Synthesis of chiral hydroxythiolanes as potential catalysts for asymmetric organozinc additions to carbonyl compounds

Article abstract of DOI:10.1002/hc.20076

Optically active 3-hydroxythiolane was stereospecifically synthesized from L-aspartic acid and oxidized to give both diastereomeric S-oxides, which were chromatographicatly separated and their configuration was determined. Starting from natural (+)-(R,R)-tartaric acid, C₂-symmetric trans-(R,R)-3,4-dihydroxythiolane was stereospecifically synthesized for the first time. Some of its monofunctionalized derivatives as well as its S-oxide were also obtained and characterized. meso-cis-3,4-Dihydroxythiolane was obtained in a similar way from meso-tartaric acid and subjected to desymmetrization either by a lipase-promoted acetylation or hydrolysis of the corresponding O, O'-diacetyl derivative, to give a chiral monoacetate with ee up to 36%. After its oxidation two diastereomeric sulfoxides were obtained which were separated by chromatography. The crystalline one was subjected to X-ray analysis and its absolute configuration was determined as 1S, 3S, 4R. All the optically active products were checked as potential catalysts for asymmetric addition of diethylzinc to benzaldehyde. However, they proved to have a very low catalytic activity: yields of the products were in the range 10-90% but ee only up to 10%. A conclusion was drawn that in this type of reaction neither is the hydroxy sulfide (sulfoxide) moiety capable of properly binding diethylzinc, nor does the sulfinyl group exert its normal stereoinduction.

Full text of DOI:10.1002/hc.20076

Heteroatom Chemistry
Volume 16, Number 2, 2005
Synthesis of Chiral Hydroxythiolanes as
Potential Catalysts for Asymmetric Organozinc
Additions to Carbonyl Compounds
1
1
1
ꢀ
ꢀ
ꢀ
Piotr Kielbasin´ski, Malgorzata Albrycht, Marian Mikolajczyk,
2
3
4
ꢀ
ꢀ
Michal W. Wieczorek, Wieslaw R. Majzner, Agnieszka Filipczak,
and Piotr Ciolkiewicz
1Centre of Molecular and Macromolecular Studies, Polish Academy of Sciences, Sienkiewicza 112,
4
ꢀ
90-363 Lꢀ o´dz´, Poland
2Institute of Chemistry and Environmental Protection, Pedagogical University, Armii Krajowej
13/15, 42-200 Czestochowa, Poland
ꢀ
3Institute of Technical Biochemistry, Technical University, Stefanowskiego 4/10, 90-924 Lꢀ o´dz´,
Poland
4Institute of General Food Chemistry, Technical University, Stefanowskiego 4/10, 90-924 Lꢀ o´dz´,
Poland
Received 22 October 2004
diastereomeric sulfoxides were obtained which were
ABSTRACT: Optically active 3-hydroxythiolane was
separated by chromatography. The crystalline one was
stereospecifically synthesized from L-aspartic acid
subjected to X-ray analysis and its absolute configura-
and oxidized to give both diastereomeric S-oxides,
tion was determined as 1S, 3S, 4R. All the optically
which were chromatographically separated and their
active products were checked as potential catalysts
configuration was determined. Starting from natu-
for asymmetric addition of diethylzinc to benzalde-
ral (+)-(R,R)-tartaric acid, C2-symmetric trans-(R,R)-
hyde. However, they proved to have a very low cat-
3,4-dihydroxythiolane was stereospecifically synthe-
alytic activity: yields of the products were in the range
sized for the first time. Some of its monofunctionalized
10–90% but ee only up to 10%. A conclusion was
derivatives as well as its S-oxide were also obtained
drawn that in this type of reaction neither is the hy-
and characterized. meso-cis-3,4-Dihydroxythiolane
droxy sulfide (sulfoxide) moiety capable of properly
was obtained in a similar way from meso-tartaric
binding diethylzinc, nor does the sulfinyl group exert
acid and subjected to desymmetrization either by a
ꢁ
C
its normal stereoinduction.
2005 Wiley Periodicals,
lipase-promoted acetylation or hydrolysis of the cor-
responding O,Oꢀ-diacetyl derivative, to give a chiral
monoacetate with ee up to 36%. After its oxidation two
Inc. Heteroatom Chem 16:93–103, 2005; Published online
in Wiley InterScience (www.interscience.wiley.com). DOI
10.1002/hc.20076
Correspondence to: Piotr Kielꢀbasin´ski; e-mail: piokiel@bilbo.
cbmm.lodz.pl.
INTRODUCTION
Contract grant sponsor: State Committee of Scientific Research
(KBN).
Although 19 years have already passed since the ini-
tial report on the asymmetric addition of diethylzinc
Contract grant number: 3 T09A 085 18.
2005 Wiley Periodicals, Inc.
c
ꢁ
93

94 Kielꢀbasin´ski et al.
to benzaldehyde in the presence of leucinol [1], a
search for new chiral catalysts for this type of re-
action still continues. Over the two decades a large
variety of such catalysts has been developed, as may
be seen from several overviews which came out in
this period, the last most comprehensive being the
one written by Pu and Yu in 2001 [2]. An inspec-
tion of the types of compounds that exhibit such a
catalytic activity clearly indicates that the most ef-
ficient are chiral aminoalcohols. In a few cases the
hydroxy group has been successfully replaced by a
thiol moiety, in some other—only the hydroxy groups
(polyols) or amino groups (polyamines) were present
in the catalyst molecule. It is noteworthy that prac-
tically in all cases, it is one or more stereogenic car-
bon atoms that served as a source of chirality or the
catalyst molecule was created on the basis of an ax-
ially chiral substrate. Very few catalysts were used
which possessed a stereogenic centre located on a
heteroatom such as P or S. There are practically only
two examples of sulfur-based catalysts containing S-
chiral moieties: hydroxyalkylsulfoximines, prepared
by Bolm et al. [3a] and ꢀ-hydroxyalkylsulfoxides,
obtained by Carreno et al. [3b]; both types of com-
pounds were used as catalysts for the enantioselec-
tive diethylzinc additions to carbonyls with moder-
ate success. The latter type of compound was also
applied as a chiral component of the catalysts for
the enantioselective Diels-Alder cycloadditions [3c].
