Access to γ‐Iodo‐gem‐Diborylated Cyclopentanes and to Bicyclic Cyclopropanes

A formal atom transfer radical [3+2] annulation (ATRAn) reaction between different homoallyl radical precursors and 1,1‐diborylethene was developed. It provides a rapid access to polysubstituted cyclopentanes containing a gem ‐diboronic ester moiety. The synthetic utility of theses uniquely functionalized 5‐membered rings is highlighted by their easy conversion to attractive borylated building blocks such as 1‐borylated bicyclo[3.1.0]hexanes. The ATRAn reaction was extended to homopropagylic radicals giving access to unique allylic gem ‐diboronic esters that could be used in allylboration of aldehydes. Furthermore, this work highlights that 1,1‐diborylethene represents a synthetic equivalent to ketene, a so far elusive radical trap due to its daunting reactivity.