4.8 Article

Efficient Synthesis of Orphaned Cyclopropanes Using Sulfones as Carbene Equivalents

Journal

JOURNAL OF THE AMERICAN CHEMICAL SOCIETY
Volume 144, Issue 32, Pages 14471-14476

Publisher

AMER CHEMICAL SOC
DOI: 10.1021/jacs.2c07063

Keywords

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Funding

  1. UNC Department of Chemistry
  2. National Science Foundation [CHE-0922858, CHE-1828183, CHE-1726291]

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In this study, a new platform for transferring 1,1-dialkylcarbene units to olefins using carbometalation reactions was introduced. By reacting dialkyl sulfones with styrenes and arylbutadienes, 1,1-dialkylcyclopropanes were synthesized successfully. The potential of this method was showcased through various examples.
Small molecules containing 1,1-dimethylcyclopropanes are prevalent throughout nature but are difficult to synthesize using state-of-the-art metal-catalyzed carbene transfer methods without competing 1,2-hydride shifts. Herein, we introduce a mechanistically distinct platform to transfer 1,1-dialkylcarbene units to olefins using carbometalation reactions of dialkyl sulfonyl anions. In the presence of NaNH2 or n-BuLi in ethereal solvents, dialkyl sulfones react with styrenes and arylbutadienes between 23 and 70 degrees C to produce the corresponding 1,1-dialkylcyclopropanes. We report 40 examples of this reactivity including 16 different styrenes (up to 89% isolated yield), 9 arylbutadienes (51-88% yield), and 13 different sulfones (46-80% yield). In addition, we report an example of a sequential cyclopropanation reaction using this method. Preliminary mechanistic studies suggest a stepwise anionic process that is initiated by the direct addition of sulfonyl anions to a carbon-carbon double bond.

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