B(C6F5)3/I2 co-mediated cascade [4 + 2]/[3 + 2] cyclization to access spiroimidazolines

Abstract

A highly step- and atom-economical cascade [4 + 2]/[3 + 2] cyclization has been developed for the synthesis of structurally novel spiroimidazolines. Catalyzed by only 1 mol% B(C₆F₅)₃ in the presence of I₂, this one-pot, metal-free method assembles two rings from three readily available starting materials, affording a diverse library of products in up to 88% yields. Key to its practicality are the high step- and atom-economy, avoidance of pre-constructed rings, and operational simplicity. Mechanistic studies support a sequential pathway, offering a practical and sustainable approach to access privileged spiro scaffolds with potential medicinal chemistry applications.