Phosphorylation of Betti bases

ISSN 1070-4280, Russian Journal of Organic Chemistry, 2014, Vol. 50, No. 11, pp. 1573–1578. © Pleiades Publishing, Ltd., 2014.

Original Russian Text © K.E. Metlushka, D.N. Sadkova, L.N. Shaimardanova, K.A. Nikitina, O.A. Lodochnikova, O.N. Kataeva, V.A. Al’fonsov, 2014, published in Zhurnal Organicheskoi Khimii, 2014, Vol. 50, No. 11, pp. 1589–1593.

1573

Phosphorylation of Betti Bases

K. E. Metlushka, D. N. Sadkova, L. N. Shaimardanova, K. A. Nikitina, O. A. Lodochnikova, O. N. Kataeva, and V. A. Al’fonsov

Arbuzov Institute of Organic and Physical Chemistry, Kazan Scientific Center, Russian Academy of Sciences, ul. Arbuzova 8, Kazan, Tatarstan, 420088 Russia

-mail: [email protected]

Received July 22, 2014

Abstract—Reaction of N-substituted 1-(α-aminobenzyl)-2-naphthols (Betti bases) with phosphorus(III) com-pounds followed by sulfurization afforded new cyclic phosphorylated and thiophosphorylated diastereomeric derivatives of N-substituted Betti bases. In most cases individual diastereomers were isolated and their characteristic spectral features were determined.

R = H (I, III), Me (II, IV).

Compounds of trivalent three-coordinated phosphorus are important precursors in the syntheses of biologically active enantiomerically pure chiral organophosphorus compounds [1]. Chiral compounds of this series are widely used as ligands in the preparation of transition metal complexes, which are enantioselective processes catalysts [2, 3]. Increasing the number of such compounds is a topical target of the modern chemistry.

An available chiral auxiliary for the preparation of pure enantiomers of organophosphorus compounds is 1-(α-aminobenzyl)-2-naphthol (Betti base). This com-pound has been known since the beginning of the last century [4], but only lately it has been used in the asymmetric synthesis owing to developing simple and convenient methods of its preparation and isolation in the enantiomerically pure form [5–7]. Betti base derivatives with phosphorus-containing substituents are mentioned in publications very seldom [8, 9].

Betti base has two active nucleophilic functional amino and phenol groups, and it is expectable to bring it into nucleophilic substitution reaction with compounds of trivalent three-coordinated phosphorus possessing at least two easily leaving groups leading to the formation of phosphorus-containing heterocycles. We have chosen as initial compounds two chiral racemic N-substituted Betti bases, (±)-1-[α-(benzyl-amino)-benzyl]-2-naphthol (I) and (R,R/S,S)-1-[α-(1-phenylethylamino)benzyl]-2-naphthol (II), which are also easily available in the enantiomerically pure form

[10, 11] and hexaethyltriamidophosphite as a highly reactive substrate in nucleophilic substitution of amino groups (Scheme 1).

DOI: 10.1134/S1070428014110062

Scheme 1.

NH

OH

*N

O

P(NEt2)3*

R Ph

P

R Ph

NEt2

5 mol% Et2NH HCl, Δ.

*:

I, (R,R/S,S)-II III, IV

Diethylamine hydrochloride was used as catalyst [12]. Without the catalyst only monosubstitution occurred, and we did not isolate the product in the pure state. At the addition to the reaction mixture of 5 mol% of diethylamine hydrochloride the reaction proceeded readily with the substitution of both amino groups and with the closure of a six-membered heterocycle. Owing to this double substitution the phosphorus atom becomes asymmetric resulting in the appearance of diastereomerism. The analysis of 31Р NMR spectra of the reaction mixtures after 5 h at reflux in benzene under argon flow of compounds I and II with hexaethyltriamidophosphite has revealed the formation of diastereomeric oxazaphosphinines III (δP 123.57, 135.23 ppm) and IV (δP 114.83, 135.66 ppm) in the ratio 1 : 1 and 1 : 1.4 respectively.

RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 50 No. 11 2014

METLUSHKA et al. 1574

The obtained compounds of trivalent three-coordinated phosphorus III and IV are unstable in air, easily hydrolysable or oxidized. To prove their structure they were subjected to sulfurization into far

The structure and composition of diastereomers were confirmed by NMR, IR, and mass spectra and by elemental analysis.

The molecular structure of compounds VIА and VIB was established by X-ray single crystal diffraction (see the figure).

Diastereomers VIА and VIB crystallized as racemates in centrosymmetrical space groups. As seen from the figure, diastereomer VIА that is the first to crystallize from the mixture has a relative (R,R,PR/S,S,PS)-configuration, and diastereomer VIB possesses the relative (R,R,PS/S,S,PR)-configuration. Taking into consideration the data of NMR spectra of diastereomers VА, VIА and VB, VIB, namely, the close values of chemical shifts and coupling constants in the 31P and 1Н NMR spectra (see the table), it is possible by analogy suggest the relative configurations as (R,PR/S,PS)-(VА) and (R,PS/S,PR)-(VB).

The conformations of the six-membered heterocycles in the diastereomers are different. In the crystal of diastereomer VIА it may be regarded as boat, the atoms P1, N1, C22, C23 are located in one plane [within 0.000(2) Å], atoms O1 and C1 are deviated from the plane in the same direction by 0.370(1) and 0.497(2) Å respectively, the diethylamino group at the phosphorus atom occupies the axial position, and the sulfur atom is in the equatorial position.

In the VIB crystal the conformation of the heterocycle may be regarded as half-boat with a flat [within 0.020(3) Å] fragment C1C22C23O1, atoms P1

R = H (V), Me (VI).

Scheme 2.

III, IVS8, Δ

N

O

*P

R Ph

NEt2*

V, VI

S

more stable sulfides by sulfur treatment in benzene at reflux (Scheme 2). The obtained stable derivatives of pentavalent phosphorus V and VI made it possible to isolate all existing individual diastereomers VА, VB, VIА, and VIB by fractional crystallization of diastereomeric mixtures from acetonitrile.

VIA

VIB

Molecular structure of diastereomers А and B of 3-(diethyl-amino)-1-phenyl-2-(1-phenylethyl)naphtho[1,2-e][1,3,2]-oxazaphosporinine 3-sulfide (VI).

C22 C1

N

N2

C2

P1 C23 O1 S12

S1

P1 C23

C22 C1 N1 C2

N2

O1

Compound no. δP, ppm δН, ppm (C1H)

3JНР, Hz (P1N1C1H)

VА 67.43 5.82 27.1

VB 72.17 5.81 16.4

VIА 66.86 5.98 25.0

VIB 76.71 5.71 19.5

VIIIА 68.65 5.85 23.2

VIIIB 66.85 5.80 16.3

Some characteristic parameters of NMR spectra (CDCl3) of diastereomers of compounds V, VI, and VIII

PHOSPHORYLATION OF BETTI BASES


1575

and N1 (numeration of atoms see in the figure) are deviated from the plane to the same side by 0.9985(9) and 0.504(3) Å respectively. The location of substituents at the phosphorus atom is unlike that above described for diastereomer VIА: the diethylamino group occupies the equatorial, and sulfur atom, in the axial position.

We believe that the value of the torsion angle P1N1C1H is related to the spin-spin coupling constant 3JНР in a characteristic way since the atoms P

1, N1, C1 are a part of a conformationally rigid [1,3,2]oxaza-phosporinine ring with the planar naphthalene frag-ment, and the hydrogen atom at C1 is located in a pseu-doequatorial position due to the effect of 1,2-allylic strain. It is therefore presumable that the conformation of compounds in solution is not considerably different from that in the crystal. It proved that in diastereomer VIА the angle P1N1C1H was 158.79°, and in com-pound VIB, 120.33°, i.e., in compound VIА it was nearer to 180° (maximum coupling constant value according to Karplus), and therefore its constant 3JНР was larger than that of diastereomer VIB. Since in compound VIA the more bulky (compared with thione sulfur) di-ethylamino group is in the axial position whereas in di-astereomer VIB it is situated equatorially it is possible to conclude that the equatorial position of the diethyl-amino group in compound VIB results in the decrease in the torsion angle P1N1C1H. Hence, the comparison of 3JНР (P

1N1C1H) in NMR spectra may be probably applied to the analysis of the conformational and stereoisomeric composition of this type heterocycles.

