Iridium-Catalyzed StereocontrolledC(sp³)–C(sp³) Cross-Coupling of BoronicEsters and AllylicCarbonates Enabled by Boron-to-Zinc Transmetalation

The stereocontrolled C(sp³)–C(sp³) cross-coupling represents a considerable challenge of great contemporary interest. While this has been achieved through the reactions of boronate complexes with π-allyl iridium complexes, such reactions suffered from a limited substrate scope. We now report that following transmetalation from boronate complexes to organozinc reagents enables previously unreactive substrates to engage in stereocontrolled C(sp³)–C(sp³) cross-coupling. The broader substrate scope has enabled their application to the synthesis of biologically active molecules. The organozinc reagents react through a stereoinvertive coupling pathway with π-allyl iridium complexes, in contrast to reactions with other electrophiles that occur with retention of stereochemistry. The reaction uniquely combines the enantiospecific reactivity of an enantioenriched organometallic nucleophile with the enantioselective engagement of a racemic electrophile, enabling access to all stereoisomers.