The limited number of chiral sulfoxides used as cat-
alysts is particularly surprising as they are known
to exert high asymmetric induction [4] and to easily
form complexes with organometallic reagents. Hav-
ing this in mind, we have decided to synthesize and to
examine various types of optically active hydroxy sul-
foxides and their derivatives for their applicability as
catalysts for the above reaction. We have focused our
attention particularly on the derivatives of hydrox-
ythiolanes that contain both the hydroxyl function
and the sulfide or sulfoxide moiety within the ring.
Such a constitution may be expected to secure an ef-
ficient hindering of one side of the catalyst and thus
promote a highly enantioselective transformation.
tion was ascribed on the basis of the publication by
Quallich and Lackey [8], and the particular diastere-
omers were fully characterized. Additionally, the cor-
responding sulfone 3 was also isolated (Scheme 1).
The compounds 1 and 2 were expected to be good
catalysts for the reaction under discussion, by anal-
ogy with structurally similar 3-hydroxypyrrolidine
[9] which was found to lead to the addition products
with ee >90%.
Synthesis of trans-(R,R)-3,4-Dihydroxythiolane
and its Derivatives
The synthesis of trans-(R,R)-3,4-dihydroxythiolane
6 was accomplished as shown in Scheme 2. Us-
ing simple and commonly known procedures, nat-
ural (+)-(R,R)-tartaric acid was transformed into
properly protected L-threitol 4. An attempt to per-
form its direct reaction with sodium sulfide proved
unsuccessful due to the volatility of the expected
product. Therefore, the acetonide protecting group
was removed first to give butanetetraol 1,4-ditosylate
5, which was ultimately transformed into the de-
sired product 6. This product, having a C2 sym-
metry, seemed also very promising, as a vari-
ety of different types of C2-symmetric compounds
were extensively studied and proved to be effi-
cient catalysts, e.g. trans-1,2-bis(trifluoromethane-
sulfonamido)cyclohexane [10]. Oxidation of 6 led
to the formation of one sulfoxide 7 in which the
sulfinyl moiety is not a stereogenic center. More-
over, the sulfoxide 7 is no more a C2-symmetric com-
pound, since the sulfinyl oxygen atom is in a trans
position to one of the hydroxy groups and cis to the
other one. As we expected that the two different rela-
tions between the hydroxy and sulfinyl groups may
result in exerting an opposite stereochemical effect,
RESULTS AND DISCUSSION
Synthesis of 3-Hydroxythiolane S-Oxide
The synthesis of 3-hydroxythiolane 1 was performed
according to the procedure described by Volkmann
et al. [5]. Its oxidation, using a NaIO4/Al2O3 system
[6] or iodosobenzene in the presence of montmo-
rillonite [7], gave a diastereomeric mixture of cis
and trans sulfoxides 2, which were separated by
column chromatography. Their absolute configura-
SCHEME 1

Synthesis of Chiral Hydroxythiolanes as Potential Catalysts for Asymmetric Organozinc Additions 95
Monofunctionalized
Difunctionalized
[X]
X
Yield
(%)
[α]D
(CHCl3)
Yield
(%)
[α]D
(CHCl3
BuLi/Me3SiCl
Ac2O/Yb(OTf)3
NaH/PhCH2Br
TsCl/Et3N
SiMe3
Ac
Bn
8
28
54
15
46
+46.4
+72.9
+70.7
+38.6
9
37
18
14
36
+58.6
+112.0
+82.6
+13.0
10
12
14
11
13
15
Ts
SCHEME 2
we decided to selectively functionalize the hydroxy
groups. Two approaches were used: functionaliza-
tion of one of the equal hydroxy groups in 6 prior to
sulfoxidation, and functionalization of the nonequiv-
alent hydroxy groups in the sulfoxide 7. The first ap-
proach comprised monosilylation, monoacetylation,
monobenzylation, and monotosylation of 6. For ob-
vious reasons, the desired products 8, 10, 12, and
14, respectively were accompanied by the products
of a double functionalization, i.e. 9, 11, 13, and
15, respectively. However, of the monofunctionalized
products only 10 was subjected to oxidation to give

96 Kielꢀbasin´ski et al.
the sulfoxide 16 as an inseparable diastereomer mix-
ture (d.r. 7:1 with the trans prevailing). Nevertheless,
all the remaining monofunctionalized products were
also checked as potential catalysts (vide infra). The
second approach consisted of several attempts at the
enzymatic diastereoselective formation of 16, via ei-
ther a lipase-catalyzed acetylation of 7 or an enzyme-
catalyzed hydrolysis of the O,Oꢀ-diacetoxy sulfoxide
17, of which only one was successful, namely the
acetylation of the sulfoxide 7 in the presence of li-
pase AK (AMANO). The reaction proved to be highly
diastereoselective and resulted in the formation of
cis-16 (thus the minor diastereomer formed in the
oxidation of 10) in 65% yield, accompanied by small
amounts of the diacetyl derivative 17.
Lipase
Method Yield
[α]D
ee (%)
(%) (CHCl3) (at least) Abs. conf.
AMANO PS
AMANO AK
AMANO PS
A
A
B
81
34
28
−13.7
−5.8
36
13.5
7
3S, 4R
3S, 4R
3R, 4S
+2.85
Synthesis of meso-cis-3,4-Dihydroxythiolane
and its Enzymatic Desymmetrization
SCHEME 4
The synthesis of the derivatives of cis-3,4-dihydro-
xythiolane 18 was undertaken to complement the
investigations of the stereochemical influence of var-
iously constructed dihydroxythiolane molecules on
the possible catalyst activity. It was performed in an
analogous way as the preparation of 6, but using
meso-tartaric acid as a precursor (Scheme 3). The
compound 18 was earlier described in the literature,
but its preparation involved other substrates [11].
