An efficient synthesis of the optically active isomers of 2H-1,4-benzoxazine derivatives, novel KATP channel modulators

Article abstract of DOI:10.1016/j.tetasy.2013.05.027

2H-1,4-Benzoxazine amidine derivatives are drugs acting as modulators of the skeletal muscle and pancreatic beta cell ATP-sensitive-K⁺ (KATP) channels. With the aim of evaluating the influence of absolute configuration on the biological activity of these drugs, we herein report the optimization of a synthetic route to obtain both enantiomers of some of these compounds with improved chemical yield and high enantiomeric excess.

Full text of DOI:10.1016/j.tetasy.2013.05.027

Tetrahedron: Asymmetry 24 (2013) 791–795
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Tetrahedron: Asymmetry
journal homepage: www.elsevier.com/locate/tetasy
An efficient synthesis of the optically active isomers
of 2H-1,4-benzoxazine derivatives, novel KATP channel modulators
Luca Piemontese, Antonio Laghezza, Giuseppe Fracchiolla, Giuseppe Carbonara, Paolo Tortorella,
⇑
Fulvio Loiodice
Dipartimento di Farmacia-Scienze del Farmaco, Università degli Studi di Bari ‘Aldo Moro’, via E. Orabona 4, 70125 Bari, Italy
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 18 March 2013
Accepted 29 May 2013
2H-1,4-Benzoxazine amidine derivatives are drugs acting as modulators of the skeletal muscle and
pancreatic beta cell ATP-sensitive-K+ (KATP) channels. With the aim of evaluating the influence of
absolute configuration on the biological activity of these drugs, we herein report the optimization of a
synthetic route to obtain both enantiomers of some of these compounds with improved chemical yield
and high enantiomeric excess.
Ó 2013 Elsevier Ltd. All rights reserved.
1. Introduction
R2
O
R1
Potassium channel openers (KCO) are chemically diverse com-
pounds that belong to a number of structural classes. Many studies
report the activities of these derivatives against the ATP-sensitive
K+ (KATP) channel subunits expressed in cell lines, primary targets
for KCO action. These compounds show a broad range of therapeu-
tic applications, including hypertension, angina, hypoglycemia,
neuromuscular disorders, and epilepsy and exert their effects on
pancreatic beta cells, neurons, and cardiac muscle by modulating
KATP channels, changing the cellular electrical activity.1,2
Recently we reported on some 2H-1,4-benzoxazine amidine
derivatives, which have emerged as novel skeletal muscle KATP
channel modulators. In the presence of ATP, these molecules
display KCO activity, whereas in the absence of the nucleotide they
display a blocking action. Moreover, in vitro and in vivo, they show
a combined activating/blocking action toward pancreatic beta cell
KATP channels that confers a significant glycemic control, which
supports their use as novel antidiabetic drugs.3–5 With the aim of
investigating the influence of the absolute configuration on the
biological activity of these drugs, we decided to synthesize the
stereoisomers of a series of chiral compounds (Fig. 1). For this rea-
son, a preliminary study was conducted on compound 1 in order to
identify the best pathway to follow.
Cl
N
NH
N
Cpd
(R)-1
(S)-1
(R)-2
(S)-2
(R)-3
(S)-3
(R)-4
(S)-4
R1
R2
CH3
H
Cpd
R1
H
R2
H
CH3
(R)-5
(S)-5
(R)-6
(S)-6
(R)-7
(S)-7
(R)-8
(S)-8
Cy
Cy
H
CH2Cy
H
CH2Ph
H
(CH2)2Ph
H
H
CH2CH3
H
CH2CH3
H
H
(CH2)2CH3
H
CH2Cy
H
(CH2)2CH3
H
CH2Ph
H
CH(CH3)2
H
CH(CH3)2
(CH2)2Ph
Figure 1.
zoxazine-3-ones 9a, 9b, obtained by the nitration of commercially
available (S)- or (R)-2-(4-chloro-phenoxy)propanoic acid, respec-
tively, followed by a one-pot reduction-cyclization with iron in
hydrochloric acid as shown in Scheme 1.
