Synthesis of alicyclic N-substituted 1,3-amino alcohols via 1,3-oxazines

Article abstract of DOI:10.1002/jhet.5570440219

(Chemical Equation Presented) Alicyclic N-substituted 1,3-amino alcohols 13-18 were prepared in a facile way in a one-pot procedure from 1,3-oxazines 5-8 in the presence of a ketone 9-12. The complex reaction involves palladium-catalyzed reduction, debenz

Full text of DOI:10.1002/jhet.5570440219

Mar-Apr 2007
403
Synthesis of Alicyclic N-Substituted 1,3-Amino Alcohols via
1,3-Oxazines
Árpád Balázs, Zsolt Szakonyi and Ferenc Fülöp*
Institute of Pharmaceutical Chemistry, University of Szeged, POB 427, H-6701 Szeged, Hungary,
E-mail: fulop@pharm.u-szeged.hu
Received July 18, 2006
O
R3
R4
R3
R4
N
N
H2 , Pd/C, 50 atm, rt.
H
n
n
R3 = R4 = Me
R2
O
OH
R1
R3 = R4 = -(CH2)5-
R3 = R4 = Et
R1
n = 1, R1 = H, R2 = Ph
n = 2, R1 = H, R2 = Ph
n = 2, R1 = H, R2 = Me
n = 2, R2 = Me, R2 = Ph
R3 = Me, R4 = Et
n = 1, R1 = H, R3 = R4 = Me
n = 2, R1 = H, R3 = R4 = Me
n = 2, R1 = H, R3 = R4 = -(CH2)5-
n = 2, R1 = H, R3 = R4 = Et
n = 2, R1 = H, R3 = Me, R4 = Et
n = 2, R1 = Me, R3 = R4 = Me
Alicyclic N-substituted 1,3-amino alcohols 13-18 were prepared in a facile way in a one-pot procedure
from 1,3-oxazines 5-8 in the presence of a ketone 9-12. The complex reaction involves palladium-
catalyzed reduction, debenzylation and/or transimination and further reduction.
J. Heterocyclic Chem., 44, 403 (2007).
1,3-amino alcohols, starting from cycloalkane-fused 1,3-
INTRODUCTION
oxazines 5-8.
Amino alcohols are of great interest because of their
biological and structural importance. Since 1,3-amino
alcohols are convenient starting materials for the synthesis
of various 1,3-heterocycles [1-4], the simple and
economic preparation of these compounds is a key factor.
Additionally, enantiopure 1,3-amino alcohols may serve
as excellent chiral auxiliaries in enantioselective
transformations [5-7]. Although, 1,2-amino alcohols have
been thoroughly investigated [8], methods for the
preparation and transformation of 1,3-amino alcohols are
still undergoing development [9-13]. Alicyclic 1,3-amino
alcohols can be obtained by several methods, e.g. through
reduction of the appropriate β-amino acid, amino esters
[1] or 2-hydroxycycloalkanecarbonitrile [14-16], or via
the catalytic reduction of cycloalkane-fused 1,3-oxazines
[17-19]. In most cases, the further alkyl substitution of the
nitrogen atom requires reductive alkylation, for example.
Our present aim was to develop a simple one-pot
procedure for the synthesis of alicyclic N-alkyl substituted
RESULTS AND DISCUSSION
The synthetic route for the preparation and transfor-
mation of cycloalkane-fused 5,6-dihydro-4H-1,3-oxazines
5-8 is shown in Scheme 1.
Starting from cycloalkenes 1-3, the 1,4-cycloaddition of
N-hydroxymethylacylamides (4a and b) furnished 1,3-
oxazines 5-8 stereospecifically, according to literature
data [17,18]; and, in the case of 1-methyl-1-cyclohexene
3, the reaction was regiospecific also, in accordance with
Markovnikov’s rule [19].