To transform the meso compound 18 into a chi-
ral derivative, its desymmetrization was carried out
to produce the monoacetate 19 in either of two
possible ways: an enzymatic acetylation of 18 (A)
and enzymatic hydrolysis of the diacetate 20 (B)
(Scheme 4). In both cases, the enzymatic reactions
were performed in an organic solvent, diisopropyl
ether, which for the hydrolysis was saturated with a
phosphate buffer (pH 7.2). It should be noted that
the application of the two reverse procedures en-
abled us to obtain each enantiomerically enriched
form of 19 (for the determination of ee and of the
absolute configuration see below). This is due to a
common feature of enzymes that exhibit the same
sense of enantioselectivity toward substrates, irre-
spective of direction of the reversible reaction they
catalyze (e.g. ester formation versus ester hydroly-
sis). Another point which should be stressed is that
19 turned out to be configurationally stable in con-
trast to its carba analogue, namely cis-1-acetoxy-2-
hydroxycyclopentane which was found to undergo
fast racemization due to a 1,2-acetyl shift [12]. How-
ever, certain further experiments have cast doubt
on this stability. Thus, several attempts at the de-
termination of the absolute configuration and enan-
tiomeric excess of monoacetates 19 have been unsuc-
cessful due to the loss of optical activity of the prod-
ucts obtained. For example, the reaction of (−)-19
with tosyl chloride in the presence of triethylamine
led to cis 2-tosyloxy-3-acetoxythiolane which showed
practically no optical rotation. A similar situation
was observed when silylation of (−)-19 was under-
taken. The only transformation that was partially
successful and allowed chemical correlation was the
Mitsunobu reaction [13] of (−)-19 with acetic acid
(Scheme 5).
SCHEME 3
SCHEME 5

Synthesis of Chiral Hydroxythiolanes as Potential Catalysts for Asymmetric Organozinc Additions 97
As a result, trans-diacetoxythiolane (−)-11 was
obtained, whose absolute configuration and specific
rotation is known from Scheme 2. As the Mitsunobu
reaction proceeds with inversion of configuration at
the hydroxyl carbon atom and the absolute configu-
ration of (−)-11 obtained is (S, S), the absolute con-
figuration of (−)-19 must be (3S, 4R). The optical
rotation of (−)-11 obtained [ꢁ]D = −15.1 indicates
that its enantiomeric excess is 13.5%. This means
that the enantiomeric excess of the starting (−)-19,
having [ꢁ]D = −5.8, must be at least 13.5%. It can
of course be higher, as the racemization of (−)-19
during the reaction cannot be excluded.
Another attempt to determine the absolute con-
figuration of 19 consisted of its oxidation in the hope
of obtaining a crystalline sulfoxide for an X-ray anal-
ysis. As a result, two diastereomeric sulfoxides were
formed in a comparable proportion that could be
separated by a careful slow column chromatography
(Scheme 6).
Gratifyingly, one of the diastereomers turned out
to be crystalline and after an additional crystalliza-
tion from benzene gave a sample suitable for an X-
ray analysis. Although its specific rotation was very
low, it proved to be a pure enantiomer, as could
be deduced from the value of the Flack coefficient
(χ = 0.01(3)). Its absolute configuration was (1S, 3S,
4R) (vide infra), thus the same at the C3 and C4 of
the thiolane ring as determined via the Mitsunobu
reaction.
FIGURE 1 Thermal ellipsoidal view with atom numbering in
the 21a molecule. Ellipsoids are shown with 50% probability.
ety) as an opening atom. The envelope is, however,
strongly distorted (see the data in the Experimen-
tal section). The observed difference in the length
˚
of both C S bonds (0.03 A, 10 δ) may be explained
by different conformations at C3 (pseudoequatorial)
and C4 (pseudoaxial); the same can account for the
difference in the lengths of C2 C3 and C4 C5 bonds
˚
(0.028 A).
Attempts at the Application of the
Hydroxythiolane Derivatives as Catalysts
All the chiral products described in previous sections
were checked for their catalytic activity in the asym-
metric addition of diethylzinc to benzaldehyde that
was chosen as a reference reaction (Scheme 7). The
results are collected in Table 1.
X-ray Analysis of 21a—Determination of its
Absolute Configuration
As can be seen from the molecular structure of 21a
that is shown in Fig. 1, the absolute configurations
at the particular stereogenic centers of the molecule
are 1S, 3S, and 4R. This, in other words, means that
the sulfinyl oxygen atom is situated in a trans posi-
tion to both remaining oxygen atoms, which in turn
are obviously in a cis relation. The five-membered
thiolane ring adopts the conformation of an open
envelope with C3 (connected with the acetoxy moi-
Unfortunately, all the hydroxythiolane deriva-
tives proved to be inefficient as catalyst for the above
reaction. Not only were the yields generally low (with
some exceptions), but the ee of the alcohol 22 never
exceeded 10% in spite of applying a variety of sol-
vents, additives, and conditions. Some side-products
were always formed, among them was benzyl alcohol
which is known to arise from benzaldehyde as a re-
sult of its reduction by diethylzinc [14]. Practically no
difference was observed in the enantiomeric excess
of 22 when a sulfoxide was used instead of the cor-
responding sulfide or sulfone (entries 1–4 and 9, 10
versus entries 5–8, 11–13 versus 14–17, 23 versus 24
SCHEME 6
SCHEME 7

98 Kielꢀbasin´ski et al.
TABLE 1 Asymmetric Diethylzinc Additions to Benzaldehyde Yielding 22
Entry
Catalyst
Solvent
Additives
Yield (%)
[α]D (CHCl3)
ee (%)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
1
1
1
1
Benzene
Cyclohexane
Toluene
–
–
–
BuLi
BuLi
–
–
–
–
–
60
25
30
41
30
60
60
50
20
25
30
30
50
50
50
60
90
20
15
15
10
36
10
15
15
10
20
67
60
50
13
+2.8
+4.4
+4.1
−0.9
+2.6
+7
7
10
9
<5
7
16
<5
<5
<5
<5
<5
0
<5
<5
<5
6
8
10
8
<5
<5
6
<5
<5
<5
<5
14
<5
36
32
8
Toluene
Toluene
cis-2
cis-2
trans-2
trans-2
Benzene
Benzene
Cyclohexane
Cyclohexane
Benzene
Benzene
Toluene
Toluene
Benzene
Toluene
−0.5
−1.2
−0.7
+1.0
+0.9
0
3
3
6
6
6
7
7
7
BuLi
Ti(OiPr)4
–
BuLi
Ti(OiPr)4
Ti(OiPr)4
−0.7
+0.5
+0.8
+2.3
+3.3
+4.5
+3.5
−1.0
−1.2
−2.36
−1.0
−0.7
−0.4
+2.2
+6.2
−0.3
−16
Toluene
Toluene
7 equimolar
10
12
14
Benzene
Benzene
Benzene
Benzene
Benzene
Benzene
Benzene
Benzene
Benzene
Benzene
Benzene
Benzene
Benzene
Benzene
–
–
–
–
–
–
–
–
–
–
–
–
–
–
16 (diast.mixt.)
cis-16
19
cis-21
trans-21
23
24
25
26
27
−14
28
−3.3
and 25) that indicates a complete lack of the asym-
metric induction of the sulfinyl group. Location of
both potential diethylzinc-binding sites (S or SO and
OH) in a ring, even in a cis relation (entries 5, 6, and
24), proved to be also an insufficient factor to in-
duce an enantiofacial differentiation of the reagent.