To prepare the corresponding heterocycles with an alkoxy group at the phosphorus atom we used as initial compound -ethyl-N,N,N′,N′-tetraethyldiamidophos-phite. In the reaction of this compound with base I the substitution of two amino groups occurs under the same conditions as in reaction with hexaethyltriamido-phosphite, but in a longer time interval (16 instead 5 h). On completion of the reaction in the 31Р NMR spec-trum of the reaction mixture the signals of the dia-stereomeric pair VIIА and VIIB are observed at δP

119.04 and 127.57 ppm in the ratio 1 : 1.3. The treatment with elemental sulfur led to the formation of the corresponding diastereomeric sulfides VIIIА and VIIIB in the same ratio (Scheme 3). Analogous chemi-cal and stereochemical result was obtained under mil-der conditions at the use as the phosphorylating agent ethyl dichlorophosphite in the presence of triethyl-amine with the subsequent treatment with elemental sulfur (Scheme 2). We failed to isolate these dia-stereomers in a pure form. Therefore the oily compound VIII was characterized as diastereomers mixture by 1Н and 31Р NMR spectra and by elemental analysis.

By analogy with compounds V and VI and basing on the 3JНР values (see the table) it is presumeble that in the diastereomer VIIIА the ethoxy group is in the axial position as shows the larger value of 3JНР, whereas in diastereomer VIIIB this group occupies the equatorial position.

New phosphorus-containing six-membered hetero-cycles with a fragment of Betti base as the main chiral block are promising reagents for asymmetric organo-phosphorus synthesis.

EXPERIMENTAL

31Р NMR spectra were recorded on a Bruker AVANCE-500 (202.45 МHz) instrument, external re-ference 85% Н3РО4,

1Н NMR spectra, on a Bruker AVANCE-500 (500.13 МHz) instrument, relative to the signals of residual protons of the deuterated solvent (CDCl3). IR spectra were recorded on a Bruker Vector 22 Fourier spectrometer from pellets with KBr. ESI mea-surements were performed using an AmazonX mass spectrometer. As drying gas in the ion source nitrogen was used at 220°С, the voltage on the source was 4.5 kV. The solutions of samples were diluted with 2-propanol to the concentration ~10–3 mg/mL. The samples were injected using autosampler for the liquid chromatograph Agilent 1260 Infinity. Melting points were measured on a Boёtius melting point microscope.

Scheme 3.

N

O

*P

CH2Ph

OEt*

VII

S8, ΔN

O

*P

CH2Ph

OEt*

SNH

OH

* a: EtOP(NEt2)2, 5 mol% Et2NH HCl, Δ

CH2Ph

.

b: EtOPCl2, NEt3

I VIII



1-[α-(Benzylamino)benzyl]-2-naphthol (I) was syn-thesized by procedure [10]. (R,R/S,S)-1-[α-(1-Phenyl-ethylamino)benzyl]-2-naphthol (II) was prepared by the method described for the enantiomerically pure compound [11] and was recrystallized from ace-tonitrile.

(R,R/S,S)-1-[α-(1-Phenylethylamino)benzyl]-2-naphthol (II). Yield 62%, mp 141–142°С. IR spec-trum, ν, cm–1: 3318, 1620, 1600. 1Н NMR spectrum, δ, ppm: 1.53 d (3H, CH3,

3JНН 6.8 Hz), 2.32 br.s (1H, NH), 3.93 br.q (1H, PhCHMe, 3JНН 6.8 Hz), 5.49 s (1H, PhCH), 7.20–7.77 m (16HAr). Found, %: C 84.85; H 6.41; N 3.88. C25H23NO. Calculated, %: C 84.95; H 6.56; N 3.96.

