Aryl tert-butyl sulfoxide-promoted highly enantioselective addition of allyltrichlorosilane to aldehydes

Article abstract of DOI:10.1039/b909850j

A series of enantiomerically pure mono- and bis-aryl tert-butyl sulfoxides were synthesised to promote the enantioselective allylation of aldehydes with allyltrichlorosilane. Moderate to good yields and modest to high enantioselectivities were achieved. The absence of nonlinear effect, spacer effect, promoter loading and concentration effect indicate that only one molecule of aryl tert-butyl sulfoxide is involved in the stereodetermining step.

Full text of DOI:10.1039/b909850j

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www.rsc.org/obc | Organic & Biomolecular Chemistry
Aryl tert-butyl sulfoxide-promoted highly enantioselective addition of
allyltrichlorosilane to aldehydes†
Peng Wang,a,b Junmin Chen,a,b,c Linfeng Cun,a Jingen Deng,a,b Jin Zhua,b and Jian Liao*a,b
Received 19th May 2009, Accepted 17th June 2009
First published as an Advance Article on the web 13th July 2009
DOI: 10.1039/b909850j
A series of enantiomerically pure mono- and bis-aryl tert-butyl sulfoxides were synthesised to promote
the enantioselective allylation of aldehydes with allyltrichlorosilane. Moderate to good yields and
modest to high enantioselectivities were achieved. The absence of nonlinear effect, spacer effect,
promoter loading and concentration effect indicate that only one molecule of aryl tert-butyl sulfoxide is
involved in the stereodetermining step.
context, we became interested in improving the enantioselectivity
of this reaction using chiral sulfoxides as promoters.
It is well documented that the S-chiral tert-butylsulfinyl moiety
aldehydes represents an important method for enantioselective
is an excellent stereocontrolling element that has been involved
Introduction
The asymmetric addition of allylic organometallic reagents to
in chiral auxiliaries,17 ligands18 and the Lewis base catalysts used
for the asymmetric reduction of ketimines with trichlorosilane.19
However, the utilisation of tert-butyl sulfoxides as promoters for
the allylation of aldehydes with allyltrichlorosilane so far has
seen little success. Rowlands found that oxazoline-based tert-butyl
sulfoxide was ineffective in promoting this reaction.15a Khiar also
found tert-butylsulfinylferrocene and bis(tert-butylsulfinyl)ethane
less stereoselective than their less hindered sulfoxide counterparts
in the allylation of acyl hydrazones with allyltrichlorosilane.20
Nonetheless, finding out whether tert-butyl sulfoxides can be
developed into highly stereoselective Lewis base catalysts requires
a systematic study that includes fine-tuning the substituents on
the sulfinyl sulfur. Herein, we report our preliminary study on
the synthesis of mono- and bis-aryl tert-butyl sulfoxides and their
application in promoting the asymmetric allylation of aldehydes
with allyltrichlorosilane. The results are encouraging not only
because these sulfoxides represent the most enantioselective Lewis
base catalysts for this reaction (up to 90% ee), but also because
the mechanistic study indicates that only one sulfoxide is involved
in the stereodetermining step, which is unknown for sulfoxide-
promoted allylation reactions.
carbon–carbon bond formation. The homoallylic alcohol prod-
ucts are useful chiral building blocks in organic synthesis and
can be readily converted to other functionalised molecules that
are of great value to the pharmaceutical and fine-chemicals
industries.1 Different strategies, including the use of chirally mod-
ified allylmetal reagents,2 chiral Lewis acid-catalysed addition of
allylmetal reagents to aldehydes,3–5 and chiral Lewis base-catalysed
allylation of aldehydes with allyltrichlorosilane,6 have been applied
to achieve this transformation. Pioneered by Kobayashi7 and
Denmark,8 the chiral Lewis base strategy features a catalytic
format and excellent diastereoselectivity originating from a closed
transition state structure and, therefore, has attracted great
attention in the last decades. A wide variety of chiral Lewis bases
has been demonstrated to be effective in the enantioselective ad-
dition of allyltrichlorosilane to aldehydes. Among these are chiral
phosphoramides,9 N-oxides,10 formamides,11 phosphine oxides,12
amines13 and ureas.14 In 2003, Rowlands and Massa independently
reported that chiral sulfoxides were effective in promoting the
enantioselective allylation of aldehydes with allyltrichlorosilane.15
However, two major disadvantages existed. First, the enan-
tioselectivities achieved by these chiral sulfoxides were modest.
Second, stoichiometric or more than stoichiometric amounts of
the promoters were needed to attain satisfying yields. Very recently,
Massa found that with the use of a tetradentate bis-sulfoxide, the
reaction can be rendered catalytic and satisfying yields can be
obtained. Still, modest enantioselectivities were observed.16 In this
Results and discussion
We first synthesised a series of enantiomerically pure mono-aryl
tert-butyl sulfoxides with different electronic and steric properties
and evaluated these in promoting the allylation of benzaldehyde
with allyltrichlorosilane. Sulfoxides 3a–e were prepared in one step
with high yields (72–92%) according to a literature procedure.21
Starting from 3e, sulfoxides 5a–d can also be readily prepared in
two steps (Scheme 1).
The model reaction was carried out on a 0.4 mmol scale of
benzaldehyde 6a in CH2Cl2. Similar to methyl-p-tolyl sulfoxide,15b
the use of phenyl tert-butyl sulfoxide 3a resulted in moderate
yield (48%) and enantioselectivity (59% ee, Table 1, entry 1).