Moreover, the use of an open-chain hydroxy sulfox-
ide [15] 23 (entry 26) gave a comparable result (see
Scheme 8). Application of a chiral carboxy sulfoxide
[15] 24 (entry 27) slightly improved the ee of 22; how-
ever, the yield was very low. The cyclic carboxy sul-
foxide [16] 25, although sterically more congested,
gave a completely disappointing result (entry 28).
Finally, the camphor-derived highly hindered sulfide
26 and sulfoxide 27 (Scheme 9), synthesized accord-
ing to the method described by Ridley et al. [17],
proved to be the best catalysts from among all so far
tested, although still far from expectations (entries
29 and 30). Moreover, as there was no difference in
the enantioselection between sulfide 26 and sulfox-
ide 27, the influence of the SO chiral group seems
negligible.
The last compound 28, synthesized by Tanaka
et al. [18], having a helical chirality ([ꢁ]D = −1973,
SCHEME 8
SCHEME 9

Synthesis of Chiral Hydroxythiolanes as Potential Catalysts for Asymmetric Organozinc Additions 99
c = 0.055, CHCl3) also proved to be inefficient as a
sulfone 3: (0.070 g, 11%), [ꢁ]D = +14.2 (c = 1.18,
CHCl3.); 1H NMR (CDCl3): δ = 2.25–3.50 (m, 2H),
3.85 (s, 1H), 3.05–3.45 (m, 4H), 4.70–4.80 (m, 1H).
13C NMR (CDCl3): δ = 31.77, 49.55, 59.35, 67.95. MS
(CI): m/z 137 (M+1).
catalyst (entry 31). Because of the generally disap-
pointing results obtained, no attempts were made to
change the aldehyde applied or replace diethylzinc
with other organozinc derivatives.
On the basis of the negative results presented,
a conclusion can be drawn that the hydroxy sulfide
or hydroxy sulfoxide moiety is incapable of properly
binding diethylzinc, most probably due to the insuf-
ficient basicity of the sulfur and sulfinyl oxygen cen-
ters. The diethylzinc-catalyst complex is either not
formed or its reactivity is very low, which can be seen
from the low yields of the desired alcohol 22 and the
formation of by-products resulting from concurrent
reactions. Obviously, in such a case even introducing
a steric hindrance could not substantially improve
the yield and stereoselectivity. This may also account
for the fact that the chiral sulfinyl group does not ex-
ert any stereoinduction unlike in many other cases
known from the literature.
Similar results were obtained when the NaIO4/
Al2O3 was used as an oxidizing agent.
Synthesis of
1,4-Ditosyl-2,3-O-isopropylidene-L-threitol 4
A solution of 2,3-O-isopropylidene-L-threitol, ob-
tained from L-tartaric acid [19], (1.9 g, 0.012 mol)
in pyridine (14 mL) was cooled to −10◦C and tosyl
chloride (7.145 g, 0.037 mol) was added. The mixture
was stirred overnight at room temperature. Water
(80 mL) was added and the mixture was left for 2 h
in a refrigerator. The precipitate was filtered, washed
with water and EtOH, to give, after drying, 4 (4.409
g, 80%), [ꢁ]D = −12.75 (c = 1.09, CHCl3.).
1H NMR (CDCl3): δ = 1.29 (s, 6H), 2.46 (s, 6H),
4.01 (m, 2H), 4.10 (m, 4H), 7.33–7.81 (m, 8H).
EXPERIMENTAL
NMR spectra were recorded on Bruker instruments
at 200 MHz for 1H and 81 MHz for 31P, with CD3OD
or CDCl3 as solvents. Optical rotations were mea-
sured on a Perkin-Elmer 241 MC polarimeter. Col-
umn chromatography was carried out using Merck
60 silica gel. TLC was performed on Merck 60 F254
silica gel plates. The enzymes were purchased from
AMANO or FLUKA.
Synthesis of 1,4-Ditosyl-L-threitol 5
To a solution of 4 (0.3 g, 0.641 mmol) in methanol
(5 mL) was added 0.5 N hydrochloric acid (a few
drops) and the resulting mixture was refluxed for 5 h
(TLC control: hexane–ethyl acetate 2:1). The solvents
were removed under vacuum, the residue was dis-
solved in CHCl3 and dried over MgSO4. After filtra-
tion and evaporation 5 was obtained (0.275 g, 100%),
[ꢁ]D = +1.05 (c = 1.33, CHCl3.).
Synthesis of (R)-3-Hydroxythiolane-1-oxide 2
1H NMR (CDCl3): δ = 2.45 (s, 6H), 3.25–3.97 (m,
2H), 4.05–4.13 (m, 4H), 7.33–7.83 (m, 8H). MS (FAB):
m/z 431 (M+1).
To a solution of 1 [5] (0.5 g, 4.8 mmol) in acetoni-
trile (20 mL) was added PhIO (1.058 g, 4.8 mmol)
and montmorillonite K 10 (1.058 g). The mixture
was stirred at room temperature until the substrate
was completely consumed, as was detected by TLC
(CHCl3–MeOH 15:1). The precipitate was filtered off
and washed with substantial amounts of a 1:1 mix-
ture of CHCl3 and MeOH. The filtrate was evaporated
to give a crude reaction mixture (1.5 g) The latter was
purified by column chromatography using hexane–
i-PrOH (1:3) as eluent to afford:
Synthesis of (R,R)-3,4-Dihydroxythiolane 6
A mixture of 5 (0.267 g, 0.624 mmol) and Na2S · 9H2O
(0.374 g, 1.559 mmol) in EtOH (5 mL) was re-
fluxed for 5 h (TLC control: ethyl acetate–hexane
2:1). After filtration through Celite and evaporation
the residue was dissolved in CHCl3. The precipitate
was filtered off and washed with a large amount
of CHCl3. The solvent was removed under vacuum
and the residue was purified by column chromatog-
raphy, using CHCl3 to CHCl3–MeOH 10:1 (in gradi-
ent) as solvent to give 6 (65 mg, 88%), [ꢁ]D = +76.9
(c = 1.22, MeOH.).
cis- sulfoxide 2: (0.226 g, 40%), [ꢁ]D = +46.8 (c =
1
2.26, CHCl3.); H NMR (CDCl3): δ = 2.10–2.35 (m,
2H), 2.55–3.50 (m, 4H), 3.50 (s, 1H), 4.77 (m, 1H).
