ORGN 26 |
Mechanistic studies on LDA-mediated ortholithiation and anionic Fries rearrangement of N,N-dialkyl phenylcarbamates
| Kanwaljit Singh and David B. Collum. Department of Chemistry and Chemical Biology, Cornell University, Baker Laboratory, Ithaca, NY 14853-1301 |
| An LDA-mediated ortholithiation of N,N-dialkyl phenylcarbamates followed by anionic Fries rearrangement was investigated. Low-temperature 6Li, 13C and 15N NMR spectroscopies were used to characterize solution structures of the intervening mixed aggregates. In THF/pentane solutions, ortholithiation affords exclusively mixed dimers. Rate studies on anionic Fries rearrangement of the mixed dimers reveal an inverse dependence on LDA concentration and a second order dependence on THF concentration. A solvent-assisted dissociative mechanism for the rearrangement of the mixed organolithium aggregate is proposed. Characterization and reactivities of various organolithium species arising from subtle changes in substrate, solvent and reaction conditions are described. 
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