Gratifyingly, it was found that the substituents on the phenyl ring
played an important role in the enantioselectivity. While the use
of 3b and 3d bearing ortho-methyl and para-methoxy substituents
aNational Engineering Research Center of Chiral Drugs and Key Laboratory
of Asymmetric Synthesis and Chirotechnology of Sichuan Province, Chengdu
Institute of Organic Chemistry, Chinese Academy of Sciences, Chengdu,
610041, China. E-mail: jliao10@cioc.ac.cn; Fax: +86 28 8522 3978;
Tel: +86 28 8522 9250
bGraduate School of Chinese Academy of Sciences, Beijing, 100049, China
cCollege of Chemistry and Chemical Engineering, Jiangxi Normal Univer-
sity, Nanchang, 330022, China
† Electronic supplementary information (ESI) available: 1H NMR, 13C
NMR and high-resolution mass spectra of mono- and bis-sulfoxides;
HPLC/GC chromatograms of homoallylic alcohol products. See DOI:
10.1039/b909850j
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Table 1 Enantioselective allylation of benzaldehyde 6a with allyl-
trichlorosilane promoted by mono-aryl tert-butyl sulfoxides
Table 2 Enantioselective allylation of aromatic aldehydes promoted by
5ba
Entrya Promoter
7/equiv.
Time/h
Yieldc (%)
eed (S, %)
Entry
6 (Ar)
Time/h
Yieldb (%)
eec (S, %)
1
2
3
4
5
6
7
8
9
3a
3b
3c
3d
3e
5a
5b
5c
5d
5d
5d
5d
5d
1.5
1.5
1.5
1.5
1.5
1.5
1.5
1.5
1.5
1.5
3.0
3.0
3.0
12
12
12
12
12
12
12
12
12
12
6
48
58
68
56
67
69
67
52
46
55
72
74
75
59
43
72
39
78
79
86
87
89
58
86
85
84
1
2
6a (Ph)
6
4
6
6
8
8
8
8
6
5
3
6
72
89
65
47
62
45
53
57
80
68
82
35
86
81
59
84
88
83
81
79
82
76
63
80 (R)
6b (o-MeOC6H4)
6c (p-MeOC6H4)
6d (p-BrC6H4)
6e (o-BrC6H4)
6f (p-ClC6H4)
6g (o-ClC6H4)
6h (p-MeC6H4)
6i (m-O2NC4H6)
6j (1-naphthyl)
3d
4
5
6
7e
8
9
10b
11
12
13
10
11
12
=
6k ((E)-C6H5CH CH)
6l (C6H5CH2CH2)
12
24
a The reaction was carried out with 0.4 mmol of 6 (1 equiv.), 3 equiv. of 5b,
3 equiv. of 7 and 5 equiv. of i-Pr2NEt in 2.0 ml CH2Cl2 at -78 ◦C. b Isolated
yield. c ee was determined by chiral GC-HPLC analysis and the absolute
configuration of 8a–k was determined by comparison of optical rotation
to the literature. d The aldehyde was purified by silica gel chromatography
before use. e The ee was determined after acetylation.
a Unless otherwise stated, the allylation was carried out with 0.4 mmol
(1 equiv.) of 6a, 3 equiv. of the promoter and 5 equiv. of i-Pr2NEt in 2 ml
CH2Cl2 at -78 ◦C. b At -40 ◦C. c Isolated yield. d ee was determined by
chiral HPLC analysis and the absolute configuration of 8a was determined
by comparison of optical rotation values in the literature.
temperature is a prerequisite for high enantioselectivity. Increasing
the temperature to -40 ◦C led to a decreased enantioselectivity
(65% ee, Table 1, entry 10). With an increased amount of
allyltrichlorosilane (3.0 equiv.), the yield was improved to 72%
after only 6 h and the enantioselectivity was not affected (Table 1,
entry 11). In addition, the promoter can be recovered in 97% yield
and >99% ee (Table 1, entry 11) by eluting with EtOAc. Prolonged
reaction time resulted in a slight decrease in the ee values and a
slight increase in yields after 12 h and 24 h (Table 1, entries 14 and
15), which means that 6 h is a very reasonable, if not the best, time
for the model reaction.
Next, we tested the substrate scope by using 5b as promoter. The
reactions of aldehydes with allyltrichlorosilane were monitored
by thin layer chromatography (TLC) and quenched when the
aldehydes were not being consumed at an appreciable rate. The
results are shown in Table 2.
All the aromatic and a,b-unsaturated aldehydes we used to
test the substrate scope were converted to the corresponding
homoallylic alcohols in moderate to high yields (45–89%) and
good to high enantioselectivities (59–88% ee). Even for aliphatic
aldehyde 6l, the enantioselectivity is good (80% ee), although the
yield is moderate (35%, Table 2, entry 12). It is noteworthy that 5b
exhibits quite different reactivities and selectivities towards ortho-
methoxy benzaldehyde 6b and para-methoxy benzaldehyde 6c
(Table 2, entries 2–3), which again demonstrates the significant yet
unknown effect of the “ortho-oxygen” on the enantioselectivities.
To make a comparison with the allylation of aldehydes
promoted by mono-aryl tert-butyl sulfoxides, bis-aryl tert-butyl
sulfoxides 9a–c with varying tether lengths from one to three
carbons were also synthesised (Scheme 2). The ortho-oxygen
was incorporated into the structures of 9a–c to ensure a better
comparison with the most stereoselective mono-sulfoxides.
