Novel C2-symmetric chiral ligands: enantioselective transformation of cyclic 1,2-diols into 1,2-bis(phenylsulfenyl) and 1,2-bis(phenylselenyl) derivatives

Article abstract of DOI:10.1016/j.tetasy.2008.02.001

Chiral C₂-symmetric S,S- and Se,Se-donating ligands as well as the C₁ mixed S,Se-donating ligands were prepared from optically active 1,2-cyclohexanediol and 1,2-cyclopentanediol via the respective S_N2 reactions. The bis(chalcogen) ligands obtained effectively catalyze the asymmetric allylic alkylation with enantioselectivities of up to 50% ee.

Full text of DOI:10.1016/j.tetasy.2008.02.001

Available online at www.sciencedirect.com
Tetrahedron: Asymmetry 19 (2008) 593–597
Novel C2-symmetric chiral ligands: enantioselective transformation
of cyclic 1,2-diols into 1,2-bis(phenylsulfenyl) and
1,2-bis(phenylselenyl) derivatives
*
_
´
_
Elzbieta Wojaczynska and Jacek Skarzewski
Department of Organic Chemistry, Faculty Chemistry, Wrocław University of Technology, 50-370 Wrocław, Poland
Received 23 December 2007; accepted 1 February 2008
Available online 4 March 2008
Abstract—Chiral C2-symmetric S,S- and Se,Se-donating ligands as well as the C1 mixed S,Se-donating ligands were prepared from opti-
cally active 1,2-cyclohexanediol and 1,2-cyclopentanediol via the respective SN2 reactions. The bis(chalcogen) ligands obtained effectively
catalyze the asymmetric allylic alkylation with enantioselectivities of up to 50% ee.
Ó 2008 Elsevier Ltd. All rights reserved.
1. Introduction
sulfur–selenium donor five- and six-membered cyclic
ligands and their use in the AAA reaction.
Chiral chelating ligands with both nitrogen- and phospho-
rus-donating atoms are regarded as the most effective cat-
alysts in various transition-metal catalyzed asymmetric
reactions.1 Generally, chiral C2-symmetric derivatives with
a rigid, cyclic structure constitute the best ligands, such as
trans-1,2-diaminocyclohexane derivatives.2 Recently, sul-
fur- and selenium-donating ligands have also been devel-
oped with much success.3 In particular, hetero-donating
C1-symmetric chalcogen/nitrogen and chalcogen/phospho-
rous ligands have performed well in the Pd-catalyzed asym-
metric allylic alkylation (AAA) due to the trans-effect
additionally stereodifferentiating the intermediate Pd-com-
plex.4 On the other hand, a few C2-symmetric homo-donat-
ing sulfur ligands have already been tested, in some cases
even outperforming others in catalytic activity.5 This has
stimulated interest in the synthesis of new compounds of
this type.6 Within our program to explore the preparation
and use of chiral organochalcogen compounds in
asymmetric catalysis, we have synthesized optically active
1,2-bis(phenylsulfenyl)cyclopentane and its heterocyclic
analogues.7 However, when we attempted to obtain the
corresponding chiral vic-cyclohexane derivative, simple
synthetic methods failed.7a Herein, we report the successful
preparation of the sulfur–sulfur, selenium–selenium, and
2. Results and discussion
Commercially available trans-diols: 1,2-cyclopentanediol 1
and 1,2-cyclohexanediol 2 were chosen as substrates for the
title transformations. It should be noted that attempted
substitution of the corresponding bis-sulfonyl esters gave
a complex mixture. Thus, we introduced phenylsulfenyl
group into these molecules using the Hata reaction.7,8 As
we reported previously, the nucleophilic substitution of
enantiomerically pure (1R,2R)-1 with (PhS)2/Bu3P in
benzene gave exclusively (1S,2S)-bis(phenylsulfenyl)cyclo-
pentane 3; both de and ee exceeded 95%.7 However, the
corresponding reaction of (S,S)-1,2-cyclohexanediol
resulted in a mixture containing 1,2-bis(phenylsulfenyl)-
cyclohexane 4 (42% yield) along with the elimination
side-products and butyl phenyl sulfide. The disubstituted
product obtained was mainly trans-4 (83% de), containing
also the cis-meso-isomer (by GC/MS), and was consider-
ably racemized (22% ee by chiral HPLC).7a The reasons
for this outcome have already been discussed there.7a The
reaction of (1R,2R)-2 with 6 equiv of (PhS)2/Bu3P in tolu-
ene yielded bis(phenylsulfenyl)cyclohexane 4, still formed
as a diastereomeric mixture (Scheme 1).