When compound 6 was hydrogenated in the presence of
additional acetone and 10% palladium on charcoal as
catalyst under 50 atm at room temperature, N-isopropyl
1,3-amino alcohol 14 was obtained in 91% yield. During
the optimization of the reaction, the amount of acetone
could be successfully reduced to 1.2 equivalents without a
noteworthy decrease in yield. Next, we extended the
method to cyclopentene- and methylcyclohexene-fused
Scheme 1
O
O
R2
N
OH
H
R3
R4
R3
R4
4a R2 = Ph
N
N
4b R2 = Me
H2, Pd/C, 50 atm, rt.
H
n
n
n
R3 = R4 = Me
concd. H2SO4/ AcOH
15 oC to rt.
O
R2
OH
R1
9
R1
R1
10 R3 = R4 = -(CH2)5-
11 R3 = R4 = Et
1
2
3
n = 1, R1 = H
n = 2, R1 = H
n = 2, R1 = Me
5
6
7
8
n = 1, R1 = H, R2 = Ph
n = 2, R1 = H, R2 = Ph
n = 2, R1 = H, R2 = Me
n = 2, R1 = Me, R2 = Ph
12 R3 = Me, R4 = Et
13 n = 1, R1 = H, R3 = R4 = Me
14 n = 2, R1 = H, R3 = R4 = Me
15 n = 2, R1 = H, R3 = R4 = -(CH2)5-
16 n = 2, R1 = H, R3 = R4 = Et
17 n = 2, R1 = H, R3 = Me, R4 = Et
18 n = 2, R1 = Me, R3 = R4 = Me

404
Á. Balázs, Z. Szakonyi and F. Fülöp
Vol 44
oxazines 5 and 8. The yields of the corresponding N-
isopropyl-substituted amino alcohols 13 and 18 were 37
and 43%, respectively. In the following step, the reaction
based on oxazine 6 was extended to aliphatic and alicyclic
ketones 10-12, and under the similar conditions described
above, derivatives 15-17 were obtained in 50-71% yields,
respectively.
methyl-1-cyclohexanol hydrochloride, prepared according
to a literature procedure [21].
Scheme 3
N
H2, Pd/C
50 atm
NH
O
O
The pathway proposed for the preparation of N-
isopropyl derivative 14 as a representative is indicated in
Scheme 2. The initial step is the reduction of the C=N
double bond of 6 to form saturated oxazine 19, which is in
ring-chain tautomeric equilibrium [20] with imine 20.
From this intermediate 20, imine 22 would be formed
through the two pathways; (a) amino alcohol 21, which is
formed by the reduction of the C=N double bond on
compound 20 and followed by debenzylation [21] give
compound 22 by the reductive alkylation with acetone;
(b) imine 22 is produced by the transimination of 20 with
acetone directly [22]. Compound 14 would be formed by
the reduction of 22.
7
23
N
acetone
N
OH
OH
22
24
reduction
reduction
N
H
N
H
OH
OH
14
25
Scheme 2
ratio: 2 : 3
N
H2, Pd/C
50 atm
NH
Ph
Thus, we have developed a simple method for the
synthesis of cis-N-alkyl-substituted cycloalkane-based
1,3-amino alcohols from the readily available dihydro-
1,3-oxazines. Although the reaction involves a number of
possible intermediates, the N-substituted amino alcohols
were produced in acceptable to excellent yields as single
products. This one-pot method might well prove
competitive to the widely applied two-step reductive
alkylation technique.
O
Ph
O
6
19
Ph
N
OH
acetone
N
OH
22
20
acetone
1. reduction
2. debenzylation
reduction
EXPERIMENTAL
1H and 13C nmr spectra were recorded on a Bruker Avance
DRX400 spectrometer at 400.13 MHz (1H δ=0 (TMS)) and
100.61 MHz (13C), in an appropriate solvent. Chemical shifts are
expressed in ppm (δ) relative to TMS as internal reference.
