The first pincer-type phosphodiamidite ligand containing chiral phosphorus atoms

Full text of DOI:10.1007/s11172-009-0176-2

Russian Chemical Bulletin, International Edition, Vol. 58, No. 6, pp. 1325—1327, June, 2009
1325
Letters to the Editor
The first pincerꢀtype phosphodiamidite ligand containing
chiral phosphorus atoms
K. N. Gavrilov,a E. A. Rastorguev,a A. A. Shiryaev,a T. B. Grishina,a
A. S. Safronov,b S. E. Lyubimov,b and V. A. Davankovb
aS. A. Esenin Ryazan State University,
46 ul. Svobody, 390000 Ryazan, Russian Federation.
Fax: +7 (491 2) 77 5498. Eꢀmail: k.gavrilov@rsu.edu.ru
bA. N. Nesmeyanov Institute of Organoelement Compounds, Russian Academy of Sciences,
28 ul. Vavilova, 119991 Moscow, Russian Federation.
Fax: +7 (499) 135 6471. Eꢀmail: lssp452@mail.ru
Chiral phosphite ligands that form pincerꢀtype metal
complexes are an interesting group of stereoselectors for
asymmetric catalysis.1—4 Besides, the known ligands of
this type are phosphites (PO3) and phosphoamidites
(PO2N) according to the structure of the phosphorus cenꢀ
ters,1—8 while their phosphodiamidite analogs (PON2)
have not been described. It should also be noted that
no examples of the use of the pincerꢀtype ligands with
P*ꢀstereogenic centers in the catalytic processes have
been published. We synthesized bis(phosphodiamidite) 1
bearing the stereogenic phosphorus atoms by oneꢀstep
phosphorylation of resorcinol (Scheme 1). Ligand 1
is homochiral, since only single narrow signal at δ 124.1 is
observed in the 31Р NMR spectrum (CDCl3). The stereoꢀ
genic centers of compound 1 have Rꢀconfiguration, which
was assigned from the 13C NMR spectrum judging by the
large coupling constant value 2JC(8),P = 35.1 Hz (see Ref.9,10
and references cited therein). It is also worth mentioning
that compound 1 is stable in air and can be stored for a
long time in dry atmosphere.
Scheme 1
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1288—1290, June, 2009.
1066ꢀ5285/09/5806ꢀ1325 © 2009 Springer Science+Business Media, Inc.

