Recyclable catalytic synthesis of substituted quinolines: copper-catalyzed heterocyclization of 1-(2-aminoaryl)-2-yn-1-ols in ionic liquids

Article abstract of DOI:10.1016/j.tet.2009.08.017

A convenient and simple approach for the recyclable catalytic synthesis of substituted quinolines is presented. The method is based on CuCl₂-catalyzed heterocyclization of readily available 1-(2-aminoaryl)-2-yn-1-ols in BmimBF₄ as the solvent at 100 °C for 15-24 h. The solvent-catalyst system could be successfully recycled up to six times without significant loss of activity.

Full text of DOI:10.1016/j.tet.2009.08.017

Tetrahedron 65 (2009) 8507–8512
Contents lists available at ScienceDirect
Tetrahedron
journal homepage: www.elsevier.com/locate/tet
Recyclable catalytic synthesis of substituted quinolines: copper-catalyzed
heterocyclization of 1-(2-aminoaryl)-2-yn-1-ols in ionic liquids
,
b
b
b
b
Bartolo Gabriele a , Raffaella Mancuso , Elvira Lupinacci , Rosella Spina , Giuseppe Salerno ,
*
Lucia Veltri b, Angela Dibenedetto c
a
`
Dipartimento di Scienze Farmaceutiche, Universita della Calabria, 87036 Arcavacata di Rende (CS), Italy
Dipartimento di Chimica, Universita della Calabria, 87036 Arcavacata di Rende (CS), Italy
Dipartimento di Chimica, Universita di Bari, 70126 Bari, Italy
b
c
`
`
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 22 May 2009
Received in revised form 22 July 2009
Accepted 7 August 2009
Available online 11 August 2009
A convenient and simple approach for the recyclable catalytic synthesis of substituted quinolines is
presented. The method is based on CuCl2-catalyzed heterocyclization of readily available 1-(2-amino-
aryl)-2-yn-1-ols in BmimBF4 as the solvent at 100 ꢀC for 15–24 h. The solvent–catalyst system could be
successfully recycled up to six times without significant loss of activity.
Ó 2009 Elsevier Ltd. All rights reserved.
1. Introduction
2. Results and discussion
Ionic liquids (ILs) are now a well-established class of non-con-
ventional reaction media, which present several useful character-
istics: they are stable, non-flammable, non-volatile, recyclable, and
in several cases may even promote organic reactions.1,2 Another
attractive facet of these solvents is related to the possibility to easily
separate the products from the reaction mixture (by simple ex-
traction procedures) and, in catalytic reactions, to recycle the sol-
vent–catalytic system several times.1,2
The first experiments were carried out using 2-(2-amino-
phenyl)oct-3-yn-2-ol 2aa (R1¼R2¼H, R3¼Me, R4¼Bu) as the
substrate. The reaction of 2aa, carried out in BmimBF4 (1-butyl-3-
methylimidazolium tetrafluoroborate) as the solvent in the pres-
ence of CuCl2 (2 mol %) at 100 ꢀC for 15 h, led to the formation of
2-butyl-4-methylquinoline 3aa in 71% isolated yield based on
starting 2-aminoacetophenone 1a (Table 1, Entry 1, Run 1).5 This
result was very promising, since showed that the hetero-
cyclodehydration reaction could indeed occur in an ionic liquid as
the solvent. We then verified the possibility to recycle the solvent–
catalyst: the reaction crude was extracted several times with Et2O,
in order to separate the product, while freshly prepared 2aa was
added to the ionic liquid phase, and the resulting mixture let to
react again under the above-mentioned conditions (see the Ex-
perimental Section for details). As can be seen from the results
shown in Table 1, Entry 1, Runs 2–7, no significant decrease of ac-
tivity was observed, even after the sixth recycle.
The reaction carried out with 1 mol % of catalyst, led, after 15 h,
to a mixture of 3aa (66% yield) and the enynic derivative 4aa (7%),
deriving from dehydration of the alcoholic function of the substrate
(Table 1, Entry 2, Run 1). Similar results were obtained after 4 re-
cycles (Table 1, Entry 2, Runs 2–5). We have verified that 4aa can be
a possible intermediate in the formation of 3aa: in fact, when pure
4aa was let to react under the same reaction conditions as those
reported in Table 1 (Entry 2), 3aa was obtained in 95% isolated yield.