Coupling Constants (J) are given in Hz. Melting points were
N
H
NH2
OH
OH
14
21
determined on
a Kofler apparatus and are uncorrected.
Elemental analyses were performed with a Perkin-Elmer 2400
CHNS elemental analyzer. Ft-ir spectra were recorded on a
Perkin-Elmer model 1000 spectrophotometer. Low-resolution
CR = 1000-1500 mass spectra were run on a Finnigan MAT95S
double focusing mass spectrometer. Samples were introduced
directly into the ion source. The electron impact ion source
conditions were: temperature 170 °C; electron energy 20 eV; ion
current 150 mA.
To acquire evidence concerning the above mechanisms,
a method was applied in which primary amino alcohol
intermediate 21 could not be formed (Scheme 3). 2-
Methyl-5,6-dihydro-4H-oxazine 7, prepared from cyclo-
hexene and N-hydroxymethylacetamide [17], was
submitted to reduction in the presence of acetone. As
1
expected, the H nmr spectrum of the product indicated
N-Hydroxymethylbenzamide [23] (4a), N-hydroxymethyl-
acetamide [24] (4b), the 5,6-dihydro-4H-1,3-oxazine derivatives
[17] (5-7) and 6-methyl-2-phenyl-5,6-dihydro-4H-cyclohexa[e]-
[1,3]oxazine [19] (8) were prepared according to literature
processes.
cis-2-Phenyl-4,4a,5,6,7,7a-hexahydrocyclopenta[e][1,3]ox-
azine (5). This compound was obtained from 20.0 g (0.132 mol)
of N-hydroxymethylbenzamide and 10.81 g (0.159 mol) of
the presence of N-isopropyl derivative 14 as the minor,
and N-ethyl derivative 25 as the major components, in a
ratio of 2:3. Compound 14 can be formed only via trans-
iminated product 22. The above experiment clearly proves
the competitive reaction pathways given in Scheme 2.
Major component 25 was identified by comparison with
the nmr, ir and ms spectra of pure cis-2-ethylamino-

Mar-Apr 2007
Synthesis of Alicyclic N-Substituted 1,3-Amino Alcohols via 1,3-Oxazines
405
cyclopentene as a pale-yellow oil, in a yield of 16.56 g (62%);
1
(M+), 142, 124, 81, 72, 58, 44, 36. Anal. Calcd. for C9H20ClNO:
C, 55.80; H, 10.41; N, 7.23. Found: C, 55.92; H, 10.37; N, 7.10.
cis-2-(N-Isopropylaminomethyl)-1-cyclohexanol hydro-
chloride (14). This compound was obtained from 0.5 g (2.33
mmol) of 6 and 0.17 g (2.8 mmol) of acetone as white crystals,
in a yield of 0.44 g (91%); mp: 199-201 ºC; ir: 976, 1449, 1585,
ir: 697, 1120, 1654, 2937 cm-1; H nmr (deuteriochloroform): δ
1.50-2.30 (m, 7H), 3.52 (dd, 1H, J = 2.52, 16.62 Hz), 3,73 (dd,
1H, J = 5.54, 16.62 Hz), 4.56-4.60 (m, 1H), 7.33-7.43 (m, 3H),
7.90-7.95 (m, 2H); 13C nmr (deuteriochloroform): δ 22.4, 27.7,
33.7, 36.7, 44.9, 79.2, 127.5, 128.5, 129.0, 130.7, 131.8, 134.8,
156.0; ms: m/z 201 (M+), 134, 105, 77, 67. Anal. Calcd. for
C13H15NO: C, 77.58; H, 7.51; N, 6.96. Found: C, 77.45; H, 7.62;
N, 7.10.
