Published on Web 03/06/2003
Direct Episulfidation of Alkenes and Allenes with Elemental
Sulfur and Thiiranes as Sulfur Sources, Catalyzed by
Molybdenum Oxo Complexes
†
‡
Waldemar Adam, Rainer M. Bargon,* and Wolfdieter A. Schenk
Contribution from the Institut f u¨ r Organische and Anorganische Chemie der UniVersit a¨ t
W u¨ rzburg, Am Hubland, D-97074 W u¨ rzburg, Germany
Abstract: The molybdenum oxo complexes 1a and 1b catalyze efficiently the sulfur transfer to a series of
alkenes 4 and allenes 6, for which elemental sulfur, phenylthiirane, or methylthiirane have been employed
as sulfur sources to afford the corresponding episulfides 5 and 7. The most effective catalytic episulfidation
system to date is the combination of the dithiophosphate-ligated oxo complex 1b and phenylthiirane (Iâ).
This metathesis process is efficient enough to convert usually reluctant alkenes (cyclopentene, cycloheptene,
Z-cyclooctene, Z-cyclononene, E-cyclodecene, norbornene, and even bicyclopropylidene) to their episulfides
in good yields under mild conditions. The direct catalytic sulfuration of allenes (cyclonona-1,2-diene,
cyclonona-1,2,5-triene, cyclodeca-1,2-diene, and 2,4-dimethylpenta-2,3-diene) to their labile methylene-
thiiranes is unprecedented.
5
Introduction
past for the direct episulfidation of alkenes, most recently also
6
5a
by our group. Specifically, Capozzi used trimethylsilylsulfenyl
bromide to episulfidate 1,2-disubstituted E-alkenes and Bruice5b
transferred sulfur from carbon disulfide to 2,3-dimethyl-2-
butene. As direct sulfur donors, our group used a thiophene
endoperoxide, thermally or photochemically generated oxa-
thiiranes from sulfines or R-triketones; a cyclic sulfenate;
and 5-aryloxy-1,2,3,4-thiatriazoles to effect the episulfidation
of E-cyclodecene, E- and Z-cyclooctenes, norbornene, cyclo-
heptene, and cyclopentene. One of the few uses of elemental
sulfur as sulfur source for direct episulfidation is the formation
The traditional method to prepare thiiranes is from the
corresponding epoxides, by attack with an appropriate sulfur
nucleophile and subsequent cyclization, a sequence that is still
commonly employed, giving effective access to the episulfides
of unstrained acyclic and cyclic alkenes, for example, styrene
6
a,b
6c
6d
6e,f
1
and cyclohexene. In contrast, the conversion of an alkene to a
6g
2
thiirane by direct sulfur-atom transfer is as yet a scarce
transformation and remains a synthetic challenge of timely
interest. Like the epoxidation, which for synthetic purposes is
one of the best investigated oxidations in organic chemistry, a
stereoselective one-step episulfidation of alkenes to thiiranes
without oligomerization and polymerization would constitute
3
7
a
of bis(adamantylidene)episulfide or 9,9′-bibenzonorborne-
7
b
nylidene episulfides by heating in DMF without a catalyst. In
all of the above-mentioned episulfidations, the sulfur source is
also the sulfur-transferring agent and used necessarily stoichio-
metrically.
4
an attractive but demanding aim. In this context, several
electrophilic sulfur-transfer agents have been developed in the
†
‡
To date little is known about the catalytic episulfidation of
Institut f u¨ r Organische Chemie.
Institut f u¨ r Anorganische Chemie.
alkenes with metal complexes. Simpkins and co-workers8
(
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convert norbornene and norbornadiene to their episulfides.
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(
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10.1021/ja029292p CCC: $25.00 © 2003 American Chemical Society
J. AM. CHEM. SOC. 2003, 125, 3871-3876
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