Control of the regioselectivity of sulfonamidyl radical cyclization by vinylic halogen substitution.
The radical cyclization reactions of unsaturated sulfonamides were investigated. The photolysis of N-(4-halo-4-pentenyl)sulfonamides (X = I, Br, or Cl) with (diacetoxyiodo)benzene (DIB) and iodine at room temperature afforded exclusively the corresponding piperidines in 73-98% yield via 6-endo radical cyclization. On the other hand, the reactions of N-(5-halo-4-pentenyl)sulfonamides with DIB/I2 led to the only formation of the pyrrolidine products in 84-99% yield via 5-exo radical cyclization. The vinylic halogen substitution not only successfully inhibits the competing ionic iodocyclization process to allow the radical cyclization to proceed smoothly but also shows a remarkable effect in controlling the regioselectivity of cyclization.[1]References
- Control of the regioselectivity of sulfonamidyl radical cyclization by vinylic halogen substitution. Lu, H., Chen, Q., Li, C. J. Org. Chem. (2007) [Pubmed]
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