Studies in selective 6-membered bromoether formation via bromonium and thiiranium-induced cyclizations
2015
Levinson, Adam M. | Milner, Phillip J. | Snyder, S. A. (Scott A.)
The formation of 6-endo bromoether ring systems from linear alkenol precursors through bromonium-induced cyclizations has historically proven challenging, with 5-exo products typically predominating, even on rigid scaffolds. This Letter describes our efforts to achieve such cyclizations directly using new bromonium sources such as BDSB (Et2SBr·SbCl5Br) as well as two alternative, stepwise approaches based on either thiiranium-induced cyclization and subsequent sulfur manipulation or bromonium-induced closure of secondary alcohols and oxidative functionalization to generate fully substituted carbon centers. In some cases, 6-endo bromoethers could be controllably formed without generating 5-exo alternatives.
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