(R,PR/S,PS)-2-Benzyl-3-(diethylamino)-1-phenyl-2,3-dihydro-1Н-naphtho[1,2-e][1,3,2]oxazaphos-phorinine 3-sulfide (VА). To a solution of 0.95 g (2.8 mmol) of compound I in 6 mL of anhydrous benzene was first added 0.015 g (5 mol%) of diethyl-amine hydrochloride, and then was added dropwise a solution of 0.693 g (2.8 mmol) of hexaethyltriami-dophosphite in 6 mL of anhydrous benzene. The obtained reaction mixture was kept at reflux and vigorous stirring under argon for 5 h (the reaction completion was indicated by the disappearance of the signal of initial hexaethyltriamidophosphite in the 31Р NMR spectrum of the reaction mixture). The solution was cooled and 0.09 g (2.8 mmol) of elemental sulfur was added, and the reaction mixture was kept at reflux and vigorous stirring for 2 h. The solution was cooled again and the solvent was removed in a vacuum. The residue was recrystallized from acetonitrile (15 mL). The first portion of crystals was filtered off and dried. Yield 0.38 g (29%), mp 193–195°С. IR spectrum, ν, cm–1: 1623, 1600, 1229, 1207, 1170, 1028, 692. 1Н NMR spectrum, δ, ppm: 1.10 t (6Н, NCH2CH3,

3JНН 7.0 Hz), 3.19–3.29 m (2Н, NCH2CH3, Н), 3.40–3.50 m (2Н, NCH2CH3, Н), 3.99 d.d (1Н, PhCH2, Н,

2JНН 15.7, 3JНР 2.7 Hz), 4.56 d.d (1Н, PhCH2, Н,

2JНН 15.7, 3JНР 10.4 Hz), 5.82 d (1Н, PhСН,

3JНР 27.1 Hz), 7.23–7.82 m (16НAr).

31P NMR spectrum, δ, ppm: 67.43. Mass spectrum: m/z 473.2 [M + H]+. Found, %: С 71.02; Н 6.29; N 5.81; P 6.71; S 6.59. С28Н29N2OPS. Calculated, %: С 71.16; Н 6.19; N 5.93; P 6.55; S 6.79.

(R,PS/S,PR)-2-Benzyl-3-(diethylamino)-1-phenyl-2,3-dihydro-1Н-naphtho[1,2-e][1,3,2]oxazaphos-phorinine 3-sulfide (VB). The mother liquor after separation of the first portion of crystals of diaste-

reomer VА was evaporated to the half of the initial volume. Some time later the second portion of crystals precipitated that was filtered off and dried. Yield 0.33 g (25%), mp 141–143°С. IR spectrum, ν, cm–1: 1624, 1600, 1229, 1207, 1170, 1031, 700. 1Н NMR spectrum, δ, ppm: 1.12 t (6Н, NCH2CH3,

3JНН 7.0 Hz), 3.12–3.22 m (2Н, NCH2CH3, Н), 3.29–3.39 m (2Н, NCH2CH3, Н), 3.95 d.d (1Н, PhCH2, Н,

2JНН 15.8, 3JНР 11.2 Hz),

4.65 d.d (1Н, PhCH2, Н, 2JНН 15.8,

3JНР 11.8 Hz), 5.81 d (1Н, PhСН, 3JНР 16.4 Hz), 7.23–7.88 m (16НAr).

31P NMR spectrum, δ, ppm: 72.17. Mass spectrum: m/z 473.2 [M + H]+. Found, %: С 71.04; Н 6.30; N 5.99; P 6.68; S 6.65. С28Н29N2OPS. Calcula-ted, %: С 71.16; Н 6.19; N 5.93; P 6.55; S 6.79.