In agreement with this result, when the reaction of Entry 2 was
carried out for 24 h rather than 15 h, no formation of 4aa was ob-
served, and the yield of 3aa increased to 76% (Table 1, Entry 3, Run 1).
It is worth noting that the yield obtained under these conditions is
We have very recently reported that 1-(2-aminoaryl)-2-yn-1-ols
2, easily obtained by the Grignard reaction between the appropriate
alkynylmagnesium bromide and 2-aminoaryl ketones 1, can un-
dergo a selective Cu- or Pd-catalyzed 6-endo-dig dehydrative het-
erocyclization to give substituted quinolines 3 in good yields,
according to Scheme 1.3,4 The crude substrates 2 could be used
without further purification for the subsequent step. Hetero-
cyclizations were typically carried out in MeOH or 1,2-di-
methoxyethane (DME) as the solvent at 100 ꢀC in the presence of
CuCl2 (2 mol %) or PdX2 (2 mol %) in conjunction with an excess of
KX (X¼Cl, I) as the catalyst.
We have now found that this reaction can also effectively take
place in ionic liquids as the reaction media, using 1–2 mol % of
CuCl2, and that the solvent–catalyst system can be conveniently
recycled several times without appreciable loss of catalytic
activity.
* Corresponding author.
E-mail address: b.gabriele@unical.it (B. Gabriele).
0040-4020/$ – see front matter Ó 2009 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2009.08.017

8508
B. Gabriele et al. / Tetrahedron 65 (2009) 8507–8512
R3
N
HO R3
R2
O
R2
R2
1) R4C
catalyst
–H2O
R3
CMgBr
2) H+
R4
R4
NH2
NH2
R1
R1
R1
2 (crude product)
Scheme 1. Heterocyclodehydration of 1-(2-aminoaryl)-2-yn-1-ols 2 (crude products obtained by alkynylation of 2-aminoaryl ketones 1) leading to quinolines 3.
1
3
Table 1
Reactions of 2-(2-aminophenyl)oct-3-yn-2-ol 2aa in different ionic liquids (ILs) in the presence of CuCl2 as the catalysta
Me
O
HO Me
CuCl2
1) BuC
2) H
CMgBr
Me
NH2
1a
+
Bu
Bu
ionic liquid
H2O
N
Bu
NH2
4aa
NH2
2aa (crude product)
3aa
Entry
1
Solvent
Mol % of CuCl2
2
Time (h)
15
Runc
Yield of 3aa (%)d
Yield of 4aa (%)d
b
BmimBF4
1
2
3
4
5
6
7
1
2
3
4
5
1
2
3
4
5
6
7
1
2
3
4
5
6
7
1
2
3
4
5
6
7
1
2
3
4
5
1
2
3
4
5
6
7
71
74
70
69
70
71
70
66
65
63
64
66
76
70
71
69
68
72
68
65
62
61
61
55
50
49
51
48
54
53
58
56
55
48
40
38
42
43
82
76
67
59
60
56
48
2
3
BmimBF4
BmimBF4
1
1
15
24
7
5
5
5
4
4
5
BmimNTf2
BmimOTf
1
1
24
24
6
7
BmimCl
1
1
24
24
17
16
15
18
20
BmimPF6
6
10
11
11
18
a
All reactions were carried out at 100 ꢀC in the given ionic liquid as the solvent (0.22 mmol of starting 2-aminoacetophenone 1a per mL of solvent, 1 mmol scale based on
1a). Conversion of 2aa was quantitative in all cases.
b
Mol % of CuCl2 with respect to starting 1a.
Run 1 corresponds to the first experiment, the next runs to recycles. See text for details.
Isolated yield based on starting 1a.
c
d
similar to that observed in MeOH as the solvent (80%), which,
however, was obtained using 2 mol % of CuCl2.
