Synthesis of Carboxylic Acids Containing α-All-Carbon Quaternary Centers from Diazo Compounds and Trialkylboranes

The construction of C–C bonds to form all-carbon quaternary centers remains a significant challenge in synthetic chemistry. Herein, we report a tandem process involving a 1,2-migration of a tetra-coordinated boron intermediate followed by a Claisen rearrangement of the boron enolate, achieved through a reaction between allyl diazoacetates and trialkylboranes. The transformation forms two C–C bonds at the carbenic position of diazo substrate in a single-step operation under neutral conditions. Using this method, we successfully realized the gram-scale formal total synthesis of Vincamine, an indole alkaloid with significant pharmacological activity.