Phosphorylation of betti base with diethyl chlorophosphate

Article abstract of DOI:10.1134/S107036321603004X

Phosphoric acid derivatives containing chiral Betti base fragment were synthesized by reacting racemic and enantiopure N-Boc-protected 1-(α-aminobenzyl)-2-naphthols with diethyl chlorophosphate followed by deprotection.

Full text of DOI:10.1134/S107036321603004X

ISSN 1070-3632, Russian Journal of General Chemistry, 2016, Vol. 86, No. 3, pp. 515–521. © Pleiades Publishing, Ltd., 2016.
Original Russian Text © K.E. Metlushka, D.N. Sadkova, K.A. Nikitina, L.N. Shaimardanova, O.N. Kataeva, V.A. Alfonsov, 2016, published in Zhurnal
Obshchei Khimii, 2016, Vol. 86, No. 3, pp. 371–377.
To the 100th Anniversary of A.N. Pudovik
Phosphorylation of Betti Base with Diethyl Chlorophosphate
K. E. Metlushkaa,b, D. N. Sadkovaa, K. A. Nikitinaa,
L. N. Shaimardanovaa, O. N. Kataevaa, and V. A. Alfonsova
a Arbuzov Institute of Organic and Physical Chemistry, Kazan Scientific Center, Russian Academy of Sciences,
ul. Akademika Arbuzova 8, Kazan, Tatarstan, 420088 Russia
e-mail: alfonsov@yandex.ru
b Butlerov Chemistry Institute, Kazan Federal University, Kazan, Tatarstan, Russia
Received January 28, 2016
Abstract—Phosphoric acid derivatives containing chiral Betti base fragment were synthesized by reacting
racemic and enantiopure N-Boc-protected 1-(α-aminobenzyl)-2-naphthols with diethyl chlorophosphate
followed by deprotection.
Keywords: Betti base, chiral shift reagent, phosphoric acid derivatives
DOI: 10.1134/S107036321603004X
Betti base, 1-(α-aminobenzyl)-2-naphthol prepared
in the beginning of the last century [1] now gets
popular in asymmetric organic synthesis due to the
recently elaborated simple and convenient methods of
its isolation in the enantiomerically pure forms [2–4].
Simplicity of the preparation of Betti base and its
derivatives as enantiopure species allows regarding
them among the limited number of the other accessible
enantiopure natural and synthetic compounds widely
used in organic asymmetric synthesis. However, this
simple, versatile and effective chiral scaffold has been
rarely used in organophosphorus chemistry [5–7].
Indeed, the reaction of unsubstituted racemic Betti
base with diethyl chlorophosphate in the presence of
triethylamine at 1 : 1 : 1.5 ratio of the starting reagents
afforded a mixture of the reaction products as shown
by 31P NMR spectroscopy. Thus, in the 31P NMR
spectrum four signals appeared corresponding most
probably to the products of N-phosphorylation (±)-1
(δP = 9.8 ppm), O-phosphorylation (±)-2 (δP
=
–4.5 ppm), and O,N-phosphorylation of Betti base (±)-3
(δP = –5.6, 9.3 ppm). Addition of an excess of diethyl
chlorophosphate and triethylamine to the reaction
resulted in complete phosphorylation of the starting
Betti base and isolation of (±)-3 (Scheme 1).
Recently we have showed that Betti base could be
used as an effective chiral auxiliary in asymmetric
synthesis of enantiopure α-aminophosphonic acids
prepared easily from Betti base imines by the Pudovik
reaction [8, 9]. Here we report on a possibility to use
1-(α-aminobenzyl)-2-naphthol not only as chiral
auxiliary, but in asymmetric synthesis of organophos-
phorus compounds containing chiral Betti base
fragment.