*
However, when we treated (1R,2R)-2 with 3 equiv of
Corresponding author. Tel.: +48 71 320 2464; fax: +48 71 328 4064;
e-mail: jacek.skarzewski@pwr.wroc.pl
(PhS)2/Bu3P, the nucleophilic substitution of one hydroxy
0957-4166/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetasy.2008.02.001

594
E. Wojaczyn´ska, J. Skarz_ewski / Tetrahedron: Asymmetry 19 (2008) 593–597
SPh
SPh
OH
OH
(PhS)2, Bu3P
Ref. 7a
(1S,2S)-1
(1R,2R)-3
OH
OH
SPh
(PhS)2 (6 eq.)
Bu3P
SPh
(1R,2R)-2
(1R,2R)-2
4 72%, 62% de, 50% ee
SPh
(PhS)2 (3 eq.)
Bu3P
OH
(1R,2S)-5
OH
SePh
OH
SePh
SePh
PhSeCN, Bu3P
PhSeCN, Bu3P
+
OH
(1S,2R)-6
(1S,2S)-1
(1R,2R)-7
SePh
SePh
SePh
OH
(1R,2R)-2
+
(1S,2S)-9
(1R,2S)-8
SePh
SPh
SPh
(PhS)2 (6 eq.)
Bu3P
(PhS)2 (3 eq.)
Bu3P
(1R,2S)-5
(1R,2S)-8
SPh
(1S,2S)-10
(1S,2S)-4
S
SC OPr-i
(i-PrO-C(S)S-)2
(1R,2R)-2
Bu3P
OH
(1S,2R)-11
Scheme 1.
group proceeded in a highly stereoselective manner and
furnished cis-(1R,2S)-2-phenylsulfenylcyclohexanol 5 in
34% yield and >95% ee. Recently, this enantiomeric prod-
uct has also been obtained via bromomandelation of
cyclohexene.9
cis-(1R,2S)-5 was submitted to a Hata reaction with
6 equiv of (PhS)2/Bu3P, the desired (1S,2S)-bis(phenyl-
sulfenyl)cyclohexane 4 (80% yield, >95% ee) was formed.
Apparently, the Hata reaction of 2 should be conducted
in a two-step manner, while the isolation of monosub-
stituted product is required to achieve complete stereo-
selectivity.
We were also interested in the preparation of the corres-
ponding 1,2-bis(phenylselenyl) derivatives. Thus, (1S,2S)-
trans-1,2-cyclopentanediol
1
reacted smoothly with
Moreover, facing failures in our earlier substitution exper-
iments,7a we have separately developed a protocol for the
resolution of racemic 1,2-bis(phenylsulfenyl)cyclohexane
4, comprising of an enantioselective sulfoxidation, separa-
tion of diastereomeric bissulfoxides, and subsequent deox-
ygenation of pure diastereomers.11 The product proved to
be identical to that obtained via the two-step substitution
procedure.
PhSeCN/Bu3P according to Grieco protocol10 and stereo-
selectively gave both, mono- 6 (37%) and bis-substituted
7 (43%) products (>98% de, >95% ee).
Surprisingly, under similar reaction conditions, also both
mono-8 (25%) and bis-phenylselenyl cyclohexane deriva-
tives
9 (23%) were obtained from (1R,2R)-2 and
PhSeCN/Bu3P with a de and ee exceeding 97%.
