Highly regioselective addition of benzenethiol to allenes catalyzed by palladium acetate

Full text of DOI:10.1021/jo9521357

J . Org. Chem. 1996, 61, 4161-4163
4161
Ta ble 1. P d (II)-Ca ta lyzed Ad d ition of P h SH to
Mon oa lk yla llen esa
High ly Regioselective Ad d ition of
Ben zen eth iol to Allen es Ca ta lyzed by
P a lla d iu m Aceta te
Akiya Ogawa,* J un-ichi Kawakami,
Noboru Sonoda,* and Toshikazu Hirao
Department of Applied Chemistry, Faculty of Engineering,
Osaka University, Suita, Osaka 565, J apan
Received December 1, 1995
The addition reaction of thiols to allenes is one of the
most straightforward routes to vinylic sulfides, which are
well-known to be important synthetic intermediates.1 It
has been reported that thiols add to allenes by a free-
radical mechanism.2-5 However, thiyl radicals, as the
key species in the radical addition, usually attack at both
the center and terminal carbons of allenes, so the radical
reaction results in the formation of a regioisomeric
mixture of thiol adducts. For example, the radical
addition of benzenethiol to monoalkyl-substituted allenes
was reported to provide a regio- and stereoisomeric
mixture of the adducts 1, 2, and 3, with ratios of 38:37:
25 (R ) t-Bu)5 and 2:81:17 (R ) n-Bu)5 (eq 1). These
features make the radical reaction synthetically less
useful. Contrary to this, we here report that palladium-
(II) acetate exhibits excellent catalytic activity toward the
highly regioselective addition of thiols to allenes (eq 2).
reaction conditions may come to in mind, no conversion
of 1d to 2d was observed in the experiment using 1d as
the substrate. Presumably, the formation of 2d may be
accounted for by the coordination of the terminal double
bond of the allene to palladium(II) species, because the
terminal double bond has higher electron density com-
pared with that of the inner one (vide post).
We have also investigated the palladium-catalyzed
addition of 1,1-dimethylallene with benzenethiol in detail.
The radical addition to 1,1-dimethylallene proceeded very
rapidly and produced the thermodynamically more stable
adduct 4 (96%), exclusively (Scheme 1).4,5 In contrast,
the Pd(OAc)2-catalyzed addition to 1,1-dimethylallene
provided its regioisomer (5, 67%) as a sole product.
Accordingly, both methods are complementary to each
other for the regioselective synthesis of vinylic sulfides
from 1,1-dialkyl-substituted allenes. In the case of the
Pd(OAc)2-catalyzed addition, the amount of catalyst used
is important to obtain the adduct 5 selectively. In the
presence of 3 mol % of Pd(OAc)2 both vinylic sulfides 5
(15%) and 4 (73%) were obtained. The use of 10 mol %
of Pd(OAc)2 resulted in the formation 5 (67%) and 4
(22%). Exclusive formation of the adduct 5 (67%) could
be attained by using 15 mol % of Pd(OAc)2.
The reaction of tert-butylallene (1 mmol) with ben-
zenethiol (1 mmol) in the presence of 3 mol % of Pd(OAc)2
at 67 °C for 2 h in THF (0.5-1.0 mL) led to high-yield
formation of terminal vinylic sulfide 1a , in which a
phenylthio group is introduced at the center carbon of
the allene, regioselectively (Table 1, entry 1). Similarly,
n-butylallene and cyclohexylallene undergo regioselective
addition of benzenethiol successfully to provide the
corresponding terminal vinylic sulfides 1b and 1c in high
yields (entries 2 and 3). With phenylallene as an
aromatic allene, the addition also proceeded but gave a
mixture of regioisomers (1d and 2d ) (entry 4). Although
the double-bond isomerization of 1d to 2d under the
To explore the mechanism of this palladium-catalyzed
addition, the stoichiometric reaction of Pd(OAc)2 with
benzenethiol (2 equiv to Pd(OAc)2) in THF at 15 °C for
0.5 h in the presence of 1,1-dimethylallene was examined.
As a result, the reaction afforded AcOH and a brown
solid. The elemental analysis of the brown solid sug-
6-8
gested the formation of [Pd(SPh)2]n
(eq 3). Further-
(1) Organic Compounds of Sulphur, Selenium, and Tellurium; The
Chemical Society: Burlington House, London, 1970-79; Vol. 1-5.
(2) Griesbaum, K.; Oswald, A. A.; Quiram, E. R.; Naegele, W. J . Org.
Chem. 1963, 28, 1952.
(3) Van der Ploeg, H. J .; Knotnerus, J .; Bickel, A. F. Recl. Trav.
Chem. Pays-Bas 1962, 81, 775.
(4) J acobs, T. L.; Illingworth, G. E., J r. J . Org. Chem. 1963, 28, 2692.
(5) Pasto, D. J .; Warren, S. E.; Morrison, M. A. J . Org. Chem. 1981,
46, 2837.
