Chiral diphenylthiophosphoramides: A new class of chiral ligands for the silver(I)-promoted enantioselective allylation of aldehydes

Article abstract of DOI:10.1016/S0957-4166(99)00580-7

Chiral C₂-symmetric diphenylthiophosphoramides 1 and 2 were prepared in high yields from the reaction of diphenylthiophosphinic chloride with (1R,2R)-(-)-1,2-diaminocyclohexane and (1R,2R)-(+)-1,2-diphenylethylenediamine, respectively. Another novel chiral ligand 4 was prepared from reaction of diphenylthiophosphinic chloride with (R)-(+)-1,1'-binaphthyl-2,2'-diamine using butyllithium as a base. They were used as catalytic chiral ligands in the silver(I)-promoted enantioselective allylation reaction of aldehydes with allyltributyltin. Copyright (C) 2000 Elsevier Science Ltd.

Full text of DOI:10.1016/S0957-4166(99)00580-7

TETRAHEDRON:
ASYMMETRY
Pergamon
Tetrahedron: Asymmetry 11 (2000) 773–779
Chiral diphenylthiophosphoramides: a new class of chiral ligands
for the silver(I)-promoted enantioselective allylation of aldehydes
Min Shi a,∗ and Wen-Sheng Sui b
aLaboratory of Organometallic Chemistry, Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences,
354 Fenglin Lu, Shanghai 200032, China
bEast China University of Science and Technology, 130 Mei Long Lu, Shanghai 200237, China
Received 8 November 1999; accepted 6 December 1999
Abstract
Chiral C2-symmetric diphenylthiophosphoramides 1 and 2 were prepared in high yields from the reaction of
diphenylthiophosphinic chloride with (1R,2R)-(−)-1,2-diaminocyclohexane and (1R,2R)-(+)-1,2-diphenyl-
ethylenediamine, respectively. Another novel chiral ligand 4 was prepared from reaction of diphenyl-
thiophosphinic chloride with (R)-(+)-1,10-binaphthyl-2,20-diamine using butyllithium as a base. They were
used as catalytic chiral ligands in the silver(I)-promoted enantioselective allylation reaction of aldehydes with
allyltributyltin. © 2000 Elsevier Science Ltd. All rights reserved.
1. Introduction
Catalytic asymmetric synthesis is a valuable method for the preparation of optically active substances.1
In this context, the stereoselective addition of organometallics to one of the two heterotopic faces
of a carbonyl group has been extensively studied. In particular, the enantioselective allylation of
carbonyl compounds is a challenging problem in organic synthesis. Although numerous important
examples of the reaction using a stoichiomeric amount of chiral Lewis acids have been reported,2
there are only a few methods available for a catalytic process including chiral (acyloxy)borane (CAB)
complex/allylic silanes3 or allylic stannanes4 and binaphthol-derived chiral titanium complexes/allylic
stannanes.5 Recently Yamamoto reported a new catalytic enantioselective allylation reaction of aldehydes
with allyltributyltin using a BINAP·silver(I) complex as a catalyst.6 To the best of our knowledge, this
is the only case using a chiral silver(I) complex in a catalytic asymmetric reaction. This interesting
result prompted us to design and synthesize other chiral ligands which are suitable for making chiral
silver(I) complexes for catalytic asymmetric reactions. We wanted to try some chiral ligands containing
∗
Corresponding author. E-mail: mshi@pub.sioc.ac.cn
0957-4166/00/$ - see front matter © 2000 Elsevier Science Ltd. All rights reserved.
PII: S0957-4166(99)00580-7
tetasy 3214

