Merging Ketyl Radical Chemistry and Allylboration via Strain Release: One-Pot Multicomponent Access to Sterically Congested Ketone-Functionalized Organoborons.

Ketyl radical-mediated ring opening and [2σ+2π] cycloaddition of cyclopropyl ketones (CPKs) with alkynes typically require activation by alkyl, aryl, or carbonyl groups yielding cyclopentenes having one or two non-adjacent stereocenters. We developed a one-pot multicomponent reaction of diboryl-activated CPKs with alkynes and aldehydes that merges ketyl radical chemistry with allylboration. This method enabled highly diastereoselective access to densely functionalized cyclopentenes featuring homoallylic alcohol, ketone, and alkenyl boronate motifs on adjacent quaternary, tertiary, and secondary stereogenic centers. Additionally, diboryl CPKs also allowed the synthesis of rare ketone-functionalized γ,γ-disubstituted allylic diborons.