1
2931, 3403 cm-1; H nmr (deuteriowater): δ 1.29-1.80 (m, 13H),
1.95 (br s, 1H), 2.99 (dd, 1H, J = 7.55, 12.59 Hz), 3.15 (dd, 1H,
J = 6.55, 12.59 Hz), 3.39-3.50 (m, 1H), 4.00 (br s, 1H); 13C nmr
(deuteriowater): δ 18.5, 18.6, 20.5, 23.7, 24.8, 31.8, 38.4, 47.2,
51.7, 68.5; ms: m/z 171 (M+), 156, 95, 72, 67, 56, 44. Anal.
Calcd. for C10H22ClNO: C, 57.82; H, 10.67; N, 6.74. Found: C,
57.70; H, 10.55; N, 6.65.
cis-2-Phenyl-4a,5,6,7,8,8a-hexahydro-4H-1,3-benzoxazine
(6). This compound was obtained from 29.32 g (0.194 mol) of
N-hydroxymethylbenzamide and 20.0 g (0.243 mol) of cyclo-
hexene as a colorless oil, in a yield of 13.88 g (30%); ir: 695,
1
1121, 1652, 2929, 3059 cm-1; H nmr (deuteriochloroform): δ
cis-2-(N-Cyclohexylaminomethyl)-1-cyclohexanol hydro-
chloride (15). This compound was obtained from 0.5 g (2.33
mmol) of 6 and 0.23 g (23.4 mmol) of cyclohexanone as white
crystals, in a yield of 0.41 g (71%); mp: 234-237 ºC; ir: 981,
1.30-2.10 (m, 9H), 3.40 (dd, 1H, J = 2.0, 16.62 Hz), 3.66 (dd,
1H, J = 5.54, 16.62 Hz), 4.38-4.43 (m, 1H), 7.32-7.43 (m, 3H),
7.91-7.97 (m, 2H); 13C nmr (deuteriochloroform): δ 20.9, 25.0,
25.9, 31.0, 32.6, 37.1, 49.5, 73.2, 127.4, 128.5, 130.7, 134.7,
155.5; ms: m/z 215 (M+), 134, 105, 94, 77, 67. Anal. Calcd. for
C14H17NO: C, 78.10; H, 7.96; N, 6.51. Found: C, 78.22; H, 7.92;
N, 6.43.
1
1458, 1589, 2934, 3373 cm-1; H nmr (deuteriowater): δ 1.10-
2.13 (m, 20H), 3.01 (dd, 1H, J = 7.05, 13.09 Hz), 3.07-3.22 (m,
2H), 3.99 (br s, 1H); 13C nmr (deuteriowater): δ 20.5, 23.6, 24.4,
24.9, 25.0, 29.2, 29.3, 31.8, 38.4, 47.0, 58.3, 68.6, 115.4; ms:
m/z 211 (M+), 180, 168, 131, 119, 112, 69, 56. Anal. Calcd. for
C13H26ClNO: C, 63.01; H, 10.58; N, 5.65. Found: C, 62.97; H,
10.47; N, 5.58.
cis-2-Methyl-4a,5,6,7,8,8a-hexahydro-4H-1,3-benzoxazine
(7). This compound was obtained from 6.5 g (73.03 mmol) of N-
hydroxymethylacetamide and 7.5
g
(91.29 mmol) of
cyclohexene as a pale-yellow oil, in a yield of 2.15 g (42%); ir:
1001, 1219, 1677, 2929, 3275 cm-1; 1H nmr (deuteriochloro-
form): δ 1.20-2.10 (m, 12H), 3.13 (dd, 1H, J = 1.51, 16.12 Hz),
cis-2-{N-(1-Ethylpropyl)aminomethyl}-1-cyclohexanol hydro-
chloride (16). This compound was obtained from 0.5 g (2.33
mmol) of 6 and 2.01 g (23.3 mmol) of diethyl ketone as white
crystals, in a yield of 0.28 g (51%); mp: 142-145 ºC; ir: 979,
3.40 (ddd, 1H, J = 1.51, 5.54, 16.12 Hz), 4.18-4.23 (m, 1H); 13
C
1
1458, 1591, 3373 cm-1; H nmr (deuteriowater): δ 0.97 (t, 6H, J
nmr (deuteriochloroform): δ 20.7, 21.8, 24.7, 25.7, 30.7, 32.0,
48.6, 72.8, 157.7; ms: m/z 153 (M+), 94, 82, 72, 67. Anal. Calcd.
for C9H15NO: C, 70.55; H, 9.87; N, 9.14. Found: C, 70.47; H,
9.85; N, 8.99.
