Highly regioselective thiocarbonylation of conjugated dienes via palladium-catalyzed three-component coupling reactions

Article abstract of DOI:10.1021/jo000231o

Three-component coupling reaction of conjugated dienes, thiols, and carbon monoxide affords an atom-economical thiocarbonylation of the dienes to give β,γ-unsaturated thioesters as the sole products. A catalyst system based on [Pd(OAc)₂] and Ph

Full text of DOI:10.1021/jo000231o

4
138
J . Org. Chem. 2000, 65, 4138-4144
High ly Regioselective Th ioca r bon yla tion of Con ju ga ted Dien es via
P a lla d iu m -Ca ta lyzed Th r ee-Com p on en t Cou p lin g Rea ction s
†
Wen-J ing Xiao, Giuseppe Vasapollo, and Howard Alper*
Department of Chemistry, University of Ottawa, 10 Marie Curie, Ottawa, Ontario K1N 6N5
Received February 18, 2000
Three-component coupling reaction of conjugated dienes, thiols, and carbon monoxide affords an
atom-economical thiocarbonylation of the dienes to give â,γ-unsaturated thioesters as the sole
products. A catalyst system based on [Pd(OAc)
thiocarbonylation was performed under an atmosphere of carbon monoxide (400 psi) at 110 °C in
CH Cl for 60 h. A wide variety of thioesters were synthesized in good to excellent yields from
2 3
] and Ph P showed excellent catalytic activity. The
2
2
3
easily accessible starting materials. The reaction is believed to proceed via a η -allylpalladium
intermediate. The thiocarbonylation, which is applicable to a wide variety of conjugated dienes,
occurs in high regioselectivity, the latter dependent on the steric characteristics and stability of
3
the η -allylpalladium complex.
In tr od u ction
Transition metal-catalyzed synthetic transformations
have developed a series of transition metal-catalyzed
reactions of organic sulfur compounds. Examples include
the iridium-catalyzed group transfer reaction of 1,3-
1
employing heteroatom compounds containing silicon,
9
thiazanes, and the rhodium(I)-catalyzed regioselective
2
3
4
boron, phosphorus, or germanium are versatile meth-
carbonyl insertion reaction of C-S bonds of R-substituted
ods to the formation of heteroatom-carbon bonds in
10
tetrahydrofuran thioethers. Processes involving ruthe-
5
organic synthesis. The use of organosulfur compounds
11
12
nium and palladium complexes as catalysts have also
as a direct reagent for the preparation of C-S bonds
catalyzed by transition metal catalysts has had some
notable successes6 but, for the most part, it has been
13
14
been investigated. For example, thiols or disulfides
react with propargyl alcohols in the presence of [Pd-
PPh
(
3 4
) ] to afford â-(arylthio)-R,â-unsaturated γ-lactones
15
7
much less studied than its oxo and nitro analogues. One
as the thiolactonization products. Allylic alcohols and
possible reason is that chalcogen compounds may act as
poisons for the transition metal, rendering them incom-
16
allenes react similarly with thiophenols. In 1994, Back-
vall and co-workers reported the regioselective addition
of thiophenol to conjugated enynes,17 and most recently,
we developed the thiocarbonylation version of such a
8
patible with catalytic species. Recently, we and others
†
18
Present address: Department of Materials Science, University of
reaction. In the latter case, it was found that the
Lecce, Lecce, Italy.
thiocarbonylation of enynes could afford two products (eq
1), depending on the concentrations of the reactants. It
(1) (a) Horn, K. A. Chem. Rev. 1995, 95, 1317. (b) Ojima, I. In The
Chemistry of Organic Silicon Compounds; Patai, S., Rappoport, Z.,
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I.; Alper, H. J . Am. Chem. Soc. 1995, 117, 4419. (d) Zhou, J .-Q.; Alper,
H. Organometallics 1994, 13, 1586.
(2) (a) Beletskaya, I.; Pelter, A. Tetrahedron 1997, 53, 4957. (b)
Burgess, K.; Ohlmeyer, M. J . Chem. Rev. 1991, 91, 1179. (c) Ishiyama,
T.; Yamamoto, Miyaura, M. N. Chem. Commun. 1996, 2073.