In order to obtain monophosphorylated product,
one of the nucleophilic sites of Betti base should be
selectively protected. tert-Butoxycarbonyl group (Boc)
is known to be a convenient protection for amino
group [10]. Introduction of the protecting group with
subsequent phosphorylation of free naphthol hydroxyl
fragment followed by deprotection would lead to the
formation of chiral phosphorus-containing amino acids
with free primary amino group. Such compounds may
be interesting as asymmetric organocatalysts [11].
Direct phosphorylation of Betti base presents some
difficulties. Thus, 1-(α-aminobenzyl)-2-naphthol pos-
sesses two active nucleophilic proton-containing sites,
which are able to react with electrophilic phosphorous
reagents like phosphorus halides that may vary the
reaction pathway.
The analysis of publications revealed that N-Boc-
protected Betti base has been characterized only as
racemic compound. Moreover, it has been prepared not
515

516
METLUSHKA et al.
Scheme 1.
NH2
OH +
O
OEt
OEt
Cl
P
O
O
P(OEt)2
NH
P(OEt)2
NH
NH2
_
.
NEt3, NEt3 HCl
C6H6/Et2O
+
+
OH
O
O
P(OEt)2
P(OEt)2
O
O
(±)-1
(±)-3
(±)-2
Scheme 2.
O
O
O
NH2
OH
NH
Ot-Bu
CH2Cl2,
Δ
+
t-BuO
O
Ot-Bu
OH
4
1
by the direct reaction of free base with di-tert-butyl
dicarbonate, but by reacting of β-naphthol with Boc-
benzalimine, which is difficult to obtain [12]. Some
researchers tried to prepare enantiopure N-Boc-
protected Betti base by the same reaction under enan-
tioselective catalysis, but scalemic product was iso-
lated with ee 91% [13]. Therefore enantiopure N-Boc-
protected Betti base has not been described earlier.
compound (±)-4 in CDCl3 complicated the H NMR
spectral pattern. The doublet signal of methine proton
at the α-carbon of naphthyl fragment is the most
informative for the analysis of enantiomeric purity of
the product (Fig. 1a). When mixing (R)-(–)-3,5-dinitro-
N-(1-phenylethyl)benzamide with racemic product (±)-
4 at a molar ratio of 1 : 1, the second doublet signal
appeared in the same field of the spectrum (Fig. 1b).
Complete resolution of the signals succeeded at the
molar ratio of the shift reagent and the analyzed
compound of 2 : 1 (Fig. 1c). In the case of compound
(S)-(–)-4, under the same conditions the appearance of
the second doublet was not observed that evidenced its
high enantiomeric purity (ee > 98%) (Fig. 2).
Aiming to obtain N-Boc-protected Betti bases, we
performed the reactions of (±)- and (S)-(+)-1-(α-
aminobenzyl)-2-naphthols with di-tert-butyl dicarbo-
nates. The reactions proceeded under mild conditions
with the formation of the target products in 80–86%
yield (Scheme 2).
Therefore, (R)-(–)-3,5-dinitro-N-(1-phenylethyl)benz-
amide was found to be an effective chiral shift reagent
allowing estimation of the enantiomeric purity of both
Betti base and its N-Boc-derivative.
In addition, we elaborated the method of analysis of
enantiomeric purity of the prepared compounds by H
NMR spectroscopy using the (R)-(–)-3,5-dinitro-N-(1-
phenylethyl)benzamide as a chiral shift reagent, which
proved to be suitable when analyzing free Betti bases
[2]. An addition of the reagent to the solution of
1
The reaction of compound (±)-4 with diethyl chloro-
phosphate led to the formation of the O-phosphory-
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517
PHOSPHORYLATION OF BETTI BASE WITH DIETHYL CHLOROPHOSPHATE
(a)
(b)
(c)
δ, ppm
δ, ppm
δ, ppm
1
Fig. 1. Fragments of H NMR spectrum (500 MHz, CDCl3) of compound (±)-4 in the absence of the shift reagent (a) and in the
presence of equimolar amount (b) and two-fold molar excess of the shift reagent (c).
