Unusual Carbon-Carbon Bond Formations between Allylboronates and Acetals or Ketals Catalyzed by a Peculiar Indium(I) Lewis Acid

In(1)OTf has been uncovered as an effective Lewis acid catalyst for unprecedented nucleophilic substitution of acetals or ketals with allylboronates. A transmetalative S(N)1 mechanism is proposed in which a single In(1) center acts as a dual catalyst to activate both reagents sequentially. Contrary to the classic gamma-selectivity of allylsilanes (Hosomi-Sakurai reaction), this In(1)-catalyzed borono variant displays distinct alpha-selectivity. Substrate scope and functional group tolerance proved to be excellent.