(
3) (a) Han, L.-B.; Tanaka, M. J . Am. Chem. Soc. 1996, 118, 1571.
b) Han, L.-B.; Choi, N.; Tanaka, M. Organometallics 1996, 15, 3259.
4) (a) Monteil, F.; Alper, H. Chem. Commun. 1995, 1601. (b) Oda,
H.; Morizawa, Y.; Oshima, K.; Nozaki, H. Tetrahedron Lett. 1984, 25,
221.
5) (a) Tsuji, J . Palladium Reagents and Catalysts: Innovations in
(
(
3
(
Organic Synthesis; J ohn Wiley & Sons: Chichester, 1995. (b) Hiyama,
T.; Kusumoto, T. In Comprehensive Organic Synthesis; Trost, B. M.,
Ed.; Pergamon: Oxford, 1991.
(6) (a) Shim, S. C.; Antebi, S.; Alper, H. J . Org. Chem. 1985, 50,
(9) Alper, H.; Crudden, C.; Khumtaveeporn, K. Chem. Commun.
1995, 1199.
1
47. (b) Antebi, S.; Alper, H. Tetrahedron Lett. 1985, 26, 2609. (c)
Antebi, S.; Alper, H. Organometallics 1986, 5, 596. (d) Calet, S.; Alper,
H. Tetrahedron Lett. 1986, 27, 3573. (e) Calet, S.; Alper, H.; Petrignani,
J .-F.; Arzoumanian, H. Organometallics 1987, 6, 1625. (f) Wang, M.-
D.; Calet, S.; Alper, H. J . Org. Chem. 1989, 54, 20. (g) Baranano, D.;
Hartwig, J . F. J . Am. Chem. Soc. 1995, 117, 2937. (h) Ciattini, P. G.;
Morera, E.; Ortar, G. Tetrahedron Lett. 1995, 36, 4133. (i) Ogawa, A.;
Ikeda, T.; Kimura, K.; Hirao, T. J . Am. Chem. Soc. 1999, 121, 5108
and reference 2 cited therein.
(10) Khumtaveeporn, K.; Alper, H. Chem. Commun. 1995, 917.
(11) Kondo, T.; Uenoyama, S.; Fujita, K.; Mitsudo, T. J . Am. Chem.
Soc. 1999, 121, 482.
(12) (a) Frank, M.; Gais, H.-J . Tetrahedron: Asymmetry 1998, 9,
3353. (b) Bohme, A.; Gais, H.-J . Tetrahedron: Asymmetry 1999, 10,
2511. (c) Ogawa, A.; Ikeda, T.; Kimura, K. J . Am. Chem. Soc. 1999,
121, 5108, and references therein.
(13) Xiao, W.-J .; Alper, H. J . Org. Chem. 1997, 62, 3422.
(14) Ogawa, A.; Kuniyasu, H.; Sonoda, N.; Hirao, T. J . Org. Chem.
1997, 62, 8361.
(15) Xiao, W.-J .; Alper, H. J . Org. Chem. 1998, 63, 7939.
(16) (a) Xiao, W.-J .; Vasapollo, G.; Alper, H. J . Org. Chem. 1998,
63, 2609. (b) Ogawa, A.; Kawakami, J .; Sonoda, N.; Hirao, T. J . Org.
Chem. 1996, 61, 4161.
(7) Although organosulfur compounds can be catalyst poisons, there
are a substantial number of examples in which they are excellent
ligands to transition metals. See: Frost, C. G.; J . Williams, M. J .
Tetrahedron Lett. 1993, 34, 2015, and ref 5 cited therein.
