BINOL derived C2-symmetric bis-sulfinates as efficient sulfinyl transfer agents in the synthesis of tert-butyl sulfoxides

Article abstract of DOI:10.1016/j.tet.2012.06.050

The reaction of novel C₂-symmetric bis-sulfinate esters derived from (R)-BINOL with Grignard reagents affords tert-butyl sulfoxides in ee up to 97%. The desired enantiomer can be generated at will by the proper selection of BINOL.

Full text of DOI:10.1016/j.tet.2012.06.050

Tetrahedron 68 (2012) 7129e7132
Contents lists available at SciVerse ScienceDirect
Tetrahedron
journal homepage: www.elsevier.com/locate/tet
BINOL derived C2-symmetric bis-sulfinates as efficient sulfinyl transfer agents
in the synthesis of tert-butyl sulfoxides
,
b
N. Gaggero a , D.C.M. Albanese
*
a
ꢀ
DISMAB, Sezione di Chimica Organica ‘A. Marchesini’, Universita degli Studi di Milano, via Golgi 19, 20133 Milano, Italy
Universita degli Studi di Milano, Dipartimento di Chimica Organica e Industriale, via Venezian 21, 20133 Milano, Italy
b
ꢀ
a r t i c l e i n f o
a b s t r a c t
Article history:
The reaction of novel C2-symmetric bis-sulfinate esters derived from (R)-BINOL with Grignard reagents
affords tert-butyl sulfoxides in ee up to 97%. The desired enantiomer can be generated at will by the
proper selection of BINOL.
Received 7 February 2012
Received in revised form 9 May 2012
Accepted 12 June 2012
Ó 2012 Elsevier Ltd. All rights reserved.
Available online 19 June 2012
1. Introduction
as a chiral sulfinyl transfer reagent, capable to react with Grignard
reagents affording enantiomerically enriched tert-butyl sulfoxides
Research in the field of synthesis of enantiomerically pure
sulfoxides is continuously developing. These unremitting efforts
find their justification in the broad applications of the sulfinyl
moiety as chiral auxiliaries for CeC and CeO bonds forming re-
actions and as ligands in catalytic stereoselective reactions.1 In
particular, in the last few years tert-butyl sulfoxides have as-
sumed great importance in asymmetric synthesis and numerous
examples are reported of their use as chiral ligands,2 chiral
auxiliaries,3 and Lewis base catalysts.4 Moreover, a variety of
pharmacological active compounds contains the sulfinyl func-
tional group.5 The major synthetic strategies to sulfoxides rely on
the direct oxidation of parent sulfides6 and the more versatile
nucleophilic displacement by organometallic species at the
stereogenic sulfur atom of diastereoisomerically pure sulfinylat-
ing species.1b,c,7 Numerous diastereoisomerically pure sulfinates,8
thiosulfinates,9 sulfinamides,10 cyclic sulfites,11 oxathiazolidine-
2-oxides12 for transfer of the sulfinyl group have been developed.
The success of the latter approach is based on the stereospeci-
ficity of the substitution at the sulfur atom, which proceeds with
inversion of configuration.13 In this context it is surprising that no
literature report deals with the use of chiral auxiliaries having
a C2-symmetry axis. In fact, it is often observed that auxiliaries
with a C2-symmetry axis provide higher levels of stereochemical
control with respect to other auxiliaries, which lack such
symmetry.14
6 (Scheme 1).
O
S
n-BuLi
t-BuSOCl
O
O
t-Bu
t-Bu
(R)-1
S
O
5,6a, R = Ph
2
5,6b, R = p-Me-C6H4
5,6c, R = 1-C10H7
5,6d, R = Me
RMgBr
O
5a-d
S
(R)-1 + 2
R
6a-d
t-Bu
THF
Scheme 1. Synthesis of aryl tert-butyl sulfoxides 6aed.
