Chemoselective Hydroalumination of 1-Aza-but-1-en-3-ynes (C-Iminoalkynes): Formation of Propargylamines by Imine Reduction and of 5-Aluminazoles and 1-Aza-butadienes by Anti-Michael Attack

Article abstract of DOI:10.1021/acs.organomet.8b00036

Hydroalumination of 1-aza-but-1-en-ynes 1 provides facile access to propargylamines 4 by reduction of the C=N bonds or alternatively to 1-aza-buta-1,3-dienes 6 by reduction of the triple bond. The chemoselectivity depends not only on the steric properties of both the hydroalumination agent (di-iso-butylaluminum (DIBAL-H, iBu₂AlH) versus di-tert-butylaluminum hydride (tBu₂AlH)) and the substrates but also on the reaction temperatures. In several cases, initial aluminum species of 5-aluminazole type 5 could be isolated and characterized by X-ray diffraction, indicating an "anti-Michael" addition of the hydride to the triple bond. Aqueous workup of those species led to 1-azabutadiene derivatives 6. High-level DFT calculations indicate that the observed chemoselectivity is only compatible with a dimeric nature of the hydroaluminating agent. Using such a dimer, the imine reduction corresponds to the kinetically controlled pathway, whereas the triple bond reduction leads to the thermodynamically much more stable 5-aluminazoles, 5.

Full text of DOI:10.1021/acs.organomet.8b00036

Article
Cite This: Organometallics XXXX, XXX, XXX−XXX
Chemoselective Hydroalumination of 1‑Aza-but-1-en-3-ynes
(C‑Iminoalkynes): Formation of Propargylamines by Imine Reduction
and of 5‑Aluminazoles and 1‑Aza-butadienes by Anti-Michael Attack
J. Matthias Dahlkamp,† Michael Tolzmann,‡ Ralph Lucchesi,† Constantin-Gabriel Daniliuc,†
Birgit Wibbeling,† Werner Uhl,‡,* and Ernst-Ulrich Wurthwein*,†
̈
†Organisch Chemisches Institut der Universitat Munster and Center for Multiscale Theory and Computation (CMTC),
̈
̈
Corrensstrasse 40, D-48149 Munster, Germany
̈
‡Institut fur Anorganische und Analytische Chemie der Universitat Munster, Corrensstrasse 30, D-48149 Munster, Germany
̈
̈
̈
̈
S
* Supporting Information
ABSTRACT: Hydroalumination of 1-aza-but-1-en-ynes 1
provides facile access to propargylamines 4 by reduction of
the CN bonds or alternatively to 1-aza-buta-1,3-dienes 6 by
reduction of the triple bond. The chemoselectivity depends
not only on the steric properties of both the hydroalumination
agent (di-iso-butylaluminum (DIBAL-H, iBu2AlH) versus di-
tert-butylaluminum hydride (tBu2AlH)) and the substrates but
also on the reaction temperatures. In several cases, initial
aluminum species of 5-aluminazole type 5 could be isolated
and characterized by X-ray diffraction, indicating an “anti-
Michael” addition of the hydride to the triple bond. Aqueous
workup of those species led to 1-azabutadiene derivatives 6.
High-level DFT calculations indicate that the observed chemoselectivity is only compatible with a dimeric nature of the
hydroaluminating agent. Using such a dimer, the imine reduction corresponds to the kinetically controlled pathway, whereas the
triple bond reduction leads to the thermodynamically much more stable 5-aluminazoles, 5.
According to quantum chemical and experimental studies,
dialkylaluminum hydrides react with polar alkynes in a
concerted manner via a four-membered transition state.7 The
hydride ion is transferred to the more positively polarized
carbon atom, whereas the dialkylaluminum moiety is bonded to
the negatively polarized carbon atom of the triple bond
resulting in a cis-addition. However, often isomerization to the
more stable trans-diastereomer is observed. Eisch et al.
explained in 1963 the cis−trans isomerization by a second
addition of an aluminum hydride, subsequent rotation around
the resulting C−C-single bond, and elimination of the
dialkylaluminum hydride (retro-hydroalumination). Very polar
alkenes may even rotate around the CC-double bond
without addition of a Lewis acid.8 On the basis of a quantum
INTRODUCTION
■
Hydroboration and hydroalumination of homo- and hetero-
nuclear multiple bonds are versatile and widely applied
reduction methods in organic synthesis.1,2 In general hydro-
alumination of alkynes proceeds faster than those of alkenes.
Thus, conjugated or nonconjugated enynes are regioselectively
hydroaluminated at the triple bond. Apolar CC-double
bonds often require the use of catalysts or harsh reaction
conditions.3 Replacement of carbon atoms by heteroatoms (O,
N, S) raises the polarity of the triple and double bonds
considerably, allowing milder reaction conditions and better
regio- and stereoselectivities, even in absence of a catalyst.4
Depending on steric shielding by the substituents dialkyl- or
diarylaluminum hydrides form trimeric, dimeric or monomeric
species in the solid state. Equilibria between dimeric and
trimeric formula units have been observed in solution for
relatively small groups such as methyl, iso-butyl, or neo-
pentyl,5,6 while bulky groups such as bis(trimethylsilyl)methyl
resulted in dissociation to yield monomeric species. The activity
of these oligomeric hydrides in hydrometalation processes
depends on steric shielding and the facile dissociation in
solution. On the basis of our empirical observations, the
dimethylaluminum compound is accordingly less reactive than
the di-tert-butylaluminum derivative.
chemical study by Uhl, Wurthwein et al. a dimer with two Al−
̈
C(vinyl)−Al bridges and a significantly lower bond order of the
CC bond was suggested recently as key intermediate for cis−
trans isomerization.9
Metal-catalyzed hydroalumination reactions are also known.
Hoveyda et al. showed that the stereoselectivity of the Al−H-
addition in case of Nickel-catalyzed hydroalumination highly
depends on the nature of the catalyst employed.10 The resulting
Received: January 21, 2018
© XXXX American Chemical Society
A
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Figure 1. NBO-Charges (B3LYP/def2TZVP) for 1-aza-but-1-en-3-yne 1 vs but-1-en-3-yne 2.
α-vinylic aluminum compounds are excellent starting materials
for the generation of various functional compounds. They were
treated with electrophiles like N-bromosuccinimide or boron
compounds to obtain the respective α,α-disubstituted ethenes.
Similarly useful are aluminum acetylides.11 Micouin et al.
prepared such compounds by treatment of terminal alkynes
with trimethylaluminum. Subsequent reaction with aryl halides
in the presence of Pd(0) catalysts gave the respective cross-
coupling products.12
Due to their conjugated triple and double bonds, 1-aza-but-1-
en-3-ynes 1 form a highly interesting class of compounds with
challenging regio- and chemoselectivities in hydroalumination
reactions.13 The polar iminic double bond14 is expected to
induce higher reactivity compared to that of but-1-en-3-ynes
like 2. Figure 1 presents the NBO charges,15 based on B3LYP/
def2TZVP calculations. These data clearly indicate the
alternating charge distribution for the imino compound. Its
influence on the regioselectivity of hydroalumination reactions
of such 1-aza-but-1-en-3-ynes is the subject of this study, thus
continuing our research in the field of hydroalumination of
unsaturated nitrogen compounds.16
Scheme 1. Synthesis of 1-Aza-but-1-en-3-ynes 1a−g
Table 1. 1-Aza-but-1-en-3-ynes 1a−g
compound
R′
phenyl
R′′
yield
1a
adamantyl
p-tolyl
73%
71%
90%
62%
34%
76%
84%
1b
phenyl
1c26
1d26
1e27
1f
phenyl
N-piperidinyl
N-morpholinyl
p-tolyl
phenyl
trimethylsilyl
n-butyl
p-tolyl
1g
phenyl
p-bromophenyl
compound 1d was elucidated using X-ray crystallography
(Figure 2). 1d crystallizes with two independent molecules in
In 1966, the first 1-aza-but-1-en-3-yne 1 was reported by
Chauvelier et al., who prepared an ethinyl-imidic ester from
phenylethinyl ethylglyoxylate and aniline.17 Normant et al.
described in 1973 a synthetic pathway for the preparation of 1-
aza-but-1-en-3-ynes, based on the formation of intermediate
lithium cuprates, which were reacted with N-phenyl-benzimi-
doyl chloride.18 Stadnichuk et al.19 and Vyazankin et al.20
published in 1982 and 1983, respectively, a simple synthetic
pathway to 1-aza-but-1-en-3-ynes by condensing trimethylsilyl-
substituted propargylaldehydes with aliphatic and aromatic
amines. Recently, Micouin et al. published a new access to α-
silylated alkynylhydrazones by treatment of dimethylaluminum
alkynides with trimethylsilyldiazomethane.21
Figure 2. Molecular structure of 1d (one of two independent
molecules). Displacement ellipsoids are drawn at the 30% probability
level.
1-Aza-but-2-en-3-ynes 1 are useful starting materials for a
number of chemical reactions. Thus, Gevorgyan et al. described
a copper-catalyzed synthesis for pyrroles and annelated
pyrroles.22 Alper et al. reacted various 1-aza-but-1-en-3-ynes
under high pressure with hydrogen and carbon monoxide using
a Rh-catalyst to obtain 4-carbaldehydepyrrolin-2-ones in good
yields.23 Fu et al. found simple access to fluorinated quinolines,
starting from 1-aza-but-1-en-3-ynes by base-catalyzed propargyl
allenyl isomerization and subsequent aza-electrocyclization.24
the asymmetric unit and adopts an (E)-configurated CN
bond with the neighboring lone pairs on the nitrogen atoms in
almost perpendicular orientation. The mean values of the
central bonds are N1−C2 1.278 Å, C2−C3 1.426 Å, C3−C4
1.198 Å, C4−C11 1.439 Å, and N1−N2 1.366 Å (on average)
indicating the π-conjugated nature of this part of the molecule.
Regioselectivity of Hydroalumination Reactions.
Hydroalumination of 1a−g with Di-iso-butylaluminum
Hydride. Imines 1b−f were reacted with 1.1 equiv of di-iso-
butylaluminum hydride (DIBAL-H (iBu2AlH)) in toluene at
−30 °C. The resulting solutions were stirred for 2 h at −30 °C.