(8) (a) Hutton, A. T. In Comprehensive Coordination Chemistry;
Wilkinson, G., R. Gillard, D., McCleverty, J . A., Eds.; Pergamon
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Poisoning; Marcel Dekker: New York, 1984. (c) Dubois, M. R. Chem.
Rev. 1989, 89, 1.
(17) Backvall, J . E.; Ericsson, A. J . Org. Chem. 1994, 59, 5850.
(18) Xiao, W.-J .; Vasapollo, G.; Alper, H. J . Org. Chem. 1999, 64,
2080.
1
0.1021/jo000231o CCC: $19.00 © 2000 American Chemical Society
Published on Web 06/01/2000

Thiocarbonylation of Conjugated Dienes
J . Org. Chem., Vol. 65, No. 13, 2000 4139
is clear that 4 might also arise by further reaction of 3and
thiophenol. Inspired by these results, we realized that
the carbonylative addition of three components, conju-
gated dienes, thiols, and carbon monoxide, could, in
principle, afford the corresponding â, γ-unsaturated
thioesters.
Ta ble 1. Op tim iza tion of Ca ta lyst System s for th e
P a lla d iu m -Ca ta lyzed Th ioca r bon yla tion of Con ju ga ted
Dien esa
The synthesis of thioesters is an important subject in
organic synthesis,19 with selectivity and atom economy
20
21
as key issues. The present methodology (shown in eq 2)
represents a highly regioselective and atom-economical
route to â,γ-unsaturated thioesters.
Resu lts a n d Discu ssion
Rea ction Con d ition s for th e Th ioca r bon yla tion
of 2-Meth yl-1,3-bu ta d ien e. In flu en ce of th e Ca ta lyst
System on th e Rea ction . Initially, the reaction of
2
-methyl-1, 3-butadiene (5a ) with thiophenol and carbon
a
monoxide was investigated. The optimal reaction condi-
tions [5 equiv of diene, 1 equiv of thiophenol, 3 mol %
Reaction conditions: thiophenol (1 mmol), 2-methyl-1,3-buta-
diene (5 mmol), catalyst (0.05 mmol), Ph3P, PCy3, or PBu3 (0.2
mmol, if used), 1,4-bis(diphenylphosphino)butane (dppb), 1,3-
bis(diphenylphosphino)propane (dppp), 1,2-bis(diphenylphosphi-
no)ethane (dppe), or 1,1′-bis(diphenylphosphino)ferrocene (dppf)
[
Pd(OAc)
2
], 6 mol % 1,3-bis(diphenylphosphino)propane
(dppp), 400 psi of carbon monoxide, and THF (15 mL per
mmol of thiophenol)], employed previously for the thio-
carbonylation of conjugated enynes18 were used to check
the feasibility of the process (eq 3).
0.1 mmol, if used), CH2Cl2 (5 mL), 110 °C. b Isolated yield. The
c
(
presence of the phenylthiocarbonyl group was indicated by an IR
of the crude product, but attempts to isolate the carbonylation
product were unsuccessful. d The reaction gave a deep red and very
insoluble solid, which might be a polymer.22
ene (Table 1, entry 4). Palladium(0) complexes, such as
[Pd(PPh
3
)
4
] and Pd
2
(dba)
3
3
‚CHCl , with added triphenyl-
phosphine, were also good catalysts for the thiocarbony-
lation reaction (Table 1, entries 8 and 9). It was observed
that the ligands employed played an important role in
the selectivity of the reaction (Table 1, entries 1-7 and
1
0). For example, using [Pd(OAc)
precursor in the presence of bidentate phosphines gave
,4-addition as the sole or major pathway (Table 1,
2
] as the catalyst
1
The reaction gave two products 7a and 7a ′ in yields of
% and 47%, respectively, with 16% recovery of unreacted
entries 1-4), while only carbonylative 1,4-adducts were
isolated in the case of monodentate phosphines (Table
1, entries 5-7). Under the same conditions, the yield of
7a increased by changing the ligand from dppe to dppp
or dppb. These results are in accord with the observation
by Van Leeuwen and co-workers that the rate of carbon
monoxide insertion into a Pd-C bond is faster for
alkylpalladium bisphosphine complexes containing a
flexible metal ligand chelate ring.23 In addition to tri-
4
thiophenol after 48 h. Although the yield of the desired
product 7a was low, we were nevertheless encouraged
and examined the reaction in detail under a variety of
conditions in an attempt to increase the yield. Several
palladium complexes and phosphine ligands were exam-
ined as catalytic systems, and the results are summarized
in Table 1.