We found that bis-sulfoxide 9b with a two-carbon tether
was the most stereoselective bis-sulfoxide for the allylation of
Scheme 1 Synthesis of mono-aryl tert-butyl sulfoxides.
led to an increase in yield (58% and 56%, respectively) and a drop
in enantioselectivity (43% ee and 39% ee, respectively, Table 1,
entries 2 and 4), improved enantioselectivities (72% ee and 78%
ee) and yields (60% and 67%, Table 1, entries 3 and 5) were
observed when using 3c and 3e with ortho-methoxy and ortho-
methoxymethoxy substituents as the promoters, which might
be attributed both to the electron donating character of these
alkoxy substituents and to the silicon coordination ability of the
ortho-alkoxy group. Inspired by these results, a series of ortho-
alkoxyphenyl tert-butyl sulfoxides, 5a–d, were further evaluated
in promoting the model reaction. Moderate to good yields (46–
69%) as well as high enantioselectivities (up to 89% ee) were
obtained (Table 1, entries 6–9). Since sulfoxide 5b has a superior
reactivity to sulfoxides 5c and 5d, it was chosen as the promoter for
further investigation. In line with the observation by Massa,15b low
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Table 3 Allylation of benzaldeyde promoted by bidentate aryl tert-butyl
of benzaldehyde (0.4 mmol, 1 equiv.) with allyltrichlorosilane
(0.6 mmol, 1.5 equiv.) promoted either by 3a or 5d (1.2 mmol,
3 equiv.), a linear relationship between the enantiomeric excess
of the promoter and the product was observed (Fig. 1), which
bolstered our assumption that only one molecule of the aryl tert-
sulfoxide was involved in the stereodetermining step.
sulfoxides with varying tether lengthsa
Finally, we investigated the influence of the promoter loading
and concentration on the enantioselectivity, which were previously
studied by Khiar to probe the operating pathway of the allylation
of acyl hydrazones with allyltrichlorosilane promoted by chiral
sulfoxides.20b We selected three representative promoters, 3a, 3c
and 5d, to see if there is any promoter loading and concentration
effect. The results are shown in Table 4. For all the chosen
promoters, no significant change in enantioselectivity was found
when both the promoter loading and concentration decreased
(Table 4, entries 1–6). This is in contrast with Khiar’s observation
that decreasing the promoter loading or concentration leads to
a dramatic decline in enantioselectivity.20b The independence of
enantioselectivity on the promoter loading and concentration in
our case indicates that there might be only one coordination
pattern of sulfoxide to allylsilane (if not, then high promoter
loading and concentration will favor two-sulfoxide coordination
pattern, which is supposed to be more enantioselective). Combined
with our previous findings that there was no spacer or nonlinear
effect, we assume that only one molecule of aryl tert-butyl
sulfoxide is coordinated to the allylsilane in the stereodetermining
Entry
Promoter
Yieldb(%)
eec(S, %)
1
2
3
9a
9b
9c
74
77
76
86
90
88
a The allylation was carried out with 0.4 mmol (1 equiv.) 6a, 1.5 equiv.
of 9, 1.5 equiv. of 7 and 5 equiv. of i-Pr2NEt in 2 ml CH2Cl2 at -78 ◦C
for 6 h. b Isolated yield. c ee was determined by chiral HPLC analysis and
the absolute configuration of 8a was determined by comparison of optical
rotation values in the literature.
Scheme 2 Synthesis of bis-aryl tert-butyl sulfoxides.
Table 4 Enantioselective allylation of benzaldehyde with the use of
sulfoxides 3a, 3c and 5ba
benzaldehyde with allyltrichlorosilane (Table 3, entry 2). High
enantioselectivity (90%) and high yield (77%) were obtained,
which represents the best result of this reaction promoted by
chiral sulfoxides. What attracted us more is that bis-sulfoxides 9a–c
demonstrated similar reactivities and enantioselectivities (Table 3,
entries 1–3). These results are in sharp contrast to those of the
bis-phosphoramide-catalysed allylation of benzaldehyde with al-
lyltrichlorosilane where a great dependence of enantioselectivities
on the tether lengths was observed,9b,e suggesting that the two
sulfoxide moieties might be operating independently rather than
cooperatively, i.e., only one sulfoxide moiety is involved in the
coordination sphere of the allyltrichlorosilane.
To find further support for the hypothesis that only one
sulfoxide moiety is involved in the stereodetermining step in our
case, we examined whether there is a nonlinear effect in the
model reaction promoted by non-substituted sulfoxide 3a and
sulfoxide 5d bearing an ortho-benzyloxy group. In the allylation
Entry
Promoter
Equiv.
[P]/M
Yieldb(%)
eec (%)
1
2
3
4
5
6
3a
3a
3c
3c
5b
5b
3.0
1.0
3.0
1.0
3.0
1.0
0.6
0.2
0.6
0.2
0.6
0.2
48
36
68
46
67
41
59
61
72
71
86
86
a The reaction was carried out with 1.5 equiv. of allyltrichlorosilane and
5 equiv. of i-Pr2NEt in 2 ml CH2Cl2 at -78 ◦C for 12 h. b Isolated yield.
c Determined by chiral HPLC analysis.
Fig. 1 (a) Linear effect of allylation with promoter 3a. (b) Linear effect of allylation with promoter 5b.
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step. Although apparently, differently from Khiar’s two-sulfoxide
coordination mechanism, these observations can also be well
understood: due to the steric bulkiness of the tert-butyl group,
the coordination sphere of the silicon of the allyltrichlorosilane
can only accommodate one molecule of aryl tert-butyl sulfoxide.
300 MHz): d 7.59–7.56 (m, 2H), 7.48–7.46 (m, 3H), 1.15 (s, 9H).
13C NMR (CDCl3, 75 MHz): d 139.8, 131.1, 128.3, 126.3, 55.8,
22.7. IR (KBr) (cm-1): 2863–3070, 1440, 1362, 1034, 751. HRMS:
Calcd. for C10H14OS + Na: 205.1099, found: 205.0653.
1-(R)-(+)-tert-Butylsulfinyl-2-methylbenzene (3b). Pale yellow
oil. Yield 72%. [a]D = +112.4 (c 1.0, EtOAc). 1H NMR (CDCl3,
25
Conclusion
300 MHz): d 7.83–7.79 (m, 1H), 7.39–7.34 (m, 2H), 7.21–7.18
(m, 1H), 2.43 (s, 3H), 1.20 (s, 9H). 13C NMR (CDCl3, 75 MHz):
d 139.1, 137.5, 130.8, 130.5, 126.5, 126.2, 57.5, 23.0, 19.5. IR (KBr)
(cm-1): 2875–3084, 1463, 1440, 1360, 1028, 759. HRMS: Calcd. for
C11H16OS + Na: 219.0814, found: 219.0811.