Thereafter, different reaction conditions were investigated for
the optimization of the pathway leading to (R)- or (S)-1. At first,
we chose the same synthetic method used for the preparation of
the racemate reacting 9a or 9b with 3-amino-pyridine in the
presence of TiCl4 and anisole (Scheme 2, method A).4,6 This proce-
dure gave reasonably good chemical yields but led to racemization.
For our next attempt, a good leaving group at the 3-position of
the benzoxazinones 9a–b was introduced in order to facilitate a
nucleophilic substitution reaction from 3-amino-pyridine. Thus
we turned these key intermediates into the corresponding (S)-
or (R)-6-chloro-2-methyl-2H-1,4-benzoxazine-3-thiones using
2. Results and discussion
Different attempts were carried out in order to obtain both
enantiomers of this derivative. All synthetic routes included the
involvement of key intermediates 6-chloro-2-methyl-2H-1,4-ben-
⇑
Corresponding author. Tel.: +39 080 5442778; fax: +39 080 5442231.
E-mail address: fulvio.loiodice@uniba.it (F. Loiodice).
0957-4166/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.tetasy.2013.05.027

792
L. Piemontese et al. / Tetrahedron: Asymmetry 24 (2013) 791–795
R2
R1
O
NO2
O
O
i
ii
O
O
OH
OH
R1
R1
R2
R2
Cl
N
H
O
Cl
Cl
R1=H; R2=CH3
R1=CH3; R2=H
9a, 9b
Scheme 1. Reagents and conditions: (i) 90% HNO3, 0 °C, 4 h; (ii) Fe, 6 M HCl, 1,4-dioxane, reflux, 4 h.
O
METHOD A
racemization
Cl
N
NH
N
O
N
O
O
METHOD B
i
ii
iii
Cl
NH
Cl
N
H
O
Cl
N
H
S
partial
racemization
N
9a
O
N
METHOD C
no
racemization
Cl
NH
N
Scheme 2. Reagents and conditions: Method A: 3-amino-pyridine, TiCl4, anisole, anhydrous toluene, reflux, 24 h. Method B: (i) P2S5, toluene, reflux, 9 h or Lawesson’s
reagent, anhydrous toluene, reflux, 1 h; (ii) 1 M KOH, CH3I, rt, 2 h; (iii) 3-amino-pyridine, 120 °C, 3 h. Method C: 3-amino-pyridine, Et3N, POCl3, anhydrous acetonitrile, rt, 4 h.
Lawesson’s reagent or P2S5; sulfur was then methylated to give the
corresponding iminothioethers, which were finally reacted with 3-
Table 1
O
N
R
amino-pyridine (Scheme 2, method B). In this way, the target com-
pounds were obtained in optically active forms, but unfortunately
their enantiomeric excess was not reproducible. We also found
that the preparation of the thiones occurred with partial racemiza-
tion which was dependent on the reaction time, concentration of
the reaction solution, and crystallization conditions.
Cl
NH
N
On the basis of these results, we attempted to design a synthetic
process, which involved milder conditions, short reaction times
and, at the same time, avoided the problems due to the malodor-
ous properties of sulfurated compounds. We decided to follow a
different synthetic route (Scheme 2, method C) which in a single
step, transformed 9a–b into the corresponding imido chloride
intermediates with POCl3 and easily converted them into (S)- or
(R)-1 by smooth condensation with 3-amino-pyridine. This proce-
dure was previously reported in the literature but not applied to
the preparation of optically active chiral amidines.7,8
Under these conditions, the reaction led to the isolation of the
target compounds in moderate to good yields with an easy purifi-
cation procedure consisting of a filtration of the solid residue,
which was washed out and crystallized from chloroform/n-hexane.
This method did not show any racemization and also allowed us to
retrieve the unreacted starting products 9a–b by column chroma-
tography of the mother liquors. The amount of unreacted benzox-
azinones was higher if the purification of (R)- or (S)-1 was carried
out by column chromatography allowing us to hypothesize that
silica gel catalyzes the conversion of (R)- or (S)-1 into the starting
benzoxazinones.
