Job/Unit: O20770
/KAP1
Date: 25-07-12 10:48:46
Pages: 6
M. Vellakkaran, M. M. S. Andappan, N. Kommu
SHORT COMMUNICATION
The formation of products 21 and 30 was investigated
under previously reported conditions (DMSO-AcOH as
solvent).[6c] While 21 was obtained only in 20% yield, it was
not possible to obtain 30 at all. This indicated the compati-
bility of the present method in the case of substrates bear-
ing acid-sensitive groups.
Preliminary mechanistic investigation suggested a chela-
tion-controlled cationic PdII catalytic cycle. Addition of
LiCl suppressed product formation, indicating the neutral-
ization of the cationic complex by halide coordination,
thereby blocking the vacant site necessary for olefin coordi-
nation (entry 23, Table 1). Incomplete reaction on exclusion
of oxidant supported the generation of Pd0 and the neces-
sity of oxidant to regenerate PdII (entry 24). A detailed ex-
perimental and theoretical investigation of the mechanism
is in progress.
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Conclusions
A ligand-mediated PdII-catalyzed regioselective arylation
was demonstrated to yield highly functionalized β-aryl
carbonyl derivatives in high yields. The mild conditions
(acid free, base-free, and relatively low temperature) allowed
the tolerance of a wider range of functionalities than pre-
viously possible. This methodology prospers as an alterna-
tive to “Rh-catalyzed arylboronic addition to enones” with
the advantage of using inexpensive and stable allyl alcohols
as enone equivalents. Incorporation of ligands has now
made the method feasible for asymmetric arylation, which
is to be reported in due course.
Experimental Section
General Procedure for the Synthesis of β-Aryl Carbonyl Compounds
from Allyl Alcohols: A mixture of arylboronic acid (2.00 mmol),
Pd(OAc)2 (0.022 g, 0.10 mmol), and 2,9-dimethyl-1,10-phenan-
throline (0.042 g, 0.20 mmol), allyl alcohol (1.00 mmol), and
Ag2CO3 (2.00 mmol) was dissolved in acetonitrile (3.0 mL) in a
10 mL round-bottomed flask. The mixture was vigorously stirred
at 60 °C for 24.0 h. After cooling to room temperature, the reaction
mixture was partitioned between ethyl acetate (25.0 mL) and water
(25.0 mL) and filtered through a Celite pad. The filtrate was trans-
ferred to a separatory funnel. The organic layer was washed with
water and brine, dried with anhydrous Na2SO4 (s), and concen-
trated in vacuo. The residue was purified by column chromatog-
raphy by using a gradient of hexane and ethyl acetate (eluent sys-
tem) to afford the pure product.
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Supporting Information (see footnote on the first page of this arti-
cle): General experimental details, experimental procedures, and
analytical data of all the compounds.
Acknowledgments
We thank the Director of the Indian Institute of Chemical Technol-
ogy (IICT) for the generous support. M. V. thanks the Council of
Scientific and Industrial Research for a Junior Research Fellow-
ship.
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