In summary, we have synthesised a series of enantiomerically
pure mono- and bis-aryl tert-butyl sulfoxides and evaluated their
ability to promote the asymmetric allylation of aldehydes with
allyltrichlorosilane. We found that the ortho-oxygen on the phenyl
group of the sulfoxide was a prerequisite for high enantioselec-
tivities and good yields. The highest enantioselectivity (90% ee)
was achieved by bis-sulfoxide 9b with a two-carbon linkage, which
is also the highest enantioselectivity ever known for this reaction
promoted by a chiral sulfoxide. Besides, the method developed
here is quite general for aromatic aldehydes and a,b-unsaturated
aldehydes. Even for aliphatic aldehydes, the enantioselectivity
is good, although the yield is moderate. Mechanistic studies,
including the investigation of spacer effect, nonlinear effect,
promoter loading and concentration effect, indicate that the
activation of allyltrichlorosilane is through the coordination of
one molecule of aryl tert-butyl sulfoxide to the allyltrichlorosilane.
1-(R)-(+)-tert-Butylsulfinyl-2-methoxybenzene (3c). Pale yel-
25
1
low oil. Yield 84%. [a]D = +281.9 (c 1.0, EtOH). H NMR
(CDCl3, 300 MHz): d 7.73 (dd, J = 7.7 Hz, 1.7 Hz, 1H), 7.43–7.38
(m, 1H), 7.13–7.08 (m, 1H), 6.88 (d, J = 8.3 Hz, 1H), 3.81 (s, 3H),
1.17 (s, 9H). 13C NMR (CDCl3, 75 MHz): d 157.1, 132.2, 128.6,
127.3, 120.9, 110.6, 57.3, 55.4, 22.8. IR (KBr) (cm-1): 2863–3070,
1478, 1361, 1278, 1031, 756. HRMS: Calcd. for C11H16O2S + Na:
235.0763, found: 235.0781.
1-(R)-(+)-(tert-Butylsulfinyl)-4-methoxybenzene (3d). White
solid. Yield 81%. mp = 80–82 ◦C. [a]D = +171.5 (c 1.0, EtOH).
25
1H NMR (CDCl3, 300 MHz): d 7.51 (dd, J = 6.8 Hz, 2.0 Hz, 2H),
6.99 (dd, J = 6.9 Hz, 2.0 Hz, 2H), 3.85 (s, 3H), 1.14 (s, 9H). 13C
NMR (CDCl3, 75 MHz): d 162.0, 130.9, 127.9, 113.9, 55.6, 55.4,
22.7. IR (KBr) (cm-1): 2861–3086, 1493, 1404, 1250, 1030, 793.
HRMS: Calcd. for C11H16O2S + Na: 235.0763, found: 235.0767.
Experimental
General methods
1-(R)-(+)-tert-Butylsulfinyl-2-(methoxymethoxy)benzene (3e).
◦
25
Unless otherwise stated, materials were obtained from commercial
suppliers and used without further purification. (R)-tert-Butyl tert-
butanethiosulfinate was prepared according to our method.21 All
reactions were performed under an argon atmosphere in flame-
dried glassware. 1H NMR and 13C NMR spectra were acquired at
300 MHz and 75 MHz, respectively. Melting points were measured
with BUCHI melting point B-545. Optical rotations were recorded
on a PE Polarimeter-341. Enantiomeric excess was determined
by chiral HPLC or chiral GLC. Electrospray ionisation high-
resolution mass spectra (ESI-HRMS) were recorded on a Bruker
P-SIMS-Gly FT-ICR mass spectrometer. THF was dried with
sodium/benzophenone. CH2Cl2 was dried with CaH2.
White solid. Yield 91%. mp = 81–82 C. [a]D = +323.8 (c 1.0,
1
EtOAc). H NMR (CDCl3, 300 MHz): d 7.76 (dd, J = 7.8 Hz,
1.6 Hz, 1H), 7.43–7.37 (m, 1H), 7.20–7.13 (m, 2H), 5.19 (AB,
J = 6.9 Hz, 2H), 3.47 (s, 3H), 1.21 (s, 9H). 13C NMR (CDCl3,
75 MHz): d 155.0, 132.3, 129.1, 127.4, 122.1, 114.1, 94.8, 57.5,
56.5, 22.9. IR (KBr) (cm-1): 2865–3026, 1471, 1365, 1268, 1033,
776. HRMS: Calcd. for C12H18O3S + Na: 265.0874, found:
265.0877.
General procedure for the synthesis of sulfoxides 5a–d
Synthesis of 4. To a solution of 3e (2.42 g, 10 mmol) was added
12 M HCl (40 ml). The resulting mixture was stirred at room
temperature for 12 h and then the solvent was evaporated under
reduced pressure. The aqueous layer was extracted with CH2Cl2
(50 ml ¥ 3). The organic layer was washed with brine and dried
over anhydrous MgSO4. After filtration, the solvent was removed
under reduced pressure. The product was purified by silica gel
column chromatography (9 : 1 petroleum ether : ethyl acetate)
General procedure for the synthesis of sulfoxides 3a–e
At -78 ◦C, n-BuLi (4.4 ml, 2.5 M in hexane, 11.0 mmol, 1.1 equiv.)
was added dropwise to the solution of the corresponding bro-
mobenzene (1.05 ml, 10.0 mmol) or its derivatives in anhydrous
THF (50 ml) over 3 min. The resulting mixture was stirred
for 30 min at -78 ◦C and a solution of (R)-tert-butyl tert-
butanethiosulfinate (2.13 g, 11.0 mmol, 1.1 equiv.) in THF (10 ml)
was added. The resulting mixture was stirred for 2 h at -78 ◦C and
then quenched with H2O (5 ml). The solvent was evaporated under
reduced pressure. The aqueous layer was extracted with CH2Cl2
(30 ml ¥ 3). The organic layer was washed with brine and dried
over anhydrous MgSO4. After filtration, the solvent was removed
under reduced pressure. The product was purified by silica gel
column chromatography (7 : 1 petroleum ether : ethyl acetate).