1326
Russ.Chem.Bull., Int.Ed., Vol. 58, No. 6, June, 2009
Gavrilov et al.
To estimate stereodifferentiating ability of ligand 1 a
test reaction of Pdꢀcatalyzed enantioselective allylic
sulfonylation of (E)ꢀ1,3ꢀdiphenylpropꢀ2ꢀenyl acetate 2a
and (E)ꢀ1,3ꢀdiphenylpropꢀ2ꢀenyl ethyl carbonate 2b was
used (Scheme 2, route a, Table 1). In the case of substrate
2a, product 3 was obtained with 72—80% ee (Table 1,
entries 1—3). The virtually identical asymmetric inducꢀ
tion was observed for two different sources of palladium,
however in the case of the latter the yield of the product 3
is substantially lower (entry 3). At the same time, the use
of 2b as the starting substrate resulted in allylic sulfone
(R)ꢀ3 in nearly quantitative chemical yield and stereoꢀ
chemical outcome (Table 1, entry 4).
Bis(phosphodiamidite) 1 is a promising stereoselector,
its further application for the asymmetric catalysis is studꢀ
ied in our laboratories.
All reactions were carried out in anhydrous solvents under
1
dry argon. 31P, H and 13C NMR spectra were recorded on a
Bruker AMXꢀ400 spectrometer (161.98, 400.13 and 100.61 MHz)
relative to 85% Н3РО4 in D2О and Me4Si, respectively. The
signals in the 13C NMR spectra were assigned using the DEPT
technique. Mass spectra with electron impact ionization were
measured on a Varian MATꢀ311 mass spectrometer (EI, 70 eV),
mass spectra with electrospray ionization (ESI) were recorded
on a Finnigan LCQ Advantage instrument. Elemental analysis
was carried out at the Laboratory of Organic Microanalysis of
the A. N. Nesmeyanov Institute of Organoelement Compounds,
Russian Academy of Sciences. The phosphorylating reagent,
(2R,5S)ꢀ2ꢀchloroꢀ3ꢀphenylꢀ1,3ꢀdiazaꢀ2ꢀphosphabicyclo[3.3.0]ꢀ
octane was synthesized according to the known procedure.9 The
catalytic experiments on asymmetric sulfonylation of substrates
2a,b and on deracemization of substrate 2b, determination of
the conversion of 2b and of the enantiomeric excesses in products
3 and 4 (HPLC, chiral columns (R,R)ꢀWHELKꢀ01 and Daicel
Chiralcel ODꢀH) were carried out by the known procedures.9,12
The starting substrates (E)ꢀ1,3ꢀdiphenylpropꢀ2ꢀenyl acetate 2a
and (E)ꢀ1,3ꢀdiphenylpropꢀ2ꢀenyl ethyl carbonate 2b, as well as
the starting complexes [Pd(allyl)Cl]2 and [Pd2(dba)3]•CHCl3
were synthesized by the known procedures.13—15 Resorcinol,
sodium pꢀtoluenesulfinite, and tetrabutylammonium hydrogen
sulfate are commercial reagents (Aldrich).
Scheme 2
1,3ꢀBis[(2R,5S)ꢀ3ꢀphenylꢀ1,3ꢀdiazaꢀ2ꢀphosphabicycloꢀ
[3.3.0]octyloxy]benzene (1). To a solution of (2R,5S)ꢀ2ꢀchloroꢀ
3ꢀphenylꢀ1,3ꢀdiazaꢀ2ꢀphosphabicyclo[3.3.0]octane (2.41 g,
10 mmol) and Et3N (1.53 mL, 11 mmol) in 30 mL of toluene, a
solution of resorcinol (0.55 g, 5 mmol) in 15 mL of toluene was
added dropwise over a period of 20 min with vigorous stirring.
The resulted mixture was refluxed for 10 min and cooled to
room temperature, then Et3N•HCl was filtered off, the filtrate
was concentrated in vacuo (40 Torr). After purification by silica
gel column chromatography using hexane—ethyl acetate, 5 : 1
as the eluent, compound 1 was obtained (1.81 g, 70%) as a white
powder, m.p. 112—114 °C. Rf 0.55 (hexane—ethyl acetate, 5 : 1).
Found (%): C, 65.01; H, 6.28; N, 10.68. C28H32N4O2P2.
Calculated (%): C, 64.86; H, 6.22; N, 10.80. 1H NMR (CDCl3)
δ: 1.58 (dq, 2 H, J = 11.4 Hz, J = 6.8 Hz); 1.85 (m, 4 H); 1.95
(dq, 2 H, J = 11.4 Hz); 3.15 (m, 2 H); 3.25 (m, 2 H); 3.46 (dd,
2 H, J = 8.7 Hz, J = 6.5 Hz); 3.64 (m, 2 H); 3.74 (q, 2 H,
J = 6.5 Hz); 6.63 (m, 3 H); 6.93 (br.t, 2 H, J = 9.8 Hz); 7.08
(m, 4 H); 7.31 (m, 5 H). 13С NMR (CDCl3) δ: 26.2 (d, С(7´),
3J = 4.4 Hz); 31.6 (s, C(6´)); 47.7 (d, С(8´), 2J = 35.1 Hz); 53.7
(d, С(4´), 2J = 7.7 Hz); 62.5 (d, С(5´), 2J = 8.8 Hz); 115.0
a. 4ꢀMeC H SO Na, THF, catalyst; b. NaHCO , Bu NHSO ,
6
4
2
3
4
4
CH Cl , catalyst. X = Ac (2a), CO Et (2b)
2
2
2
Ligand 1 was also involved in an important Pdꢀcataꢀ
lyzed deracemization reaction of compound 2b (Scheme
2, route b) opening the access to valuable optically active
allylic alcohols, including chalcol 4.11 Traditionally, the
deracemization of allylic esters have been carried out in
CH2Cl2—H2O (9 : 1),11 however we applied the original
procedure12 and carried out the reaction in anhydrous
CH2Cl2. This allowed excluding the ester hydrolysis step
from a catalytic cycle and the use of moistureꢀsensitive
phosphorusꢀcontaining ligands. Under these conditions,
the catalytic system [Pd(allyl)Cl]2/2L (L = 1) provided
good conversion of 2b (81%) and enantiomeric excess of
(R)ꢀ4 (80%).
3
3
Table 1. The data of the Pdꢀcatalyzed allylic sulfonylation of
substrates 2a,b with sodium pꢀtoluenesufinite (THF, 20 °C, 48 h).
(d, CHAr, J = 12.6 Hz); 115.5 (d, CHAr, J = 4.9 Hz); 116.5
(d, CHAr
3J = 4.4 Hz); 119.0 (s, CHAr); 128.8 (s, CHAr);
129.0 (s, CHAr); 145.1 (d, CAr ,
2J = 15.4Hz); 154.2 (d, CAr
,
,
2J = 3.8 Hz). MS (EI), m/z (Irel (%)): 519 [M]+ (9), 205
[C10H15N2P]+ (100). MS (ESI), m/z (Irel (%)): 519 [M]+ (100),
205 [C10H15N2P]+ (37).
Entry Subꢀ
strate
Precatalyst
L/Pd Yield
(%)
ee
(%)
1
2
3
4
2a
2a
[Pd(allyl)Cl]2
[Pd(allyl)Cl]2
1
2
1.5
2
93 72 (R)
92 80 (R)
40 72 (R)
97 99 (R)
This work was financially supported by INTAS (Grant
05ꢀ1000008ꢀ8064) and the Russian Foundation for Basic
Research (Project 08ꢀ03ꢀ00416ꢀa).
2a [Pd2(dba)3].CHCl3
2b
[Pd(allyl)Cl]2

Pincerꢀtype phosphodiamidite ligand
Russ.Chem.Bull., Int.Ed., Vol. 58, No. 6, June, 2009
1327
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Received November 10, 2008;
in revised form March12, 2009