We then tested the influence of sulfur nucleophiles on the
reactivity and stereoselectivity of substitution of hydroxy
groups in (1R,2R)-1,2-cyclohexanediol 2. When we used
6 equiv of isopropylxanthicdisulfide in a Hata reaction,
we observed the formation of (1S,2R) O-isopropyl-S-(2-
hydroxycyclohexyl) dithiocarbonate 11, that is, the mono-
substitution product, as a single enantiomer. Identical
results were obtained when 3 equiv of the reagents was
used. Another independent attempts with sulfur nucleo-
Additionally, when (1R,2S)-2-phenylselenylcyclohexanol 8
was treated with 3 equiv of (PhS)2/Bu3P, it was converted
to the mixed sulfide–selenide derivative (1S,2S)-1-phenyl-
sulfanyl-2-phenylselenylcyclohexane 10 with complete
inversion of configuration at the 1-C atom (42% yield).
These outcomes prompted us to examine a similar reaction
with the mono-phenylsulfenyl derivative 5. When this pure

E. Wojaczyn´ska, J. Skarz_ewski / Tetrahedron: Asymmetry 19 (2008) 593–597
595
H2C(CO2Me)2, BSA (3 eq.), AcOK (3 mol%)
Ph
Ph
Ph
*
Ph
OAc
Pd2(C3H5)2Cl2 (2.5 mol%), Ligand (10 mol%)
CH3CN, r.t.
MeO2C
CO2Me
Scheme 2.
philes, namely diethyl dithiophosphate (EtO)2P(S)SH and
potassium thiocyanate, under Mitsunobu reaction condi-
tions were unsuccessful and led to the complete recovery
of unreacted substrate.
3. Conclusions
In conclusion, the successful enantioselective displacement
of one hydroxy group in enantiomeric trans-1,2-cyclo-
pentanediol and trans-1,2-cyclohexanediol leading to the
corresponding cis-2-phenylchalcogen cyclic alcohols opens
up a route for the synthesis of a series of chiral homo- and
hetero-donor ligands. Accordingly, chiral C2-symmetric
S,S- and Se,Se-donating ligands and the C1 mixed S,
Se-donating one were easily prepared. The asymmetric
allylic alkylation was effectively catalyzed by these
compounds; however, the obtained enantioselectivities
were rather moderate. Further applications of the obtained
compounds in asymmetric reactions are currently under
investigation.
Thus, as yet, the stereoselective introduction of two sulfhy-
dryl groups into trans–vic-cyclohexane positions could not
be accomplished. Nevertheless, the enantiomeric mono-
chalcogen-functionalized cyclic alcohols obtained 5, 6, 8,
and 11 offer various possibilities for further transforma-
tions into interesting chiral building blocks and ligands.
Next, we tested enantiomerically pure sulfides and selenides
3, 4, 7, 9, and 10 as ligands in the Pd-catalyzed allylic sub-
stitution reaction (AAA reaction, Scheme 2).4 The results
obtained for the reaction of dimethyl malonate with rac-
1,3-diphenyl-2-propenyl acetate, using 3 mol % of N,O-
bis(trimethylsilyl)acetamide-potassium acetate as a base,
2.5 mol % of [Pd(g3-C3H5)Cl]2, and 10 mol % chiral ligand
in acetonitrile solution, are collected in Table 1. The reac-
tion yield documents palladium complexation to the
ligands, because in the absence of ligands no reaction
occurs. The moderate enantioselectivities observed are in
agreement with the fact that metal complexation to sulfur
makes these donors stereogenic, and even in the case of
C2-symmetric S,S-donating ligands multiply the number
of diastereomeric complexes that can be formed. More-
over, these stereogenic centers can rapidly epimerize. It is
noteworthy that the softer selenium donors performed bet-
ter than their sulfur analogues. In both the cases, the same
type of complexed species prevail since the same sense of
stereoinduction (configuration of product vs configuration
of ligand) was observed.
