C2-C1-N1 173.92(14).
planar arrangement, either with each other or with the C C
double bond, as, for instance, indicated by the torsion angles
C3-N-C2-N’=47.38 and C4-N-C2-N’=57.08.
Fortunately, this route could also be applied to the bromi-
nation of the aliphatic ketene aminals 1b–1d, which can be
obtained in high yield from the reaction of N,N-dimethyl-
ly.[22] In agreement with the theoretical prediction,[24] the
amino substituents in 3a and 3c exhibit strongly twisted ori-
entations, affording approximately C2-symmetric molecules
with axial chirality. The nitrogen atoms in 3a are in a trigo-
nal-planar environment (sum of angles at N1/N2=359.88/
360.08), and the angle between these two NC3 planes is
77.18, indicating a pronounced deviation from a perfectly
ACHTUNGTRENNUNGacetamide dimethylacetal, MeCACHTUGNTREN(NUNG OMe)2NMe2 with the ap-
propriate amines piperidine (1b), 4-methylpiperidine (1c),
and homopiperidine (1d). This method was recently de-
scribed for the preparation of a morpholine derivative and
is driven by the volatility of methanol and dimethylamine.[23]
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M. Tamm et al.
perpendicular orientation, which might be ascribed to crys-
tal packing effects. In contrast, the nitrogen atoms in 3c
reside in a distinctly trigonal-pyramidal coordination sphere
as indicated by the angle sums of 341.68 (N1) and 344.68
(N2). The dihedral angle between the two NC3 planes is
78.58, revealing a similar twist as observed for 3a. In both
molecules, the N-C-C-N axes are close to linearity with C-C-
N angles of 174.10(9)8/176.28(9)8 in 3a and 177.87(14)8/
Figure 4. ORTEP diagram of 4 with thermal displacement parameters
À
drawn at 50% probability. Selected bond lengths [ꢃ] and angles [8]: C1
À
À
À
N1 1.3878(16), C1 N2 1.4047(16), C1 C2 1.3661(18); N1-C1-C2
110.17(11), N1-C1-N2 119.53(11), C2-C1-N2 130.23(12).
173.92(14) in 3c. The C1 C2 bond lengths are 1.1992(12) ꢃ
in 3a and 1.206(2) ꢃ in 3c, in agreement with the presence
À
À
of C C triple bonds; a similar, albeit slightly shorter C C
bond length of 1.189(5) ꢃ was recently reported for an
ortho-anisyl-substituted ynamide, which also displays an or-
thogonal conformation in the solid state.[26]
common, whereas examples of solution-state insertion into
À
significantly less reactive aromatic C H bonds are rare and
During the formation of 3a from the reaction 2a with
nBuLi in toluene, we were able to isolate a minor byproduct
in approximately 3% yield, which was identified as 2-(N’-
methyl-N’-phenylamino)-N-methylindole (4) by comparison
of its NMR spectroscopic data with those reported in the lit-
erature (Scheme 3).[27] The yield of 4 increased to 54% if
were only relatively recently reported.[29] Similar reactivity
was also observed for N-arylaminovinylidene species that
were generated by addition of anilides to alkynyliodonium
triflates.[30]
The observed dependence of the 3a/4 ratio on the solvent
polarity can be satisfactorily explained by postulating that
lithiation of the dibromide 2a does not generate the free vi-
nylidene Int, but rather affords a LiBr–carbenoid adduct
(see Scheme 1) of the type [Li(Br)C=C{N(Me)Ph}2]
AHCTUNGTREG(NNUN Int·LiBr), the aggregation and reactivity of which is strong-
ly affected by the coordinating ability of the solvent, as gen-
erally observed for a-halogenoorganolithium com-
pounds.[16,31] Apparently, polar solvents such as THF disfa-
vor the FBW rearrangement by providing a long-lived vinyl-
idene intermediate that undergoes intramolecular 1,5-CH-
insertion, whereas the observed predominant formation of
the diaminoalkyne 3a in a nonpolar solvent such as toluene
by 1,2-migration is in full agreement with recent high-level
DFT calculations, showing “that the most facile FBW path-
ways occur in aggregated species.”[32]
Another interesting reactivity pattern associated with the
presence of N-phenyl substituents in the diaminoacetylene
3a was discovered upon studying its coordination chemistry
towards transition metals. Whereas a rich organometallic
chemistry can be established based on the aliphatic diami-
noacetylenes 3b–3d,[10,33] the addition of electrophilic metal
ions, such as Au+, Pd2+, exclusively afforded 3-(N’-methyl-
N’-phenylamino)-N-methylindole (5), which represents a
structural isomer of 4. Apparently, these electrophiles cata-
Scheme 3. Formation of indole derivatives by intramolecular CH inser-
tions.