All attempts to isolate and characterize the intermediate
aluminum species by X-ray diffraction or NMR spectroscopy
after precipitation and recrystallization failed. Thus, after
warming to room temperature the reaction mixtures were
poured on a 5 cm pad of nondried silica gel in a 7 cm thick
column to achieve hydrolysis. After complete absorption, the
pad was covered with a 2 cm pad of sea sand. Then, diethyl
ether was used as eluent to separate the reaction products from
inorganic aluminum species. After removal of diethyl ether
DISCUSSION
■
Preparation of Imines and Hydrazones. 1-Aza-but-1-en-
3-ynes 1 used in this study were prepared by imine
condensation in analogy to literature procedures.21,25 The
corresponding propargylaldehydes 3 and amines or hydrazines
were reacted to yield imines respectively hydrazones (Scheme
1, Table 1).
All compounds 1 were characterized by IR, 1H NMR and 13C
NMR spectroscopy, and mass spectrometry (Supporting
Information). The structure in the crystalline state of
B
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purification of the products was achieved by chromatography
over nondried silica gel28 using cyclohexane/ethyl acetate-
mixtures as eluent. Propargylamines 4a−e were obtained in
45−84% yield (Scheme 2, Table 2) and were characterized by
afforded yellowish highly air- and moisture-sensitive crystals of
compound 5a after removal of the solvent in vacuo and
recrystallization of the residue from n-hexane at −30 °C in 31%
yield. X-ray crystallography revealed an unexpected structure of
this product (Figure 4 and Supporting Information).
Scheme 2. Preparation of Propargylamines 4a−e
Table 2. Secondary Propargylamines 4a−e
starting material product
R′
phenyl
R′′
p-tolyl
yield
1b
1c
1d
1e
1f
4a
4b
4c
4d
4e
84%
55%
45%
75%
72%
phenyl
N-piperidinyl
N-morpholinyl
p-tolyl
phenyl
trimethylsilyl
n-butyl
p-tolyl
Figure 4. Molecular structure of 5a. Displacement ellipsoids are drawn
at the 30% probability level.
NMR spectroscopy (typical sp-carbon signals in 13C NMR were
at 90−100 ppm) and mass spectrometry. We were able to
obtain the molecular structure in the solid state of 4d by X-ray
diffraction (Figure 3). Compounds 4a−e result from the
addition of the aluminum hydride to the imine CN double
bond and cleavage of the resulting Al−N bond by reaction with
water.
The almost planar heterocycle of the 5-aluminazole type
(dihedral angles C1−C2−C3−N1 2.8(2)° and C1−Al1−N1−
C3 4.2(1)°) is characterized by bond lengths in the normal
range:29 C1−C2 1.345(4) Å, C2−C3 1.451(4) Å, C3−N1
1.288(4) Å, Al1−C1 2.014(3) Å, and Al1−N1 1.997(2) Å, but
the bond angles indicate a strong ring strain in the molecule
(C1−Al1−N1 85.6(1), C1−C2−C3 117.6(3), C2−C3−N1
120.3(3)°).
1
In the H NMR spectrum, the signal of the iminic hydrogen
atom is found at δ = 8.28 ppm as a doublet (3JHH coupling
constant of 2.8 Hz),30 whereas the signal of the vicinal
hydrogen atom appears at δ = 7.12 ppm. In the 13C NMR
spectrum the vinylic carbon atom attached to aluminum is
detected at δ = 193.9 ppm. Mechanistically, the surprising
formation of 5a may be traced back to the attack of the
nucleophilic hydride of DIBAL-H at the nucleophilic α-alkynyl
carbon atom of the propargylimine 1a (see Figure 1). This
indicates an unusual “anti-Michael” selectivity of this reaction
(for NBO-charges of compound 1 see Figure 1 and also the
“Quantum Chemical Calculations” section) initiated by the
strong Lewis acid−base interaction of the aluminum species
with the lone pair of the nitrogen atom.31
Figure 3. Molecular structure of 4d. Displacement ellipsoids are drawn
at the 30% probability level.
The bond lengths C1−C2 (1.201(3) Å), C2−C3 (1.479(3)
Å), Si1−C1 (1.843(2) Å), and C3−N1 (1.452(3) Å) are close
to standard values of triple and single bonds.29 The linearity of
the alkynyl moiety is confirmed by the angles C1−C2−C3
(178.2(2)°) and Si1−C1−C2 (177.1(2)°). The p-tolyl
substituent is tilted with respect to the alkynyl group (dihedral
angle C1−C2−C11−C16 70.3(3)°). The average bond angle
around the silicon atom Si1 amounts to 109.5° indicating its
tetrahedral environment. The nitrogen atom N1 has a distorted
trigonal-pyramidal structure as indicated from its average bond
angle of 116.5°.
In order to study the temperature dependence of the
hydroalumination reaction 1a was treated with DIBAL-H at
−30 °C. The mixture was warmed to 60 °C for 2 h. Subsequent
hydrolysis by filtration over nondried silica gel using diethyl
ether as eluent as described above gave 1-azabutadiene 6a as a
yellow solid in 71% yield (Scheme 4).28 1H NMR spectra of the
crude reaction mixture gave no indication for the presence of
propargylamine 4f. The observed structural properties of 6a
[(E),(E)-configuration] are in accordance with those of
3
Treatment of sterically more encumbered compound 1a with
DIBAL-H for 2 h at −30 °C (without hydrolysis; Scheme 3)
intermediate 5a as seen from the JHH coupling constants of
Hα (d, 8.1 Hz), Hβ (dd, 8.1 Hz, 16.0 Hz), and Hγ (d, 16.0 Hz).
In a second experiment, compound 1a was treated with
DIBAL-H at −60 °C for 2 h (using the same concentration as
above). After immediate hydrolysis, NMR spectra indicated the
formation of a mixture of propargylamine 4f and 1-
azabutadiene 6a in ca. 2:3 ratio, from which propargylamine
4f could be isolated after chromatography in 23% yield.
The temperature dependence of the regioselectivity of these
hydroalumination reactions of 1a indicates an active competi-
Scheme 3. Hydroalumination of Compound 1a to afford 5a
C
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Scheme 4. Preparation of Propargylamine 4f and 1-Aza-butadiene 6a Depending on Reaction Temperatures
Scheme 5. Preparation of Quinoline 7 and N-Methylaniline 8 at Elevated Temperature
tion of kinetic and thermodynamic control involving equilibria
of the participating species (see quantum chemical results
below) allowing the isolation of both chemo- and regioisomeric
reduction products 4f and 6a.
hydroalumination reactions but also the nature of the
hydroalumination agent. Therefore, we employed the sterically
more encumbered di-tert-butylaluminum hydride (tBu2AlH)38
as a reagent in further transformations. Similar to the reactions
described above, the sterically less shielded 1-aza-but-1-en-3-
ynes 1b and 1c were dissolved in toluene and treated at −30 °C
with 1.1 equiv of di-tert-butylaluminum hydride. After
concentration of the solution in vacuo and cooling to −30
°C, we isolated highly moisture- and air-sensitive crystals of
compounds 5b and 5c in low yield (Scheme 6). The 1H NMR
Applying higher temperatures in other reactions of the
iminoalkynes led to the formation of other products. Thus,
compound 1b gave known 6-methyl-4-phenylquinoline 7a in
59% yield upon treatment with DIBAL-H, mixing the
compounds at −30 °C, subsequent heating to 55 °C for 48
h, and hydrolysis. The formation of quinolines from alkynyl
imines (propargylimines)24,32−34 and from alkynyl amines
(propargylamines)35 is known; however, our experiment did
not require the presence of transition metal catalysts. It is quite
likely that DIBAL-H in a small excess of 1.1 equiv as applied
here not only serves as a hydride donor but also as a Lewis acid,
catalyzing the electrophilic aromatic substitution reaction to
give quinoline 7. Other propargylimines gave only traces of the
corresponding quinolines at higher temperatures.
Scheme 6. Synthesis of Anti-Michael Products 5b−c
In other cases, N-methylanilines were identified as products.
Thus, 1g gave only small quantities of corresponding quinoline
7b. The main product was identified as N-methyl-4-bromoani-
line 8 (48% isolated yield), possibly originating from a Lewis-
acid catalyzed fragmentation of the in situ formed propargyl-
amine into a terminal alkyne and an iminium ion. It is known
from tert-propargylalcohols to fragment in a similar manner
into terminal alkynes and ketones, a reaction which is used to
protect terminal alkynes.36 Lanthanide-catalyzed C−C bond
breaking of propargylamines has recently been reported.37 We
assume that an intermediate iminium salt is reduced by the
aluminum hydride to form observed N-methylaniline 8
(Scheme 5).
spectra of 5b and 5c support the molecular configuration which
results from the unexpected reduction of the CC triple bond.
The iminic (about 8.0 ppm) and vinylic [7.31 ppm (5b) and
3
6.80 ppm (5c)] hydrogen atoms feature a JHH coupling
constant of 2.9 (3b) and 3.2 Hz (5c) confirming the respective
syn-arrangement. Due to the quadrupole moment of the
aluminum atoms, the signals of the vinylic carbon atoms bound
to aluminum could not be detected. The chemical shifts for the
iminic carbon atoms are 169.3 ppm (5b) and 147.0 ppm (5c).
As described above, formally the hydride transfer from t-
Bu2AlH to the acetylenic α-carbon atom of imines 1 follows an
“anti-Michael” regioselectivity (see also the “Quantum
Chemical Calculations” section). The molecular structures of
Hydroalumination of 1b and 1c with Di-tert-butylalumi-
num Hydride. Not only the steric shielding exerted by the N-
substituents of 1a versus 1d,e may influence the outcome of the
D
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compounds 5b−c were analyzed by X-ray diffraction (Figures 5
and 6).
applicability in organic and metalorganic synthesis is subject
of ongoing studies. Cui et al. published the synthesis of a
monomeric NHC-stabilized iminoalane featuring an AlC3N-
ring system, and some of its reactions, for example the insertion
of CO.39 Schmidt et al. prepared a corresponding LiC3N-
heterocycle and obtained upon reaction with Et2AlCl a bicyclic
AlC3N-compound.40 A more recent example was published by
Kingsley et al.41 Further examples of five-membered AlC3N-
heterocycles were reported by Roesky et al.42 and by Cui et
al.;43 in both studies the tetrahedrally coordinated aluminum
atom is bound to an imine-anion-type nitrogen atom and to an
N,N′-bidentate ligand. Mu et al. published a tricyclic bis-
(imino)aryl NCN pincer aluminum system with two five-
membered AlC3N rings featuring a common five-coordinate
aluminum atom.44 Comparable AlC3N-heterocycles, containing
Al(I) ions, were obtained by different routes and have
additional donor ligands attached to their metal ions. Five-
membered MC3N-heterocycles are also known: Tenreiro et al.
published in 2003 a compound with M = Pd2+, where Pd2+ is
coordinated in a chelating manner by a C3N-ligand.45 Similar
transition metal coordination compounds with M = Fe3+,46
Rh2+,47 Ru2+,48 and Ir3+,49 have also been reported.