2. Results and discussion
The reaction of (R)-1 with n-butyllithium (n-BuLi) (2.2 equiv,
THF, ꢀ78 ꢁC) followed by addition of tert-butylsulfinyl chloride
(2 equiv, THF, ꢀ78 ꢁC) gave a mixture of three bis-sulfinate ester
diastereoisomers 2e4 where mono-sulfinates were absent
(Scheme 2).
The diastereoselectivity of the process could be determined
through 1H NMR spectroscopic analysis of the reaction mixture.
Homotopic 2,20-tert-butyl groups of C2-symmetric stereoisomers
are singlets with a chemical shift of 0.69 and 0.61 ppm for 2 and 4,
respectively. On the other hand, each diastereotopic tert-butyl
group of 3 is a singlet with a chemical shift of 0.75 and 0.62 ppm.
Moreover, the composition of the crude material could also be
In the present study we report a new C2-symmetric bis-
sulfinate 2 derived from (R)-1,10-binaphthyl-2,20-diol (1) (BINOL)
* Corresponding author. Tel.: þ39 0250314470; fax: þ39 0250314476; e-mail
address: nicoletta.gaggero@unimi.it (N. Gaggero).
0040-4020/$ e see front matter Ó 2012 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.tet.2012.06.050

7130
N. Gaggero, D.C.M. Albanese / Tetrahedron 68 (2012) 7129e7132
anhydrous potassium carbonate and subsequent reaction with
O
S
0.5 M equiv of tert-butylsulfinyl chloride.17
1. n- BuLi
THF, - 78 °C
In order to test the efficiency of bis-sulfinate esters as sulfinyl
transfer agents, the mixture of 2e4 (Table 1, entry 1) was dissolved
in THF and phenylmagnesium bromide (5a) was dropwise added
at ꢀ78 ꢁC. After complete addition, the temperature was allowed to
reach ꢀ20 ꢁC in 1 h and quenched with NH4Clsat. The reaction
afforded (S)-(-)-tert-butyl phenyl sulfoxide (6a) in 53% chemical
yield and 80% ee as determined by chiral HPLC analysis (Table 2,
entry 1). Moreover, enantiomerically pure (R)-BINOL was recovered
in almost quantitative yield after flash chromatography. Assuming
that the displacement step at the sulfur atom occurs with complete
inversion,13 the absolute configuration of the major bis-sulfinate 2
was determined to be R,RS,RS.
O
O
t-Bu
t-Bu
(R)-1
+
2. t-BuSOCl
S
O
2
O
O
S
S
O
t-Bu
t-Bu
O
O
t-Bu
t-Bu
+
O
S
S
O
4
O
3
Table 2
Synthesis of (S)-tert-butyl sulfoxides 6aee by displacement reactions of sulfinate 2a
Scheme 2. Synthesis of bis-sulfinates 2e4.
Entry
R
Solvent
Time (h)
Yield (%)
ee (%)
1b,c
2c,d
3c
4e
5
6
7
8
9
C6H5 5a
C6H5 5a
C6H5 5a
C6H5 5a
THF
Et2O
Et2O
THF
THF
THF
THF
THF
THF
2
1
1
2
3
3
4
3
3
53
66
63
69
84
85
71
73
77
80
79
78
85
97
95
94
97
87
assigned by HPLC. Under the previously described reaction condi-
tions, a mixture of 2/3/4 in 82:16:2 ratio was obtained in 95%
overall yield (Table 1, entry 1). Silica gel flash chromatography
provided 2, in 77% yield with 97% diastereoisomeric excess.15
C6H5 5a
p-CH3eC6H4 5b
1-Naphthyl 5c
p-CH3OeC6H4 5d
CH3 5e
Table 1
Influence of the base on diastereoselectivity of bis-sulfinates synthesisa
Entry
Base
Time (h)
Yield (%)
2b (%)
4b (%)
3b (%)
a
Reaction conditions: 2 (1 equiv), RMgBr (1.5 equiv), THF, at ꢀ78 ꢁC.
Grignard reagent (1 M equiv) was used in entry 1.