À
the lithiation reaction was performed in tetrahydrofuran
(THF) or if coordinating additives such as N,N,N’,N’-tetra-
methylethylenediamine (tmeda) were added to the toluene
solution prior to the addition of nBuLi. Compound 4 could
be isolated in pure form by fractional crystallization at
+38C from a 3a/4 mixture dissolved in hexane. Single-crys-
tal X-ray diffraction analysis confirmed the molecular struc-
ture of 4 (Figure 4).[22] Mechanistically, the formation of 4
can be rationalized by an intramolecular insertion of the in-
lyze the 1,2-addition of an ortho-C H bond of one of the
À
phenyl rings across the C C triple bond (Scheme 3). The
same reaction can be achieved by acid catalysis, and treat-
ment of a solution of 3a in acetone with p-toluenesulfonic
acid resulted in a markedly exothermic reaction and cleanly
afforded the indole 5, the molecular structure of which was
additionally established by X-ray diffraction analysis
(Figure 5).[22] In analogy to the reactivity of ynamines and
ynamides,[7] the formation of 5 can be rationalized by forma-
tion of an intermediate keteniminium ion, which triggers the
observed intramolecular hydroarylation reaction. A closely
related mechanism was recently proposed for the formation
of related indoles from aminochlorocarbenes under compa-
ratively harsh conditions (DMSO, 110–1508C, 7–18 h).[34] Fi-
À
termediate vinylidene species Int into an ortho-C H bond
of one of the phenyl rings (Scheme 3), which resembles the
formation of cyclopentene derivatives from thermally gener-
ated alkenylidenes by 1,5-CH insertion.[16,28] It should be
À
noted, however, that insertion into alkyl C H bonds is
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Chem. Eur. J. 2010, 16, 11804 – 11808

Diaminoalkynes
COMMUNICATION
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with thermal displacement parameters drawn at 50% probability. Select-
À
À
ed bond lengths [ꢃ] and angles in molecule 1 [8]: C1 N1 1.374(2), C1
À
C2 1.367(2) C2 N2 1.414(2); N1-C1-C2 110.26(11), N2-C2-C1 125.67(12),
C1-N1-C9 125.20(11). In molecule 2, the indole ring is disordered over
two positions (minor component 7% occupied).
nally, exclusive formation of 5 is also observed in the pres-
ence of water, indicating that intramolecular cyclization is
much faster than intermolecular nucleophilic addition. In
contrast, aliphatic ynediamines are extremely moisture-sen-
sitive and readily add water to form the corresponding ami-
[7]
À
noacid amides R2NCH2 C(O)NR2.
We envisage that the new general approach for the prepa-
ration of diaminoacetylenes of type 3 provided herein will
advance the application of these electron-rich compounds in
organometallic chemistry and material science. In addition,
the facile FBW rearrangement upon lithiation of the fairly
stable 2,2-dibromo-1,1-ethenediamines 2 also allows the gen-
eration of these species on demand and the development of
novel organic transformations without the prerequisite of
isolating larger quantities of these highly reactive alkyne de-
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Keywords: alkynes
Fritsch–Buttenberg–Wiechell rearrangement
vinylidenes
·
carbenoids
·
diaminoacetylenes
·
·
· indoles
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b=6.9995(2), c=54.0623(13) ꢃ, V=2293.82(11) ꢃ3, Z=6, 1calcd
=
1.721 MgmÀ3
, , T=100(2) K, CuKa radiation (l=
m=6.6 mmÀ1
1.54184 ꢃ). The structure was refined by using the program
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,
m=0.07 mmÀ1
,
T=
100(2) K, MoKa radiation (l=0.71073 ꢃ). wR2=0.1079 for 165 pa-
Chem. Eur. J. 2010, 16, 11804 – 11808
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11807