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a sulfur atom because it is well known that sulfur can easily coordinate to various metals such as Co,
Cu and Zn giving stable chiral metal complexes.7 Based on this concept, we started to prepare the
chiral C2-symmetric diphenylthiophosphoramides 1 and 2 from (1R,2R)-(−)-1,2-diaminocyclohexane
and (1R,2R)-(+)-1,2-diphenylethylenediamine, respectively. Moreover, using (R)-(+)-1,10-binaphthyl-
2,20-diamine as a chiral scaffold we also prepared a novel chiral ligand 4. In this paper, we wish to
report the results using them as catalytic chiral ligands for silver(I)-promoted enantioselective allylation
reaction of various aldehydes with allyltributyltin.
2. Results and discussion
Diphenylthiophosphoramides 1 and 2 were synthesized from the reaction of diphenylthiophosphinic
chloride with (1R,2R)-(−)-1,2-diaminocyclohexane and (1S,2S)-(−)-1,2-diphenylethylenediamine, res-
pectively, in the presence of diisopropylethylamine in dichloromethane (Scheme 1). After usual workup
and purification by silica gel column chromatography or recrystallization, compounds 1 and 2 were
obtained as colorless solids in over 90% yield.8 In addition, using C2-symmetric (R)-(+)-1,10-binaphthyl-
2,20-diamine as a chiral scaffold, we tried to synthesize the novel chiral ligand 3. No reaction took place
between (R)-(+)-1,10-binaphthyl-2,20-diamine and diphenylthiophosphinic chloride using diisopropyle-
thylamine or triethylamine as a base in dichloromethane. Thus, we selected butyllithium as a base to
prepare the corresponding lithium amide and then react with diphenylthiophosphinic chloride (Scheme
2). This synthetic method was used for the preparation of (R)-2,20-bis(diphenylphosphinamino)-1,10-
binaphthyl.9 But surprisingly we found that the compound 4 was formed as the only product (Scheme
2). Namely, only one diphenylthiophosphinyl group could be introduced into the 1,10-binaphthyl-2,20-
diamine chiral scaffold. This may be due to the steric hindrance of the diphenylthiophosphinyl group.
Their structures were confirmed by spectral data and microanalysis. Moreover, the structures of 2 and
4 were established by X-ray analysis (Figs. 1 and 2).10 Interestingly, one dichloromethane molecule
was included into the crystal lattice of 2 during the recrystallization from dichloromethane.10 Those
chiral ligands were used for the silver(I)-promoted enantioselective allylation reaction of aldehydes with
allyltributyltin. The ees of the products were determined by HPLC analysis using a chiral stationary-
phase column (Chiralcel OD and OJ) and the absolute configuration of the major enantiomer was
assigned according to the sign of the specific rotation. Of silver(I) salts, silver(I) triflate is a good catalyst
for allylation of aldehydes, but the reaction is sluggish using AgNO3 and AgBF4. Utilizing 1 and 2 as
chiral ligands, the ees of sec-alcohol are very low in THF or dichloromethane. The results are shown in
Table 1. By means of the novel chiral ligand 4, the ee can reach 52% in THF and 50% in dichloromethane
at −20°C. In DMF, obviously the silver(I) complex decomposed with the precipitation of black solid. In
addition, if the reaction was carried out below −20°C, the reaction proceeded very slowly. The best
result is shown in Table 1, entry 4. By means of these optimized reaction conditions, various aldehydes
were used as substrates for this addition reaction and the corresponding sec-alcohol could be obtained in
65–85% yield and 54–63% ee with R-configuration. These results are summarized in Table 2. It should
be emphasized that the chiral phosphoramide ligands 1, 2 and 4 could be recovered from the reaction
mixture in 90% yield after usual workup and can be used again in the asymmetric reaction without loss
of enantioselectivity. Thus, the chiral phosphoramides 1, 2 and 4 are quite stable chiral ligands. For
chiral ligands 1 and 2, as expected the phosphoryl sulfur atoms can coordinate to the silver(I) metal
center to some extent giving a chiral environment, although the achieved ee is low. We also found that
this allylation reaction takes place only when the heteroatom on the phosphorus atom is sulfur; if it is an
oxygen or selenium atom no reaction occurs. This result strongly suggests that the coordination between

M. Shi, W.-S. Sui / Tetrahedron: Asymmetry 11 (2000) 773–779
775
the sulfur atom and silver(I) metal plays an important role in this reaction. Thus, we believe that chiral
ligand 4 is a bidentate chiral ligand, namely, the nitrogen and phosphoryl sulfur atoms can coordinate to
the silver(I) metal affording a chiral silver(I) Lewis acid. In order to verify this speculation, we attempted
to obtain a single crystal of the catalyst to confirm its structure. But despite extensive efforts, we could
not obtain a single crystal of chiral silver(I) complex which could be subjected to X-ray crystal analysis.
Scheme 1.
Scheme 2.
Fig. 1. The crystal structure of 2
In conclusion, the chiral bidentate phosphoramide 4 prepared from C2-symmetric (R)-(+)-1,10-
binaphthyl-2,20-diamine was found to be a new class of relatively effective chiral ligands for the silver(I)-
promoted enantioselective allylation reaction of aldehydes with allyltributyltin, although they are not as
effective as BINAP·silver(I) complex.6 This paper, for the first time, discloses that chiral phosphoryl
sulfide can catalyze the enantioselective allylation reaction using silver(I) salt. These results open a
new way to design and synthesize new chiral ligands for asymmetric reactions. Efforts are underway to
elucidate the mechanistic details of this addition reaction and to disclose the exact structure of the active
species. Moreover, we are planning to synthesize similar bidentate chiral phosphoramides embedded into
a C2-symmetric chiral scaffold in order to find more effective and stereoselective chiral ligands and to
utilize these novel chiral ligands with regard to other catalytic asymmetric reactions.