Compound
R
Yield
eea (%)
(R)-1
(S)-1
(R)-2
(S)-2
(R)-3
(S)-3
(R)-4
(S)-4
(R)-5
(S)-5
(R)-6
(S)-6
(R)-7
(S)-7
(R)-8
(S)-8
CH3
CH3
19b
45
76
87
83
37b
25b
37
62
39b
71
85
59
64
65
52
95
97
91
94
96
97
99
98
99
99
99
98
99
99
99
99
CH2CH3
CH2CH3
(CH2)2CH3
(CH2)2CH3
CH(CH3)2
CH(CH3)2
Cy
Cy
CH2Cy
CH2Cy
CH2Ph
CH2Ph
(CH2)2Ph
(CH2)2Ph
a
Determined by HPLC analysis on Chiralcel OD or Chiralcel OD-R column (see
Supplementary data).
In these cases, the purification process was carried out by column
chromatography.
b
The stereoisomers of analogues 2–8 were also prepared by
following this procedure and in Table 1 the chemical yields and
enantiomeric excesses obtained in the last step of the synthesis
of these compounds are reported.

L. Piemontese et al. / Tetrahedron: Asymmetry 24 (2013) 791–795
793
OD-R column, methanol/water 90:10 as a mobile phase, flow rate:
0.4 mL minꢀ1, detection: 254 nm).
3. Conclusion
In conclusion, we have reported on an alternative and efficient
method to synthesize highly pure optically active isomers of chiral
2H-1,4-benzoxazine amidine derivatives overcoming problems
due to the lability of the stereogenic center under the conditions
used in previous attempts. This will allow us to study how the
absolute configuration can affect the biological activity of these
promising modulators of the pancreatic and skeletal muscle ATP-
sensitive-K+ channels.
4.3. Synthesis of (R)-6-chloro-2-methyl-3-(pyridin-3-yl-amino)-
2H-1,4-benzoxazine (R)-1: Method A
To an ice-cooled suspension of TiCl4 (6 mmol) in anhydrous tol-
uene (35 mL) and anisole (1 mL) was added 3-amino-pyridine
(50 mmol) and (R)-6-chloro-2-methyl-2H-1,4-benzoxazine-3-one
(5 mmol) at 0 °C and then refluxed for 24 h. The reaction was cooled
at room temperature, quenched with 96% ethanol and ammonium
hydroxide (30%), filtered on a Celite pad, dried over anhydrous
Na2SO4, filtered, and concentrated in vacuo to give a dark brown
oil, which was purified by column chromatography over silica gel
using petroleum ether/ethyl acetate/methanol (8:1.5:0.5) and then
crystallized from chloroform/n-hexane to afford the title compound
4. Experimental
4.1. General
Column chromatography was performed on ICN Silica Gel 60 Å
(63–200 lm) as a stationary phase. Melting points were deter-
as a white powder. 28% Yield. ½a D20
ꢂ
¼ 0 (c 1.0, MeOH), ee = 0% (Chi-
mined in open capillaries on a Gallenkamp electrothermal appara-
tus and are uncorrected. Mass spectra were recorded on an HP GC/
MS 6890-5973 MSD spectrometer, electron impact 70 eV,
equipped with HP chemstation. 1H NMR spectra were recorded
in CDCl3 or DMSO-d6 on a Varian-Mercury 300 (300 MHz) spec-
trometer at room temperature. Chemical shifts are expressed as
parts per million (d). The purity of the final compounds was
>95%, as confirmed by combustion analysis carried out with a
Eurovector Euro EA 3000 model analyzer.
Optical rotations were measured with a Perkin–Elmer 341
polarimeter at room temperature (20 °C): Concentrations are
expressed as g (100 mL)ꢀ1. The enantiomeric excesses of the final
compounds were determined by HPLC analysis on Chiralcel OD
or Chiralcel OD-R column (4.6 mm i.d. ꢁ 250 mm, Daicel Chemical
Industries, Ltd, Tokyo, Japan). Analytical liquid chromatography
was performed on a PE chromatograph equipped with a Rheodyne
7725i model injector, a 785A model UV/vis detector, a series 200
model pump and an NCI 900 model interface. Chemicals were from
Aldrich (Milan, Italy), AlfaAesar (Karlsruhe, Germany) or Acros
(Milan, Italy) and were used without any further purification.
ralcel OD-R column, methanol/water 90:10 as a mobile phase, flow
rate: 0.4 mL minꢀ1, detection: 254 nm).