1
to yield pure 4 as a white solid (1.80 g, 91% yield). H NMR
(CDCl3, 300 MHz): d 10.9 (br, 1H), 7.36–7.33 (m, 1H), 6.94–
6.91 (m, 1H), 6.90–6.87 (m, 2H), 1.33 (s, 9H). 13C NMR (CDCl3,
75 MHz): d 161.8, 132.9, 127.8, 119.6, 118.7, 116.4, 58.8, 22.9.
HRMS: Calcd. for C10H14O2S + H: 199.0793, found: 199.0792.
Synthesis of 5a–d. To a mixture of 4 (1.98 g, 10 mmol) and
anhydrous K2CO3 (13.8 g, 100 mmol) in DMF (50 ml) was added
the corresponding bromoalkane (12 mmol). The resulting mixture
was stirred at 60 ◦C for 1 h and then filtered. The DMF was
removed under reduced pressure and H2O (10 ml) was added. The
mixture was extracted with CH2Cl2 (50 ml ¥ 3). The organic layer
(R)-(+)-tert-Butylsulfinylbenzene (3a). White solid. Yield 92%.
mp = 89–91 ◦C. [a]D = +295.5 (c 1.0, EtOH). 1H NMR (CDCl3,
25
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was washed with brine and dried over anhydrous MgSO4. After
filtration, the solvent was removed under reduced pressure. The
product was purified by silica gel column chromatography (7 : 1
petroleum ether : ethyl acetate).
Bis(2-((R)-tert-butylsulfinyl)phenoxy)methane
(9a). White
solid. Yield 42%. mp = 113–115 ◦C. [a]D = +260.4 (c 1.0,
25
1
CH2Cl2). H NMR (CDCl3, 300 MHz): d 7.80 (d, J = 7.8 Hz,
2H), 7.46 (t, J = 7.2 Hz, 2H), 7.29–7.19 (m, 4H), 5.75 (s, 2H),
1.19 (s, 18H). 13C NMR (CDCl3, 75 MHz): d 154.5, 132.5, 130.0,
127.9, 123.3, 114.4, 92.0, 57.6, 23.0. IR (KBr) (cm-1): 2866–3071,
1475, 1365, 1272, 1031, 769. HRMS: Calcd. for C21H28O4S2 + H:
409.15, found: 409.1499.
1-(R)-(+)-tert-Butylsulfinyl-2-propoxybenzene (5a). Pale yel-
25
1
low oil. Yield 87%. [a]D = +255.0 (c 1.0, EtOH). H NMR
(CDCl3, 300 MHz): d 7.70 (dd, J = 7.8 Hz, 1.7 Hz, 1H), 7.38–7.32
(m, 1H), 7.08–7.03 (m, 1H), 6.85 (d, J = 8.2 Hz, 1H), 3.99–3.82
(m, 2H), 1.82–1.70 (m, 2H), 1.15 (s, 9H), 0.99 (t, J = 7.4 Hz, 3H).
13C NMR (CDCl3, 75 MHz): d 156.6, 132.1, 128.7, 127.3, 120.6,
111.5, 70.0, 57.2, 22.9, 22.3, 10.5. IR (KBr) (cm-1): 2866–3057,
1457, 1360, 1272, 1031, 755. HRMS: Calcd. for C13H20O2S + Na:
263.1076, found: 263.1075.
1,2-Bis(2-((R)-tert-butylsulfinyl)phenoxy)ethane (9b). White
solid. Yield 28%. mp = 188–190 ◦C. [a]D = +182.2 (c 1.0,
25
1
CH2Cl2). H NMR (CDCl3, 300 MHz): d 7.78 (d, J = 7.8 Hz,
2H), 7.45 (t, J = 7.4 Hz, 2H), 7.10 (t, J = 7.5 Hz, 2H), 6.68 (d,
J = 8.3 Hz, 2H), 4.42–4.32 (m, 4H), 1.16 (s, 18H). 13C NMR
(CDCl3, 75 MHz): d 156.0, 132.3, 129.5, 127.7, 121.9, 112.4, 67.4,
57.5, 22.9. IR (KBr) (cm-1): 2922–3062, 1479, 1379, 1279, 1028,
762. HRMS: Calcd. for C22H30O4S2 + H: 423.17, found: 423.1668.
1-(R)-(+)-(Benzyloxy)-2-(tert-butylsulfinyl)benzene (5b). Pale
◦
25
yellow solid. Yield 90%. mp = 75–76 C. [a]D = +187.8 (c 1.0,
1
EtOH). H NMR (CDCl3, 300 MHz): d 7.76 (dd, J = 7.8 Hz,
1-((R)-tert-Butylsulfinyl)-2-(3-(2-((R)-tert-butylsulfinyl)phe-
noxy)propoxy)benzene (9c). Colorless oil. Yield 24%. [a]D
1.7 Hz, 1H), 7.39–7.33 (m, 6H), 7.10 (d, J = 0.7 Hz, 1H), 6.93
(dd, J = 8.3 Hz, 0.6 Hz, 1H), 5.06 (s, 2H), 1.16 (s, 9H). 13C NMR
(CDCl3, 75 MHz): d 156.1, 135.9, 132.0, 129.0, 128.4, 127.9, 127.3,
126.9, 121.1, 112.1, 70.4, 57.3, 22.8. IR (KBr) (cm-1): 2860–3058,
1478, 1361, 1277, 1020, 756. HRMS: Calcd. for C17H20O2S + Na:
311.1076, found: 311.1074.