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M. Shi, W.-S. Sui / Tetrahedron: Asymmetry 11 (2000) 773–779
Fig. 2. The crystal structure of 4
Table 1
Enantioselective allylation reaction of benzaldehyde in the presence of chiral ligands 1, 2, 4 and
silver(I) triflate under different reaction conditions
3. Experimental
3.1. General
Melting points were obtained with a Yanagimoto micro melting point apparatus and remain uncor-
rected. Optical rotations were determined in a solution of CHCl3 at 20°C using a Perkin–Elmer 241
1
MC polarimeter; [α]D values are given in units of 10−1 deg cm2 g−1. H NMR spectra were recorded
on a Bruker AM-300 spectrometer for solution in CDCl3 with tetramethylsilane (TMS) as internal
standard; J values are given in hertz. Mass spectra were recorded with an HP-5989 instrument and
HRMS was measured using a Finnigan MA+ mass spectrometer. The organic solvents used were dried
by standard methods when necessary. All solid compounds reported in this paper gave satisfactory CHN
microanalyses with an Italian Carlo–Erba 1106 analyzer. Commercially obtained reagents were used
without further purification. All reactions were monitored by TLC with Huanghai 60F254 silica gel
coated plates. Flash column chromatography was carried out using 300–400 mesh silica gel at increased
pressure. All allylation experiments were performed under argon using standard Schlenk techniques.
The enantiomeric excesses of sec-alcohols were determined by HPLC analysis using a chiral stationary
phase column (column, Daicel Co. Chiralcel OD and OJ; eluent, 100:0.5 2 hexane:2-propanol mixture;

M. Shi, W.-S. Sui / Tetrahedron: Asymmetry 11 (2000) 773–779
777
Table 2
Enantioselective allylation reaction of aldehyde in the presence of chiral ligand 4 and silver(I) triflate
under different reaction conditions
flow rate, 1.0 ml min−1; detection, 254 nm light) and the absolute configuration of the major enantiomer
was assigned according to the sign of the specific rotation. The preparation of chiral ligand 1 has been
reported previously.8
3.2. Preparation of chiral phosphoramide 2
To a solution of (1S,2S)-(−)-1,2-diphenylethylenediamine (214 mg, 1.0 mmol) and triethylamine (300
mg, 3.0 mmol, 0.42 ml) in dichloromethane (20 ml) was added diphenylthiophosphinic chloride (504
mg, 2.0 mmol) at 0°C. After stirring of the reaction mixture for 10 h, the solvent was removed under
reduced pressure. The crude product was extracted with ether and washed with water (3×50 ml), 10%
Na2CO3 (50 ml) and brine. The organic layer was dried over anhydrous Na2SO4 and then evaporated
under reduced pressure. The residue was recrystallized from dichloromethane and hexane (4:1) to give
2 as colorless crystals (680 mg, 95%). Mp 178–180°C (dec.); [α]D −63.4 (c 1.16, CHCl3); δH (CDCl3)
4.40–4.65 (2H, m, CH), 5.56–5.76 (2H, m, NH), 6.80–6.95 (4H, dd, J 7.4, 1.3 Hz, Ar), 7.0–7.20 (8H, m,
Ar), 7.24–7.50 (10H, m, Ar), 7.55–7.75 (4H, m, Ar), 7.75–8.0 (4H, m, Ar); MS (EI) m/z (%) 645 (MH+,
10.3), 322 (100), 290 (4.7), 217 (97.7), 139 (46.4); [found: C, 64.17; H, 4.90; N, 3.80%. HRMS (EI) m/z
644.1628 (M+); C38H34N2S2P2·CH2Cl2 requires: C, 64.19; H, 4.97; N, 3.84%; M, 644.1639].
3.3. Preparation of chiral thiophosphoramide 4
To a solution of (R)-(+)-1,10-binaphthyl-2,20-diamine (148 mg, 0.5 mmol) in THF (10 ml) was added
dropwise 2.0 M n-butyllithium in cyclohexane (0.70 ml, 1.4 mmol) at −40°C over 40 min and the reaction
mixture was stirred for 1 h. Then diphenylthiophosphinic chloride (440 mg, 1.8 mmol, 0.344 ml) was
added dropwise and the reaction solution was stirred for a further 10 h at −40°C to room temperature.
The mixture was filtered to remove the solid and the THF was removed under reduced pressure. The
organic product was extracted with ether and the organic layer was washed with water, 10% Na2CO3 and
brine. The extract was dried over MgSO4 and then evaporated under reduced pressure. The residue was