4.4. Synthesis of (R)-6-chloro-2-methyl-3-(pyridin-3-yl-amino)-
2H-1,4-benzoxazine (R)-1: Method B
(R)-6-Chloro-2-methyl-2H-1,4-benzoxazine-3-one (2.4 g) and
P2S5 (12 g) were dissolved in toluene and refluxed for 9 h. The reac-
tion was then cooled to room temperature and filtered. The solu-
tion was concentrated in vacuo, dissolved in chloroform, washed
with brine, dried over anhydrous Na2SO4, filtered, and concen-
trated to give a yellow solid, which was purified by column chro-
matography over silica gel using petroleum ether/ethyl acetate
(95:5) and then crystallized from chloroform/n-hexane to afford
(R)-6-chloro-2-methyl-2H-1,4-benzoxazine-3-thione as a yellow
powder (1.69 g; yield 69%). 1H NMR (300 MHz, DMSO-d6) d: 1.50
(3H, d, J = 7.5 Hz, CH3), 4.97 (1H, q, J = 7.5 Hz, CH), 6.91–7.17 (3H,
m, aromatics), 11.1 (1H, s, NH, exchange with D2O). The thio-deriv-
ative so obtained was dissolved in 1 M KOH (50 mL) after which
was added CH3I (1.76 g). The resulting mixture was stirred for
2 h at room temperature, then diluted with H2O, and extracted
(3 ꢁ 75 mL) with diethyl ether. The organic portion was washed
with brine, dried over anhydrous Na2SO4, filtered, and concen-
trated in vacuo to give (R)-6-chloro-2-methyl-3-methylsulfanyl-
2H-1,4-benzoxazine as a yellow oil, in quantitative yield. GC–MS
m/z 229 [28, (M+2)+], 227 (76, M+), 182 (36), 180 (100).
4.2. Synthesis of (S)- or (R)-6-chloro-2-methyl-2H-1,4-benzoxa-
zine-3-one 9a, 9b
An ice-cooled solution of (S)- or (R)-2-(4-chloro-phenoxy)prop-
anoic acid (6 g) in 90% HNO3 (10 mL) was stirred at 0 °C for 4 h.
After the reaction was complete, the mixture was poured into ice
and then extracted by diethyl ether (3 ꢁ 50 mL). The combined or-
ganic phases were washed with brine, dried over anhydrous
Na2SO4, filtered, and concentrated in vacuo to give a yellow oil
(7.18 g), which was dissolved in 1,4-dioxane (140 mL), after which
were added with Fe (15.1 g) and 6 M HCl (140 mL) and refluxed.
The reaction progress was checked by thin layer chromatography
(TLC). After 4 h, the resulting mixture was poured into ice and ex-
tracted with diethyl ether (3 ꢁ 70 mL). The combined organic
phases were washed with brine, dried over anhydrous Na2SO4,
filtered, and concentrated giving a red-brown solid that was puri-
fied by column chromatography over silica gel using petroleum
ether/ethyl acetate (8:2) and then crystallized from n-hexane to af-
ford the title compound as a white powder (5.2 g). 90% Yield. 1H
NMR (300 MHz, DMSO-d6) d: 11.5 (1H, s, NH, exchange with
D2O), 6.91–7.17 (3H, m, aromatics), 4.88 (1H, q, J = 7.5 Hz, CH),
1.54 (3H, d, J = 7.5 Hz, CH3). GC–MS m/z: 199 [34, (M+2)+], 197
(100, M+), 156 (30), 154 (90). (R)-6-Chloro-2-methyl-2H-1,4-ben-
This product was mixed with 3-amino-pyridine at 120 °C. The
reaction progress was checked by thin layer chromatography
(TLC) and after 3 h the crude was purified by column chromatogra-
phy over silica gel using petroleum ether/ethyl acetate/methanol
(8:1,5:0,5) and crystallized from chloroform/n-hexane to afford
the title compound as a white powder. 72% Yield. mp = 199–
200 °C. (R)-1, ½a D20
¼ þ46 (c 1.0, MeOH), ee = 20%. (Chiralcel OD-R
ꢂ
column, methanol/water 90:10 as a mobile phase, flow rate:
0.4 mL minꢀ1, detection: 254 nm).