(a)
(b)
δ, ppm
δ, ppm
Fig. 2. Fragments of 1H NMR spectrum (500 MHz, CDCl3) of compound (S)-(–)-4 in the absence of the shift reagent (a) and in the
presence of two-fold molar excess of the shift reagent (b).
1
lated product (±)-5; the composition and structure of
which was established by elemental analysis, IR and
NMR spectroscopy data. The O-phosphorylation was
confirmed by the presence of a doublet signal of the
methine proton of the Betti base residue in H NMR
spectrum of compound (±)-5; the signal did not split
into doublet of doublets by the phosphorus nuclei that
would happen at the N-phosphorylation.
Scheme 3.
NHBoc
OH
NHBoc
O
P
OEt
OEt
t-BuOK, C6H6
_KCl
+
Cl
O
P(OEt)2
O
5
4
NH2
(1) Me3SiBr, CH2Cl2
(2) MeOH
O
P(OH)2
O
6
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 86 No. 3 2016

518
METLUSHKA et al.
Fig. 3. Crystal structure of (S)-(–)-О-1-[amino(phenyl)methyl]naphth-2-yl phosphate (S)-6 (hydrogen bond with solvate molecule
of methanol is shown as dashed line).
To prepare phosphorylated Betti base derivative
containing free amino group it was necessary to
deprotect the nitrogen atom in the molecule of 5 and to
remove the ethyl group in the phosphoryl fragment.
Bromotrimethylsilane is known to be an effective
reagent, which allow to carry out both reactions under
mild conditions [14]. Indeed, the treatment of
compound (±)-5 with this reagent followed by an
addition of methanol led to the formation of acid (±)-6
(Scheme 3).
(S)-6 from methanol allowed to obtain the solvate
crystals suitable for X-ray single-crystal diffraction
study.
In the crystal of (S)-6 a complex system of
hydrogen bonds was present: intramolecular N–H···O
bonds and numerous intermolecular hydrogen bonds
with participation of both the target compound and
methanol were detected (Fig. 3, Table 1).
In summary, we accomplished the synthesis of N-
Boc-protected
1-(α-aminobenzyl)-2-naphthols
in
The total yield of (±)-6 was 48%. We succeeded to
improve it up to 68% in the case of one-pot synthesis
starting from compounds (±)-4 and (S)-4 without
isolation of intermediate 5.
racemic and enantiopure forms. The method of the
optical purity determination of these compounds by
1H NMR spectroscopy with the use of (R)-(–)-3,5-
dinitro-N-(1-phenylethyl)benzamide as a chiral shift
reagent was elaborated. Simple and effective approach
to synthesis of racemic and enantiopure phosphoric
acids containing chiral Betti base fragment with free
amino group was developed.
Like other aminocarboxylic and aminophosphonic
acids, compounds (±)-6 and (S)-6 exist as inner salts
(betaines); their structure was confirmed by NMR and
IR spectra. Recrystallization of enantiopure betaine
Parameters of hydrogen bonds in the crystal of compound (S)-6
D–H
N1–H1A
d(D–H), Å
d(H···A), Å
∠DHA, deg
d(D···A), Å
A
0.883
1.881
174.48
2.762
O1
O4
N1–H1A
N1–H1B
N1–H1C
O3–H3
0.883
0.907
0.947
0.856
0.955
2.501
1.836
1.852
1.724
1.705
116.75
169.00
158.74
165.05
167.65
3.004
2.731
2.757
2.561
2.646
O2' (x, y–1, z)
O1' (–x+2, y–1/2, –z+2)
O22' (x+1, y–1, z)
O2' (x–1, y, z)
O22–H22
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PHOSPHORYLATION OF BETTI BASE WITH DIETHYL CHLOROPHOSPHATE
EXPERIMENTAL
(±)-tert-Butyl (2-hydroxynaphth-1-yl)(phenyl)me-
thylcarbamate (±)-4. A solution of di-tert-butyl di-
carbonate (2.45 g, 11.2 mmol) in 10 mL of methylene
chloride was added to a solution of (±)-1-(α-amino-
benzyl)-2-naphthol (2 g, 8 mmol) in 25 mL of
methylene chloride. The obtained mixture was stirred
at room temperature for 1 h followed by refluxing for
5 h. After the solvent removal the residue was
crystallized from acetonitrile. Yield 2.25 g (80.3%),
mp 217–219°С (CH3CN) (mp = 218–219.1°С [12]). IR
spectrum, ν, cm–1: 1519 s (C=O), 1581 w (C=CAr),
NMR spectra were recorded on a Bruker Avance-
400 [400.13 (1Н) and 161.97 MHz (31Р)] and Avance-
500 [500.13 (1Н) and 202.45 MHz (31P)] instruments
relative to the signals of residual protons of deuterated
solvents (CDCl3, D2O) as an internal reference or to
the external standard (85% H3PO4). IR spectra were
recorded on a Bruker Tensor 27 spectrometer from
KBr pellets. Optical rotations were measured on a
Perkin Elmer (Model 341) polarimeter at 20°C.
