SCHEME 1. Allyl Cross-Coupling Reactions with Xantphos
Xantphos as an Efficient Ligand for
Palladium-Catalyzed Cross-Coupling Reactions of
Aryl Bromides and Triflates with Allyl Acetates
and Indium
Dong Seomoon and Phil Ho Lee*
National Research Laboratory for Catalytic Organic Reaction,
Department of Chemistry, and Institute for Basic Science,
Kangwon National UniVersity, Chunchon 200-701, Republic of
Korea
cross-coupling reactions using a variety of organoindium
reagents,2,5 we demonstrated inter- and intramolecular Pd-
catalyzed allyl cross-coupling reactions using aryl iodides and
vinyl bromides and triflates via π-allylpalladium(II) complexes
and their transmetalation with indium and indium trichloride
in the presence of catalytic Pd(PPh3)4.6 However, we failed
unexpectedly to get the allyl cross-coupling products in the case
of aryl bromides and triflates. Therefore, there is still a strong
need for efficient catalytic systems for the cross-coupling
reactions of aryl bromides and triflates with allylindiums derived
from allyl acetates. Herein, we report Xantphos as an efficient
ligand for palladium-catalyzed allyl cross-coupling reactions of
aryl bromides and triflates with allylindium obtained from allyl
acetates (Scheme 1).
ReceiVed October 22, 2007
In a test reaction of trifluoromethanesulfonate (1) derived
from 2-naphthol with allyl acetate (2), we found that cross-
coupling reactions could be largely affected by ligands in the
presence of Pd catalyst (Table 1). A variety of ligands with
varied structural and electronic properties was scrutinized.
Among the ligands tested, Xantphos gave the best results (entry
9). Generally, diphosphines have a marked influence on the
reactivity and selectivity of a catalyst. Due to the effects of wide
Xantphos was found to be an efficient ligand for palladium-
catalyzed allyl cross-coupling reactions of aryl bromides and
triflates with allylindium reagents generated in situ from allyl
acetates and indium. These reactions occur in high yield with
good functional group tolerance.
Palladium-catalyzed cross-coupling reactions are among the
most useful synthetic methods for carbon-carbon bond forma-
tion.1 Among them, allyl cross-coupling reactions with allylin-
dium reagents have received much attention due not only to
further applicability of the double bond in allyl groups but also
their reactivity and selectivity, ease of preparation and handling,
and operational simplicity.2 Allylindium reagents are easily
prepared from allyl halides and indium metal in polar solvents,
including water.3 Recently, new methods for the preparation of
allylindiums via a reductive transmetalation of π-allylpalladium-
(II) complexes from allyl alcohols and its derivatives have been
reported, and many successful examples of palladium and
indium-mediated allylation have been described.4 With regard
to our ongoing research interest in transition metal-catalyzed
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10.1021/jo702279t CCC: $40.75 © 2008 American Chemical Society
Published on Web 01/09/2008
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