4. Experimental
4.1. General
Melting points were determined using a Boetius hot-stage
apparatus and are uncorrected. IR spectra were recorded
on a Perkin Elmer 1600 FTIR spectrophotometer. 1H
and 13C NMR spectra were measured on a Bruker CPX
(1H, 300 MHz) or a Bruker Avance (1H, 500 MHz) spec-
trometer using TMS as an internal standard. 77Se NMR
spectra were recorded at 115 MHz on a Bruker Avance
spectrometer using dimethyl selenide as an external stan-
dard. Optical rotations were measured using an Optical
Activity Ltd, Model AA-5 automatic polarimeter. High
resolution mass spectra were recorded using a microTOF-
Q instrument utilizing electrospray ionization mode. Sepa-
rations of products by chromatography were performed on
Silica Gel 60 (230–400 mesh) purchased from Merck. Thin
layer chromatography analyses were performed using Silica
Gel 60 precoated plates (Merck). HPLC measurements
were performed on a Knauer HPLC Pump 64 using a
Knauer Variable Wavelength Monitor and CHIRACEL
OD-H column.
Table 1. Pd-catalyzed alkylation of dimethyl malonate with 1,3-diphenyl-
2-propenyl acetate in the presence of S,S-, S,Se-, and Se,Se-donating
ligandsa
Entry Ligand
Yield (%) ee (%) Configuration of product
1b
2
3
4
(1R,2R)-3
68
88
92
90
90
42
42
30
34
50
(À)-(S)
(À)-(S)
(+)-(R)
(+)-(R)
(+)-(R)
(1R,2R)-7
(1S,2S)-4
(1S,2S)-10
(1S,2S)-9
4.2. Preparation of sulfides
5
Tributylphosphine (3.2 mmol, 0.65 g, 0.80 mL) was added
via syringe to a solution of diol 2 (0.8 mmol) and diphenyl-
disulfide (2.4 mmol, 0.52 g) in dry toluene. The mixture was
transferred to an ampoule, filled with argon and sealed.
This reaction mixture was kept at the at 80 °C in an oil
for three days. Diethyl ether (20 mL) was added to the
cooled solution, the organic layer was washed with 10%
aqueous NaOH, water, and brine, and dried over
anhydrous Na2SO4. The solvent was evaporated and the
monosubstituted product 5 was purified by column
a For the catalytic procedure and product analysis, see Ref. 7b.
b The results for entry 1 were taken from Ref. 7b.
Additionally, the results obtained seem to support our ear-
lier conclusions concerning the catalytic performance of
3,4-bis(phenylsulfenyl)pyrrolidines. Those ligands gave in
the same reaction with up to 90% ee, thus acting rather
as N,S- other than S,S-donors.7b

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E. Wojaczyn´ska, J. Skarz_ewski / Tetrahedron: Asymmetry 19 (2008) 593–597
chromatography. This compound was converted to bissul-
fide 4 using a similar procedure, using 0.48 mmol (0.1 g) of
5, 3.84 mmol of tributylphosphine, and 2.88 mmol of
diphenyldisulfide.
2.47 (m, 2H, cyclopentane ring), 3.75–3.77 (m, 2H, CHSe),
7.16–7.36 (m, 10H, ArH); 13C NMR (CDCl3): d 23.8 (C-4),
31.5 (C-3, C-5), 49.4 (C-1,C-2), 127.7, 129.5, 129.6, 134.5;
77Se NMR (CDCl3): d 401.4. Anal. Calcd for C17H18Se2:
C, 53.70; H, 4.77. Found: C, 53.64; H, 4.85. Rf 0.68 (hex-
ane/ethyl acetate = 9:1).
4.2.1. (1S,2S)-1,2-Bis(phenylsulfenyl)cyclohexane 4. Yield
80%. [a]D = +120.0 (c 2.20, CH2Cl2) >95% ee. Spectral
characteristics in agreement with those described for the
less enantioenriched product 4.7a
4.3.3. (1R,2S)-2-Phenylselenylcyclohexanol 8. Yield 25%,
de = 100%. [a]D = À8.3 (c 1.08, CH2Cl2) >95% ee. IR-
(film): 3445, 2933, 2855, 1578, 1477, 1437, 991, 739,
1
4.2.2. (1R,2S)-2-Phenylsulfenylcyclohexanol 5. Yield 34%.
