The First Boron-Tethered Radical Cyclizations and Intramolecular Homolytic Substitutions at Boron.

5-, 6-, and even 7-exo-trig radical cyclizations (1→2) are possible by applying a new boron-tethering approach with alkenylboronic esters. For certain substitution patterns, a subsequent intramolecular homolytic substitution (SH i) reaction at boron occurs (2→3) and leads to rearranged products. The C-B bond of the intermediate boracycles is readily oxidized to give diol products. © 1999 WILEY-VCH Verlag GmbH, Weinheim, Fed. Rep. of Germany.