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M. Shi, W.-S. Sui / Tetrahedron: Asymmetry 11 (2000) 773–779
purified by alumina (Al2O3) column chromatography to give the compound 4 as a colorless solid (264
mg, 97%). Mp 80–81°C (dec.); [α]D −4.4 (c 1.20, CHCl3); δH (CDCl3) 4.10 (2H, s, br., NH2), 5.12 (1H,
d, J 7.4 Hz), 7.0–7.50 (10H, m, Ar), 7.50–7.70 (4H, m, Ar), 7.70–8.0 (8H, m, Ar); MS (EI) m/z (%) 500
(M+, 3.6), 559 (0.6), 467 (100), 371 (0.7); [found: C, 76.65; H, 5.07; N, 5.74%. HRMS (EI) m/z 500.1458
(M+). C32H25N2PS requires: C, 76.78; H, 5.03; N, 5.60%; M, 500.1467].
3.4. Typical reaction procedure
To a solution of phosphoramide 4 (50.0 mg, 0.1 mmol) and AgOTf (25.7 mg, 0.1 mmol) in THF (2
ml) was added benzaldehyde (53 mg, 0.5 mmol, 50 µl) at room temperature. After stirring the reaction
mixture for 0.5 h, allyltributyltin (199 mg, 0.6 mmol, 186 µl) was added into the reaction solution at
−20°C and the reaction mixture was stirred at −20°C for 8 h. The reaction was quenched by a mixture of
15% aq. HCl (5 ml) and solid KF (1 g) at ambient temperature for 30 min. The resulting precipitate was
filtered off, and the filtrate was dried over MgSO4 and then concentrated under reduced pressure. The
residue was purified by silica gel column chromatography to give the homoallylic alcohol as a colorless
oil (52 mg, 70%).
Acknowledgements
We thank Professor Albert S. C. Chan and the National Natural Sciences Foundation of China
for financial support. We also thank the Inoue Photochirogenesis Project (ERATO, JST) for chemical
reagents.
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10. (a) The crystal data of 2. Empirical formula: C39H36N2S2P2Cl2; formula weight: 729.70; crystal color, habit: colorless,
prismatic; crystal dimensions: 0.20×0.20×0.30 mm; crystal system: orthorhombic; lattice type: primitive; lattice parameters:
a=19.715(2) Å, b=20.071(2) Å, c=9.453(1) Å, V=3740.6(7) Å3; Space group: P212121(#19); Z value=4; Dcalcd=1.296 g cm−3
F000=1520.00; µ(MoKα)=4.01 cm−1; diffractometer: Rigaku AFC7R; temperature: 20°C; scan type: ω-2θ.
;
(b) The crystal data of 4. Empirical formula: C32H25N2SP; formula weight: 500.60; crystal color, habit: colorless, prismatic;
crystal dimensions: 0.20×0.20×0.30 mm; crystal system: monoclinic; lattice type: primitive; lattice parameters: a=9.267(4)
Å, b=14.554(3) Å, c=10.404(2) Å, β=113.04(3)°, V=1291.2(9) Å3; space group: P21(#4); Z value=2; Dcalcd=1.288 g cm−3
F000=524.00; µ(MoKα)=2.11 cm−1; diffractometer: Rigaku AFC7R; temperature: 20°C; scan type: ω-2θ.
;