13C NMR (CDCl3): δ = 35.28, 52.77, 59.01, 75.47. MS
(CI): m/z 121 (M+1);
trans- sulfoxide 2: (0.226 g, 40%), [ꢁ]D = +2.65 (c =
1H NMR (CD3OD): δ = 2.63–3.13 (m, 4H), 4.17–
4.23 (m, 2H). 13C NMR (CD3OD): δ = 36.19, 79.08.
MS (CI): m/z 121 (M+1). HRMS calcd. for C4H9SO2
(M+1) 121.0322; found 121.0323.
1
2.26, CHCl3.); H NMR (CDCl3): δ = 2.15–3.50 (m,
2H), 4.86 (m, 1H). 13C NMR (CDCl3): δ = 34.31,
50.77, 64.28, 72.21. MS (CI): m/z 121 (M+1); and

100 Kielꢀbasin´ski et al.
11 (0.204 g, 18%), [ꢁ]D = +112.0 (c = 2.04, CHCl3);
1H NMR (CDCl3): δ = 2.08 (s, 6H), 2.85–3.33 (m,
4H), 5.29–5.41 (m, 2H). 13C NMR (CDCl3): δ = 20.96,
33.75, 77.62, 169.80.
Synthesis of
(R,R)-3,4-Dihydroxythiolane-1-oxide 7
To a solution of 6 (0.5 g, 4.167 mmol) in acetoni-
trile (40 mL) was added PhIO (0.917 g, 4.167 mmol)
and montmorillonite K 10 (0.917 g). The mixture was
stirred at room temperature until the substrate was
completely consumed (TLC ethyl acetate–methanol
9:1). After filtration and evaporation, the crude re-
action mixture was purified by column chromatog-
raphy using AcOEt–MeOH 30:1 to AcOEt–MeOH
9:1 as eluent to give 7 (0.331 g, 58%), [ꢁ]D = +62.7
(c = 1.11, MeOH.).
Synthesis of (R)-3-Benzyloxy-(R)-4-hydroxythio-
lane 12 and (R,R)-3,4-Dibenzyloxythiolane 13
A solution of 6 (0.0513 g, 0.428 mmol) in THF (3 mL)
was cooled to 0◦C and a natrium hydride dispersion
50–60% in oil (0.0206 g, 0.860 mmol) was added.
After 5 min Bu4NI (a few milligrams) and benzyl
bromide (0.0728 g, 0.428 mmol) were added. The
mixture was stirred at room temperature for 5 days.
Although TLC control (hexane–ethyl acetate 2:1) re-
vealed that a substantial amount of the substrate was
still present, the mixture was filtered through Celite.
After evaporation of the solvent the residue was pu-
rified by preparative TLC using hexane–ethyl acetate
2:1 as solvent to give:
1H NMR (CD3OD): δ = 2.77–3.66 (m, 4H), 4.42–
4.59 (m, 2H). 13C NMR (CD3OD): δ = 58.35, 61.12,
78.46. MS (CI): m/z 137 (M+1).
Synthesis of
(R)-3-(Trimethylsilyl)-(R)-4-hydroxythiolane 8
and (R,R)-3,4-Di(trimethylsilyl)thiolane 9
To a solution of 6 (0.116 g, 0.967 mmol) in THF
(5 mL), a 2.5 M solution BuLi in hexane (0.45 mL,
1.125 mmol) and chlorotrimethylsilane (0.147 mL,
0.126 g, 1.160 mmol) were added at room tempera-
ture and the mixture was stirred overnight (TLC con-
trol: ethyl acetate–hexane 2:1). After the substrate
was completely consumed the solution was evap-
orated. The residue was purified by column chro-
matography using AcOEt–hexane 1:20 to AcOEt–
hexane 2:1 as solvent to give:
12 (0.0141 g, 15%), [ꢁ]D = +70.7 (c = 1.41, CHCl3);
1H NMR (CDCl3): δ = 1.95 (s, 1H), 2.70–3.20 (m, 4H),
4.01–4.07 (m, 1H), 4.34–4.40 (m, 1H), 4.50–4.69 (m,
2H). MS (CI): m/z 211 (M+1); and
13 (0.0180 g, 14%), [ꢁ]D = +82.6 (c = 0.90, CHCl3);
1H NMR (CDCl3): δ = 2.73–3.19 (m, 4H), 4.01–4.07
(m, 1H), 4.31–4.40 (m, 1H), 4.50–4.70 (m, 4H), 7.13–
7.44 (m, 10H). MS (CI): m/z 301 (M+1).
Synthesis of (R)-3-Tosyloxy-(R)-4-hydroxythio-
lane 14 and (R,R)-3,4-Ditosyloxythiolane 15
8 (0.052 g, 28%), [ꢁ]D = +46.4 (c = 1.47, CHCl3); 1H
NMR (CDCl3): δ = 0.14 (s, 9H), 2.65–2.76 (m, 2H),
3.00–3.18 (m, 2H), 4.18–4.30 (m, 2H); and
To a solution of 6 (0.110 g, 0.916 mmol) in methy-
lene chloride (5 mL) were added tosyl chloride
(0.175 g, 0.916 mmol) and triethylamine (0.092 g,
0.916 mmol). The mixture was stirred at room tem-
perature until the substrates were completely con-
sumed (TLC control: hexane–ethyl acetate 2:1). The
solvent was evaporated and residue was purified by
preparative TLC using ethyl acetate–hexane 2:1 as
solvent to give:
9 (0.0939 g, 37%), [ꢁ]D = +58.6 (c = 2.23, CHCl3); 1H
NMR (CDCl3): δ = 0.12 (s, 18H), 2.60–3.05 (m, 4H),
4.08–4.12 (m, 2H).
