A simple and efficient synthesis of new dihydrospirol[(1H)quinoline-2, 1′-cyclohexane] derivatives via internal Friedel-Crafts alkene alkylation of N-(1-allylcyclohexanyl)ethylphenylamine

Article abstract of DOI:10.1081/SCC-200049815

New substituted dihydrospiro[(1H)quinoline-2,1′-cyclohexanes] were prepared by the internal alkene alkylation of N-(1-allylcyclohexanyl) ethylphenylamine obtained from the corresponding ketimine and allylmagnesium bromide. The 1-allyl-6-ethyl-4-methyl-3,4

Full text of DOI:10.1081/SCC-200049815

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A Simple and Efficient Synthesis of New
Dihydrospiro[(1H)Quinoline‐2,1′‐Cyclohexane]
Derivatives Via Internal
Friedel‐Crafts Alkene Alkylation of
N‐(1‐Allylcyclohexanyl)Ethylphenylamine
Vladímir V. Kouznetsov a , Luz Dary Avellaneda Duarte a & Elena E.
Stashenko a
a Laboratorio de Síntesis Orgánica Fina, Escuela de Química, Universidad
Industrial de Santander, Bucaramanga, Colombia
Version of record first published: 12 Apr 2011.
To cite this article: Vladímir V. Kouznetsov, Luz Dary Avellaneda Duarte & Elena E. Stashenko (2005): A
Simple and Efficient Synthesis of New Dihydrospiro[(1H)Quinoline‐2,1′‐Cyclohexane] Derivatives Via Internal
Friedel‐Crafts Alkene Alkylation of N‐(1‐Allylcyclohexanyl)Ethylphenylamine, Synthetic Communications: An
International Journal for Rapid Communication of Synthetic Organic Chemistry, 35:4, 621-629
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Synthetic Communicationsw, 35: 621–629, 2005
Copyright # Taylor & Francis, Inc.
ISSN 0039-7911 print/1532-2432 online
DOI: 10.1081/SCC-200049815
A Simple and Efficient Synthesis of
New Dihydrospiro[(1H)Quinoline-2,10-
Cyclohexane] Derivatives Via Internal
Friedel-Crafts Alkene Alkylation of
N-(1-Allylcyclohexanyl)Ethylphenylamine
´
Vladımir V. Kouznetsov, Luz Dary Avellaneda Duarte,
and Elena E. Stashenko
´ ´ ´
Laboratorio de Sıntesis Organica Fina, Escuela de Quımica, Universidad
Industrial de Santander, Bucaramanga, Colombia
Abstract: New substituted dihydrospiro[(1H)quinoline-2,10-cyclohexanes] were
prepared by the internal alkene alkylation of N-(1-allylcyclohexanyl) ethylphenylamine
obtained from the corresponding ketimine and allylmagnesium bromide. The 1-allyl-6-
ethyl-4-methyl-3,4-dihydrospiro[(1H)quinoline-2,10-cyclohexane] undergoes an amino-
.
Claisen transposition (BF3 Et2O) to afford the 8-allyl-6-ethyl-4-methyl substituted
¨
spiroquinolines or a second internal alkylation reaction promoted by Bronsted acid
(H2SO4) to give a new unnatural lilolidine spiroderivative.
Keywords: Internal alkene Friedel-Crafts alkylation, amino-Claisen transposition,
spiroquinolines
Despite the large number of published synthetic routes to quinoline and its
derivatives there are only a few that describe the construction of the tetra-
or dihydroquinoline ring spiro annulated at positions C-2 cycloalkanes or
heterocycles.[1,2] The chemistry and biological activity of this type of spiro
Received in the USA 17 November 2004
´ ´
Address correspondence to Vladımir V. Kouznetsov, Laboratorio de Sıntesis
´
´
Organica Fina, Escuela de Quımica, Universidad Industrial de Santander, A.A. 678,
Bucaramanga, Colombia. Fax: 57-76-349069 (or) 57-76-358210; E-mail: kouznet@
uis.edu.co

