Ni(acac) -catalyzed cross-coupling and carbonylative cross-coupling
2
of organostannanes with hypervalent iodonium salts
Suk-Ku Kang,* Hyung-Chul Ryu and Sang-Woo Lee
Department of Chemistry, Sungkyunkwan University, Natural Science Campus,
Suwon 440-746, Korea
Received (in Cambridge, UK) 27th July 1999, Accepted 31st August 1999
The Ni-catalyzed cross-coupling and carbonylative cross-
coupling of organostannanes with hypervalent iodonium
phenyliodonium tetrafluoroborate (1a) reacted with 2-thienyl-
tributylstannane (2c) in the presence of Ni(acac) (10 mol%) in
2
7
salts were achieved in the presence of Ni(acac) (10 mol%)
NMP at 70 ЊC for 8 h to afford 2-phenylthiophene (3a) in 79%
2
in NMP at 70 ЊC in moderate yields.
yield (entry 1 in Table 1). Under the same conditions, treatment
of the iodonium salt 1a with 2-furyltributylstannane (2d) gave
8
The palladium-catalyzed cross-coupling and carbonylative
2-phenylfuran (3b) in 78% yield (entry 2). This coupling
cross-coupling of organostannanes with organic electrophiles
was applied to alkenyl- and alkynylstannane 2e and 2f. The
iodonium salt 1a was readily coupled with 2e and 2f to provide
the coupled alkene 3c and alkyne 3d in 82 and 80% yields,
respectively (entries 3 and 4) (see Experimental section). For
the p-methoxyphenyl(phenyl)iodonium tetrafluoroborate (1b),
reaction with p-methoxyphenyltributylstannane (2b) gave 4,4Ј-
dimethoxy-1,1Ј-biphenyl (3e) in 73% yield (entry 5). Coupling
of 1b with 2-furyl- and 2-thienyltributylstannane (2d) and (2c)
afforded p-methoxyphenyl-substituted furan and thiophene
1
(
i.e., halides and triflates) are known as the Stille reaction and
have become an extremely powerful tool for carbon–carbon
bond formation. In the search for alternatives to the palladium
catalyst, the copper and manganese-catalyzed cross-coupling2
of organostannanes with organic halides has been reported.
Hypervalent iodine compounds have received much attention
as the electrophiles with organostannanes in palladium-
3
catalyzed reactions due to their good reactivities, ready avail-
4
9
ability and nontoxic properties. Recently we have reported
3f and 3g in 71 and 77% yields, respectively (entries 6 and 7).
copper()-catalyzed cross-coupling and carbonylative cross-
coupling of organostannanes with hypervalent iodine com-
pounds. Here we wish to report nickel-catalyzed cross-coupling
and carbonylative cross-coupling of iodonium salts with
organostannanes.
For the p-methoxyphenyl(phenyl)iodonium triflate and bromide
(1c) and (1d), which have different counterions from 1b,
reaction with 2c afforded the coupled product 3g in 75 and
78% yields (entries 8 and 9). It is notable that the yields of cross-
coupling were not dependent on the counterions.
Generally, to generate active nickel(0) species a reducing
In considering a plausible mechanism for the coupling, it
is presumed that the oxidative addition of highly reactive
electrophilic iodonium salt 1a with Ni(0) gives polar and
agent such as Zn, NaBH , or DIBAL-H is needed. Thus, in the
4
nickel-catalyzed cross-coupling of organostannanes with aryl-
5
methanesulfonates by Percec et al. the presence of zinc was
reactive PhNi()L , which if subjected to transmetallation with
2
essential to get an active catalyst. However in the literature,
organostannanes followed by reductive elimination would give
the cross-coupled product.
Ni(dppf)Cl -catalyzed cross-coupling of chloroarenes with
2
arylboronic acids was realized in the absence of a reducing
agent. We have studied nickel-catalyzed cross-coupling and
carbonylative cross-coupling of hypervalent iodonium salts
This cross-coupling was extended to carbonylation cross-
coupling and the results of carbonylative cross-coupling
of hypervalent iodonium salts with organostannanes under
atmospheric pressure are summarized in Scheme 2 and Table 2.
6
with organostannanes and found that the catalyst Ni(acac) is
2
effective and surprisingly the catalyst performed much better
when the reducing agent was omitted (Scheme 1).
Scheme 2
Scheme 1
Initially, we examined the cross-coupling of p-methoxy-
phenyl(phenyl)iodonium tetrafluoroborate (1b) with 2-thienyl-
tributylstannane (2c) to form the coupled product 3g and to
find optimum conditions. After a series of experiments, it was
found that of the catalysts tested [Ni(acac) , [Ni(acac) –Zn,
The iodonium salt 1a reacted with phenyltributylstannane
(2a) in the presence of Ni(acac) (10 mol%) in NMP under an
2
atmospheric pressure of carbon monoxide at 70 ЊC for 8 h to
afford benzophenone (4a) in 81% yield (entry 1 in Table 2)
(see Experimental section). Under the same conditions, 2-
thienyltributylstannane (2c) was readily coupled with carbon
2
2
NiCl (Ph P) , NiCl (Ph P) –Zn, NiCl (dppe), Ni(acac) –Zn–
2
3
2
2
3
2
2
2
10
Ph P, Ni(acac) –Et Zn, Ni(acac) –ZnCl , NiCl (dppe)–Zn,
monoxide to give the ketone 4b in 76% yield (entry 2). This
carbonylative cross-coupling was applied to alkenyl- and
alkynyl-substituted stannanes 2e and 2f which were smoothly
3
2
2
2
2
2
NiCl ] Ni(acac)2 was the only catalyst which afforded the
2
coupled product in a high yield. Of the solvents tested (NMP,
DMF, CH CN, CHCl , THF, CHCl –NMP) the solvents NMP
11
coupled to afford unsaturated ketones 4c and 4d in 72 and
78% yields, respectively (entries 3 and 4). For p-methoxy-
phenyl(phenyl)iodonium tetrafluoroborate (1b), 2-thienyltri-
butylstannane (2c) was readily coupled under CO to give aryl
3
3
3
and DMF were effective and NMP was the best choice.
The nickel-catalyzed cross-coupling of hypervalent iodonium
salts with organostannanes is summarized in Table 1. The di-
J. Chem. Soc., Perkin Trans. 1, 1999, 2661–2663
This journal is © The Royal Society of Chemistry 1999
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