We then tested the effect of the nature of the ionic liquid on re-
activity. The results using BmimNTf2, BmimOTf, BmimCl, and
BmimPF6 are shown inTable 1, Entries 4–7. As can be seen, among the
LIs tested, BmimBF4 led to the most satisfactory results: in particular,
BmimNTf2 and BmimOTf consistently led to lower yields of quinoline
3aa with respect to that achieved with BmimBF4 (compare Entries 4
and 5 with Entry 3). In the case of BmimCl, the main product 3aa was
obtained in a mixture with 4aa (Entry 6). With BmimPF6, the yields

B. Gabriele et al. / Tetrahedron 65 (2009) 8507–8512
8509
HO
HO
HO
Me
HO
Me
Me
Me
CuCl2
Bu
CuCl2
CuCl
Bu
HCl
HCl
–CuCl2
Bu
Bu
N
NH2
N
NH2
H
H
2aa
–H2O
–H2O
–H2O
Me
Me
N
CuCl
Bu
HCl
–CuCl2
Bu
NH2
N
3aa
Bu
CuCl2
CuCl2
Bu
CuCl
Bu
HCl
HCl
–CuCl2
Bu
N
H
N
H
NH2
Scheme 2. Proposed reaction mechanism for the conversion of 2-(2-aminophenyl)oct-3-yn-2-ol 2aa and 2-(1-methylenehept-2-ynyl)aniline 4aa into 2-butyl-4-methylquinoline 3aa.
in the first two runs (Table 1, Entry 7, Runs 1–2) were higher with
respect to those observed with BmimBF4 (Table 1, Entry 3, Runs 1–2).
However, starting from the third recycle, the reaction led to a mix-
ture of 3aa and 4aa (Table 1, Entry 7, Runs 3–7).
A plausible reaction mechanism for the formation of 3aa from
2aa or 4aa is shown in Scheme 2. The key steps of the mechanism
involve the 6-endo-dig nucleophilic attack of the amino group to
the triple bond of 2aa or 4aa coordinated to CuCl2, followed by
protonolysis and aromatization or vice versa.
The next experiments, aimed at generalizing the process to the
use of variously substituted 1-(2-aminoaryl)-2-yn-1-ols, were
therefore carried out using BmimBF4 as the solvent, under the same
conditions as those of Entry 3, Table 1. The results obtained with
substrates bearing different substituents on the triple bond, at the
benzylic position, and on the phenyl ring are shown in Table 2. As
can be seen, the corresponding quinolines were consistently
obtained in good yields, and in all cases the ionic liquid containing
the catalyst could be recycled and reused up to six times without
significant loss of activity. In some cases, the reaction led to better
results working with 2 mol % of CuCl2 rather than 1 mol % (Entries
9, 14, and 15). In the case of 2-(2-aminophenyl)-4-trimethylsyla-
nylbut-3-yn-2-ol 2ac (R1¼R2¼H, R3¼Me, R4¼TMS), as we already
observed in the process carried out in DME,3 the TMS group was
lost in the course of the process (Entries 13–14).
recorded at 25 ꢀC on a Bruker DPX Avance 300 spectrometer in
CDCl3 solutions at 300 MHz and 75 MHz, respectively, with Me4Si
as internal standard. Chemical shifts (d) and coupling constants (J)
are given in ppm and in Hz, respectively. IR spectra were taken
with a Jasco FT-IR 4200 spectrometer. Mass spectra were obtained
using a Shimadzu QP-2010 GC–MS apparatus at 70 eV ionization
voltage. Microanalyses were carried out with a Carlo Erba Ele-
mental Analyzer Mod. 1106. All reactions were analyzed by TLC on
silica gel 60 F254 and by GLC using a Shimadzu GC-2010 gas
chromatograph and capillary columns with polymethyl-
siliconeþ5% phenylsilicone as the stationary phase (HP-5). Col-
umn chromatography was performed on silica gel 60 (Merck,
70–230 mesh).
