ORGANIC
LETTERS
2000
Vol. 2, No. 22
3439-3442
Highly Regioselective and
Stereoselective Allylation of Aldehydes
via Palladium-Catalyzed in Situ
Hydrostannylation of Allenes
Hao-Ming Chang and Chien-Hong Cheng*
Department of Chemistry, Tsing Hua UniVersity, Hsinchu, Taiwan 30043
Received August 14, 2000
ABSTRACT
Highly regio- and stereoselective allylation of aldehydes by allenes proceeds smoothly in aqueous/organic media in the presence of PdCl2-
(PPh3)2, HCl, and SnCl2. The reaction likely occurs via hydrostannylation of allenes and allylation of aldehydes by the in situ generated
allyltrichlorotins to afford the final products.
Palladium-mediated substitution of allylic substrates is a
powerful organometallic process for carbon-carbon and
carbon-heteroatom bond formation.1 The catalytic reactions
generally proceed via the addition of a nucleophile to the
electrophilic π-allylpalladium intermediate.2 Recent studies
on the transformation of a π-allylpalladium electrophilic
species to a nucleophilic allyl group that is then used for
the carbonyl allylation of aldehydes3 and ketones4 further
widened the synthetic application of the π-allylpalladium
chemistry. The charge reversal is achieved by reacting the
π-allylpalladium intermediate with a low-valent metal com-
pound to generate the corresponding allylic organometallic
reagent.5 Examples of the low-valent metal (compounds)
used included SnCl2,3 Et2Zn,4 SmI2,6 Zn,7 In,8 and InI,9 etc.
Our interest in the development of new palladium-
mediated allene chemistry leads us to explore the possibility
of employing allenes as the source for generating π-allylpal-
ladium species10 and the application of the charge reversal
method in the carbonyl allylation of aldehydes. Herein, we
report a highly regio- and stereoselective carbonyl allylation
of aldehydes by allenes mediated by the PdCl2(PPh3)2-HCl-
SnCl2 system (Scheme 1). This new reaction proceeds
smoothly in an aqueous/organic solvent system via an
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Yasui, K.; Goto, S.; Tanaka, S. Angew. Chem., Int. Ed. Engl. 1995, 34,
787.
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10.1021/ol0064563 CCC: $19.00 © 2000 American Chemical Society
Published on Web 10/06/2000