Tetrahedron Letters
Palladium-catalyzed C–P(III) bond formation reaction
with acylphosphines as phosphorus source
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Rongrong Yu , Xingyu Chen , Zhiqian Wang
State Key Laboratory of Chemical Resource Engineering, College of Science, Beijing University of Chemical Technology, Beijing 100029, China
a r t i c l e i n f o
a b s t r a c t
Article history:
Palladium-catalyzed C–P(III) bond formation reaction employing acylphosphines as the phosphorus
source was developed. Under the optimized conditions, acylphosphines could react with aryl halides
directly affording trivalent phosphines in up to 94% yield.
Received 28 May 2016
Revised 15 June 2016
Accepted 20 June 2016
Available online 21 June 2016
Ó 2016 Published by Elsevier Ltd.
Keywords:
Acylphosphines
Pd catalysis
C–P bond formation
Phosphorus source
Syntheses of phosphines
Transition-metal-catalyzed carbon-phosphorus bond formation
reaction is taken as an important method for the preparation of
diverse organo-phosphorus compounds,1 in which trivalent phos-
phines play an essential role in modern organic synthesis.2 The
phosphorus source employed in C–P bond formation includes pri-
mary, secondary and tertiary phospines, secondary phosphine-bor-
ane complexes, silyl- and stannylphosphines, and phosphate
derivatives.1,3 In the syntheses of trivalent phosphines, the H-phos-
phine is considered to be formally direct phosphorus source, while
its borane complex is more commonly employed.3b,c A two-step
synthesis is actually utilized more including the syntheses of
phosphine oxide and the consequent reduction of phosphine
oxide to the relevant phosphine, in which the H-phosphine
oxides are usually employed as the phosphorus source for their
better reactivity and reliability.3d–i Despite the notable
development on C–P bond formation methodologies, excavation
of new phosphorus source is still in strong demand. The
acylphosphine, which is conveniently prepared from H-
phosphine, is much more stable against air and moisture4 for the
electron density of phosphorus was decreased by the adjacent car-
bonyl group.5 Its characteristics as electron-deficient ligands have
been reported in recent years,5,6 but to the best of our knowledge
their chemical reactivities,7 especially as phosphorus source in
transition-metal-catalyzed C–P bond formation reaction, have not
been well explored. Herein, we report an example of palladium-
catalyzed direct trivalent phosphines synthesis with acylphosphi-
nes as the phosphorus source.8 (Scheme 1).
Initially the reactions catalyzed by 3 mol % of Pd(OAc)2 with
iodobenzene 1a and 4-methylbenzoyl-diphenylphosphine 2a were
found to be of very poor reactivity referring to the conditions uti-
lized in aryl iodide cross-coupling reactions with silyl- or stan-
nylphosphines.9 The desired product triphenylphosphine 3a was
afforded only in 5% yield at 100 °C (Table 1, entry 1) and approxi-
mately 20% yield at 140 °C (not shown in table). To our delight, the
addition of Cs2CO3 successfully increased the yield to 73% even at
100 °C (Table 1, entry 2), and 1.1 equiv of Cs2CO3 to acylphosphine
2a could further increase the yield to 93% (Table 1, entries 4, 5).
With the promotion from Cs2CO3, this Pd-catalyzed C–P bond for-
mation reaction could maintain the high efficiency even at lower
temperatures (Table 1, entry 6) and with lower catalyst loadings
(Table 1, entry 7). To demonstrate the role of acylphosphines, a
control reaction was carried out with the mixture of acylphosphine
2a and Cs2CO3 heated in toluene at 80 °C. Monitored by 31P NMR,
neither the decomposition of acylphosphine 2a nor the generation
of diphenylphosphine 4 could be detected in 12 h, which indicated
the acylphosphine directly played as the phosphorus source
instead of the precursor of diphenylphosphine. Under these condi-
tions, the reactivity of acylphosphines was found to be robust to
the changing of solvents (Table 1, entries 8, 9), and good yields
could be achieved even in high polar and coordinative solvents
such as DMF. After the scope of adducts, Cs2CO3 was found to be
the best one comparing to other organic or inorganic bases (Table 1,
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Corresponding author.
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These authors contributed equally.
0040-4039/Ó 2016 Published by Elsevier Ltd.