Among the catalysts examined, [Pd(OAc)
equiv of PPh showed high activity for the catalytic
thiocarbonylation reaction (Table 1, entry 5), while [Pd-
OAc) ] with dppf (2 equiv) as the added ligand resulted
in the 1,4-addition of thiophenol to 2-methyl-1,3-butadi-
2
], with 4
phenylphosphine, PCy
this reaction, but they are inferior to PPh
entries 5-7). When the reaction was performed without
any ligand, a deep red precipitate was formed, and there
was 68% and 47% recovery of 2-methylbutadiene and
thiophenol, respectively.22
3
and PBu
3
can also be used for
(Table 1,
3
3
(
2
(
19) (a) Murai, T.; Kakami, K.; Hayashi, A.; Komuro, T.; Takada,
H.; Fujii, M.; Karida, T.; Kato, S. J . Am. Chem. Soc. 1997, 119, 8592.
b) Vogel, K. W.; Drueckhanmer, D. G. J . Am. Chem. Soc. 1998, 120,
Solven t Op tim iza tion . The reaction is sensitive to
the solvent as shown by the results in Table 2. As noted
(
3
2
275. (c) Wallace, O. B.; Springer, D. M. Tetrahedron Lett. 1998, 39,
693. (d) Halcomb, R. L.; Boyer, S. H.; Wittman, M. D.; Olson, S. H.;
(22) (a) Nyholm, R. S.; Skinner, J . F.; Stiddard, M. H. B. J . Chem.
Soc: A 1968, 38. (b) Kuniyasu, H,; Ogawa, A.; Sato, K.-I.; Ryu, I.;
Kambe, N.; Sonoda, N. J . Am. Chem. Soc. 1992, 114, 5902.
(23) (a) Dekker, G. P. C. M.; Elsevier: C. J .; Vrieze, K.; van Leeuwen,
P. W. N. M. Organometallics 1992, 11, 1598. (b) Dekker: G. P. C. M.;
Elsevier: C. J .; Vrieze, K.; van Leeuwen, P. W. N. M. J . Organomet.
Chem. 1992, 430, 357.
Denhart, D. J .; Liu, K. K. C.; Danishefsky, S. J . J . Am. Chem. Soc.
995, 117, 5720. (e) Thuillier, A.; Metzner, P. Sulfur Reagents in
Organic Synthesis; Academic Press: New York, 1994.
1
(
20) Trost, B. M. Science 1983, 219, 245.
(21) (a) Trost, B. M. Science 1991, 254, 1471. (b) Trost, B. M. Angew.
Chem., Int. Ed. Engl. 1995, 34, 259.

4
140 J . Org. Chem., Vol. 65, No. 13, 2000
Xiao et al.
Ta ble 2. Solven t Effects on th e P a lla d iu m -Ca ta lyzed
Rea ction of 2-Meth ylbu ta d ien e w ith Th iop h en ol a n d
arenethiols, such as 2-naphthalenethiol (6d ), gave an
approximately 1:1 mixture of the carbonylation 7e and
a
Ca r bon Mon oxid e
1
,4-addition products (7e′) (Table 3, entry 5). In the case
of alkanethiols, it was observed that increasing the length
of the alkyl group caused the thiols to become less
reactive, with a mixture of addition and carbonylative
addition products formed in all the cases (Table 3, entries
7
-9). When cyclohexyl mercaptan was employed as the
substrate, no products were obtained at all.
