Studies on the regio- and stereoselectivity of halohydroxylation of 1,2-allenyl sulfides or selenides

Article abstract of DOI:10.1021/jo049593c

It was observed that the halohydroxylation of 1,2-allenyl sulfides or selenides with Br₂ (CuBr₂ or NBS) or I₂ and water demonstrated a fairly good regioselectivity (i.e., the C=C bond that is remote from the S or Se atom w

Full text of DOI:10.1021/jo049593c

Stu d ies on th e Regio- a n d Ster eoselectivity of Ha loh yd r oxyla tion
of 1,2-Allen yl Su lfid es or Selen id es
Shengming Ma,*,†,‡ Xueshi Hao,† Xiaofeng Meng,† and Xian Huang†
Laboratory of Molecular Recognition and Synthesis, Department of Chemistry, Zhejiang University,
Hangzhou 310027, P. R. China, and State Key Laboratory of Organometallic Chemistry,
Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences, 354 Fenglin Lu,
Shanghai 200032, P. R. China
masm@mail.sioc.ac.cn
Received March 12, 2004
It was observed that the halohydroxylation of 1,2-allenyl sulfides or selenides with Br2 (CuBr2 or
NBS) or I2 and water demonstrated a fairly good regioselectivity (i.e., the CdC bond that is remote
from the S or Se atom was halohydroxylated with the halogen atom connecting to the middle carbon
atom and the hydroxyl group connecting to the non-S terminal carbon or Se-substituted terminal
carbon atom of the allene moiety), leading to the synthesis of synthetically important 3-organosulfur
or seleno-2-haloallylic alcohols. The stereoselectivity depends on the nature of X+ and S or Se,
showing a Z-selectivity with the matched Lewis acid-base pair.
In tr od u ction
the regio- and stereoselectivity.6 Recently, we observed
the following: (1) The electron-withdrawing group of the
electron-deficient allenes determines the regioselectivity
of the corresponding hydrohalogenation reaction, leading
to â,γ unsaturated functionalized alkenes.7 (2) The ex-
cellent regioselectivity and E-stereoselectivity of the
iodohydroxylation reaction of 1,2-allenyl sulfoxides was
determined by the participation of the sulfinyl group,
because of the formation of a five-membered cyclic
intermediate.8
Allenes show unique reactivity in organic synthesis due
to the presence of the cumulated CdC double bonds.1
Recently, much attention has been paid to the study on
their reactivity, especially the control of the related
selectivity.2,3 An addition reaction of a carbon-carbon
multiple bond is synthetically attractive because two
functional groups are introduced within one operation.4
However, reports on the addition reactions of allenes5 are
limited, probably because of the problem of controlling
In a preliminary communication, we have demon-
strated that the iodohydroxylation reaction of 1,2-allenyl
sulfides is high-yielding with excellent Z-selectivity,
which is opposite to what was observed with 1,2-allenyl
sulfoxides.9 In this paper, we wish to report the scope,
regioselectivity, and stereoselectivity of the halohydroxy-
lation of 1,2-allenyl sulfides or selenides. The combination
of a different X+ with S or Se showed that the Z-
selectivity may be controlled by the nature of Lewis
basicity of the S or Se atom and the Lewis acidity of X+.
* Corresponding author. Fax: (+86) 21-64167510.
† Zhejiang University.
‡ Shanghai Institute of Organic Chemistry.
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Bruneau, C.; Dixneuf, P. H. Compr. Org. Funct. Group Transform.
1995, 1, 953. (e) Marshall, J . A. Chem. Rev. 1996, 96, 31. (f) Schuster,
H. F.; Coppola, G. M. Allenes in Organic Synthesis; Wiley: New York,
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Chem. Soc. 2001, 123, 5578. (b) Ma, S.; Wu, S. Chem. Commun. 2001,
441. (c) Ma, S.; Wu, S. Tetrahedron Lett. 2001, 42, 4075. (d) Ma, S.;
Shi, Z.; Wu, S. Tetrahedron: Asymmetry 2001, 12, 193. (e) Ma, S.; Shi,
Z. Chem. Commun. 2002, 540. (f) Ma, S.; J iao, N.; Zhao, S.; Hou, H. J .
Org. Chem. 2002, 67, 2837. (g) Ma, S.; Duan, D.; Wang, Y. J . Comb.
