Copper-Catalyzed Borylative Ring Closing C-C Coupling toward Spiro- and Dispiroheterocycles

The synthesis of spiroheterocyclic structures with a pendant methylene boronate substituent has been accomplished to promote further functionalization. A Cu-catalyzed borylative ring closing C-C coupling of an alkenyl halide is the key step toward the synthesis of [m.n]-spirocycles (m,n = 3-5). Computational studies on the mechanism reproduced all the experimental trends and explain the enhanced reactivity of systems leading to strained smaller rings. The optimized protocol also gives access to dispirocycle scaffolds, fully characterized by X-ray diffraction.