Crude reaction mixture of bis-sulfinates 2e4.
b
c
1
2
3
4
5
6
7
8
9
n-BuLi
1
1
1
3
2
1
1
2.5
2
95
90
95
81
71
93
94
80
75
82
84
75
68
57
56
76
31
39
2
2
6
16
14
19
25
28
32
19
48
46
n-BuLi/LiClc
t-BuLi
d
Addition at room temperature of a bis-sulfinates 2e4 solution (Et2O) to a solu-
NaHd
7
tion of 5a in Et2O.
iPr2NEt
15
12
5
21
15
e
After RMgBr addition the temperature was allowed to reach 25 ꢁC.
LiN[Si(CH3)3]2
LiN[Si(CH3)3]2/LiClc
DBUe
Reaction conditions with Grignard reagent were optimized after
several trials in which solvent, temperature, reagents addition or-
der were analyzed. The best results have been obtained by the
addition of 1.5 M equiv of phenylmagnesium bromide solution to
the sulfinate dissolved in THF at ꢀ78 ꢁC.
Pyridinee
a
Reaction conditions: the base (2.2 mmol) was added to a THF solution of (R)-
BINOL (1 mmol) at ꢀ78 ꢁC. After 30 min tert-butylsulfinyl chloride (4 mmol) was
dropwise added and stirring was continued at ꢀ78 ꢁC.
b
Diastereoisomeric ratios were determined by 1H NMR spectroscopic analysis
After completion of the Grignard reagent addition, the tem-
perature was allowed to gradually increase to ꢀ20 ꢁC in 1 h and the
reaction mixture was quenched with NH4Clsat. Chromatographic
purification afforded (S)-(ꢀ)-tert-butylphenyl sulfoxide (6a) in 84%
chemical yield and 97% ee (Table 2, entry 5). The ee of the sulfoxide
did not change during the progress of the reaction as verified by
chiral HPLC injections of several crude samples at different times.
In an effort to expand the scope of the process we compared
a series of Grignard reagents (5bee) in the displacement reaction.
The results are depicted in Table 2. The corresponding sulfoxides
6bee have been isolated in good yields and ees up to 97%.
The next goal was to verify if structural modifications on the
chiral auxiliary could exert an effect on the ratio of sulfinates. (R)-
3,30-Diphenyl-1,10-bis-(2-naphthol) was prepared from the com-
mercial available (R)-3,30-dibromo-1,10-bis-(2-naphthol),18 and
then converted to bis-sulfinate ester diastereoisomers by using n-
BuLi as base. However, since the presence of phenyl groups in 3,30
positions of the aromatic rings did not increase the diaster-
eoselection nor simplify the purification of the crude bis-sulfinates
mixture, we did not proceed with the displacement reaction with
Grignard reagent.
and HPLC analysis.
c
A 0.5 M (8 mL, 4 mmol) LiCl solution in THF was added after base addition.
d
T¼0e25 ꢁC.
e
T¼ꢀ78/ꢀ40 ꢁC.
In order to investigate the influence of the base on the stereo-
chemical outcome, different bases were used in sulfinate esters
synthesis (Table 1). In fact, it is well known from the literature that
an achiral base could have a stereocontrolling effect on the pre-
vailing sulfinate diastereoisomer formation.16 Sulfinate 2 is the
major diastereoisomer when n-butyllithium (entry 1), tert-butyl-
lithium (entry 3), sodium hydride (entry 4), N,N-di-iso-propyle-
thylamine (entry 5), and hexamethyldisilazane lithium salt (LiN
[Si(CH3)3]2) (entry 6) were used as bases. On the other hand, sulfi-
nate 3 was preferentially formed when 1,8-diazabicyclo[5.4.0]
undec-7-ene (DBU) (entry 8) and pyridine (entry 9) were employed.
The best diastereoselectivity was obtained with n-butyllithium.
