Tetrahedron
Letters
Tetrahedron Letters 45 (2004) 6063–6065
Convenient stereoselective synthesis of 3-hydroxy-
2
-iodo-2(E)-alkenyl sulfides via iodohydroxylation
of 1,2-allenyl sulfoxides in the presence of BnSH
a
Chunling Fu, Xian Huang and Shengming Ma
a
a,b,
*
a
Laboratory of Molecular Synthesis and Recognition, Department of Chemistry, Zhejiang University,
10027 Hangzhou, Zhejiang, PR China
3
b
State Key Laboratory of Organometallic Chemistry, Shanghai Institute of Organic Chemistry,
Chinese Academy of Sciences, 354 Fenglin Lu, Shanghai 200032, PR China
Received 29 March 2004; revised 21 May 2004; accepted 26 May 2004
2
Abstract—The iodohydroxylation of 1,2-allenyl sulfoxides with I in the presence of BnSH affords 3-hydroxy-2-iodo-2(E)-alkenyl
sulfides in good yields and selectivities. The stereochemistry for the products of this transformation is opposite to what was obtained
from the iodohydroxylation of 1,2-allenyl sulfides. Based on the results of some control experiment, a mechanism was proposed.
Ó 2004 Published by Elsevier Ltd.
The electrophilic or nucleophilic addition reaction of
allenes is versatile providing that the regio- and stereo-
selectivity can be addressed since two functionalities can
be introduced into the final products in one ‘operation’.
Recently, we have demonstrated the regioselective
selectivity defined by the participation of the sulfoxide
functionality (Scheme 1).
2;5
As a first try, we treated 1,2-propadienyl phenyl sulf-
6
oxide 1a with benzyl thiol and I in anhydrous MeCN.
2
1
nucleophilic addition of electron-deficient allenes.
Quite recently we also observed the regio- and stereo-
selective halohydroxylation reaction of 1,2-allenyl sulf-
Some typical results are summarised in Table 1. It is a
surprise for us that with 1.2 equiv of I and 1 equiv of
2
BnSH, besides the iodohydroxylation product 5a, E-3-
phenylthio-2-iodopropenol 4a was isolated in 37% yield
with an E=Z ratio of 96/4 as the major product (Table 1,
entry 1). The formation of 3-type product (Nu ¼ SBn)
was not observed. In the absence of BnSH the reaction
in MeCN afforded E-5a as the major product (Table 1,
2
3
4
oxides, sulfides and selenides. In these reactions, the
presence of sulfinyl group or organosulfur/selenium
group is important for the unique stereoselectivity of the
halohydroxylation reaction. In this paper we wish to
report our recent observation on the iodohydroxylation
of the readily available 1,2-allenyl sulfoxides in the
presence of benzyl thiol affording 3-hydroxy-2-iodo-2(E)-
alkenyl sulfides, the C@C bond configuration of which is
opposite to what was synthesised via the iodohydroxyl-
2
entry 2). After some screening it was clear that E-4a can
2
be formed in 50% yield with 1.5 equiv of I and 1 equiv
of BnSH (Table 1, entry 3). The stereochemistry of E-4a
was determined by the NOE study and comparison with
3
3
ation of 1,2-allenyl sulfides.
the authentic sample of the Z-isomer.
We initiated this study with the notion that the cyclic
2
In order to see the generality of this interesting trans-
formation, some differently substituted 1,2-alkadienyl
sulfoxides were prepared and the corresponding reac-
intermediate 2 involved in the electrophilic E-halo-
hydroxylation of 1,2-allenyl sulfoxides may react with
nucleophiles to produce 3-type products with the stereo-
6
2
tion with I in the presence of 1 equiv of BnSH were
studied. Some typical results are shown in Table 2.
From Table 2, the following points should be
noted: (1) the reaction is general since it proceeded well
with unsubstituted 3-mono, 3,3-disubstituted and
1,3,3-trisubstituted 1,2-alkadienyl sulfoxides; (2) the
Keywords: Allenes; Sulfoxides; Iodohydroxylation.
*
7
0
040-4039/$ - see front matter Ó 2004 Published by Elsevier Ltd.
doi:10.1016/j.tetlet.2004.05.160