Synthesis of
(R)-3-Acetoxy-(R)-4-hydroxythiolane 10 and
(R,R)-3,4-Diacetoxythiolane 11
To a solution of 6 (0.694 g, 5.7 mmol) in methy-
lene chloride (15 mL) Yb(OTf)3 was added (0.342 g,
0.551 mmol) followed by Ac2O (0.54 mL, 0.581 g, 5.7
mmol). The mixture was stirred at room temperature
(TLC control: ethyl acetate–hexane 2:1). The solvent
was evaporated and the residue was purified by col-
umn chromatography using AcOEt–hexane 1:20 to
AcOEt–hexane 2:1 as solvent to give:
14 (0.1156 g, 46%), [ꢁ]D = +38.6 (c = 3.47, CHCl3);
1H NMR (CDCl3): δ = 2.28 (s, 1H), 2.45 (s, 3H), 2.78–
3.16 (m, 4H), 4.40–4.46 (m, 1H), 4.85–4.91 (m, 1H),
7.34–7.83 (m, 4H). MS (CI): m/z 275 (M+1); and
15 (0.1412 g, 36%), [ꢁ]D = +13.0 (c = 0.54, CHCl3);
1H NMR (CDCl3): δ = 2.47 (s, 6H), 2.77–3.20 (m, 4H),
4.99–5.01 (m, 4H), 7.27–7.81 (m, 4H).
10 (0.497 g, 54%), [ꢁ]D = +72.9 (c = 1.37, CHCl3);
1H NMR (CDCl3): δ = 2.05 (s, 3H), 2.76–3.28 (m,
4H), 4.30–4.41 (m, 1H), 5.16–5.21 (m, 1H). 13C NMR
(CDCl3): δ = 21.01, 33.13, 36.27, 76.34, 80.04, 170.48;
and
Synthesis of (R)-3-Acetoxy-(R)-4-hydroxythio-
lane-1-oxides 16
To a solution of 10 (0.100 g, 0.617 mmol) in ace-
tonitrile (3 mL) was added PhIO (0.136 g, 0.617

Synthesis of Chiral Hydroxythiolanes as Potential Catalysts for Asymmetric Organozinc Additions 101
mmol) and montmorillonite K 10 (0.136 g). The mix-
amount of CHCl3. The solvent was removed under
vacuum and the residue was purified by column
chromatography, using CHCl3 to CHCl3–MeOH 10:1
(in gradient) as solvent to give 18 (1.286 g, 65%).
1H NMR (CD3OD): δ = 2.70–2.95 (m, 4H), 4.13–
4.20 (m, 2H).
ture was stirred at room temperature until the sub-
strate was completely consumed (TLC control: ethyl
acetate–methanol 9:1). After filtration through Celite
and evaporation a crude reaction mixture was ob-
tained (0.112 g, 100%, trans : cis 3:2). Preparative
TLC (AcOEt–MeOH 9:1) gave the pure compound
16 (0.033 g, 30%) as 7:1 diastereomer mixture with
trans 16 prevailing.
Synthesis of
cis-3-Acetoxy-4-hydroxythiolanes 19
1H NMR (CD3OD): δ = 2.01 (s, 3H), 2.11 (s, 3H),
2.89–3.63 (m, 4H), 3.94 (s, 1H), 4.68–4.71 (m, 1H),
4.80–4.83 (m, 1H), 5.27–5.33 (m, 1H), 5.72–5.78
(m, 1H). The peaks characteristic of the prevailing
trans diastereomer are underlined.
Method A. A mixture of 18 (0.1 g, 0.833 mmol),
a lipase (ca. 10 mg), and vinyl acetate (0.5 mL) in
i-Pr2O was stirred overnight at room temperature.
Then the enzyme was filtered off and the solvent
was evaporated under vacuum. The residue was puri-
fied by column chromatography using ethyl acetate–
hexane 1:20 to ethyl acetate–hexane 1:5 as solvent,
to give 19 (0.110 g, 81%) [ꢁ]D = −13.7 (c = 1.35,
CHCl3.).
Synthesis of (R)-3-Acetoxy-(R)-4-hydroxythio
lane 1-(S)-oxide cis-16
A mixture of 7 (0.050 g, 0.367 mmol), lipase AK (ca.
10 mg), and vinyl acetate (0.5 mL) in CHCl3 was
stirred at room temperature until the substrate was
completely consumed (AcOEt–MeOH 9:1). Then the
enzyme was filtered off and the solvent was evapo-
rated under vacuum. The residue was purified by col-
umn chromatography using ethyl acetate–methanol
20:1 to ethyl acetate–methanol 9:1 as solvent, to
give cis-16 (0.042 g, 65%) [ꢁ]D = +62.58 (c = 1.51,
CHCl3.); 1H NMR (CDCl3.): δ = 2.11 (s, 3H), 2.90–3.62
(m, 5H), 4.80–4.83 (m, 1H), 5.29–5.32 (m, 1H).
1H NMR (CDCl3.): δ = 2.13 (s, 3H), 2.30 (br.s, 1H),
2.81–3.15 (m, 4H), 4.39–4.49 (m, 1H), 5.15–5.38
(m, 1H).
HRMS (CI): calc. for C6H11SO3 m/z =
163.042892, found m/z = 163.0433.
Method B. A mixture of 20 (0.0945 g, 0.460
mmol) and a lipase (ca. 10 mg) in a i-Pr2O (5 mL) sat-
urated with a phosphate buffer (pH 7.2) was stirred
overnight at room temperature. Then anhydrous
magnesium sulfate was added to remove water. The
precipitates were filtered off, the solvents were re-
moved under vacuum, and the residue was puri-
fied by column chromatography using ethyl acetate–
hexane 1:20 to ethyl acetate–hexane 1:5 as solvent,
to give 19 (0.021 g, 28%), [ꢁ]D = +2.85 (c = 0.74,
CHCl3.).
Synthesis of
(R,R)-3,4-Diacetoxythiolane-1-oxide 17
To a solution of 11 (0.185 g, 0.907 mmol) in acetoni-
trile (5 mL) was added PhIO (0.199 g, 0.907 mmol)
and montmorillonite K 10 (0.199 g). The mixture was
stirred at room temperature until the substrate was
completely consumed (TLC control: ethyl acetate–
methanol 9:1). After filtration through Celite and
evaporation the crude reaction mixture was puri-
fied by column chromatography using AcOEt–MeOH
30:1 to AcOEt–MeOH 9:1 as eluent to give 17 (0.199
g, 100%), [ꢁ]D = +81.29 (c = 1.08, CHCl3).