= 7.55 Hz), 1.27-1.77 (m, 13H), 1.99 (br s, 1H), 3.02 (dd, 1H, J
= 6.04, 12.59 Hz), 3.10-3.25 (m, 2H), 4.07 (br d, 1H, J = 3.02
Hz); 13C nmr (deuteriowater): δ 8.9, 9.0, 20.8, 22.4, 23.4, 25.2,
31.6, 37.9, 47.3, 61.8, 69.1; ms: m/z 198 (M+), 182, 170, 152,
100, 95, 70, 58, 41. Anal. Calcd. for C12H26ClNO: C, 61.12; H,
11.11; N, 5.94. Found: C, 60.96; H, 10.97; N, 6.03.
cis-2-(N-sec-Butylaminomethyl)-1-cyclohexanol hydro-
chloride (17). This compound was obtained from 0.5 g (2.33
mmol) of 6 and 1.68 g (23.3 mmol) of 2-butanone as white
crystals of the diastereomeric mixture, in a yield of 0.26 g
(50%); mp: 156-161 ºC; ir: 979, 1458, 1592, 3365 cm-1; 1H nmr
(deuteriowater): δ 0.97 (t, 3H, J = 7.55 Hz), 1.27-1.85 (m, 15H),
1.97 (br s, 1H), 2.95-3.07 (m, 1H), 3.13-3.30 (m, 2H), 4.01 (br s,
1H); 13C nmr (deuteriowater): δ 9.4, 15.3, 20.5, 20.7, 23.5, 23.7,
24.9, 25.0, 25.9, 31.7, 31.8, 38.2, 47.1, 47.2, 56.8, 68.8; ms: m/z
185 (M+), 170, 156, 138, 95, 86, 44. Anal. Calcd. for
C11H24ClNO: C, 59.57; H, 10.91; N, 6.32. Found: C, 59.42; H,
10.98; N, 6.25.
cis-2-(N-Isopropylaminomethyl)-1-methyl-1-cyclohexanol
hydrochloride (18). This compound was obtained from 0.5 g
(2.18 mmol) of 8 and 1.26 g (21.8 mmol) of acetone as white
crystals, in a yield of 0.21 g (43%); mp: 121-123 °C; ir: 1597,
2429, 2940, 3457 cm-1; 1H nmr (deuteriowater): δ 1.24-1.78 (m,
18H), 3.00 (dd, 1H, J = 8.56, 13.09 Hz), 3.30 (dd, 1H, J = 4.03,
13.09 Hz), 3.40-3.50 (m, 1H); 13C nmr (deuteriowater): δ 18.4,
18.9, 21.6, 24.1, 25.9, 27.8, 38.8, 42.7, 46.5, 51.8, 72.0; ms: m/z
185 (M+), 170, 152, 109, 96, 81, 72, 44. Anal. Calcd. for
C11H24ClNO: C, 59.57; H, 10.91; N, 6.32. Found: C, 59.63; H,
10.88; N, 6.26.
