Synthetic Approach to Benzocyclobutenones Using Visible Light and a Phosphonate Auxiliary.

Reported herein is a two-step procedure to synthesize benzocyclobutenones from (o-alkylbenzoyl)phosphonates. It consists of a visible-light-driven cyclization reaction forming phosphonate-substituted benzocyclobutenols and subsequent elimination reaction of the H-phosphonate, which assumes a key role as the recyclable auxiliary. A wide variety of functionalized benzocyclobutenones, which include those difficult to synthesize by conventional methods, are efficiently synthesized.