Chem. 2002, 4, 239. (h) Ma, S.; Yu, Z. Angew. Chem., Int. Ed. 2002,
41, 1775.
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2 1998, 6, 1523. (b) Breuer, K.; Teles, J . H.; Demuth, D.; Hibst, H.;
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39, 1401. (c) Barbero, A.; Garcia, C.; Pulido, F. J . Tetrahedron Lett.
1999, 36, 6649. (d) Yang, F.; Wu, M.; Cheng, C. J . Am. Chem. Soc.
2000, 122, 7122. (e) Grigg, R.; MacLachlan, W.; Rasparini, M. Chem.
Commun. 2000, 2241. (f) Suginome, M.; Ohmori, Y.; Ito, Y. J .
Organomet. Chem. 2000, 611, 403.
(6) For intramolecular haloalkoxylation of 2-phenythio-2,3-allenols
leading to 2,5-dihydrofurans, see: (a) Yano, Y.; Ohshima, M.; Sutoh,
S. J . Chem. Soc., Chem. Commun. 1984, 695. (b) Florio, S.; Ronzini,
L.; Epifani, E.; Sgarra, R. Tetrahedron 1993, 49, 10413.
(7) (a) Ma, S.; Shi, Z.; Li, L. J . Org. Chem. 1998, 63, 4522. (b) Ma,
S.; Wei, Q. J . Org. Chem. 1999, 64, 1026. (c) Ma, S.; Li, L.; Xie, H. J .
Org. Chem. 1999, 64, 5325. (d) Ma, S.; Wei, Q. Eur. J . Org. Chem.
2000, 1939. (e) Ma, S.; Li, L. Synlett 2001, 1206. (f) Ma, S.; Li, L.;
Wei, Q.; Xie, H.; Wang, G.; Shi, Z.; Zhang, J . Pure Appl. Chem. 2000,
72, 1739. (g) Ma, S.; Xie, H.; Wang, G.; Zhang, J .; Shi, Z. Synthesis
2001, 713. (h) Ma, S.; Yin, S.; Li, L.; Tao, F. Org. Lett. 2002, 4, 505.
(8) (a) Ma, S.; Wei, Q.; Wang, H. Org. Lett. 2000, 2, 3893. (b) Ma,
S.; Ren, H.; Wei, Q. J . Am. Chem. Soc. 2003, 125, 4817.
(4) (a) Nakhmanovich, A. S.; Komarova, T. N.; Lopyrev, V. A. Russ.
J . Org. Chem. 2000, 11, 1551. (b) Chemistry of Dienes & Polyenes;
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10.1021/jo049593c CCC: $27.50 © 2004 American Chemical Society
Published on Web 07/29/2004
5720
J . Org. Chem. 2004, 69, 5720-5724

Halohydroxylation of Sulfides or Selenides
SCHEME 1
SCHEME 3
TABLE 1. Iod oh yd r oxyla tion of 1,2-Allen yl Su lfid es
2
time
(h)
yield
Z/E
of 6
entry
R2
R3
of 6a (%)
1
2
3
4
5
6
7
8
Bn
H
H
H
H
H
H
CH3
CH3
CH3
CH3
CH3 (2a )
H (2b)
CH3 (2c)
13
9
9
68 (6a )
41 (6b)
61 (6c)
56 (6d )
74 (6e)b
67 (6f)c
65 (6g)d
63 (6h )
94 (6i)
99/1
99/1
97/3
96/4
98/2
96/4
96/4
94/6
94/6
99/1
97/3
98/2
95/5
97/3
i-Pr (2d )
10
13.5
9.5
9.5
10.5
10
12
9
SCHEME 2
n-C4H9 (2e)
n-C7H15 (2f)
Bn (2g)
CH3 (2h )
C2H5 (2i)
i-Bu (2j)
t-C4H9 (2k )
C2H5 (2l)
n-C4H9 (2m )
n-C5H11 (2n )
9
10
11
12
13
14
53 (6j)e
85 (6k )
72 (6l)
C2H5
n-C4H9
n-C5H11
8
10
10
93 (6m )
80 (6n )
a
Unless otherwise stated, the corresponding aldehyde 5 was
isolated in trace amount. 14% of 5e was isolated. c 18% of 5f was
b
Resu lts a n d Discu ssion
isolated. 18% of 5g was isolated. e 14% of 5j was isolated.