The deprotonation step to give a dianionic species is responsible
for the formation of ion-pair aggregate structures, whose reactivity
could be modified by LiCl addition. Therefore, the synthesis of bis-
sulfinates 2e4 has also been carried out by addition of LiCl to the
reaction mixture when n-BuLi and LiN[Si(CH3)3]2 were used (Table
1, entries 2 and 7). In the case of LiN[Si(CH3)3]2 a remarkable in-
crease in bis-sulfinate 2 formation was observed, whereas only
a slight increase was found when n-BuLi was used.
3. Conclusion
In summary, we developed a new practical approach to enan-
tiomerically enriched sulfoxides through conversion of (R)-BINOL 1
to bis-sulfinate 2, followed by displacement of the latter with
Grignard reagents. Direct displacement of the crude bis-sulfinates
The mono-sulfinates were never detected in the experimental
conditions of Table 1, as we verified by comparison with an au-
thentic sample prepared by treating (R)-BINOL with 0.5 M equiv of

N. Gaggero, D.C.M. Albanese / Tetrahedron 68 (2012) 7129e7132
7131
2e4 mixture afforded sulfoxide 6a in good chemical yield but with
ee in the 80% range. However, high ees of the desired sulfoxides
had been obtained by using pure sulfinate 2, recovered by standard
chromatographic purification. As expected, the ee of the sulfoxides
was found to be strictly correlated with the diastereoisomeric
excess of the bis-sulfinate. Moreover, as determined by chiral
HPLC of the crude reaction mixture at uncomplete conversions,
the ee of the sulfoxide did not change during the displacement
reaction.
The stereochemical outcome of the bis-sulfinate synthesis is
influenced by the base employed in the BINOL deprotonation step.
It is also worth noting that 2 mol of sulfoxide could be obtained per
each mole of BINOL, a cheap commercially available chiral auxiliary
that was recovered in almost quantitative yield.
1589, 1563, 1458, 1335, 1204, 1127, 968, 745. Anal. Calcd for
C
28H30O4S2 (494.67): C, 67.98; H, 6.11. Found: C, 67.78; H, 6.13.
HPLC (Chiralcel OD hex/iPrOH 99:1) tR 12.4 min (tR 3 11.4 min; tR
4 10.0 min); de 97%.
Sulfinates 3 and 4 were also recovered as a mixture:
3: dH (300 MHz, CDCl3) 0.62 (s, 9H, CeCH3), 0.75 (s, 9H, CeCH3),
7.13 (d, 2H, J 8.5 Hz, ArH), 7.29 (d, 2H, J 7.4 Hz, ArH), 7.43 (m, 2H,
ArH), 7.67 (d, 2H, J 8.8 Hz, ArH), 7.90 (d, 2H, J 8.1 Hz, ArH), 7.96 (d,
2H, J 8.8 Hz, ArH); HPLC (Chiralcel OD hex/iPrOH 99:1) tR 11.4 min.
4: dH (300 MHz, CDCl3) 0.61 (s, 18H, CeCH3), 7.13 (d, 2H, J 8.5 Hz,
ArH), 7.29 (d, 2H, J 7.4 Hz, ArH), 7.43 (m, 2H, ArH), 7.67 (d, 2H, J
8.8 Hz, ArH), 7.90 (d, 2H, J 8.1 Hz, ArH), 7.96 (d, 2H, J 8.8 Hz, ArH);
HPLC (Chiralcel OD hex/iPrOH 99:1) tR 10.0 min.
4.3. Synthesis of 20-hydroxy-1,10-binaphthyl-2-yl 2-
methylpropane-2-sulfinate (7)
The displacement reaction by Grignard reagents affords tert-
butyl sulfoxides with high ee, good yields, and a predictable ab-
solute configuration. In fact the desired sulfoxide enantiomer can
be generated at will by the proper selection of the starting chiral
auxiliary.
For these reasons this paper fills a gap in the use of C2 chiral
auxiliaries and appears to be a useful complement to existing
routes to enantiopure sulfoxides.