622
V. V. Kouznetsov, L. D. A. Duarte, and E. E. Stashenko
heterocompounds remain largely unexplored. Nevertheless, these particular
heterocycles are useful for many sectors of the chemical industry and have
attracted the attention of synthetic organic chemists recently due to antibacter-
ial, anti-inflammatory, and herbicidal properties.[3,4]
On the other hand, the condensed tricyclic system of 1,2,5,6-tetrahydro-
pyrrolo[3,2,1-ij]quinolines is the basic skeleton of lilolidine alkaloids and
its derivatives possess a wide spectrum of biological activity.[5–8]
Over a period of years we were involved in the preparation of bioactive
nitrogen-containing heterocycles from imines. As results of these studies a
new practical synthesis of the dihydrospiro[(1H)quinoline-2,10-cycloalkanes]
developed which allowed us to investigate some chemical and biological
properties of this spiro heterosystem.[9,10] Herein, we report an efficient
synthesis of new spiranes 3 and 4 and the chemical behavior of 1-allyl-6-
ethyl-4-methyl-dihydrospiro[(1H)quinoline-2,10-cyclohexane] (4). The latter
.
compound undergoes an amino-Claisen transposition (BF3 Et2O) to afford
the 8-allyl-6-ethyl-4-methyl substituted spiroquinoline 5 or a second
¨
internal alkylation reaction promoted by Bronsted acid (H2SO4) to give a
new unnatural lilolidine spiroderivative 6.
RESULTS AND DISCUSSION
The starting material for this work, 4-N-(1-allylcyclohexanyl)ethylphenyl-
amine 1, was obtained from p-ethylaniline via a well-known two-step
procedure: ketimine formation and addition of allyl magnesium bromide to
the obtained imine.[10] N-Allylation of this amine in common way gave
N-allyl ethylphenylamine 2, which possesses an p-electron rich aromatic
ring and two allyl (electrophilic C3 synthon) fragments that make it a
versatile source of synthetic materials for constructing (1H)-quinolines spiro-
annulated at C-2. The acid cyclization (85% H2SO4/CHCl3/608C/4 h) of
p-ethylphenylamine 1 and N-allyl substituted amine 2 proceeded smoothly
to give respective 4,6-dialkyl substituted quinoline 3 and 1-allyl-4,6-dialkyl
substituted quinoline 4 in excellent yield. Both quinolines are 6-exo-trig
1
products of internal alkene Friedel-Crafts alkylation. The H NMR spectro-
scopic data allowed an unambiguous statement of the formation of the
4-methylquinoline ring of 3 and 4. In the case of the quinoline 4, the NMR
data indicated the presence of the N-allyl moiety. Moreover, conversion of
3 into 4 was realised under the same allylation reaction conditions in good
yield (Scheme 1).
The N-allyl spiroquinoline 4 is a suitable precursor for the construction of
diverse unknown heterospiranes containing a nitrogen atom. Thus, a mixture
.
of the quinoline 4 and equimolar amounts of Lewis acid (BF3 Et2O) was
heated at 908C for 1 h to give amino-Claisen rearranged product 5, which
was isolated by silica gel column chromatography as a viscous oil in 72%

New Dihydrospiro[(1H)Quinoline-2,10-Cyclohexane] Derivatives
623

624
V. V. Kouznetsov, L. D. A. Duarte, and E. E. Stashenko
yield. The same quinoline precursor was heated at 908C with 85% sulfuric
acid for prolonged time to give a new unnatural lilolidine spiroderivative 6
in moderate yield. This tetracyclic molecule is a 5-exo-trig product of an
¨
internal alkylation reaction promoted by Bronsted acid (Scheme 2).
Both analytical and spectral data of final products 5,6 are in full
agreement with the proposed structures. The best spectral proof for these
structures is the appearance of two singlets assignable to aromatic protons
5-H (d 6.94) and 7-H (d 6.76) in compound 5, and 7-H (d 6.87) and 9-H
(d 6.65) in tricyclic molecule 6, while the three aromatic protons of the
precursor 4 give one singlet (d 7.01) and two doublets (d 6.91 and 6.50,
J ¼ 8.5 Hz). The presence of a pyrrolidine moiety in compound 6 was
proven by a set of signals, that is a quartet (d 2.41, J ¼ 7.5 Hz), multiplet
(d 2.92) and doublet (d 1.20, J ¼ 7.8 Hz) assignable to corresponding
protons 1-H, 2-H and 1-CH3.
CONCLUSION
Using the classical Friedel-Crafts internal alkylation we synthesized new
8-allyl-6-ethyl-3,4-dihydro-4-methylspiro[(1H)quinoline-2,10-cyclohexane] (5)
and 1,6-dimethyl-8-ethyl-1,2,5,6-tetrahydro-4H-pyrrolo[3,2,1-ij]quinoline (6),
which were structurally related to the tricyclic nuclei of the basic skeleton of
lilolidine alkaloids.
EXPERIMENTAL
IR spectra were recorded on a Nicolet Avatar 360 FT-IR spectrometer as KBr
1
pellets. The H spectra were determined on Bruker AM-300, in CDCl3 with
tretramethylsilane as internal standard. Data are reported as follows:
chemical shifts (multiplicity, number of protons, coupling constants, and
group). Mass spectra were recorded with a HP 5890 A Series II, link to a
network mass selective detector HP 5972, a spectrometer with 70 eV
electron impact ionization. The purities of the obtained substance were moni-
toring by thin-layer chromatography on Silufol UV254 sheets. Solvents and
common reagents obtained from Merck and Aldrich were reagent grade.
N-(1-Allylcyclohexanyl)ethylphenylamine (1)
Imine obtained from p-ethylaniline and cyclohexanone (10.44 g, 0.052 mol)
was dissolved in 50 mL of absolute ether and added slowly at 108C to a mag-
netically stirred solution (170 mL of Et2O) of allyl magnesium bromide,