(R,R,PR/S,S,PS)-3-(Diethylamino)-1-phenyl-2-(1-phenylethyl)-2,3-dihydro-1Н-naphtho[1,2-e][1,3,2]-oxazaphosporinine 3-sulfide (VIА) was obtained similarly to compound VА from 0.99 g (2.8 mmol) of (R,R/S,S)-1-[α-(1-phenylethylamino)benzyl]-2-naph-thol (II). Yield 0.35 g (26%), mp 216–218°С. IR spec-trum, ν, cm–1: 1625, 1599, 1225, 1205, 1170, 1022, 698. 1Н NMR spectrum, δ, ppm: 1.02 t (6Н, NCH2CH3, 3JНН 7.0 Hz), 1.57 d (3Н, CHCH3,

3JНН 7.1 Hz), 3.09–3.18 m (2Н, NCH2CH3, Н), 3.24–3.34 m (2Н, NCH2CH3, Н), 5.08 d.q (1Н, PhСНMe,

3JНH 7.1, 3JНР

9.6 Hz), 5.98 d (1Н, PhСН, 3JНР 25.0 Hz), 7.18–7.88 m (16НAr).

31P NMR spectrum, δ, ppm: 66.86. Mass spectrum: m/z 487.2 [M + H]+. Found, %: С 71.42; Н 6.54; N 5.80; P 6.56; S 6.47. С29Н31N2OPS. Calcu-lated, %: С 71.58; Н 6.42; N 5.76; P 6.37; S 6.59.

(R,R,PS/S,S,PR)-3-(Diethylamino)-1-phenyl-2-(1-phenylethyl)-2,3-dihydro-1Н-naphtho[1,2-e][1,3,2]-oxazaphosporinine 3-sulfide (VIB) was obtained similarly to compound VB. Yield 0.42 g (31%), mp 149–151°С. IR spectrum, ν, cm–1: 1625, 1600, 1226, 1205, 1172, 1020, 700. 1Н NMR spectrum, δ, ppm: 1.20 t (6Н, NCH2CH3,

3JНН 7.0 Hz), 1.52 d (3Н, CHCH3,

3JНН 7.1 Hz), 3.04–3.14 m (2Н, NCH2CH3, Н), 3.54–3.63 m (2Н, NCH2CH3, Н), 5.36 d.q (1Н, PhСНMe, 3JНH 7.1,

3JНР 13.4 Hz), 5.71 d (1Н, PhСН, 3JНР 19.5 Hz), 7.07–7.81 m (16НAr).

31P NMR spect-rum, δ, ppm: 76.71. Mass spectrum: m/z 487.2 [M + H]+. Found, %: С 71.46; Н 6.34; N 5.89; P 6.52; S 6.42. С29Н31N2OPS. Calculated, %: С 71.58; Н 6.42; N 5.76; P 6.37; S 6.59.

Mixture of (R,PS/S,PR)- and (R,PR/S,PS)-dia-stereomers of 2-benzyl-1-phenyl-3-ethoxy-2,3-di-hydro-1Н-naphtho[1,2-e][1,3,2]oxazaphosporinine 3-sulfide (VIII). . To a solution of 0.51 g (1.5 mmol) of

PHOSPHORYLATION OF BETTI BASES


1577

compound I in 3 mL of anhydrous benzene was first added 0.008 g (5 mol%) of diethylamine hydrochlo-ride, and then was added dropwise a solution of 0.33 g (1.5 mmol) of -ethyl-N,N,N′,N′-tetraethyldiamido-phosphite in 3 mL of anhydrous benzene. The reaction mixture was kept at reflux and vigorous stirring under argon for 16 h (the reaction completion was indicated by the disappearance of the signal of initial amidophosphite in the 31Р NMR spectrum of the reaction mixture). The solution was cooled and 0.048 g (1.5 mmol) of elemental sulfur was added, and the reaction mixture was kept at reflux and vigorous stirring for 2 h. The solution was cooled again and the solvent was removed in a vacuum. Then to the residue diethyl ether was added, and the solution was left standing for 24 h. The precipitate was filtered off, and the solvent was removed in a vacuum. Yield 0.54 g (81%), oily sub-stance, the mixture of diastereomers А and B, 1.3 : 1. 1Н NMR spectrum , δ, ppm: 1.11 t (OCH2CH3,