cis-8a-Methyl-2-phenyl-4a,5,6,7,8,8a-hexahydro-4H-1,3-
benzoxazine (8). This compound was obtained from 30.0 g
(0.198 mol) of N-hydroxymethylbenzamide and 22.90 g (0.238
mol) of 1-methylcyclohexene as a white solid, in a yield of
1
25.35 g (56%); ir: 699, 1118, 1646, 2929, 3053 cm-1; H nmr
(deuteriochloroform): δ 1.20-1.80 (m, 11H), 1.99 (d, 1H, J =
13.56 Hz), 3.33 (d, 1H, J = 17.12 Hz), 3.81 (dd, 1H, J = 5.54,
17.12 Hz), 7.32-7.42 (m, 3H), 7.90-7.98 (m, 2H); 13C nmr
(deuteriochloroform): δ 22.5, 25.6, 26.3, 27.5, 27.8, 36.8, 38.4,
41.1, 48.0, 75.8, 127.5, 128.5, 129.2, 130.7, 135.2, 155.1; ms:
m/z 229 (M+), 134, 122, 108, 105, 96, 81, 77, 68. Anal. Calcd.
for C15H19NO: C, 78.56; H, 8.35; N, 6.11. Found: C, 78.48; H,
8.39; N, 6.20.
General Procedure for the Preparation of Alicyclic 1,3-
Amino Alcohols 13-18. The appropriate oxazine and ketone (10
equivalents, except for compounds 13 and 14, 1.2 equivalents)
were stirred with 0.11 g of 10% palladium-on-charcoal in 25 mL
of methanol under 50 atmospheres of hydrogen at room
temperature for 24 hours. After the mixture had been filtered,
the solvent was evaporated off and the oily residue was purified
as the hydrochloride salt from ethanol/diethyl ether.
cis-2-(N-Isopropylaminomethyl)-1-cyclopentanol hydro-
chloride (13). This compound was obtained from 0.5 g (2.49
mmol) of 5 and 0.18 g (2.99 mmol) of acetone as white crystals,
in a yield of 0.18 g (37%); mp: 121-123 °C; ir: 1009, 1590,
1
2963, 3386 cm-1; H nmr (deuteriowater): δ 1.35-1.55 (m, 7H),
cis-2-(N-Ethylaminomethyl)-1-cyclohexanol hydrochloride
(25). Compound 7 (0.5 g, 3.27 mmol) was stirred with 0.15 g of
10% palladium-on-charcoal in 30 mL of methanol, under 50
atmospheres of hydrogen at room temperature for 24 hours.
1.60-1.78 (m, 2H), 1.82-2.05 (m, 3H), 2.15-2.27 (m, 1H), 3.11
(dd, 1H, J = 7.55, 12.59 Hz), 3.29 (dd, 1H, J = 7.55, 12.59 Hz),
3.46-3.55 (m, 1H), 4.33-4.38 (m, 1H); 13C nmr (deuteriowater):
δ 18.5, 18.7, 21.7, 27.3, 34.3, 41.9, 45.5, 51.6, 73.8; ms: m/z 157

406
Á. Balázs, Z. Szakonyi and F. Fülöp
Vol 44
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After the mixture had been filtered, the solvent was evaporated
off and the oily residue was purified as the hydrochloride salt
from ethanol/diethyl ether, in a yield of 0.19 g (30%); mp: 163-
1
168 ºC; ir: 975, 1449, 2927, 3402 cm-1; H nmr (deuteriowater):
δ 1.26-1.78 (m, 12H), 1.97 (m, 1H), 2.99 (dd, 1H, J = 7.05,
12.59 Hz), 3.07-3.17 (m, 3H), 3.99 (br s, 1H); 13C nmr
(deuteriowater): δ 10.8, 20.4, 23.6, 24.7, 31.8, 38.3, 43.9, 49.7,
68.5; ms: m/z. Anal. Calcd. for C9H20ClNO: C, 55,80; H, 10.41;
N, 7,23. Found: C, 55.85; H, 10.43; N, 7.21.
Acknowledgements. This work was supported by the
Hungarian Research Foundation (OTKA T 049407) and the
National Research and Development Office, Hungary (GVOP-
311-2004-05-0255/3.0).
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