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Pentacoordinate organosilicate as an alkylating reagent: Palladium catalyzed methylation of aryl halides
Tetrahedron Letters, Vo1.29, Printed in Great Britain
No.1,
pp 97-98,
1988
$3.00 + .oo Journals Ltd.
0040-4039jaa
Pergamon
PENTACOORDINATE ORGANOSILICATE AS AN ALKYLATING REAGENT: PALLADIUM CATALYZED METHYLATION OF ARYL HALIDES Yasuo HATANAKA and Tamejiro HIYAMA* Sagami Chemical Research Center 4-4-l Nishiohnuma,
Sagamihara, Kanagawa 229, Japan
Under the influence of palladium catalyst, tris(diethylamino)sulfonium difluorotrimethylsilicate is found to deliver the methyl group to aryl halides highly chemoselectively, and the corresponding methylated aromatic compounds are produced in moderate to high yields. Trimethylsilylation of organic halides has recently been achieved by using a palladium catalyst and hexamethyldisilane
activated by coordination of fluoride ion. 1 The concept of organosilicon/F-/Pd
catalyst reagent system is extended to vinylation, ethynylation Thereby, tris(diethylamino)sulfonium
difluorotrimethylsilicate
and allylation of organic halides.2 (TASF)3 was found to be the best F-
reagent. Reported herein is that TASF itself delivers methyl group to organic halides in the presence of a palladium catalyst and in the absence of any other organosilicon compounds.
Ar-x
Ar-CH,
-
+ cI--I@F~
Pd
A typical experimental
procedure follows.
A tetrahydrofuran
solution, 0.40 ml, 0.40 mmol) was added to I-iodonaphthalene
(THF) solution of TASF (1.0 M
(51 mg, 0.20 mmol) and allylpalladium
chloride dimer (1.8 mg, 0.0025 mmol) dissolved in THF at room temperature under an argon atmosphere, and the reaction mixture was stirred at 50 “C for 20 h. After completion of the reaction, bulk of the solvent was removed by passing the reaction mixture through a silica-gel column with pentane as the eluent. Evaporation of the pentane gave pure I-methylnaphthalene results obtained with other haldies are summarized in Table 1. methylated products than bromides.
(22 mg, 78%). The
Generally iodides gave better yields of
The new methylation reaction is characterized by mild reaction
conditions: unlike many other similar reactions which employ organometallic reagents derived from main group elements,4 the palladium catalyzed methylation using TASF does not affect the reactive founctional groups on the substrate (e.g. nitro, ester and ketone carbonyls). Although palladium-mediated
cross-coupling
reactions through hexacoordinate
have precedents in fhe literature,sa organosilicon
organosilicate
compounds in general lack enough reactivity to
undergo transmetallation in a catalytic cycle and are therefore rather useless in synthetic viewpoint: low yield of products and drastic reaction conditions. 5
In this respect, the reaction disclosed herein
has synthetic advantage over the existing methods in regard of easy preparation of reagent and simple experimental procedure.
97
98
Table 1 Methylation of Aromatic halides Using TASF
Halide
Yield %a
PKJdUCt
78
81 82
86 84 67 59 a: Isolatedyields. lx The starting material c: Recovery
of the starting
recovered
amounted
to na, yield.
material was 52%.
Though the precise reaction mechanism is uncertain, a catalytic cycle may be considered which involves
transmetallation
difluorotrimethylsilicate
between
the
arylpalladium
halide
species
Ar-Pd(II)-X
and
FzSiMes- to generate Ar-I?d(II)-Me species whose reductive elimination
gives rise to the coupling product Ar-Me and I’d(O) catalyst. References Hatanaka, Y.; Hiyama, T. Tetrahedron Lett. in press. Hatanaka, Y.; Hiyama, T. 54th National Meeting of the Chemical Society of Japan, Tokyo, April 1987, Abstr., No 4111M10; I. Am. C/rem.Sot., in press. Middleton, W. J. U.S. Patent 3940402; Chem. Abstr., 1976,85,-j; Org. Synth. 1985,64,221. (a) Kochi, J. K. “Organometallic Mechanism and Catalyst,” Academic Press, New York, 1987. (b) Davis, S. G. “Organotransition Metal Chemistry. Application to Organic Syntheses,” Pergamon Press, Oxford, 1982. (a) Yoshida, J.; Tamao, K.; Yamamoto, H.; Kakui, T.; Uchida, T.; Kumada, M. Organometaflics, 1982,1,542. (b) Hallberg, A.; Westerlund, C. Chem. Left., 1982, 1993. (c) Kikukawa, K.; Ikenaga, K.; Kono, K.; Toritani, T.; Wada, F.; Matsuda, T. J. Orgunernet. Chem., 1984,270,277. (Received in Japan 12 October 1987)
No.1,
pp 97-98,
1988
$3.00 + .oo Journals Ltd.