O
S
OH
O
t-Bu
4. Experimental section
4.1. General remarks
7
To a solution of R-(þ)-BINOL (572 mg, 2 mmol) in acetone
(2 mL) under nitrogen was added K2CO3 (346 mg, 2.5 mmol) at
room temperature. After stirring for 15 min at the same tempera-
ture tert-butylsulfinyl chloride (281 mg, 2 mmol) was dropwise
added and stirring was continued for 3 h. The resulting mixture was
quenched by the addition of saturated aqueous ammonium chlo-
ride (5 mL) and diluted with ethyl acetate (5 mL). The aqueous layer
was extracted with ethyl acetate (3ꢂ20 mL) and the combined or-
ganic layers were dried and concentrated to a small volume. Flash
chromatography of the crude material with Et2O/PE (1:3) afforded
€
Melting points were determined on a BUCHI 535. NMR spectra
were recorded on Bruker AC 300 or AC 200 spectrometers, oper-
ating at 300.13 or 200.13 MHz for 1H NMR and 75.3 or 50 MHz for
13C NMR. Coupling constants J are in hertz. Chemical shifts were
reported by using CHCl3 as external standard (7.24 ppm for 1H NMR
and 77.0 for 13C NMR). Column chromatography on silica gel
(230e400 mesh) was performed by the flash technique. Petroleum
ether (PE) refers to the fraction boiling in the range of 40e60 ꢁC.
Mass spectra were measured on an LCQ Advantage Thermo-
the title compound (437 mg, 56% yield) mp 160 ꢁC, [
a]
25 þ326.2 (c,
Finnigan spectrometer. Optical rotations were measured with
D
25
0.7, CHCl3) dH (300 MHz, CDCl3) 0.71 (s, 9H, CeCH3), 7.14 (d, 1H, J
7.9 Hz, ArH), 7.26e7.43 (m, 5H, ArH), 7.53 (m, 1H, ArH), 7.73 (d, 1H, J
8.9 Hz, ArH), 7.86 (d, 1H, J 8.5 Hz, ArH), 7.93 (d, 1H, J 8.9 Hz, ArH),
8.00 (d, 1H, J 8.2 Hz, ArH), 8.08 (d, 1H, J 8.9 Hz, ArH); dC (75 MHz,
CDCl3) 20.9 (CH3), 58.8 (C),114.0 (C),117.4 (CH), 121.2 (C), 121.7 (CH),
123.6 (CH), 124.8 (CH), 125.3 (CH), 126.0 (CH), 126.8 (CH), 127.7
(CH), 127.9 (CH), 128.4 (CH), 129.0 (C), 130.3 (CH), 131.1 (CH), 131.9
(C), 133.3 (C), 133.7 (C), 151.2 (C), 151.4 (C); IR (neat, cmꢀ1) 3420,
2945, 2910, 2830, 1580, 1535, 1465, 1342, 1212, 1133, 973, 725; m/z
(ESI) 413 [MþNa]þ. Anal. Calcd for C24H22O3S (390.50): C, 73.82; H,
5.68. Found: C, 73.74; H, 5.76.
a PerkineElmer 241 polarimeter; the [
a]
values are reported in
D
10ꢀ1 deg cm2
g
ꢀ1, concentration (c) is reported in g per 100 mL.
Chiral HPLC separations were performed on an Agilent HP 1100
apparatus, equipped with a diode array detector, using mixtures of
hexane/2-propanol as eluant, detection at 230 nm unless otherwise
stated. The flux was set to 1 ml minꢀ1 and the volume of injection
was 20 mL.
