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.