4.2. Preparation of substrates and ionic liquids
2-Aminoacetophenone 1a and 2-aminobenzophenone 1d were
commercially available (Aldrich, Fluka) and were used as received.
2-Amino-3-methoxyacetophenone 1b and 2-amino-5-chloro-
acetophenone 1c were prepared as we already reported.3 Ionic
liquids BmimNTf2,10 BmimOTf11 were prepared according to liter-
ature procedures. All the other ionic liquids were prepared as de-
scribed below.
3. Conclusion
4.3. Preparation of BmimCl
In conclusion, we have shown that the CuCl2-catalyzed hetero-
cyclodehydration of 1-(2-aminoaryl)-2-yn-1-ols may efficiently take
place in an ionic liquid, such as BmimBF4, as the reaction medium.
The yields obtained in BmimBF4 are similar to those obtained under
the ‘classical’ conditions (in MeOH or DME as the solvent)3; however,
the use of the ionic liquid has allowed to recycle the solvent–catalytic
system several times, without appreciable loss of activity. The
present recyclable catalytic method for synthesis of substituted
quinolines thus represents a simple and convenient approach for the
production of a very interesting class of heterocyclic compounds,
whose importance in various fields of Science is well known.6–9
A mixture of 1-methylimidazole (40 mL, 41.2 g, 502 mmol) and
toluene (50 mL) maintained at 0 ꢀC under nitrogen was stirred for
10 min. 1-Chlorobutane (58 mL, 51.4 g, 555 mmol) was quickly
added at 0 ꢀC and the resulting mixture was vigorously stirred for
15 min at the same temperature. The solution was allowed to
warm up to room temperature and then heated at 110 ꢀC for 24 h
with stirring. After cooling to room temperature, the mixture was
refrigerated (ꢁ20 ꢀC) and allowed to stand for 24 h. After this
time, two phases separated; toluene was removed by decantation,
while the residue was taken up with MeCN. The solvent was re-
moved under vacuum and MeCN (ca. 30 mL) and THF (ca. 30 mL)
were added. The resulting mixture was cooled with the aid of an
ice-water bath, to give, on standing, BmimCl as a whitish solid.
The mixture was then cooled at ꢁ20 ꢀC overnight. After de-
cantation and removal of the solvent, the residue was washed
with cold THF and eventually dried in vacuo to give pure BmimCl
as a whitish solid, which was stored at ꢁ20 ꢀC under nitrogen
(77.6 g, 89%).
4. Experimental section
4.1. General
Melting points were determined with a Reichert Thermovar
apparatus and are uncorrected. 1H NMR and 13C NMR spectra were

8510
B. Gabriele et al. / Tetrahedron 65 (2009) 8507–8512
Table 2
a
Synthesis of quinolines 3 by heterocyclization CuCl2-catalyzed of 1-(2-aminoaryl)-2-yn-1-ols 2 in BmimBF4
R3
N
O
R3
HO
R2
R2
R4C
2) H+
CMgBr
R2
CuCl2
1)
R3
R4
BmimBF4
R4
NH2
NH2
R1
R1
R1
–H2O
1
3
2 (crude product)
R1
R2
R3
R4
2
Mol % of CuCl2
3
Runc
Yield of 3 (%)d
b
Entry
1
8
9
1b
1b
OMe
OMe
H
H
Me
Me
Bu
Bu
2ba
2ba
1
2
3ba
3ba
1
1
2
3
4
5
6
7
1
2
3
4
5
6
7
1
2
3
4
5
6
7
1
2
3
4
5
6
7
1
1
2
3
4
5
6
7
1
2
3
4
5
6
7
46e
73
66
68
66
65
66
66
71
69
66
65
66
65
65
81
81
75
83
79
76
75
70
68
62
60
63
61
61
57h
61
59
60
58
60
61
61
60
58
57
55
51
50
52
10
11f
12
1c
1d
1a
H
H
H
Cl
H
H
Me
Ph
Bu
2ca
2da
2ab
1
1
1
3ca
3da
3ab
Bu
Me
t-Bu
13
14
1a
1a
H
H
H
H
Me
Me
TMS
TMS
2ac
2ac
1
2
3acg
3acg
15
1d
H
H
Ph
Ph
2dd
2
3dd
a
Unless otherwise noted, all reactions were carried out at 100 ꢀC for 24 h in BmimBF4 as the solvent (0.22 mmol of starting 2-aminoaryl ketones 1 per mL of solvent, 1 mmol
scale based on 1). Conversion of 2 was quantitative in all cases.
b
Mol % of CuCl2 with respect to starting 1.