Th ioca r bon yla tion of Acyclic Con ju ga ted Dien es
Usin g Th iop h en ol (2). A series of acyclic conjugated
dienes were thiocarbonylated smoothly, by [Pd(OAc)
and PPh , to give the corresponding â,γ-unsaturated
thioesters in good to excellent yields (Table 4).
2
]
3
R,â-Unsaturated thioesters were not detected among
the products either before or after purification, although
it is well-known that isomerizations of â,γ-unsaturated
2
4
thioesters to R,â-unsaturated isomers might occur.
Importantly, the reaction exhibits excellent regioselec-
tivity in all cases. Depending on the structural charac-
teristics of the dienes employed, the reaction could
selectively afford carbonylative 1,4- or 1,2-addition prod-
ucts. Usually, the monosubstituted and 2,3-substituted
dienes reacted with 2 and CO to afford carbonylative 1,4-
addition products (Table 4, entries 1-5, 7, 10, and 11),
while 1,1-disubstituted dienes such as 5f and 5i, as well
as tert-butyl-substituted butadiene (5h ), underwent thio-
carbonylation to form products of carbonylative 1,2-
addition (Table 4, entries 6, 8, and 9). A substitutent at
the C-2 position of the dienes was found to direct the H
of 2 exclusively to the C-1 position, and the phenylthio-
carbonyl group to the C-4 position of the molecule,
although the reaction might give two isomeric carbony-
lative 1,4-adducts. The regioselectivity can be explained
a
Reaction conditions: 2-Methyl-1,3-butadiene (5 mmol). Thiophe-
nol (1 mmol), [Pd(OAc)2] (0.05 mmol), PPh3 (0.2 mmol), 400 psi of
carbon monoxide, solvent (5 mL), 110 °C. Phenylcarbonyl group
was identificated by IR of the crude product, but attempts to isolate
the carbonylation product were unsuccessful. 15% of thiophenol
b
c
was recovered.
already, THF was not an ideal solvent for the thiocar-
bonylation of 5a (eq 3).
When [Pd(OAc) ] with PPh was used as the catalyst
2 3
precursor, the reaction in THF gave the thioester (7a )
and sulfide (7a ′) in 27% and 52% yield, respectively
(
Table 2, entry 1). The reaction worked very well in CH
Cl and afforded 7a as the sole product in 83% isolated
yield (Table 2, entry 6); however, under the same condi-
tions, using CH CN or benzene as the solvent, 7a ′ was
formed as the major or the sole product (Table 2, entries
and 3). Reactions in 1,2-dimethoxyethane (DME) and
2
-
2
3
3
by the nature of the diene and the stability of the η -
2
allylpalladium complex. For example, in the case of 5a
(Scheme 1), the H of 2 can attack either at C-1 or C-4 to
form two isomeric π-allylpalladium complexes 8 or 9,
which would then give thioester 7a or 10, respectively.
With an electron-donating group in the C-2 position, C-1
is more protophilic than C-4.25 Furthermore, η -allylpal-
diethyl ether gave a mixture of 7a and 7a ′ (Table 2,
entries 4 and 5).
On the basis of these results, the reaction of a variety
of conjugated dienes and thiols were performed, and the
results are summarized in Tables 3-5.
Th ioca r bon yla tion of 2-Meth yl-1,3-bu ta d ien e(5a )
Usin g Va r iou s Th iols. The results in Table 3 indicate
the scope and limitations of the palladium-catalyzed
carbonylative coupling reaction of 5a and representative
thiols. In most cases, thiophenols were found to work
more effectively than alkanethiols. For example, 5a
reacted with thiophenol (2), p-nitrobenzenethiol (6b), and
p-bromobenzenethiol (6c) affording only the carbonylative
3
2
6
ladium complex 8 is known to be more stable than 9.
Therefore, it can be envisaged that the reaction of 5a with
2 and CO can only occur by path (a) to give the thioester
7a as the sole product.