(6) The results of elemental analysis are in fair agreement with the
calculated values of [Pd(SPh)2]n. Anal. Calcd for [Pd(SPh)2]n: C, 44.38;
H, 3.10. Found: C, 44.67; H, 3.21.
(7) It is reported by Nyholm et al. that the reaction of Pd(OAc)2 with
pentafluorobenzenethiol at room temperature in THF for 0.5 h provided
Pd(SC6F5)2. Nyholm, R. S.; Skinner, J . F.; Stiddard, M. H. B. J . Chem.
Soc. A 1968, 38.
S0022-3263(95)02135-9 CCC: $12.00 © 1996 American Chemical Society

4162 J . Org. Chem., Vol. 61, No. 12, 1996
Notes
Sch em e 1
Sch em e 2
more, the attempted reaction of 1,1-dimethylallene by
using the brown solid as a catalyst afforded 5 in 59%
yield.9
Although the true reaction pathway is still unknown,
a mechanistic proposal includes the following: (1) ligand
exchange of the acetoxyl groups of Pd(OAc)2 with PhS
groups to give the palladium sulfide complex (as an active
catalyst) with the concomitant formation of AcOH; (2)
coordination of the allene double bond bearing higher
electron density to the palladium species; (3) syn-thio-
palladation10 to form (σ-allyl)palladium; (4) immediate
quenching of the (σ-allyl)palladium intermediate by
PhSH,11 without being changed into (π-allyl)palladium
to give the desired adduct with regeneration of the
catalyst. As shown in Scheme 2, the addition to alkyl-
substituted allenes takes place selectively at the inner
double bond of allenes, because the inner double bond is
more electron-rich than the terminal one. Contrary to
this, in the case of phenylallene, electron density of the
terminal double bond is believed to be higher, so the
thiopalladation seems to take place preferentially at the
terminal double bond.
In summary, we have developed a palladium-catalyzed
regioselective addition of benzenethiol to allenes. In
general, organic sulfur compounds seem to be widely
accepted as the catalyst poisons. On the contrary, the
present reaction dose suggest the utility of transition-
metal-catalyst in the reaction of sulfur compounds.8,10,12
The clarification of precise mechanism of this reaction
and the development of new transition-metal-catalyzed
reactions of sulfur compounds is now under investigation.
Exp er im en ta l Section
Gen er a l Com m en ts. 1H NMR spectra were recorded on a
J EOL J NM-GSX-270 (270 MHz) spectrometer using CDCl3 as
the solvent with Me4Si as the internal standard. 13C NMR
spectra were taken on a J EOL J NM-GSX-270 using CDCl3 as
the solvent. Chemical shifts in 13C NMR were measured relative
to CDCl3 and converted to δ(Me4Si) values by using δ(CDCl3) )
76.9 ppm. IR spectra were determined on a Perkin-Elmer Model
1600 spectrometer. Mass spectra were obtained on a J EOL
J MS-DX303 in the analytical section of our department. El-
emental analyses were also performed there.
Gen er a l P r oced u r e for th e Syn th esis of Ter m in a l Vi-
n ylic Su lfid e (1a ). Representative procedure for the addition
of allenes with thiols is as follows: In a two-necked flask
equipped with a reflux condenser and a magnetic stirring bar
under an argon atmosphere were placed Pd(OAc)2
(3 mol %),
THF (1 mL), tert-butylallene (1 mmol), and benzenethiol (1
mmol). The reaction was conducted with magnetic stirring for
2 h upon heating at 67 °C. After the reaction was complete,
the resulting mixture was filtered through Celite and concen-
trated in vacuo. Purification by MPLC (silica gel, 25-40 µm,
length 310 mm, i.d. 25 mm, eluent n-hexane:Et2O ) 4:1)
provided 0.179 g (87%) of 3-tert-butyl-2-(phenylthio)-1-propene
(1a ).
3-ter t-Bu tyl-2-(p h en ylth io)-1-p r op en e (1a ): 1H NMR (270
MHz, CDCl3) δ 1.00 (s, 9 H), 2.17 (s, 2 H), 4.82 (s, 1 H), 5.04 (s,
1 H), 7.31-7.34 (m, 3 H), 7.44 (d, J ) 7.8 Hz, 2 H); 13C NMR (68
MHz, CDCl3) δ 29.92, 31.53, 50.03, 114.28, 127.85, 129.14,
133.57, 133.72, 143.67; IR (NaCl) 3074, 2955, 2905, 2865, 1602,
1475, 1439, 1393, 1365, 1236, 1198, 1025, 859, 748, 707, 691
cm-1; MS (EI), m/ e ) 206 (M+, 41). Anal. Calcd for C13H18S:
C, 75.67; H, 8.79. Found: C, 72.42; H, 8.95.
(8) Kuniyasu, H.; Ogawa, A.; Sato, K.; Ryu, I.; Kambe, N.; Sonoda,
N. J . Am. Chem. Soc. 1992, 114, 5902.
(9) When the brown solid was used as the catalyst, 5 (59%) was
formed accompanied by 4 (11%).