d
Syn th esis of th e Sta r tin g Ma ter ia ls. The starting
1,2-allenylic sulfides (2) were prepared via the reduction
of 1,2-allenylic sulfoxides (1), which are easily available
from the reaction of the readily available propargylic
alcohols with PhSCl (Scheme 1).10,11
3-benzyl-1,2-butadienyl phenyl sulfide (2a ) with I2 and
H2O. When we performed the iodohydroxylation under
the same reaction conditions as those for 1,2-allenyl
sulfoxides,8 only a Z/E mixture of 2-iodo-2-propenal (5a )
was formed via the intermediacy of 7a (Scheme 3),
indicating a different regioselectivity with the OH group
attacking the carbon atom connected with the PhS group.
The configuration of the CdC bond in 5a was determined
by the NOE study. However, after some trial and error,
we were pleased to note that the regioselectivity of this
reaction can be reversed to a fairly high extent, leading
to the formation of synthetically useful 2,3-iodohydroxy-
lation product Z-6a in 68% yield, with 99/1 E/Z-selectiv-
ity, along with 16% yield of 5a when the reaction was
conducted in aqueous acetone (acetone/H2O ) 4:1) (Scheme
3).
1,2-Butadienyl-3-yl phenyl sulfide (2s) was prepared
via the rearrangement of 3-phenylthio-1-butyne (eq 1).12
1,2-Allenylic selenides (4) were prepared similarly via
the rearrangement of propargyl aryl selenides (3) (Scheme
2).13
Iod oh yd r oxyla tion of 1,2-Allen ylic Su lfid es (2).
We started this research with the iodohydroxylation of
Some typical results of the Z-iodohydroxylation of 1,2-
allenyl sulfides are summarized in Table 1.9 Z-2-Iodo-3-
(organosulfur)-2-alkenols (6) were formed in moderate-
to-high yields highly stereoselectively: Both 3-mono- and
3,3-disubstituted allenyl sulfides reacted smoothly with
I2 in aqueous acetone. The stereoselectivity, which was
determined by the NOE experiment of Z-6e and the
(10) (a) Cookson, R. C.; Parsons, P. J . J . Chem. Soc., Chem.
Commun. 1978, 822. (b) Taing, M.; Moore, H. W. J . Org. Chem. 1996,
61, 329-340. (c) Conrads, M.; Mattay, J . Synthesis 1991, 1, 111.
(11) Conrads, M.; Mattay, J . Synthesis 1991, 1, 11.
(12) Pourcelot, G. C. R. Seances. Acad. Sci. Fr. 1965, 260, 2847.
(13) (a) Pourcelot, G.; Cadiot, P. Bull. Soc. Chim. Fr. 1966, 3016-
3024. (b) Saito, S.; Hamano, S.; Inaba, M.; Moriwake, T. Synth.
Commun. 1984, 14, 1105.
J . Org. Chem, Vol. 69, No. 17, 2004 5721

Ma et al.