New Dihydrospiro[(1H)Quinoline-2,10-Cyclohexane] Derivatives
625

626
V. V. Kouznetsov, L. D. A. Duarte, and E. E. Stashenko
prepared from allyl bromide (18.85 g, 0.156 mol) and magnesium (6.31 g,
0.259 mol). The reaction mixture was heated to 30–358C during 6 h, cooled
to 08C and treated with water and then with saturated ammonium chloride
solution. The organic layer was separated and the aqueous layer was
extracted with ether (3 ꢀ 40 mL). The combined organic extracts were
dried (Na2SO4) and concentrated. The residue was fractionated at reduced
pressure to give 11.48 g of 1 as yellowish liquid.
Yield 91%; b.p. 125–1308C/10 mm Hg, n2D0 1.5340; IR (KBr): n 3419,
1
1637, 911 cm21; H NMR (300 MHz): d 7.02 (1H, d, J ¼ 8.0 Hz, 3(5)-H),
6.64 (1H, d, J ¼ 8.3 Hz, 2(6)-H), 5.90–5.84 (2H, m, 55CH-), 5.16–5.00
(1H, m, 55CH2), 3.38 (1H, br.s, N-H), 2.58 (2H, q, J ¼ 7.6 Hz, 22CH2CH3),
2.45 (2H, d, J ¼ 7.3 Hz, -CH2-), 2.32–1.36 (10H, m, H-cyclohexane), 1.24
(3H, t, J ¼ 7.6 Hz, 22CH2CH3); GC-MS: tR 22.43 min., (m/z, %): 243
(Mþ, 3), 202 (100); Anal. Calcd for C17H25N: C, 83.89; H, 10.35; N, 5.75.
Found: C, 83.55; H, 10.76; N, 5.43.
N-(1-Allylcyclohexyl)-N-(4-ethylphenyl)allylamine (2)
A suspension of 1 (1.0 g, 0.004 mol) in 10 mL acetone with allyl bromide
(2.48 g, 0.020 mol) and potassium carbonate (1.70 g, 0.012 mol) was allowed
to reflux for 4 days. The reaction was monitored by TLC. The mixture was
treated with water. The products were extracted with CH2Cl2 (3 ꢀ 20 mL)
Organic layer was dried (sodium sulfate) and the residue purified by chroma-
tography on a short column (alumina) to give 1.02 g of 2 as yellowish
viscous oil.
1
Yield 88%; n2D0 1.5260; IR (KBr):n 910 cm21; H NMR (300 MHz):
d 7.11–7.03 (4H, m, HPh), 6.08–5.97 (2H, m, N-CH2CH22CH2), 5.69–5.59
(2H, m, 55CH2), 5.08–5.03 (1H, m,22CH55), 4.95 (1H, dd, J ¼ 17.3,1.8 Hz,
N-CH2CH55CH2, Ha), 4.82 (1H, dd, J ¼ 10.0, 1.8 Hz, N-CH2CH55CH2,
Hb), 3.75 (2H, d, J ¼ 5.9 Hz, N-CH2-), 2.61 (2H, q, J ¼ 7.7 Hz,
22CH2CH3), 2.37 (2H, d, J ¼ 7.4 Hz,22CH222), 1.58–1.32 (10H, m, H-cyclo-
hexane), 1.23 (3H, t, J ¼ 7.7 Hz, 22CH2CH3); GC-MS: tR 24.07 min., (m/z,
%): 283 (Mþ, 1), 242(100); Anal. Calcd for C20H29N: C, 84.75; H, 10.31;
N, 4.94. Found: C, 84.34; H, 10.67; N, 4.68.
6-Ethyl-3,4-dihydro-4-methylspiro[(1H)quinoline-2,10-cyclohexane] (3)
85% Sulfuric acid (5.0 mL) was added dropwise at 08C to a solution of the
amine 1 (2.5 g, 0.010 mol) in CHCl3 (5 mL). The resulting mixture was
heated at 60–808C for 4 h while stirring vigorously. The reaction progress
was monitored via TLC. At the end of the reaction the mixture was cooled
down to room temperature and concentrated ammonium hydroxide solution