(10) Kuniyasu, H.; Ogawa, A.; Miyazaki, S.; Ryu, I.; Kambe, N.;
Sonoda, N. J . Am. Chem. Soc. 1991, 113, 9796.
(11) For the cleavage of the alkyl-metal bond by thiol, see: J ohnson,
A.; Puddephatt, R. J . J . Chem. Soc., Dalton Trans. 1975, 115.
(12) (a) Antebi, S.; Alper, H. Organometallics 1986, 5, 596. (b) Shim,
S. C.; Antebi, S.; Alper, H. J . Org. Chem. 1985, 50, 147. (c) Shim, S.
C.; Antebi, S.; Alper, H. Tetrahedron Lett. 1985, 26, 1935. (d) Dzhemi-
lev, U. M.; Kunakova, R. V.; Gaisin, R. L. Izu. Akad. Nauk SSSR, Ser.
Khim. 1981, 11, 2655. (e) Talley, J . J .; Colley, A. M. J . Organomet.
Chem. 1981, 215, C38. (f) McKervey, M. A.; Ratananukul, P. Tetra-
hedron Lett. 1982, 23, 2509. (g) Holmquist, H. E.; Carnahan, J . E. J .
Org. Chem. 1960, 25, 2240. (h) Iqbal, J .; Pandey, A.; Shukla, A.;
Srivastava, R. R.; Tripathi, S. Tetrahedron 1990, 46, 6423. (i) Ba¨ckvall,
J .; Ericsson, A. J . Org. Chem. 1994, 59, 5850. (j) Crudden, C. M.; Alper,
H. J . Org. Chem. 1995, 60, 5579.
3-n -Bu tyl-2-(p h en ylth io)-1-p r op en e (1b): 1H NMR (270
MHz, CDCl3) δ 0.88 (t, J ) 6.8 Hz, 3 H), 1.28 (m, 4 H), 1.55
(quint, J ) 7.3 Hz, 2 H), 2.23 (t, J ) 7.6 Hz, 2 H), 4.87 (s, 1 H),
5.14 (s, 1 H), 7.25-7.35 (m, 3 H), 7.43 (d, J ) 7.8 Hz, 2 H); 13C
NMR (68 MHz, CDCl3) δ 13.99, 22.41, 28.09, 31.10, 36.51, 112.42,
127.68, 129.04, 133.20, 133.26, 146.14; IR (NaCl) 3074, 2957,
2931, 2858, 1608, 1475, 1439, 1025, 857, 748, 706, 691 cm-1
;
MS (EI), m/ e ) 206 (M+, 11). Anal. Calcd for C13H18S: C, 75.67;
H, 8.79. Found: C, 75.73; H, 8.84.

Notes
3-Cycloh exyl-2-(p h en ylth io)-1-p r op en e (1c): 1H NMR (270
J . Org. Chem., Vol. 61, No. 12, 1996 4163
Ack n ow led gm en t. This research was supported in
part by a Grant-in-Aid for Scientific Research from the
Ministry of Education, Science, and Culture, J apan.
A.O. is grateful to the Izumi Science and Technology
Foundation for financial support. Thanks are due to
the Instrumental Analysis Center, Faculty of Engineer-
ing, Osaka University, for assistance in obtaining mass
spectra with a J EOL J MS-DX303 instrument and
elemental analyses.
MHz, CDCl3) δ 0.83-0.91 (m, 2 H), 1.10-1.28 (m, 3 H), 1.61-
1.70 (m, 6 H), 2.11 (d, J ) 6.8 Hz, 2 H), 4.81 (s, 1 H), 5.07 (s, 1
H), 7.30-7.35 (m, 3 H), 7.44 (d, J ) 6.4 Hz, 2 H); 13C NMR (68
MHz, CDCl3) δ 26.21, 26.53, 32.89, 36.10, 44.59, 112.89, 127.78,
129.06, 133.17, 133.46, 144.64; IR (NaCl) 3073, 2922, 2850, 1607,
1476, 1448, 1440, 748, 691 cm-1; MS (EI), m/ e ) 232 (M+, 31).
Anal. Calcd for C15H20S: C, 77.53; H, 8.67. Found: C, 77.31;
H, 8.85.
3,3-Dim eth yl-2-(p h en ylth io)-1-p r op en e (5): 1H NMR (270
MHz, CDCl3) δ 1.17 (d, J ) 6.8 Hz, 6 H), 2.44 (septet, J ) 6.8
Hz, 1 H), 4.80 (s, 1 H), 5.18 (s, 1 H), 7.24-7.34 (m, 3 H), 7.41-
7.44 (m, 2 H); 13C NMR (68 MHz, CDCl3) δ 22.28, 34.92, 110.25,
127.58, 129.07, 133.15, 133.67, 152.99; IR (NaCl) 3074, 2964,
2928, 2871, 1598, 1583, 1477, 1439, 1362, 1025, 860, 748, 691
cm-1; MS (EI), m/ e ) 178 (M+, 100); exact mass (M+) calcd for
C11H14S 178.0817, found 178.0821.
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