Figure 5. Molecular structure of 5b. Displacement ellipsoids are drawn
at the 30% probability level.
Earlier investigations by Suvorova and Stadnichuk showed
that the reduction of silicon-containing propargylimines by
LiAlH4 gave propargylamines in the case of N-aryl
propargylimines and mixtures of alkyne and imine reduction
products in cases of N-alkyl imines. NaBH4 led to cleavage of
the Si−C bond.50
Quantum Chemical Calculations. The surprising influence
of the N-substituents and the reducing agents (iBu2AlH versus
tBu2AlH) on the regio- and chemoselectivity of hydro-
alumination reactions of imines 1 was also studied by quantum
chemical gas phase DFT methods using the functional TPSS51
with the basis set def2-TZVP52 as integrated in the Gaussian
0953 package of programs. Dispersion correction using the
GD3BJ-method54 was included. Pathways (a) and (b) for the
hydroalumination reactions of the phenyl derivative (1h) and
the adamantyl derivative (1a) were considered as typical
examples for the experimentally observed selectivity of these
reactions. Pathway (a) uses one molecule of DIBAL-H as
reducing agent, and pathway (b) uses dimers of DIBAL-H-
molecules (Figure 7).
Pathway (a) (conversion of species A into B−D, R = Ph,
Ad): The reactions start with adduct A formed from alkynes 1a
and 1h and one molecule of DIBAL-H. The calculated pathway
results in substantially higher barriers (TS A−B) for the imine
reduction compared to the respective barriers (TS A−C and
TS C−D) for the alkyne reduction. The transition state
geometries for the imine reduction (TS A−B) for 1a (R = Ad)
and 1h (R = Ph) indicate strained four-membered heterocycles,
resulting from a coordination of the aluminum atom to the
nitrogen lone-pair and a perpendicular orientation of the
approaching hydrogen atom. In contrast, for the alkyne
reduction of both compounds 1a and 1h less-strained five-
membered cyclic transition state structures (TS A−C) are
obtained, which result from the coordination of the aluminum
atom to nitrogen and the approach of the hydrogen atom to the
α-alkyne carbon atom. This leads via first intermediates C in a
very exothermic reaction to experimentally observed cyclic
forms D (5) involving a low barrier for the necessary rotation
around the Cα−Cimine bond. Thus, in pathway (a) both kinetics
as well as thermodynamics favor the alkyne reduction.
Consequently, pathway (a) is not able to explain the
Figure 6. Molecular structure of 5c. Displacement ellipsoids are drawn
at the 30% probability level.
Similar to 5a, both heterocycles are almost planar. The bond
lengths involving the aluminum atoms are Al1−C1 2.027(2) Å
(5b), 2.011(3) Å (5c), as well as Al1−N1 2.007(3) Å (5b),
2.030(2) Å (5c), which are in the typical range of four-
coordinate metal atoms in aluminates. The endocyclic angles at
aluminum [N1−Al1−C1 84.7(1) (5b), 84.6(2)° (5c)] are
expectedly very acute.
Finally, 1-aza-but-1-en-3-yne 1c was treated with tBu2AlH
under standard hydroalumination conditions (Scheme 7)
Scheme 7. Preparation of 1-Aza-butadiene 6b
followed by hydrolysis over nondried silica gel. Imine 6b was
obtained in 42% yield. The structural properties as derived from
NMR data are quite similar to those of 6a (see above).
Unfortunately, analogous experiments of this type with other
imines 1 were not successful, possibly due to the high moisture
sensitivity of the resulting 1-azabutadienes.
The novel synthesis of AlC3N-heterocycles 5 described here
is a versatile method for the generation of such reactive
aluminum compounds. Investigations of their potential
E
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on the regiochemical outcome is a nice example for the
influence of cooperativity in metalorganic transformations.55
CONCLUSION
■
The regioselectivity of hydroalumination reactions of acetylenic
imines (propargylimines) 1 depends on the reaction temper-
ature and the steric shielding of the hydroalumination reagents
(iBu2AlH versus tBu2AlH) and the respective substituents at
the nitrogen atoms. Thus, iBu2AlH generally result in the
reduction of the CN bond (examples 1b−1f with small
substituents at nitrogen) with formation of propargylamines
4a−e after hydrolysis. In contrast, sterically encumbered N-
adamantyl derivative 1a gives an aluminazole with an AlNC3-
heterocycle 5a as a result of a formal “anti-Michael” hydride
transfer from the aluminum reagent to the α-acetylenic carbon
atom of 1a, providing facile access to 1-aza-butadiene-derivative
6a after hydrolysis. In contrast, tBu2AlH as hydroaluminating
agent generally leads to aluminazoles 5b,c, even with small
substituents bound to nitrogen.
According to high-level quantum chemical DFT calculations,
the dominating steric effect exerted either from the hydro-
alumination reagent or from the N-substituents is best
explained by coordination of a dimeric hydroalumination
reagent. In the case of iBu2AlH, only a dimeric aggregate is
able to explain the experimental product distribution by
cooperative reaction control. The kinetic product with
reduction of the CN bond was obtained for small
substituents on nitrogen, while thermodynamic control for
the spacious N-adamantyl derivative gave reduction of the C
C triple bond. In contrast, for monomeric hydrometalation
reagents both kinetic as well as thermodynamic control result in
the reduction of the triple bond.
Figure 7. Calculated energy profiles for the hydroalumination
reactions of N-adamantyl- (1a, dashed and dotted line) and N-
phenyl-substituted (1h, straight line) imino alkynes. Pathway (a): use
of monomeric DIBAL-H, pathway (b): use of dimeric DIBAL-H.
ΔG(298) [kcal/mol] data as obtained by TPSSTPSS/def2TZVP
+GD3BJ-optimizations.
experimentally observed formation of propargylamines 4a−e at
low temperatures.
EXPERIMENTAL SECTION
■
In pathway (b) (conversion of species E into F and G, R =
Ad, Ph) dimeric DIBAL-H was applied to yield coordination
compounds E. Small barriers TS E−F were obtained for
formation of imine reduction products F in a slightly
exothermic reaction for both 1a (R = Ad) and 1h (R = Ph).
The very exothermic formation of alkyne reduction products G
(which will give compounds D after DIBAL-H elimination)
involves higher barriers (TS E−G). Thus, kinetic control leads
to imine reduction products F at low temperatures.
The CN reduction of adamantyl-substituted imine 1a is
slightly exothermic. The system approaches an equilibrium
situation and across low activation barriers the thermodynami-
cally favored 1-azabutadiene is formed. The imine-reduction
product of the phenyl-substituted propargyl derivative 1h is
more stable, and the triple bond reduction is hindered by a
higher activation barrier. Products G may form compounds D
by elimination of 1 equiv of DIBAL-H, a reaction which is
calculated to be exothermic by 3−5 kcal/mol. (For the related
tBu2AlH-calculations see Supporting Information.)
Thus, the coordination of imines 1 to dimeric dialkylalumi-
num hydrides helps to understand the different outcome of
these reactions. The unusual anti-Michael addition leading to
the alkyne reduction is explained by the initial coordination of
the dimeric aluminum species to the lone pair at the iminic
nitrogen atoms of compounds 1. This leads to sterically
favorable five- or seven-membered transition states TS C−D
and TS E−G, followed by enormous stabilization by formation
of five- or seven-membered heterocyclic products D and G.
The influence of the dimeric structure of the reduction reagent
All procedures were carried out under purified argon in dry, argon-
flushed glassware using syringe and septum techniques. n-Hexane and
toluene were dried over sodium/benzophenone. tBu2AlH was
obtained according to literature procedures.38 Solutions of iBu2AlH
and n-butyl lithium (nBuLi) were applied as purchased. The NMR
spectra are referenced to tetramethylsilane or to the used deuterated
solvent.
Propargylaldehydes (3a−c). General Procedure 1 (GP 1).
Propargylaldehydes 3 were synthesized according to a literature
procedure.25 The corresponding acetylene was dissolved in dry
tetrahydrofuran and cooled to −40 °C. Afterward, 1 equiv of nBuLi
(1.6 M solution in hexanes) was added and stirred for 30 min. After
the subsequent addition of 2 equiv of dimethylformamide, the solution
was allowed to warm to room temperature. Subsequently, the solution
was added to a vigorously stirred solution of 10% KH2PO4 solution at
0 °C, and afterward, the layers were separated at r.t. After washing the
organic layer three times with methyl t-butyl ether and drying the
combined organic phases over MgSO4, the resulting solution was
evaporated in vacuo and the resulting aldehydes were used without
further purification.
Phenylpropagylaldehyde (3a).25 According to general procedure
GP 1, phenylacetylene (1.38 mL, 12.5 mmol, 1.0 equiv) was dissolved
in 30 mL of tetrahydrofuran and reacted with nBuLi (1.6 M solution in
hexanes) (7.82 mL, 12.5 mmol, 1.0 equiv) and dimethylformamide
(1.94 mL, 25.0 mmol, 2.0 equiv). After aqueous workup, the
corresponding phenylpropargylaldehyde was obtained as a brown oil.
Any further purification was not necessary; the product was used
directly. 1H NMR (400 MHz, CD2Cl2): δ (ppm) = 9.42 (s, 1H,
CHO), 7.64−7.54 (m, 2H, CHarom.), 7.53−7.51 (m, 1H, CHarom.),
7.50−7.41 (m, 2H, CHarom.). 13C NMR (101 MHz, CD2Cl2): δ (ppm)
= 177.3 (CHO), 133.8 (Carom.), 131.9 (Carom.), 129.3 (Carom.), 120.0
(Cipso), 95.1 (Calkyne), 88.8 (Calkyne).
