Organic Letters
Letter
acyclic keto acids.11d,f,19 We investigated lactonization of
substrates 6a−c; the results are presented in Scheme 5. The
ASSOCIATED CONTENT
* Supporting Information
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S
The Supporting Information is available free of charge on the
Scheme 5. Lactonization of Keto Acids
Experimental procedures and NMR spectra for all new
Accession Codes
CCDC 1919362 contains the supplementary crystallographic
data for this paper. These data can be obtained free of charge
bridge Crystallographic Data Centre, 12 Union Road,
Cambridge CB2 1EZ, U.K.; fax: +44 1223 336033.
method requires higher temperature and longer reaction times,
but lactone 3a could be obtained in high yield from 6a.
Substrate 6b, with two enolizable positions, resulted in the
formation of numerous side products, thus yielding the desired
lactone 3c in only 30% yield. Finally, the oxidative
lactonization of keto acid 6c resulted in the desired lactone
3g in 84% yield, but with no diastereoselectivity. The oxidative
contraction of 3,4-dihydropyran-2-ones thus provides numer-
ous advantages in terms of both reaction rate and selectivity.
Finally, on the basis of our success in the enantioselective
conversion of enol esters to enantioenriched α-tosyloxy
ketones, we performed a preliminary evaluation of an
enantioselective variant of the oxidative contraction of
dihydropyranone 2a (Scheme 6). Lactone 3a was obtained
AUTHOR INFORMATION
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Corresponding Author
ORCID
Author Contributions
†R.D. and T.L. contributed equally to this work.
Notes
The authors declare no competing financial interest.
Scheme 6. Enantioselective Conditions
ACKNOWLEDGMENTS
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This work was supported by the National Science and
Engineering Research Council (NSERC) of Canada, the
Canada Foundation for Innovation (CFI), the FRQNT Centre
in Green Chemistry and Catalysis (CGCC), and the Universite
de Sherbrooke. We thank Antoine Jobin-Des Lauriers for
preliminary results.
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