Melting points were measured on a Boetius melting
point microscope.
1
1627 w (C=CAr), 1673 s (C=O), 3420 m (NH). Н
NMR spectrum (500 MHz, CDCl3), δ, ppm: 1.50 s
3
(±)-1-(α-Aminobenzyl)-2-naphthol was synthesized
by hydrolysis of 1,3-diphenylnaphthoxazine [4]
prepared by the known procedure [15]. (S)-(+)-1-(α-
Aminobenzyl)-2-naphthol was prepared by the method
described in [3]. Free bases were obtained by treating
with sodium carbonate.
[9Н, C(CH3)3], 6.88 d (1Н, PhCH, JНН = 9.4 Hz),
7.17–7.42 m (9Н, НAr), 7.73–7.82 m (2Н, НAr), 7.84
br.s (1Н, NH). Found, %: С 75.40; Н 6.53; N 4.22.
С22Н23NO3. Calculated, %: С 75.62; Н 6.63; N 4.01.
(S)-(–)-tert-Butyl (2-hydroxynaphth-1-yl)(phenyl)-
methylcarbamate (S)-(–)-4 was prepared similarly
from (S)-(+)-1-(α-aminobenzyl)-2-naphthol. Yield
2.4 g (85.8%), mp 224–226°С (CH3CN), [α]D20 = –69
(c 0.25, CHCl3). IR spectrum, ν, cm–1: 1515 s (C=O),
1586 w (C=CAr), 1630 w (C=CAr), 1671 s (C=O), 3428
(±)-О,О-Diethyl [2-(diethoxyphosphoryloxy)-naphth-
1-yl](phenyl)methylphosphoramidate (±)-3. A solu-
tion of triethylamine (0.61 g, 6 mmol) in 1 mL of
anhydrous benzene and a solution of diethyl chloro-
phosphate (0.69 g, 4 mmol) in 4 mL of anhydrous
benzene were successively added under argon to a solu-
tion of (±)-1-(α-aminobenzyl)-2-naphthol (1 g, 4 mmol)
in a mixture of anhydrous benzene (10 mL) and diethyl
ether (10 mL). The reaction mixture was stirred at
room temperature under argon for 24 h following by
sampling for the analysis by 31P NMR spectroscopy.