1H NMR (CDCl3.): δ = 2.13 (s, 3H), 2.30 (br.s, 1H),
2.81–3.15 (m, 4H), 4.39–4.49 (m, 1H), 5.15–5.38
(m, 1H).
Synthesis of meso-3,4-Diacetoxythiolane 20
To a solution of 18 (0.1 g, 0.833 mmol) in
dichloromethane (5 mL) Yb(OTf)3 was added
(0.045 g, 0.072 mmol) followed by Ac2O (0.24 mL,
0.256 g, 2.498 mmol). The mixture was stirred at
room temperature until the substrate was completely
consumed (TLC control: ethyl acetate–hexane 2:1).
The reaction mixture was washed with water, aque-
ous saturated NaHCO3 solution and water. The or-
ganic layer was dried over anhydrous magnesium
sulfate. The precipitate was filtered and the solvent
was evaporated. The residue was purified by column
chromatography using chloroform as solvent to give
20 (0.154 g, 90%).
1H NMR (CDCl3): δ = 2.05 (s, 3H), 2.13 (s, 3H),
3.00–3.58 (m, 4H), 3.42–3.47 (m, 1H), 5.71–5.77 (m,
1H). MS (CI): m/z 221 (M+1).
Synthesis of meso-3,4-Dihydroxythiolane 18
A mixture of 1,4-ditosyl-meso-threitol obtained in
an analogous way as 5, (7.089 g, 0.016 mol) and
Na2S·9H2O (10.023 g, 0.042 mol) in EtOH (140 mL)
was refluxed for 5 h (TLC control: ethyl acetate–
hexane 2:1). After filtration through Celite and evap-
oration the residue was dissolved in CHCl3. The pre-
cipitate was filtered off and washed with a large

102 Kielꢀbasin´ski et al.
hyde (1 mmol) was added at 0◦C, and the reaction
mixture was stirred for 2 h at 0◦C, then overnight
at room temperature. Then it was treated with 5%
cold aqueous HCl solution. The layers were sepa-
rated and the water layer was extracted with di-
ethyl ether (4 × 5 mL). The combined organic ex-
tracts were washed with brine (10 mL) and dried
over anhydrous magnesium sulfate. After filtration
and evaporation the residue was purified by prepar-
ative TLC using hexane–ethyl acetate 5:1 as solvent
to give optically active 1-phenylpropan-1-ol 22.
1H NMR (CDCl3): δ = 2.07 (s, 3H), 2.86–3.14 (m,
4H), 5.33–5.41 (m, 2H). 13C NMR (CDCl3): δ = 20.85,
30.74, 74.01, 170.11. MS (CI): m/z 205 (M+1).
Synthesis of (3S,4R)-3-Acetoxy-4-hydroxythio-
lane-1-oxides 21
To a solution of (−)-19 (0.3 g, 1.852 mmol) in ace-
tonitrile (10 mL) was added PhIO (0.407 g, 4.852
mmol) and montmorillonite K 10 (0.407 g). The mix-
ture was stirred at room temperature until the sub-
strate was completely consumed (TLC control: ethyl
acetate–methanol 9:1). After filtration and evapora-
tion the crude reaction mixture was purified by col-
umn chromatography using AcOEt–MeOH 20:1 to
AcOEt–MeOH 9:1 as eluent to give: 21b (0.058 g) as
an oil.
TABLE 2 Crystal Data and Experimental Details of 21a
Molecular formula
Formula weight
C6H10O4S
178.20
Pna21
1H NMR (CDCl3.): δ = 2.14 (s, 3H), 2.89–3.67 (m,
4H), 4.64–4.70 (m, 1H), 5.12–5.21 (m, 1H), 13C NMR
(CDCl3): δ = 20.76, 55.47, 73.74, 75.02, 170.39. MS
(CI): m/z 179 (M+1).
Crystallographic system
Space group
Orthorhombic
˚
a (A)
9.118(2)
9.701(2)
9.243(2)
817.6(3)
4
˚
b (A)
(1S, 3S, 4R)-21a (0.0255 g), mp. 101–103◦C,
[ꢁ]D = −0.51 (c = 2.55, CHCl3); 1H NMR (CDCl3.):
δ = 2.13 (s, 3H), 2.94–3.44 (m, 4H), 4.91–4.98 (m,
1H), 5.66–5.75 (m, 1H). 13C NMR (CDCl3): δ = 20.82,
30.87, 54.50, 57.83, 72.06, 75.02, 169.98. MS (CI):
m/z 179 (M+1) and an inseparable mixture of both
diastereomers of 21 (0.119 g). Total yield 62%.
˚
c (A)
3
˚
V (A )
Z
Dc (g/cm3)
1.448
3.294
µ (mm−1
)
Crystal dimensions (mm)
0.10 × 0.12 × 0.32
Maximum 2θ (◦)
150
˚
Radiation, λ (A)
Cu Kα, 1.54178
ω/2θ
Scan mode
Scan width (◦)
hkl ranges:
0.65 + 0.14tanθ
Synthesis of (S,S)-3,4-Diacetoxythiolane
11—Chemical Correlation Using
Mitsunobu Reaction
h =
k =
l =
0 11
−12 12
0
11
DECAY correction: min.
1.00002
1.01098
1.00544
0.8950
0.9993
0.9548
898
To a solution of 19 (0.0709 g, 0.4376 mmol), triph-
enylphosphine (0.1965 g, 0.75 mmol), and diethyl
azodicarboxylate (0.147 mL, 0.1515 g, 0.75 mmol)
in THF (3 mL) was added acetic acid (0.042 mL,
0.045 g, 0.75 mmol) at −78◦C. The resulting solu-
tion was stirred at this temperature for 1.5 h and
then was allowed to reach room temperature and
stirred for 12 h. Then the solvent was evaporated. The
residue was purified by flash chromatography using
ethyl acetate–hexane 1:10 as eluent to give product
11 (0.0061 g, 7%), [ꢁ]D = −15.1 (c = 0.61, CHCl3).
1H NMR (CDCl3): δ = 2.05 (s, 3H), 2.76–3.28 (m,
4H), 4.30–4.41 (m, 1H), 5.16–5.21 (m, 1H).
max.
ave.
min.
max.
ave.