Alternatively, the intermediate (R)-6-chloro-2-methyl-2H-1,
4-benzoxazine-3-thione could be synthesized by adding Lawes-
son’s reagent (2.5 mmol) to a stirred solution of (R)-6-chloro-2-
methyl-2H-1,4-benzoxazine-3-one (5 mmol) in anhydrous toluene
(50 mL) and heating at reflux for 1 h. Next the solvent was concen-
trated and the crude solid purified by column chromatography
over silica gel using petroleum ether/ethyl acetate (85:15) to give
a yellow solid (90% yield). In both cases, the conversion of benzox-
azine-3-one into benzoxazine-3-thione was associated with partial
racemization (Chiralcel OD-R column, methanol/water 90:10 as a
mobile phase, flow rate: 0.4 mL minꢀ1, detection: 254 nm) whose
extension depended on the reaction time, concentration of the
reaction solution, and crystallization conditions.
zoxazine-3-one, ½a D20
¼ þ39 (c 1.0, MeOH); ee = 99% (Chiralcel
ꢂ
OD-R column, methanol/water 90:10 as a mobile phase, flow rate:
0.4 mL minꢀ1, detection: 254 nm); (S)-6-chloro-2-methyl-2H-1,4-
benzoxazine-3-one, ½a D20
¼ ꢀ39 (c 1.0, MeOH); ee = 99% (Chiralcel
ꢂ

794
L. Piemontese et al. / Tetrahedron: Asymmetry 24 (2013) 791–795
4.5. Synthesis of (R)- or (S)-6-chloro-2-methyl-3-(pyridin-3-yl-
amino)-2H-1,4-benzoxazine (R)-1 or (S)-1: Method C
4.11. (R)-6-Chloro-2-propyl-3-(pyridin-3-yl-amino)-2H-1,4-benz-
oxazine (R)-3
At first, Et3N (2 mmol) and POCl3 (2 mmol) were added under a
nitrogen atmosphere to a solution of (R)- or (S)-6-chloro-2-methyl-
2H-1,4-benzoxazine-3-one (1 mmol) in anhydrous acetonitrile
(5 mL) at room temperature. After 20 min, 3-amino-pyridine
(2 mmol) was added and the mixture was stirred for 4 h. Then
the resulting precipitate was filtered off, dissolved in ethyl acetate,
washed with cooled 1.5 M NaOH and brine, dried over anhydrous
Na2SO4, filtered, and concentrated in vacuo to give a pale yellow
solid. Compound (R)-1 was purified by column chromatography
over silica gel using petroleum ether/ethyl acetate/methanol
(8:1.5:0.5) and crystallized from chloroform/n-hexane to give a
white powder; compound (S)-1 was directly purified by crystalli-
zation from chloroform/n-hexane.
83% Yield. 1H NMR (300 MHz, DMSO-d6) d: 0.87 (3H, t, J = 7.1 Hz,
CH2CH3), 1.30–1.66 (4H, m, CH2CH2CH3), 4.77 [1H, dd, J = 9.6, 6.6 Hz,
CH(CH2)2], 6.85–7.08 (3H, m, aromatics), 7.32–7.36, 8.29–8.39 and
8.91 (4H, m, aromatics), 9.64 (1H, s, NH, exchange with D2O); GC–
MS m/z 303 [20, (M+2)+], 301 (60, M+), 259 (100), ½a 2D0
¼ þ272 (c
ꢂ
1.0, MeOH), ee = 96% (Chiralcel OD column, n-hexane/isopropa-
nol/DEA 95:5:0.1 as a mobile phase, flow rate: 1 mL minꢀ1, detec-
tion: 254 nm); mp = 168–169 °C. Anal. Calcd for C16H16N3ClO: C,
63.68; H, 5.34; N, 13.92. Found: C, 63.18; H, 5.62; N, 13.50.