F
DOI: 10.1021/acs.organomet.8b00036
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
n-Butylpropargylaldehyde (3b).25 As described in general
procedure GP 1, 1-hexyne (3.45 mL, 30.0 mmol, 1.0 equiv) was
dissolved in 50 mL of tetrahydrofuran and cooled to −40 °C. After
addition of nBuLi (1.6 M solution in hexanes) (18.75 mL, 30.00
mmol, 1.0 equiv) the solution was stirred for 30 min at this
temperature, followed by addition of dimethylformamide (4.65 mL,
60.0 mmol, 2.0 equiv) and aqueous workup; the corresponding n-
butylpropargylaldehyde was obtained as yellow oil. No further
(w), 919 (m), 861 (m), 812 (s), 785 (w), 763 (m), 752 (s), 710 (w),
686 (s), 647 (w), 565 (w). 1H NMR (400 MHz, CD2Cl2): δ (ppm) =
7.95 (s, 1H, CHN), 7.61−7.59 (m, 2H, CHarom.), 7.45−7.40 (m,
3H, CHarom.), 7.21 (d, 3JHH = 8.0 Hz, 2H, CHarom.,tolyl), 7.11 (d, 3JHH
=
8.3 Hz, 2H, CHarom.,tolyl), 2.37 (s, 3H, CH3). 13C NMR (101 MHz,
CD2Cl2): δ (ppm) = 149.1 (CN), 143.0 (Cipso−N), 138.0 (Cipso),
132.9 (Carom.), 130.4 (Carom.), 129.2 (2C, Carom.), 122.0 (Cipso), 121.3
(Carom.), 94.4 (Calkyne), 88.3 (Calkyne), 21.3 (CH3). MS (ESI): m/z =
220 [M + H]+, 242 [M + Na]+. HRMS (ESI) m/z: [M + Na]+ Calcd
for C16H13NNa 242.0940. Found 242.0944. Anal. Calcd for C16H13N
(219.29): C 87.64 H 5.98 N 6.39. Found: C 87.52 H 5.89 N 6.50.
1-N-Piperidinyl-4-phenyl-1-aza-but-1-ene-3-yne (1c).26 In anal-
ogy to GP 2, 1-aminopiperidine (1.19 mL, 11.0 mmol, 1.1 equiv) was
dissolved in 40 mL of dichloromethane, and molecular sieves were
added. After addition of 3a (1.22 mL, 10.0 mmol, 1.0 equiv), the
reaction mixture was stirred for 96 h at room temperature.
Subsequently, the molecular sieves were filtered off, and the crude
mixture was distilled in a Kugelrohr oven (150 °C/1.3 × 10−2 mbar).
The literature-known compound26 was obtained as a yellow oil. Yield:
1
purification was necessary; the aldehyde was used directly. H NMR
4
(300 MHz, CDCl3): δ (ppm) = 9.15 (t, JHH = 0.9 Hz, 1H, CHO),
2.42 (td, 3JHH = 7.0 Hz, 4JHH = 0.8 Hz, 2H, −CH2−CH2−CH2−CH3),
1.63−1.51 (m, 2H, −CH2−CH2−CH2−CH3), 1.50−1.36 (m, 2H,
3
−CH2−CH2−CH2-CH3), 0.92 (t, JHH = 7.3 Hz, 3H, −CH2−CH2−
CH2−CH3). 13C NMR (75 MHz, CDCl3): δ (ppm) = 177.7 (CHO),
99.5 (Calkyne), 82.1 (Calkyne), 30.2 (−CH2−CH2−CH2−CH3), 22.5
(−CH2−CH2−CH2−CH3), 19.3 (−CH2−CH2−CH2−CH3), 13.8
(−CH2−CH2−CH2−CH3).
Trimethylsilylpropargylaldehyde (3c).56 According to general
procedure GP 1, trimethylsilylacetylene (4.27 mL, 30.0 mmol, 1.0
equiv) was dissolved in 75 mL of tetrahydrofuran and reacted with
nBuLi (1.6 M solution in hexanes) (18.75 mL, 30.0 mmol, 1.0 equiv)
at −40 °C. Subsequently, dimethylformamide (4.62 mL, 60.0 mmol,
2.0 equiv) was added, followed by aqueous workup. The
corresponding aldehyde was obtained as yellow oil and used without
further purification. 1H NMR (300 MHz, CD2Cl2): δ (ppm) = 9.14 (s,
1H, CHO), 0.26 (s, 9H, Si(CH3)3). 13C NMR (75 MHz, CD2Cl2): δ
(ppm) = 177.4 (CHO), 102.7 (Calkyne), 68.3 (Calkyne), 0.69 (Si(CH3)3).
Syntheses of 1-Aza-but-1-ene-3-ynes (1a−g). General Proce-
dure 2 (GP 2). 1.1 Equivalents of the corresponding amine were
dissolved in dry dichloromethane and molecular sieves were added.
After subsequent addition of 1 equiv of the corresponding
propargylaldehyde, the mixture was stirred for the indicated time.
After completion of the reaction, the molecular sieves were filtered off,
and the resulting 1-aza-but-1-ene-3-yne was isolated using the
indicated purification method.
̃
9.0 mmol (1.9 g, 90%), yellow oil. IR (ATR): ν = 2938 (s), 2855 (w),
2817 (w), 2350 (w), 2343 (w), 2190 (m, alkyne), 1596 (w), 1560 (w),
1539 (m, CN), 1489 (s), 1465 (w), 1443 (s), 1345 (s), 1260 (w),
1245 (m), 1169 (m), 1124 (w), 1092 (s), 972 (w), 919 (w), 859 (m),
1
793 (w), 754 (s), 689 (s), 628 (m), 533 (m). H NMR (400 MHz,
CD2Cl2): δ (ppm) = 7.47−7.45 (m, 2H, CHarom.), 7.33−7.32 (m, 3H,
3
CHarom.), 6.78 (s, 1H, CHN), 3.15−3.12 (t, JHH = 5.5 Hz, 4H,
3
3
CH2,piperidine), 1.73−1.67 (p, JHH = 5.8 Hz, JHH = 5.5 Hz, 4H,
3
CH2,piperidine), 1.57−1.53 (p, JHH = 5.8 Hz, 2H, CH2,piperidine). 13C
NMR (101 MHz, CD2Cl2): δ (ppm) = 131.9 (o-Carom.), 128.9 (m-
Carom.), 128.7 (p-Carom.), 123.7 (Cipso), 115.2 (CN), 89.8 (Calkyne),
87.8 (Calkyne), 51.9 (Cpiperidine), 25.4 (Cpiperidine), 24.4 (Cpiperidine). MS
(ESI): m/z = 213 [M + H]+, 235 [M + Na]+. HRMS (ESI) m/z: Calcd
+
for C14H17N2 [M + H] 213.1386. Found 213.1393.
1-N-Morpholinyl-4-phenyl-1-aza-but-1-ene-3-yne (1d).26 Accord-
ing to GP 2, 1-aminomorpholine (1.06 mL, 11.0 mmol, 1.1 equiv) was
dissolved in 40 mL of dichloromethane. Molecular sieves were added,
followed by slow addition of 3a (1.22 mL, 10.0 mmol, 1.0 equiv). The
mixture was stirred for 90 h at room temperature, and afterward, the
molecular sieves were filtered off. The crude mixture was purified by
recrystallization from diethyl ether. The literature-known compound26
was obtained as colorless crystals. Yield: 6.2 mmol (1.49 g, 62%),
1-Adamantyl-4-phenyl-1-aza-but-1-ene-3-yne (1a). According to
GP 2, 1-adamantylamine (0.83 g, 5.5 mmol, 1.1 equiv) was dissolved
in 20 mL of dichloromethane and molecular sieves were added. 3a
(0.61 mL, 5.0 mmol, 1.0 equiv) was added slowly, and the mixture was
stirred for 30 h. After filtration, the crude mixture was distilled in a
Kugelrohr oven (210 °C/3 × 10−2 mbar). The title compound was
obtained as an oil, which became a yellowish solid after cooling to
room temperature. Yield: 3.6 mmol (0.93 g, 72%), yellowish solid.
̃
colorless crystals. Melting point: 86−87 °C. IR (ATR): ν = 3059 (w),
2968 (m), 2895 (w), 2841 (s), 2766 (w), 2368 (w), 2344 (w), 2204
(m, alkyne), 1847 (w), 1729 (w), 1594 (s), 1570 (m), 1543 (s, C
N), 1489 (s), 1441 (s), 1392 (w), 1349 (s), 1277 (w), 1264 (m), 1192
(m), 1139 (s), 1111 (s), 1067 (m), 1040 (w), 999 (s), 931 (m), 862
(s), 803 (m), 758 (s), 691 (s), 651 (m). 1H NMR (300 MHz,
CD2Cl2): δ (ppm) = 7.49−7.46 (m, 2H, CHarom.), 7.35−7.33 (m, 3H,
CHarom.), 6.88 (s, 1H, CHN), 3.82−3.80 (m, 4H, CH2,morpholinyl),
3.14−3.11 (m, 4H, CH2,morpholinyl). 13C NMR (75 MHz, CD2Cl2): δ
(ppm) = 132.0 (Carom.), 129.0 (Ciarom.), 128.9 (Carom.), 123.2 (Cipso),
117.6 (CN), 90.6 (Calkyne), 86.9 (Calkyne), 66.6 (CH2,morpholine), 51.7
(CH2,morpholine). MS (ESI): m/z = 215 [M + H]+, 237 [M + Na]+.
HRMS (ESI) m/z: [M + H] + Calcd for C13H15N2O 215.1179. Found
215.1185. For detailed X-ray crystal structure data, see the Supporting
Information.