It was observed that the regioselectivity decreased
when a substrate with a substituent at C-1 of the diene
was employed in this reaction (Table 4, entries 3-5). It
is probable, therefore, that during the reaction, two
3
1
(
,4-addition products 7a , 7c, and 7d in similar yields
Table 3, entries 1, 3, and 4), while the corresponding
isomeric η -allylpalladium complexes were formed (Scheme
2, illustrated for piperylene). The ratio of the two
reaction with alkanethiols always gave mixtures of
thiocarbonylation and simple 1,4-addition products (Table
products (7k and 7l) may depend on steric factors.
3
, entries 6-9). Reactions involving alkanethiols took
(24) Alcock, S. G.; Baldwin, J . E.; Bohlmann, R.; Harwood: L. M.;
Seeman, J . I. J . Org. Chem. 1985, 50, 3526.
longer to complete than those with arenethiols. The
reaction was rather sensitive to both the acidity (elec-
tronic factor) and the effective bulk (steric factors) of the
thiols. For example, 6a (p-methoxybenzenethiol), an
arenethiol with an electron-donating p-methoxy group,
and 6b (p-nitrobenzenethiol), an arenethiol with an
electron-withdrawing group, show somewhat different
behavior in this reaction. Using 6a as the substrate gives
a mixture of 7b (60%yield) and 7b′ (18% yield) after a
period of 72 h (Table 3, entry 2), whereas 6b gives only
the carbonylative 1,4-addition product in 80% yield (Table
(
25) Ab initio calculations showed that the electron distribution of
-methyl-1,3-butadiene (5a ) (after 6-31G geometry optimization) is as
follows:
2
(26) (a) Backvall, J . E.; Nystrom, J . E.; Nordberg, R. E. J . Am. Chem.
Soc. 1985, 107, 3677. (b) Rowe, J . M.; White, D. A. J . Chem. Soc. A
1967, 1451.
3
, entry 3) after a period of 48 h. Reactions with

Thiocarbonylation of Conjugated Dienes
J . Org. Chem., Vol. 65, No. 13, 2000 4141
Ta ble 3. P a lla d iu m -Ca ta lyzed Rea ction of 5a w ith Th iols a n d COa
a
Reaction conditions: 2-Methyl-1,3-butadiene (10 mmol), thiol (2 mmol), [Pd(OAc)2] (0.1 mmol), PPh3 (0.4 mmol), 400 psi of carbon
monoxide, CH2Cl2 (10 mL).
For 1,1-disubstituted dienes, the phenylthiocarbonyl
group exclusively attacked the least substituted terminal
allylic carbon of the η -allylpalladium complexes, afford-
double thiocarbonylation of the triene did not occur. It is
interesting to note that the thiocarbonylation reactions
of (E)- and (Z)-piperylene (5d and 5e) afford a 9:1 mixture
of (E)- and (Z)-phenyl 2-methyl-3-pentenethioate (7l),
independent of the stereochemistry of the starting dienes
(Table 4, entries 4 and 5). It is likely that the variation
of the stereochemistry is due to the η -η -η isomerization
of the intermediate π-allylpalladium complexes 10 and
12 (Scheme 4),28 with preference for the thermodynami-
cally more stable (E)-isomer product.
3
ing the carbonylative 1,2-addition products (Scheme 3).
Fine stereoselectivity for the â,γ-unsaturated thioesters
resulted using some dienes as substrates. The thermo-
dynamically more stable (E)-isomers were obtained pref-
erentially, irrespective of the stereochemistry of the
starting reactants (Table 4, entries 3-10). For example,
homogeranic acid, which is a precursor of tetrahydro-
astinidiolides,27 can be obtained stereoselectively (E/Z )
3
1
3
Th ioca r bon yla tion of Cyclic Dien es Usin g Th io-
1
9/1) from myrcene (5j) (Table 4, entry 10). Noth that
p h en ol (2). Table 5 shows the results of the [Pd(OAc)
2
]/
PPh -catalyzed thiocarbonylation of PhSH with several
3
cyclic conjugated dienes. Consistent with the pattern
(27) (a) Kato, T.; Kumazawa, S.; Kitahara, Y. Synthesis 1972, 573.