EAC correction:
No. of reflections: unique
with I > 0σ(I )
881
obs. with I > 0σ(I )
851
141
0.296
No. of parameters refi−n3ed
˚
Largest diff. peak (eA
)
)
−3
˚
Largest diff. hole (eA
−0.203
Shift/esd max.
R obs
0.000
0.0280
0.0805
1.052
0.055800
0.107500
0.0040(9)
0.0201
293(2)
376
wRobs
Sobs
weighting coeff.a
m
n
k
General Procedure of Asymmetric Addition
of Et2Zn to Benzaldehyde
extinction coeff.b
Rint
Tmeas
A catalyst (0.1 mmol) and benzene (10 mL) were
placed in a flask. To ensure dryness some benzene
was distilled off. To this solution a solution of Et2Zn
(1 M in hexane solution) (3 mmol) was added un-
der argon at 0◦C. After stirring for 0.5 h benzalde-
F(000)
aWeighting scheme w = [σ2(Fo 2) + (mP)2 + nP ]−1
,
where P =
∗
2
(Fo + 2Fc2)/3.
bExtinction method SHELXL, extinction expression Fc = kFc[1 +
0.001 × Fc2λ3/ sin(2θ)]−1/4
.

Synthesis of Chiral Hydroxythiolanes as Potential Catalysts for Asymmetric Organozinc Additions 103
ric and Stereoselective Synthesis; CRC Press: Boca
Raton, FL, 1997.
Crystallographic Data of 21a
Crystal and molecular structure of 21a was deter-
mined using data collected at room temperature on
a CAD4 diffractometer. Crystal data and experimen-
tal details are shown in Table 2. The lattice constants
were refined by least-squares fit of 25 reflections in
the θ range 17.00–32.64◦. The decline in intensities of
three control reflections (4,1,2; 1,0,−4; 3,−1,−5) was
−2.2% during 25.3 h of exposure time, the intensity
corrections was applied (DECAY program) [20]. An
empirical absorption correction was applied by the
use of the ꢂ -scan method (EAC program) [20,21]. A
total of 881 observed reflections with I > 0σ(I) were
used to solve the structure by direct methods and to
refine it by full matrix least-squares [22,23] using F2.
Hydrogen atoms were found on difference Fourier
map and refined isotropically. Anisotropic thermal
parameters were refined for all non-hydrogen atoms.
The final refinement converged to R = 0.028 for 141
refined parameters and 851 observed reflections with
I > 2σ(I) with inclusion of extinction parameter into
refinement (the obtained value of extinction param-
eter was 0.0040(9)). The absolute configurations at
the chiral atoms were established as S , S , RC4.
[5] Volkmann, R. A.; Kelbaugh, P. R.; Nason, D. M.; Jasys,
V. J. J Org Chem 1992, 57, 4352–4361.
[6] Liu, K.-T.; Tong, Y.-C. J Org Chem 1978, 43, 2717–
2718.
[7] Kannan, P.; Sevvel, R.; Rajagopal, S.; Pitchumani,
K.; Srinivasan, C. Tetrahedron 1997, 53, 7635–
7640.
[8] Quallich, G. J.; Lackey, J. W. Tetrahedron Lett 1990,
31, 3685.
[9] Mehler, T.; Martens, J.; Wallbaum, S. Synth Commun
1993, 23, 2691–2699.
[10] For a review see: Knochel, P.; Perea, J. J. A.; Jones, P.
Tetrahedron 1998, 54, 8275–8319.
[11] Naka, T.; Nishizono, N.; Minakawa, N.; Matsuda, A.
Tetrahedron Lett 1999, 40, 6297–6300.
[12] Ganesh, K. N.; Argade, N. P.; Desai, S. B.; Easwar, S.
Tetrahedron: Asymmetry 2002, 13, 1367–1371.
[13] Mitsunobu, O. Synthesis 1981, 1–28.
[14] Bolm, C.; Mu¨ller, J. Tetrahedron 1994, 50, 4355–
4362.
˙
[15] Mikoꢀlajczyk, M.; Kieꢀlbasin´ski, P.; Zurawin´ski, R.;
Wieczorek, M. W.; Bꢀlaszczyk, J. Synlett 1994, 127–
129.
[16] Kieꢀlbasin´ski, P.; Zwanenburg, B.; Damen, T. J. G.;
Wieczorek, M. W.; Majzner, W. R.; Bujacz, G. D. Eur
J Org Chem 1999, 2573–2578.
[17] Goodridge, R. J.; Hambley, T. W.; Haynes, R. K.;
Ridley, D. D. J Org Chem 1988, 53, 2881–2889.
[18] The authors express their sincere thanks to Profes-
sor Kazuhiko Tanaka from the Wakayama Univer-
sity (Japan) for a generous gift of a sample of com-
pound 27. For its synthesis see: Tanaka, K.; Osuga,
H.; Suzuki, Y.; Kitahara, Y. J Chem Soc, Perkin Trans
1 1998, 935–940.
[19] Mash, E. A.; Nelson, K. A.; Deusen, S. V.; Hemperly,
S. B. Org Synth 1990, 68, 92–103.
[20] Frenz, B. A. Structure Determination Package; SPD
User’s Guide, version of 17; Enraf-Nonius, Delft,
Holland, 1994.
S
C3
The absolute structure was determined by the Flack
method [24] with result χ = 0.01(3). Data corrections
were carried out with the Enraf-Nonius SPD crys-
tallographic computing package [20]; structure so-
lution SHELXS [22]; structure refinement SHELXL
[23]. The authors have deposited all crystallographic
data for this structure with the Cambridge Crystal-
lographic Data Centre [25].
[21] North, A. C. T.; Philips, D. C.; Mathews, F. S. Acta
Cryst 1998, A24, 351–359.
[22] Sheldrick, G. M.; Kruger, G. M.; Goddard, R.
SHELXS-86. Structure Solution Program. Acta Cryst
1990, A46, 467–473.
[23] Sheldrick, G. M. SHELXL-93. Structure Refinement
Program. University of Go¨ttingen, 1993.
[24] Flack, H. D. Acta Cryst 1983, A39, 876–881.
[25] Crystallographic data for the structure have been
deposited with the Cambridge Crystallographic
Data Centre as supplementary publication number
244831. Copies of the data can be obtained free
of charge on application to CCDC, 12 Union Road,
Cambridge CB2 1EZ, UK (fax: +44(0)-1223-336033
or e-mail: deposit@ccdc.cam.ac.uk).
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