Sulfur as a Bridge: Synthesis of Medium Rings via a Bicyclic Sulfonium Ion

A facile and efficient synthesis of medium rings via a bicyclic sulfonium ion was developed. Spectroscopic evidence for the formation of an intermediate sulfonium moiety is provided. The sulfur atom served as a “bridge” to access the medium ring system and could be removed after use via a Ramberg–Bäcklund process. As a result of the readily available starting materials, simple operation, and mild conditions, these reactions should be an appealing strategy in organic synthesis.