(
3
4
b) Hoye, T. R.; Caruso, A. J .; Kurth, M. J . J . Org. Chem. 1981, 46,
550. (c) Gnonlonfoun, N.; Zamarlik, H. Tetrahedron Lett. 1987, 28,
035.
(28) Mackenzie, P. B.; Whelan, J .; Bosnich, B. J . Am. Chem. Soc.
1985, 107, 2046.

4
142 J . Org. Chem., Vol. 65, No. 13, 2000
Xiao et al.
Ta ble 4. P a lla d iu m -Ca ta lyzed Th ioca r bon yla tion of Acyclic Con ju ga ted Dien es Usin g Th iop h en ol a n d COa
a
Reaction conditions: Diene (10 mmol), thiophenol (2 mmol), [Pd(OAc)2] (0.1 mmol), PPh3 (0.4 mmol), CO (400 psi), CH2Cl2 (10 mL),
reaction time (60 h), reaction temperature (110 °C). The ratio of E to Z was determined by 1H NMR.
b
Sch em e 1
substrates (Table 5, entries 1-3), the substituted cyclic
dienes afford 1,4- or 1,2-products, depending on the
substrates. For example, only the 1,4-product was formed
when exo-methylene cyclohexene (5o) was the reactant
(
Table 5, entry 4). In contrast, the 1,2-product was
obtained in the case of 1-methyl-1,3-cyclohexadiene (5p )
Table 5, entry 5). It is conceivable that the reactions of
o and 5p proceed through the same intermediate
Scheme 5), and this could be the reason both reactions
(
5
(
gave identical products.
Mech a n istic Asp ects. A possible pathway for the
palladium-catalyzed thiocarbonylation of 5 (using 5b as
the example) with thiophenol (2) is outlined in Scheme
6. It is well-known that Pd(0) is readily formed in situ
found for acyclic analogues, the regioselectivity of the
reaction employing cyclic dienes was quite high. While
1
,4- and 1,2-thiocarbonylative adducts are structurally
identical when unsubstituted cyclic dienes were used as
2
by the reduction of [Pd(OAc) ] in the presence of phos-

Thiocarbonylation of Conjugated Dienes
J . Org. Chem., Vol. 65, No. 13, 2000 4143
Sch em e 2
Sch em e 3
Sch em e 5
Sch em e 4
Sch em e 6
Ta ble 5. P a lla d iu m -Ca ta lyzed Th ioca r bon yla tion of
a
Cyclic Con ju ga ted Dien es
3
afford the η -allylpalladium complex 16. Insertion of CO
into the Pd-S bond of 16 or into the Pd-C bond of the
σ-allyl analogue of 16, followed by regioselective intramo-
lecular transfer would afford the acylpalladium complex
3
2
1
7. Reductive elimination of 17 would afford the
thioester (7j), with regeneration of the palladium cata-
lyst.
Con clu sion s
In summary, a highly effective catalytic system ([Pd-
(
OAc)
2
3
]-PPh ) has been developed for the carbonylative
coupling reaction of conjugated dienes, thiols, and carbon
(
29) (a) Amatore, C.; J utand, A.; M′Barki, M. Organometallics 1992,
1, 3009. (b) Amatore, C.; Cane, E.; J utand, A.; M′Barki, M. Organo-
metallics 1995, 14, 1818.
30) Ogawa, A.; Kawakami, J .; Mihara, M.; Ikeda, T.; Sonoda, N.;
Hirao, T. J . Am. Chem. Soc. 1997, 119, 12380.
(31) Lukas, J .; Kramer, P. A. J . Organomet. Chem. 1971, 31, 111.
