Copper-Catalyzed, Stereoselective Cross-Coupling of Cyclic Allyl Boronic Acids with α‑Diazoketones

In this study, we present the synthesis of new, stereodefined allylboronic acids employed to investigate the stereochemistry of the Cu-catalyzed cross-coupling of allylboronic acids with α-diazoketones. According to our results, this reaction proceeds with retention of the relative configuration of the allylboronic acid substrate. We suggest that the stereoinduction step involves a syn S_E2′-type transmetalation of the allylboronic acid substrate with a Cu–carbene species.