4.12. (S)-6-Chloro-2-propyl-3-(pyridin-3-yl-amino)-2H-1,4-
benzoxazine (S)-3
37% Yield. ½a 2D0
¼ ꢀ274 (c 1.0, MeOH), ee = 97%; mp = 164–165
ꢂ
4.6. (S)-6-Chloro-2-methyl-3-(pyridin-3-yl-amino)-2H-1,4-benz-
oxazine (S)-1
°C. Anal. Calcd for C16H16N3ClO: C, 63.68; H, 5.34; N, 13.92. Found:
C, 62.66; H, 5.51; N, 13.57.
45% Yield. 1H NMR (300 MHz, DMSO-d6) d: 1.30 (3H, d,
J = 6.7 Hz, CH3), 4.91 (1H, q, J = 6.7 Hz, CH), 6.84–7.09 (3H, m,
aromatics), 7.32–7.37, 8.21–8.26, 8.36–8.39 and 8.91 (4H, m, aro-
matics), 9.63 (1H, s, NH, exchange with D2O); GC–MS m/z 275
4.13. (R)-6-Chloro-2-isopropyl-3-(pyridin-3-yl-amino)-2H-1,4-
benzoxazine (R)-4
[32, (M+2)+], 273 (100, M+), 131 (39), ½a 2D0
¼ ꢀ256 (c 1.0, MeOH),
ꢂ
25% Yield. 1H NMR (300 MHz, CDCl3) d: 1.04 and 1.09 [6H, 2 d,
J = 6.6 Hz, CH(CH3)2], 2.15 [1H, m, J = 6.6 Hz, CH(CH3)2], 4.31 (1H, d,
J = 8.0 Hz, CHCH), 6.82–7.00 (3H, m, aromatics), 7.26–7.31,
8.10–8.23 (4H, m, aromatics), 8.49 (1H, s, NH, exchange with
D2O); GC–MS m/z 303 [37, (M+2)+], 301 (100, M+), 258 (94),
ee = 97% (Chiralcel OD-R column, methanol/water 90:10 as a mo-
bile phase, flow rate: 0.4 mL minꢀ1
,
detection: 254 nm);
mp = 200–202 °C. Anal. Calcd for C14H12N3ClO: C, 61.43; H, 4.42;
N, 15.35. Found: C, 61.21; H, 4.48; N, 15.37.
½
a 2D0
ꢂ
¼ þ373 (c 1.0, MeOH), ee = 99% (Chiralcel OD column, n-hex-
ane/isopropanol/DEA 95:5:0.1 as mobile phase, flow rate:
1 mL minꢀ1, detection: 254 nm); mp = 108–109 °C. Anal. Calcd for
16H16N3ClO: C, 63.68; H, 5.34; N, 13.92. Found: C, 63.18; H,
a
4.7. (R)-6-Chloro-2-methyl-3-(pyridin-3-yl-amino)-2H-1,4-benz-
oxazine (R)-1
C
19% Yield. ½a 2D0
¼ þ250 (c 1.0, MeOH), ee = 95%; mp = 202–
ꢂ
5.32; N, 13.77.
204 °C. Anal. Calcd for C14H12N3ClO: C, 61.43; H, 4.42; N, 15.35.
Found: C, 61.13; H, 4.44; N, 15.52.
4.14. (S)-6-Chloro-2-isopropyl-3-(pyridin-3-yl-amino)-2H-1,4-
benzoxazine (S)-4
4.8. Synthesis of (R)- or (S)-6-chloro-2-substituted-3-(pyridin-3-
yl-amino)-2H-1,4-benzoxazines 2–8
37% Yield. ½a 2D0
¼ ꢀ373 (c 1.0, MeOH), ee = 98%; mp = 106–109
ꢂ
°C. Anal. Calcd for C16H16N3ClO: C, 63.68; H, 5.34; N, 13.92. Found:
All compounds were synthesized using Method C.
C, 63.598; H, 5.37; N, 13.46.