New Dihydrospiro[(1H)Quinoline-2,10-Cyclohexane] Derivatives
627
was added to pH 10. Three 20 mL extractions with ether were performed. The
organic layers were combined, dried (sodium sulfate) and concentrated. The
oily residue was purified by column chromatography over silica gel with
heptane: ethyl acetate ¼ 20 : 1 to give 2.35 g of 3 as yellow viscous oil.
1
Yield 94%; n2D0 1.5400; IR (KBr): n 3408 cm21; H NMR (300 MHz):
d7.00 (1H, s, 5-H), 6.84 (1H, d, J ¼ 8.4 Hz, 7-H), 6.44 (1H, d, J ¼ 8.0 Hz,
8-H), 3.83 (1H, br.s, N-H), 2.96–2.87 (1H, m, 4-H), 2.55 (2H, q,
J ¼ 7.7 Hz, 22CH2CH3), 1.90 (1H, dd, J ¼ 12.7, 5.7, 3-He), 1.69–1.41
(11H, m, H-cyclohexane and 3-Ha), 1.35 (3H, d, J ¼ 6.7 Hz, 4-CH3), 1.22
(3H, t, J ¼ 7.7 Hz, –CH2CH3); GC–MS: tR 24.46 min., (m/z, %): 243 (Mþ,
26), 228 (37), 214 (2), 200 (100), 187 (7), 172 (16), 149 (1), 91 (2), 77 (2)
41 (10); Anal. Calcd for C17H25N: C, 83.89; H, 10.35; N, 5.75. Found: C,
83.62; H, 10.76; N, 5.63.
Synthesis of 1-Allyl-6-ethyl-3,4-dihydro-4-methylspiro[quinoline-
2,10-cycloxane] (4)
Method A. 85% Sulfuric acid (2.5 mL) was added dropwise at 08C to a
solution of 2 (1.0 g, 0.004 mol) in CHCl3 (5 mL). The resulting mixture was
heated at 80–908C for 5 h while stirring vigorously. The reaction progress
was monitored via TLC. At the end of the reaction the mixture was cooled
down to room temperature and concentrated ammonium hydroxide solution
was added to pH 10. Three 20 mL extractions with dichloromethane were
performed. The organic layers were combined, dried (sodium sulfate) and con-
centrated. The oily residue was purified by column chromatography over silica
gel with heptane: ethyl acetate ¼ 20 : 1 to give 0.98 g of 4 as pale yellow oil.
Yield 98%; n2D0 1.5410; IR (KBr): n1644, 914 cm21; 1H NMR (300 MHz):
d 7.01 (1H, s, 5-H), 6.91 (1H, d, J ¼ 8.5 Hz, 7-H), 6.50 (1H, d, J ¼ 8.0 Hz,
8-H), 5.95–5.87 (1H, m, –CH55), 5.26 (1H, dd, J ¼ 10.3, 1.8 Hz, 55CH2,
Ha), 5.13 (1H, dd, J ¼ 17.7, 1.8 Hz, 55CH2, Hb), 4.51(1H, dt, J ¼ 1.8 Hz,
N-CH2), 3.69 (1H, dt, J ¼ 1.8 Hz, N-CH2), 2.90–2.81 (1H, m, 4-H), 2.57
(2H, q, J ¼ 7.7 Hz, 22CH2CH3), 2.40 (1H, dd, J ¼ 13.3, 4.4 Hz, 3-He),
1.84–1.51 (10H, m, H-cyclohexane), 1.28 (1H, t, J ¼ 13.3, 3-Ha), 1.39 (3H,
d, J ¼ 6.6 Hz, 4-CH3), 1.23 (3H, t, J ¼ 7.7 Hz, 22CH2CH3); GC-MS: tR
27.24 min., (m/z, %): 283 (Mþ, 29), 268 (70), 254 (12), 240 (61), 227 (38),
212 (100), 41 (55); Anal. Calcd for C20H29N: C, 84.75; H, 10.31; N, 4.94.
Found: C, 84.53; H, 10.43; N, 5.06.
Method B. A suspension of 3 (1.0 g, 0.004 moles)) in 10 mL acetone with
allyl bromide (2.48 g, 0.020 mol) and potassium carbonate (1.70 g, 0.012 mol)
was allowed to reflux for 4 days. The reaction was monitored by TLC. The
mixture was treated with water. The products were extracted with CH2Cl2
(3 ꢀ 20 mL) Organic layer was dried (sodium sulfate) and the residue

