C O M M U N I C A T I O N S
Scheme 2. Allylation of 2a with Various Homoallyl Alcoholsa
Scheme 4
Taking advantage of retro-allylation as a bond-cleavage strategy,
we have devised a new method for the preparation of σ-allyl-
palladium, which is difficult to generate in a stereo- and regio-
selective manner. Coupled with immediate use of the σ-allyl-
palladium, the retro-allylation realizes stereo- and regiospecific
allylations of aryl halides. The retro-allylation system will be
applicable to other transformations catalyzed by other transition
metals.
a The reaction conditions are the same as those in Table 1, except for
the reaction of 1e (2 equiv of 1e and 2.4 equiv of Cs2CO3 were used).
Scheme 3. Regio- and Stereospecific Allylation with
Diastereomerically Pure Homoallyl Alcohols
Acknowledgment. This work was supported by Grants-in-Aid
for Scientific Research from MEXT, Japan. K.H. acknowledges
JSPS for financial support.
Supporting Information Available: Experimental details, char-
acterization data for new compounds, and stereochemical assignment
of 1h (PDF, CIF). This material is available free of charge via the
References
(1) (a) Negishi, E.; Fang, L. In Handbook of Organopalladium Chemistry
for Organic Synthesis; Negishi, E., Ed.; Wiley: New York, 2002; Vol. 1,
Chapter III.2.9. (b) Tamao, K. In ComprehensiVe Organic Synthesis; Trost,
B. M., Fleming, I., Pattenden, G., Eds.; Pergamon: Oxford, 1991; Vol.
3, Chapter 2.2. (c) Magid, R. M. Tetrahedron 1980, 36, 1901-1930. (d)
Lipshutz, B. H.; Sengupta, S. Org. React. 1992, 41, 135-631.
(2) Exceptionally excellent R- and γ-selective coupling reactions of organic
halides with substituted allylfluorosilanes were reported: (a) Hatanaka,
Y.; Ebina, Y.; Hiyama, Y. J. Am. Chem. Soc. 1991, 113, 7075-7076. (b)
Hatanaka, Y.; Goda, K.; Hiyama, Y. Tetrahedron Lett. 1994, 35, 1279-
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(3) (a) Fujita, K.; Yorimitsu, H.; Oshima, K. Chem. Rec. 2004, 4, 110-119.
(b) Fujita, K.; Yorimitsu, H.; Shinokubo, H.; Oshima, K. J. Org. Chem.
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K. Org. Lett. 2005, 7, 3577-3579.
(4) Retro-allylations from lithium, magnesium, tin, and zinc alkoxides were
observed: (a) Benkeser, R. A.; Siklosi, M. P.; Mozdzen, E. C. J. Am.
Chem. Soc. 1978, 100, 2134-2139. (b) Gerard, F.; Miginiac, P. Bull. Chim.
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64, 186-195. (d) Peruzzo, V.; Tagliavini, G. J. Organomet. Chem. 1978,
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T.; Kodoi, K.; Nishinaga, E.; Okada, T.; Morisaki, Y.; Watanabe, Y.;
Mitsudo, T. J. Am. Chem. Soc. 1998, 120, 5587-5588.
(5) Cross-coupling reactions of organic halides with tertiary alcohols via
â-carbon elimination were reported. Arylation with arylmethanols: (a)
Terao, Y.; Wakui, H.; Satoh, T.; Miura, M.; Nomura, M. J. Am. Chem.
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stereospecific synthesis of (E)- and (Z)-3k (Scheme 3). Treatment
of 2a with threo-1g6 under the palladium catalysis afforded (E)-3k
stereoselectively. On the other hand, formation of (Z)-3k was more
favored over that of (E)-3k in the reaction of erythro-1g.6 The
allylation controlled by the relative stereochemistry of 1 was
applicable to stereospecific synthesis of vinyl ether 3n starting from
diastereomerically pure 1h. Highly stereoselective synthesis of silyl
enolate 3o also underscores the utility of the retro-allylation strategy.
We are tempted to rationalize the stereospecificity controlled by
starting homoallyl alcohols as follows (Scheme 4). Upon the retro-
allylation reaction of threo-1g, a chair transition state 4a would be
the most stable, because of steric reasons, compared to other
possible transition states including another chair transition state 4b
and twist-boat transition states. Formation of (E)-crotyl(naphthyl)-
palladium (E)-5 is thus favored. The intermediate probably
undergoes reductive elimination so rapidly that its isomerization
into π-allylpalladium and any other isomers is negligible.
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