Run 1 corresponds to the first experiment, the next runs to recycles. See text for details.
Isolated yield based on starting 1.
The reaction also led to the formation of 2-methoxy-6-(1-methylenehept-2-ynyl)aniline 4ba in 9% isolated yield.
c
d
e
f
Reaction time was 15 h.
g
R4¼H in the final quinoline 3ac.
h
The reaction also led to the formation of 2-(1-methylene-3-trimethylsilanylprop-2-ynyl)aniline 4ac in 18% isolated yield.
4.4. Preparation of BmimBF4
4.5. Preparation of BmimPF6
NaBF4 (5.7 g, 51.9 mmol) was added to 9.0 g (51.8 mmol) of
BmimCl maintained at 80 ꢀC under vigorous stirring. The mixture
was allowed to stir at 80 ꢀC for 8 h and then at room temperature
for 15 h. CH2Cl2 (ca. 30 mL) was added with stirring, and the so-
lution was cooled to ꢁ20 ꢀC and allowed to stand at this temper-
ature overnight. The precipitate (NaCl) was removed by filtration,
and the solvent was removed under vacuum to give pure BmimBF4,
which was stored under nitrogen at room temperature (9.3 g, 80%).
KPF6 (9.5 g, 51.6 mmol) was added to 9.0 g (51.8 mmol) of
BmimCl maintained at 80 ꢀC under vigorous stirring. The mixture
was allowed to stir at 80 ꢀC for 8 h and then at room temperature for
15 h. CH2Cl2 (ca. 30 mL) was added with stirring, and the solution
was cooled to ꢁ20 ꢀC and allowed to stand at this temperature
overnight. The precipitate (KCl) was removed by filtration, and the
solvent was removed under vacuum to give pure BmimPF6, which
was stored under nitrogen at room temperature (11.8 g, 81%).

B. Gabriele et al. / Tetrahedron 65 (2009) 8507–8512
8511
4.6. General procedure for the synthesis of quinolines 3 in
4.9. Characterization of products
ionic liquids (Tables 1 and 2)
All quinolines 3 were characterized by comparison with litera-
ture data.3 Enynic derivatives 4 were fully characterized by ele-
mental analysis, MS spectrometry, and IR, 1H NMR, and 13C NMR
spectroscopies, as reported below.
To a suspension of Mg turnings (700.0 mg, 28.8 mmol) in anhy-
drous THF (2.0 mL), maintained under nitrogen and under reflux,
was added pure EtBr (0.5 mL) to start the formation of the Grignard
reagent. The remaining bromide was added dropwise (ca. 20 min) in
THF solution (1.5 mL of EtBr in 15.0 mL of THF; total amount of EtBr
added: 2.92 g, 26.8 mmol). The mixture was then allowed to reflux
for additional 20 min. After cooling, the solution of EtMgBr thus
obtained was transferred under nitrogen to a dropping funnel and
was added dropwise to a solution of the 1-alkyne (26.8 mmol) in
anhydrous THF (7.0 mL) at 0 ꢀC with stirring. Afteradditional stirring
at 0 ꢀC for 15 min, the mixture was allowed to warm up to room
temperature, maintained at 50 ꢀC for 2 h, and then used as such for
the next step. 2-Amino ketone 1 (8.9 mmol) was dissolved under