0040-4039jaa
Pergamon
PENTACOORDINATE ORGANOSILICATE AS AN ALKYLATING REAGENT: PALLADIUM CATALYZED METHYLATION OF ARYL HALIDES Yasuo HATANAKA and Tamejiro HIYAMA* Sagami Chemical Research Center 4-4-l Nishiohnuma,
Sagamihara, Kanagawa 229, Japan
Under the influence of palladium catalyst, tris(diethylamino)sulfonium difluorotrimethylsilicate is found to deliver the methyl group to aryl halides highly chemoselectively, and the corresponding methylated aromatic compounds are produced in moderate to high yields. Trimethylsilylation of organic halides has recently been achieved by using a palladium catalyst and hexamethyldisilane
activated by coordination of fluoride ion. 1 The concept of organosilicon/F-/Pd
catalyst reagent system is extended to vinylation, ethynylation Thereby, tris(diethylamino)sulfonium
difluorotrimethylsilicate
and allylation of organic halides.2 (TASF)3 was found to be the best F-
reagent. Reported herein is that TASF itself delivers methyl group to organic halides in the presence of a palladium catalyst and in the absence of any other organosilicon compounds.
Ar-x
Ar-CH,
-
+ cI--I@F~
Pd
A typical experimental
procedure follows.
A tetrahydrofuran
solution, 0.40 ml, 0.40 mmol) was added to I-iodonaphthalene
(THF) solution of TASF (1.0 M
(51 mg, 0.20 mmol) and allylpalladium
chloride dimer (1.8 mg, 0.0025 mmol) dissolved in THF at room temperature under an argon atmosphere, and the reaction mixture was stirred at 50 “C for 20 h. After completion of the reaction, bulk of the solvent was removed by passing the reaction mixture through a silica-gel column with pentane as the eluent. Evaporation of the pentane gave pure I-methylnaphthalene results obtained with other haldies are summarized in Table 1. methylated products than bromides.
(22 mg, 78%). The
Generally iodides gave better yields of
The new methylation reaction is characterized by mild reaction
conditions: unlike many other similar reactions which employ organometallic reagents derived from main group elements,4 the palladium catalyzed methylation using TASF does not affect the reactive founctional groups on the substrate (e.g. nitro, ester and ketone carbonyls). Although palladium-mediated
cross-coupling
reactions through hexacoordinate
have precedents in fhe literature,sa organosilicon
organosilicate
compounds in general lack enough reactivity to
undergo transmetallation in a catalytic cycle and are therefore rather useless in synthetic viewpoint: low yield of products and drastic reaction conditions. 5
In this respect, the reaction disclosed herein
has synthetic advantage over the existing methods in regard of easy preparation of reagent and simple experimental procedure.
97
98
Table 1 Methylation of Aromatic halides Using TASF
Halide
Yield %a
PKJdUCt
78
81 82
86 84 67 59 a: Isolatedyields. lx The starting material c: Recovery
of the starting
recovered
amounted
to na, yield.
material was 52%.
Though the precise reaction mechanism is uncertain, a catalytic cycle may be considered which involves
transmetallation
difluorotrimethylsilicate
between
the
arylpalladium
halide
species
Ar-Pd(II)-X
and
FzSiMes- to generate Ar-I?d(II)-Me species whose reductive elimination
gives rise to the coupling product Ar-Me and I’d(O) catalyst. References Hatanaka, Y.; Hiyama, T. Tetrahedron Lett. in press. Hatanaka, Y.; Hiyama, T. 54th National Meeting of the Chemical Society of Japan, Tokyo, April 1987, Abstr., No 4111M10; I. Am. C/rem.Sot., in press. Middleton, W. J. U.S. Patent 3940402; Chem. Abstr., 1976,85,-j; Org. Synth. 1985,64,221. (a) Kochi, J. K. “Organometallic Mechanism and Catalyst,” Academic Press, New York, 1987. (b) Davis, S. G. “Organotransition Metal Chemistry. Application to Organic Syntheses,” Pergamon Press, Oxford, 1982. (a) Yoshida, J.; Tamao, K.; Yamamoto, H.; Kakui, T.; Uchida, T.; Kumada, M. Organometaflics, 1982,1,542. (b) Hallberg, A.; Westerlund, C. Chem. Left., 1982, 1993. (c) Kikukawa, K.; Ikenaga, K.; Kono, K.; Toritani, T.; Wada, F.; Matsuda, T. J. Orgunernet. Chem., 1984,270,277. (Received in Japan 12 October 1987)