4.2. Synthesis of (R,SR,SR)-1,10-binaphthalene-2,20-diyl-bis-
(tert-butylsulfinate) (2)
To a solution at ꢀ78 ꢁC of R-(þ)-BINOL (286 mg, 1 mmol) in dry
tetrahydrofuran (5 mL) under nitrogen was added dropwise n-
butyllithium (1.96 mL, 1.12 M in hexane, 2.2 mmol). After 30 min,
tert-butylsulfinyl chloride (563 mg, 4 mmol) was dropwise added
and stirring was continued for 80 min at ꢀ78 ꢁC. The resulting
mixture was quenched by the addition of saturated aqueous am-
monium chloride (5 mL) and diluted with ethyl acetate (5 mL). The
aqueous layer was extracted with ethyl acetate (3ꢂ20 mL) and the
combined organic layers were dried and concentrated to a small
volume. Flash chromatography of the crude material with hexane/
4.4. Typical procedure for the synthesis of sulfoxides 6aee
To a solution of sulfinate ester 2 (494 mg, 1 mmol) in anhydrous
THF under nitrogen at ꢀ78 ꢁC, a solution of phenylmagnesium
bromide (5a) (3 mmol, 3 mL of 1 M THF solution) was dropwise
added over a 5 min period. The reaction mixture was stirred
at ꢀ78 ꢁC for 30 min, then was allowed to reach ꢀ20 ꢁC, quenched
by the addition of saturated aqueous ammonium chloride solution.
The temperature was allowed to reach 20 ꢁC and ethyl acetate
(10 mL) was added. The aqueous layer was extracted with ethyl
acetate (3ꢂ20 mL), the combined organic layers were dried and the
solvent was removed in vacuo. Flash chromatography of the crude
material with dichloromethane/ethyl acetate (8:2) afforded 306 mg
ethyl acetate (1:10) afforded the title compound as a white solid
25
(381 mg, 77% yield); mp 178e180 ꢁC [
a]
ꢀ160 (c 1, CHCl3); dH
D
(300 MHz, CDCl3) 0.69 (s, 18H, CeCH3), 7.13 (d, 2H, J 8.5 Hz, ArH),
7.29 (d, 2H, J 7.4 Hz, ArH), 7.43 (m, 2H, ArH), 7.67 (d, 2H, J 8.8 Hz,
ArH), 7.90 (d, 2H, J 8.1 Hz, ArH), 7.96 (d, 2H, J 8.8 Hz, ArH); dC
(75 MHz, CDCl3) 20.9 (CH3), 58.6 (C), 121.0 (CH), 122.9 (C), 125.4
(CH), 126.1 (CH), 126.9 (CH), 128.0 (CH), 130.1 (CH), 131.2 (C), 133.7
(C), 150.4 (C); m/z (APCI) 495; IR (neat, cmꢀ1) 2951, 2922, 2853,
(84% yield) of (S)-(ꢀ)-tert-butylsulfinylbenzene (6a) as a white solid
25
mp 89 ꢁC [lit.2 (S)-6a, 90 ꢁC]. [
a]
ꢀ171 (c 1, CHCl3), [lit.2 (S)-6a
D
ꢀ175 (CHCl3)]; HPLC Chiralcel OD hex/iPrOH 99:1, tR (S) 26.7 min; tR
(R) 24.7 min, ee 97%.

7132
N. Gaggero, D.C.M. Albanese / Tetrahedron 68 (2012) 7129e7132
6. (a) Colonna, S.; Gaggero, N.; Carrea, G.; Pasta, P. In Asymmetric Oxidation
Sulfoxides 6bed are known compounds and have been pre-
Reactions; Katsuky, T., Ed.; Oxford University: Oxford, 2001; pp 227e235; (b)
Bryliakov, K. P.; Talsi, E. P. Curr. Org. Chem. 2008, 12, 386e404; (c) Gaggero, N.;
Colonna, S.; Albanese, D.; Del Monte, F. Phosphorous, Sulfur 2009, 184,
1332e1339.
7. (a) Wojaczynska, E.; Woiaczynski, J. Chem. Rev. 2010, 110, 4303e4356; (b)
Capozzi, M. A. M.; Cardellicchio, C.; Naso, F. Eur. J. Org. Chem. 2004, 1855e1863;
(c) Mata, E. G. Phosphorus, Sulfur 1996, 117, 231e286.
pared by using the same procedure described above for 6a by using
the proper Grignard reagent 5bed. Physical and spectroscopic
properties of 6bed are identical to those previously reported. Op-
tical purity has been determined by comparison of [
reported in the literature.
a]
25 with those
D
25 ꢀ180 (c
8. (a) Andersen, K. K. Tetrahedron Lett. 1962, 3, 93e95; (b) Whitesell, J. K.; Wong,
(S)-(ꢀ)-1-Methyl-4-tert-butylsulfinylbenzene (6b) [
a
]
D
0.8, EtOH), ee 95% [lit.19 (R)-6b [
a
]
25 þ190 (EtOH)].