4.9. (R)-6-Chloro-2-ethyl-3-(pyridin-3-yl-amino)-2H-1,4-benz-
oxazine (R)-2
4.15. (R)-6-Chloro-2-cyclohexyl-3-(pyridin-3-yl-amino)-2H-1,4-
benzoxazine (R)-5
76% Yield. 1H NMR (300 MHz, DMSO-d6) d: 0.94 (3H, t, J = 7.1 Hz,
CHCH2CH3), 1.60 (2H, q, J = 7.1 Hz, CHCH2CH3), 4.67 (1H, t,
J = 7.1 Hz, CHCH2CH3), 6.86–6.98 and 7.07–7.09 (3H, m, aromatics),
7.27–7.37, 8.21–8.23, 8.37–8.40 and 8.91 (4H, m, aromatics), 9.67
(1H, s, NH, exchange with D2O); GC–MS m/z 289 [36, (M+2)+], 287
62% Yield. 1H NMR (300 MHz, CDCl3) d: 1.09–1.99 (11H, m, Cy),
4.33 (1H, d, J = 7.7 Hz, CHCH), 6.82–7.03 (3H, m, aromatics),
7.29–7.33, 8.24–8.25 (4H, m, aromatics), 8.55 (1H, s, NH, exchange
with D2O); GC–MS m/z 343 [37, (M+2)+], 341 (100, M+), 259 (100),
½
a D
ꢂ
¼ þ353 (c 1.0 in MeOH), ee = 99% (Chiralcel OD column, n-hex-
ane/isopropanol/DEA 95:5:0.1 as mobile phase, flow rate:
1 mL minꢀ1, detection: 254 nm); mp = 168–169 °C. Anal. Calcd for
19H20N3ClO: C, 66.76; H, 5.90; N, 12.29. Found: C, 66.28; H,
(100, M+), 259 (65); ½a 2D0
¼ þ273 (c 1.0, MeOH), ee = 91% (Chiralcel
ꢂ
a
OD-R column, methanol/0.02N HClO4/NaClO4 70:30 pH 3.5 as a mo-
bile phase, flow rate: 0.4 mL minꢀ1, T = 35 °C, detection: 254 nm);
mp = 169–170 °C. Anal. Calcd for C15H14N3ClO: C, 62.61; H, 4.90;
N, 14.60. Found: C, 62.18; H, 4.97; N, 14.67.
C
5.93; N, 11.74.
4.16. (S)-6-Chloro-2-cyclohexyl-3-(pyridin-3-yl-amino)-2H-1,4-
benzoxazine (S)-5
4.10. (S)-6-Chloro-2-ethyl-3-(pyridin-3-yl-amino)-2H-1,4-benz-
oxazine (S)-2
39% Yield. ½a 2D0
¼ ꢀ353 (c 1.0, MeOH), ee = 99%; mp = 170–172
ꢂ
87% Yield. ½a 2D0
¼ ꢀ280 (c 1.0, MeOH), ee = 94%; mp = 165–
ꢂ
°C. Anal. Calcd for C19H20N3ClO: C, 66.76; H, 5.90; N, 12.29. Found:
167 °C. Anal. Calcd for C15H14N3ClO: C, 62.61; H, 4.90; N, 14.60.
C, 66.34; H, 5.88; N, 12.16.
Found: C, 62.24; H, 4.92; N, 14.54.