TABLE 3. Br om oh yd r oxyla tion of 1,2-Hep ta d ien yl
P h en yl Su lfid e (2e)
SCHEME 4
time yield of
entry [Br] (equiv) additive (equiv) T (°C) (h) 10d (%) Z/Ea
1
2
3
4
5
7
8
9
10
11
12
14
15
16
17
18
NBS (2)
NBS (2)
Br2 (1)
Br2 (1)
Br2 (1.5)
Br2 (2)
Br2 (2)
Br2 (2)
Br2 (2)
Br2 (2)
Br2 (2)
Br2 (2)
Br2 (2)
Br2 (2)
Br2 (2)
25 12
34
46
45
54
30
39
51
52
50
41
51
58
52
46
53
45
27/1
34/1
99/1
99/1
99/1
99/1
99/1
99/1
99/1
99/1
99/1
96/1
99/1
99/1
99/1
99/1
0
7
25 15
0
6
25 12
25 12
25 10
TABLE 2. Br om oh yd r oxyla tion of 1,2-P r op d ien yl
P h en yl Su lfid e (2b)
Na2CO3 (1)
NaHCO3 (1)
K2CO3 (1)
LiOAc‚2H2O (1)
Na2CO3 (1)
Na2CO3 (1)
Na2CO3 (1)
Na2CO3 (1.5)
Na2CO3 (2)
25
25
25
6.5
9
9
25 10
0
2
-10 13
time yield of
0
0
0
7
16
6
entry [Br] (equiv) solventa T (°C)
(h)
10b (%)
Z/Eb
Br2 (2.5) Na2CO3 (1)
1
2
3
4
5
6
7
8
CuBr2 (2)
CuBr2 (2)
CuBr2 (10)
NBS (2)
NBS (2)
NBS (2)
Br2 (2)
Br2 (2)
Br2 (2)
Br2 (2)
Br2 (2)
4:1
4:1
4:1
4:1
4:1
4:1
4:1
4:1
15
25
25
50
25
0
9
7.5
6
3
9
7
7
3
9
34
39
30
10
31
49
26
29
47
12
17
1.83/1
2.88/1
99/1
99/1
99/1
4.38/1
21/1
99/1
99/1
3.94/1
16/1
a
The Z/E ratio was determined by 300 MHz 1H NMR spectra
of the crude product.
that, in terms of both yield and stereoselectivity, the
reaction proceeded more efficiently with Br2 than with
NBS (compare entries 1-2 with 3-4, Table 3). To avoid
the influence of the in-situ-formed HBr on stereoselec-
tivity, the effect of different bases on stereoselectivity was
studied. The yield increased slightly when Na2CO3 (1
equiv) was added (entry 8, Table 3). NaHCO3, K2CO3, or
LiOAc‚2H2O can also be applied (entries 9-11, Table 3).
The best results were realized when the reaction was run
with Br2 (2 equiv) with the addition of Na2CO3 at 0 °C to
afford 10e in 58% yield and a Z/E ratio of 99/1 (entry 14,
Table 3). Increasing the amount of Br2 or base did not
yield better results (entries 16-18, Table 3).
Some typical results of Z-bromohydroxylation of 1,2-
allenyl sulfides are summarized in Table 4, showing that
both 3-mono- and 3,3-disubstituted allenyl sulfides (2)
reacted smoothly with Br2 in aqueous acetonitrile to give
the products Z-10 in reasonably high yields with excellent
Z-selectivity.
When 1-alkyl-substituted 1,2-allenyl phenyl sulfides
(2r -s) were used, 10r -s were produced with fairly high
Z/E ratios (Scheme 5).
When sulfide 2p was treated with Br2 in aqueous
acetone, Z-11p was formed in 65% yield with a ratio of
Z/E > 99/1 (Scheme 4).