628
V. V. Kouznetsov, L. D. A. Duarte, and E. E. Stashenko
purified by chromatography on a short column (alumina) to give 1.06 g (91%)
of oily compound those chemical data were identical to 4.
Synthesis of 8-Allyl-6-ethyl-3,4-dihydro-4-
methylspiro[(1H)quinoline-2,10-cyclohexane] (5)
.
Allylamine 4 (0.23 g, 8 mmol) was heated at 908C for 1 h in BF3 Et2O
(0.46 mL), cooled and poured into ice. The pH was brought to 8 with
Na2CO3. The organic products were extracted with Ch2Cl2 (3 ꢀ 10 mL).
The combined extracts were dried (Na2SO4) and concentrated. The oily
residue was purified by column chromatography (silica gel, heptane/ethyl
acetate, from 25:1 to 20:1) to afford 0.16 g of 5 as brown oil.
1
Yield 72%; IR (KBr): n3410, 1634, 912 cm21; H NMR (300MHz): d
6.94 (1H, s, 5-H), 6.76 (1H, d, J ¼ 1.2, 7-H), 6.10–5.68 (1H, m, -CH55),
5.21–5.10 (2H, m, 55CH2), 3.29 (2H, d, J ¼ 6.4, 22CH2), 4.00 (1H, br.s,
N-H), 2.96–2.88 (1H, m, 4-H), 2.54 (2H, q, J ¼ 7.7 Hz, 22CH2CH3), 1.87–
1.25 (10H, m, H-cyclohexane), 1.85–1.80 (1H, dd, J ¼ 12.8, 4.3 Hz, 3-He),
1.37 (1H, t, J ¼ 12.6, 3-Ha), 1.34 (3H, d, J ¼ 6.8 Hz, 4-CH3), 1.25 (3H, t,
J ¼ 7.7 Hz, 22CH2CH3); GC-MS: tR 26.66 min., (m/z, %): 283 (Mþ, 32),
268 (40), 254 (3), 240 (100), 227 (3), 212 (15), 41 (6); Anal. Calcd for
C20H29N: C, 84.75; H, 10.31; N, 4.94. Found: C, 84.94; H, 10.53; N, 4.60.
Synthesis of 1,6-Dimethyl-8-ethyl-1,2,5,6-tetrahydro-4H-
spiro[pyrrolo-[3,2,1-ij]quinoline-4,1-cyclohexane] (6)
85% Sulfuric acid (3.2 mL) was added dropwise at 08C to a solution of the
amine 1 (0.32 g, 1 mmol) in CHCl3 (5 mL). The resulting mixture was
heated at 60–808C for 4 h while stirring vigorously. The reaction progress
was monitored via TLC. At the end of the reaction the mixture was cooled
down to room temperature and concentrated ammonium hydroxide solution
was added to pH 10. Three 20 mL extractions with chloroform were
performed. The organic layers were combined, dried (sodium sulfate) and con-
centrated. The oily residue was purified by column chromatography over silica
gel with a heptane–ethyl acetate mixture to give 0.18 g of 6 as brown oil.
Yield 57%; n2D0 1.5560; 1H NMR (300 MHz): d 6.87 (1H, s, 7-H), 6.65 (1H,
s, 9-H), 2.92 (1H, m, 2-H), 2.85 (1H, m, 6-H), 2.53 (2H, q, J ¼ 7.7 Hz,
22CH2CH3), 2.41 (1H, q, J ¼ 7.5, 1-H), 1.62–1.10 (12H, m, H-cyclohexane
and 5-H), 1.33 (3H, d, J ¼ 6.8 Hz, 6-CH3), 1.20 (3H, d, J ¼ 7.8 Hz, 1-CH3),
1.09 (3H, t, J ¼ 7.7 Hz, 22CH2CH3); GC–MS: tR 27.68 min., (m/z, %): 283
(Mþ, 32), 268 (40), 254 (3), 240 (100), 227 (3), 212 (15), 41 (6); Anal.
Calcd for C20H29N: C, 84.75; H, 10.31; N, 4.94. Found: C, 84.58; H, 10.63;
N, 4.81.

New Dihydrospiro[(1H)Quinoline-2,10-Cyclohexane] Derivatives
629
ACKNOWLEDGMENTS
This work was supported by the grant of the Colombian Institute for Science
and Research (COLCIENCIAS, projects: 1102-05-11429). Thanks are also
due to Dr. F. Zubkov (Organic Chemistry Department of the Russian
1
Peoples Friendship University) for providing H NMR spectra.
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