To synthesize of the diphosphorylated Betti base, a
solution of triethylamine (1 g, 10 mmol) in 2 mL of
anhydrous benzene and a solution of diethyl chlorophos-
phate (1.385 g, 8 mmol) in 8 mL of anhydrous benzene
were added to the reaction mixture. The obtained
mixture was stirred at room temperature under argon
for 24 h. Then triethylamine hydrochloride was filtered
off, and washed with 10 mL of anhydrous diethyl
ether. The filtrate was evaporated, and the residue was
crystalized from acetonitrile. Yield 0.91 g (43.5%), mp
135–137°С (CH3CN). IR spectrum, ν, cm–1: 1026 s
(P–O–CAlk), 1240 s (P=O), 1599 w (C=CAr), 1625 w
(C=CAr), 3211 br (NH). 1Н NMR spectrum (400 MHz,
CDCl3), δ, ppm: 1.00 t (3Н, OCH2CH3, 3JНН = 7.0 Hz),
1.17–1.27 m (9Н, OCH2CH3), 3.55–3.64 m (1Н,
OCH2CH3), 3.84–4.09 m (7Н, OCH2CH3), 6.48 t (1Н,
1
m (NH). Н NMR spectrum (500 MHz, CDCl3), δ,
3
ppm: 1.50 s [9Н, C(CH3)3], 6.88 d (1Н, PhCH, JНН
=
9.2 Hz), 7.16–7.41 m (9Н, НAr), 7.73–7.81 m (2Н,
НAr), 7.83 br.s (1Н, NH). Found, %: С 75.67; Н 6.79;
N 4.17. С22Н23NO3. Calculated, %: С 75.62; Н 6.63; N
4.01.
(±)-tert-Butyl [2-(diethoxyphosphoryloxy)naphth-
1-yl](phenyl)methylcarbamate (±)-5. Potassium tert-
butylate (0.42 g, 3.75 mmol) was added to a sus-
pension of compound (±)-4 (1 g, 2.87 mmol) in 20 mL
of anhydrous benzene. The reaction mixture was
stirred for 20 min under argon followed by addition of
a solution of diethyl chlorophosphate (0.545 g,
3.16 mmol) in 4 mL of anhydrous benzene. The
obtained reaction mixture was stirred under argon for
24 h, centrifuged, decanted, and the solvent was
distilled off. The residue was dissolved at heating in a
mixture of cyclohexane and ethyl acetate (4 : 1) and
kept for 2 days at 10°C. The precipitate was filtered off
and dried. Yield 0.9 g (64.8%), mp = 131–132°С
(cyclohexane–ethyl acetate). IR spectrum, ν, cm–1:
1036 s (P–O–CAlk), 1221 s (P=O), 1527 s (C=O), 1599
w (C=CAr), 1626 w (C=CAr), 1703 s (C=O), 3316 br
3
3
PhCH, JPН = 11.3, JНН = 11.3 Hz), 7.19–7.90 m
(11Н, НAr), 8.12 br.s (1Н, NH). 31P NMR spectrum
(CDCl3), δP, ppm: –6.97, 8.08. Found, %: С 57.71; Н
6.48; N 2.81; P 11.67. С25Н33NO7P2. Calculated, %: С
57.58; Н 6.38; N 2.69; P 11.88.
1
(NH). Н NMR spectrum (400 MHz, CDCl3), δ, ppm:
1.23 t and 1.28 2t (6Н, OCH2CH3, 3JНН = 7.1 Hz), 1.49
s [9Н, C(CH3)3], 3.92–4.11 m (4Н, OCH2CH3), 6.27
br.s (1Н, PhCH), 7.08–7.90 m (11Н, НAr), 8.22 br.s
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 86 No. 3 2016

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METLUSHKA et al.
(1Н, NH). 31P NMR spectrum (CDCl3): δP –6.96 ppm.
Found, %: С 64.57; Н 6.75; N 2.97; P 6.58.
С26Н32NO6P. Calculated, %: С 64.32; Н 6.64; N 2.88;
P 6.38.
CH3OH. Calculated, %: С 59.83; Н 5.58; N 3.88; P
8.57.
X-Ray diffraction study of the crystals of com-
pound (S)-6 was done on a Bruker SMART Apex II
diffractometer (graphite monochromator, МоKα-irradia-
tion, λ = 0.71073 Å) at 150(2) K. Empirical absorption
correction was carried out using a SADABS program
[16]. The structures were solved by the direct method
applying SHELXS software [17]. Non-hydrogen atoms
were refined isotropically followed by anisotropic
approximation using SHELXS program package [17].