̃
Melting point: 108−109 °C. IR (ATR): ν = 3060 (w), 2899 (s), 2850
(m), 2208 (s, alkyne), 1609 (s, CN), 1490 (m), 1442 (m), 1343
(m), 1307 (m), 1183 (w), 1118 (w), 1090 (w), 1030 (w), 981 (w),
1
917 (m), 814 (w), 785 (w), 752 (s), 685 (s), 646 (w), 530 (m). H
NMR (500 MHz, CDCl3): δ (ppm) = 7.71 (s, 1H, CHN), 7.54−
7.52 (m, 2H, CHarom.), 7.36−7.31 (m, 3H, CHarom.), 2.16 (s, 3H,
CHadamantyl), 1.77−1.72 (m, 9H, CHadamantyl), 1.69−1.65 (m, 3H,
CHadamantyl). 13C NMR (126 MHz, CDCl3): δ (ppm) = 140.5 (CN),
132.3 (Carom.), 129.3 (Carom.), 128.4 (Carom.), 122.0 (Cipso), 91.6
(Calkyne), 87.5 (Calkyne), 59.5 (Cq,adamantyl−N), 42.8 (CH2,adamantyl), 36.5
(CH2,adamantyl), 29.5 (CHadamantyl). MS (ESI): m/z = 264 [M + H]+, 549
[2M + Na]+. HRMS (ESI) m/z: Calcd for C19H22N [M + H]+
264.1747. Found 264.1755. Anal. Calcd for C19H21N (263.38): C
86.65 H 8.04 N 5.32. Found: C 86.44 H 8.03 N 5.25.
1-(4-Methylphenyl)-4-phenyl-1-aza-but-1-ene-3-yne (1b). As de-
scribed in GP 2, p-toluidine (1.18 g, 11.0 mmol, 1.1 equiv) was
dissolved in 25 mL of dichloromethane, and molecular sieves were
added. 3a (1.22 mL, 10 mmol, 1.0 equiv) was added slowly, and the
mixture was stirred for 20 h. After filtration, the excess of p-toluidine
was removed in a Kugelrohr oven (100 °C/2.2 × 10−2 mbar), and the
product was isolated with a Kugelrohr distillation (150 °C/2.2 × 10−2
mbar). The title compound was obtained as a yellow solid. Yield: 4.3
1-(4-Methylphenyl)-4-trimethylsilyl-1-aza-but-1-ene-3-yne (1e).27
According to general procedure GP 2, p-toluidine (1.18 g, 11.0 mmol,
1.1 equiv) was dissolved in 40 mL of dichloromethane and molecular
sieves were added. 3c (1.48 mL, 10.0 mmol, 1.0 equiv) was added
dropwise, and after 24 h of stirring at room temperature, the molecular
sieves were filtered off. The raw product was distilled in a Kugelrohr
oven (160 °C/2.7 × 10−2 mbar), and the literature-known27
compound was obtained as an orange oil. Yield: 3.4 mmol (0.74 g,
34%), orange oil. IR (ATR): ν = 3025 (w), 2960 (m), 2923 (w), 2900
̃
mmol (0.94 g, 43%). Melting point: 89−90 °C. IR (ATR): ν
̃
= 3052
(w), 2872 (w), 2360 (w), 2165 (m, alkyne), 1608 (m, CN), 1581
(s), 1504 (s), 1451 (w), 1410 (w), 1379 (w), 1344 (w), 1296 (w),
1250 (s), 1214 (w), 1190 (w), 1171 (w), 1110 (w), 1066 (s), 1016
(w), 937 (w), 864 (w), 840 (s), 816 (w), 759 (s), 702 (m). 1H NMR
(400 MHz, CD2Cl2): δ (ppm) = 7.70 (s, 1H, CHN), 7.19−7.17 (m,
(w), 3028 (w), 2917 (w), 2897(s), 2851 (m), 2362 (m), 2202 (s,
alkyne), 2164 (w), 1885 (w), 1609 (s, CN), 1564 (m), 1502 (w),
1489 (m), 1441 (s), 1361 (w), 1307 (m), 1274 (w), 1202 (w), 1183
(w), 1155(w), 1091 (w), 1069 (w), 1031 (m), 1014 (w), 996 (w), 969
G
DOI: 10.1021/acs.organomet.8b00036
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
2H, CHarom.), 7.06−7.04 (m, 2H, CHarom.), 2.35 (s, 3H, CH3,tolyl), 0.27
(s, 9H, Si(CH3)3). 13C NMR (100 MHz, CD2Cl2): δ (ppm) = 148.9
(CN), 142.8 (Cipso), 138.1 (Cipso), 130.3 (Carom.), 121.2 (Carom.),
102.9 (Calkyne), 101.2 (Calkyne), 21.3 (CH3, tolyl), −0.27 (Si(CH3)3). 29Si
NMR (60 MHz, CD2Cl2): δ (ppm) = −15.8. MS (ESI): m/z = 216
[M + H]+, 238 [M + Na]+. HRMS (ESI) m/z: [M + H]+ Calcd for
C13H18NSi 216.1203. Found [M + H+]: 216.1201.
1-(4-Methylphenyl)-4-n-butyl-1-aza-but-1-ene-3-yne (1f). Ac-
cording to GP 2, p-toluidine (0.93 g, 8.65 mmol, 1.1 equiv) was
dissolved in 25 mL of dichloromethane, and molecular sieves were
added. 3b (0.87 g, 7.86 mmol, 1.0 equiv) was added at room
temperature, and the mixture was stirred for 18 h. The title compound
was obtained by distillation in a Kugelrohr oven (160 °C/2.2 × 10−2
mbar). The obtained oil showed high light- and air-sensitivity. Yield:
chromatography (SiO2; cyclohexane/ethyl acetate 9:1) to yield the
title compound. Yield: 0.44 mmol (96.3 mg, 84%), yellow solid. Rf
value: 0.54 (cyclohexane/ethyl acetate 9:1). Melting point: 50−51 °C.
̃
IR (ATR): ν = 3399 (br m, N−H), 3056 (w), 2961 (w), 2919 (w),
2856 (w), 2361 (m), 2344 (m), 1734 (w), 1717 (w), 1700 (w), 1684
(w), 1653 (w), 1617 (s), 1590 (w), 1540 (w), 1519 (s), 1498 (m),
1457 (w), 1442 (w), 1405 (w), 1375 (w), 1349 (w), 1316 (w), 1302
(w), 1259 (s), 1184 (w), 1126 (w), 1081 (w), 1071 (s), 1011 (s), 914
(w), 861 (w), 805 (s), 755 (s), 690 (s), 668 (w), 609 (w), 585 (w)
1
550 (w), 529 (m). H NMR (400 MHz, CD2Cl2): δ (ppm) = 7.42−
7.47 (m, 2H, CHarom.), 7.32−7.36 (m, 3H, CHarom.), 7.07 (d, 3JHH = 8.3
3
Hz, 2H, o-CHarom.), 6.70 (d, JHH = 8.3 Hz, 2H, m-CHarom.), 4.15 (s,
2H, CH2), 3.83 (br s, 1H, NH), 2.29 (s, 3H, CH3,tolyl). 13C NMR (100
MHz, CD2Cl2): δ (ppm) = 145.6 (Cipso), 132.1 (Carom.), 130.2 (Carom.),
128.9 (Carom.), 128.8 (Carom.), 128.1 (Cipso), 123.5 (Cipso), 114.2
(Carom.), 87.5 (Calkyne), 83.3 (Calkyne), 35.2 (CH2), 20.7 (CH3,tolyl). MS
(ESI): m/z = 222 [M + H]+. HRMS (ESI) m/z: [M + H]+: Calcd for
C16H16N 222.1277. Found 222.1273.
̃
5.2 mmol (1.04 g, 66%), yellow oil. IR (ATR): ν = 3024 (w), 2958
(m), 2932 (m), 2362 (w), 2216 (s, alkyne), 1890 (w), 1735(w), 1700
(w), 1664 (w), 1616 (w), 1584 (m, CN), 1559 (w), 1541 (w), 1518
(w), 1504 (m), 1457 (m), 1376 (w), 1353 (w), 1325 (w), 1278 (w),
1240 (w), 1217 (w), 1173 (w), 1156 (m), 1109 (w), 1046 (w), 1016
(w), 960 (w), 938 (w), 899 (w), 813 (s), 753 (w), 727 (w), 711 (w),
N-(3-phenylprop-2-yn-1-yl)-piperidinyl-1-amine (4b). According
to GP 3, compound 1c (137.0 mg, 0.65 mmol, 1.0 equiv) was reacted
with DIBAL-H (0.13 mL, 0.71 mmol, 1.1 equiv) in 5 mL of toluene.
The raw product was purified via column chromatography (SiO2;
cyclohexane/ethyl acetate 1:1) to yield the title compound. Yield: 0.35
mmol (75.5 mg, 55%), yellowish oil. Rf value: 0.57 (cyclohexane/ethyl
1
639 (w), 575 (w), 536 (m), 518 (w), 505 (m). H NMR (300 MHz,
CD2Cl2): δ (ppm) = 7.66 (t, 5JHH = 1.6 Hz, 1H, CHN), 7.20−7.15
3
(m, 2H, CHarom.), 7.06−7.01 (m, 3H, CHarom.), 2.48−2.42 (td, JHH
=
5
6.9 Hz, JHH = 1.6 Hz, 2H, −CH2−CH2−CH2−CH3), 2.35 (s, 3H,
CH3,tolyl), 1.66−1.56 (m, 2H, −CH2−CH2−CH2−CH3), 1.53−1.43
(m, 2H, −CH2−CH2−CH2−CH3), 0.96 (t, 3H, −CH2−CH2−CH2−
CH3). 13C NMR (75 MHz, CD2Cl2): δ (ppm) = 149.3 (CN), 143.8
(Cipso), 137.4 (Cipso), 130.3 (Carom.), 121.1 (Carom.), 97.5 (Calkyne), 80.2
(Calkyne), 30.8 (−CH2−CH2−CH2−CH3), 22.6 (−CH2−CH2−CH2−
CH3), 21.3 (CH3,tolyl), 19.7 (−CH2−CH2−CH2−CH3), 13.9 (−CH2−
CH2−CH2−CH3). MS (ESI): m/z = 200 [M + H]+, 222 [M + Na]+.
HRMS (ESI) m/z: [M + H]+ Calcd for C14H18N 200.1434. Found
200.1452.
̃
acetate 1:1). IR (ATR): ν = 3207 (br m, N−H), 3057 (w), 2934 (m),
2854 (w), 2784 (w), 2727 (w), 2664 (w), 2360 (w), 2345 (w), 2015
(w), 1717 (w), 1700 (w), 1685 (w), 1653 (w), 1598 (w), 1559 (w),
1541 (w), 1522 (w), 1507 (w), 1490 (m), 1474 (w), 1457 (w), 1442
(m), 1419 (w), 1373 (w), 1331 (m), 1286 (w), 1264 (m), 1154 (w)
1092 (m), 1070 (w), 1037 (m), 1013 (w), 997 (w), 937 (w), 911 (m),
874 (m), 822 (m), 754 (s), 690 (s), 669 (w), 629 (w), 598 (w), 582
1
(w), 505 (w), 527 (m). H NMR (400 MHz, CD2Cl2): δ (ppm) =
7.41−7.43 (m, 2H, CHarom.), 7.32−7.30 (m, 3H, CHarom.), 3.76 (s, 2H,
CH2), 2.57−2.71 (m, 4H, CH2,piperidine), 1.58−1.65 (m, 4H,
CH2,piperidine), 1.38−1.41 (m, 2H, CH2,piperidine). 13C NMR (101
MHz, CD2Cl2): δ (ppm) = 132.0 (Carom.), 128.9 (Carom.), 128.6
(Carom.), 123.8 (Cipso), 88.2 (Calkyne), 83.3 (Calkyne), 58.2 (CH2), 39.7
(CH2,piperdine), 26.7 (CH2,piperdine), 24.4 (CH2,piperdine). MS (ESI): m/z =
215 [M + H]+. HRMS (ESI) m/z: [M + H]+ Calcd for C14H19N2
215.1543. Found [M + H+]: 215.1547.
1-(4-Bromophenyl)-4-phenyl-1-aza-but-1-ene-3-yne (1g). Ac-
cording to GP 2, p-bromoaniline (1.89 g, 11.0 mmol, 1.1 equiv) was
dissolved in 25 mL of dichloromethane and molecular sieves were
added, followed by 3a (1.22 mL, 10.0 mmol, 1.0 equiv). The mixture
was stirred for 24 h, and afterward, the molecular sieves were filtered
off. The title compound was purified by recrystallization from diethyl
ether as yellow needles. Yield: 8.4 mmol (2.37 g, 84%). Melting point:
100−101 °C. IR (ATR): ν
̃
= 2900 (s), 2851 (m), 2359 (m), 2340 (w),
N-(3-Phenylprop-2-yn-1-yl)morpholin-4-amine (4c). According to
general procedure GP 3, compound 1d (0.23 g, 1.05 mmol, 1.0 equiv)
was dissolved in 5 mL of toluene and cooled to −30 C. At this
temperature, DIBAL-H (0.21 mL, 1.16 mmol, 1.1 equiv) was added.
