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temperature.18 However, in our opinion, the more likely
explanation for the disparity is the authors’ use of chiral shift
reagent NMR analysis to determine the enantiomeric
composition of the dibromide products. Unfortunately, the
spectral data are not provided. Our own attempt to observe
signal separation in a racemic sample of 1-(2,3-dibromo-
propoxy)-4-methoxybenzene 5a using Eu(hfc)3 was incon-
clusive. After portionwise addition of 4 equiv of the chiral shift
reagent, some degree of signal separation was observed,
showing roughly equal quantities of each enantiomer. However,
the level of signal broadening precluded any quantitative
determination of enantiomeric ratios.
In conclusion, four dibromination and four chlorohydrox-
ylation reactions of allylic ethers catalyzed by chiral mono- or
dinuclear palladium(II) complexes reported by Henry and co-
workers were repeated. Although the reaction yields were
reproduced, the dibromide and chlorohydrin products were
generated in racemic form.
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(13) The true yield of methyl crotonate dibromination is
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ASSOCIATED CONTENT
* Supporting Information
■
(16) (a) Hamed, O.; Henry, P. M. Organometallics 1998, 17, 5184−
5189. (b) Henry, P. M. J. Org. Chem. 1974, 39, 3871−3874. (c) It is
possible that a transient Pd(IV) species may be formed during this
step. Pd(IV) is competent for dichlorination of alkenes; see: McCall,
A. S.; Wang, H.; Desper, J. M.; Kraft, S. J. Am. Chem. Soc. 2011, 133,
1832−1848.
S
The Supporting Information is available free of charge on the
Full experimental procedures, analyses, characterization
(17) Qaseer, H. A. Pol. J. Chem. 2007, 81, 31−38.
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AUTHOR INFORMATION
Corresponding Author
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Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
We are grateful to the National Institutes of Health (R01
GM085235) for generous financial support.
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REFERENCES
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