1
(
phine ligands.29 Oxidative addition of 2 to palladium(0)
3
0
can then give the thiopalladium complex (14), which
(
32) A similar mechanism for the insertion of acetylene into the Pd-
4
can coordinate with the diene to form a Pd-η -diene
CO σ bond has been reported. See: Samsel, E. G.; Norton, J . R. J .
Am. Chem. Soc. 1984, 106, 5505.
complex 15.31 Intramolecular hydropalladation would

4
144 J . Org. Chem., Vol. 65, No. 13, 2000
Xiao et al.
monoxide to form the corresponding â,γ-unsaturated
thioesters. These reactions take place in a highly regio-
selective manner, depending on the steric characteristics
and stability of the proposed η -allylpalladium complex.
Furthermore, the reactions exhibit good to excellent
stereoselectivity.
three times with CO, the autoclave was fill-vented three times
with CO to displace the air, and the pressure was subsequently
increased to 400 psi. The mixture was stirred in the autoclave
at 110 °C (oil bath temperature) for 48-144 h. After cooling,
the excess CO was released. The reaction mixture was filtered
through Florisil, and the solvent was removed by rotary
evaporation. The residue was separated by preparative TLC
3
(
silica gel GF254, eluant: n-hexane/ethyl acetate 10:1).
Exp er im en ta l Section
P h en yl 4-Meth yl-3-p en ten eth ioa te (7a ). Colorless oil; IR
-
1 1
(
(
7
2
1
neat): υ ) 1708 cm ; H NMR (200 MHz, CDCl
3
): δ ) 1.70
Ma ter ia ls. Benzene, THF, 1,2-dimethoxyethane, and di-
ethyl ether were dried and distilled from sodium/benzophenone
ketyl under nitrogen before use. Dichloromethane was freshly
s, 3H), 1.78 (s, 3H), 3.35 (d, 2H, J ) 7.4 Hz), 5.36 (t, 1H, J )
.4 Hz), 7.40 (s, 5H); 13C NMR (50 MHz, CDCl
): δ ) 18.10,
3
5.76, 43.10, 115.10, 127.76, 128.68, 129.07, 133.27, 137.82,
2 3
distilled from CaH under nitrogen. CH CN was dried by
+
96.36; MS (70 eV, EI): 206.1 [M ]; HRMS (70 eV, EI): calcd
storing over molecular sieves (4A) and distilled under nitrogen.
All other common solvents and chemicals were used as
for C12
14
H14OS 206.0765, found 206.0790. Anal. Calcd for C12H -
3
3
OS: C 69.80, H 6.84. Found: C 69.88, H 6.92.
received. 3-Methylenecyclohexene (5o), 1-methyl-1,3-cyclo-
3
4
35
hexadiene (5p ), and Pd
2
(dba)
3
‚CHCl
3
were prepared ac-
cording to literature procedures.
Ack n ow led gm en t. We are grateful to the Natural
Sciences and Engineering Council of Canada for the
support of this research. We are indebted to Dr. David
Butler and Ms. Helen Clark for helpful discussions and
valuable comments.
Gen er a l P r oced u r e for th e P a lla d iu m -Ca ta lyzed Th io-
ca r bon yla tion of Con ju ga ted Dien es. To a 45-mL Parr
autoclave fitted with a glass liner and stirring bar were added
[
(
Pd(OAc)
2
] (0.1 mmol), PPh
3
(0.4 mmol), diene (10 mmol), thiol
2
(10 mL). The CO line was flushed
0.2 mmol), and dry CH
2
Cl
(
33) Smithson, T. L.; Ibrahim, N.; Wieser, H. Can J . Chem. 1983,
Su p p or tin g In for m a tion Ava ila ble: The characteriza-
tion data for all products. This material is available free of
charge via the Internet at http://pubs.acs.org.
6
1
6
1, 442.
(34) Spangler, C. W.; Hartford, T. W. J . Chem. Soc., Perkin Trans.
1976, 1792.
(
5, 253.
35) Ukai, T.; Kawazura, H.; Ishii,Y. J . Organomet. Chem. 1974,
J O000231O