After 2 h of stirring and filtration over a pad of SiO2, the crude mixture
was purified by column chromatography (SiO2; cyclohexane/ethyl
acetate 1:1) to yield the title compound. Yield: 0.48 mmol (0.10 g,
45%), pale yellow solid. Rf value: 0.46 (cyclohexane/ethyl acetate 1:1).
2201 (s, alkyne), 1884 (w), 1609 (m, CN), 1587 (w), 1570 (m),
1441 (m), 1345 (m), 1201 (m), 1068 (w), 1031 (m), 917 (m), 854
(m), 821 (s), 763 (w), 750 (m), 686 (s), 655 (w), 628 (w), 564 (w),
1
507 (w). H NMR (300 MHz, CD2Cl2): δ (ppm) = 7.92 (s, 1H,
CHN), 7.63−7.58 (m, 2H, CHarom.), 7.54−7.50 (m, 2H, CHarom.),
7.46−7.40 (m, 3H, CHarom.), 7.11−7.06 (m, 2H, CHarom.). 13C NMR
(75 MHz, CD2Cl2): δ (ppm) = 150.7 (1C, Cipso−N), 144.6 (1C, C
N), 133.0 (2C, Carom.), 132.8 (2C, Carom.), 130.6 (1C, Carom.), 129.2
(2C, Carom.), 123.1 (2C, Carom.), 121.7 (1C, Cipso), 121.1 (1C, Cipso),
95.5 (1C, Calkyne), 88.0 (1C, Calkyne). MS (ESI): m/z = 284 [M + H]+,
305 [M + Na]+. HRMS: Calcd for C15H10NBr [M + H+]: 284.0069.
Found [M + H]+: 284.0063. Anal. Calcd for C15H10NBr (284.16): C
63.40 H 3.55 N 4.93. Found: C 63.67 H 3.36 N 5.05.
Propargylamines (4a−f). General Procedure 3 (GP 3). The
corresponding imine was dissolved in 5 mL of toluene and cooled to
−30 °C. At this temperature, 1.1 equiv of DIBAL-H was added. After 2
h of stirring at −30 °C, the solution was allowed to warm to room
temperature and was poured on a 5 cm pad of nondried silica gel in a 7
cm diameter column to achieve hydrolysis. After complete absorption,
the pad was covered with a 2 cm pad of sea sand. Then, diethyl ether
was used as eluent to separate the reaction products from inorganic
aluminum species. After removal of the diethyl ether in vacuo, the
crude product was purified by column chromatography to yield the
corresponding secondary propargylamine. The eluents used for
column chromatography are indicated for each compound.
̃
Melting point: 52−53 °C. IR (ATR): ν = 3055 (w), 3092 (w), 2957
(m), 2921 (w), 2899 (w), 2853 (m), 2853 (w) 2813 (w), 2724 (w),
2684 (w), 1737 (w), 1597 (w), 1571 (w), 1490 (m), 1458 (w), 1441
(w), 1388 (w), 1363 (w), 1342 (m), 1305 (w), 1280 (m) 1264 (m),
1234 (w), 1204 (w), 1177 (w), 1156 (w), 1107 (s), 1071 (m), 1035
(w), 1016 (m), 981 (w), 968 (w), 928 (w), 915 (w), 870 (s) 834 (w),
1
779 (w), 756 (s), 722 (w), 695 (s), 666 (w), 640 (m), 607 (w). H
NMR (300 MHz, CD2Cl2): δ (ppm) = 7.43−7.39 (m, 2H, CHarom.),
7.37−7.30 (m, 3H, CHarom.), 3.79 (s, 2H, CH2), 3.71−3.68 (m, 4H,
CH2,morpholine), 2.74 (s, 4H, CH2,morpholine). 13C NMR (75 MHz,
CD2Cl2): δ (ppm) = 132.0 (Carom.), 128.9 (Carom.), 128.7 (Carom.),
123.6 (Cipso), 87.9 (Calkyne), 83.5 (Calkyne), 67.5 (CH2,morpholine), 57.5
(CH2), 39.5 (CH2,morpholine). MS (ESI): m/z = 216 [M + H]+. HRMS
(ESI) m/z [M + H+] Calcd for C13H17N2O 217.1335. Found
217.1344. Anal. Calcd for C13H16N2O (216.28) C 72.19 H 7.46 N
12.95. Found: C 72.15 H 7.65 N 12.88.
4-Methyl-N-(3-(trimethylsilyl)prop-2-yn-1-yl)-aniline (4d).50 Ac-
cording to general procedure GP 3, compound 1e (0.15 g, 0.70
mmol, 1.0 equiv) was dissolved in 5 mL of toluene and cooled to −30
°C. After addition of DIBAL-H (0.14 mL, 0.77 mmol, 1.1 equiv), the
solution was stirred for 2 h at this temperature. Filtration over a pad of
SiO2 and purification by column chromatography (SiO2; cyclohexane/
4-Methyl-N-(3-phenylprop-2-yn-1-yl)-aniline (4a). According to
general procedure GP 3, compound 1b (114.0 mg, 0.52 mmol, 1.0
equiv) was reacted with DIBAL-H (0.10 mL, 0.57 mmol, 1.1 equiv) in
5 mL of toluene. The raw product was purified by column
H
DOI: 10.1021/acs.organomet.8b00036
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
ethyl acetate 9:1) obtained the literature-known title compound50 as
yellow oil. Yield: 0.52 mmol (0.11 g, 75%), yellow oil. Rf value: 0.52
(cyclohexane/ethyl acetate 9:1). Melting point: 33−34 °C. IR (ATR):
Found [M + H]+ = 266.1913. Anal. Calcd for C19H23N (265.40): C
85.99 H 8.74 N 5.28. Found: C 85.78 H 8.78 N 5.12.
1-Adamantyl-4-phenyl-5-di-iso-butyl-5-aluminazole (5a). Com-
pound 1a (0.17 g, 0.63 mmol, 1.0 equiv) was dissolved in 5 mL of
toluene and DIBAL-H (0.13 mL, 0.70 mmol, 1.1 equiv) was added at
room temperature. The mixture was stirred for 20 h; afterward, the
solvent was removed in vacuo and the residue dissolved in n-hexane.
Suitable crystals for X-ray analysis were obtained at −28 °C.
Compound 5a was obtained as a yellowish solid. Yield: 0.19 mmol,
(0.08 g, 31%). Decomposition point: 100−101 °C. IR (Nujol, KBr
̃
ν = 3397 (br m, N−H), 3104 (w), 3020 (w), 2959 (m), 2920 (w),
2865 (w), 2365 (w), 2172 (m, alkyne), 1700 (w), 1653 (w) 1617 (m),
1559 (w), 1519 (s), 1474 (w), 1457 (w), 1437 (w), 1406 (w), 1345
(w), 1316 (w), 1302 (w), 1249 (s), 1184 (m), 1127 (m), 1088 (m),
1025 (w), 982 (m), 839 (s), 805 (m), 759 (m), 700 (m), 643 (m), 578
1
(w), 557 (w), 513 (m). H NMR (300 MHz, CD2Cl2): δ (ppm) =
7.05−7.02 (m, 2H, CHarom.), 6.62−6.59 (m, 2H, CHarom.), 3.92 (s, 2H,
CH2), 3.73 (br s, 1H, NH), 2.27 (s, 3H, CH3), 0.19 (s, 9H, Si(CH3)3).
13C NMR (75 MHz, CD2Cl2): δ (ppm) = 145.6 (Cipso), 130.2 (Carom.),
128.1 (Cipso), 114.1 (Carom.), 104.1 (Calkyne), 88.1 (Calkyne), 35.5 (CH2),
20.7 (CH3), 0.19 (Si(CH3)3). 29Si NMR (60 MHz, CD2Cl2): d (ppm)
= −18.1. MS (ESI): m/z = 218 [M + H]+, 240 [M + Na]+. HRMS
plates): ν = 2721 (w), 2675 (w), 2663 (w), 1591 (s), 1398 (w), 1310
̃
(m), 1271 (w), 1238 (w), 1169 (s), 1126 (m), 1099 (m), 1053 (s),
1037 (w), 1008 (w), 989 (m), 958 (m), 939 (w), 910 (m), 854 (s),
837 (w), 814 (s), 798 (w), 754 (s), 723 (m), 687 (s), 642 (s), 592
(m), 555 (w), 530 (w), 480 (s), 444 (m). 1H NMR (400 MHz,
3
+
CD2Cl2): δ (ppm) = 8.28 (d, JHH = 2.8 Hz, 1H, CHN), 7.53−7.50
(ESI) m/z: [M + H] Calcd for C13H20NSi 218.1360. Found [M +
H+]: 218.1362. For detailed X-ray crystal structure data, see the
Supporting Information.
(m, 2H, CHarom.), 7.38−7.33 (m, 2H, CHarom.), 7.30−7.25 (m, 1H, p-
3
CHarom.), 7.12 (d, JHH = 2.7 Hz, 1H, CHvinyl), 2.20−2.17 (m, 3H,
CHadamantyl), 2.00−1.97 (m, 6H, CHadamantyl), 1.77−1.72 (m, 6H,
N-(Hept-2-yn-1-yl)-4-methylaniline (4e). As described in general
procedure GP 3, compound 1f (0.21 g, 1.03 mmol, 1.0 equiv) was
dissolved in 5 mL of toluene. Afterward, DIBAL-H (0.20 mL, 1.13
mmol, 1.1 equiv) was added at −30 °C and the mixture was stirred for
2 h at this temperature. Purification of the raw product was done by
column chromatography (SiO2; cyclohexane/ethyl acetate 9:1). Yield:
0.74 mmol (0.15 g, 72%), yellow oil. Rf value: 0.54 (cyclohexane/ethyl
CHadamantyl), 0.81 (d, 3JHH = 6.5 Hz, 12H, CH(CH3)2), 0.13 (d, 3JHH
=
7.0 Hz, 4H, CH2CH(CH3)2). The corresponding signals of the CH
hydrogen atoms of the iso-butyl substituents cannot be integrated
correctly, due to overlap with a signal of the adamantyl moiety. 13C
NMR (101 MHz, CD2Cl2): δ (ppm) = 193.8 (br, Cvinyl−Al), 167.2
(CN), 143.4 (Cipso), 128.8 (Carom.), 128.7 (p-Carom.), 128.5 (Carom.),
127.7 (CHvinyl), 58.5 (N−Cq,adamantyl), 43.9 (CH2,adamantyl), 36.3
(CH2,adamantyl), 30.2 (CHadamantyl), 28.5 (CH2CH(CH3)2), 28.4
(CH2CH(CH3)2), 27.4 (CH2CH(CH3)2), 23.7 (br, Al−(CH2CH-
(CH3)2). MS (EI) = m/z = 405 [M]+, 350 (2), 349 (13), 348 [M −
iBu]+, (54), 294 (2), 293 (20), 292 [M − 2iBu]+ (100), 265 (4), 135
(9). For detailed X-ray crystal structure data, see the Supporting
Information.