L. Piemontese et al. / Tetrahedron: Asymmetry 24 (2013) 791–795
795
4.17. (R)-6-Chloro-2-cyclohexylmethyl-3-(pyridin-3-yl-amino)-
2H-1,4-benzoxazine (R)-6
4.21. (R)-6-Chloro-2-phenethyl-3-(pyridin-3-yl-amino)-2H-1,4-
benzoxazine (R)-8
71% Yield. 1H NMR (300 MHz, DMSO-d6) d: 0.81–1.87 (13H, m,
CH2Cy), 4.85–4.89 (1H, m, CHCH2), 6.84–6.96 and 7.07–7.09 (3H,
m, aromatics), 7.32–7.37, 8.20–8.23, 8.36–8.39 and 8.91 (4H, m,
aromatics), 9.68 (1H, s, NH, exchange with D2O); GC–MS m/z 357
65% Yield. 1H NMR (300 MHz, DMSO-d6) d: 1.84–1.91 (2H, m,
CH2CH), 2.62–2.83 (2H, m, PhCH2), 4.77 (1H, CH2CH), 6.86–7.36
(8H, m, aromatics), 8.21–8.23, 8.36–8.39 and 8.88–8.90 (4H, m,
aromatics), 9.70 (1H, s, NH, exchange with D2O); GC–MS m/z 365
[10, (M+2)+], 355 (29, M+), 259 (100), ½a 2D0
ꢂ
¼ þ256 (c 1.0, MeOH),
[15, (M+2)+], 363 (43, M+), 259 (100); ½a 2D0
¼ þ244 (c 1.0, MeOH),
ꢂ
ee = 98% (Chiralcel OD column, n-hexane/isopropanol/DEA
98:2:0.01 as a mobile phase, flow rate: 0.5 mL minꢀ1, detection:
254 nm); mp = 129–131 °C. Anal. Calcd for C20H22N3ClO: C, 67.50;
H, 6.23; N, 11.81. Found: C, 67.39; H, 6.31; N, 11.95.
ee = 99% (Chiralcel OD column, n-hexane/isopropanol/DEA
80:20:0.1 as a mobile phase, flow rate: 1 mL minꢀ1, detection:
320 nm); mp = 179–181 °C. Anal. Calcd for C21H18N3ClO: C, 69.32;
H, 4.99; N, 11.55. Found: C, 69.36; H, 4.98; N, 11.35.
4.18. (S)-6-Chloro-2-cyclohexylmethyl-3-(pyridin-3-yl-amino)-
2H-1,4-benzoxazine (S)-6
4.22. (S)-6-Chloro-2-phenethyl-3-(pyridin-3-yl-amino)-2H-1,4-
benzoxazine (S)-8
85% Yield. ½a 2D0
ꢂ
¼ ꢀ256 (c 1.0, MeOH), ee = 99%; mp = 132–134
52% Yield. ½a 2D0
¼ ꢀ244 (c 1.0, MeOH), ee = 99%; mp = 183–
ꢂ
°C. Anal. Calcd for C20H22N3ClO: C, 67.50; H, 6.23; N, 11.81. Found:
185 °C. Anal. Calcd for C21H18N3ClO: C, 69.32; H, 4.99; N, 11.55.
C, 67.37; H, 6.33; N, 11.22.
Found: C, 69.18; H, 5.16; N, 11.20.
4.19. (R)-2-Benzyl-6-chloro-3-(pyridin-3-yl-amino)-2H-1,4-
benzoxazine (R)-7
Acknowledgements
This work was accomplished thanks to the financial support of
the Ministero dell’Istruzione, dell’Università e della Ricerca (MIUR
2009K7R7NA).
59% Yield. 1H NMR (300 MHz, DMSO-d6) d: 2.84–2.87 (2H, m,
CH2CH), 4.95–4.99 (1H, m, CH2CH), 6.78–6.81, 6.98–7.02 and
7.13–7.40 (8H, m, aromatics), 8.24–8.26, 8.38–8.41 and 8.92 (4H,
m, aromatics), 9.76 (1H, s, NH, exchange with D2O); GC–MS m/z
References
351 [15, (M+2)+], 349 (44, M+), 258 (100); ½a 2D0
¼ þ273 (c 1.0,
ꢂ
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DEA 80:20:0.1 as a mobile phase, flow rate: 1 mL minꢀ1, detection:
320 nm); mp = 207–208 °C dec. Anal. Calcd for C20H16N3ClO: C,
68.67; H, 4.61; N, 12.01. Found: C, 68.29; H, 4.68; N, 11.76.
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benzoxazine (S)-7
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64% Yield. ½a 2D0
¼ ꢀ273 (c 1.0, MeOH), ee = 99%; mp = 204–206
ꢂ
°C. Anal. Calcd for C20H16N3ClO: C, 68.67; H, 4.61; N, 12.01. Found:
C, 68.17; H, 4.70; N, 11.72.