Iod oh yd r oxyla tion of 1,2-Allen ylic Selen id es. Sev-
eral selenium-substituted allenes are known as isolable
compounds or reactive intermediates;14 however, there
is only very limited study on their reactivities.15,16 Ac-
cording to our results on allenyl sulfides, we wish to
expand this reaction to 1,2-allenyl selenides. Some typical
0
50
25
25
25
9
10
11
4:1
4:1c
2:2:1d
13
13
a
Unless otherwise noted, solvents are CH3CN/H2O in the
b
volume ratio indicated. The Z/E ratio determined by 300 MHz
1H NMR spectra. c CH2Cl2/H2O were used as the solvents. MeCN/
d
CH2Cl2/H2O were used as the solvents.
oxidation of Z-6e with m-CPBA in CH2Cl2 or H2O2 in
HOAc to the corresponding sulfoxide Z-8e,9 is completely
opposite to that for the corresponding sulfoxides.8
When 2o and 2p were used as the starting allenyl
sulfides, Z-(1-iodo-2-phenylthioethenyl)cycloalkenes 9o
and 9p 9 were formed via the dehydration of the iodohy-
droxylation product (Scheme 4).
Br om oh yd r oxyla t ion of 1,2-Allen ylic Su lfid es.
Some typical results of the bromohydroxylation of 1,2-
propadienyl phenyl sulfide (2b) under different conditions
are summarized in Table 2, from which it can be seen
that, under similar conditions used for the halohydroxy-
lation of allenylsulfoxides,8 the bromohydroxylation reac-
tion of 1,2-allenyl sulfides can occur to afford 10b with
different stereoselectivities when NBS, Br2, or CuBr2 was
chosen as the halogen source. With CuBr2, the stereose-
lectivity was high and the yield was as low as 30%, even
with 10 equiv of CuBr2 (entries 1-3, Table 2). The yield
was higher when the reaction was conducted with NBS
at a lower temperature, but the reaction was less ste-
reoselective (entries 4-6, Table 2). The stereoselectivity
was improved when Br2 was used, with the highest yield
(10b) at 47% and a Z/E ratio of 99/1 (entry 9, Table 2).
The results in other solvents were poor (entries 10 and
11, Table 2). The stereoselectivity of this reaction was
established by the NOE experiment of Z-10b.
(14) (a) Yamazaki, S.; Fujitsuka, H.; Yamabe, S.; Tamura, H. J . Org.
Chem. 1992, 57, 5610-5619. (b) Reich, H. J .; Shah, S. K.; Gold, P. M.;
Olson, R. E. J . Am. Chem. Soc. 1981, 103, 3112.
(15) (a) Yamazaki, S.; Fujitsuka, H.; Yamabe, S.; Tamura, H. J . Org.
Chem. 1992, 57, 5610-5619. (b) Reich, H. J .; Ringer, J . W. J . Org.
Chem. 1988, 53, 455. (c) Brown, R. F. C.; Coulston, K. J .; Eastwood,
F. W.; Hill, M. P. Aust. J . Chem. 1988, 2, 215.
Similar results were also observed with 1,2-heptadienyl
phenyl sulfide (2e) (entries 1-6, Table 3). It is obvious
(16) Ma, S.; Hao, X.; Huang, X. Chem. Commun. 2003, 1082.