̃
acetate 9:1). IR (ATR): ν = 3399 (br m, N−H), 3020 (w), 2958 (w),
2931 (w), 2863 (w), 1869 (w), 1701 (w), 1617 (m), 1584 (w), 1559
(w), 1519 (s), 1458 (m), 1405 (w), 1379 (w), 1350 (w), 1316 (m),
1301 (m), 1249 (m), 1184 (w), 1126 (w), 1072 (w), 988 (w), 929
(w), 806 (s), 728 (w), 704 (w), 645 (w), 593 (w), 550 (w). 1H NMR
(300 MHz, CD2Cl2): δ (ppm) = 7.05−7.01 (m, 2H, CHarom.), 6.61−
5
6.58 (m, 2H, CHarom.), 3.87 (t, JHH = 2.2 Hz, 2H, CH2), 3.66 (br s,
5
3
1-(p-Tolyl)-4-phenyl-5-di-tert-butyl-5-aluminazole (5b). Com-
pound 1b (0.16 g, 0.53 mmol, 1.0 equiv) was dissolved in 5 mL of
toluene and cooled to −30 °C. A solution of di-tert-butylaluminum
hydride38 (0.08 g, 0.58 mmol, 1.1 equiv) in 5 mL of toluene was
added, and the solution was stirred for 2 h at this temperature.
Afterward the mixture was concentrated, and crystals suitable for X-ray
analysis were obtained at −30 °C. Yield: 0.02 mmol (0.01 g, 4%), red
1H, NH), 2.26 (s, 3H, CH3,tolyl), 2.23−2.15 (tt, JHH = 2.2 Hz, JHH
=
7.0 Hz, 2H, −CH2−CH2−CH2−CH3), 1.54−1.34 (m, 4H, −CH2−
3
CH2−CH2−CH3), 0.92 (t, JHH = 7.2 Hz, 3H, −CH2−CH2−CH2−
CH3). 13C NMR (75 MHz, CD2Cl2): δ (ppm) = 145.8 (Cipso), 130.1
(Carom.), 127.8 (Cipso), 114.1 (Carom.), 83.8 (Calkyne), 77.8 (Calkyne), 34.8
(CH2), 31.5 (−CH2−CH2−CH2−CH3), 22.5 (−CH2−CH2−CH2−
CH3), 20.7 (CH3,tolyl), 18.8 (−CH2−CH2−CH2−CH3), 14.0 (−CH2−
CH2−CH2−CH3). MS (ESI): m/z = 202 [M + H]+. HRMS (ESI) m/
̃
solid. Melting point: 155−156 °C. IR (Nujol, KBr plates): ν = 2355
+
(m), 1898 (w), 1568 (s), 1506 (w), 1410 (w), 1304 (m), 1265 (w),
1230 (w), 1171 (w), 1153 (w), 1111 (m), 1070 (w), 1053 (m), 1022
(w), 1001 (w), 952 (w), 934 (w), 862 (m), 812 (s), 758 (s), 723 (s),
696 (m), 590 (m), 559 (m), 530 (w), 511 (w), 457 (m), 434 (m). 1H
z: [M + H] Calcd for C14H20N calculated 202.1590. Found [M +
H+]: 202.1600. Anal. Calcd for C14H19N (201.31): C 83.53 H 9.51 N
6.96. Found: C 83.20 H 9.42 N 7.10.
N-(3-Phenylprop-2-yn-1-yl)-adamantan-1-amine (4f). Com-
pound 1a (0,277 g, 1.05 mmol, 1.0 equiv) was dissolved in dry
toluene (15 mL) and cooled to −60 °C. At this temperature, DIBAL-
H (0.210 mL, 1.16 mmol, 1.1 equiv) was added. After 2 h of stirring at
−60 °C, the reaction mixture was poured into ice−water (100 mL).
The product was extracted with dichloromethane (3 × 10 mL),
washed with brine (20 mL) and dried over magnesium sulfate. The
solvents were removed in vacuo, and the crude product was purified by
column chromatography (SiO2; cyclohexane/ethyl acetate 4:1) to
yield the product as a yellowish solid. Yield: 0.24 mmol (0.06 g, 23%),
yellowish solid. Rf value: 0.29 (cyclohexane/ethyl acetate 4:1). Melting
3
NMR (600 MHz, CD2Cl2): δ (ppm) = 8.45 (d, JHH = 2.9 Hz, 1H,
CHN)), 7.59−7.56 (m, 2H, o-CHarom.), 7.41−7.38 (m, 2H, m-
3
CHarom.), 7.34−7.31 (m, 1H, p-CHarom.), 7.31 (d, JHH = 2.9 Hz, 1H,
CHvinyl), 7.29−7.26 (m, 2H, CHarom.), 7.25−7.23 (m, 2H,CHarom.),
2.39 (s, 3H, CH3), 0.90 (s, 18H, C(CH3)3). 13C NMR (151 MHz,
CD2Cl2): δ (ppm) = 169.3 (CN), 144.1 (Cq), 143.9 (Cq), 138.4
(Cq), 130.7 (CHarom.), 130.2 (CHvinyl), 129.5 (p-CHarom.), 129.3 (o-
CHarom.), 129.0 (m-CHarom.), 122.6 (CHarom.), 31.1 (C(CH3)3), 21.3
(CH3). The signal corresponding to the vinylic carbon atom was not
observed. MS (EI): m/z (%) = 361 [M]+ (1), 306 (2), 305 (18), 304
[M − t-Bu]+ (100), 276 (2), 263 (9), 262 (54), 249(1), 248 [M − 2t-
Bu]+ (11), 247 (2), 222 (1), 220 (2), 200 (2), 197 (3), 118 (1).
Formula: C24H32AlN (M = 361.24 g/mol). For detailed X-ray crystal
structure data, see the Supporting Information.
̃
point: 59−60 °C. IR (KBr): ν = 3314 (br w, N−H), 3079(w), 3054
(w), 3031 (w), 2902 (s), 2848 (s), 2668 (w), 2423 (w), 2331 (w),
2244 (w), 2132 (w), 1968 (w), 1951 (w), 1897 (w), 1880 (w), 1825
(w), 1806 (w), 1752 (w), 1729 (w), 1713 (w), 1671 (w), 1648 (w),
1598 (m), 1571 (w), 1553 (w), 1517 (w), 1490 (s), 1461 (s), 1443
(m), 1310 (m), 1285 (w), 1258 (w), 1216 (w), 1187 (w), 1144 (s),
1098 (s), 1071 (m), 1029 (m), 1004 (w), 971 (w), 934 (w), 911 (m),
884 (w), 842 (w), 815 (m), 757 (s), 691 (s), 643 (m), 618 (m), 531
(m). 1H NMR (400 MHz, 300 K, CDCl3): δ (ppm) = 7.43−7.40 (m,
2H, CHarom.), 7.30−7.27 (m, 3H, CHarom.), 3.66 (s, 2H, CH2), 2.09 (br
s, 3H, CHadamantyl), 1.72 (m, 6H, CH2, adamantyl), 1.70−1.59 (m, 6H,
CH2, adamantyl). 13C NMR (100 MHz, 300 K, CDCl3): δ (ppm) = 131.6
(Cortho), 128.2 (Cmeta), 127.9 (Cpara), 123.4 (Cipso), 88.8 (Calkyne), 82.9
(Calkyne), 51.4 (N−Cq, adamantyl), 42.5 (CH2, adamantyl), 36.6
(CH2, adamantyl), 31.0 (CH2), 29.6 (CHadamantyl). MS (ESI): m/z = 266
[M + H]+, 531 [2M + H]+. HRMS: Calcd [M + H]+ = 266.1909.
1-N-Piperidinyl-4-phenyl-5-di-tert-butyl-5-aluminazole (5c).
Compound 1c (0.22 g, 1.01 mmol, 1.0 equiv) was dissolved in 5
mL of toluene and cooled to −30 °C. A solution oftBu2AlH38 (0.16 g,
1.11 mmol, 1.1 equiv) in 5 mL of toluene was added, and the solution
was stirred for 2 h at this temperature. Afterward, the mixture was
concentrated, and crystals suitable for X-ray analysis were obtained at
−30 °C. Yield: 0.14 mmol (0.05 g, 13%), yellow crystals. Melting
̃
point: 167−168 °C. IR (Nujol, KBr plates): ν = 2723 (w), 2693 (w),
2359 (m), 1571 (s), 1404 (w), 1300 (w), 1273 (w), 1257 (w), 1240
(m), 1169 (m), 1153 (w), 1119 (w), 1099 (s), 1072 (w), 1029 (w),
1003 (m), 964 (w), 931 (m), 903 (w), 862 (s), 810 (s), 756 (s), 723
(m), 696 (s), 642 (m), 594 (s), 543 (m), 519 (w), 471 (s), 438 (w).
