Journal
CHEMISTRY-A EUROPEAN JOURNAL
Volume 20, Issue 25, Pages 7803-7810Publisher
WILEY-V C H VERLAG GMBH
DOI: 10.1002/chem.201402183
Keywords
chemoselectivity; difluoromethyl 2-pyridyl sulfone; Julia-Kocienski reaction; olefination; rearrangements
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Funding
- National Basic Research Program of China [2012CB215500, 2012CB821600]
- National Natural Science Foundation of China [21372246, 21202189]
- Shanghai QMX program [13QH1402400]
- Chinese Academy of Sciences
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The direct conversion of diaryl ketones and enolizable aliphatic aldehydes into gem-difluoroalkenes has been a long-standing challenge in organofluorine chemistry. Herein, we report efficient strategies to tackle this problem by using difluoromethyl 2-pyridyl sulfone as a general gem-difluoroolefination reagent. The gem-difluoroolefination of diaryl ketones proceeds by acid-promoted Smiles rearrangement of the carbinol intermediate; the gem-difluoroolefination is otherwise difficult to achieve through a conventional Julia-Kocienski olefination protocol under basic conditions due to the retro-aldol type decomposition of the key intermediate. Efficient gem-difluoroolefination of aliphatic aldehydes was achieved by the use of an amide base generated in situ (from CsF and tris(trimethylsilyl)amine), which diminishes the undesired enolization of aliphatic aldehydes and provides a powerful synthetic method for chemoselective gem-difluoroolefination of multi-carbonyl compounds. Our results provide new insights into the mechanistic understanding of the classical Julia-Kocienski reaction.
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