5722 J . Org. Chem., Vol. 69, No. 17, 2004

Halohydroxylation of Sulfides or Selenides
TABLE 4. Br om oh yd r oxyla tion of Allen yl Su lfid es w ith
Br 2 in Aqu eou s MeCN in th e P r esen ce of Na 2CO3
TABLE 5. Ad d ition Rea ction of 4a w ith I2 u n d er
Differ en t Con d ition sa
I2
T
time
(h)
yield of
11a (%)
entry (equiv) MeCN/H2O (°C)
Z/Ed
1b
2
2
7:1
4:1
4:1
4:1
4:1
4:1
4:1
4:1
1:1
1:4
7:1
7:1
4:1
4:1
4:1
4:1
4:1
1:1
21 10
28
26
49
54
70
68
66
46
37
trace
75
28
73
61
75
61
69
70
12.5/1
e
e
2
time
(h)
yield of
10 (%)
entry
R1
R2
Z/Ea
1.2
1.5
2
2
2
2
2
2
2
2
2
3
4
4
2
4
5
27
27
5.5
5.5
3
1b
2
3
4
6
7
8
9
10
11
12
13
14c
H
H
H
H
H
H (2b)
CH3 (2c)
i-Pr (2d )
n-C4H9 (2e)
n-C7H15 (2f)
CH3 (2h )
C2H5 (2i)
i-Bu (2j)
t-C4H9 (2k )
C2H5 (2l)
n-C4H9 (2m )
n-C5H11(2n )
n-C4H9 (2q)
9
3
4
2
5
6
3
5.5
4.5
3
3
3
47 (10b)
60 (10c)
61 (10d )
58 (10e)
72 (10f)
86 (10h )
86 (10i)
68 (10j)
85 (10k )
70 (10l)
54 (10m )
68 (10n )
64 (10q)
99/1
72/1
77/1
96/1
99/1
99/1
99/1
56/1
99/1
31/1
99/1
99/1
36/1
4c
5
-10 10.5
26/1
41/1
35/1
13.5/1
22/1
32/1
e
16/1
12.5/1
52/1
3.50/1
10/1
3.5/1
99/1
99/1
-5 10
6
7
8
9
10
11
12
13
14
15
16
17
18
0
20
13 17
25 15
CH3
CH3
CH3
CH3
C2H5
n-C4H9
n-C5H11
H
9
5
11
11
22 20
21 10
0
27
14
0
17
7.5
7
3
7.5
The Z/E ratio was determined by 300 MHz 1H NMR spectra
a
0
0
10.5
17.5
of the crude product; No Na2CO3 was used. c p-Bromophenyl
b
sulfide was used instead of phenyl sulfide.
a
4a was added into the solution of I2/nitrile/H2O within a
minute. 2 equiv of LiOAc‚2H2O was used. c 4a was added into a
b
d
solution of I2/nitrile/H2O over 30 min. Determined by 300 MHz
SCHEME 5
1H NMR spectra of the crude product. e Not determined.
TABLE 6. Iod oh yd r oxyla tion of Allen yl Selen id es
time
(h)
yield of
11 (%)
entry
R
Z/Ea
results of iodohydroxylation of 1,2-propadienyl phenyl
selenide (4a ) with I2 and H2O are summarized in Table
5. When the iodohydroxylation of 4a with I2 and H2O was
carried out under the same conditions as those employed
for 1,2-allenyl sulfoxides,8 the expected product (11a ) was
isolated in only 28% yield with a Z/E ratio of 12.5:1 (entry
1, Table 5).16 The stereoselectivity was determined
unambiguously by the X-ray diffraction study of Z-11e.17
We explored the effect of the ratio of nitrile/water on the
reaction. The reaction could not proceed when there was
too much water in the mixed solvent (entry 10, Table 5).
The stereoselectivity can be tuned by reaction tempera-
ture: The reaction at 0 °C in MeCN/H2O (4:1) afforded
11a in 70% yield with a Z/E ratio of 99/1 (entry 18, Table
5). Some typical results of Z-iodohydroxylation of 1,2-
allenyl selenides are summarized in Table 6.
1
2
3
4
5
6
7
8
Ph (4a )
17.5
20.5
10
19.5
19
69 (11a )
72 (11b)
72 (11c)
74 (11d )
66 (11e)
72 (11f)
74 (11g)
58 (11h )
64 (11i)
33 (11j)
99/1
99/1
99/1
28/1
99/1
99/1
25/1
99/1
99/1
64/1
p-CH3C6H4 (4b)
o-CH3C6H4 (4c)
m-CH3C6H4 (4d )
p-BrC6H4 (4e)
p-ClC6H4 (4f)
p-CH3OC6H4 (4g)
PhCH2 (4h )
19
11.5
11.5
10.5
8
9
10
n-C7H15 (4i)
n-C12H25 (4j)
Determined by 300 MHz 1H NMR spectra of the crude
product.
a
SCHEME 6
The bromohydroxylation of 1,2-allenyl selenides 4a , 4b,
or 4o with Br2 under similar reaction conditions as those
for sulfides failed to yield the expected products (12)
(Scheme 6).
