To effect the desired transformation, a 1:1.28 mixture
of organic halide (1) and carbamoylsilane (2)9 and 4 mol
% of tetrakis(triphenylphosphine)palladium(0) was heated
in toluene (65 or 100 °C) until the disappearance of 1
was observed. Conditions and results for the preparation
of individual tertiary amides (3) are shown in Table 1.
As expected, benzylic bromides exhibited faster reaction
rates than benzylic chlorides (compare entries 2 and 7,
6 and 9). Either electron-donating or electron-withdraw-
ing groups are tolerated on the ring without significant
change in rate at 100 °C, although the former is some-
what more reactive (compare entry 9 vs entry10). Entries
3-5 and 8 indicate that steric effects introduced by ortho
substituents in the aryl ring (including those of the
mesityl group) may be significant but can be easily
overcome by slightly longer reaction times or use of the
higher reaction temperature. The addition of a third
phenyl substituent at the benzylic chloride reaction
center (entries 11 and 12) does slow the reaction consid-
erably, but the anticipated products are still obtained,
albeit in low yield in the case of chlorotriphenylmethane.
However, when the corresponding bromides were em-
ployed, carbamoylsilane was consumed but none of
the expected amide was obtained. NMR examination of
the products indicated that they were a mixture of
aromatic compounds showing no TMS or dimethylamide
absorptions. Both p- and m-bis(chloromethyl)benzene
proceeded to the diamide product, but the ortho isomer
gave only the dibenzylically coupled “dimer”, dibenzo-
1,5-cyclooctadiene (4). Again the para and meta dibro-
mides (at 65 °C) were anomolous, in that no diamide
was formed; instead, a white insoluble solid precipitated
that appeared to be polymeric in nature.10 4-Bromo-
benzyl chloride was investigated (entry 16) in the hope
that the method could be made chemoselective, since
aryl bromides are known to undergo carbamoylation
under the higher temperature (100 °C) conditions.4 At
65 °C, only the amide having been introduced at the
benzylic position was obtained, and that in 92% yield.
The behavior of terminal allylic halides involved in
entries 19-21 was regioselective, only affording the
terminal amide and none of the allylicly transposed
internal product. However, when either the internal
halide of entry 22 was employed or its terminal isomer
(entry 23), approximately equivalent amounts of amides
3q and 3r were obtained in each instance (entry 22, 51:
49; entry 24, 46:54). Small amounts of the R,â-unsatur-
ated (conjugated) isomer were detected only in the
amide product derived from runs 17 (10%) and 19 (trace).
Since a Pd(II)-catalyzed reaction between allylic tri-
fluoroacetates and acylsilanes has been reported to
afford â,γ-unsaturated ketones,11 we investigated the
behavior of both allyl trifluoroacetate and benzyl tri-
flouroacetate under our conditions. In either instance, no
reaction occurred. However, since the conditions de-
scribed11 involved phospine-free Pd(II) complexes as
Palladium-Catalyzed Conversion of
Benzylic and Allylic Halides into r-Aryl
and â,γ-Unsaturated Tertiary Amides by
the Use of a Carbamoylsilane
Robert F. Cunico* and Rajesh K. Pandey
Department of Chemistry and Biochemistry, Northern
Illinois University, DeKalb, Illinois 60115
Received June 16, 2005
Treatment of allylic and benzylic halides with N,N-dimeth-
ylcarbamoyl(trimethyl)silane in the presence of tetrakis-
(triphenylphosphine)palladium(0) affords tertiary amides,
which arise from the replacement of the halogen by the N,N-
dimethylcarbamoyl group.
Although benzylpalladium halides are known and can
be aminocarbonylated with CO and amines,1 the pal-
ladium-catalyzed aminocarbonylation of benzyl or allyl
halides is not a generally useful methodology because of
concomitant production of allylamines and double car-
bonylation products.2 In addition, the necessity of ma-
nipulating carbon monoxide in aminocarbonylations3 is
a disadvantage that we have previously addressed in
other contexts by using a carbamoylsilane to convert aryl
and alkenyl halides directly into tertiary amides under
catalysis by palladium(0) complexes.4,5 This approach has
now been extended to benzyl and allyl halides and offers
an entry into â,γ-unsaturated amides. These are com-
pounds of synthetic utility,6 but only a few examples of
their preparation from the halides exist.7
(1) Lin, Y.-S.; Yamamoto, A. Organometallics 1998, 17, 3466-3478.
(2) Yamamoto, A. Bull. Soc. Chem. Jpn. 1995, 68, 433-446.
(3) For a review of carbon monoxide-free carbonylations, see: Morim-
oto, T.; Kakiuchi, K. Angew. Chem., Int. Ed. 2004, 43, 5580-5588.
(4) Cunico, R. F.; Maity, B. C. Org. Lett. 2002, 4, 4357-4359.
(5) Cunico, R. F.; Maity, B. C. Org. Lett. 2003, 5, 4947-4949.
(6) For a summary of entries to this compound class from nonhalides
and references to applications, see: Luo, F.-T.; Lu, T.-Y.; Xue, C.
Tetrahedron Lett. 2003, 44, 7249-7251. A Pd-catalyzed aminocarbo-
nylation of an allylic carbonate has been reported: Tsuji, J.; Sato, K.;
Okumoto, H. J. Org. Chem. 1984, 49, 1341-1344.
(7) (a) From allyl and benzyl magnesiocuprates and carbamoyl
chloride: Lemoucheux, L.; Seitz, T.; Rouden, J.; Lasne, M.-C. Org. Lett.
2004, 6, 3703-3706. (b) From benzyl chloride, metallic (stoichiometric)
nickel, and carbamoyl chloride: Inaba, S.; Rieke, R. D. J. Org. Chem.
1985, 50, 1373-1381.
(8) Some adventitious protonolysis of 2 invariably occurs to give
DMF and hexamethyldisiloxane.
(9) Cunico, R. F.; Chen, J. Synth. Commun. 2003, 33, 1963-1968.
(10) The noncrystalline, tacky solid was insoluble in, separately, hot
toluene, methanol, chloroform, and DMF.
10.1021/jo0512406 CCC: $30.25 © 2005 American Chemical Society
Published on Web 09/24/2005
9048
J. Org. Chem. 2005, 70, 9048-9050