25
=
+155.1 (c 1.0, CH2Cl2). 1H NMR (CDCl3, 300 MHz): d 7.68 (dd,
J = 7.8 Hz, 1.6 Hz, 2H), 7.39–7.33 (m, 2H), 7.10–7.04 (m, 2H), 6.87
(d, J = 8.1 Hz, 2H), 4.24–4.03 (m, 4H), 2.24–2.16 (m, 2H). 1.13 (s,
18H). 13C NMR (CDCl3, 75 MHz): d 156.0, 132.3, 128.5, 127.3,
121.0, 111.4, 64.6, 57.2, 28.8, 22.8. IR (KBr) (cm-1): 2922–3062,
1479, 1379, 1279, 1028, 762. HRMS: Calcd. for C23H32O4S2 + H:
437.18, found: 437.1815.
1-(R)-(+)-((2-(tert-Butylsulfinyl)phenoxy)methyl)naphthalene
(5c). Pale yellow oil. Yield 88%. [a]D = +188.2 (c 1.0, EtOH). 1H
25
NMR (CDCl3, 300 MHz): d 7.99–7.81 (m, 4H), 7.58–7.44 (m, 5H),
7.17–7.09 (m, 2H), 5.52 (s, 2H), 1.15 (s, 9H). 13C NMR (CDCl3,
75 MHz): d 156.4, 133.6, 132.2, 131.4, 131.0, 129.4, 129.0, 128.6,
127.6, 126.4, 126.0, 125.9, 125.2, 123.3, 121.4, 112.3, 69.1, 57.3,
22.9. IR (KBr) (cm-1): 2863–3057, 1467, 1362, 1273, 1029, 754.
HRMS: Calcd. for C21H22O2S + Na: 361.1233, found: 361.1236.
General procedure for the enantioselective allylation of
aldehydes with allyltrichlorosilane promoted by mono-aryl
tert-butyl sulfoxides
The procedure described here is under optimized reaction condi-
tions. Under an argon atmosphere, allyltrichlorosilane (0.173 ml,
1.2 mmol, 3 equiv.) was added to a solution of aldehyde (0.4 mmol,
1 equiv.), aryl tert-butyl sulfoxide (1.2 mmol, 3 equiv.) and
diisopropylethylamine (0.348 ml, 2.0 mmol, 5 equiv.) in CH2Cl2
(2 ml) at -78 ◦C. The reaction was monitored by TLC and
quenched with saturated aqueous solution of NaHCO3 (1 ml).
The mixture was allowed to warm to room temperature and
extracted with CH2Cl2 (10 ml ¥ 2). The combined organic layer was
dried over anhydrous MgSO4. After filtration, the solution was
concentrated under reduced pressure. The product was purified
by silica gel column chromatography to afford pure compound 8,
followed by ethyl acetate to recover the sulfoxide.
1-(R)-(+)-(2-Methoxybenzyloxy)-2-(tert-butylsulfinyl)benzene
◦
25
(5d). White solid. Yield 86%. mp = 72–74 C. [a]D = +245.3
(c 1.0, EtOH). 1H NMR (CDCl3, 300 MHz): d 7.78 (dd, J = 7.7 Hz,
1.6 Hz, 1H), 7.46–7.37 (m, 2H), 7.31–7.26 (m, 1H), 7.13 (t, J =
7.5 Hz, 1H), 7.02–6.88 (m, 3H), 5.14 (dd, J = 14.7 Hz, 12.9 Hz,
2H), 3.85 (s, 3H), 1.20 (s, 9H). 13C NMR (CDCl3, 75 MHz): d
156.6, 132.2, 129.1, 129.0, 128.2, 127.5, 124.5, 121.0, 120.6, 112.2,
110.1, 65.7, 57.4, 55.2, 23.0. IR (KBr) (cm-1): 2835–3063, 1476,
1361, 1271, 1240, 1032, 762. HRMS: Calcd. for C18H22O3S + Na:
341.1182, found: 341.1183.
(S)-1-Phenyl-3-buten-1-ol (8a)10e
. Colorless oil. Yield 72%.
General procedure for the synthesis of bis-sulfoxides 9a–c
25
25
[a]D = -62.3 (c 1.0, CHCl3) (lit.10e (R)-8a (87% ee) [a]D = +62
At -78 ◦C, n-BuLi (8.8 ml, 2.5 M in hexane, 22.0 mmol, 2.2 equiv.)
was added dropwise to the solution of the corresponding dibromo
compounds (10.0 mmol) in anhydrous THF (50 ml) over 6 min.
The resulting mixture was stirred for 30 min at -78 ◦C and a solu-
tion of (R)-tert-butyl tert-butanethiosulfinate (4.26 g, 22.0 mmol,
2.2 equiv.) in THF (10 ml) was added. The resulting mixture was
stirred for 2 h at -78 ◦C and then quenched with H2O (10 ml). The
solvent was evaporated under reduced pressure and the aqueous
layer was extracted with CH2Cl2 (50 ml ¥ 3). The organic layer
was washed with brine and dried over anhydrous MgSO4. After
filtration, the solvent was removed under reduced pressure. The
product was purified by silica gel column chromatography (4 : 1
petroleum ether : ethyl acetate).
1
(c 1.0, CHCl3)). H NMR (CDCl3, 300 MHz): d 7.37–7.28 (m,
5H), 5.86–5.74 (m, 1H), 5.19–5.13 (m, 2H), 4.69 (dt, J = 6.5 Hz,
3.1 Hz, 1H), 2.59 (d, J = 3.2 Hz, 1H), 2.49–2.54 (m, 2H). The
enantiomeric excess (86% ee, S-isomer major) was determined by
HPLC (Chiracel OD column, hexane : propan-2-ol = 95 : 5; flow
rate 1.0 ml min-1; UV 254 nm; tminor = 7.4 min, tmajor = 8.2 min).
(S)-1-(2-Methoxyphenyl)-3-buten-1-ol (8b)10c
. Colorless oil.