nitrogen in anhydrous THF (7.0 mL) and then added dropwise to the
solution of the alkynylmagnesium bromide in THF (prepared as
described above) at 50 ꢀC under nitrogen. After stirring at 50 ꢀC for
1 h (R1¼R2¼H, R3¼Me, R4¼Bu; R1¼OMe, R2¼H, R3¼Me, R4¼Bu;
R1¼H, R2¼Cl, R3¼Me, R4¼Bu), 2 h (R1¼R2¼H, R3¼Me, R4¼t-Bu;
R1¼R2¼H, R3¼Me, R4¼TMS), or 3 h (R1¼R2¼H, R3¼Ph, R4¼Bu;
R1¼R2¼H, R3¼R4¼Ph), the mixture was cooled to room tempera-
ture. Saturated NH4Cl was added with stirring to achieve a weakly
acidic pH. After additional stirring at room temperature for 15 min,
AcOEt (ca. 20 mL) was added and phases were separated. The
aqueous phase was extracted with AcOEt (3ꢂ30 mL), and the col-
lected organic layers were washed with brine to neutral pH and
eventually dried over Na2SO4. After filtration, the solvent was
evaporated and crude products 2 were diluted with Et2O and
transferred into a volumetric flask (50 mL). 6.2 mL of the solution
(formally deriving from 1.10 mmol of 1) were transferred under ni-
trogen to a Schlenk flask containing the ionic liquid (5.0 mL) and
CuCl2 (1.5 mg, 1.1ꢂ10ꢁ2 mmol, Tables 1 and 2, Entries 2–8, 10–13, or
3.0 mg, 2.2ꢂ10ꢁ2 mmol, Tables 1 and 2, Entries 1, 9,14,15). Et2O was
removed under vacuum, and the resulting mixture was heated at
100 ꢀC for 15 h (Entry 1, 2,11) or 24 h (3–10,12–15). After cooling, the
product was extracted with Et2O (6ꢂ4 mL), and the residue (still
containing the catalyst dissolvedin the ionicliquid) was used as such
for the next recycle (see below). The collected ethereal phases were
concentrated and the product purified by column chromatography
(SiO2, hexane/AcOEt from 99:1 to 95:5) to give pure quinolines 3. In
the case of the reactions also leading to the formation of enynes 4
(Entry 2, 6–8, 13), the order of elution was 4, 3. The isolated yields
obtained in each experiment are reported in Tables 1and 2.
4.9.1. 2-(1-Methylenehept-2-ynyl)aniline (4aa). Pale yellow oil. IR
(film): 3462 (m, br), 3375 (m, br), 2957 (m), 2931 (m), 2871 (w),
2220 (w), 1618 (s), 1494 (m), 1455 (m), 1308 (m), 904 (m), 748 (s)
cmꢁ1. 1H NMR (300 MHz, CDCl3):
d
7.17 (1H, dd, J¼7.8, 1.6 Hz, H-3),
7.12–7.05 (1H, m, H-5), 6.72 (1H, td, J¼7.5, 1.2 Hz, H-4), 6.65 (1H, dd,
J¼7.7, 1.2 Hz, H-6), 5.67 (1H, d, J¼2.0 Hz, ]CHH), 5.56 (1H, d,
J¼2.0 Hz, ]CHH), 4.15 (1H, s, br, NH2), 2.34 (2H, t, J¼7.1 Hz,
^CCH2), 1.60–1.34 (4H, m, CH2CH2CH3), 0.91 (3H, t, J¼7.3 Hz, Me).
13C NMR (75 MHz, CDCl3):
d 143.7, 129.7, 129.4, 128.9, 125.2, 124.3,
118.3, 116.0, 92.1, 79.9, 30.7, 22.1, 19.1, 13.6. MS (70 eV, EI): m/z (%):
199 (64) [Mþ], 184 (9), 170 (35), 157 (100), 156 (85), 155 (27), 154
(40), 144 (16), 130 (38), 129 (43), 128 (44), 127 (20), 115 (20), 89 (13),
77 (28). Anal. Calcd for C14H17N (199.29): C, 84.37; H, 8.60; N, 7.03.
Found: C, 84.45; H, 8.56; N, 7.01.
