Synthesis of Tricyclic Spiranoid Lactones via I₂/Sm(II)- and I₂/Pd(0)-Mediated Cyclizations of a Common Cycloalkylmethylene Precursor

A general synthesis of phylogenetically and structurally different tricyclic angularly fused spiranoid lactones, frequently observed as scaffold segments of various biochemical compounds and drugs of natural origin, is demonstrated via controlled cyclization of simple and easily accessible cycloalkylmethylene key precursors. The rapid composition of the key architecture yields an assembly of stable bicyclic iodolactones, which are converted to form a wide range of angularly fused tricyclic scaffolds.