25
Yield 89%. [a]D = -48.8 (c 1.0, CH2Cl2) (lit.10c (S)-8b (89% ee)
1
[a]D = -25.6 (c 0.47, CH2Cl2)). H NMR (CDCl3, 300 MHz):
d 7.34 (dd, J = 7.5 Hz, 1.6 Hz, 1H), 7.24 (dd, J = 8.1 Hz,
1.8 Hz, 1H), 6.98 (dd, J = 7.5 Hz, 0.9 Hz, 1H), 6.88 (d, J =
8.2 Hz, 1H), 5.91–5.75 (m, 1H), 5.17–5.09 (m, 2H), 4.98–4.95
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(dt, J = 6.5, 3.1 Hz, 1H), 3.85 (s, 3H), 2.63–2.48 (m, 3H). The
enantiomeric excess (81% ee, S-isomer major) was determined by
HPLC (Chiracel OD column, hexane : propan-2-ol = 98 : 2; flow
rate 1.0 ml min-1; UV 254 nm; tmajor = 13.9 min, tminor = 15.4 min).
(S)-1-(3-Nitrophenyl)-3-buten-1-ol (8i)10e
.
Yellow oil. Yield
25
25
80%. [a]D = -54.1 (c 1.0, CHCl3) (lit.10e (R)-8i (72% ee) [a]D
=
1
+47 (c 1.0, CHCl3)). H NMR (CDCl3, 300 MHz): d 8.20 (t,
J = 1.9 Hz, 1H), 8.11–8.07 (m, 1H), 7.67 (d, J = 7.7 Hz, 1H),
7.50 (t, J = 7.6 Hz, 1H), 5.76–5.72 (m, 1H), 5.18–5.12 (m, 2H),
4.82 (dd, J = 4.6 Hz, 2.6 Hz, 1H), 2.58–2.43 (m, 3H). The
enantiomeric excess (82% ee, S-isomer major) was determined by
HPLC (Chiracel AS column, hexane : propan-2-ol = 98 : 2; flow
rate 1.0 ml min-1; UV 254 nm; tminor = 45.7 min, tmajor = 49.4 min).
(S)-1-(4-Methoxyphenyl)-3-buten-1-ol (8c)10e
. Pale yellow oil.
Yield 65%. [a]D = -35.7 (c 1.0, CHCl3) (lit.10e (R)-8c (87% ee)
25
[a]D = +57 (c 1.0, CHCl3)). 1H NMR (CDCl3, 300 MHz): d 7.30–
25
7.26 (m, 2H), 6.91–6.87 (m, 2H), 5.84–5.75 (m, 1H), 5.19–5.11 (m,
2H), 4.69 (t, J = 6.5 Hz, 1H), 3.80 (s, 3H), 2.50 (t, J = 6.5 Hz,
2H), 2.02 (br, 1H). The enantiomeric excess (59% ee, S-isomer
major) was determined by HPLC (Chiracel OD column, hexane :
(S)-1-(1-Naphthyl)-3-buten-1-ol (8j)10e
. Yellow oil. Yield 68%.
25
25
[a]D = -82.2 (c 1.0, CHCl3) (lit.10e (R)-8j (79% ee) [a]D = +84
(c 1.0, CHCl3)). 1H NMR (CDCl3, 300 MHz): d 8.09 (d, J = 8.0 Hz,
1H), 7.89 (d, J = 8.4 Hz, 1H), 7.79 (d, J = 8.0 Hz, 1H), 7.68 (d,
J = 6.8 Hz, 1H), 7.55–7.47 (m, 3H), 5.96–5.78 (m, 1H), 5.55 (t, J =
4.2 Hz, 1H), 5.27–5.18 (m, 2H), 2.82–2.74 (m, 1H), 2.66–2.56 (m,
1H), 2.18 (d, J = 3.3 Hz, 1H). The enantiomeric excess (76% ee,
S-isomer major) was determined by HPLC (Chiracel OD column,
hexane : propan-2-ol = 90 : 10; flow rate 1.0 ml min-1; UV 254 nm;
tminor = 8.3 min, tmajor = 14.0 min).
propan-2-ol = 98 : 2; flow rate 1.0 ml min-1; UV 254 nm; tminor
=
18.1 min, tmajor = 21.4 min).
(S)-1-(4-Bromophenyl)-3-buten-1-ol (8d)5. Pale yellow oil.
Yield 47%. [a]D = -21.3 (c 1.0, benzene) (lit.5 (S)-8d (96% ee)
23
23
1
[a]D = -26.1 (c 1.1, benzene)). H NMR (CDCl3, 300 MHz):
d 7.48–7.44 (m, 2H), 7.26–7.20 (m, 2H), 5.78–5.72 (m, 1H), 5.18–
5.16 (m, 1H), 5.13–5.12 (m, 1H), 4.69–4.66 (m, 1H), 2.49–2.40
(m, 2H), 2.23 (d, J = 3.1 Hz, 1H). The enantiomeric excess (84%
ee, S-isomer major) was determined by chiral GLC (Supelco Beta
Dex 120, 160 ◦C, 12 psi, tminor = 36.4 min, tmajor = 37.1 min).
(1E,3S)-1-Phenyl-1,5-hexadiene-3-ol (8k)10e
. Yellow oil. Yield
82%. [a]D = -19.8 (c 1.0, CHCl3) (lit.10e (R)-8k (71% ee) [a]D
=
25
25
1
+23 (c 1.0, CHCl3)). H NMR (CDCl3, 300 MHz): d 7.41–7.23
(m, 5H), 6.61 (d, J = 16.0 Hz, 1H), 6.25 (dd, J = 16.0 Hz,
6.4 Hz, 1H), 5.92–5.83 (m, 1H), 5.23–5.16 (m, 2H), 4.36 (dd,
J = 12.2 Hz, 5.9 Hz, 1H), 2.45–2.39 (m, 2H), 2.11 (br, 1H). The
enantiomeric excess (63% ee, S-isomer major) was determined by
HPLC (Chiracel OD column, hexane : propan-2-ol = 85 : 15; flow
rate 1.0 ml min-1; UV 254 nm; tminor = 6.2 min, tmajor = 8.7 min).
