12380
J. Am. Chem. Soc. 1997, 119, 12380-12381
the efficacy of the transition metal catalysts in synthetic reactions
of organic sulfur compounds.
Highly Regioselective Hydrothiocarboxylation of
Acetylenes with Carbon Monoxide and Thiols
Catalyzed by Pt(PPh3)4
Akiya Ogawa,*,† Jun-ichi Kawakami,† Masatoshi Mihara,†
Takuma Ikeda,† Noboru Sonoda,*,‡ and Toshikazu Hirao*,†
Department of Applied Chemistry
Faculty of Engineering, Osaka UniVersity
Suita, Osaka 565, Japan
Department of Applied Chemistry
Faculty of Engineering, Kansai UniVersity
Suita, Osaka 564, Japan
ReceiVed August 4, 1997
In transition-metal-catalyzed addition and related reactions,
controlling regiochemistry, as well as stereochemistry, is always
of great importance. As previously reported,3c the RhH(CO)-
(PPh3)3-catalyzed thioformylation reaction of acetylenes with
PhSH and CO (Y ) H in eq 1) exhibits the excellent
regioselectivity where carbon monoxide and phenylthio group
are introduced selectively into the terminal and internal positions
of acetylenes, respectively. Herein, we report an interesting
finding that switching the catalyst simply from RhH(CO)(PPh3)3
to Pt(PPh3)4 leads to a sharp reVersal of regioselectiVity of CO
introduction (eq 2).
For the last two decades, the utility of transition metal
catalysts for effecting a wide range of synthetic transformations
using heteroatom compounds such as organic silicon, tin, and
boron compounds has been established.1 Nonetheless, use of
transition metal catalysts for synthetic reactions of organic sulfur
compounds has remained largely unexplored,2 partly because
of the widespread prejudice that sulfur compounds often bind
strongly to the catalysts, thus poisoning them and making the
catalytic reactions ineffective. On the contrary, we have recently
developed a series of transition-metal-catalyzed addition and
carbonylative addition reactions of organic disulfides and thiols
to acetylenes (eq 1).3 These novel reactions clearly demonstrate
† Osaka University.
‡ Kansai University.
Since thiols are known to add oxidatively to platinum(0)
complex forming platinum hydride complex bearing a sulfide
ligand,4 we investigated in detail the reactions between thiols,
acetylenes, and carbon monoxide in the presence of platinum-
(0) catalysts. Surprisingly dramatic changeover of the regiose-
lectivity of CO introduction was observed, and a novel
“hydrothiocarboxylation” of acetylenes (that a hydride and a
thiocarboxyl group are introduced into the terminal and internal
positions of acetylenes, respectively) was found to take place
successfully (entry 1 in Table 1).5 The hydrothiocarboxylation
product (3a), which has an R,â-unsaturated carbonyl unit, is
subject to conjugate addition of PhSH, giving 4a concomitantly.
However, the use of excess acetylene afforded 3a predominantly
(entry 3). On the other hand, the reaction using excess thiol
gave rise to 4a exclusively (entry 4). Cobalt complexes such
as Co2(CO)8 and CoCl(PPh3)3 also exhibited the catalytic activity
toward the “hydrothiocarboxylation”, but the reaction was
accompanied by the formation of unidentified byproducts
(entries 5 and 6). As mentioned in our previous paper,
palladium catalysts bearing phosphine ligands, such as Pd(PPh3)4
and PdCl2(PPh3)2, resulted in the formation of a complex
mixture, which, however, included a regioisomeric mixture
of the hydrothiocarboxylation products (1- and 2-(phenyl-
thiocarbonyl)-1-octene was obtained in 10 and 15% yields,
respectively).3c
(1) For silicon compounds, see: (a) Hiyama, T.; Kusumoto, T. In
ComprehensiVe Organic Synthesis; Trost, B. M., Ed.; Pergamon: Oxford,
1991; Vol. 8, p 763. (b) Ojima, I. In The Chemistry of Organic Silicon
Compounds; Patai, S., Rappoport, Z., Eds.; John Wiley & Sons: Chichester,
1989; Part 2, p 1479. (c) Tsuji, J. Palladium Reagents and Catalysts:
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Table 2 lists the representative results of the Pt(PPh3)4-
catalyzed hydrothiocarboxylation using several thiols and
terminal acetylenes.6 The procedure for this hydrothiocarboxy-
(4) Ugo, R.; La Monica, G.; Cenini, S.; Segre, A.; Conti, F. J. Chem.
Soc. A 1971, 522.
(5) Reppe, W. Liebigs Ann. Chem. 1953, 582, 1.
(6) The general procedure for the hydrothiocarboxylation of acetylenes
with thiols and carbon monoxide is as follows: In a 50 mL stainless steel
autoclave with a magnetic stirring bar under argon atmosphere were placed
Pt(PPh3)4 (3 mol%), acetonitrile (5 mL), acetylene (5 mmol), and cyclo-
hexanethiol (5 mmol). Carbon monoxide was purged three times and then
changed at 30 atm. The reaction was conducted with magnetic stirring for
2 h upon heating at 120 °C. After the carbon monoxide was purged, the
resulting mixture was filtered through Celite and concentrated in vacuo.
Purification of the product was carried out by MPLC (silica gel, 25-40
µm, length 310 mm, i.d. 25 mm, eluent hexane:Et2O ) 4:1).
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