(17) Crystal data for Z-11e: C9H8BrIOSe, Mw ) 417.92, monoclinic,
space group P21/c, Mo KR, final R indices [I > 2σ(I)] R1 ) 0.0592, wR2
) 0.1428, a ) 11.6887(17) Å, b ) 4.4071(7) Å, c ) 12.1232(18) Å, â )
110.230(2)°, V ) 585.98(15) Å3, T ) 20.0 °C, Z ) 2, reflections collected/
total 3559/unique 2201 (Rint ) 0.1447), no. observation [I > 2.00σ(I)]
1671, parameters126. CCDC 186926 contains the supplementary
crystallographic data for this paper. These data can be obtained free
of charge via www.ccdc.cam.ac.uk/conts/retrieving.html (or from the
Cambridge Crystallographic Data Center, 12 Union Road, Cambridge
CB2 1EZ, U.K.; fax (+44) 1223-336-033; or deposit@ccdc.cam.ac.uk).
It has been reported that Hg(OAc)2 can react easily
with an allene to yield methoxy-mercuration products,
i.e., vinylic Hg derivatives Z/ E-14 with Z-14 as the major
product. The stereoselectivity was determined by the
relative stability of the σ-bridged mercurinium ions and
J . Org. Chem, Vol. 69, No. 17, 2004 5723

Ma et al.
SCHEME 7
SCHEME 8
In conclusion, we have developed a highly regio- and
stereoselective addition reaction of 1,2-allenyl sulfides or
selenides. Although the real nature controlling the ste-
reoselectivity needs further attention, this reaction pro-
vides an efficient route to the isomers of the Z-3-
organosulfur- or seleno-group-substituted 2-halo-allylic
alcohols in a highly stereoselective manner, and it may
open up a new area for the control of selectivity in
addition reactions of allenes. Further studies in this area
are currently being carried out in our laboratory.
the steric hindrance of the incoming methoxy group
(Scheme 7).18
However, even with 1,2-allenyl sulfides 2r and 2s, the
bromohydroxylation products 10r -s were formed in 35%
yield (Z/E ) 43:1) and 43% yield (Z/E ) 36:1), respec-
tively, indicating that the methyl or butyl group is not
playing a critical role in determining the stereoselectivity
(Scheme 5). Thus, a rationale for this reaction was shown
in Scheme 8. The Z-stereoselectivity for these reactions
may be explained by the soft Lewis base-acid interaction
between the sulfur or selenium atom and the positively
charged X+ in Z-16.19,20 The regioselectivity in these
reactions may be controlled by the combined steric and
electronic effects of the substituents at the two terminal
positions of the allenes.
Ack n ow led gm en t. Financial support from the Ma-
jor State Basic Research Development Program (Grant
G2000077500), National Natural Science Foundation of
China, and Chenng Kang Scholar Program are greatly
appreciated. Shengming Ma is jointly appointed by
Shanghai Institute of Organic Chemistry and Zhejiang
University. This work was conducted at Zhejiang Un-
versity.
Su p p or tin g In for m a tion Ava ila ble: Experimental sec-
tion, analytical data for compounds not listed in the text, and
1H NMR and 13C NMR spectra of those compounds. Crystal-
lographic data in CIF format. This material is available free
of charge via the Internet at http://pubs.acs.org.
(18) Waters, W. L.; Linn, W. S.; Caserio, M. C. J . Am. Chem. Soc.
1968, 90, 6741.
(19) Lowry, T. H.; Richardson, K. S. Mechanism and Theory in
Organic Chemistry, 3rd ed.; Harper & Row Publishers: New York,
1987; p 319.
(20) For the intermolecular interaction between I and O, see: Chu,
Q.; Zhu, S. J . Am. Chem. Soc. 2001, 123, 11069.
J O049593C
5724 J . Org. Chem., Vol. 69, No. 17, 2004