ꢁ
H.-S. J. Org. Chem. 1991, 56, 4552e4554; (c) Llera, J. M.; Fernandez, I.; Alcudia, F.
D
Tetrahedron Lett. 1991, 32, 7299e7302.
9. Cogan, D. A.; Liu, G.; Kim, K.; Backes, B. J.; Ellman, J. A. J. Am. Chem. Soc. 1998,
120, 8011e8019.
(S)-(ꢀ)-tert-Butylsulfinyl-1-naphthalene (6c) [
a
]
25 ꢀ310 (c 1.30,
D
25
CHCl3) ee 94% [lit.4 (S)-6c [
a]
ꢀ330 (c 1.39, CHCl3)].
D
25
10. (a) Jacobus, J.; Mislow, K. J. Chem. Soc., Chem. Commun. 1968, 253e254; (b)
Evans, D. A.; Faul, M. M.; Colombo, L.; Bisaha, J. J.; Clardy, J.; Cherry, D. J. Am.
Chem. Soc. 1992, 114, 5977e5985; (c) Oppolzer, W.; Froelich, O.; Wiaux-Zamar,
C.; Bernardinelli, G. Tetrahedron Lett. 1997, 38, 2825e2828.
11. Rebiere, F.; Kagan, H. B. Tetrahedron Lett. 1989, 30, 3659e3662.
12. (a) Wudl, F.; Lee, T. B. K. J. Chem. Soc., Chem. Commun. 1972, 61e62; (b) Roe, C.;
Hobbs, H.; Stockman, R. A. J. Org. Chem. 2011, 76, 9452e9459; (c) Han, Z. S.;
Meyer, A. M.; Xu, Y.; Zhang, Y.; Busch, R.; Shen, S.; Grinberg, N.; Lu, B. Z.;
Krishnamurthy, D.; Senanayake, C. H. J. Org. Chem. 2011, 76, 5480e5484.
13. (a) Mikolajczyk, M.; Drabowicz, J. Top. Stereochem. 1982, 13, 333e468; (b)
Jacobus, J.; Mislow, K. J. Am. Chem. Soc. 1967, 89, 5228e5234; (c) The Chemistry
of Sulfinic Acids, Esters and Their Derivatives; Patai, S., Ed.; Wiley: New York, NY,
1990.
(S)-(ꢀ)-1-Methoxy-4-tert-butylsulfinylbenzene (6d) [
a]
ꢀ148
D
(c 1.35, CHCl3) ee 97% [lit.20 (R)-6d [
a
]
D
25 þ116 (c 0.9, CHCl3) ee 76%].
(S)-(ꢀ)-tert-Butyl-methylsulfoxide (6e) [
a]
25 þ6.8 (c 6.5, CHCl3)
D
ee 87% [lit.21 (S)-6e [
a
]
25 þ7.8 (c 7, CHCl3)].
D
Acknowledgements
The research has been supported by MIUR: ‘Nuovi metodi
catalitici stereoselettivi e sintesi stereoselettiva di molecole fun-
zionali’ and by the University of Milan Research Funds (PUR).
14. Whitesell, J. K. Chem. Rev. 1989, 89, 1581e1590.
15. The diastereoisomeric excess was measured by 1H NMR spectroscopic analysis,
which revealed a 2/3þ4 ratio of 98.5 to 1.5.
References and notes
ꢁ
16. (a) Fernandez, I.; Khiar, N.; Roca, A.; Benebra, A.; Alcudia, A.; Espartero, J. L.;
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