(S)-1-(2-Bromophenyl)-3-buten-1-ol (8e)10e
. White solid. Yield
62%. mp 45–46 ◦C. [a]D = -82.6 (c 1.0, CHCl3) (lit.10e (R)-8e (82%
25
25
1
ee) [a]D = +77 (c 1.0, CHCl3)). H NMR (CDCl3, 300 MHz):
d 7.57–7.50 (m, 2H), 7.36–7.31 (m, 1H), 7.15–7.10 (m, 1H), 5.89–
5.83 (m, 1H), 5.22–5.16 (m, 2H), 5.12–5.07 (m, 1H), 2.67–2.59
(m, 1H), 2.40–2.30 (m, 2H). The enantiomeric excess (88% ee, S-
isomer major) was determined by chiral GLC (Supelco Beta Dex
120, 150 ◦C, 12 psi, tminor = 42.3 min, tmajor = 43.1 min).
(R)-1-Phenylhex-5-en-3-ol (8l)5. Colorless oil. Yield 35%.
[a]D = +23.2 (c 1.0, benzene) (lit.5 (R)-8l (88% ee) [a]D
=
23
23
1
+25.3 (c 1.0, benzene)). H NMR (CDCl3, 300 MHz): d 7.33–
7.28 (m, 2H), 7.26–7.20 (m, 3H), 5.93–5.74 (m, 1H), 5.18–5.13
(m, 2H), 3.74–3.62 (m, 1H), 2.83–2.70 (m, 2H), 2.43–2.28 (m,
1H), 2.25–2.18 (m, 1H), 1.84–1.77 (m, 2H), 1.71 (s, 1H). The
enantiomeric excess (80% ee, R-isomer major) was determined by
HPLC (Chiracel OD column, hexane : propan-2-ol = 95 : 5; flow
rate 1.0 ml min-1; UV 254 nm; tminor = 9.5 min, tmajor = 14.4 min).
(S)-1-(4-Chlorophenyl)-3-buten-1-ol (8f)10e
. Pale yellow oil.
Yield 45%. [a]D = -63.5 (c 1.0, CHCl3) (lit.10e (R)-8f (84% ee)
25
25
1
[a]D = +62 (c 1.0, CHCl3)). H NMR (CDCl3, 300 MHz): d
7.33–7.26 (m, 4H), 5.79–5.73 (m, 1H), 5.19–5.13 (m, 2H), 4.73–
4.68 (m, 1H), 2.53–2.41 (m, 2H), 2.14 (d, J = 3.2 Hz, 1H). The
enantiomeric excess (83% ee, S-isomer major) was determined by
chiral GLC (Supelco Beta Dex 120, 140 ◦C, 12 psi, tminor = 52.1 min,
tmajor = 53.4 min).
Acknowledgements
(S)-1-(2-Chlorophenyl)-3-buten-1-ol (8g)10h
.
Pale yellow oil.
Financial support from the National Natural Science Foundation
(Grant No. 20872139) and National Engineering Research Center
of China Drugs is greatly acknowledged by the authors.
Yield 53%. [a]D = -61.2 (c 1.0, CHCl3). 1H NMR (CDCl3,
300 MHz): d 7.56 (dd, J = 7.5, 1.6 Hz, 1H), 7.34–7.27 (m, 2H),
7.21 (dd, J = 8.2, 1.8 Hz, 1H), 5.90–5.73 (m, 1H), 5.21–5.13 (m,
3H), 2.65–2.59 (m, 1H), 2.40–2.35 (m, 1H), 2.25 (s, 1H). The
enantiomeric excess (81% ee, S-isomer major) was determined by
HPLC (Chiracel OD column, hexane : propan-2-ol = 99 : 1; flow
rate 0.6 ml min-1; UV 254 nm; tminor = 7.1 min, tmajor = 9.3 min)
after acetylation.
25
Notes and references
1 For reviews on enantioselective carbonyl allylation, see: (a) Y.
Yamamoto and N. Asao, Chem. Rev., 1993, 93, 2207; (b) J. A. Marshall,
Chem. Rev., 1996, 96, 31; (c) S. E. Denmark and J. Fu, Chem. Rev., 2003,
103, 2763.
2 (a) W. R. Roush, A. E. Walts and L. K. Hoong, J. Am. Chem. Soc.,
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3 For titanium catalysed allylation of aldehydes, see: (a) S. Aoki, K.
Mikami, M. Terada and T. Nakai, Tetrahedron, 1993, 49, 1783; (b) A. L.
Costa, M. G. Piazza, E. Tagliavini, C. Trombini and A. Umani-Ronchi,
J. Am. Chem. Soc., 1993, 115, 7001; (c) G. E. Keck and L. S. Geraci,
Tetrahedron Lett., 1993, 34, 7827.
4 For zirconium catalysed allylation of aldehydes, see: (a) P. Bedeschi, S.
Casolari, A. L. Costa, E. Tagliavini and A. Umani-Ronchi, Tetrahedron
(S)-1-(4-Methylphenyl)-3-buten-1-ol (8h)10a
.
Pale yellow oil.
Yield 57%. [a]D = -31.5 (c 1.0, CHCl3) (lit.10a (S)-8h (87% ee)
[a]D = -31.1 (c 0.9, CHCl3)). 1H NMR (CDCl3, 300 MHz):
d 7.27–7.17 (m, 4H), 5.86–5.77 (m, 1H), 5.20–5.13 (m, 2H),
4.68 (t, J = 6.5 Hz, 1H), 2.53–2.47 (m, 3H), 2.38 (s, 3H). The
enantiomeric excess (79% ee, S-isomer major) was determined by
HPLC (Chiracel AD column, hexane : propan-2-ol = 95 : 5; flow
rate 0.5 ml min-1; UV 254 nm; tminor = 15.9 min, tmajor = 16.8 min).
25
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