M. Tamm et al.
rameters and 3628 unique reflections, with R1 =0.0365, GOF=1.1.
Crystal data for 3c: C14H24N2, Mr =220.35, triclinic, P1, a=
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¯
5.5739(10), b=9.9713(14), c=12.4075(18) ꢃ, a=102.813(12)8, b=
98.707(14)8, g=94.473(12)8, V=660.21(18) ꢃ3, Z=2, 1calcd
=
1.108 MgmÀ3
, , T=100(2) K, CuKa radiation (l=
m=0.5 mmÀ1
1.54184 ꢃ). wR2=0.1134 for 147 parameters and 2702 unique re-
flections, with R1 =0.0412, GOF=0.98. Crystal data for 4: C16H16N2,
Mr =236.31, monoclinic, P21/c, a=7.1049(2), b=16.0471(6), c=
11.3223(4) ꢃ, b=104.878(4)8, V=1247.61(7) ꢃ3, Z=4, 1calcd
=
1.258 MgmÀ3
,
m=0.6 mmÀ1
,
T=100(2) K, CuKa radiation (l=
1.54184 ꢃ). wR2=0.1143 for 165 parameters and 2578 unique re-
flections, with R1 =0.0437, GOF=1.07. a significant difference peak
of 0.8 eꢃÀ3 could not be satisfactorily explained. Crystal data for 5:
¯
C16H16N2, Mr =236.31, triclinic, P1, a=10.1550(6), b=11.9707(6),
c=12.2685(8) ꢃ, a=112.448(6)8, b=106.138(6)8, g=96.567(5)8, V=
1282.56(13) ꢃ3, Z=4, 1calcd =1.224 MgmÀ3
,
m=0.6 mmÀ1
,
T=
100(2) K, CuKa radiation (l=1.54184 ꢃ). wR2=0.1063 for 370 pa-
rameters and 5295 unique reflections, with R1 =0.0396, GOF=1.09.
Details of the X-ray crystal structure determinations can be found
in the Supporting Information. CCDC-784154 (2a), 784155 (3a),
784156 (3c), 784157 (4) and 784158 (5) contain the supplementary
crystallographic data for this paper. These data can be obtained free
of charge from The Cambridge Crystallographic Data Centre via
www.ccdc.cam.ac.uk/data_request/cif.
[32] L. M. Pratt, N. V. Nguyen, O. Kwon, Chem. Lett. 2009, 38, 574–575.
[33] A. R. Petrov, M. Tamm, unpublished results.
[34] Y. Cheng, Y.-H. Zhan, H.-X. Guan, H. Yang, O. Meth-Cohn, Synthe-
sis 2002, 2426–2430.
[35] See, for instance: a) G. R. Humphrey, J. T. Kuethe, Chem. Rev. 2006,
106, 2875–2911; b) S. Cacchi, G. Fabrizi, Chem. Rev. 2005, 105,
2873–2920.
[23] S. N. Gradl, J. J. Kennedy-Smith, J. Kim, D. Trauner, Synlett 2002,
0411–0414.
[24] DFT calculations at the B3LYP/6-31+G* level predict the orthogo-
nal conformer of H2NC CNH2 to be more stable by 5.2 kcalmolÀ1
than the planar conformer, see: S. Ohashi, S. Inagaki, Tetrahedron
2001, 57, 5361–5367.
ꢀ
Received: August 2, 2010
Published online: September 13, 2010
11808
www.chemeurj.org
ꢂ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2010, 16, 11804 – 11808