Mp = 48–49 °C; [a]D = À23.0 (c 1.04, CH2Cl2), >95% ee,
lit. [a]D = À25.2 (c 1.15, CHCl3).9 IR (KBr): 3404, 2916,
692 cmÀ1. H NMR (300 MHz, CDCl3): d 1.29–1.33 (m,
2H, cyclohexane ring), 1.53–1.86 (m, 6H, cyclohexane
ring), 2.36–2.37 (d, 1H, J = 4.7 Hz, OH), 3.41–3.44 (m,
1H, cyclohexane ring), 3.62–3.64 (m, 1H, cyclohexane
ring), 7.15–7.20 (m, 3H, ArH), 7.47–7.50 (m, 2H, ArH);
13C NMR (CDCl3): d 21.0, 24.5, 29.1, 32.5, 53.7 (CHSe),
68.3 (CHOH), 127.5, 127.7, 129.2, 134.5; 77Se NMR
(CDCl3): d 355.5. Anal. Calcd for C12H16OSe: C, 56.47;
H, 6.32. Found: C, 56.55; H, 6.24.
2852, 1579, 1436, 1066, 734, 689 cmÀ1
.
1H NMR
(300 MHz, CDCl3): d 1.33–1.37 (m, 2H, cyclohexane ring),
1.62–1.80 (m, 6H, cyclohexane ring), 2.43 (m, 1H, OH),
3.30–3.32 (m, 1H, CHS), 3.74 (dd, J1 = 5.8 Hz,
J2 = 3.2 Hz, 1H, CHOH), 7.23–7.26 (m, 3H, ArH), 7.40–
7.43 (m, 2H, ArH).
4.3. Preparation of selenides
4.3.4. (1S,2S)-1,2-Bis(phenylselenyl)cyclohexane 9. Yield
23%, de = 100%. [a]D = +90.8 (c 0.98, CH2Cl2) >95% ee.
Spectral characteristics in agreement with the literature
data for rac-9.12 IR(film): 3068, 2931, 2852, 1578, 1476,
PhSeCN (1.5 mL, 12 mmol) was added via syringe to the
solution of diol 1 or 2 (5 mmol) in dry toluene (80 mL) un-
der an argon atmosphere. The mixture was cooled to 0 °C
in an ice bath, and tributylphosphine (0.74 mL, 3 mmol)
was injected to the stirred solution. The mixture was kept
at room temperature for 20 h. After evaporation of the sol-
vent, chloroform (30 mL) was added to the reaction mix-
ture, and washed with 10% aqueous NaOH, water, and
brine. The organic layer was dried over anhydrous
Na2SO4. The solvent was evaporated and the product puri-
fied by column chromatography. Elution with n-hexane
yields two separate fractions containing products of bis-
and monosubstitution.
1436, 1173, 1022, 999, 737, 691 cmÀ1
.
1H NMR
(300 MHz, CDCl3): d 1.39–1.54 (m, 4H, cyclohexane ring),
1.72–1.77 (m, 2H, cyclohexane ring), 2.21–2.23 (m, 2H,
cyclohexane ring), 3.47–3.49 (m, 2H, CHSe), 7.09–7.18
(m, 6H, ArH), 7.31–7.34 (m, 4H, ArH); 13C NMR
(CDCl3): d 24.2, 30.5, 47.7 (C-1,C-2), 127.5, 129.1, 129.6,
134.7; 77Se NMR (CDCl3): d 393. Anal. Calcd for
C18H20Se2: C, 54.83; H, 5.11. Found: C, 55.14; H, 5.10.
4.3.5. (1S,2S)-1-Phenylsulfanyl-2-phenylselenylcyclohexane
10. Yield 42%; >98% de; [a]D = +100.0 (c 0.91, CH2Cl2)
>95% ee. Spectral characteristics in agreement with the lit-
erature data for rac-10.13 IR(film): 3070, 3056, 2932, 2853,
A mixed sulfide–selenide derivative 10 was prepared from
(1R,2S)-2-phenylselenylcyclohexanol 8 using the Hata
reaction as described above (Section 4.2), using 0.58 mmol
of 8, 2.35 mmol of tributylphosphine, and 1.76 mmol of
diphenyldisulfide.
1579, 1476, 1437, 1023, 738, 691 cmÀ1
.