3JНН 7.0 Hz, А), 1.27 t (OCH2CH3, 3JНН

7.0 Hz, B), 3.77–3.88 m (OCH2CH3, Н, А), 3.95 d.d (PhCH2, Н,

2JНН 16.3, 3JНР 12.8 Hz, B), 4.09–4.33 m

[OCH2CH3, Н (А), Н + Н (B)], 4.43 d.d (PhCH2, НA, 2JНН 15.3,

3JНР 8.7 Hz, A), 5.00 d.d (PhCH2, НB,

2JНН 15.3, 3JНР 11.4 Hz, A), 5.06 d.d (PhCH2, Н

B, 2JНН 16.3, 3JНР 11.8 Hz, B), 5.80 d (PhСН,

3JНР 16.3 Hz, B), 5.85 d (PhСН, 3JНР 23.2 Hz, А), 7.12–7.91 m (НAr, А + B). 31P NMR spectrum, δ, ppm: 66.85 (Б), 68.65 (А). Found, %: С 70.37; Н 5.64; N 3.40; P 6.66; S 7.48. С26Н24NO2PS. Calculated, %: С 70.09; Н 5.43; N 3.14; P 6.95; S 7.20.

b. To a solution of 0.51 g (1.5 mmol) of compound I in 15 mL of anhydrous diethyl ether was added 0.334 g (3.3 mmol) of triethylamine in 5 mL of diethyl ether. The mixture was cooled on a cooling bath, and at vigorous stirring under argon was added a solution of 0.22 g (1.5 mmol) of ethyl dichlorophosphite in 5 mL of diethyl ether maintaining the rate of addition so that the temperature of the reaction mixture was below 5°С. The cooling was removed, the resulting suspension was stirred for 3 h more, the precipitate was filtered off, the solvent was removed in a vacuum. The formed oily residue was dissolved in 6 mL of anhydrous benzene, 0.048 g (1.5 mmol) of elemental sulfur was added. The solution obtained was kept at reflux and vigorous stirring for 2 h, cooled, and the solvent was removed in a vacuum. Yield 0.59 g (88%), oily subs-tance, the mixture of diastereomers А and B, 1.3 : 1.

X-ray diffraction study of crystals of dia-stereomers VIА and VIB was carried out on a diff-

ractometer Bruker SMART Apex II (graphite mono-chromator, λMoKα 0.71073 Å) at 293 K. Empirical absorption correction was performed using SADABS program [13]. The structure was solved by the direct methods applying program SHELXS [14]. Non-hydrogen atoms were refined first in isotropic, then in anisotropic approximation using the program SHELXL-97 [14]. Hydrogen atoms were placed in the calculated positions and refined in the rider model. All calculations were carried out using programs WinGX [15] and АРЕХ2 [16].

Crystals of diastereomer VIА monoclinic. C29H31N2OPS. At 20°С a 11.104(4), b 16.391(6), c 13.870(5) Å, β 92.415(6)°, V 2522.2(17) Å3, Z 4, dcalc 1.281 g/cm

3, space group P21/n, μМо 2.17 cm–1.

22471 reflections were measured, 3867 were observed with I 2σ. The final R-factors are R 0.0508, RW 0.1267.

Crystals of diastereomer VIB rhombic. C29H31N2OPS. At 20°С a 15.698(4), b 15.410(4), c 21.453(5) Å, V 5190(2) Å3, Z 8, dcalc 1.246 g/cm

3, space group Pbca, μМо 2.11 cm–1. 45632 reflections were measured, 2473 were observed with I 2σ. The final R-factors are R 0.0662, RW 0.2009.

CCDC 1013002 (VIА) and 1013001 (VIB) contain the supplementary crystallographic data for this paper. These data can be obtained free of charge via www.ccdc.cam.ac.uk/conts/retrieving.html (or Camb-ridge Crystallographic Data Center, 12 Union Road, Cambridge CB2 1EZ, UK; Fax: +44(1223)336-033, or: [email protected]).

This work was supported by the Russian Foun-dation for Basic Research (grant no. 11-03-00463-a).

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Phosphorylation of Betti bases