4.9.2. 2-Methoxy-6-(1-methylenehept-2-ynyl)aniline (4ba). Pale yel-
low oil. IR (film): 3471 (m, br), 3378 (m, br), 2957 (s), 2932 (s), 2864
(w), 2231 (w), 1614 (m), 1562 (m), 1475 (s), 1287 (m), 1211 (m), 1048
(m) cmꢁ1. 1H NMR (300 MHz, CDCl3):
d
6.84 (1H, distorted dd, J¼7.3,
1.6 Hz, H-3), 6.78–6.65 (1H, m, H-4þH-5), 5.68 (1H, distorted d,
J¼2.0 Hz, ]CHH), 5.59 (1H, distorted d, J¼2.0 Hz, ]CHH), 4.36 (2H, s,
br, NH2), 3.85 (3H, s, OMe), 2.35 (2H, t, J¼7.1 Hz, ^CCH2), 1.60–1.35
(4H, m, CH2CH2CH3), 0.91 (3H, t, J¼7.3 Hz, Me). 13C NMR (75 MHz,
CDCl3): d 147.1, 133.9,129.5, 124.9,124.2,121.4, 117.2, 109.6, 92.0, 79.9,
55.7, 30.7, 22.1, 19.1, 13.6. MS (70 eV, EI): m/z (%): 229 (100) [Mþ], 214
(14), 200 (19), 187 (51), 186 (40), 172 (54), 171 (27), 170 (27), 154 (25),
144 (17), 127 (15), 115 (22). Anal. Calcd for C15H19NO (229.32): C,
78.56; H, 8.35; N, 6.11. Found: C, 78.65; H, 8.33; N, 6.10.
4.9.3. 2-(1-Methylene-3-trimethylsilanylprop-2-ynyl)aniline(4ac). Pale
yellow oil. IR (film): 3466(m, br), 3378 (m, br), 2960 (m), 2144 (m),1620
(s), 1495 (m), 1455 (m), 1250 (s), 957 (m), 842 (vs), 759 (m) cmꢁ1. 1H
NMR (300 MHz, CDCl3):
d
7.16 (1H, distorted ddd, J¼7.5, 1.6, 0.3 Hz, H-
3), 7.09 (1H, distorted ddd, J¼8.0, 7.5, 1.6 Hz, H-5), 6.72 (1H, td, J¼7.5,
1.1 Hz, H-4), 6.64 (1H, distorted ddd, J¼8.0,1.1, 0.3 Hz, H-6), 5.79 (1H, d,
J¼1.8 Hz, ]CHH), 5.67 (1H, d, J¼1.8 Hz, ]CHH), 4.17 (2H, s, br, NH2),
0.20 (9H, s, TMS). 13C NMR (75 MHz, CDCl3):
d 144.2, 129.8, 129.7, 129.5,
126.8, 124.4, 118.7, 116.4, 104.3, 96.3, 0.2. MS (70 eV, EI): m/z (%): 215
(100) [Mþ], 200 (97), 198 (33), 184 (44), 174 (16), 170 (15), 160 (56), 100
(14). Anal. Calcd for C13H17NSi (215.37): C, 72.50; H, 7.96; N 6.50. Found:
C, 72.64; H, 7.99; N, 4.47.
4.7. Recycling procedure (Tables 1 and 2)
To the residue obtained as described above, still containing the
catalyst dissolved in the ionic liquid, were added 6.2 mL of the
ethereal solution containing crude 2. Et2O was removed under
vacuum, and then the same procedure described above was
followed.
Acknowledgements
`
This work was supported by the Ministero dell’Universita e della
Ricerca (Progetto di Ricerca di Interesse Nazionale PRIN 2006031888,
Roma, Italy).
4.8. Conversion of 2-(1-methylenehept-2-ynyl)aniline 4aa
into 2-butyl-4-methylquinoline 3aa
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was transferred under nitrogen to a Schlenk flask containing
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removed under vacuum, and the resulting mixture was heated at
100 ꢀC for 15 h. After cooling, the product was extracted with Et2O
(6ꢂ4 mL). The collected ethereal phases were concentrated, and
the residue was purified by column chromatography (SiO2, 95:5
hexane/AcOEt) to give 281.7 mg of quinoline 3aa (95%).
´
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