1H NMR
(300 MHz, CDCl3): d 1.20–1.67 (m, 6H, cyclohexane ring),
2.17–2.26 (m, 2H, cyclohexane ring), 3.30–3.40 (m, 2H,
cyclohexane ring), 7.14–7.25 (m, 8H, ArH), 7.39–7.42 (m,
2H, ArH); 13C NMR (CDCl3): d 22.4, 23.3, 29.2, 29.3,
45.6, 49.5, 125.9, 126.6, 127.9, 128.0, 128.3, 131.1, 133.8,
134.0; 77Se NMR (CDCl3): d 391.0. Anal. Calcd for
C18H20Ss: C, 62.24; H, 5.80, S, 9.23. Found: C, 62.02; H,
5.74, S 9.70. Rf 0.23 (n-hexane).
4.3.1. (1S,2R)-2-Phenylselenylcyclopentanol 6. Yield 37%,
de = 100%. [a]D = +49.3 (c 1.52, CH2Cl2) >95% ee.
IR(film): 3439, 2962, 2869, 1579, 1478, 1437, 1301, 1022,
1007, 738, 692 cmÀ1 1H NMR (300 MHz, CDCl3): d
.
1.61–1.65 (m, 1H, cyclopentane ring), 1.75–1.81 (m, 2H,
cyclopentane ring), 1.88–1.92 (m, 2H, cyclopentane ring),
2.08–2.13 (m, 1H, cyclopentane ring), 2.48 (s, 1H, OH),
3.49–3.54 (m, 1H, cyclopentane ring), 4.07 (br s, 1H, cyclo-
pentane ring), 7.12–7.28 (m, 3H, ArH), 7.55–7.65 (m, 2H,
ArH); 13C NMR (CDCl3): d 22.4, 29.8, 32.5, 52.5 (CHSe),
72.9 (CHOH), 127.9, 129.6, 134.1, 134.2; 77Se NMR
(CDCl3): d 254.3. Anal. Calcd for C11H14OSe: C, 54.78;
H, 5.85. Found: C, 54.55; H, 5.74. Rf 0.25 (hexane/ethyl
acetate = 9:1).
4.4. Preparation of xanthic derivative
A similar procedure as for sulfide preparation (Section 4.2)
was used with 1.0 mmol of trans-1,2-cyclohexanol 2,
8.0 mmol of tributylphosphine, and 6.0 mmol of isopro-
pylxanthicdisulfide. Only the product of monosubstitution
was observed.
4.4.1. (1S,2R)-O-Isopropyl-S-(2-hydroxycyclohexyl) dithio-
carbonate 11. Yield 54%, de = 100%. [a]D = À27.9 (c
1.02, CH2Cl2) >95% ee. IR(film): 3416, 2981, 2940, 2864,
1453, 1354, 1275, 1248, 1176, 1110, 1057, 963, 908, 834,
4.3.2. (1R,2R)-1,2-Bis(phenylselenyl)cyclopentane 7. Yield
43%, de = 100%. [a]D = À18.0 (c 1.00, CH2Cl2) >95% ee.
IR(film): 3375, 3069, 3055, 2958, 2931, 2870, 1578, 1476,
1
619 cmÀ1. H NMR (500 MHz, CDCl3): d 1.23–1.39 (m,
1437, 1150, 1022, 736, 690 cmÀ1
.
1H NMR (300 MHz,
10H), 1.69–1.72 (m, 2H), 2.01–2.06 (m, 1H), 2.20–2.24
CDCl3): d 1.76–1.87 (m, 4H, cyclopentane ring), 2.39–
(m, 2H), 3.69–3.77 (m, 1H), 4.99–5.04 (m, 1H), 5.42 (septet,

E. Wojaczyn´ska, J. Skarz_ewski / Tetrahedron: Asymmetry 19 (2008) 593–597
597
1H, J = 6.2 Hz). 13C NMR (CDCl3): d 21.7, 24.1, 24.2,
29.5, 33.2, 72.9, 77.9, 86.9, 194.9 (C@S). HRMS (ESI)
calcd for C10H19O2S2 ([M+H]+) 235.0818, found
235.0771. Rf 0.22 (hexane/ethyl acetate = 9:1).
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Acknowledgment
We are grateful to the Ministry of Science and Higher Edu-
cation for financial support (Grant PBZ-KBN-126/T09/
2004).
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