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M. Arisawa, M. Yamaguchi / Tetrahedron Letters 50 (2009) 45–47
conversion, it was suggested to be a kinetic product. Camphorsul-
fonic acid was recovered in more than 90% yield, which was con-
firmed by the 1H NMR analysis of the crude product with the
addition of an authentic sample. Notably, dimethylthiophosphinic
anhydride 5 was isolated in 80% yield, the structure of which was
confirmed by 31P NMR at d 87.5, being consistent with the reported
values.10 EI-MS analysis results showed the parent peak, which
gave a correct elemental analysis (C4H12OP2S2).
When less than 1 equiv of 3 was used, the yield decreased with
poor reproducibility. Comparable results were obtained with other
acids, methanesulfonic acid (85%), p-chlorobenzenesulfonic acid
(63%), and p-toluenesulfonic acid monohydrate (74%). A trace
amount of 4, however, was obtained in the presence of trifluoro-
methanesulfonic acid. The reaction was applied to several 1,2-
dienes with primary and secondary alkyl groups as shown in Table
1. Tetraethyl- and tetrapropyldiphosphine disulfides11 gave the
corresponding (E)-2-dialkylthiophosphinoyl-2-alkenes at 87% and
90% yields, respectively, which were accompanied by the dialkyl-
thiophosphinic anhydrides.
Scheme 3.
The reaction of a bulky diphosphine, tetracyclohexyldiphos-
phine disulfide, resulted in a lower yield of the product along with
an isomer (Z)-1-thiophosphinoyl-2-alkene in 38% yield (Scheme 2).
The structure of the byproduct suggested its formation by the P–H
addition of HPS(cyclo-C6H11)2. The involvement of a different
mechanism in this reaction from the above reaction was also sup-
ported by the lack of thiophosphinic anhydride. Tetraphenyldi-
phosphine and its dioxide did not give the organophosphorus
compounds.
When 2 and 3 were treated in THF at room temperature for 6 h
in the absence and presence of RhH(PPh3)4 (9 mol %), 2 and 3 were
recovered quantitatively as indicated by 1H NMR. It was not likely
that HPSMe2 was the reactive intermediate in this reaction. The
regioselectivity in the C–P bond formation did not coincide with
the hydrophosphinoylation mechanism, since the nickel- and pal-
ladium-catalyzed P–H addition reactions to 1,2-dienes were re-
ported to give allylphosphorus compounds.12 An exception was
reported only in an ytterbium-catalyzed reaction.13 The results
suggested that P–P bond cleavages, transfer of the thiophosphinoyl
group to 1,2-diene, and acid anhydride formation took place on the
rhodium metal.
The present reaction involved the transfer of a thiophosphinoyl
group to 1,2-dienes, and the fate of the other thiophosphinoyl
group was a subject of interest. It is likely that what was initially
formed was a mixed anhydride 6 of 3 and dimethylthiophosphinic
acid, which then underwent disproportionation giving 5 and cam-
phorsulfonic anhydride (Scheme 3). The latter anhydride was
hydrolyzed to 3, although the origin of water was unclear. Use of
20 mol % camphorsulfonic acid in the presence of varying amounts
of water decreased the yield, and the acid could not be catalytic.
Various attempts failed to detect camphorsulfonic anhydride and
mixed anhydride 6.
Scheme 4.
reactions via P–P and S–S bond cleavage, although the reactive het-
eroatom species could be different, diphosphine and thiol. Another
notable feature of this reaction was the difference from the palla-
dium-catalyzed phosphine addition reaction to 1,2-dienes previ-
ously reported.3 The C–P bond was formed at the 1-carbon of
1,2-dienes in the phosphine addition, whereas the C–P bond was
formed at the 2-carbon in the present reaction. The origin of the
different orientation may be ascribed to the difference in the metal,
or alternatively, the difference in the phosphorous group.
In summary, a rhodium complex catalyzed the three-compo-
nent reaction of tetraalkyldiphosphine disulfide, 1,2-dienes, and
camphorsulfonic acid giving (E)-2-thiophosphinoyl-2-alkenes.
The rhodium catalyst is involved in the P–P bond cleavage, transfer
of the phosphorous group, and anhydride formation. It may be
interesting that a thermodynamically high-energy compound of
acid anhydride was formed as the product of the metal-catalyzed
reaction.
We previously reported that a rhodium-catalyzed reaction of
organic disulfides with 1,2-alkadienes gave (E)-2-alkylthio-2-al-
kenes (Scheme 4).14 The same regio- and stereoselectivities were
observed in the rhodium-catalyzed C–P and C–S bond-forming
Synthesis of (E)-2-dimethylthiophosphinoyl-2-undecene 4: In a
two-necked flask were placed 1,2-undecadiene (0.125 mmol, 19.0
mg), tetramethylbiphosphine disulfide 2 (0.125 mmol, 23.3 mg),
anhydrous (R)-(À)-camphor-10-sulfonic acid 3 (0.125 mmol, 29.0
mg), and RhH(PPh3)4 (9 mol %, 13 mg) in distilled THF (1 mL)
under an argon atmosphere, and the solution was stirred at room
temperature for 6 h. Then, the solvent was removed under reduced
pressure, and the residue was purified by flash column chromato-
graphy on silica gel to give 4 (25.6 mg, 83%) and dimethylthiophos-
phinic anhydride 5 (10.1 mg, 0.05 mmol, 80% based on 2) as pale
yellow oil.
Scheme 2.
Arisawa, Mieko
