Synthesis of Alkynylmethylidene‐benzoxasiloles through a Rhodium‐Catalyzed Cycloisomerization Involving 1,2‐Silicon and 1,3‐Carbon Migration

It is shown that a cationic rhodium(I)/biphep complex catalyzes the cycloisomerization of 2‐(alkynylsilylethynyl)phenols, leading to alkynylmethylidene‐benzoxasiloles through concomitant silicon and carbon migration. This unprecedented cycloisomerization presumably proceeds via the formation of rhodium vinylidenes through 1,2‐silicon migration, followed by 1,3‐carbon (alkyne) migration via the formation of hypervalent silicon centers.