Hydrogen atoms were placed into the calculated
positions and refined in a riding model. The hydrogen
atoms of hydroxyl and ammonium groups were
revealed from the difference Fourier synthesis, their
positions were refined isotropically in the final step of
the refinement. All calculations were performed with
the help of APEX2 program [18].
(±)-О-1-[Amino(phenyl)methyl]naphth-2-yl phos-
phate (±)-6. A mixture of compound (±)-5 (0.5 g,
1.03 mmol) and bromotrimethylsilane (0.788 g,
5.15 mmol) in 5 mL of methylene chloride was stirred
at room temperature under argon for 24 h. The solvent
was distilled off, and methanol (5 mL) was added. The
obtained mixture was stirred for 1 h. The precipitate
was filtered off, washed with 2 mL of methanol, and
dried. Yield 0.28 g (75.3%), solvate with methanol,
mp = 191–192°С (CH3OH). IR spectrum, ν, cm–1:
1231 s (P=O), 1597 w (C=CAr), 1624 w (C=CAr), 2850
br (NH3+). 1Н NMR spectrum (500 MHz, D2O, K2CO3),
δ, ppm: 3.33 s (3Н, CH3OH), 6.28 s (1Н, PhCH),
7.21–7.90 m (14Н, НAr, NH3). 31P NMR spectrum
(D2O, K2CO3): δP 0.07 ppm. Found, %: С 59.99; Н
5.66; N 3.63; P 8.38. C17H16NO4P·CH4O. Calculated,
%: С 59.83; Н 5.58; N 3.88; P 8.57.
Crystals of compound (S)-6 are monoclinic,
C17H16NO4P·CH4O, M = 361.32, space group P21,
a = 10.560(1), b = 5.997(1), c = 13.558(2) Å, β =
97.656(2)°, V = 850.9(1) Å3, Z = 2, dcalc = 1.410 g/cm3,
μ = 0.191 mm–1, θmax = 29°; 10819 reflections were
The total yield of compound (±)-6 after two steps
was 47.9%. To improve the yield of the target product
the synthesis was repeated with the same loading in the
first step, but without isolation of intermediately
formed carbamate (±)-5. A solution of bromotri-
methylsilane (2.19 g, 14.3 mmol) in 10 mL of
methylene chloride was immediately added to a
viscous substance obtained from the reaction of
compound (±)-4 with diethyl chlorophosphate. The
reaction mixture was stirred at room temperature for
24 h under argon. After the solvent removal methanol
(10 mL) was added, and the mixture was stirred for
1 h. The precipitate was filtered off, washed with
methanol (5 mL), and dried. Yield of compound (±)-6
is 0.7 g (67.7%).
collected, 4347 from them were independent (Rint
=
0.028) and 4103 were observed with [I > 2σ(I)],
262 parameters of refinement, R1 = 0.031, wR2 = 0.079
[I > 2σ(I)], residual electron density 0.379/–0.210 e/Å3,
GoF = 1.030.
ACKNOWLEDGMENTS
This work was supported by the Russian
Foundation for Basic Research (grant no. 15-43-
02486-r_povolzh’e_a) and the Russian Government
Program of Competitive Growth of the Kazan Federal
University.
(S)-(–)-О-1-[Amino(phenyl)methyl]naphth-2-yl
phosphate (S)-(-)-6 was prepared similarly from
compound (S)-(–)-4 without isolation of the
intermediate product. Yield 0.72 g (69.6%), mp = 189–
191°С (CH3OH), [α]D20 = –134 (c 0.1, DMSO), –109
[c 0.5, H2O + K2CO3, potassium carbonate was added
in three folder excess regarding to phosphate (S)-(–)-6].
IR spectrum, ν, cm–1: 1232 s (P=O), 1597 w (C=CAr),
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