I
DOI: 10.1021/acs.organomet.8b00036
Organometallics XXXX, XXX, XXX−XXX

Organometallics
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1H NMR (300 MHz, CD2Cl2): δ (ppm) = 7.47 (d, 3JHH = 3.2 Hz, 1H,
CHN), 7.33−7.28 (m, 2H, o-CHarom.), 7.25−7.19 (m, 2H, m-CHarom.),
crude product was purified by column chromatography (SiO2;
cyclohexane/ethyl acetate 4:1) to yield the known product35 as a
yellowish oil. Yield: 0.43 mmol (95,5 mg, 59%), yellowish oil. 1H
3
7.15−7.07 (m, 1H, p-CHarom.), 6.80 (d, JHH = 3.2 Hz, 1H, CHvinyl),
3
NMR (400 MHz, 300 K, CDCl3): δ (ppm) = 8.88 (d, JHH = 4.4 Hz,
3.03−2.98 (m, 4H, α-CH2,piperdinyl), 1.71 (m, 4H, β-CH2,piperdinyl),
1.50−1.41 (m, 2H, γ-CH2,piperdinyl), 0.83 (s, 18H, C(CH3)3). 13C NMR
(75 MHz, CD2Cl2): δ (ppm) = 178.5 (Cvinyl−Al), 147.0 (CN),
145.8 (Cipso), 128.7 (Carom.), 128.6 (p-Carom.), 128.3 (Carom.), 127.4
(Cvinyl), 53.9 (α-CH2,piperdinyl), 30.8 (C(CH3)3), 25.6 (β-CH2,piperdinyl),
23.7 (γ-CH2,piperdinyl), 15.4 (br, C(CH3)3). MS (EI): m/z (%) = 354
[M]+ (1), 299 (2), 298 (21), 297 [M − t-Bu]+ (100), 270 (3), 242
(5), 243 [M − 2t-Bu]+, 214 (13), 212 (5), 158 (5), 127 (22). For
detailed X-ray crystal structure data, see the Supporting Information.
1-Adamantyl-4-phenyl-1-aza-but-1,3-diene (6a). Compound 1a
(0.150 g, 0.57 mmol, 1.0 equiv) was dissolved in dry toluene (15 mL)
and cooled to −30 °C. At this temperature DIBAL-H (0.110 mL, 0.63
mmol, 1.1 equiv) was added. After 2 h of stirring at 60 °C, the reaction
mixture was poured into ice−water (50 mL). The product was
extracted with dichloromethane (3 × 10 mL), washed with brine (10
mL), and dried over magnesium sulfate. The solvents were removed in
vacuo, and the crude product was purified by column chromatography
(SiO2; cyclohexane/ethyl acetate 4:1 and 1% NEt3) to yield the
product as a colorless oil. Yield: 0.41 mmol (0.11 g, 71%), colorless oil.
1H, CHquinoline‑2), 8.08 (d, 3JHH = 8.6 Hz, 1H, CHquinoline‑8), 7.66 (br s,
3
4
1H, CHquinoline‑5), 7.56 (dd, JHH = 8.6 Hz, JHH = 2.0 Hz, 1H,
CHquinoline‑7), 7.52 (m, 3H, m-CHphenyl, p-CHphenyl), 7.51 (m, 2H, o-
CHphenyl), 7.29 (d,, 3JHH = 4.4 Hz, 1H, CHquinoline‑3), 2.47 (s, 3H, CH3).
13C NMR (101 MHz, 300 K, CDCl3): δ (ppm) = 149.0 (CHquinoline‑2),
147.8 (Cquinoline‑4), 147.2 (Cquinoline‑8a), 138.2 (i-Cphenyl), 136.6
(Cquinoline‑6), 131.6 (CHquinoline‑7), 129.5 (o-Cphenyl), 128.6 (m-Cphenyl),
128.3 (p-Cphenyl),126.7 (Cquinoline‑4a), 125.5 (CHquinoline‑8), 124.6
(CHquinoline‑5), 121.4 (CHquinoline‑3) 21.8 (CH3).
4-Bromo-N-methylaniline (8).58 Compound 1g (0.300 g, 1.21
mmol, 1.0 equiv) was dissolved in dry toluene (15 mL) and cooled to
−30 °C. At this temperature, DIBAL-H (0.24 mL, 1.33 mmol, 1.1
equiv) was added. After 48 h of stirring at 55 °C, the reaction mixture
was poured into ice−water (50 mL). The product was extracted with
dichloromethane (3 × 10 mL), washed with brine (10 mL), and dried
over magnesium sulfate. The solvents were removed in vacuo, and the
crude product was purified by column chromatography (SiO2;
cyclohexane/ethyl acetate 4:1) to yield the known product58 as a
yellowish oil. Yield: 0.58 mmol (108 mg, 48%), yellowish oil. 1H NMR
̃
IR (ATR): ν = 3056 (w), 3029 (w), 2902 (s), 2849 (m), 1682 (w),
3
(400 MHz, 300 K, CDCl3): δ (ppm) = 7.26 (d, JHH = 8.9 Hz, 2H,
1633 (m), 1615 (m), 1540 (w), 1492 (w), 1449 (m), 1365 (w), 1343
(w), 1307 (m), 1294 (w), 1263 (w), 1188 (w), 1151 (w), 1119 (w),
1090 (m), 1071 (w), 1031 (w), 991 (m), 973 (m), 957 (w), 922 (w),
852 (w), 813 (m), 745 (s), 687 (s), 651 (w), 617 (w), 581 (w), 559
CHarom.), 6.50 (d, 3JHH = 8.9 Hz, 2H, CHarom.), 3.92 (br s, 1H, N−H),
2.81 (s, 1H, CH3). 13C NMR (101 MHz, 300 K, CDCl3): δ (ppm) =
148.1, 131.9, 114.1, 109.0, 30.8.
1
(w), 542 (w). H NMR (400 MHz, 300 K, CDCl3): δ (ppm) = 8.05
(dd, 3JHH = 5.3 Hz, 4JHH = 2.9 Hz, 1H, CHN), 7.47 (d, 3JHH = 7.1 Hz,
2H, o-CHarom.), 7.35 (t, 3JHH = 7.2 Hz, 2H, m−CHarom.), 7.32−7.27 (m,
1H, p-CHarom.), 6.95 (m, 2H, CHvinyl), 2.16 (s, 3H, CHadamantyl), 1.71−
1.65 (m, 12H, CH2,adamantyl). 13C NMR (101 MHz, 300 K, CDCl3): δ
(ppm) = 157.0 (CN), 140.9 (CHvinyl), 136.1 (Cipso), 129.6 (CHvinyl),
128.9 (p-Carom.), 128.8 (m-Carom.), 127.1 (o-Carom.), 57.5 (Cq−N), 43.2
(CH2,adamantyl), 36.6 (CH2,adamantyl), 29.6 (CHadamantyl). MS (ESI): m/z =
266 [M + H]+, 288 [M + Na]+. HRMS (ESI): Calcd for C19H24N [M
+ H]+: 266.1903. Found [M + H]+: 266.1916.
ASSOCIATED CONTENT
* Supporting Information
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.organo-
met.8b00036.
■
S
Experimental details (NMR spectra and detailed X-ray
data) and quantum chemical DFT results (PDF)
All computed molecular Cartesian coordinates in xyz-
format for convenient visualization (TXT)
1-N-Piperidinyl-4-phenyl-1-aza-but-1,3-diene (6b).57 Compound
1c (0.50 g, 2.33 mmol, 1.0 equiv) was dissolved in 5 mL of toluene,
and the solution was cooled to −30 °C. A solution of di-tert-
butylaluminum hydride (0.37 g, 2.57 mmol, 1.1 equiv) in 10 mL of
toluene was added at this temperature, and the mixture was stirred for
2 h. After warming to room temperature, the solution was filtered
through a pad of aluminum oxide (activity grade 1) with diethyl ether
as the eluent. Literature-known compound 6b57 was isolated after
column chromatography (SiO2; cyclohexane/ethyl acetate 9:1 and 1%
NEt3). Yield: 0.97 mmol (0.21 g, 42%), yellowish solid. Melting point:
Accession Codes
CCDC 1587070−1587074 contain the supplementary crystal-
lographic data for this paper. These data can be obtained free of
charge via www.ccdc.cam.ac.uk/data_request/cif, or by email-
ing data_request@ccdc.cam.ac.uk, or by contacting The
Cambridge Crystallographic Data Centre, 12 Union Road,
Cambridge CB2 1EZ, UK; fax: +44 1223 336033.
̃
65−66 °C. IR (ATR): ν = 3028 (w), 2990 (w), 2937 (s), 2854 (m),
AUTHOR INFORMATION
Corresponding Authors
*E-mail: uhlw@uni-muenster.de.
*E-mail: wurthwe@uni-muenster.de.
ORCID
2808 (s), 2385 (w), 1668 (w), 1617 (w), 1594 (w), 1575 (w), 1557
(m), 1488 (m), 1446 (s), 1349 (s), 1293 (w), 1273 (w), 1250 (s),
1161 (s), 1123 (m), 1082 (s), 1034 (w), 988 (s), 965 (s), 918 (m),
■
1
895 (w), 853 (s), 770 (w), 749 (s), 689 (s), 655 (m), 610 (s). H
NMR (400 MHz, CD2Cl2): δ (ppm) = 7.44−7.41 (m, 2H, o-CHarom.),
3
7.39 (d, JHH = 8.8 Hz, 1H, CHN), 7.34−7.29 (m, 2H, m-CHarom.),
3
3
7.24−7.19 (m, 1H, p-CHarom.), 6.91 (dd, JHH = 16.0 Hz, JHH = 8.8
Werner Uhl: 0000-0002-7178-5517
3
Hz, 1H, β-CH), 6.63 (d, JHH = 16.0 Hz, 1H, γ-CH), 3.10−3.05 (m,
Ernst-Ulrich Wurthwein: 0000-0003-1327-3721
̈
4H, α-CH2,piperidine), 1.70 (m, 4H, β-CH2,piperidine), 1.54−1.49 (m, 2H,
γ-CH2,piperidine). 13C NMR (101 MHz, CD2Cl2): δ (ppm) = 137.7
(Cipso), 136.5 (CN), 132.6 (β-CH), 129.0 (γ-CH), 128.4 (Carom.),
127.8 (p-Carom.), 126.6 (Carom.), 52.3 (α-CH2,piperdine), 25.5 (β-
CH2,piperdine), 24.5 (γ-CH2,piperdine). MS (ESI): m/z = 215 [M + H]+,
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
Dedicated to Prof. Dr. Herbert Mayr on the occasion of his
70th birthday. Financial support from the Deutsche For-
schungsgemeinschaft (SFB 858, IRTG Munster − Nagoya)) is
gratefully acknowledged.
■
+
237 [M + Na]+. HRMS (ESI) m/z: [M + H] : Calcd for C14H19N2
215.1543. Found 215.1548.
6-Methyl-4-phenylquinoline (7a).35 Compound 1b (0.162 g, 0.74
mmol, 1.0 equiv) was dissolved in dry toluene (15 mL) and cooled to
−30 °C. At this temperature, DIBAL-H (0.15 mL, 0.81 mmol, 1.1
equiv) was added. After 48 h of stirring at 55 °C, the reaction mixture
was poured into ice−water (50 mL). The product was extracted with
dichloromethane (3 × 10 mL), washed with brine (10 mL), and dried
over magnesium sulfate. The solvents were removed in vacuo, and the
̈
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